The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, Papua New Guinea. Danny Danahun Orwe

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1 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, Papua New Guinea by Danny Danahun Orwe Thesis submitted to the University of South Australia for the Degree of Master of Applied Science in Chemical Technology June, 2

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3 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG ABSTRACT Ok Tedi Mining treats a copper-gold ore in the Star Mountains of Papua New Guinea. The predominant ore type, porphyry, is composed of both monzonite and monzodiorite porphyry. Investigations therefore center on these two ore types. Mineralogical examination of Concentrator products treating a typical ore blend show that the principal copper sulphide minerals are chalcopyrite, digenite and bornite, and that the primary losses of copper to tailings are as both digenite and chalcopyrite. Losses of both digenite and chalcopyrite are as fine liberated particles and coarse binary composite particles with nonsulphide gangue and in ternary sulphide/gangue particles. Laboratory flotation of the two porphyry ore types also shows poor recovery in the same ranges of the size distribution. The use of NaHS to improve copper recovery in porphyry ores is investigated and found to improve copper recovery after sulphidisation of the rougher feed to Eh = mv (SHE) at ph 11.5, improving recovery in both the fine (-31 tim) and coarse (+1 ranges of the size distribution. Single mineral studies on chalcocite, covellite and bornite with electrophoresis, EDTA extraction and XPS techniques show that a proportion of sulphide copper surfaces are partially covered with hydrophilic layer(s) of copper hydroxide species as a consequence of operation at highly alkaline ph. After treatment with NaHS, the copper hydroxide species are found to be absent. Plant trials of the application of CPS to rougher feed show an improved overall copper recovery of up to 4%, however as the Concentrator currently treats a blended porphyry-skarn feed, separate treatment of the ore types must be awaited to allow long term utilisation of NaHS.

4 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG To my parents; Orwe Seiwain and Pain Masil II

5 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG This is to certify that this thesis contains no material which has been accepted for the award of any other degree or diploma and that, to the best of my knowledge and belief, this thesis contains no material previously published or written by any other person, except when due reference is made in the text of the thesis. Danny Danahun Orwe Ill

6 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG ACKNOWLEDGEMENTS I wish to thank Ok Tedi Mining Limited (OTML) and The Australian Mineral Industries Research Association (AMIRA) for their sponsorship over the last three years. In particular, the support and guidance of my supervisors, Professor John Ralston and Dr Stephen Grano from The Ian Wark Research Institute, University of South Australia, my site supervisor, Dr David Lauder, Senior Metallurgist Development (OTML) for organising and assisting in my research program. The encouragement given to me by Mr. Jonathan Glatthaar, Chief Metallurgist (OTML) and Mr Bill Blenkhorn, Executive Manager Mill (OTML) are warmly acknowledged. My thanks are also due to Mill Operations under Mr Glen Kuri, Manager Mill Operations (OTML) and Mr Frank Henderson, Superintendent Mill Operations for their tolerance and allowing all plant trials to be conducted with a minimum of fuss, the Chemical and Environment laboratories for all analytical work and the tireless Metallurgy personnel who participated laboratory and plant trials. Finally, I would like to express my sincere thanks to my wife Agatha and three children, Jasmine, Selwyn and Shannon for their patience in bearing with my lack of support during the research period. iv

7 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG PUBLICATIONS Orwe, D., Grano, S. and Lauder, D. W., 1997, Chalcocite Oxidation and its Influence on Fine Copper Recovery at the Ok Tedi Concentrator, Papua New Guinea, Sixth Mill Operators' Conference, Madang, PNG. The Aus. I.M.M., p Orwe, D., Grano, S. and Lauder, D. W., 1998, Increasing Fine Copper Recovery at the Ok Tedi Concentrator, Papua New Guinea. Minerals Engineering, 11(2): p V

8 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG TABLE OF CONTENTS vi

9 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Abstract Page Signed Statement Acknowledgments Publications Table of Contents List of Figures List of Tables I iv v vi xiii xvi CHAPTER I - GENERAL INTRODUCTiON Introduction Ok Tedi Orebody and Mineralogy Specific Ore Types Concentrator Description Ore Reclaim and Grinding Flotation Circuit Project Objectives and Research Methodology Convergence of Institutional Investigations 11 CHAPTER II- LITERATURE REVIEW Introduction Flotation Flotation Model The Influence of Pulp Chemistry Surface Chemistry of Copper Minerals Stability of Suiphide Copper Minerals in an Aqueous System 17 VII

10 The Influence of Sodium Hydrogen Suiphlde on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 2.4 Oxidation of Copper Minerals Chalcopyrite Oxidation Chalcocite Oxidation Bornite Oxidation Covellite Oxidation Pyrite Oxidation Self-Induced Flotation Collector Induced Systems Mineral-Collector Interactions in Mixed Suiphide Systems Effect of Grinding Media on Copper Flotation Sulphidisation Concluding Remarks 31 CHAPTER III - EXPERIMENTAL Introduction Laboratory Ore Studies Equipment and Reagents Laboratory Ores Characterisation of Laboratory Ores by QEM*SEM Flotation Test Procedure Examination of Flotation Eh-pH Environment Controlled Sulphidisation of Flotation Feed Continuous Suiphidisation during Flotation Sulphidisation during Grinding Subsequent Handling of Flotation Products Single Mineral Studies Composition of Single Minerals Dissolution Studies Zeta Potential by Electrophoresis EDTA Extraction and XPS Analysis Plant Investigations 46 VIII

11 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Plant Surveys Metallurgical Samples Pulp Chemical Measurements EDTA Extraction Samples Sampling for XPS Analysis Sulphidisation Plant Trials Sulphidisation Control System Plant NaHS Trial # Plant NaHS Trial # Plant NaHS Trial # Miscellaneous Analytical Techniques Assay Evaluation of Copper Recovery and Rate Constant 54 CHAPTER IV - EXAMINATION OF CONCENTRATOR PERFORMANCE ON A TYPICAL FEED BLEND Introduction Previous Survey of Concentrator New Survey of Concentrator Eh-pH Conditions EDTA Extraction XPS Analysis of Concentrator Streams Analysis of Size by Size Mineralogical Data from Flotation Survey on 14 February Manipulation of Size and Mineralogical Data Examination of New Rougher Feed Size by Size Recovery of Copper in the Concentrator Mineralogical Recovery of Copper in the Concentrator Specification of Copper Loss Concluding Remarks 68 CHAPTER V - LABORATORY FLOTATION BEHAVIOUR OF TWO PORPHYRY ORES 7 ix

12 The Influence of Sodium Hydrogen on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 5.1 Introduction Standard Flotation Rougher Tests at Varying ph Distribution of Copper in Laboratory Ground Samples Copper Recovery as a Function of ph Size by Size Recovery as a Function of ph Eh-pH Trends Effect of Lime Addition to the Grinding Mill Dissolution and EDTA Extraction Tests on Ore Samples Copper Dissolution at Varying ph EDTA Extraction Flotation Tests in an Acid Environment Concluding Remarks 81 CHAPTER VI- SULPHIDISATION OF TWO PORPHYRY ORES Introduction Controlled Potential of Flotation Feed Continuous Sulphidisation during Flotation Effect of NaHS Addition to Laboratory Mill Effect of Sulphidisation on a Size by Size Basis Concluding Remarks 9 CHAPTER VII - SINGLE MINERAL STUDIES Introduction Dissolution of Copper Minerals Chalcocite Covellite Bornite Chalcopyrite Summary of Dissolution Studies 96 x

13 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 7.3' Oxidation of Copper Minerals Zeta-Potential Studies Chalcocite Covellite Bornite Chalcopyrite Summary of Zeta - Potential Studies EDTA Extraction of Oxidised Chalcocite Sulphidisation of Chalcocite Effect of Suiphidisation on EDTA Extraction of Oxidised Chalcocite Effect of Suiphidisation on Zeta - Potential of Oxidised Chalcocite XPS Analysis of Suiphidisation of Oxidised Chalcocite XPS Examination of Sample #1 - Chalcocite after Oxygen purging at ph XPS Examination of Sample #2 - Chalcocite after Sulphidisation at ph 11.5 in Nitrogen Concluding Remarks 111 CHAPTER VIII - SULPHIDISATION PLANT TRIALS Introduction Plant Studies Trial #2 Results Trial #3 Results Trial #4 Results Flotation Circuit Surveys Pulp Chemistry Effect of NaHS on Copper Recovery XPS Analysis of Plant Survey Samples Concluding Remarks 127 xi

14 The Influence of Sodium Hydrogen SulpNde on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CHAPTER IX - CONCLUSIONS AND RECOMMENDATIONS Conclusions Recommendations 129 REFERENCES 132 APPENDICES 142 Appendix #1 Characteristics of a Typical Concentrator Feed Blend 143 Appendix #2 Characterisation of Porphyry Ore Samples 162 Appendix #3 Sulphidisation 17 Appendix #4 Plant Trials and Surveys 184 Appendix #5 Plant NaHS Survey Report 2 XII

15 The Influence of Sodium Hydrogen SulpMde on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG UST OF FIGURES Figure 1.1 Figure 1.2 Figure 1.3 Figure 1.4 Figure 1.5 Figure 2.1 Figure 2.2 Figure 2.3 Figure 3.1 Figure 4.1 Figure 4.2 Figure 5.1 Figure 5.2 Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Ok Tedi Location Geological Mine Plan (Rush and Seegers, 199) Grinding Circuit - Unit 2 Flotation Circuit Average Size by Size Copper Recovery for a Six Month Period (November, 1996 to April, 1997) Flotation threshold values (critical surface coverage or advancing water contact angle) as a function of particle size showing existence of flotation domain (Adapted from Crawford and Ralston, 1988) Potential-pH equilibrium diagram for the copper-sulphur-water system at 25 C, for unit activities of the sulphur ligands. (Abstracted from Garrels and Christ, 1965) Potential-pH equilibrium diagram for the copper-iron-sulphur-water system at 25 C, for unit activities of all dissolved salts. (Abstracted from Garrels and Christ, 1965) Simplified CPS Control Loop EDTA Sampling Points Rougher-Scavenger and Total Plant Copper Recoveries Copper Recovery as a Function of ph for Monzonite 'A' Copper Recovery as a Function of ph for Monzodiorite 'A' Size by Size Copper Recovery of Monzonite 'A' Size by Size Copper Recovery of Monzodiorite 'A' Rmax versus Size as a Function of ph for Monzonite 'A' Rate Constant (k) versus Size as a Function of ph for Monzonite 'A' Rmax versus Size as a Function of ph for Monzodiorite 'A' XIII

16 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Figure 5.8 Figure 5.9 Rate Constant (k) versus Size as a function of ph for Monzodiorite 'A' ph and Eh Profiles for Monzonite 'A' and Monzodiorite 'A' Figure 5.1 Copper Dissolution-Monzonite Porphyry Sulphide 'A' Figure 5.11 Copper Dissolution-Monzodiorite Porphyry Suiphide 'A' Figure 5.12 EDTA Extractable Copper as a Function of ph-monzonite 'A' Figure 5.13 EDTA Extractable Copper as a Function of ph-monzodiorite 'A' Figure 6.1 Effect of NaHS on Size by Size Copper Recovery at ph 11.5 (Monzonite and Monzodiorite 'B' Samples) Figure 6.2 Figure 6.3 Figure 7.1 Figure 7.2 Figure 7.3 Figure 7.4 Figure 7.5 Figure 7.6 Figure 7.7 Figure 7.8 Effect of NaHS on size by size Recovery (Monzonite 'A') Effect of NaHS on size by size Recovery (Monzodiorite 'A') Dissolution of Chalcocite as a function of ph Dissolution of Covellite as a function of ph Dissolution of Bornite as a function of ph Zeta-potential of Chalcocite conditioned for 5 and 6 minutes with N2 and 2 purging Zeta-potential of Covellite conditioned at ph 11.5 for 5 minutes with 2 purging Zeta-potential of Bornite conditioned with 2 purging for 5 minutes Oxidation of Chalcocite as measured by EDTA Extraction Effect of NaHS on EDTA Extractable copper from Chalcocite conditioned at ph Figure 7.9 Effect of M NaHS on the zeta-potential of Oxidised Chalcocite. Figure 7.1 Copper (2p) spectrum for (a) chalcocite with oxygen purging and (b) after subsequent NaHS conditioning with nitrogen purging Figure 7.11 Sulphur (2p) spectrum for (a) chalcocite with oxygen purging and (b) after subsequent NaHS conditioning with nitrogen purging xiv

17 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Figure 7.12 Figure 8.1 Figure 8.2 Figure 8.3 Figure 8.4 Figure 8.5 Figure 8.6 Figure 8.7 Oxygen (2p) spectrum for (a) chalcocite with oxygen purging and (b) after subsequent NaHS conditioning with nitrogen purging Potential Measurements Dissolved Oxygen Levels Temperature Profiles Effect of NaHS on Size by Size Copper Recovery Carbon (is) spectrum for (a) Rougher Feed NaHS off (OTO1 ), (b) Rougher Feed NaHS on (T7), (c) Rougher Concentrate NaHS off (OTO1 1) and (d) Rougher Concentrate NaHS on (18). All spectra for unetched surfaces. Iron (2p) spectrum for (a) Rougher Feed NaHS off (OTO1O), (b) Rougher Feed NaHS on (T7), (C) Rougher Concentrate NaHS off (OTO1 1) and (d) Rougher Concentrate NaHS on (T8). All spectra for unetched surfaces. Sulphur (2p) spectrum for (a) Rougher Concentrate NaHS off (OTO1 1)-unetched surface, (b) Rougher Concentrate NaHS off (OTO11)-etched surface, (C) Rougher Concentrate NaHS on (T8)-unetched surface and (d) Rougher Concentrate NaHS on (T8)-etched surface. No feed sample surfaces shown. Figure 8.8 Copper (2p) spectrum for (a) Rougher Concentrate NaHS off (OTO1 1)-unetched surface, (b) Rougher Concentrate NaHS off (OTO11)-etched surface, (C) Rougher Concentrate NaHS on (T8)-unetched surface and (d) Rougher Concentrate NaHS on (T8)-etched surface. No feed sample surfaces shown. xv

18 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG LIST OF TABLES Table 1.1 Ok Tedi Pit Ore Reserves as at 31 May, 1996 Table 1.2 Average Ore Processing Characteristics Summarised From Laboratory Flotation Database (Lauder, 1997) Table 1.3 Folomian Mill Production Statistics For Fiscal Year 1997 Table 3.1 Copper Partitioning Across The Copper Bearing Phases In Monzodiorite 'A' and Monzonite 'A' Table 3.2 Copper Partitioning Across Phases In Monzodiorite 'B' and Monzonite 'B' Table 3.3 PSSA (p.m) Derived Mean Grain Sizes in Monzodiorite 'A' and Monzonite 'A' Table 3.4 PSSA Derived Mean Grain Sizes in Monzodiorite 'B' and Monzonite 'B' Table 3.5 Table 3.6 Table 3.7 Table 4.1 Elemental Compositions of Experimental Single Minerals BET Surface Area of Single Minerals Samples Pulp Chemistry Sampling Points Unit 2 Flotation Survey : 12 October 1994 (Lauder and Erepan, 1996) Table 4.2 Mass Balanced Flotation Data of Unit 2 Survey: 14 February, 1996 Table 4.3 Table 4.4 Table 4.5 Table 4.6 Table 4.7 Table 4.8 Table 5.1 EDTA Extraction Test Results from Unit 2 Survey, 14 February Simplified Modal Analysis of New Rougher Feed (Jenkins and Adair, 1996) Point Counting Analysis of New Rougher Feed Total Plant Mineral Recovery Rougher-Scavenger Mineral Recovery Point Counting Analysis of Final Tailing Mass, Assay and Copper Distribution in Monzonite 'A' xvi

19 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Table 5.2 Table 5.3 Table 6.1 Table 6.2 Table 6.3 Table 6.4 Mass, Assay and Copper Distribution in Monzodiorite 'A' Total Copper Recovery: Effect of Lime Addition to Mill versus Lime Addition to Cell (Monzonite 'A' and Monzodiorite 'A') Effect of ph and Controlled Sulphidisation-Monzodiorite 'B' Effect of ph and Controlled Sulphidisation-Monzonite 'B' Effect of ph and Continuous Sulphidisation-Monzodiorite 'B' Effect of NaHS Addition to Mill for Monzodiorite 'B' Table 7.1 XPS Atomic Concentrations (mole %) for Chalcocite Samples #1 and #2 Table 8.1 Summary of Results of the NaHS Trial #2 (Abstracted from Senior and Heyes,1996) Table 8.2 Copper Recovery-NaHS Trial #3 Table 8.3 Gold Recovery-NaHS Trial #3 Table 8.4 Acid Soluble Copper Recovery-NaHS Trial #3 Table 8.5 Effect of NaHS at Reduced ph of 11.O-NaHS Trial #4 Table 8.6 Effect of NaHS at Reduced ph of 1O.5-NaHS Trial #4 Table 8.7 Table 8.8 Table 8.9 Table 8.1 NaHS "On-Off" Survey Comparison Sample Nomenclature and Conditions XPS Atomic Concentrations of Samples before Etching (Units: Mole%) XPS Atomic Concentrations of Samples after Etching (Units: Mole%) xvii

20 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CHAPTER I 1. GENERAL INTRODUCTION 1.1 Introduction The Ok Tedi copper-gold deposit is located (Figure 1.1) in the Western Province of Papua New Guinea, approximately 75 km north-west of Port Moresby. The deposit is mined and processed by Ok Tedi Mining Limited (OTML). The Ok Tedi ore body was discovered in 1969 by Kennecott geologists and was finally developed by a consortium consisting of BHP Mineral Holdings Pty. Ltd. (3%), Amoco Minerals (PNG) Ltd. (3%), a group of German companies led by Metallgesellschaft AG (2%) and The independent State of Papua New Guinea (2%). BHP Mineral Holdings Pty. Ltd. was the managing company (Newman, 1985). Figure 1.1 OkTedi Location 1

21 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG The ore body comprised a significant outcrop of gold which had to be exploited prior to exposing the main porphyry copper-gold system. A conventional CIPleach plant was commissioned at Folomian in May 1984 to treat the gold cap at a rate of 1.5 million tonnes per annum. Mining and flotation of copper bearing ore commenced in April 1987, with the C1P plant still used to leach flotation plant tailings. In September 1988, use of the CIP plant was discontinued and a second line of grinding mills and flotation cells commissioned (Stapleton, 1993). Changes in the consortium over the years has resulted in the current ownership with BHP Pty. Ltd. (52%), The Independent State of Papua New Guinea (3%) and Inmet Mining Corporation (18%). Since 1989, the concentrator has undergone a number of significant process developments, the most notable being the installation of columns (Coleman and Kilgour, 1991) an additional lime kiln and the Bailey 9 process control computer (England, 1993). Metallurgical development work in recent years has focused on understanding the differences in the available ore types and methods to improve copper and gold recovery. One of the development projects undertaken was the sponsorship of the AMIRA P26B project. This project is a collective Mining Industry project aimed at improving the recovery of fine particles in the flotation process. At Ok Tedi, the project was focused specifically on the fine particles emanating from the porphyry ores. This thesis is produced as a result of extensive laboratory and plant studies conducted between 1995 and 1997 as part of the AMIRA P26B project. Laboratory ore and plant studies were conducted on-site whilst laboratory single mineral studies were conducted at The Ian Wark Research Institute, University of South Australia. 1.2 Ok Tedi Orebody and Mineralogy The Ok Tedi ore deposit is a porphyry-skarn intrusive system located within the raised sediments of the Hindenberg ranges in the Star Mountains of the Western 2

22 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Province. The copper mineralisation results from the intrusion and alteration of monzonite and monzodiorite porphyry stocks. Subsequent leaching and redeposition of copper minerals resulted in a leached cap with low copper but significant gold, and a secondary enriched copper ore overlying the primary mineralisation. Figure 1.2 shows a geological plan of the ore bodies currently mined for coppergold flotation (Rush and Seegers, 199). From Figure 1.2, it can be seen that the porphyry ores are effectively ringed by skarn ore bodies, which exhibit high iron mineralisation, coupled with higher copper and gold contents than the porphyry ores. The copper-gold mineralisation typically consists of fine-medium-grained (< disseminated sulphides and gold. The principal copper minerals are chalcocite, chalcopyrite, bornite and covellite. Most gold occurs in association with copper but is also intruded in pyrite systems with silver occurring in solution within the copper sulphides, particularly chalcopyrite and bornite. Ore reserves as at3l May 1996 are given in Table 1.1. Table 1.1 OkTedi Pit Ore Reserves as at 31 May 1996 Oretype % of Total Ore Million Tonnes %Cu Au (g/t) Porphyry Skarn Siltstone Oxide Skarn Total Specific Ore Types As shown in Table 1.1 (above) there are four basic ore types with some subgrouping in each ore type. In each ore type, if the proportion of total copper that is oxide copper exceeds 25%, then the ore is defined as oxide ore. For example, a porphyry ore with total copper equal to.8% Cu and.25% acid soluble copper 3

23 The Influence of Sodium Hydrogen Suiphide on Porphyry Copper Recovery at Ok Tedi, PNG (ASCu, a chemical test, described in Appendix 2.2 for oxide copper) will be termed an oxide porphyry ore. Porphyry ore may consist of either monzonite or monzodiorite. These names refer to the host rock type and are based geologically on the relative proportion of alkali- and plagioclase feldspars respectively. If the alkali feldspar predominates, then the rock type is monzonite. The porphyry ores are the acid intrusive rocks that comprise the majority of the Ok Tedi deposit and are named geographically as the Northern (or Fubilan) Porphyry and the Southern Porphyry (Rush and Seegers, 199). Skarn ores are formed at the contact of the acid intrusive, particularly with limestone. Hence the skarn ores tend to geographically surround the porphyry ores. The skarn ore types nomenclature is based on the lithology of the rock, i.e., magnetite skarn, pyrite skarn or calc-silicate skarn. The skarn ore bodies are named from the early OTML geological tradition of naming each ridge after some other noted part of the world. Hence the important skarn ore bodies are named Edinburgh, Paris, Gold Coast, New Glasgow and Perth. Note that all types of skarn ore may be found in any skarn ore body. Also contained within the skarn ore reserves is the endoskarn. This ore type is from the contact of the skarn and porphyry ores and normally combines a porphyritic mineralogy with the more massive suiphide depositional qualities of the skarn. Siltstone ore is from the original country rock prior to the intrusion which has copper minerals deposited along the fractures due to its' proximity to the intrusion. Oxide skarn comprises other types of skarn ore that have been subjected to almost total oxidation. A large proportion of the copper has been altered to goethitic copper which is not recoverable. The ore is normally mined for the gold content rather than the copper, and will be depleted in the next few years (Lauder, 1997). 4

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25 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Table 1.2 Average Ore Processing Characteristics Summarised From Laboratory Flotation Database (Lauder, 1997) Oretype J R.W.I. Lime Head Recovery (%) [ J[ (kg/t) %Cu %ASCuT Au(g/t) Cu Au Monzonite Monzodiorite Siltstone Endoskarn Magnetite Skarn Pyrite Skarn Caic-Silicate Skarn Oxide Skarn (where R.W.I is the relative work index, and lime consumption (kg/t) to achieve ph 11.5) 1.4 Concentrator Description The Concentrator is located at Folomian, about one kilometer from the mine. A full and detailed description of equipment sizing is given in England (1993) and will not be repeated here. However, a brief process description is necessary to provide background information for the reader. The description is divided into two parts ; grinding and flotation. It should be noted that the Concentrator consists of two parallel grinding and flotation units, which are almost, but not quite, arranged in mirror image Ore Reclaim and Grinding Coarse ore is delivered from the Inpit and Taranaki crushing locations at the mine by overland conveyor belts to a 3, tonne intermediate stockpile. This arrangement not only allows steady throughput, but allows blending of various ore types for recovery and concentrate grade control. Since the concentrator is divided into two process lines, the ore delivered from the intermediate stockpile is split into two 3, tonne stockpiles. The ore is then drawn from each stockpile by apron feeders that feed conveyor belts 6

26 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG which subsequently feed semi-autogenous (SAG) mills charged with 5 1/2" grinding balls. The grinding mills operate at 65% solids nominal density. 1 kg/t 15g/t +12 mm 2 tph (App. 12mm) (3.7m x 8.5m) 2 g/t P8 i 5 microns Rougher Flotation Concentrate Reg rind Cleaner Circuit Allis Charmers 5m x 8.5m (4.4 MW) Koppers 5m x 8.5m (3.7 MW) Figure 1.3 Grinding C!rcuit - Unit 2 Each grinding circuit comprises a SAG mill with 13% ball charge and two parallel ball mills charged at 3% ball load (Paki, 1997) in closed circuit with a total design capacity of 2,5 tph. The grinding circuit of Unit 2 is shown in Figure 1.3. SAG mill discharge is screened by a vibratory screen. Screen oversize (>12 mm) returns to the SAG mill for further size reduction while the undersize (<12 mm) is pumped to in-line cyclone clusters inclined at 2. Cyclone overflows are 5% solids by weight, with particulate size described as 8% passing (P8) 15 Cyclone overflow streams flow by gravity to their respective flotation circuits. Cyclone underflows are split to feed two "flash" flotation cells. The flash flotation cell concentrates are pumped to the concentrate regrind mills while flash flotation cell tailings return to their respective mills. 7

27 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Flotation Circuit The flotation circuits each consist of rougher-scavenger, cleaner, recleaner and column flotation. Cleaner feed is reground in parallel ball mills. Figure 1.4 shows a schematic flow diagram of the flotation circuit. Recycle Feed New Feed Final Tail Flash Concentrate Final Concentrate Figure 1.4 Flotation Circuit Rougher-scavenger flotation is performed in each circuit by 3 Outokumpu OK- 38 flotation cells arranged in parallel lines of 15 cells. The first 18 cells in each line comprise the rougher stage, whilst the remaining 12 cells comprise the scavenger stage. Scavenger tailing is final tailing and is pumped to the tailings water reclamation thickeners. Rougher concentrate is pumped to the regrind cyclones. Cyclone underfiow is further ground in regrind ball mills to both improve liberation and ensure that final concentrate is fine enough so as not to scour the concentrate pipeline. Cyclone overflow is subjected to the three cleaning stages, comprising cleaner, recleaner and column cells. Cleaner tailings and scavenger concentrate are returned to the 8

28 - The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG roughers as recycled feed, whilst column and recleaner tailings are recycled to the regrind ball mill cyclones. Reagents used are slaked lime as a ph regulator, Cytec 7249 collector (a blend of diisobutyldithiophosphate and dilsobutylmonothiophosphate) and OTX 14 frother (an alcohol-glycol blend). These three reagents are added to, and only to, the SAG mill feed chute. When talc bearing skarn ores are treated by the mill, carboxy methyl cellulose (CMC) is added to cleaner feed to suppress the recovery of talc to the final concentrate. Historically, sodium hydrosulphide (NaHS) and potassium amyl xanthate (PAX) were added to scavenger feed (cell 9) for the activation of oxide copper minerals, notably malachite, azurite and cuprite. NaHS addition was controlled by the electrochemical potential as recorded by a platinum electrode. Typical reagent consumptions for lime, collector and frother are 1.5 kg/t, 15 g/t and 2 g/t respectively. The flotation ph is A typical metallurgical balance is given in Table 1.3. Table 1.3 Folomian Mill Production Statistics for Fiscal Year 1997 (1/6/96-31/5/97) Stream Kilotonnes Assays Recoveries - Au (g/t) Cu Au %Cu I Feed 28, I Concentrate j Tailing 27, I Figure 1.5 shows the size by size copper flotation recovery for a six month period (November April 1997). Highest copper recovery occurs in the 1-3 decreasing recovery above and below this range. size range with sharply 9

29 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG U) > U U) 4 I.- U) Size (micron) Figure 1.5 Average size by size copper recovery for a six month period (November 1996 to April 1997) 1.5 Project Objectives and Research Methodology The P26B project objectives for fine suiphide mineral flotation were defined generally to identify the mechanism(s) by which pulp chemistry influences fine particle flotation behaviour and to determine strategies by which manipulation and control can improve grade and recovery. Given the number of ore types at Ok Tedi, it was decided to limit the investigation to the predominant ore type (i.e., porphyry). The research program was divided into three sections. Investigate laboratory flotation behaviour of the two porphyry ore types and the metallurgical response of the concentrator. Determination of the reason(s) for poor flotation response of value minerals (copper and gold) with particular emphasis on fine particles. Propose and test solutions to improve flotation of poorly floating fine particles. 1

30 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG The investigations were carried out in the following manner: Investigate size by size behaviour of two porphyry ores in the laboratory. Determine flotation response across the total plant on a size by size basis. Ascertain if ph modification during grinding influences fine particle recovery. Determine the role of copper hydroxide derived from individual sulphide copper minerals by studying the dissolution, electrophoresis and their suiphidisation to assist in interpreting the flotation response. 1.6 Convergence of Institutional Investigations In the early 199's, OTML contracted the then CSIRO Division of Mineral and Process Engineering to investigate the reasons for poor fine copper recovery in some Ok Tedi ores. On the basis of laboratory ore studies combined with EDTA extractions, Senior and Creed (1992) hypothesized the formation of copper hydroxides on sulphide particulate surfaces and suggested the use of sodium hydrogen suiphide (NaHS) to convert the copper hydroxides to copper sulphides, promoting flotation of fine particles. Senior and Heyes followed up their work in 1995, demonstrating in the laboratory that NaHS could provide significant benefits to the sulphide flotation in Ok Tedi ores. With the commencement of Project 26B in 1995, initial investigations tended to confirm the observations of Senior and Creed (1992), and it is not surprising that the project gravitated towards the use of NaHS as a method of improving the flotation of the fine particles. From the point-of-view of OTML, the convergence of the research themes has been of significant benefit. 11

31 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CHAPTER U 2. LITERATURE REVIEW 2.1 Introduction The froth flotation of sulphide minerals as a means of beneficiation has been practiced successfully since the introduction of xanthates (1925) and dithiophosphates (1926) as sulphide collectors (Patterson and Salman, 1968). However, although the process is very robust in providing acceptable concentrate grades at economically acceptable profit margins, the factors which underpin the technical aspects of the process have only been slowly unraveled. In recent years, significant effort has been made to clarify many of those technical aspects, leading to a situation where any future improvements to the flotation process may only be achieved through a more complete understanding of the mechanisms involved. Due to the wealth of published information on the subject, no attempt is made in this work to review the literature with respect to all the chemical and physical variables that are known or suspected of impacting the efficiency of the process. The literature review is therefore limited to those variables specifically related to the current study, i.e., the important aspects of the chemistry of flotation of the copper sulphide minerals that occur in the Ok Tedi ore bodies, viz., chalcocite, bornite, chalcopyrite and covellite. Accordingly, this Chapter briefly reviews the flotation process and the importance of pulp and surface chemistry before considering the stability of sulphide copper minerals in aqueous systems and the available literature on the oxidation of copper minerals. This is followed by a review of the difference between selfinduced (or inherent) and collector-induced systems, the importance of mineralcollector interactions and the effect of grinding media. 12

32 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Finally, the use of a suiphide reagent in flotation processing is examined, not only with respect to the traditional usage for oxide copper mineral flotation, but also for the improved recovery of suiphide copper minerals. 2.2 Flotation Flotation may be described as an extremely complex physiochemical process involving a number of sub-processes (Trahar and Warren, 1976) which involves the separation of solid phases in a liquid phase via the introduction of a gas phase. Originally patented in 196, it allowed the processing of low grade ores which would otherwise have been classified as uneconomic (Wills, 1992). As noted previously, prior to discussing the intricacies of sulphide mineral surface chemistry, it is necessary to briefly review the rate model of flotation, followed by the influence of pulp chemistry and the importance of surface chemistry to the flotation process Flotation Model In the simplest terms, the batch flotation rate of mineral particles may be represented by a first order rate equation as dc dt (2.1) where C = the particle concentration per unit mass, at time, t k a rate constant. However, it was noted over 6 years ago (Gaudin, Groh and Henderson, 1931) that the rate constant was significantly different for particles of different size. In particular, they noted that flotation efficiency peaks in the size range and decreases above and below this range. More recently, Trahar and Warren 13

33 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG (1976), and Jameson, Nam and Moo-Young (1977), reviewed work in this area and concluded that the flotation rate of ultrafine particles (< 1 is low relative to other sizes primarily due to the decreased probability of collision between particles and air bubbles as particle size is reduced (Sutherland (1948), Flint and Howarth (1971), Reay and Ratcliff (1973)). The most recent theoretical analysis suggests the relationship between flotation rate and particle size as where d = particle diameter n = a number between 1.5 and 2. (2.2) Several workers (e.g., Sutherland (1948), and Dukhin (1961), Schulz (1977), Anfruns and Kitchener (1977) and Schulz (1989)) have attempted to model batch flotation of single particles, but with little success to plant applications. Expanding on the theme, Ralston (1992) used methylated quartz as a model system and incorporated the terms Ea and to represent collision, attachment and separation efficiencies respectively. The resultant rate equation considering other parameters (i.e., gas volumetric flow rate, G, bubble diameter, db, and Vr is the reference volume of height h, through which the bubble must rise) was postulated as: 3G EcEaEsh k= (2.3) 2dbVr The significance of these parameters were experimentally confirmed by Crawford and Ralston (1988), who established that a flotation domain exists within which particles float and is unity. Outside this range no flotation occurs, i.e., E5 is zero. 14

34 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG They showed that the equation 2.3 could be extended to the flotation of suiphide minerals, although the reactive nature of these minerals poses complexity to the model system (Ralston, 1994). Advancing Water Contact Angle no flotation. 2 2 flotation 2 I I Critical Surface Coverage, (%) Figure 2.1 Flotation threshold values (critical surface coverage or advancing water contact angle) as a function of particle size showing existence of flotation domain (Adapted from Crawford and Ralston, 1988) The Influence of Pulp Chemistry It is a common mistake for plant operators to think of the liquid phase in the flotation process as water (Lauder,1996). In fact, the liquid phase is a low strength ionic solution. Natural waters used in processing plants may contain varying concentrations of calcium, magnesium, sulphate and chloride ions. Added to the natural waters are soluble minerals in the ore and reagents (e.g., 15

35 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG lime) used for pulp chemistry manipulation. Concentrations of constituent ions from the latter often increase due to the practice of recycling water within the processing plant. All of the above have been shown to have an impact on the flotation rate of valuable minerals from gangue, usually acting through the generic terms of "activation" and "depression". Simply, activation implies an increase in flotation rate, whilst depression implies a decrease in flotation rate. Of particular interest in this work is the role of metal ions adsorbed onto suiphide mineral surfaces, which act as either activators or depressants depending on the ph of the system and the concentration of the metal ions (Shen, 1995). The activation mechanism involves the adsorption of metal ions onto the sulphide mineral surface which may act as a bridge between the surface and the collector. Even without collector, the formation of hydrophobic species such as elemental sulphur or polysuiphide may also occur. The depression mechanism arising from metal ions occurs in the ph region where metal hydroxides (or carbonates) are formed in solution and are associated with adsorption/precipitation of the hydroxide species onto the mineral surface. If the depression is undesirable, it may be reduced mechanically by abrasion with High Intensity Conditioning (HIC) or chemically with alternative ph adjustment or the use of chelating agents or dispersants. The exact solution will depend both on the nature of the adsorbed species on the mineral and the prevailing pulp chemistry Surface Chemistry of Copper Minerals The surface chemistry of copper minerals also plays an important (if not the most important) role in successful selective flotation. In particular, Attia (1975) noted that solubility, oxidation and surface electrical properties of copper minerals play a particularly significant role in the behaviour of sulphide minerals in aqueous 16

36 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG systems. Since these factors are inter-related, the knowledge of surface chemistry becomes vital to the flotation process. Quite often, the potential determining ions are supplied by the mineral surfaces, the presence of which are controlled by the solubility of the mineral and the hydrolysis of metal ions. The solubility itself is determined by the presence of different electrolytes, particle size and the oxidation-reduction process. Almost all minerals in a well divided state exhibit an electric charge in aqueous media, where ions having a charge opposite to that on the surface are drawn to the surface to form an electrical double-layer. This double-layer influences the processes by which collectors are adsorbed onto mineral surfaces. For silicate and oxide minerals, which are generally characterised as chemically inert, the adsorption phenomenon is dominated by the properties of the double-layer alone, whereas for sulphide minerals with chemically active surfaces, adsorption may be also accomplished by chemisorption. Since minerals exhibit surface charge in an aqueous environment, such charges can be manipulated by chemical control of the aqueous phase, particularly the ph. The charge of the surface then determines whether the collector will be adsorbed onto the mineral surface. It is interesting to note that even though copper suiphide minerals have been known since the pre-dynastic Egyptians, their surface chemistry is still complex and not completely understood (Attia, 1975). 2.3 Stability of Suiphide Copper Minerals in an Aqueous System The stability of sulphide copper minerals in aqueous systems can be best described with reference to Eh-pH diagrams. Figure 2.2 shows such a diagram for the copper-sulphur-water-system. An Eh-pH diagram shows the predominant species under any combination of electrochemical conditions, specified as the activity of the hydrogen ion and the electrochemical potential with respect to the standard hydrogen electrode. It is important to realise that the diagram shows 17

37 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG the thermodynamically predominant species and makes no prediction about the kinetics of any reaction which may occur if the conditions are altered. Further, the diagram is calculated (not measured) for specific activities of its constituent species in water, hence the boundaries will change according to the activity of those species and the activity of any other species that may also be present a w ph Figure 2.2 Potential-pH equilibrium diagram for the copper-sulphur-water system at 25 C, for unit activities of the sulphur ligands. (Abstracted from Garrels and Christ, 1965) 18

38 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG In Figure 2.2, chalcocite (Cu2S) can be seen as thermodynamically stable in a broad wedge across the diagram at all ph values, at potentials which are neither highly oxidising nor highly reducing. Contained within this wedge is a thermodynamically stable zone for covellite (CuS). In oxidising alkaline environments, chalcocite will tend to oxidise to cuprite, Cu2 and tenorite, CuO. In an oxidising acid environment, chalcocite will tend to dissolve, providing CuSO4. Reducing environments will produce copper metal and various hydrogenated forms of sulphide ion, the exact form of the latter depending on ph. Figure 2.3 shows an Eh-pH diagram for the copper-iron-sulphur-water system. Note that both chalcopyrite and bornite are contained in this diagram. It can be observed that like chalcocite, chalcopyrite is thermodynamically stable across the ph range, but at much more reducing potentials. As before, there is the possibility of alteration to the mineral unless the potential is controlled within the stability region. Since puips in mineral concentrating plants never maintain the reducing environments necessary for the stability of chalcopyrite due to the presence of oxygen in the water, on the basis of this diagram it would be reasoned that chalcopyrite is thermodynamically unstable and should show significant oxidation. However, the oxidation of chalcopyrite (unlike chatcocite) is known to be kinetically restricted within the times experienced in flotation plants and severe oxidation does not readily occur (Lauder, 1996). Hence, on the basis of these diagrams alone, it is reasonable to expect that if electrochemical environments are encountered in flotation puips such that suiphide copper minerals are not the thermodynamically stable species, then surface reactions may occur produce a different surface and alter the flotation properties of the mineral concerned. 19

39 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG > I w ph Figure 2.3 Potential-pH equilibrium diagram for the copper-iron-sulphur-water system at 25 C, for unit acfivities of all dissolved salts. (Abstracted from Garrels and Christ, 1965) 2.4 Oxidation of Copper Minerals From the foregoing discussion it is apparent that the oxidation of copper minerals, at least on the surface, is a very real possibility, not only prior to milling, but also in the generally mild oxidising conditions encountered in milling environments. An examination of the understanding of the oxidation reactions of 2

40 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG the copper minerals predominant in the Ok Tedi ore bodies is therefore warranted. In particular, this understanding is related to the more general argument as to whether or not copper sulphide minerals are naturally hydrophilic in the absence of collector. This argument contained many contradictions (Sutherland and Wark (1955)) and has only been partially resolved with the aid of modern analytical devices and the greater understanding of electrochemical processes. In the last twenty years, work led by Heyes and Trahar (1977) has shown that under certain experimental conditions, chalcopyrite exhibits natural floatability, particularly in a more oxidising environment. Woods (1988), Chander (1988) and Ralston (1991) confirmed that at the very least, an oxidising potential is required for collectorless flotation of sulphide minerals. Based on extensive studies on the oxidation of sulphide minerals (which are subsequently described for individual copper minerals), sulphide minerals in general undergo oxidation through stages of metal-deficient sulphides to form elemental sulphur. The generalised reaction may be represented as: MS e (2.4) (for acidic solution) and: MS + 2H2 M(OH)2 + S +2W + 2e (2.5) (for neutral and alkaline solutions) These reactions assume the formation of for the purposes of the current discussion. The natural hydrophobicity of any suiphide mineral is therefore governed by the degree of availability of metal-deficient sulphide zones provided that the zones are free of hydroxide species. The influence of oxidation products is therefore of paramount importance to the flotation process, since it is the oxidation products on the suiphide mineral surfaces that require the addition of surfactants (e.g., collector) to enhance flotation (Wills, 1992). 21

41 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Chalcopyrite Oxidation The oxidation of chalcopyrite in alkaline solution as proposed by Gardner and Woods (1979) was: CuFeS2+ 3H2 CuS + Fe(OH)3 + S + + 3e (2.6) This was examined by Biegler and Home (1984) who used cyclic voltammetry studies to detect elemental sulphur and proposed the alternative: CuFeS2.75CuS W + 3& (2.7) However, based on XPS studies, Buckley and Woods (1984) did not detect elemental sulphur and proposed that the initial oxidation of chalcopyrite proceeds as: CuFeS2 + 3H2 CuS2 + Fe(OH)3 + 3W + 3e (2.8) Chalcocite Oxidation Sato (196) examined the oxidation of chalcocite and found that chalcocite oxidizes rapidly at the surface to form compounds with varying degrees of copper deficiency, ultimately leading to covellite, i.e., Cu2S CuS + + 2e Eh log (2.9) Covellite itself is slowly oxidised to cupric ions and sulphur, i.e., CuS + S + 2e (2.1) Sato (196) further noted that oxidation was possible in the ph range 2 to 11.5, and since the electrochemical potential of chalcocite was independent of sulphate ions (S42), it was concluded that the surface of chalcocite is generally coated with covellite mineral as an oxidation product. 22

42 The Influence of Sodium Hydrogen Suiphide on Porphyry Copper Recovery at Ok Tedi, PNG In slightly alkaline solutions, Chander and Fuerstenau (1974) proposed that chalcocite undergoes reduction to give copper and soluble species at potentials less than -.4V according to: Cu2S + + 2e 2Cu + HS (2.11) and that the reverse of equation 2.11 occurs at potential range between -.5 and +.2V producing: Cu2S + H2 CuO, Cu (OH)2] + [S, GuS, S232 etc.] (2.12) In corroborating work, Leki and Laskowski (1971) measured the electrode potential of a chalcocite electrode in alkaline solutions and concluded that the chalcocite electrode could be treated as an oxide electrode on the assumption that cupric hydroxide forms under these conditions Bornite Oxidation According to Buckley, Hamilton and Woods (1984), the oxidation of bornite above -O.3V yields an iron-free copper sulphide by the following reaction at ph 9: Cu5FeS4 + 3H2 Cu5S4 + Fe(OH)3 + 3W + 3& (2.13) Above -.5V, further oxidation of sulphide occurs producing decreased copper containing sulphide. Cu5S4 + xh2o + xcu (OH) e (2.14) The cathodic reactions at -.4V and -.3V were observed to be the reverse of reactions 2.13 and 2.14 respectively. Thus, the analysis of the voltammograms showed that the total anodic current charge was greater than cathodic current charge resulting from electrode rotation, indicating the formation of soluble species. These observations were in agreement to those of Walker et al. (1984), 23

43 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG i.e., that mineral oxidation produces a Cu(Il) dissolution product, thought to be either oxo- or hydroxo- complexes such as Cu22, or Cu(OH)22t Thus, bornite, with a copper-iron ratio of 5:1, would be expected to behave more like chalcocite than chalcopyrite. The surface analysis of a ground product indicated that rapid oxidation producing hydroxide iron oxide and copper sulphate similar to that of reaction 2.13, with Buckley, Hamilton and Woods (1984) reporting that as oxidation proceeds, the iron hydroxy-oxide segregates to the surface forming an overlayer on the copper suiphide Covellite Oxidation The surface oxidation of covellite between ph 2 and 12 according to Sato (196) is: CuS + S + 2& (Eh = log (2.15) where the Eh of covellite oxidation was found to be independent of S42 activity, indicating that the oxidation chain of reactions were not in thermodynamic equilibrium Pyrite Oxidation The mechanism of pyrite oxidation, as proposed by Singer and Stumm (1969), is given by: FeS H2 + 2S42 + (2.16) + e (2.17) FeS H2 + 2S42 + (2.18) 24

44 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 2.5 Self-Induced Flotation The mechanisms by which sulphide minerals exhibit collectorless flotation were reviewed by Hayes et al.,(1 987), who concluded that suiphide minerals generally oxidise through a continuum of metal deficient sulphides with decreasing metal content through to elemental sulphur. The important aspect of collectorless behaviour is, therefore, that the solid/liquid interface resulting from oxidation is sulphur rich and hence possesses properties of bulk elemental sulphur. Note that further oxidation may lead to the production of thiosalts and ultimately sulphate, both of which can render a mineral hydrophilic. Further, Hayes et al., (1987) noted, the presence of metal ion hydrolysis products formed on sulphur rich surfaces may also reduce hydrophobicity under conditions of significant oxidation. The controversies surrounding natural hydrophobicity on freshly fractured sulphide minerals have been amp'y reported in the literature (Heyes and Trahar (1977), Luttrell and Yoon (1984), Trahar (1983) and Fuerstenau and Sabacky (1981). Clearly, only certain minerals (e.g., talc, mica, sulphur) display true natural flotability, due to their specific crystal structures. Comparatively, sulphide minerals such as chalcopyrite and pyrite have, prior to oxidation, only been shown to posses weak natural flotation behaviour. For chalcopyrite, this was observed under both oxidising and reducing conditions by Hayes and Ralston (1988). It was concluded by Hayes and Ralston (1988) that collectorless flotation was dependent primarily on the oxidation state of the sulphide mineral surface, as well as the stability of oxidation species in the prevailing environment. Buckley and Woods (1984) proposed the following oxidation reaction for the collectorless flotation of chalcopyrite under miodly oxidising potentials: CuFeS2 + 3H2 CuS2 + Fe(OH)3 + 3W + 3e E =.55 V (2.19) i.e., the chalcopyrite surface oxidises to chalcocite with the loss of iron from the surface. However, the iron is subsequently hydrolysed to ferric hydroxide which can remain attached to the particle surface. (This ferric hydroxide may be 25

45 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG subsequently removed by intense mechanical agitation, termed High Intensity Conditioning.) 2.6 Collector-Induced Systems The collector-induced flotation of sulphide minerals occurs by chemical adsorption and ion exchange mechanisms (Cook and Nixon (195), Sutherland and Wark (1955)). Plaksin's (1959) discovery of oxygen as a pre-requisite for flotation was initially attributed to a combination of oxidation of the mineral and the reduction of xanthate. This was subsequently disproved by Gardner and Woods (1977) who showed that flotation can occur without oxygen by manipulating the potential on the mineral sulphide electrode. For a collector based system, the selective flotation of sulphides in a mixed mineral system occurs as a result of differences in the rate of oxidation of the xanthate. In particular, Woods (1976) showed that the activity in oxygen reduction on different sulphide minerals has a greater bearing on selectivity than merely the differences in the activity for the oxidation of xanthate. Attempts to examine the collector species on the mineral surface have also lead to conflicting results. Leppinen, Basilio and Yoon (1989) used an in-situ AIR (attenuated total refectance) technique to examine both pyrite and chalcopyrite in a xanthate system. This showed dixanthogen to be the reaction product in the case of pyrite, but for chalcopyrite, the reaction products on the chalcopyrite surface were either dixanthogen or cuprous xanthate depending on the applied potential. These results were contrary to Granville, Finkelstein and Allison (1972) who detected dixanthogen on chalcopyrite. The conflicting results may be related to the differences in the rest potential of the minerals, which is highly dependent on their pretreatment. 26

46 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 2.7 Mineral-Collector Interactions in Mixed Sulphide Systems In mixed mineral systems, complex interactions may occur between sulphide minerals. These interactions occur through the aqueous phase by dissolution and redeposition of metal ions on sulphide minerals, and may be accelerated by a mechanism known as galvanic coupling. The presence of pyrite in ores is expected to increase mineral interactions and enhance oxidation of the other sulphide minerals due to the higher oxidation potential of the pyrite. The enhanced oxidation caused by galvanic coupling may then influence the collector induced properties of the other sulphide minerals. (Nakazawa and lwaski (1985, 1986)). Work by Guy and Trahar (1985) showed that the presence of other minerals could impact the selectivity of a separation. They found that good selectivity achievable in a single mineral system was not reproduced in a mixed mineral system, due to a combination of factors including surface oxidation and metal ions and their hydrolysis products forming either in solution or at the solidsolution interface. Further work by Hayes and Ralston (1988) showed that selectivity was reduced when chalcopyrite-galena mixtures were ground in an oxidising environment but was restored when mixtures were ground in a reducing environment, probably due to reduced mineral interactions during grinding. 2.8 Effect of Grinding Media on Copper Flotation The separation of value minerals in fine grained sulphide ores involves grinding. The presence of highly electrochemically active grinding media, commonly steel, may result in strongly reducing conditions (Woodcock and Jones, 197) which may affect the flotation of sulphide minerals when a mildly oxidising potential, necessary for flotation, is not attained (Johnson, Jowett and Heyes, 1982). 27

47 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG The generally accepted grinding media corrosion reduction potentials were summarised by Grano et. al. (1994) as: reactions and standard and Fe(OH)3 + e Fe(OH)2 + H E=: -.87 V (2.2) Fe(OH)2 + 2& Fe + 2H E = -.56 V (2.21) suggesting that oxidation of iron is strongly favoured due to the tow standard reduction potential. The grinding pulp also suffers a reduced oxygen content due to the balancing reaction + 2H2 + 4e 4H E = +.4 V (2.22) The effect resulting from the introduction of iron oxyhydroxide to the pulp from reactions 2.2 and 2.21, coupled with the depletion of oxygen from the pulp (Equation 2.22) accounts for the slow flotation kinetics often observed at the early stages of plant flotation (Forrsberg and Subrahmanyam, 1993). Other studies have shown that adsorption of iron oxyhydroxide species onto sulphide minerals may in part be related to the relative electrical properties of the underlying mineral, so that grinding above ph 8 assists in the dispersion of iron oxyhydroxide species from the chalcopyrite surface (AMIRA Project P397 Progress Report 4, 1995). Suiphidisation Given that the excessive oxidation of sulphide mineral surfaces results in the generic formation of metal hydroxides which impede the formation of collectormineral bonds, one mechanism by which this process may be reversed is the introduction of a sulphide reagent into the pulp. It is generally considered that the inclusion of the S2 ion is the important constituent, regardless of whether it is contained in sodium sulphide (Na2S), sodium hydrosulphide (NaHS) or 28

48 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG ammonium sulphide (NH4)2S. Laboratory work has also utilised polysulphide, though no plant applications have been discovered. The sulphidisation process was originally developed in the U.S. between 1915 and 192, specifically for oxide copper mineral flotation (Rey,1957). The early users recognised that the technique was also suitable for oxidised lead ores where the gangue is basic. Other applications have been reported (Ueno, Williams and Murray, 1979) where suiphide precipitation was demonstrated to be an alternative to hydroxide precipitation for removing heavy metals from industrial waste waters, especially in the presence of certain complexing and chelating agents. In aqueous systems, ph is the controlling variable in the oxidation of hydrogen sulphide (Malghan, 1986). Below ph 6, 'molecular hydrogen sulphide' is the predominant reduced suiphide species. Above ph 7, the reduced sulphur species is equally divided between 'dissolved hydrogen suiphide' and the 'bisuiphide species' [HS1, the latter being the predominant species between ph 8 and 11. Above ph 11, the predominant species is the S2 ion. The bisulphide species is believed to be the most reactive species in the free radical chain reaction (Chen, 1974) According to Castro, Goldfarb and Laskowski (1974), the reaction between sulphide ion and the surface of oxide minerals is significant but complex, given that other parallel reactions may be taking place. The three major steps recognised were, the adsorption of sulphide ions with the formation of copper sulphide, sulphide oxidation and desorption of oxidised compounds by ion exchange. Bustamante and Castro (1979) proposed the following reaction for malachite sulphidised with sodium hydrosulphide: CuCO3.Cu(OH)2+ HS + Oft Cu(OH)2.CuS + C32 + H2 (2.23) 29

49 The Influence of Sodium Hydrogen Suiphide on Porphyry Sufiphide Copper Recovery at Ok Tedi, PNG Reaction 2.23 continues with the bulk of the particles to form copper sulphide coatings on the malachite. In pure mineral systems, malachite floats better at high concentrations of sodium sulphide (Soto and Laskowski, 1973), whilst chrysocolla is depressed by the presence of thiosulphate ions, even if excess sulphide is removed by filtration prior to flotation (Castro, Goldfarb and Laskowski, 1974). For chrysocolla, recovery was at a maximum between ph 9 to 9.5, and deteriorated as ph was increased above 9.5 (Castro, Goldfarb and Laskowski, 1974). It was Jones and Woodcock (1978) who made the landmark discovery that the most effective use of suiphide reagent was achieved through the use of a technique called controlled potential suiphidisation, commonly abbreviated to CPS. They demonstrated that the controlling variable in the formation of sulphide coatings on oxide minerals (both copper and lead) was the maintenance of a concentration of suiphide ion in the pulp for a sufficient time to allow the suiphidisation reactions to occur. After the passage of the reaction time, the pulp potential must be raised (usually with oxygen in air) to allow flotation with collector to proceed. Measurement of the concentration of suiphide ion in the pulp was effected with a silver ion-selective-electrode (ISE), which shows a linear potential response with respect to the required concentration of sulphide ion. For oxide copper sulphidisation, the required potential of the silver ISE was -5 mv measured against a standard calomel electrode (Jones and Woodcock,1978). For oxide lead suiphidisation, the corresponding potential was -6 mv (Jones and Woodcock, 1979). Since the silver ISE is hardly a robust instrument suitable for continuous use in a mineral processing environment, the technique was extended to replace the silver ISE with a platinum electrode, recognising that daily calibration of the platinum electrode with the silver ISE was required to account for ore-dependent offsets to the platinum electrode. 3

50 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Since 1978, the CPS technique has gradually gained wide acceptance. Although Jones and Woodcock's work was performed with xanthates as collectors, Nagaraj and Gorken (1989) showed that the same principles applied, irrespective of the choice of collector (i.e., xanthate, dithiophosphate, thionocarbamate or dithiophosphinate). For oxidised sulphide copper minerals at Ok Tedi, Senior and Creed (1992) proposed that one possible way of removing hydroxide species formed on mineral surfaces was by the reaction between soluble suiphide and precipitated metal hydroxide, converting copper hydroxide to copper sulphide by the reaction: Cu(OH)2+ HS CuS + H2 + Oft (2.24) Reaction 2.24 is thermodynamicaoly favoured as the solubility product of copper sulphide (8 x is lower than that of copper hydroxide (5 x 1-2). 2.1 Concluding Remarks From the above review of literature, it is apparent that the following conclusions may be drawn with respect to the flotation of the suite of copper suiphide minerals contained within the Ok Tedi porphyry sulphide ores: 1. Pulp and surface chemistry are particularly important to the flotation of sulphide ores. 2. The prevailing electrochemical conditions in the pulp (Eh, ph) are particularly important to the stability of copper minerals in an aqueous phase. 3. Sulphide copper minerals can be expected to at least partially oxidise in a milling environment and that the surface oxidation reactions are of specific importance to the flotation behaviour. 4. Different sulphide copper minerals undergo different oxidation reactions. 31

51 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 5. Whilst self-induced (i.e., collectorless) flotation can occur, collector induced systems are generally more robust and apply over a greater range of electrochemical conditions. 6. Mixed sulphide mineral systems are generally more complex than laboratory single mineral systems, due particularly to the interaction between the sulphide minerals themselves. 7. The grinding environment can have a chemical effect on the flotation pulp chemistry, due to the corrosion reactions associated with the grinding media. 8. Sulphidisation, normally associated with the flotation of oxide copper minerals, shows some promise for the improved flotation of sulphide copper minerals. 32

52 The Influence of Sodium Hydrogen Suiphide on Porphyry Copper Recovery at Ok Tedi, PNG CHAPTER III 3. EXPERIMENTAL 3.1 Introduction The laboratory ore studies, single mineral experiments and plant trials were aimed at achieving the project objectives specified in Section 1.5. This chapter details the experimental conditions and equipment in the following manner :- (1) Laboratory Ore Studies, (2) Single Mineral Studies, (3) Plant Investigations. 3.2 Laboratory Ore Studies The laboratory ore studies were carried out in five (5) parts as follows :- (1) Standard laboratory flotation as a function of ph comparing lime addition to both the mill and cell. (2) Size by size analysis of the above tests as a function of ph. (3) Standard flotation coupled with controlled potential sulphidisation (CPS) of the feed prior to flotation. (4) Controlled potential sulphidisation (CPS) continued during flotation. (5) Addition of sodium hydrosulphide to the laboratory grinding mill. The following sub-sections discuss the equipment and reagents used in the flotation testing and sizing procedures, as well as a detailed description of the ore samples used. 33

53 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Equipment and Reagents Laboratory grinding was conducted in a mild steel mill with a 9 kilogram mixed charge of steel balls. The batch laboratory flotation unit used was a Denver 12 machine equipped with a 4 litre stainless steel cell. Reagent sourcing for the laboratory test work consisted of both plant and analytical supplies. Where a plant reagent was available, it was used. Where the reagent was not available in plant stocks, it was sourced from analytical supplies. Reagent specifications are as follows: Collector : Cytec a blend of diisobutyl di- and mono- dithiophosphates. Used as a pure solution, as supplied, and added via a micro syringe. Frother: Oreprep OTX-14 - a mixture of higher alcohols and polyglycols. Used as a pure solution, as supplied, and added via a micro syringe. Sodium Hydrosuiphide (NaHS) : a solid flake supplied as 7% active NaHS. Used in the laboratory as a 1% w/v solution, and added via a Radiometer Ehcontrolled dosing system (described below). Lime (Ca(OH)2) : manufactured at Folomian from Geneva Ridge limestone, typically 76-8% CaO. Added in the laboratory as a solid. Sulphuric Acid (H2S4) : 98% w/w, Technical Reagent Grade. Nitric Acid (HNO3) : 7% w/w, Technical Reagent Grade. Hydrochloric Acid (HCI): 36 % w/w, Technical Reagent Grade. Sodium Hydroxide (NaOH) : Pellets, 97% minimum NaOH, Technical Reagent Grade. Ethylene diaminetetraacetic acid disodium salt (EDTA), Analytical Reagent Grade. Water: Untreated tap water, typically less than 1 ppm of any particular ion. 34

54 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok TedI, PNG Controlled Potential Sulphidisation (CPS) was effected in the laboratory with a Radiometer PHM82 ph/mv meter, a calibrated Radiometer combined platinum/silver chloride electrode, a Radiometer MNV-1 magnetic valve, and a Radiometer TTT8O auto-titrator. Sodium hydrosulphide is added from a burette to achieve a pre-set Eh value, the latter determined by the combined electrode Laboratory Ores Initially, two 1 kilogram lots of monzonite and monzodiorite porphyry suiphide ore samples were obtained from the mine. The ore samples were dried in the oven at 7 C overnight, crushed to minus 1.7 mm and sub-divided with a rotary splitter to sub-samples of 215 grams. Sub-samples were stored in sealed aluminum bags until immediately before each test. Due to the number of tests required to examine the Eh-pH environment, additional ore samples of both the monzonite and monzodiorite porphyry ore types were required. Hence, initial samples were denominated as Monzonite 'A' (MZ'A') and Monzodiorite 'A' (MD'A') and the additional samples denominated as Monzonite 'B' (MZ'B') and Monzodiorite 'B' (MD'B') Characterisation of Laboratory Ores by QEM*SEM Ore samples were ground in the laboratory mill to 8% passing and submitted to the CSIRO Division of Minerals in four size fractions for Quantitative Evaluation of Mineralogy by Scanning Electron Microscope (QEM*SEM). The samples covered the entire size range except for the fraction and were composited as and size fractions. Note that QEM*SEM is limited to size fractions greater than The copper deportment of the ores by QEM*SEM analysis are shown in Tables 3.1 and

55 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Table 3.1 shows that the predominant copper mineral in the monzonite sample, MZ'A', is digenite (-45%), followed by both chalcopyrite and bornite ( 25% each). Conversely, approximately 9% of the copper mineralisation in the monzodiorite sample, MD'A', is chalcopyrite. Although there are also significant quantities of other copper minerals in both samples, the 'other Cu minerals" as determined by QEM*SEM is an iron-rich digenite phase, and may be broadly included in the digenite classification. Table 3.1 Copper Partitioning Across the Copper Bearing Phases in Monzodiorite 'A' and Monzonite 'A' Relative Cu Distribution % Monzodiorite Porphyry Sulphide 'A' Monzonite Porphyry Sulphide 'A' Size (sm) -212/ /+31-31/ /+13 Digenite Covellite Bornite Chalcopynte , Cu_Metal Cu_Ox(Cuprite) 1.2 Cu Fe_Metal/Ox Malachite Chrysocolla Turquoise Other Cu Minerals Goethite Table 3.2 shows that the second monzonite sample, MZ'B', contains a similar copper deportment to MZ'A'. However, the second monzodiorite sample, MD'B', differs from MD'A' in that significant quantities of bornite are present in the MD'B' sample. Chalcopyrite is necessarily reduced, but is still the predominant copper mineral. The predominant gangue phases in all samples belong to the feldspar group, with the relative proportion of potassium feldspar to soda/lime feldspar for the monzonite ore being substantially higher than that for the monzodiorite ore. Grain size of copper minerals is equally important, in particular size fractions outside the intermediate size range (i.e., and where most copper loss occurs. Estimated copper mineral grain size, estimated from phase specific surface area (PSSA), for each sample of monzonite and monzodiorite are presented in Tables 3.3 and

56 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Table 3.2 Copper Partitioning Across the Copper Bearing Phases in Monzodiorite 'B' and Monzonite 'B. Relative Cu Monzodiorite Porphyry Sulphide 'B' Monzonite Porphyry Sulphide 'B' II Distribution % J Size (pm) -212/+15 J[-15f /+31-31/ /+15-15/+75-75/ Digenite Covellite Bornite Chalcopyrite , Cu_Metal.6 Cu_Ox(Cuprite) CuFe_Metal/Ox Malachite Chrysocolla Turquoise Other_Cu_Minerals Goethite Table 3.3 PSSA (pm) Derived Mean Grain Sizes in Monzodiorite 'A' and Monzonite 'A' PSSA Derived Mean Monzodiorlte Porp hyry Suiphide 'A' Monzonite Porphyry_Suiphide 'A' Grain Size (pm) I[ -15/ / /+75-75/+31 ]1-31/+13 Chalcocite/Digenite Covellite Bornite/Fe-Digenite Chalcopyrite Cu_Metal Cu_Ox(Cuprite) 4 6 CuFe_Metal/Ox Malachite Chrysocolla Turquoise Other Cu Minerals Fe-Sulphides Both copper and iron sulphides in the monzodiorite ores are appreciably coarser than in the equivalent size fractions in the monzonite ores. Table 3.4: PSSA (pm) Derived Mean Grain Sizes in Monzodiorite 'B' and Monzonite 'B' PSSA Derived Mean Monzodiorite Porphyry Suiphide 'B' Monzonite Porphyry Suiphide 'B' Grain Size (pm) -212/+15-15/+75-75/+31-31/ /+15-15/+75-75/ Chalcocite/Digenite Covellite Bornite/Fe-Digenite Chalcopyrite Cu_Metal 4 Cu_Ox(Cuprite) 7 CuFe_Metal/Ox Cu-CO3 (Malachite) 1 6 CuFe_Ox/C Chrysocolla Turquoise 7 Other Cu Minerals Fe-Sulphides

57 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Flotation Test Procedure All flotation tests were conducted in the following manner; 215 gram samples were ground to 8% passing in the laboratory ball mill and transferred to the Denver D12 flotation cell. Lime was added to either the mill or cell, dependent on the conditions required. Flotation conditions involved raising the ph to 11.5 with lime or reducing ph with dilute sulphuric acid (H2S4) and then adding 15 g/t Cytec 7249 and 2 g/t Oreprep OTX-14 frother. After two minutes conditioning, flotation was conducted for 1 minutes, collecting sequential concentrates for 1, 2, 2 and 5 minutes. Where sulphidisation was required, a 1% (w/v) solution of NaHS was added after lime addition for 1 minute to a predetermined set point. The appropriate collector and frother additions were made after the suiphidisation, and a further one minute conditioning allowed. Total conditioning time was thus 2 minutes, with or without sulphidisation. The flotation behaviour of copper minerals in porphyry sulphide ores with respect to controlled potential sulphidisation (CPS) were investigated in the laboratory in two separate parts. The first part involved examining the Eh-pH environment for porphyry sulphide ores. Following the success of a temporarily reduced Eh environment with sodium hydrosuiphide in improving copper recovery, the second part of the ore studies involved the comparison of the size by size behaviour of NaHS treated samples with samples previously examined for the size by size behaviour with respect to ph Examination of Flotation Eh-pH Environment In these series of tests, a range of ph and values were evaluated using lime to adjust ph and NaHS to control potential. Three pulp potential control methods were investigated: 38

58 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG (1) Controlled Sulphidisation of Flotation Feed. (2) Continuous Sulphidisation throughout Conditioning and Flotation. (3) NaHS Addition to Laboratory Mill. The Eh was measured using a combined platinum electrode and was calibrated using a solution (Light, 1972). The smooth platinum electrode was maintained in bright condition by frequent cleaning in a chromic acid solution. This was important because of possible problems caused by poisoning of the platinum electrode by sulphide ion (Natarajan and Iwasaki, 1973). Each test series is described below Controlled Suiphidisatlon of Flotation Feed This method uses the addition of NaHS to flotation feed at an set-point for one minute prior to collector and frother additions. Controlled addition of NaHS was maintained as previously specified. Naturally, with air as the flotation gas, rises immediately after the commencement of flotation, taking approximately 15 seconds to reach the air-set potential. Air-set potential is typically = +5 to +loomv at ph Continuous Suiphidisation during Flotation Since it is generally reasoned that it is important when using NaHS to maintain the low during the conditioning period, but not during flotation (in fact, it is important that the be allowed to rise for effective flotation to occur), a series of tests were conducted to highlight this fact, i.e., that maintaining a low set point during flotation would provide poor recovery. Tests of this nature were conducted on the Monzodiorite 'B' samples. 39

59 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Sulphidisation during Grinding The required NaHS solution was added to mill post-grinding. These tests were aimed at determining if NaHS could assist lime in limiting the formation of metal hydroxides during grinding with lime at ph ph and Eh measurements were taken after the grinds and just before flotation commenced Subsequent Handling of Flotation Products All flotation products were filtered, dried and weighed. Where the copper recovery was required on a size by size basis, the samples were wet screened using a screen, retaining both the and fractions. These size fractions were dried. The fraction was sieved using a Tyler Rotap sieve shaker and 16p.m, and 38gm sieves. Sieve shaking time was fifteen minutes. The fractions from dry and wet screening were combined for cyclosizing. Approximately 5 grams of sample was slurried with water in a beaker and transferred to the sample container of the Warman cyclosizer. The sample was bled from the container into the water stream by opening the sample valve so that the whole of the sample was released over a period of five minutes. Cyclosizer products collected were: + C2 (-38/+3 1 -C2+C3 (-3 1/+22 C4 (-22/+ 15 C5 (-15/+13 C6 4

60 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Size ranges of the Cyclosizer fractions were allocated according to the manufacturer, Warman International Ltd (1981). 3.3 Single Mineral Studies Single mineral studies were conducted to examine the oxidation behaviour of sulphide copper minerals, the response of oxidised chalcocite to suiphidisation, and to correlate the observed behaviour with laboratory ore and plant studies. The following sub-sections give the composition of the single mineral samples used, as well as the details of the dissolution tests, zeta potential determinations by electrophoresis, and EDTA extraction tests Composition of Single Minerals The elemental composition of the single mineral samples are described by their chemical composition in Table 3.5. Apart from some minor contamination with silica, the samples are effectively pure minerals. Table 3.5 Elemental Compositions of Experimental Single Minerals Sample Assays Source Cu (%) Pb (%) Zn (%) Fe (%) II S (%) Si2 (%) Chalcocite 74.3 < Messina, Transvaal Bornite Arizona Coveilite 67. < Butte Montana Samples of chalcocite, covellite and bornite were subjected to BET (Braunauer, Emmet and Teller) surface area determinations to allow subsequent calculation of copper dissolution per surface area of minerals. The measurements were performed with a Micromeritics Accusorb 21 E Surface Area/Pore Volume Analyser, using nitrogen and krypton as the absorbates. The results of BET surface area analysis are given in Table

61 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok TedI, PNG Table 3.6 BET Surface Area of Single Mineral Samples Mineral BET Surface Area (m2g1) Chalcocite.346 Bornite.795 Covellite Dissolution Studies The dissolution behaviour of copper ions from chalcocite, coveuite and bornite were investigated at ph 4, 5 and grams of each mineral sample was ground with a mortar and pestle for five minutes in milli-q water. The ground product was transferred into a 5 cm3 beaker stirred with a magnetic stirrer and purged with nitrogen gas. The desired ph was attained with either dilute NaOH or HCI solutions to raise or lower ph respectively. When the desired ph was reached, the nitrogen purging gas was replaced with oxygen gas. 2 cm3 slurry aliquots were extracted with a graduated syringe at times t =, 5, 1, 2 and 3 minutes after oxygen was introduced. Slurry aliquots were filtered on millipore filter paper and concentrations of copper, iron and sulphur in solution measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). Dissolution studies were also conducted on the Monzonite 'A' and Monzodiorite 'A' ore samples. Samples of the ores were ground as for a laboratory flotation test, transferred to a laboratory flotation cell, and the ph raised to 12 with lime in one ph unit increments, removing a small amount of pulp after each increment. Second samples of each ore were similarly ground and the ph lowered with sulphuric acid in one ph unit increments, with a small amount of pulp removed 42

62 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG after each increment. The removed pulp samples were filtered to remove solids and the liquor analysed for copper content Zeta Potential by Electrophoresis Zeta potential as defined by electrophoresis experiments were conducted in three parts, i.e.; (1) Zeta potential of unoxidised chalcocite. Oxidation was restricted by the use of nitrogen as a purging gas. (2) Zeta potential of oxidised chalcocite, covellite and bornite. Oxidation was simulated with the use of oxygen as the purging gas. (3) Zeta potential of oxidised chalcocite after sulphidisation with M NaHS. XPS samples were also collected during this experiment. Two grams of single mineral samples were ground using a mortar and pestle in 1 cm3 of milli-q water and then made up to 5 cm3 with milli-q water in a glass beaker, agitated by a magnetic stirrer and purged with nitrogen to prevent oxidation during ph adjustment. The experimentally desired slurry ph was then raised or lowered with either dilute NaOH or dilute HCI solution to yield ph 4, 5, 6, 7, 8, 9, 1, 11 and 11.5, and the purging either Continued with nitrogen or replaced by oxygen for five or sixty minutes as the experiment required. For the sulphidisation of oxidised chalcocite experiment, a ten minute oxygen purge at each desired ph was followed by the addition of NaHS to yield a M NaHS solution. Since continued purging with oxygen after the NaHS addition would consume the NaHS, purging gas was switched from oxygen to nitrogen immediately prior to NaHS addition. After completion of the experimental conditions, a 1 cm3 aliquot of dilute slurry was extracted with a graduated syringe and placed in an observation cell in a 43

63 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Rank Brothers Microelectrophoresis (Mark II) apparatus and a known voltage applied across the cell. The induced velocities of particles (termed "mobility') were determined with the aid of a microscope, taking the average readings of the forward and reverse flows from ten mobility measurements at two stationary planes, successively reversing the platin urn electrode polarisation. Average mobility was subsequently converted to zeta potential using the Smoluchowski equation, as the ratio of the particle radius to double layer thickness (Ka) is large (Hunter, 1981; Shaw, 198). U = U 'Ix = = (3.1) where the electrophoretic mobility, U, is defined as electrophoretic velocity, U, per unit field strength, x; is the permitivity, is the permitivity of a vacuum and 1 is the dynamic viscosity. At room temperature (298 K), and substituting the following physical constants; =.8937 x 1 N s m2 e 8r Er E=8.854x112Fm1 into equation (3.1), the Smoluckowski equation is obtained (Hunter, 1981). = Ii m2 (3.2) EDTA Extraction and XPS Analysis The EDTA extraction of and suiphidised chalcocite was examined to determine the extent of oxidation at high ph where natural dissolution of chalcocite was not observed to occur, i.e., at ph 7 or above. 44

64 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG For the pre-oxidised part of the examination, 1-2 M EDTA was added to aliquots of ground chalcocite slurry (as in Section 3.3.3) after, 5, 1, 2 and 3 minutes purging with oxygen at ph 7, 9 and After five minutes conditioning with the EDTA, the aliquot was filtered and the filtrate assayed for copper. Results were expressed as moles Cu per square meter of mineral surface, and indicate the total surface oxidation of chalcocite, since the latter can be equated with the EDTA extractable copper. Analysis of EDTA extraction of the pre-oxidised chalcocite is described in Section The sulphidisation part of the investigation was done in two experiments ; the first involving NaHS and nitrogen, and the second involving NaHS and oxygen. In each case, a ground chalcocite sample at ph 11.5 was purged with oxygen for ten minutes to achieve oxidation of the chalcocite prior to the addition of 13M NaHS. Immediately prior to NaHS addition, the purging gas was switched to nitrogen to prevent oxidation of the NaHS. The oxidised chalcocite was allowed to condition with NaHS for five minutes. After NaHS conditioning, the purging gas remained as nitrogen for the first experiment, whilst in the second experiment it was switched to oxygen. For both experiments, aliquots were removed at, 5, 1, 2 and 3 minutes and mixed with 1.2 M EDTA for five minutes before filtration and analysis of the filtrate for copper. Results were expressed as moles Cu per square meter of mineral surface. Analysis of the sulphidisation of oxidised chalcocite is described in Section Samples of the slurry were removed for XPS analysis prior to the NaHS addition and after conditioning with NaHS for five minutes with the nitrogen purge. The XPS samples were sealed with silicone rubber and snap-frozen until analysed. Analysis of the XPS samples is described in Section

65 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 3.4 Plant Investigations Plant investigations consisted of three parts; (1) An initial survey to establish "normal" behaviour of ores within the Folomian Concentrator. Apart from the collection of metallurgical samples, Eh and ph was measured, EDTA extractions were performed on selected streams, and samples for XPS collected for later analysis. (2) After the correct conditions for the addition of NaHS had been established in the laboratory, suiphidisation plant trials were conducted with NaHS to establish the benefits within the plant. (3) An "on-off" survey was conducted with NaHS to determine the changes in pulp chemistry conditions when NaHS was used, and to allow comparison with laboratory results. As with the original survey, the "on-off" survey included collection of metallurgical samples, measurement of Eh-pH, EDTA extraction of selected samples and collection of XPS samples for later analysis. The following sub-sections describe the methodology for the plant surveys and the sulphidisation plant trials Plant Surveys Plant surveys were conducted according to traditional methodology, i.e., wait until the plant is receiving a more or less consistent feed blend and operating conditions within the plant are such that the plant is achieving "steady-state" operation. Although the acceptance of the existence of such a condition can be highly subjective, the condition may be determined after the event by the degree to which the obtained samples constitute a self-consistent data set, i.e., the amount of adjustment required by a data-smoothing routine to provide a mass and elemental balance around the circuit. The ability to obtain such a data set is made more difficult in a copper porphyry operation (compared to, say, a lead- 46

66 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG zinc operation) due to the similarity of assay values in the tailings of the rougherscavenger Unit, e.g., the true of rougher cell 9 tailings may be.3 % Cu whilst rougher cell 1 tailings may be.27% Cu. The collection of samples compounded over time to provide such a small difference can be a difficult task and requires intelligent interpretation during the data-smoothing process to ensure that a true picture emerges. Accordingly, although significant detail was attempted in the first survey (14 February 1996), the survey was reduced to 1 samples during the data smoothing due to overlap of rougher cell tailing assays. Due to the above mentioned problems, a detailed survey was not attempted in the 'on-off" survey conducted with NaHS on the 22 August The number of samples collected during the "on-off" trial were also reduced to decrease the time required for sample collection, as feed comparability was required between the two surveys. As noted previously, both surveys required the collection of samples, as well as measurement of pulp chemical conditions, EDTA extractions and XPS sample collection, all of which must be done at the same time. In the case of the "on-off" survey, it was necessary to survey the circuit with NaHS "on" for one hour, turn the NaHS off and allow the circuit to restabilise for one hour, and then collect the "off" survey for a further hour. When the NaHS was turned off, it was also necessary to increase frother addition by 5%, a requirement discovered during the NaHS trials Metallurgical samples For each sample collected during a survey, sub-samples were collected every 15 minutes, i.e., four sub-samples were composited to make one sample. 47

67 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi PNG Pulp Chemical Measurements Depending on the survey requirements, different streams were selected for pulp chemical measurements. Measurements consisted of any or all of Eh, ph, dissolved oxygen (do2) and temperature on samples selected from the list of plant streams given in Table 3.7. Table 3.7 Pulp Chemistry Sampling Points Sample Number Measurement Point 1 Ball Mill Cyclone /F 1 2 Ball Mill Cyclone /F 2 3 Distribution Box 4 Rougher cell 1 5 Rougher cell 3 6 Rougher cell 5 7 Rougher cell 7 8 Rougher cell 9 9 Scavenger cell 2 1 Scavenger cell 4 11 Scavenger cell EDTA Extraction Samples The EDTA (Ethylenediaminetetra-acetic acid, disodium salt) extraction procedure involved sub-sampling 1 cm3 of slurry with a graduated syringe from a freshly obtained sample of plant pulp, and transferring into 19 cm3 of 3% w/w EDTA solution. The resulting 2 cm3 solution was conditioned for five minutes. 2 cm3 of solution was then sub-sampled with a syringe and filtered on a.22 millipore filter paper. A background filtrate was also prepared by diluting 1 cm3 of slurry to 2 cm3 and filtering a 2 cm3 sub-sample on a second.22 millipore filter paper. The filtrate were acidified with concentrated nitric acid to prevent loss of metal ions by hydrolysis (Grano, 199). All filtrates were assayed for dissolved copper by ICP and after subtracting the background concentration, EDTA extractable copper was expressed as a percentage of total copper contained in the solids. 48

68 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG EDTA extractions were conducted on samples during ore and single mineral test work as well as plant surveys Sampling for XPS Analysis The X-Ray Photoelectron Spectroscopic (XPS) samples were collected during single mineral experiments and also during the plant surveys. Samples were collected in 5 ml vials, immediately sealed with silicon rubber and purged with high purity nitrogen prior to "snap-freezing" in liquid nitrogen. The samples were kept frozen until arrival at Adelaide. Upon arrival in Adelaide, the sample preparation procedure involved desliming by ultra-sonication followed by decantation. This process was proven (Smart, 1991) to remove colloidal iron hydroxide-oxides that are not attached to the mineral surfaces and are not relevant to flotation response. Other oxidised materials, such as suiphide fines, are not removed by this treatment. Slurries were dried under the fore-vacuum of the spectrometer prior to their introduction to the chamber. The spectrometer used for the XPS analysis was a Perkin Elmer PHi 56 unit with a Mg Kcx X-ray source Sulphidisation Plant Trials The first attempt to apply NaHS to rougher feed at Ok Tedi followed the suggestion of Senior and Creed (1992) and involved controlling NaHS dosage on a gram per tonne of new feed. Sampling was conducted every thirty minutes for two hours with NaHS and without NaHS with 3 minutes given for stabilization after NaHS was taken off (Wawako,1995). The overall results using a paired t- test comparing the mean copper and gold recoveries for the trial period showed no significant difference between the means at 95% confidence level. (Wawako, 1995). This was despite laboratory tests which showed a mean gain of 4% 49

69 The Influence of Sodium Hydrogen Suiphide on Porphyry Copper Recovery at Ok Tedi, PNG copper recovery at a dosage of 5 grams of NaHS per tonne of rougher feed (Orwe, 1993). The use of NaHS for suiphidising copper sulphide minerals was subsequently discontinued until the combined re-instigation by Glen, Heyes and Senior (1995) and the current study. For the purposes of this work, the trial conducted and reported by Wawako (1995) was NaHS Plant Trial #1. It is clear in hindsight that the initial trial was unsuccessful due to the lack of understanding of Eh measurement and control, and allowance for the increased presence of dissolved oxygen in mill pulps, compared with the laboratory. It became obvious after subsequent plant and laboratory CPS trials that the 5 g/t NaHS addition rate used in the first trial was insufficient for effective sulphidisation Sulphidisation Control System The control loop for CPS of the rougher feed is shown in Figure 3.1. The design was by David Lauder, Senior Metallurgist - Development of Ok Tedi Mining Limited, with assistance from the OTML Mill Instrument Group. The basic control ioop involved measuring in the rougher feed and using this value to control NaHS addition to the grinding circuit product. Between the NaHS addition point and the measurement point was a 5 meter pipe, which was found to have a passage time of two minutes. The pipe passage time equated very fortuitously with the required laboratory conditioning time to provide adequate suiphidisation. Further, the pipe was closed and prevented the introduction of oxygen into the pulp during suiphidisation. Not shown in Figure 3.1, the NaHS tank level was monitored by an ultrasonic level detector which caused the tank to be refilled when below 6% and not to overfill the tank. NaHS flow rate measurement, coupled with plant weightometer information, allowed the calculation of real-time NaHS consumption. 5

70 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG ph Figure 3.1 Simplified CPS Control Loop Based on laboratory test work (described in Chapter VI), the controller set point was set to -25 mv, assuming a flotation ph = However, it was realised prior to installation that if ph dropped due to lime feeding problems, then maintaining at -25 mv would result in excess addition of NaHS and subsequent copper depression. Accordingly, it was decided to use a Nernstian compensation according to; 59(11.5x) where x = measured ph of flotation feed (3.3) As shown in Figure 3.1, the measured ph of the flotation feed was therefore used in conjunction with the operator selected (assuming a flotation feed ph of 11.5) to calculate a ph dependent set point at Cl. The value at Cl was then cascaded to the controller at C2, which compared the cascaded value with the measured and controlled the NaHS addition via PID control. 51

71 The Influence of Sodium Hydrogen Suiphide on Porphyry SuOphide Copper Recovery at Ok Tedi, PNG In practice, the Nernstian compensation was observed to work extremely well, as true Nernstian behaviour has often been observed in high alkalinity systems (Lauder, 1996) Plant NaHS Trial #2 The first CPS trial (Trial #2) involved the commissioning of the prototype control system in Unit 1 of the flotation circuit. This initial testing and implementation of the control system was carried out jointly by CSIRO Division of Minerals and OTML Metallurgy and Instrument personnel, and reported by Senior and Heyes (1996). As the use of NaHS to improve the copper recovery from Ok Tedi ores had originally been suggested by Senior and Creed (1992), CSIRO personnel attended the trial to advise and assist with the implementation. Since the Folomian Concentrator consists of two parallel grinding and flotation circuits, evaluation was conducted by adding NaHS to Unit #1 for extended periods of time (say, eight hours) and comparing NaHS-induced flotation performance in Unit #1 against performance in Unit #2 (which had no NaHS addition). Extended periods of data were also collected for both Units when NaHS was not added to either side to allow for natural variation between the two Units. Data collection consisted of two-hourly samples of flotation feed, final concentrate and final tailing from each side, which after assay for %Cu were used to calculated copper recovery. The samples were collected by Chemical Laboratory personnel as part of their normal work routine, twenty-four hours per day, so that there was no influence on sample timing by the conductors of the Trial. Mean copper recoveries were subsequently calculated for both Units, with and without NaHS addition to Unit #1. Since acid soluble copper assays were not conducted on the final concentrate, acid soluble copper recoveries were 52

72 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG calculated using the difference of feed and tailings assays, divided by feed assay and expressed as a percentage. The difference between the two Units when NaHS was not added was subtracted from the difference between the two Units when NaHS was added to Unit #2 to derive an improvement in copper recovery attributable to NaHS Plant NaHS Trial #3 The second CPS plant trial (Trial #3) was conducted by OTML personnel and was fully reported in Lauder and Orwe (1996). During Trial #3, NaHS addition was made to Unit #2 (as opposed to Unit #1 in Trial #2). The second trial was conducted only on day shift (12 hours) from to As in Trail #2, this was to allow for any variation in feed characteristics and provide background data on the natural difference between the two parallel Units. General trial procedure was similar to that of Trial #2. Evaluation of the trial was the same as for Trial # Plant NaHS Trial #4 The third CPS plant trial (Trial #4) used a similar evaluation scheme to Trial #3, but was carried out in two parts. The first part of Trial #4 was aimed at confirming previous plant results with NaHS added to alternate Units ('flip/flop"). In part 2 of Trial #4, CPS was carried out at two ph values below the standard ph of 11.5, viz., 11. and 1.5. The trials at ph 11. lasted for 3 days. These trials were carried out in a "flip-flop" manner in which ph 11. was tested in alternate Units, with the other Unit at ph Having observed little change to copper recovery, it was decided to test at ph 1.5. The comparative trials were then carried out over a period of three weeks testing the lower ph on Unit #2. 53

73 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG The objective of this trial was to determine the impact of NaHS on copper and gold recoveries at reduced ph values. Previous laboratory flotation tests in this work, and by Senior and Heyes (1996) and by Glen, Senior and Heyes (1995), had shown improved copper recovery with NaHS at reduced ph, hence the plant trial of NaHS at lower ph was to ascertain if lime consumption could be reduced. Evaluation of the trial was the same as for Trials #2 and # Miscellaneous Analytical Techniques Assay Wherever required, flotation products were analysed by Atomic absorption spectrometry and X-Ray Fluorescence (XRF) for copper. For gold, fire assay and AAS methods were used Evaluation of Copper Recovery, Maximum Copper Recovery and Rate Constant Both bulk sample and size by size copper recoveries were calculated using the three product formula and expressed as a percentage described by equation 3.4. Recovery = c(f -t) * 1 (3.4) f(c -t) where f = copper assay of feed, % c = copper assay of concentrate, % t = copper assay of tail, % The maximum recovery, Rmax and rate constant, k, for size by size calculations were assumed to be of first order kinetic behaviour described by equation 3.5 (Lynch et. al.,1981). Only one floatable species is assumed to be present. Whilst such an assumption is clearly not true for Ok Tedi ore, which contains a number 54

74 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG of different copper minerals, analysis by this method allows a separation of simple recovery into the rate and maximum recovery components. Recovery (t) Rmax (1- (35) where Rmax = maximum recovery (i.e., Roc) t = maximum time k = flotation rate constant A linear least squares program was used to fit equation 3.5 to size by size laboratory batch test flotation data. 55

75 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CHAPTER IV 4. EXAMINATION OF CONCENTRATOR PERFORMANCE ON A TYPICAL FEED BLEND 4.1 Introduction The purpose of the work in this Chapter is to establish normal copper particle behaviour within the Folomian flotation circuit on a typical feed to the Concentrator. The analysis is conducted with respect to both size by size behaviour at an elemental level and extended to mineralogical behaviour within the size by size analysis. 4.2 Previous Survey of Concentrator The most detailed flotation survey of the Ok Tedi Mill was conducted on Unit 2 on 2th 1 October, The survey results are reproduced here for record purposes and to show how the circuit may be impacted by non-porphyry ores. Mill feed at the time of the survey comprised 7% skarn and 93% porphyry ores. The results, from Lauder and Erepan (1996), are summarised in Table 4.1. The Table should be examined in conjunction with Figure 4.1. During the survey, the column was off-line, hence the recleaner concentrate was the final concentrate. Rougher Tail 15 is final tailing. Copper recovery (74.4%) and go'd recovery (48.7%) during the survey were both lower than recoveries on an annualised basis due to the skarn content of the feed during the survey. Although no size by size data were obtained from this survey, general indications are that losses associated with skarn ore treatment are due to inadequate liberation (Putubu, 1996). The lower than target copper concentrate grade of 31.9% Cu and high fluorine (125 ppm F) content was also due to the presence of skarn ore in the mill feed. 56

76 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Skarn ore is also characterised (generally, but not exclusively) by an increased deportment of copper as chalcopyrite (leading to the lower concentrate grade) and the presence of talc mineralisation which contains fluorine. Table 4.1 Unit 2 Flotation Survey: 12 October 1994 (Lauder and Erepan, 1996) Stream Solids Solids Cu ASCu Au Fe tph % % % gil % J { Jj New Rougher Feed S If Combined Rougher Feed Rougher Con Rougher Tail RougherCon RougherTail Rougher Con RougherTail RougherCon , RougherTail Rougher Con , Rougher Tail Rougher Con Rougher Tail Rougher Con Rougher Con , Cleaner Feed CleanerCon ,82 21, CleanerTail , Cleaner-ScavengerCon Cleaner-Scavenger Tail , Combined-Recycle , Recleaner Con RecleanerTail 37, , New Survey of Concentrator As part of this current work, a new survey was conducted on Unit 2 flotation circuit on 14 February, Apart from the usual collection of samples from various streams for assay, this survey included the collection of samples for EDIA extraction and XPS analysis. 57

77 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG The ore types in the mill feed (according to mine records) comprised 89% porphyry and 11% skarn. The skarn was a mixture of both oxide and suiphide skarn. After the metallurgical (slurry) samples had been assayed, selected samples were sized and assayed to allow calculation of the size by size metallurgical recovery. Size fractions from the sized samples were also point-counted by Dr. Patrick Afenya of the Papua New Guinea University of Technology. The mineralogical information obtained from the point counting was used to establish mineralogical behaviour within the flotation circuit and to determine the mineralogical nature of the copper losses from the circuit. The mass balanced assay data from the survey are shown in Table 4.2. Table 4.2 Mass Balanced Flotation Data of Unit 2 Survey:14 February 1996 Stream Solids Cu ASCu Au Ag Mo Fe S F TPH % % % g/t g/t ppm % % ppm New Feed Rougher Con Final Tail Cleaner Feed Cleaner Con Cleaner Tail Reclean Con Reclean Tail Column Con Column Tail If compared with the survey shown in Table 4.1, it is apparent that significantly less streams are shown. This is due to the difficulty in obtaining good samples from the Concentrator, which resulted in the rejection of a high proportion of the tailings samples within the rougher-scavenger section, and the subsequent mass balancing of the streams as shown. The important features of the survey were that the total copper recovery achieved by the circuit was 85.9% at 36.9% Cu in final concentrate. Gold 58

78 The Influence of Sodium Hydrogen Suiphide on Porphyry Copper Recovery at Ok Tedi, PNG recovery was 83.% at 2.1 g/t of gold in final concentrate, whilst the concentrate contained only 515 ppm F. Even though the ore type blend to the mill on the day of the latter survey contained more skarn ore than the former (as evidenced by both the mine records and the higher proportion of iron in the new feed sample in Table 4.2), the latter survey shows better copper recovery and gold recovery, concentrate copper grade and lower fluorine grade of concentrate. This paradox highlights both the complexity of the varying ore types and, in particular, the variability in flotation performance of the skarn ores Eh-pH Conditions During the survey, Eh and ph measurements were made of mill feed. Pulp ph was recorded at 11.9, whilst pulp potential (Eh) was recorded at -121 mv with a platinum electrode/saturated silver nitrate couple. This latter value equates to +ll9mv (S.H.E.). The values recorded are typical of those observed when porphyritic ores are treated in the mill. The measured pulp Eh/pH conditions remained steady throughout the survey period EDTA Extraction The samples collected for EDTA extraction are shown in Figure 4.1. They were the New Rougher Feed (1), Final Tailing (2), Cleaner Feed (3), Cleaner Tailing (4), Recleaner Concentrate (5) and Final (Column) Concentrate (6). The results of the EDTA extraction tests are shown in Table 4.3. The results are expressed as a percentage of copper contained in the stream that is extracted into solution by the EDTA. Examination of Table 4.3 shows clear evidence of copper mineral oxidation as the enriched copper streams (cleaner feed, recleaner concentrate and final 59

79 The Influence of Sodium Hydrogen Sulphide on Porphyry Copper Recovery at Ok Tedi, PNG concentrate show very little EDTA extractable metal (less than.5%), whilst the final tailing and cleaner tailing show comparatively high EDTA extractable copper (greater than 3.%). The new rougher feed fits the pattern, with more than the low value streams, but less than the high value streams. The high EDTA extractable copper value for final tailing (15.4%) versus 2.1% EDTA extractable copper for the new rougher feed indicates further oxidation during the rougherscavenger flotation process. This may be partially related to the decrease in ph during flotation. Note again, that initial oxidation of copper minerals may have occurred prior to and during grinding since the natural ph of Ok Tedi ores range between ph 5 and ph 6. Figure 4.1 EDTA Sampling Points Table 4.3 EDTA Extraction Test Results from Unit 2 Survey, 14 February 1996 STREAM % EDTA Extractable Copper Rougher Feed 2.1 Final Tailing 15.4 Cleaner Feed.45 Cleaner Scavenger Tailing 3.8 Recleaner Concentrate.25 Final (Column) Concentrate.2 6

80 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG XPS Analysis of Concentrator Streams XPS samples were collected during the survey on 14 February 1996 to provide a "base-line" data source of XPS samples against any future changes in pulp chemistry. Since analysis of the XPS samples was conducted in conjunction with XPS samples collected during a later phase of the work, the analysis is discussed in Chapter VIII (Section 8.3.3). 4.4 Analysis of Size by Size and Mineralogical Data from Flotation Survey on the 14 February 1996 In this Section, the flotation behaviour is examined both on a size by size elemental basis and then a size by size mineralogical basis. Prior to this examination, however, it is necessary to consider the composition of the mill feed from a mineralogical perspective to determine the nature of the ore, in terms of both the gangue composition and the deportment of copper between different minerals Manipulation of Size and Mineralogical Data Samples of the streams in Table 4.2 were sized and cyclosized to yield the fractions : - and These fractions were assayed for copper and are discussed further in Section (Size by size recovery of copper in the Concentrator). For point-counting, size fractions were combined to yield the following larger fractions : and The bottom fraction was not point-counted, due to the inability of optical microscopy to resolve particles below When combining size by size mineralogical data to provide a mineralogical description of the whole stream, the distribution of the 61

81 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG fraction is assumed to be the same as that of the next finest fraction, i.e., the fraction. The new feed sample was also analysed by QEM*SEM (Jenkins and Adair, 1996) to provide quantification of gangue mineralogy. In point counting, suiphide copper minerals were speciated into chalcopyrite, bornite and digenite. Gangue minerals were also speciated into three groups; pyrite, iron oxides (FeO) and non-sulphide gangue (NSG). The liberation /intergrowth characteristics of all species were identified as liberated, binary locked with one other mineral or ternary, the latter term merely implying more than two minerals in the particle. Prior to manipulation of both the size by size and mineralogical data to provide both elemental and mineralogical recovery and loss information, the individual stream data was scaled to agree with the mass balanced assays shown in Table 4.2. This was done to eliminate assay error and point-counting volume estimation, ensuring that consistency was maintained during the analysis and avoiding the possibility of negative recoveries arising from error summation. Full size by size and point counting data for each stream are contained in Appendix # Examination of New Rougher Feed As noted previously, the examination of rougher feed was performed both by QEM*SEM (Jenkins and Adair, 1996) and point counting, the latter by Dr. Patrick Afenya of the Mining Engineering Department, PNG University of Technology. The four size fractions of New Rougher Feed analysed by QEM*SEM allowed the estimation of the proportion of each mineral in the sample using QEM*SEM Bulk Mineralogical Analysis (BMA) techniques. This technique uses a modal analysis which measures the volume percentage of each mineral. The weight percentage is then calculated from the volume and density of each mineral. The main 62

82 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok TedI, PNG mineral phases and groupings used for each size fraction examined are given in Table 4.4. Table 4.4 Simplified Modal Analysis of New Rougher Feed (Jenkins and Adair, 1996) Mineral Weight % New Rougher Feed pm -1 5/+75 pm -75/+31 pm -31/+13 pm Chalcocite/Digenite Covellite Bornite/Fe - Digenite Chalcopyrite Cu_Metal.3... Cu_Ox (Cuprite).... CuFe_Metal/Ox Cu_C3(Malachite) Cu_Silicates(Chrys).... Cu_Phosphates(Turq).... Other_Cu_Minerals Fe_Sulphides Mg_SIlicates (NaICa)_Feldspars K_Feldspars Mica Quartz Ca_Fe_Silicates Fe_Ox/C3(Hematite) Fe_Ox/C3(Goethite) Apatite Others Total From Table 4.4, it can firstly be established that despite the presence of geothite and hematite (which are derived from skarn ores), the abundance of both potassium and soda-lime feldspars shows that the ore is predominantly porphyry, albeit with some skarn. In broad terms, this correlates well with the previously mentioned mine records for the day (i.e., 89% porphyry ore and 11% skarn ore). 63

83 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG The summation of point counting data of the New Rougher Feed from each size fraction to yield a total for the whole unsized stream is shown in Table 4.5. Table 4.5 Point Counting Analysis of New Rougher Feed Mineral Mass% % Ternary 1 Cp Dg Bn Py NSG FeO Suip SuIp+G Cp Dg Bn Py NSG FeO Total 1 Cp = Chalcopyrite, Dg = Digenite, Bn = Bornite, Py = Pyrite NSG = Non-sulphide gangue (other than FeO), FeO = iron oxides Estimated mass percent of the copper minerals is 1.5% chalcopyrite,.3% digenite and.1% bornite. However, since chalcopyrite contains 34.6% Cu, digenite contains 78.1% Cu and bornite contains 63.3% Cu, then the deportment of copper in the mill feed is 63.6 % in chalcopyrite 28.7 % in digenite 7.7 % in bornite Hence the impact of digenite mineralisation to copper recovery is far more important than the initial examination of the mineral composition of the new feed would suggest. High liberation is apparent in the New Rougher Feed for all mineral groups, with in excess of 8% liberation obtained for copper minerals, i.e., chalcopyrite (94.%), bornite (92.9%) and digenite (83.1%). A further 1.6% of digenite is in binary particles with chalcopyrite, whilst an additional 2.2% of chalcopyrite is in binary particles with digenite. Hence over 9% of copper mineralisation is effectively liberated. 64

84 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG From a liberation perspective, the particles of concern are the ternaries which contain sulphide minerals as well as gangue. In this respect, the 4.2% of digenite contained in ternary particles with other sulphides and gangue represent a potential "non-recoverable" class, as does the.6% of chalcopyrite in ternary association with other sulphides and gangue Size by Size Recovery of Copper in the Concentrator The size by size recovery of copper (established from the size by size assay data) for the rougher-scavenger section of the plant and also the total plant are shown in Figure 4.2. Note in particular that these curves are similar in shape to that previously given in Figure I Fraction Mean Size (micron) 1 Figure 4.2 Rougher-Scavenger and Total Plant Copper Recoveries Both the rougher-scavenger and total plant copper recovery curves show high recoveries for the intermediate size fractions (i.e., for the rougherscavenger section and for the total plant) with a sharp decline in recovery outside these size ranges. While the recovery of the fraction is similar for both rougher-scavenger and total plant, the recovery differs in the coarse end of the size distribution for the two sections. The poorer coarse particle recovery in the total plant (as compared to the rougher-scavenger) is due to a combination of the regrinding of 65

85 V The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG rougher concentrates and the known poor performance of flotation columns in recovering coarse particles. This is not as detrimental as at first appearances, since coarse particles not recovered in the column are rejected to regrinding where their size is reduced to a point where they do recover in the column. Examination of the size by size copper distribution in the final tailing (Appendix I) shows the relative impact of the poor recovery in both the coarse and fine ends of the size distribution, i.e., 32% of copper lost in the final tailings is whilst 43.3% is lost in the range Mineralogical Recovery of Copper in the Concentrator Recovery on a mineral class basis is shown for total plant (Table 4.6) and the rougher-scavenger (Table 4.7). Note in the Tables, a "" indicates zero recovery to concentrate, whilst a blank entry indicates that the particle class was not observed in either the concentrate or the tailing. Table 4.6 Total Plant Mineral Recovery Mineral Total % Ternary Ternary Lib Cp Dg Bn Py NSG FeO SuIp SuIp+G Cp Dg Bn Py NSG FeO Table 4.6 shows that whilst exceolent recoveries are obtained for liberated and binary copper mineral particles, the mass recovery of digenite was only 75.9%. Since the mass recoveries of chalcopyrite and bornite are both higher than the plant copper recovery (85.9%), the digenite recovery at 75.9% suggests that the 66

86 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG digenite is the prime cause of the plant copper recovery at 85.9%. A similar trend is repeated for the rougher-scavenger mineral recoveries in Table 4.7. Table 4.7 Rougher-Scavenger Mineral Recovery Mineral Total % Ternary Ternary Lib Cp Dg Bn Py NSG FeO SuIp SuIp+G Cp Dg Bn Py NSG FeO Note in both Tables the very poor recovery of chalcopyrite and digenite in binary particles with NSG and in ternary sulphide -gangue particles Specification of Copper Loss Specification of copper loss from the circuit is made with reference to Table 4.8, which shows the point counting analysis of the final tailing. 36.3% of chalcopyrite lost to final tailing is as binary particles with NSG, whilst a further 57.5% of chalcopyrite lost to tailing is in ternary sulphide/gangue particles. 89.5% of digenite lost to tailing is contained in ternary suiphide/gangue particles. Whilst 1% of bornite lost to tailing is shown as liberated, the very small incidence of this mineral in the tailing stream (.1 % of tailing mass) renders this value irrelevant. Examination of the point counting of the final tailing in Appendix I shows that the chalcopyrite and digenite in binary particles with NSG and in ternary sulphidegangue particles only occur to any significant degree in the size fraction. The coarse copper loss from the plant is therefore attributed to these particles, as is the poor coarse copper recovery shown in Section

87 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG The poor recovery of fine copper is not apparent in the mineralogical analysis, since the fraction was not examined due to the inability to examine this fraction. However, given that both chalcopyrite and digenite were completely liberated in the size fraction immediately above (-3 131km), it is reasonable to assume that particles of digenite and chalcopyrite in the -131km fraction are also completely liberated. Table 4.8 Point Counting Analysis of Final Tailing Mineral Mass% % - Ternary Ternary TOTAL Lib Cp Dg Bn Py NSG FeO SuIp SuIp+G Cp Dg Bn Py NSG FeO TOTAL Concluding Remarks From the foregoing analysis, the following summary may be drawn. QEM*SEM analysis of the survey new feed suggests that the mine records of a typical mill teed are correct, i.e., 89% porphyry ore and 11% skarn ore. The survey is therefore of the plant treating a typical ore blend. Size by size, recovery of copper during the survey showed poor recoveries of copper in the fine (-131km) and the coarse (+161km) size ranges. This correlates well with plant performance on a monthly basis. Mineralogical analysis suggests that the fine copper loss during the survey was essentially liberated chalcopyrite and digenite. 68

88 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Mineralogical analysis suggests that the coarse copper loss was both chalcopyrite and digenite contained in binary composite particles with nonsuiphide gangue and in ternary sulphide-gangue particles. The overall impact of digenite on plant performance is very important, since digenite contains 28.7% of the copper in mill feed, but only 75.9% of the total digenite is recovered. This contrasts with chalcopyrite, which contains 63.6% of copper in mill feed, but of which 92% is recovered. EDTA extraction analysis suggests that copper minerals contained in the final tailing have a higher degree of oxidation than that observed in the final concentrate. 69

89 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CHAPTER V 5. LABORATORY FLOTATION OF TWO PORPHYRY ORES 5.1 Introduction This chapter discusses the results of standard rougher flotation tests at varying ph on two porphyry ore samples (Monzonite A and Monzodiorite A) on a size by size basis, as well as examining the dissolution of copper from the two ores at varying ph, in the presence or absence of EDTA. The mineralogy of the two ore samples was previously provided in Section 3.2.3, whilst the flotation test procedure was described in Section Appendix #2 gives the detail of the individual flotation tests. 5.2 Standard Flotation Rougher Tests at Varying ph The flotation operating ph in the Folomian Concentrator is Past laboratory flotation tests and plant experience have established this ph to yield optimum copper and gold recovery, as well as the required concentrate quality. Flotation tests were therefore performed at reduced ph values (i.e., ph<11.5) to examine the effect of reduced ph. The effect of ph is also compared with lime addition to the mill against lime addition to the flotation cell. The test procedures were fully described in Chapter Ill. The effect of ph on flotation behaviour is compared firstly by total copper recovery, followed by size by size analysis of copper recovery in terms of both the maximum recovery (Rmax) and rate constant, k. 7

90 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Distribution of Copper in Laboratory Ground Samples Copper distribution of the monzonite 'A' and monzodiorite 'A' samples are given in Tables 5.1 and 5.2 respectively. Table 5.1 Mass, Assay and Copper Distribution in Monzonite 'A' Size (sm) Mass (%) (%Cu) Cu Distribution (%) Total Table 5.2: Mass, Assay and Copper Distribution In Monzodlorite ' Size (sm) Mass (%) (%Cu) Cu Distribution (%) Total 1,

91 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Examination of Tables 5.1 and 5.2 show that whflst the monzodiorite sample contains significantly less copper than the monzonite sample (i.e.,.37% Cu versus.77% Cu), the copper distribution is generally similar Copper Recovery as a Function of ph The effect of ph on copper recovery for monzonite and monzodiorite is shown in Figures 5.1 and 5.2 respectively. Examination of these Figures reveals a marked contrast in flotation kinetics between the two porphyry ores. 1 8 C) C) I- C).. C.) Time (minute) Figure 5.1 Copper Recovery as a Function of ph for Monzonite 'A' 1 8 C) > U C) I- C) Time (minute) 1 Figure 5.2 Copper Recovery as a Function of ph for Monzodiorlte 'A' 72

92 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG The monzonite sample (Figure 5.1) exhibits apparent lower flotation rates than the monzodiorite sample (Figure 5.2). This lower flotation rate is associated with lower total copper recoveries for the monzonite sample, i.e., 72.7%, 73.4% and 74.3% for ph 6,9 and 11.5 respectively, compared with 81.3%, 81.4% and 87.6 for the monzodiorite sample at the same ph values. Note that, although small, the total copper recovery increases with increased ph. In the case of monzodiorite sample, there is a greater increase in flotation kinetics as the pulp ph is elevated to Size by Size Recovery as a Function of ph Figures 5.3 and 5.4 show size by size recovery as a function of ph for the monzonite and monzodiorite samples respectively. Whilst only a marginal increase is observed in ultra fine copper recovery for increased ph with the monzonite ore, the monzodiorite ore shows a significant increase in copper recovery with increasing ph for the fine size range The increase in -31 fraction copper recovery was coupled with decreases in copper recovery of the coarse (+1 size fraction, although the reduced recovery of the coarse fractions did not decrease the total copper recovery. 1 8 ) C.) ) I- C) Size (micron) 1 Figure 5.3 Size by Size Copper Recovery of Monzonite 'A' 73

93 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok TedI, PNG From Chapter III, Section 3.2.3, it is clear that the difference in copper deportment between the two porphyry ores is that the Monzonite 'A' sample contains significantly more digenite and bornite than the Monzodiorite 'A' sample. The flotation behaviour from the foregoing tests therefore suggests that the presence of copper as either digenite or bornite is responsible for the lower fine copper recovery in the Monzonite 'A' sample, especially since the copper content of the Monzonite 'A' sample is greater than the Monzodiorite 'A' sample. Further, since the mineralogical recovery of copper in the plant survey (Section 4.4.4) shows that bornite and chalcopyrite recoveries are similar, but digenite recovery is poorer than either bornite or chalcopyrite, it is a reasonable first approximation to suggest that digenite is probably responsible for the poorer copper recovery in the Monzonite 'A' sample. 1 6 C) Size (micron) Figure 5.4 Size by Size Copper Recovery of Monzodiorite 'A' Size by size copper recoveries were decomposed into maximum recovery and flotation rate constant according to equation 3.5 with a linear least squares program. The maximum recoveries are shown plotted against size in Figures 5.5 (Monzonite 'A') and 5.7 (Monzodiorite 'A'), whilst the flotation rate constants are plotted against size in Figures 5.6 (Monzonite 'A') and 5.8 (Monzodiorite 'A'). Examination of Figures 5.5 and 5.6 shows that for the monzonite ore, the increase in ph provides an increase in the maximum recovery of the fine fraction, combined with an increase in the flotation rate constant of the 74

94 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG intermediate fraction. Since there is very little change in the actual recoveries of the intermediate fraction (Figure 5.3), the increased rate constant of this fraction contributes very little to overall recovery. Hence the improvement to overall recovery resulting from the increased ph may be attributed to a higher maximum recovery of the fine fraction. A higher maximum recovery at higher ph is suggestive of some form of surface coating on a portion of the particles contained in the size fractions at lower ph. This will be discussed further below. 1, _o_ph 9 ph Size (micron) 1 Figure 5.5 Rmax versus Size as a Function of ph for Monzonite 'A' E 1.2 E _o_-ph 6 o_ ph 9 - ph 11.5 C g.6 a, Size (micron) 1 Figure 5.6 Rate Constant (k) versus Size as a Function of ph for Monzonlte 'A' Examination of Figures 5.7 and 5.8 shows that the increase in ph causes a significant increase in the maximum recovery of the -31 fraction, coupled with 75

95 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG an increase in the flotation rate constant of the -31 fraction and a decrease in the flotation rate constant of the +31 fraction. As for the Monzonite 'A' sample, the actual recovery of the +31 copper contributes little to the total recovery, hence the decrease in flotation rate constant has an insignificant impact on total copper recovery. The increased copper recovery in the Monzodiorite 'A' sample with increased ph may therefore be attributed to increases in both the maximum recovery and flotation rate constant of the -31 fraction. 1 8 E Size (micron) Figure 5.7 Rmax versus Size as a Function of ph for Monzodiorite 'A' 1.6 I SIze (micron) 1 Figure 5.8 Rate Constant (k) versus Size as a Function of ph for Monzodiorite 'A' 76

96 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Eh-pH Trends The other noteworthy feature of the rougher flotation tests on the porphyry 'A' ores are the Eh-pH relationships, measured after addition of lime to the laboratory flotation feed and shown in Figure 5.9. These curves show significant differences in measured electrochemical potential (Eh) as a function of ph, with the Monzodiorite 'A' sample exhibiting a more oxidising potential than the Monzonite 'A' sample by approximately 1 mv in the alkaline range and 5 mv in the weak acid range. In the strong acid range, the Monzonite 'A' sample is the more oxidising. Given the number of contributing factors to bulk potential measurements in complex systems, these results serve only to highlight the differences between the two ores. 4 A 3 LU I A > 2 E A A o Monzonite 'A' A Monzodiorite 'A' A LU 1 I I I I I I I ph Figure 5.9 ph and Eh Profiles Monzonite 'A' and Monzodiorlte 'A' Effect of Lime Addition to the Grinding Mill The effect of lime addition to the grinding mill rather than the flotation cell is shown in Table 5.3 for the Monzonite 'A' and Monzodiorite 'A' samples. The copper recoveries are compared to the total recoveries of the flotation tests previously described in Section

97 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Completely different behaviour is obtained for the two ores. Lime addition to the mill improves copper recovery for the monzonite ore but not the monzodiorite ore. The lower copper recoveries in the acid ph regime are attributed to the known poorer performance of dithiophosphate collectors in acid ph (Hartati et al., 1997). Table 5.3 Total Copper Recovery: Effect of Lime Addition to Mill versus Lime Addition to Cell (Monzonite 'A' and Monzodiorite 'A') ph Monzonite Monzodiorite Lime to Lime to Lime to Lime to Cell Mill Cell Mill Acid (Natural) Dissolution and EDTA Extraction Tests on Ore Samples Copper Dissolution at Varying ph Given the differences in flotation properties and copper mineralogy of the two ores, it was decided to examine the dissolution of copper from both ore types across the ph range from 2 to 12. This was achieved by grinding two samples of Monzonite 'A' and Monzodiorite 'A' to 8% passing at natural ph. The ph of the first sample of each ore was raised to 12 with lime in stages of one ph unit, removing a small amount of pulp at each stage for analysis of the copper concentration of the liquid phase. The same procedure was followed for the second sample of each ore, except the ph was towered with sulphuric acid. The observed copper concentrations dissolved from each ore are shown in Figures 5.1 and 5.11 for Monzonite 'A' and Monzodiorite 'A' ores respectively. 78

98 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 1.4e-2 1.2e-2 g 1.Oe-2 8.Oe-3 6.Oe Oe-3 2.Oe-3.Oe ph 12 Figure 5.1 Copper Dissolution - Monzonite Porphyry Sulphide 'A' Although the data presented in Figures 5.1 and 5.11 show a similar trend with increasing copper dissolution at ph 4, there is a massive variation in the observed copper concentrations between the two ores, with the copper concentration from the Monzonite 'A' sample one hundred times greater than the Monzodiorite 'A' sample. 1.6e-4 1.4e-4 1.2e-4 1.Oe-4 C) 8.Oe-5 6.Oe-5 4.Oe-5 2.Oe-5.Oe ph Figure 5.11 Copper Dissolution - Monzodiorlte Porphyry Sulphide 'A' Note in particular the onset of dissolution of copper in both ores below ph 5. Since the natural ph for most ores at Ok Tedi lie between 5 and 6, it is reasonable to assume that copper is dissolving during laboratory grinding and subsequently precipitating out as copper hydroxides and interfering with the collector adsorption process. 79

99 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG EDTA Extraction EDTA extractable copper levels of the two ores ground to 8% passing 1 are shown in Figures 5.12 (Monzonite 'A') and 5.13 (Monzodiorite 'A'). Generally, increasing levels of EDTA extractable copper with increasing ph are observed with both ores. In particular, as for the acid dissolution, the amount of EDTA extractable copper is much higher for the Monzonite 'A' sample. Since EDTA does not extract significant copper from unoxidised copper sulphide minerals (chalcocite, digenite and covellite) (Kant, Rao and Finch, 1994), the EDTA extractable copper is attributed to the presence of digenite in the sample Figure 5.12 EDTA Extractable Copper as a Function of ph - Monzonite 'A' 14 L ) ph Figure 5.13 EDTA Extractable Copper as a Function of ph - Monzodlorite 'A' 8

100 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Expressed as a percentage of copper in the ore sample, at ph 11.5, the EDTA extractable copper in the Monzonite 'A' and Monzodiorite 'A' samples were 12% and.8% respectively. 5.4 Flotation Tests in an Acid Environment Additional flotation tests were conducted in an acid environment by Ikis (1996) to determine if an acid regime might be more appropriate for the flotation of Ok Tedi ores than the traditional alkaline environment, especially given the naturally acidic ph of the Ok Tedi porphyry ores. Contrary to the tests shown in Table 5.3, Ikis (1996) found that copper recovery was generally, but not universally, improved for porphyry ores, but with a detriment to gold recovery that overshadowed the improvement to copper. Further, the improved copper recovery was not observed with skarn ores. The lower gold recoveries in the porphyry ores and poorer performance from skarn ores was not improved with changes to the selected collectors. Due to the findings of Ikis (1996), the investigation of the acid flotation environment was discontinued and not examined further in this study. 5.5 Concluding Remarks The foregoing examination of the rougher flotation behaviour of the two porphyry ore samples, coupled with the ph-dissolution and EDTA extraction tests, highlighted the difference in the nature of the two ores. Given the poorer overall copper recovery from the monzonite ore, the increased proportion of digenite in the monzonite ore and the observation from Chapter IV that digenite shows the poorest recovery of the predominant copper minerals in the plant, both plant and laboratory work suggest that poor recovery of copper is related to the digenite mineralisation. 81

101 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Size by size analysis shows that the poor digenite recovery is more pronounced in the fine range of the size distribution, and that this can be in some measure redressed with flotation at a high ph (11.5). In both ores, the improvement in copper recovery at high ph was shown to be related more to a change in the maximum recovery of the fine copper minerals rather than an improvement in flotation rate. Changes in the maximum copper recovery with increased ph are suggestive of the dispersion of surface coatings, in particular, copper hydroxides. Evidence for copper hydroxides, or oxidised copper, is provided by the EDTA extraction tests. 82

102 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CHAPTER VI 6. SULPHIDISATION OF TWO PORPHYRY ORES 6.1 Introduction Given the identification of fine digenite as the cause of poor copper recovery for the monzonite ore in Chapter V, and, as will be shown in Chapter VII, that the poor digenite recovery is related to copper hydroxide on the digenite surface, it was decided to investigate the propensity of sodium hydrosulphide (NaHS) to "clean" or "regenerate" the oxidised digenite surfaces. This also followed the work of Glen, Heyes and Senior (1995), who showed an improved copper recovery with suiphidisation on a predominantly porphyry ore sample from Ok Tedi. A series of laboratory flotation tests were conducted on two porphyry ore samples denoted as Monzonite 'B' and Monzodiorite 'B', the mineralogical compositions of which were provided in Chapter III. Three methods of NaHS addition were applied to the flotation feed. Controlled-potential sulphidisation (CPS) on rougher feed. Continuous CPS before and during flotation. NaHS addition to the grinding mill. The results of each method are now discussed in turn. 6.2 Controlled-Potential of Flotation Feed In the controlled-potential of flotation feed tests, NaHS was added to achieve a selected potential to the ground product after transfer to the flotation cell, and 83

103 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG maintained at this potential for one minute. Copper recovery and conditions of a series of flotation tests conducted at three ph values (i.e., 5, 9 and 11.5) and various set points on the two ores are shown in Table 6.1 (Monzodiorite 'B') and Table 6.2 (Monzonite 'B'). For the monzodiorite ore (Table 6.1), when no NaHS is added, the best result would appear to be at ph 5. However, extensive "acid" flotation test work by Ikis (1996) has shown that although this may occur for unknown reasons on some Ok Tedi ore samples, this is not a general case and is usually associated with very poor gold recovery, despite extensive examination of alternative collector chemistries, viz., mercaptobenzothiazole, dithiophosphinate, dithiophosphates, monothiophosphates, and thionocarbamates. The addition of NaHS to an set point of -3 mv (-1 mv versus SHE) yielded improved recovery for ph 9 and 11.5, but not ph 5. The same effect of NaHS was also observed with the monzonite ore (Table 6.2). In Table 6.2, anomalous behaviour is observed in that the copper recovery achieved in the absence of NaHS is very similar at all three ph values tested. It would be expected that the copper recovery at ph 9. would be less than the copper recovery at ph Table 6.1 Effect of ph and Controlled Sulphidisatlon-Monzodiorite'B' ph mv mv (SHE) NaHS g/t Conc % Cu Cu Recovery % 5(std) Nil (std) Nil (std) Nil With the best result in terms of ph and Eh for the monzodiorite ore obtained at ph 9 at mv (SHE), it is clear that both ph and Eh are important in increasing copper recovery. 84

104 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG For the monzonite sample, the addition of NaHS increases copper recovery for both ph 9 and At ph 5, the addition of NaHS decreases copper recovery significantly at low to moderate dosages, suggesting the requirement for alkaline ph values during sulphidisation. Note again that for standard (std) tests, the effect of ph on copper recovery is negligible, while for the alkaline ph values, the effect of pulp potential is dominant. Table 6.2 Effect of ph and Controlled Sulphidisation - Monzonite'B' ph mv mv (SHE) NaHS g/t Conc % Cu Cu Recovery % 5(std) Nil (std) Nil (std) Nil The best results, however, for the monzonite ore, were obtained at ph There was a marked increase in copper recovery from 89.4% (std) to 93.6% at 28g/t of NaHS. Further improvements in copper recovery were indicated when the NaHS dosage was increased. Optimum NaHS consumption therefore lies between 112 and 242g/t. 6.3 Continuous Sulphidisation during Flotation Since it is generally reasoned that it is important when using NaHS to maintain the low during the conditioning period, but not during flotation (in fact, it is important that the be allowed to rise for effective flotation to occur, (Johnson, Jowett and Heyes, 1982)), a series of tests was conducted to demonstrate this 85

105 The Influence of Sodium Hydrogen Suiphide on Porphyry Copper Recovery at Ok Tedi, PNG fact, i.e., that maintaining a low set point during flotation would provide poor recovery. Tests to demonstrate this property were conducted on the Monzodiorite 'B' sample, the results of which are given in Table 6.3, showing that continuous suiphidisation depresses copper recovery at all ph values tested. Best copper recoveries were obtained under the standard test conditions at all ph values. It was observed that the froth was very weak during flotation with some mineralisation late in the flotation time. The reduced copper recovery is attributed not only to excess sulphide (S2) ions present in the pulp, but also to the fact that the is too low for effective flotation to occur, as noted by Heyes and Trahar (1977) and Gardner and Woods (1979). Table 6.3 Effect of ph and Continuous Suiphidisation - Monzodiorite'B' ph mv ER mv (SHE) NaHS g/t if Conc % Cu Cu Recovery % 5(std) Nil (std) Nil (std) Nil J[ ][ Effect of NaHS Addition to Laboratory Mill The addition of NaHS to the laboratory mill was examined to determine if adding the NaHS during grinding could provide better recovery than when added to the flotation cell, reasoning that NaHS could provide a sulphide surface before the copper hydroxides were formed. Due to sample shortage of the Monzonite 'B' sample, only tests using Monzodiorite 'B' were carried out in this manner. The results are shown in Table

106 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Compared with the standard (i.e., no NaHS) tests, copper recoveries are better when NaHS is added to the mill, though not in a particularly linear fashion. The anomalously high copper recovery in the standard test at ph 5 (as previously noted) is also apparent. The higher values when NaHS was added to the mill (compared to the standard test) are a function of the water used to wash the ground ore from the mill. Table 6.4 Effect of NaHS Addition to Mill for Monzodlorite 'B' ph mv ER mv (SHE) NaHS g/t Conc % Cu Cu Recovery % 5 (std) Nil (natural) (std) NH (std) Nil IF 19 II Generally, the copper recoveries achieved with NaHS added to the mill are higher than when NaHS is added to the flotation cell (albeit at higher addition rates). The results of ph 9 and 11.5 show that between 2 and 5g/t NaHS is required to achieve approximately 1% increase in copper recovery while, dosage above this range has a tendency to depress copper recovery. 6.5 Effect of Suiphidisation on a Size by Size Basis Figure 6.1 shows the size by size flotation recovery of Monzonite 'B' and Monzodiorite 'B' samples with a NaHS addition set point of mv (SHE) for one minute prior to flotation compared to flotation without a suiphidisation stage. NaHS consumption was 5g/t for the Monzodiorite 'B' sample and 15g/t for the Monzonite 'B' sample. 87

107 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG From Figure 6.1, when NaHS is used, the size fractions affected most are those outside the -16/+31 lim range. Both the coarse (+16iim) and fine size ranges show significant improvement in copper recovery when sulphidised with NaHS. The increase in copper recovery (Tables 6.1 and 6.2) is associated with a decrease in concentrate grade, perhaps reflecting copper mineral and gangue intergrowth. For example, where there is decreased liberation in the coarse size fractions it is expected that copper grade will decrease when recovery of the coarse fraction is increased. 1 6 / o Monzodiorite 'B'-Std -- Monzodiorite'B'-NaHS a,. 1 I I I a- Monzonite'B'-Std Monzonite'B'-NaHS I I I Size (micron) Figure 6.1 Effect of NaHS on Size by Size Copper Recovery at ph 11.5 (Monzonlte and Monzodiorite 'B' Samples) The monzonite sample exhibited improved flotation kinetics when NaHS was used when compared to the monzodiorite sample, particularly in the -31 fraction. Since the addition of NaHS to the flotation cell with CPS control was shown to provide improved copper recovery on both the monzonite and monzodiorite 'B' samples, it was necessary to revisit the earlier size by size work on the monzonite and monzodiorite 'A' ores to examine the impact of NaHS on the size by size recovery of copper. Accordingly, multiple flotation tests were conducted on the few remaining 'A' samples using CPS at ph 11.5 to provide sufficient material for sizing and cyclosizing of the concentrates and tailing. The resultant 88

108 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG size by size recovery curves with and without NaHS at ph 11.5 for Monzonite 'A' and Monzodiorite 'A' ores are shown in Figures 6.2 and 6.3 respectively. The suiphidised tests were conducted with a set point of mv (SHE), whilst the standard results are reproduced from Chapter V. NaHS consumptions of 7g/t and 1 7g/t were recorded for the Monzodiorite 'A' and Monzonite 'A' ores respectively. 1 8 C) C.) C) C). C.) Size (micron) 1 Figure 6.2 Effect of NaHS on Size by Size Recovery (Monzonite 'A') 1 6 _-o_ Standard NaHS C). 4 C.) I I I I I I Size (micron) Figure 6.3 Effect of NaHS on Size by Size Recovery (Monzodiorlte 'A') It can be seen in Figures 6.2 and 6.3, that a significant improvement in copper recoveries is apparent for both ores when suiphidisation is practiced, particularly in the fine and coarse ends of the size distribution. The different flotation recovery of copper minerals in these ores after sulphidisation supports the contention that it is the presence of oxidation products (copper hydroxides) on 89

109 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG the copper mineral surfaces that prevent collector adsorption, i.e., sulphidisation with NaHS effectively converts copper hydroxide to copper sulphide, which is then amenable to collector adsorption. The effect of NaHS in terms of copper recovery by size appears to be similar for both porphyry ore types, though the magnitude of the increase is less marked in the case of monzodiorite. 6.6 Concluding Remarks The flotation of two porphyry ore types at Ok Tedi have been studied in the presence and absence of a suiphidising agent - sodium hydrosuiphide (NaHS) - over a range of ph-eh conditions. In particular, it was found that the addition of NaHS to either the grinding mill or flotation feed significantly improved copper recovery. As expected, the continual addition of NaHS during flotation resulted in the depression of copper. The analysis of copper recovery as a function of size after sulphidisation to Eh = o mv at ph = 11.5 shows improved recovery in both the fine (-31 and coarse (+1 ranges of the size distribution. 9

110 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG CHAPTER VII 7. SINGLE MINERAL STUDIES 7.1 Introduction Following the success with NaHS in improving fine copper mineral flotation in the laboratory ore studies, a more fundamental examination of the oxidation of the copper minerals prevalent at Ok Tedi was undertaken. As described in Chapter III, this part of the investigation initially comprised dissolution studies and the examination of the oxidation of copper minerals, the fatter by zeta-potential measurements and EDTA extractions. This preliminary investigation of the minerals was followed by an examination of the sulphidisation of chalcocite by EDTA extraction, zeta-potential measurement and XPS analysis. This chapter therefore discusses the results of the single mineral studies and highlights the oxidation behaviour of copper minerals in general, and the suiphidisation of chalcocite in particular. 7.2 Dissolution of Copper Minerals When considering the solubility of copper minerals in water, it is important to realise that dissolution is often slow (Attia, 1975) and that full equilibrium is rarely reached. The results reported here therefore indicate the direction if given sufficient time. As a definition, the solubility of any copper mineral is defined as the sum of the stoichiometric concentrations of all dissolved species containing copper (Garrels and Christ, 1965; Stumm and Morgan, 197; Schindler, 1967). Dissolution tests were conducted on chalcocite, covellite and bornite at ph 4, 5 and 7 in the presence of oxygen purging gas to promote oxidation. The experimental procedure for the dissolution tests on chalcocite (Section 91

111 The influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 7.2.1), covellite (Section 7.2.2) and bornite (Section 7.2.3) was previously described in Section Chalcocite The dissolution of copper from over 3 minutes at ph 4, 5 and 7 is shown in Figure 7.1. w E C. U, Time (minute) Figure 7.1 DissolutIon of Chalcocite as a Function of ph The dissolution of copper into solution as a function of ph for chalcocite increases with decreasing ph. There is a significant increase in concentration of copper in solution at ph 4, particularly in the first 5 minutes. After 5 minutes, the copper concentration continues to increase, but at a slower rate. At ph 5, the rate of copper dissolution is lower than at ph 4, whilst the curve for ph 7 shows much lower copper dissolution than those at either ph 4 or 5. This dissolution behaviour agrees with Sato (196), that chalcocite oxidises rapidly to covellite followed by slower oxidation in air to cupric ions and sulphur, according to equations (7.1) and (7.2) respectively; Cu2S CuS + + 2& (7.1) 92

112 The Influence of Sodium hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG CuS + S + 2& (7.2) Later work on the dissolution of chalcocite by Lekki and Laskowski (1971) examined the behaviour of a chalcocite electrode in alkaline solution, concluding that cupric hydroxide forms between ph 2 and According to Attia (1975), the precipitation of Cu(OH)2 is possible only when the amount of released from chalcocite is equal to or greater than that required to form Cu(OH) Covellite Figure 7.2 shows the rapid dissolution of copper ions into solution from covellite at ph 4 and 5, but at lower concentrations than observed for chalcocite in Figure 7.1. Increasing the ph to 7 with covellite shows negligible copper dissolution, but appears to increase slightly over the 3 minute period, a trend not clearly discernible with chalcocite. C 5.e-4 4.5e-4 4.OOe-4 3.5e-4. 3.OOe-4 2.5e-4 p ph 4 I E5.OOe-5..OOe Time (minute) Figure 7.2 Dissolution of Covellite as a Function of ph The dissolution of covellite was described by Attia (1975) as occurring via equation (7.3); 93

113 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CuS(s) + = H2S(g) + pk = 14.2 (7.3) Alternately, Sato (196) described the oxidation reaction occurring between ph 2 and 12 as; CuS + S + 2e; (7.4) noting that the presence of oxygen should further oxidise sulphur to sulphate ions (S4) Bornite The rate of release of copper ions from bornite into solution is shown in Figure OOe-5, 3.5e-5 3.OOe e-5 P'4 4 p ph 2.OOe-5..OOe Time (minute) Figure Dissolution of Bornite as a Function of ph The copper concentration appearing in solution for bornite is lower than those of both chalcocite and covellite at all ph values examined. The copper concentrations were below detection limits at ph 7, suggesting that dissolution of copper from bornite does not occur at ph 7. Examination of bornite oxidation by Buckley and Woods (1983) via the analysis of voltammograms showed the formation of oxo- or hydroxo- complexes such as 94

114 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Cu22, and Buckley and Woods (1983) further suggested that the mechanism for bornite oxidation in acid solution involved the preferential oxidation of the iron component of bornite, proposing the reaction; Cu5FeS & (7.5) In the alkaline environment, the species, yielding; (Ill) hydroxide or oxide is the stable iron Cu5FeS4 + 3H2 Cu5S4 + Fe(OH) & (7.6) Both reactions (7.5 and 7.6) were supported by XPS studies (Buckley and Woods, 1983) Chalcopyrite Dissolution of chalcopyrite was reported by Grano et al. (1995) and Fairthorne (1996) and is not studied by this worker. Fairthorne (1996) observed that iron, copper and suiphoxy species were present in solution and that at ph 5 with oxygen purging the solution concentration of copper was significantly less than the concentration of iron, suggesting that oxidation of copper from chalcopyrite did not occur to a significant extent at this ph. This was confirmed by XPS analysis. In nitrogen, the dissolution of copper was similar at both ph 5 and 9.5 (2x16 mol dm3), but was reduced when purged with oxygen to a fifth of this value at ph 5 and to a negligible value at ph 9.5. The surface oxidation of chalcopyrite has been studied by linear potential sweep voltammetry by Gardner and Woods (1979) in which the process giving rise to the anodic peak in acidic solution is considered to be; 95

115 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CuFeS2 CuS + S + + 2e (7.7) and in alkaline solution as; CuFeS2 + 3F-12 CuS + S + Fe(OH) e (7.8) It was confirmed by Buckley and Woods (1984) by XPS that the iron component was dissolved in acid solution, but formed an oxide layer in alkaline solution. Further XPS studies (Biegler and Home, 1984) suggested that a metal-deficient copper sulphide is formed in acid solution according to; CuFeS2 Cuo & (7.9) Finally, it has been shown (Fairthorne, 1996) that iron in acidic solution may diffuse back into the copper sulphide lattice of bornite and chalcopyrite when the potential is returned to their region of stability Summary of Dissolution Studies In the foregoing examination of both dissolution studies and literature, it apparent that copper ions from chalcocite and covellite dissolve more rapidly in acidic to neutral, oxidising environments than that of bornite and chalcopyrite. This suggests a greater tendency for precipitating as copper hydroxides in alkaline ph values to have originated from chalcocite or covellite. is The observed behaviour correlates very well with the general OTML laboratory and plant observation that since the natural ph of OTML ores is generally acidic, further oxidation is reduced and flotation recovery is improved if lime addition occurs in the milling environment rather than the flotation environment. 7.3 Oxidation of Copper Minerals The effect of oxidation on suiphide copper minerals was investigated using the 96

116 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG electrokinetic technique, with zeta potential measurements obtained to determine the oxidation behaviour of chalcocite, covellite and bornite as a function of ph and purging gas. A comparison is made with chalcopyrite (Fairthorne, 1996). Experimental procedure for the zeta potential experiments on the oxidation of chalcocite (Section ), covellite (Section ) and bornite (Section ) is provided in Section The interaction of dissolved mineral species with mineral surfaces are inferred Zeta-Potential Studies As noted in Chapter Ill, the potential difference between the mineral surface and solution cannot be measured directly (Stumm and Morgan, 1967). Zeta potential although smaller in magnitude (Hunter, 1981) is therefore computed from electrophoretic mobility and the measurements concern only the diffuse part of the electrical double layer (Attia, 1975) Chalcocite Figure 7.4 shows the zeta-potential measurements conducted between ph 4 and 11.5, using nitrogen (N2) and oxygen (2) purging gases respectively. This shows that the zeta-potential for the freshly ground chalcocite slurry purged under nitrogen is negative in the ph range 4 to 12, suggesting a predominantly unoxidised surface (Healy and Moignard, 1976). The iso-electric points of ph 4.5 and ph 5.5 for oxygen purging for 5 and 6 minutes respectively contrast with an iso-electric point of ph 3. reported by Lekki and Laskowski (1971), suggesting that a significant concentration of copper hydroxide exists on the chalcocite surface under these conditions. It is of interest to note that a similar zeta-potential dependency on ph is observed for both conditioning times investigated, suggesting that little oxidation occurs during 97

117 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG conditioning with nitrogen, and that the copper hydroxide on the surface of chalcocite probably formed during grinding ;' E N Figure 7.4 Zeta-potential of Chalcocite conditioned for 5 and 6 minutes with N2 and 2 purging The low iso-electric point of unoxidised chalcocite is generally attributed to the dissociation of protonated sulphur which occurs at low ph values. -Cu2SH -Cu2S + (7.1) where the negative sites as -Cu2SH. unoxidised suiphide sites on chalcocite are denoted as -Cu2S and protonated Equation 7.1 explains the negative zeta-potential of minerals across the ph range examined. However, when the system is purged with oxygen (Figure 7.4), the chalcocite surface exhibits two iso-electric points at ph 4.5 and 8.3 in the case of 5 minutes purging, and at ph 5.4 and 9.6 in the case of 6 minutes purging. This suggests the formation of copper hydroxide phases at the chalcocite/water interface. Chalcocite oxidation has been observed to produce a copper hydroxide phase on chalcocite and Suoninen, 1988), which strongly influences its electrokinetic properties. The oxidation of chalcocite was studied by Oestreicher and McGlashan (1972) as a function of conditioning time and equilibration ph. These studies indicated that copper hydroxide formation occurs when the chalcocite is equilibrated at a ph where dissolution can occur and high concentrations of copper are released 98

118 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG into solution (Oestreicher and McGlashan, 1972). Similar mechanisms have been proposed by Fornasiero, Eijt and Ralston (1992) in the oxidation of pyrite. The following steps are considered important: 1. Dissolution of cuprous ions and formation of a copper deficient, sulphur rich surface: Cu25 + S (7.11) 2. At oxidising potentials, the cuprous ions may be oxidised to cupric ions: (7.12) with the corresponding cathodic reaction oxygen: involving dissolved molecular & 2H2 (7.13) 3. The cupric ions may hydrolyse to various species, the concentration of which depends upon the ph and total copper concentration, e.g. Cu (OH)2 (aq) + (7.15) + 3H2 Cu(OH)3 + (7.16) Cu(OH)2 (aq) Cu(OH)2 (s) (7.17) Thus, the surface of chalcocite becomes covered with copper hydroxide, with the electrokinetic properties of copper hydroxide influencing the electrokinetic properties of the underlying chalcocite. The iso-electric point for heavily oxidised chalcocite being in the region of ph 9., suggests the formation of copper hydroxide at the chalcocite/water interface, for which the iso-electric point has been measured at ph 9.4 (Parks, 1965). This is in agreement with XPS studies which also showed evidence for copper hydroxide as being the predominant 99

119 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG oxidation product on chalcocite. At ph values below approximately 6.5, there is dissolution of the copper hydroxide with re-exposure of the underlying negatively charged chalcocite surface. This is shown to be the case by the reversal in zeta-potential at ph values below 6.5. The electrokinetic behaviour of chalcocite under extensive oxidation such as that for 6 minutes purging time shows a behaviour similar to that of covellite (Figure 7.5) confirming the observations of Sato (196). It has also been found (Biegler and Home, 1984) by infrared and thermodynamic calculations that chalcocite in aerated aqueous solution forms CuO as the oxidation product on the chalcocite surface, the amount increasing with an increase in solution ph. Mielczarski and Suoninen (1988) observed that two situations exist. Firstly, in acid conditions the oxidation products were removed from the chalcocite surface with almost a monolayer coverage by various forms of oxygen such as adsorbed oxygen and hydroxide groups. Alternately, under neutral and basic solutions, a surface layer is formed consisting mainly of cupric hydroxide and carbonates (McIntyre and Cook, 1975). The change of zeta-potential values from positive to negative potentials (Figure 7.4) in more acidic ph indicates dissolution of hydroxides via reactions (7.1) and (7.2) respectively, while the charge reversal in the alkaline ph range may indicate that dispersion of hydroxides is possible. There is therefore significant evidence of oxidation occurring at alkaline ph with the formation of copper hydroxide as the oxidation species, shown both by the literature and by zeta-potential measurements. These conclusions are supported by XPS analysis reported later Covellite Zeta-potential measurements of covellite purged with oxygen for five minutes are 1

120 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG shown in Figure 7; >2 E...' 1 ph N Figure 7.5 Zeta-Potential of Covellite Conditioned at ph 11.5 for 5 minutes with 2 purging. The zeta-potential measurements of covellite show a striking similarity to the oxidation behaviour observed for chalcocite. Like chalcocite, covellite is rapidly oxidised. The formation of hydroxide is apparent between ph 6.5 and 9.5. Given the similarity between the chalcocite and covellite behaviour already established, the lower isoelectric point (i.e.p) of 6.5 is probably the precipitation of copper hydroxides on the surface of covellite particles. The surface oxidation reaction occurring between ph 2 and 12 according to Sato (196) is given by equation (7.18) CuS + S + 2e Eh = (7.18) Born ite Figure 7.6 shows the zeta-potential measurements for bornite conditioned at ph 11.5 with oxygen and 5 minute purging time. Similar to chalcocite and covellite, bornite shows a positive charge in the neutral region, combined with iso-electric points in the mildly acidic and alkaline regions. 11

121 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG N 6-8 Figure 7.6 Zeta-Potential of Bcrnite Conditioned with 2 purging for 5 minutes It has been observed (Buckley, Hamilton and Woods, 1984) that oxidation of bornite at ph 9, and at potentials above -.3V, occurs via reaction (7.19), with further oxidation above -O.5V yielding a lower copper content sulphide and the formation of copper hydroxide described by reaction (7.2). Cu5FeS4 + 3H2 Cu5S4 + Fe(OH) e (7.19) + xh2o Cu5S4 xcu(oh) & (7.2) Chalcopyrite The zeta-potential at the chalcopyrite-water interface was studied under nonoxidising and oxidising conditions by Fairthorme (1996). Like chalcocite, the surface of unoxidised is negatively charged over a wide ph range between 3 and 1. However, for oxidised chalcopyrite, a low iso-electric point exists between ph 5 and 6, suggesting the formation of iron oxy-hydroxide at the mineral-water interface. It is well established that a hydrated iron oxyhydroxide is the dominant oxidation product under oxidising potentials and alkaline conditions as shown in reaction 7.21 (Buckley and Woods,1983; Zachwieja et al., 1989). 12

122 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CuFeS2 + 3/4x2 + 3/2xH2O CuFel-xS2 + xfe(oh)3 (7.21) Furthermore, after prolonged oxidation in air or oxidation at higher overpotentials (Buckley and Woods, 1984; Pang and Chander, 199), Cu (II) oxidation products may also form in concert with sulphate on the chalcopyrite surface Summary of Zeta Potential Studies On the basis of zeta-potential measurements, it is evident that all copper minerals studied undergo oxidation with markedly contrasting behaviours. The zeta-potential measurements reveal that chalcocite, covellite and bornite exhibit a similar electrokinetic behaviour, with copper hydroxide formed on mineral surfaces after 5 minutes purging time with oxygen in the mid range of ph (typically ph 5 to ph 9). There is charge reversal for ph values greater than the PHiep, at which ph dispersion of hydroxides from the chalcocite surface may occur, i.e., chalcocite at 8.5, covellite at 9.5 and bornite at 9.5, though the chalcocite ph increased to 9.5 with sixty minutes conditioning with oxygen. In contrast, chalcopyrite (Fairthorne, 1996) showed charge reversal at ph EDTA Extraction of Oxidised Chalcocite The EDTA extraction of pre-oxidised chalcocite was examined to determine the extent of oxidation at high ph where dissolution of chalcocite was not observed to occur, i.e., at ph 7 or above. As previously described in Section 3.3.4, 12 M EDTA was added to aliquots of chalcocite slurry after, 5, 1, 2 and 3 minutes purging with oxygen at ph 7, 9 and After five minutes conditioning with the EDTA, the aliquot was filtered and the filtrate assayed for copper. Results are shown in Figure 7.7, expressed as moles Cu per square meter of mineral surface, and indicate the total surface oxidation of chalcocite, since the latter can be equated with the EDTA extractable copper. 13

123 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG From Figure 7.7, oxidation of chalcocite at ph 7, 9 and 11.5 appears fairly static, with little increase in the EDTA extractable copper with time, suggesting that oxidation occurs fairly rapidly during the grinding step. ph 11.5 yields the lowest amount of EDTA extractable copper, suggesting that at ph 11.5 the chalcocite is less oxidised. It is likely (Attia, 1975) that the copper species predominant at this ph are CuCO3 and Cu(OH)2 both of which are extractable in EDTA solutions (Kant, Rao and Finch, 1994). :: 4.OOe-4 3.SOe-4. 3.OOe-4 2.5e-4._o_. ph 7 2.OOe-4, ph 9 1.5e-4 _.o_ph OOe-4. 5.OOe-5..OOe+ I I Time (minute) Figure 7.7 Oxidation of Chalcocite as measured by EDTA Extraction 7.4 Sulphidisation of Chalcocite The suiphidisation of chalcocite is examined by EDTA extraction, zeta potential measurement and XPS analysis Effect of Suiphidisation on EDTA Extraction of Oxidised Chalcocite A similar experiment to that in Section was conducted with a ground sample of chalcocite purged with either oxygen or nitrogen and the addition of M NaHS. As described in Section 3.3.4, aliquots were removed at, 5, 1, 2 and 3 minutes and mixed with 12 M EDTA for five minutes before filtration 14

124 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG and analysis of the filtrate for copper. Results are shown in Figure 7.8, expressed as mol Cu per square meter of mineral surface. The results for ph 11.5 without NaHS (from Figure 7.7) are included in Figure 7.8 for easy comparison. For the sample to which NaHS is added and purged with nitrogen, the quantity of oxidised copper on the surface negligible. By comparison, for the sample to which NaHS is added and purged with oxygen, the quantity of oxidised surface copper is significant at time zero and increases over ten minutes until it approximates the quantity when NaHS is not added. Since the NaHS addition in the presence of nitrogen almost eliminates the presence of oxidised copper, the presence of significant oxidised copper when oxygen is used as the purgant suggests that the initial oxidation of chalcocite is exceedingly fast, reminiscent of the two stage oxidation of chalcocite proposed by Sato (196) in equations 7.1 and 7.2. Furthermore, the gradual increase of oxidised copper when NaHS is added with an oxygen purge shows that oxygen can completely remove any benefit of sulphidisation. (U 5.OOe-4 4.5e-4 4.OOe-4 3.5e-4 3.OOe-4 2.5e-4 E & 2.OOe-4 1.5e-4 1.OOe-4 5.OOe-5 O.OOe+O Time (Minute) 3 Figure 7.8 Effect of NaHS on EDTA Extractable Copper from Chalcocite Conditioned at ph

125 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Eftect of Suiphidisation on Zeta-Potential of Oxidised Chalcocite A further electrokinetic experiment was conducted on chalcocite, but in a M NaHS solution after prior oxidation by ten minutes purging with oxygen. The experiment was previously described in Section Figure 7.9 shows the zeta potential of chalcocite after five minutes purging with oxygen (repeated from Figure 7.4) and also after ten minutes conditioning in 1 M NaHS following a ten minute oxygen purge. Examination of Figure 7.9 clearly shows that the zeta-potential is changed by the NaHS conditioning, making the chalcocite more negatively charged at all ph values examined. The expected effect of NaHS on the surface modification of chalcocite is therefore evident and supports the hypothesis of a surface conversion from Cu(OH)2 to CuS, described by reaction (7.22); Cu(OH)2 + HS CuS + H2 + H (7.22) 4-6. Condit. NaHS -w! Figure 7.9 Effect of M NaHS on the Zeta-Potential of Oxidised Chalcocite 16

126 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG XPS Analysis of Suiphidosation of Oxidised Chalcocite The experimental procedure was previously described in Section Slurry samples for XPS analysis were collected at ph 11.5 after ten minutes conditioning with oxygen (Sample #1) and then subsequently conditioned with 13M NaHS (Sample #2) to (a) confirm that excessive aeration using oxygen tends to promote the surface oxidation of chalcocite and (b) the surface of chalcocite was modified by NaHS. XPS binding energy spectrums for copper (2p), sulphur (2p) and oxygen (2p) are shown respectively in Figures 7.1, 7.11 and 7.12 for both Sample #1 and Sample # XPS Examination of Sample #1: Chalcocite after Oxygen purging at ph 11.5 The extent of charge shifting of the sample can be determined by referencing to the uncharged C (is) line at ev for carbon bonded only to other carbon atoms (Briggs and Seah, 1983). In both samples, the C (is) emission showed evidence of adventitious hydrocarbon impurities, with a major contribution from C-H groups at ev, suggesting no significant charge shifting of the chalcocite surface. A 5 mm argon etch (Art at 4kV) removed greater than 8% of the carbon signal, which confirmed that the carbon species were present as a contaminant overlayer on chalcocite. As a consequence, the proportions of each element have been recalculated after subtracting this hydrocarbon contamination (Table 7.1). Table 7.1 XPS Atomic Concentrations (mole %) for Chalcocite Samples #1 and #2 Atomic Concentration (mole %) Cu S Cu:S: II " II XPS Sample # : 1: 8.8 XPS Sample # : 1:

127 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG The elemental ratio for Sample #1 suggests considerable surface enrichment of copper in agreement with Mielczarski and Suoninen (1988). Similar C (is) and Cu (2p) spectra has been obtained by Mielczarski and Suoninen (1988) for chalcocite conditioned at ph 1.5. For unoxidised chalcocite, the Cu (2p)3/2 and (2p)i/2 spin orbit splitting emissions should occur at ev and ev respectively (Mielzcarski and Suoninen, 1988; Laajalehto, Kartio and Nowak,1994; Chawla, Sankarraman and Payer, 1992) (Figure 7.lOa). The formation of copper (II) hydroxide on the surface of the chalcocite gives rise to a signal on the higher energy side of the Cu (2p) spectrum and the satellite structure near 942 ev for this sample. After, ion sputtering these satellites were not present suggesting the copper hydroxide occurred as a superficial oxidation layer. C.3).3) E Binding Energy. ev Figure 7.1 Copper (2p) Spectrum for (a) Chalcocite with Oxygen purging and (b) after subsequent NaHS Conditioning with Nitrogen purging. The oxidation products reduce the surface exposure of sulphur below that 18

128 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG expected for stoichiometric chalcocite. The oxidation products do not contain sulphur, as there is a lack of sulphur bonds in the S (2p) spectrum other than that expected for chalcocite (Figure 7.lla), in agreement with Mielczarski and Suoninen (1988). The S (2p) spectrum of chalcocite should exhibit S (2p)3/2 spin orbit splitting at ev, with a higher binding energy component of S (2p)3/2 near ev, corresponding to metal deficient chalcocite (Mielzcarski and Suoninen, 1988). These components are clearly present in the S (2p) spectrum Binding Energy. ev Figure 7.11 Sulphur (2p) Spectrum for (a) Chalcocite with Oxygen purging and (b) after subsequent NaHS Conditioning with Nitrogen purging. The position and full width at half maximum (FWHM) of the (is) peak near ev, indicates several different forms of oxygen present on this oxidised 19

129 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG chalcocitesurface (Figure 7.12a). For precipitated Cu(ll) carbonate, the expected BE of the (is) peak is ev (Mielczarski and Suoninen, 1988). It is expected at this ph that hydroxycarbonates of similar composition to azurite [Cu3(OH)2(C3)2] or malachite [Cu2(OH)2C3] would be a major oxidation product on chalcocite. 1) C z Binding Energy. ev Figure 7.12 Oxygen (2p) Spectrum for (a) Chalcocite with Oxygen purging and (b) after subsequent NaHS Conditioning with Nitrogen purging XPS Examination of Sample #2 : Chalcocite after Suiphidisation at ph 11.5 in Nitrogen. Clear alterations to the surface of chalcocite are apparent in the atomic concentrations after the conditioning of the chalcocite in M NaHS. From Table 7.1, there is a marked reduction in oxygen, with a concomitant increase in 11

130 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG copper and sulphur. Now, the surface closely resembles that of stoichiometric chalcocite, with a smaller contribution from oxygen. There is now no evidence of copper hydroxide formation with the absence of both the higher binding energy component in the Cu (2p) spectrum and the satellite structure near 942 ev (Figure 7.lOb). Clearly, the sodium hydrosulphide has reduced these species to copper suiphide, with removal of the oxygen containing phases of hydroxide and carbonate (Figure 7.12b). As no oxidation products containing sulphur were present on the original oxidised chalcocite surface, suiphidisation had little effect on the bonding of sulphur for the substrate chalcocite (Figure 7.llb). There was also no evidence for adsorption of oxidised sulphur species caused by the oxidation of hydrogen sulphide solution, which was expected given the use of nitrogen in the suiphidisation step. 7.5 Concluding Remarks The results of the zeta-potential measurements correlate well with the dissolution and EDTA extraction results. On the basis of dissolution and zeta-potential measurements, the tendency for surface oxidation to occur in an aerated solution is most apparent and follows the order; chalcocite> covellite > bornite > chalcopyrite. The rapid precipitation of cupric hydroxide is thought (Buckley and Woods, 1984) to occur in more alkaline solutions, i.e. Cu 2+ + Cu(OH)2 (s) (7.23) In more acidic solution (ph 4), both chalcocite and covellite were found to be very soluble and bornite comparatively soluble, while at ph 5.3, Zachwieja et al., (1989) found chalcopyrite to be relatively soluble. The effect of NaHS on the conversion of Cu(OH)2 to CuS has been confirmed. 111

131 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG CHAPTER VIII 8. SULPHIDISATION PLANT TRIALS 8.1 IntrodUction Following the success with NaHS in improving copper recovery in the laboratory, a series of plant trials were conducted to determine if the laboratory tests could be reproduced in the Concentrator. In particular, It is important to remember that the Concentrator does not treat porphyry ores exclusively, but treats a blend of porphyry, siltstone and skarn ores. This Chapter details the results of three such plant trials and also examines pulp chemical, size by size and XPS data collected during a relatively short NaHS "on/off" trial. The plant trial data together with statistical and economic analysis of plant data are given in Appendix #4. Appendix #5 contains the NaHS 'on-off' survey results obtained on exclusively porphyry ore. 8.2 Plant Studies The Ok Tedi Concentrator consists of two parallel grinding and flotation units. Whenever a new chemical or strategy is to be tested, the method of testing is to make the change to one unit and compare the behaviour of the two units. This is especially useful as it allows for the minimisation of variability in mill feed, since the similarity of ore fed to both units at any point in time is generally, though not exclusively, greater than the similarity of ore fed to the same unit even two hours apart. Trials were conducted over a time frame of one to two weeks to allow at least 3 data sets to be collected for both the "NaHS-on" and "NaHS-off" situations, i.e., to allow statistical evaluation. 112

132 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG To allow for natural variation between the two units, no NaHS was added to either unit for periods interspersed throughout the trial period. This provided a "natural" difference in performance between the two units which could be subtracted from the difference between the two units when NaHS was used, yielding an improvement in performance attributed to the NaHS. The first NaHS trial was conducted and reported by Wawako (1995). This trial was not part of the work in this project and failed in hindsight due to a combination of the lack of CPS control and a failure to allow for higher than laboratory NaHS consumption, the latter due to the increased consumption of NaHS by oxygen in mill pulps. NaHS Trials #2 and #3 involved the addition of NaHS to one Unit with no addition to the other Unit. NaHS Trial #4 investigated whether a lower ph might be applicable when NaHS was added to the feed. Trials #2, #3 and #4 all used the CPS control method described in Chapter III Trial #2 Results The results of the second CPS trial were fully reported by Senior and Heyes (1996) and are reproduced in Table 8.1. Unit Table 8.1 Summary of Results of the NaHS Trial #2 (Abstracted from Senior and Heyes, 1996) Mean Feed % Cu Mean Concentrate %Cu NaHS added to Unit 1 Mean Tailing % Cu Copper Recovery % (Difference) (7.) NaHS not added to either Unit (Difference) (2.6) Copper recovery gain from NaHS = 4.4% 113

133 The Influence of Sodium Hydrogen Suiphide on Porphyry SuOphide Copper Recovery at Ok Tedi, PNG Senior and Heyes (1996) concluded that whilst sulphidisation increased copper recovery by 4% with no discernible loss to concentrate grade and gold recovery, the additional benefits indicated were A reduction in frother consumption of 3%. Reduced copper levels to flotation tailings (important due to river discharge of tailings). The major costs in full scale implementation were anticipated to cover the sulphidising reagent (NaHS) and the associated mixing and distribution system Trial #3 Results The results of Trial #3 were fully reported by Lauder and Orwe (1996), and are reproduced in Tables 8.2, 8.3 and 8.4 for copper, gold and acid soluble copper recovery respectively. Table 8.2 Copper Recovery-NaHS Trial #3 Unit Mean feed % Cu Mean Concentrate % Cu NaHS added to Unit 2 Mean Tailing % Cu Copper Recovery % 1 If { (Difference) If (2.8) NaHS not added to either Unit 1 If I[ If 8.6 (Difference) (-.6) If Copper recovery gain from NaHS = 3.4% When NaHS was added to Unit 2, the mean feed copper assay was marginally higher and the mean tailings copper assay marginally lower in Unit 2. The difference in recovery between the Units was 3.4% attributable to the use of NaHS. Statistically (see Appendix #4), the difference in recoveries between Unit 1 (without NaHS) and Unit 2 (with NaHS) lies in the range between -5.55% and -.285% at a 95% confidence interval, indicating that there is 97.5% chance that 114

134 - The Influence of Sodium Hydrogen Suiphide on Porphyry Copper Recovery at Ok Tedi, PNG NaHS will increase the copper recovery by at least.285%. Similarly, at the 8% confidence interval, NaHS would improve copper recovery by at least 1.21 %. It should be noted that copper recovery and concentrate grade are oretype dependent. Therefore, the number of ore types (including skarn, siltstone and porphyry suiphide) treated during the trial period probably contributed to the lower recovery gain compared to the results of Trial #2. Unit If Mean Feed Au (git) 11 Table 8.3 Gold Recovery-NaHS Trial #3 Mean Concentrate Au (g/t) NaHS added to Unit 2 Mean Tailing Au (g/t) Gold Recovery % ,3 (Difference) (2.6) NaH S not added to either Unit (Difference) Ii (2.) Gold Recovery Gain =.6% A similar calculation procedure was undertaken with gold, although the gold recovery gain with NaHS is somewhat lower than that for copper. The lower mean gain of.6% may be taken with less confidence since the analytical techniques are less rigorous. More data is required to improve this confidence, although historically, gold recovery tends to follow copper recovery. Unit Table 8.4 Acid Soluble Copper Recovery-NaHS Trial #3 Mean feed %AsCu Mean concentrate %AsCu NaH S added to Unit 2 AsCu recovery J) L (Difference) 111 NaHS not added to either Unit (15.7) If (Difference) (3.9) Acid soluble copper recovery gain = 11.8% The acid soluble copper recovery gain of 11.8% reflects a significant surface 115

135 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG enhancement of the minor oxide mineralisation by NaHS. The total copper recovery gain of 3.4% may therefore be at least partially, but not completely, attributed to high acid soluble copper recovery. The NaHS consumption figure for the trial was obtained by dividing the total reagent used by the average mill feed rate for the duration of the trial period. The NaHS solution used in Trial#2 amounted to a total of six batches, i.e., 54.6 tonnes of NaHS flake at an average feed rate of 2tph, equating to 252g/t of NaHS. Subsequent trials have averaged 25g/t based on actual solution flow and feed tph. Since NaHS consumption is ore dependent, the presence of skarn ores in the feed is normally reflected by a higher consumption. Subsequent experience with the NaHS addition has shown the consumption to be of the order of 1 6g/t when treating only porphyry ores. It was shown in Chapter VI that less than 25g/t NaHS was required to achieve = -25 mv on the porphyry sulphide ores. This difference is accounted for by the high levels of dissolved oxygen contained in plant puips as opposed to laboratory pulps, as grinding in the laboratory is achieved in a closed mill. By comparison, plant pulps are ground in a open to atmosphere mill and then pumped through an air-core containing cyclone, perfect conditions for maximum aeration. The increased oxygen in plant puips therefore accounts for the higher NaHS consumption of those pulps Trial #4 Results Trial #4 was conducted to achieve two objectives. They were :- To confirm results of previous plant trials (Trials #2 and #3). Establish whether improved metallurgy was attainable at reduced ph as suggested by Senior and Heyes (1996). Trial #4 results are given in Tables 8.5 and 8.6 for comparison at ph 11. and 1.5 respectively. 116

136 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Table 8.5 Effect of NaHS at Reduced ph of 11.-NaHS TrIal #4 Mean ph 11. With NaHS Copper(%) ph 11.5 With NaHS ph 11.5 W/O NaHS ph 11. With NaHS Gold(g/t) ph 11.5 With NaHS ph 11.5 W/O NaHS Feed Tailing % Recovery Examination of Table 8.5 shows quite simply that ph 11. with NaHS provided lower copper recovery than ph 11.5 with NaHS (i.e., 1.3% less). Compared with the "NaHS-off" situation, ph 11.5 with NaHS, compared to ph 11.5 without NaHS yields an improvement of 4.64%, a result similar to that of Trial #2. However, when Table 8.6 is considered, the difficulty in interpreting plant trial results is obvious. It should be noted that the data for ph 11.5 and 1.5 with NaHS were collected from the two Units treating the same material at the same time. Conversely, the data for ph 11.5 without NaHS for both Units were collected at a different time from the "with NaHS" data. Hence whilst the two "with NaHS" data sets may be compared against each other, and the "without NaHS" data sets may be compared against each other, the "with NaHS" and "without NaHS" situations are not comparable as the feed to each situation is not the same. Table 8.6 Effect of NaHS at Reduced ph of 1.5-NaHS Trial #4 Mean ph 11.5 Unit 1 NaHS ph 1.5 Unit 2 With NaHS ph 11.5 Unit 1 W/O NaHS ph 11.5 Unit 2 W/O NaHS Feed %Cu Tailing %Cu Recovery (%) The comparison of copper recovery at the two different ph values is therefore done in the following manner. First, compare the natural bias between the two sides when NaHS is not used, i.e., Unit 1 achieves a copper recovery of %, whilst Unit 2 achieves 81.59% - a difference of 3.52% in favour of Unit 1. Second, compare the difference between the two sides when NaHS is used on both sides, i.e., Unit 1 at ph 11.5 achieves a copper recovery of 83.1% whilst Unit 2 at ph 1.5 achieves 78.36% - a difference of 4.65% in favour of Unit 1. The recovery difference that is attributable to the difference in ph is therefore the 117

137 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG latter less the former (4.65%-3.52%), which is 1.13%. The result of the trial is, therefore, that NaHS at ph 11.5 provides 1.13% better recovery than NaHS at ph 1.5. The trial itself cannot be used to compare NaHS-on versus NaHS-off, as the feed material is not the same during the two situations. 8.3 Flotation Circuit Surveys Two surveys of the rougher-scavenger were carried out on Unit #2 flotation circuit to examine the influence of pulp chemistry, with and without NaHS, on copper recovery. XPS samples were also collected and the effect of NaHS on size by size copper recovery examined Pulp Chemistry Pulp chemical data is shown for pulp potential dissolved oxygen (do2) and temperature in Figures 8.1, 8.2 and 8.3 respectively. Other pulp chemical data is given in Appendix 4. The sample points in the circuit were given in Table 3.7. Figures 8.1 and 8.2 show the pulp potential and dissolved oxygen measurements by sample number from Table 3.7. The Figures show a degree of similarity in that the addition of NaHS (after sample point #2, but before sample point #3) caused a decrease in both dissolved oxygen and pulp potential. Aeration in Rougher Cell #1 quickly returned both measurements to the values observed in the absence of NaHS. The difference observed after Rougher Cell #1 between the NaHS "on" and "off" situations for potential, dissolved oxygen and temperature are interpreted as natural variation, rather than NaHS dependency. 118

138 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG c -2 C) Sample Number Figure 8.1 Potential Measurements E Q. 6 C C) 4 C) (I) Sample Number Figure 8.2 Dissolved Oxygen Levels o _ij_w/o NaHS Sample Number Figure 8.3 Temperature Profiles 119

139 The Influence of Sodium Hydrogen Suiphide on Porphyry Copper Recovery at Ok Tedi, PNG Effect of NaHS on Copper Recovery Table 8.7 shows the copper grade and recovery of the circuit with and without NaHS addition. Full survey data is shown in Appendix #4. When NaHS was used, the total copper recovery increased by 1.8%. In a later attempt to repeat the NaHS "on-off' survey (see Appendix #5), an improvement to copper recovery of 8.7% was achieved by the NaHS. The low improvement in copper recovery in the Survey described here is therefore attributed to one of the following: (1) experimental error, given the short duration of the survey in the attempt to gain comparability of mill feed, (2) a lack of copper hydroxide coated copper minerals at the time of the survey, or, (3) preferential consumption of the NaHS by minerals not present in porphyry ores, but present in the mill feed during the "on-off" surveys. Table 8.7 NaHS "On-Off" Survey Comparison Stream Mass % % Cu II Cu Recovery NaHS Off Rougher Feed Final Concentrate Final Tailing NaHS On Rougher Feed Final Concentrate Final Tailing The effect of NaHS on size by size copper recovery is shown in Figure 8.4. Clearly, the increase in copper recoveries were not as pronounced as that observed in the laboratory ore studies, though this is again attributed to the nonporphyry ore component of the mill feed. The small increase in total copper recovery was reflected across the entire size range. 12

140 I II The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 1 8 >' U a).. C) I:it I 1 b Without NaHS ci--- With NaHS I II Size (micron) I I liii! 1 1 Figure 8.4 Effect of NaHS on Size by Size Copper Recovery The size by size recoveries in Appendix #5, Table 2 show that the major copper loss of.76 tph was obtained with NaHS off against.18 tph with NaHS on for the coarse size fraction (+212 In contrast, the copper loss for fine size fraction (6 tim) in tail were.44 tph and.28 tph for NaHS off and NaHS on situations respectively. NaHS increased recovery of both these size fractions despite differences in copper content in feed XPS Analysis of Plant Survey Samples Samples for XPS analysis were collected during three surveys; on the 14/2/96 without suiphidisation, and on the 22/8/96 for two surveys with and without sulphidisation. The sample points analysed by XPS are shown in Table 8.8. Only the rougher feed and concentrate samples for each of the surveys were analysed. This was because XPS examination of the rougher feed samples did not detect a copper signal, as the exposed copper was below the detection limit by XPS (.1%). It is impossible to determine, therefore, the oxidation state of copper on the feed samples. Given the even lower copper content of the tailing samples, XPS examination was not carried out for these sample types. However, some useful conclusions may be drawn from examination of the feed and concentrate surfaces. 121

141 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Table 8.8 Sample Nomenclature and Conditions Sample Name Survey Date Sample Point NaHS Addition OTOO1 14/2/96 Rougher Feed Off T3 14/2/96 Rougher Conc Off T7 22/8/96 Rougher Feed On T8 22/8/96 Rougher 1-3 Con On OTO1 22/8/96 Rougher Feed Off OTO11 22/8/96 Rougher 1-3 Con Off For both surveys without suiphidisation, the rougher feed surface was dominated by oxygen Containing species, almost certainly indicative of the various gangue oxides in the feed (silica, alumino silicates, magnetite). Silicon occurs in the expected form of silica and occurs to a high concentration for all feed samples (Table 8.9). Table 8.9 XPS Atomic Concentrations of Samples before Etching (Units: Mole%) Sample Name C Cu Fe S Na K Si Mg Ca OTOO ND T ND ND T ND T OTO1O ND OTO The gangue assemblage gives rise to a highly insulting surface. Referencing to uncharged, adventitious hydrocarbon at ev, shows that all feed samples were charge shifted by 4.6 ev, indicating the feed surface to be highly insulating. The charge corrected C (is) spectra (4.6 ev) for the feed samples are shown in Figure 8.5 (a) and (b). The addition of NaHS (T7) did not alter the extent of charge shifting as expected given the low concentration of sulphides in the feed (Table 8.9). A 5 minute argon ion etch (Ar+ at 4 kv) removed greater than 9% of the carbon signal (Table 8.1), suggesting that the adsorbed collector present 122

142 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG on these samples was only on a small part of the total feed surface. Table 8.1 XPS Atomic Concentrations of Samples after Etching (Units: Mole%) Sample Name C Cu Fe S Na K Si Mg 1 Ca OTOO ND T ND T ND T j ND] Lo.5 OTO1O ND OTO _jJ_.7_Jj_ F Binding Energy. ev Figure 8.5 Carbon (is) spectrum for (a) Rougher Feed NaHS off (11), (b) Rougher Feed NaHS on (17), (c) Rougher Concentrate NaHS off (OTO11) and (d) Rougher Concentrate NaHS on (T8). All spectra for unetched surfaces. The other noteworthy feature of the feed samples, without suiphidisation, was the 123

143 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG occurrence of iron which occurred only in the form of ferric oxyhydroxides. The broad band between 711 and 712 ev (Figure 8.6 (a) and (b) can be assigned to Fe(OH)3, FeOOH, Fe23 or Fe34 (Pratt, Nesbitt and Muir, 1994), and is referred to collectively as iron 'oxyhydroxide'. The Fe (2p) signal of pyrite lies at a binding energy near 77.4 ev (Buckley and Woods, 1987), whilst iron in chalcopyrite occurs at 78 ev (Buckley and Woods, 1984). Neither exposed pyrite nor chalcopyrite were apparent for samples without sulphidisation. >- a) a) ) a) E z Binding Energy. ev Figure 8.6 Iron (2p) specfrum for (a) Rougher Feed NaHS off (OTO1O), (b) Rougher Feed NaHS on (T7), (c) Rougher Concentrate NaHS off (OTO11) and (d) Rougher Concentrate NaHS on (T8). All spectra for unetched surfaces. The sulphide signal for the rougher concentrate in the absence of sulphidisation is characteristic of sulphur in adsorbed collector on chalcocite near 162 ev (Laajalehto et al., 1988) and metal deficient suiphide near ev (Figure 8.7 (a)). A 5 minute argon ion etch largely removes the metal-deficient suiphide component (Figure 8.7 (b)), but increases the overall atomic concentration of sulphur derived from the underlying sulphide mineral. 124

144 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Attention will now turn to the effect of suiphidisation. Suiphidisation causes a large decrease in the surface atomic concentration of oxygen on the feed sample surface (Table 8.1). As commented previously, suiphidisation does not increase the surface exposure of sulphur on the feed sample surface to levels greater than the detection limit (Table 8.1), and does not alter the charge shifting of the feed sample (Figure 8.5( b)). (I; I a) a) ) a) Einding Energy. ev Figure 8.7 Sulphur (2p) spectrum for (a) Rougher Concentrate NaHS off (OTO11) unetched surface, (b) Rougher Concentrate NaHS off (OTO11) - etched surface, (c) Rougher Concentrate NaHS on (T8) - unetched surface and (d) Rougher Concentrate NaHS on (T8) - etched surface. No feed sample surfaces shown. The most significant alterations with suiphidisation occur in the Cu (2p) and Fe (2p) spectrum of the rougher concentrates. In the case of the Cu (2p) spectrum, and in the absence of sulphidisation, there is clear evidence for oxidised copper in the higher binding energy component near 936 ev (Figure 8.8 (a)). A 5 minute argon ion etch substantially reduces the occurrence of oxidised copper (Figure 8.8 (b)), suggesting that the oxidation products were at the surface only. it is also 125

145 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG clear, that in rougher flotation, oxidised forms of copper, if present in the feed, will not be efficiently recovered into the concentrates. In contrast, suiphidisation substantially reduces the high binding energy shoulder in the Cu (2p) spectrum. In this case, a 5 minute argon ion etch does not reduce the shoulder, suggesting that this may be a feature of the unoxidised mineral in this particular matrix. This may be a result of differential charging, as evidenced in the C (is) spectrum for this sample (Figure 8.5 (d)). E z Binding Energy. ev Figure 8.8 Copper (2p) spectrum for (a) Rougher Concentrate NaHS off (OTO11) - unetched surface, (b) Rougher Concentrate NaHS off (OTO11) - etched surface, (c) Rougher Concentrate NaHS on (T8) - unetched surface and (d) Rougher Concentrate NaHS on (T8) - etched surface. No feed sample surfaces shown. In concert with the decreased state of copper oxidation on the concentrate surfaces, there is also a relative increase in exposure of iron in pyrite and chalcopyrite for the concentrate sample with suiphidisation (Figure 8.6 (d)). For both concentrate surfaces, there is exposure of iron in pyrite near 77 ev (Figure 8.6 (c) and (d)). 126

146 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG In summary, suiphidisation causes the following surface alterations: reduces the atomic concentration of oxygen on the feed and concentrate samples. reduces copper oxidation products on the surface of the concentrate samples. increases exposure of iron in pyrite and chalcopyrite on the surface of the concentrate sample. 8.4 Concluding Remarks On the basis of laboratory ore studies and plant trials, combined with the single mineral studies reported previously, it would appear that the application of NaHS to rougher feed using a CPS technique is appropriate for the improvement of sulphide copper recovery, generally yielding an improvement in fine (-15 sulphide copper recovery. The success of this technique hinges on a balance between pulp potential and ph where the best results were shown at ph 11.5 at -25 mv In plant trials, operating at a ph lower than 11.5 resulted in reduced copper recovery. An attempt to gather pulp chemical data during an "on/off" trial was only partially successful, in that the improvement in copper recovery with the NaHS was only 1.8% during this particular time. Further data has been collected and reported in Appendix V, but at the time of writing this thesis, surface chemical data was not available. For these later surveys, there was a larger increase in copper recovery attributable to NaHS. Analysis of the XPS samples collected during the "on-off" survey suggested the effect of the NaHS was to reduce copper oxidation products on the surface of the concentrate samples, as well as to reduce the atomic concentration of oxygen on both feed and concentrate samples. 127

147 The Influence of Sodium Hydrogen on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG CHAPTER IX 9. CONCLUSIONS AND RECOMMENDATIONS 9.1 Conclusions Mineralogical examination of Folomian Concentrator products treating a typical ore blend has shown that the principal copper suiphide minerals are chalcopyrite, digenite and bornite. Further examination attributed the primary losses of copper to tailings as both digenite and chalcopyrite. The losses were as fine liberated particles (-13i.tm) and coarse binary composite particles with nonsuiphide gangue and in ternary suiphide/gangue particles. The laboratory flotation of two porphyry ores also showed poor recovery in the fine and coarse ranges of the size distribution. Following the work of Senior and Creed (1992), examination of the use of NaHS to improve copper recovery was investigated and found to improve copper recovery after suiphidisation of the rougher feed to Eh = mv (SHE) at ph This was found in the laboratory to improve recovery in both the fine (-31 and coarse ranges of the size distribution. The addition of NaHS to the laboratory mill provided improved recovery compared to sulphidisation of the rougher feed. The success of suiphidisation, not only in promoting oxide copper flotation, but also enhancing sulphide copper flotation hinges upon the pulp chemistry which is governed by the ph-eh environment. Single mineral studies showed that a proportion of sulphide copper surfaces are partially covered with hydrophilic layer(s) of hydroxide species as a consequence of operation at highly alkaline ph. Although the magnitude of these hydrophilic coatings on copper surfaces could not be quantified, electrophoresis studies have shown this to be the case for chalcopyrite, chalcocite, covellite and bornite. 128

148 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Plant trials of the application of controlled potential suiphidisation (CPS) on rougher feed have provided encouraging results. The trials provided improved overall copper recovery of 4% on a porphyry/skarn ore blend and 8% on porphyry ore with a 3% reduction in frother consumption. Plant trials at reduced ph values of 11. and 1.5 showed a decrease in both copper and gold recoveries by 1% and 2% respectively compared to that at ph 11.5, all in the presence of NaHS. The plant surveys conducted with and without CPS in conjunction with pulp chemistry measurements provide useful evidence of surface modification of copper minerals in suiphide ores. 9.2 Recommendations The success of controlled-potential sulphidisation depends on the maintenance of appropriate pulp potential prior to and during flotation. The careful control of pulp potential using this technique has led to increased copper and gold recoveries, particularly for the fines (-31 and coarse (+1 size fractions. However, these obvious benefits may be outweighed by the high NaHS consumptions resulting from the treatment of skarn ores. (1) EDTA Extraction It is shown that digenite (chalcocite) and covellite oxidation can be indicated by EDTA extraction. EDTA extraction on rougher feed prior to NaHS addition may indicate the presence and level of copper hydroxide and carbonates, as chalcocite has been shown to exhibit rapid oxidation under plant conditions. It is therefore possible that the EDTA test may be used as an indicator for the presence of copper hydroxides on suiphide minerals. Laboratory work should therefore be conducted to determine if the improvement in recovery with sulphidisation can be predicted by the EDTA extraction test. 129

149 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG (2) Addition of NaHS to Grinding Mill Since laboratory results of NaHS addition to the grinding mill have indicated the possibility of further gains in copper and gold recoveries, a plant trial is recommended. The major problem envisaged with such a test is whether the mill slurry discharge can be effectively sampled and measured for to control the NaHS addition. Another problem with NaHS addition to the mills is the consumption of HS by dissolved 2 derived from the ingress of air into the mill. A more stable sulphidising agent such as polysulphide (52) may be of benefit in this case. (3) Use of Nitrogen As NaHS consumption increases with the presence of dissolved oxygen in mill rougher feed, initial work on a laboratory scale with plant pulps (results not shown) has indicated that NaHS consumption may be reduced by 5% by purging the rougher feed with nitrogen prior to NaHS addition. The nitrogen acts to displace the oxygen from the pulp. Further laboratory work should be conducted to confirm these results, followed by a plant trial. (4) NaHS Addition to Concentrate Regrind mill EDTA extraction analysis of plant streams has shown the cleaner-scavenger feed to be oxidised, approaching the level encountered for the final tailings. NaHS addition to the concentrate regrinding mill should therefore be trialed to reduce recirculation of liberated sulphide copper to rougher feed. 13

150 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG (5) Evaluate the Economics of Separate Treatment of Skarn and Porphyry Ores. Laboratory results have shown that sulphide copper recovery from porphyry ores can be increased at reduced NaHS consumption, but that the presence of skarn ores in the mill feed blend both increases NaHS consumption and reduces the overall recovery improvement (at least partially by dilution of the porphyry ore). As the differences between skarn and porphyry ores become more apparent, and hence the need for different treatment scenarios, the separate treatment of the oretypes will become more attractive and allow the economic use of NaHS only on appropriate ores. Further, laboratory and pilot plant results have shown improved copper recoveries at finer grind of skarn ores. Under the separate treatment scenario, apart from maximising copper recoveries, NaHS consumption would be significantly reduced. 131

151 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG REFERENCES 132

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153 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Chander, S., 1988, Kinetics of Chalcopyrite Oxidation in the Absence and Presence of Collectors. Mid-Term Review Meeting of the indo-u.s. STI Programme in Mineral Engineering. pp Chander, S. and Fuerstenau, D. W., 1974, The Effect of Potasium diethyldithiophosphate on the Electrochemical Properties of Platinum, Copper and Copper Suiphide in Aqueous Solutions. Electroanal. Chem. Interfacial Electrochem., 56: pp Chawla, S. K. and Sankarraman, N. and Payer, J. H., 1992, Diagnostic spectra for XPS analysis of Cu-O-S-H compounds, J. Electron. Spectrosc. Relat. Phenom., 61: pp.1-i 8. Chen, K. Y., 1974, "Chemistry of Sulphur species and Their Removal from Water Supply," Chemistry of Water supply, Treatment and Distribution, A. J. Rubin, ed., Ann Arbor Science, Ann Arbor, Ml. Coleman, R. and Kilgour, I., 1991, The Installation of a Final Cleaning Column at Ok Tedi, Fourth Mill Operators' Conference, Burnie, The Aus. l.m.m., pp Cook, M. A. and Nixon, J. C., 195, Theory of Water Repellent Films on Solids Formed by Adsorption from Aqueous Solution of Heteropolar Compounds. J. Phys. Colloid Chem., 54, 455. Crawford, R. and Ralston, J. 1988, The Influence of Particle Size and Contact Angle in Mineral Flotation. mt. J. Miner. Process. 23: pp Deryjaguin, B. V. and Dukhin, S. S., 1961, Theory of Flotation of Small and Medium Size Particles, Bull. Inst. Mm. Metal., 7: p.221. England, J. K., 1993, Copper Concentrator Practice at Ok Tedi Mining Limited, Ok Tedi, Papua New Guinea, in Australasian Mining and Metallurgy, The Sir Maurice Mawby Memorial Volume, Second Edition, The Aus. I.M.M., pp Fairthorne, G., 1996, The Interaction of Thionocarbamate Collectors with Sulphide Mineral Surfaces, Ph.D. Thesis, University of South Australia. Flint, L. R. and Howartth, W. J., 1971, The Collision Efficiency of Small Particles with SphericalAir Bubbles. Chem. Eng. Sci., 26: pp Fornasiero, D., Eijt, V. and Ralston, J., 1992, An Electrochemical Study of Pyrite Oxidation, Coil. Surf., 62: pp Forrsberg, E. and Subrahmanyam, T. V., 1993, Grinding, Pulp Chemistry and Particle Floatability. Proc. XVIII. mt. Miner. Process. Congress. The Aus l.m.m. Melbourne, Vic., 1: pp

154 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Fuerstenau, M. C. and Sabacky, B. J., 1981, On the Natural Floatability of Suiphides. mt. J. Miner. Process., 8: pp Gardner, J. R., and Woods, R., 1977, An Electrochemical Investigation of Contact Angle and of Flotation in the Presence of Alkylxanthates. II. Galena and Pyrite Surfaces, Aust. J. Chem., 3: pp Gardner, J. R. and Woods, R., 1979, An Electrochemica! Investigation of the Natural Floatability of Chalcopyrite. mt. J. Miner. Process. 6: pp.1-i 6. Garrels, R. M. and Christ, C. L., 1965, Solutions, Minerals and Equilibra. Harper and Row, New York, N.Y., p.45. Gaudin, A.M., Groh. JO. and Henderson, H.B., 1931, Effects of Particle Size on Flotation. Am. Inst. Mi Metall. Engrs., Tech. PubI., 414: pp Glen, R. M., Heyes, G. W. and Senior, G.., 1995, A Laboratory Investigation of Some Techniques for Increasing Copper Recovery from Ok Tedi Ore. CSIRO Division of Minerals Report, DM-R13. Grano, S. R., 199, The Influence of Pyrite and Pyrrhotite on the Selective Flotation of Mount isa Mines Copper and Lead/Zinc Ores. M. App. Sc. Thesis, South Australian Institute of Technology. Grano, S. R., Sollart, M. P., Prestidge, C. A., Skinner, W. and Ralston, J., 1997, Surface Modifications in the Chalcopyrite-Sulphide System. I. Collectorless Flotation, XPS and Dissolution Study. Inter. J. Miner. Process, 5: pp Granville, A., Finkeistein, N. P. and Allison, S.A., 1972, Review of Reactions in the Flotation System Galena-Xanthate-Oxygen. Trans. Inst. Mm. Metall., 81: (784), pp.c1-c3. Guy, P. J. and Trahar, W. J., 1985, The Effects of Oxidation and Mineral Interaction on Sulphide Flotation. In: K.S. Forssberg (Ed.), Flotation of Sulphide Minerals, Elsevier, Amsterdam, pp Hartati, F., Mular, M., Stewart, A. and Gorken, A., 1997, Increased Gold Recovery at P.T. Freeport Indonesia using 7249 Promoter. Sixth Mill Operators' Conference, Madang, PNG. The Aus.l.M.M, pp Hayes, R. A., Price, D. M., Ralston, J. and Smith, R. W., 1987, Collectorless Flotation of Sulphide Minerals, Miner. Proc. Extract. Metall. Rev., 2: pp Hayes, R. A. and Ralston, J., 1988, The Collectorless Flotation and Separation of Sulphide Minerals byeh Control, Int. J. Miner. Process., 23: pp Healy, T. W. and Moignard, M. S., 1976, A Review of Electrokinetic Studies of Metal Suiphides, In: (M. C, Fuerstenau ed.) Flotation, A.M. Gaudin Memorial Volume. 135

155 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Heyes, G. W. and Trahar, W. J., 1977, The Natural Floatability of Chalcopyrite. mt. J. Mm. Process., 4: pp High Intensity Conditioning, AMIRA Project P397 Progress Report 4, June Hunter, R., 1981, Zeta Potential in Colloid Science; Principles and Applications, Academic Press, London. Ikis, D. Y., 1996, Testing of Alternative Collectors for Acid Flotation. OTML Inter- Office Memorandum. Dated 3 March, James, A., 1979, Electrophoreses of Particles in Suspensions, Surf. Coil. Sd., 11: p.121. Jameson, G. J., Nam, S. and Moo-Young. M., 1977, Physical Factors Affecting Recovery Rates in Flotation. Mm. Sd. Eng., 9: pp Jenkins, B. M. and Adair, B. J. I., 1996, The Characterisation of Three Porphyry Ores from Ok Tedi Mine, Using QEM*SEM. CSI RO Minerals Report DMR-488. Johnson, N. W., Jowett, A. and Heyes, G. W.., 1982, Oxidation-Reduction Effects in Galena Flotation : Observations on Pd-Zn-Fe Sulphides Separation. Trans. Inst. MetalI., 91: pp.c32-c37. Jones, M. H. and Woodcock, J. T., 1978, Evaluation of/on Selective Electrode for Control of Sodium Sulphide Additions during Laboratory Flotation of Oxidised Ores. Trans. Inst. Mm. Metall. Sect. C: (Miner. Process. Extr. MetaH.), 87: pp.c99-c1 6. Jones, M. H. and Woodcock, J. T., 1979, Control of Laboratory Sulphidisation with a Suiphide Ion-Selective Electrode before Flotation of Oxidised Pb-Zn-Ag Dump Material. inter. J. Miner. Process., 6: pp Kant, C., Rao, S. R. and Finch, J. A., 1994, Distribution of Surface Metal Ions among the Products of Chalcopyrite Flotation. Mm. Eng., 7: 7, pp Laajalehto, K., Kartio, I. and Nowak, P., 1994, XPS Study of Clean Metal Suiphide Surfaces, AppL Surf. Sd., pp Laajalehto, K., Johansson, L.S., Mieiczarski, J., Anderson, S. and Suoninen, E., 1988, Electron Spectroscopic Studies of Interaction of Xanthate Collectors with Different Substrates. In: K.S.E. Forssberg (Ed.), Proc. XVI mt. Mm. Process. Cong., Stockholm, Sweden, 5-1 June 1988, pp Lauder, D. W., 1996, Measurement of Electrochemistry in Flotation Pu/ps. Theory and Practice. OTML Metallurgical Development Training Manual #1, March,

156 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Lauder, D. W., 1997, Personal Communications. Lauder, D. and Erepan, P., 1996, Line 2 Flotation Survey: 12 October OTML Inter-Office Memorandum dated 12 March, Lauder, D. and Orwe, D., 1996, The Second NaHS to Rougher Feed June to 6ttJ July, OTML internal Report dated July, Lekki, J. and Laskowski, J., 1971, On the Chalcocite/Solution Interface at Alkaline ph, In Abstracts lntn. Soc. Electrochemistry 22nd Meeting; The Electrochemical Society, pp Leppinen, J.., Basillo, C. I. and Yoon, R. H., 1989, In-Situ FT-IR Study of Ethyl Xanthate Adsorption on Suiphide Minerals under Conditions of Controlled Potential. mt. J. Miner. Process, 26: pp Light, T. S., 1972, Standard Solution for Redox Potential Measurement. Anal. Chem., 44: (6) pp Luttreil, G. H. and Yoon, R. H., 1984, The Collectorless Flotation of Chalcopyrite Ores using Sodium Sulphide. mt. J. Miner. Process., 13: pp Lynch, A. J., Johnson, N. W., Manlapig, E. V. and Thorne, G. C., 1981, Mineral and Coal Flotation Circuits; Their Simulation and Control, (Elsevier Amsterdam), pp Malghan, S. G., 1986, Role of Sodium Sulphide in the Flotation of Oxidised Copper, Lead, and Zinc Ores. Miner. Met. Process., pp Mcintyre, N. S. and Cook, M. G., 1975, Anal. Chem. 47, 228. Mielzcarski, J., and Suoninen, E., 1988, XPS Study of the Oxidation of Cuprous Sulphide in Aerated Aqueous Solutions, Coil. Surf., 33: (3-4), pp Nakazawa, H. and Iwaski, I., 1985, Effect of Pyrite - Pyrrothite Contact on their Floatability. Miner. Metall. Process., 2: (4), pp Nakazawa, H. and Iwaski, I., 1986, Galvanic Contact Between Nickel Arsenide and Pyrrothite and its Effects on Flotation. mt. J. Miner. Process., 18: pp Nagaraj, D. R. and Gorken, A., 1989, Potential Controlled Flotation and Depression of Copper Sulphides and Oxides Using Hydrosuiphide in Nonxanthate Systems. Processing of Complex Ores, G. S. Dobby and S.R. Rao, Eds., Pergamon Press, New York, NY, USA, pp

157 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Natarajan, K. A. and Iwasaki, I., 1973, Effect of Poisoning of Platinum Electrodes on Eh Measurements. Trans. Am. Inst. Mm. Engrs., 254: PP Newman, I.C., 1985, The Ok Tedi project. Proc. The Aus.I.M.M., 29, 5: pp Orwe, D., 1993, Sodium Hydrosuiphide Dosage Tests. OTML Inter-Office Memorandum. Dated 31 December Orwe, 1995, Investigations Into The Methods of Improving Size By Size Kinetics Of Two Porphyry Ores At Ok Tedi. In : AMIRA P26B Report, October, : pp.92-i 2. Orwe, D., 1996, Investigations Into The Methods of Improving Size By Size Kinetics Of Two Porphyry Ores At Ok Tedi. In : AMIRA P26B Report, October, : pp Oestreicher, C. A. and McGlashan, D. W., 1972, Surface Oxidation of Chalcocite, AIME Annual Meeting, San Francisco. Paki,. K., 1997, Personal Communication. Pang, J. and Chander, S., 199, Oxidation and Wetting Behaviour of Chalcopyrite in the Absence and Presence of Xanthates, Mm. Met. Process., 7: pp Parks, G. A., 1965, The Iso-electric points of Solid oxides, Solid Hydroxides and Aqueous Hydroxo Complex Systems, Chem. Rev., 65: pp.177-i 98. Patterson, J. G. and Salman, 1., 1968, Interaction of Xanthate with Chalcocite. Can. Mm. Metal., January, pp Plaksin, I., 1959, Interaction of Minerals with Gases and Reagents on Flotation. Trans. Am. Inst. Mm. Engrs, 214, 319. Pratt, A.R., Nesbitt, H.W. and Muir, I.J., 1994, Generation of Acids from Mine Wastes: Oxidative Leaching of Pyrrhotite in Dilute H2S4 Solutions at ph 3.. Geochimica et Cosmochimica Acta, 58: (23), pp Putubu, J. K., 1996, Fine Grinding of Suiphide Skarn Ores. OTML Inter-Office Memorandum. Dated 1 June Ralston, J., 1991, Eh and its Consequences in Suiphide Mineral Flotation. Minerals Engineering, 4: (7-11), p.859. Ralston. J., 1992, The Influence of Particle Size and Contact Angle in Flotation. Chapter 6 in Colloid Chemistry in Mineral Processing (Ed: J. S. Laskowski and J. Ralston) (Elsevier: Amsterdam), pp

158 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Ralston, J., 1994, A Unified Approach to Flotation. Fifth Mill Operators' Conference, Roxby Downs, S.A., The Aus.I.M.M., pp Rank Brothers 1988, Operating Instructions and Manual for the Particle Microelectrophoreses Apparatus Mark II, Bottisham, Cambridge, UK. Reay, D. and Ratcilif, G. A., 1973, Removal of Fine Particles from Water by Dispersed Air Flotation: Effects of Bubble Size and Particle Size on Collection Efficiency. Can. J. Chem. Eng., 51: pp Rey, M., 1957, Flotation of Oxidised Ores of Lead, Copper, and Zinc. Trans. Inst. Mm. Metall., 63: pp , Rey, M., 198, Memoirs of Milling and Process Metallurgy. 2. Flotation of Suiphide Ores. Trans. Inst. Mi Metall. Roberts, M. W., 198, Advances in Catalysis (D. D. Eley, H. Pines and P. B. Weiss, Eds.), Academic Press, NY, 29: pp Rush, P. M. and Seegers, H. J., 199, Ok Tedi Copper-Gold Deposits, in Geology of the Mineral Deposits of Australia and Papua New Guinea. (Ed. F.E. Hughes), The Aus.l.M.M., pp Sato, M., 196, Oxidation of Suiphide Orebodies, Geochemical Environments in terms of Eh and ph: Oxidation Mechanism of Suiphide Minerals at 25 Econ. Geol., 55: pp Schindler, P. W., 1967, Heterogeneous Equilibra involving Oxides, Hydroxides, Carbonates and Hydroxide Carbonates. In: Equilibrium Concepts in Natural Water Systems (Washington, D.C. : American Chem. Soc., pp (Advances in Chemistry Series No. 67) Schulze, H. J., 1977, New Theoretical and Experimental Investigations on Stability of Bubble/Particle Aggregates in Flotation: A Theory on the Upper Particle Size Floatability. mt. J. Miner. Process., 4: pp Schuize, H. J., 1989, Hydrodynamics of Bubble-Mineral Particle Collisions. Miner. Process. Extr. Metall. Rev; 5: pp Seah, M. P. and Dench, W. A., 1979, Quantitative Electron Spectroscopy of Surfaces, A Standard Data base for Electron Inelastic Mean Free Paths in Solids, Surf. lnterf. Anal., 1: pp.2-il. Senior, G. H. and Creed, M. D., 1992, A Laboratory Investigation of the Factors Responsible for Poor Copper Flotation from Ok Tedi Ores. CSIRO Minerals Report, REP 743. Senior, G. D. and Heyes, G. W., 1996, Plant Testing of a New Sulphidisation Strategy at Ok Ted! Mining Limited. CSIRO Minerals Report DM-R

159 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Shaw, D. J., 198, Introduction to Co//old and Surface Chemistry, 3rd Edition, Butterworth and Co. Ltd. Shen, W. Z., 1995, Metal Ion Hydrolysis in the Control of Pyrite and Sphalerite Flotation. In : AMIRA P26B Report, September, : pp Singer, P. C. and Stumm, W., 1969, The Rate Determining Step in the Production of Acidic Mine Waters. American Chemical Society Division of Fuel Chemistry Preprints, 13: (2) pp Smart, R. St.C., 1991, Surface Layers in Base Metal Sulphide Flotation, Mm. Eng., 4: pp Soto, H. and Laskowski, J., 1973, Redox Conditions in the Flotation of Malachite with Sulphidizing Agent. Trans. Inst. Mi Metall. Vol. 81., Sec. C, pp.c1 53-Cl 57. Spiegel, R. M., 1961, Theory and Problems of Statistics, SI (metric) Edition; including Over 87 Fully Solved Problems. McGraw-Hill Book Co. Stapleton, K. E., 1993, Copper Ore Mining at Ok Tedi Mining Limited, Ok Tedi, Papua, New Guinea, in Australasian Mining and Metallurgy, The Sir Maurice Mawby Memorial Volume, Second Edition., The Aus. l.m.m., pp Stumm, W. and Morgan, J. New York) p , Aquatic Chemistry (Wiley-lnterscience: Sutherland, K. L, 1948, Physical Chemistry of Flotation. XI. Kinetics of the Flotation Process, J. Phys. Chem., 52: pp Sutherland, K. L. and Wark, I. W., 1955, Principles of Flotation. The Aus. I.M.M., Melbourne, Vic., p.15. Trahar, W. J., 1983, A Laboratory Study of the lnfuence of Sodium Sulphide and Oxygen on Collectorless Flotation of Chalcopyrite. lnt. J. Miner. Process., 11: pp Trahar, W. J. and Warren, L. J., 1976, The Floatability of Very Fine Particles-a review. Int. J. Miner. Process., 3: pp Ueno,Y., Williams, A. and Murray, F., 1979, A New Method for Sodium Suiphide Removal from an Aqueous Solution and Application to Industrial Waste Water and Sludge. Water, Air and Soil Pollution, 2: pp Wagner, C. D., Riggs, W. M., Davis, L. E., Moulder, J. F. and (ed.) Muilinberg, G. E., 1979, Handbook of X-ray Photoelectron Spectroscopy, Perkin Elmer Corporation, Eden Praire. 14

160 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Walker, G. W., Stout, J. V. and Richardson, P. E., 1984, Electrochemical Flotation of Suiphides: Reaction of Chalcopyrite in Aqueous Solution. mt. J. Miner. Process. 12: pp Warman International Ltd., 1981, Cyclosizer Instruction Manual. Particle Size Analysis in the sub-sieve range. 2nd Revision Warman International Limited, Sydney. Wawako, T., 1995, NaHS Testwork on Rougher Flotation Feed. OTML Inter- Office Memorandum dated 13 January, Wills, B. A., 1992, Mineral Processing Technology; An Introduction to the Practical Aspects of Ore Treatment and Mineral Recovery (In SI/Metric Units), Fifth Ed, Pergamon Press. Great Britain. Woodcock, J. T. and Jones, M. M., 197, Chemical Environment in Australian Lead-Zinc Flotation Plant Pulps: I. ph, Redox Potentials and Oxygen Concentrations. Aus. I.M.M. Proceed., 235: pp Woods, R., 1976, Electrochemistry of Suiphide Flotation. In: Gaudin Mem. Vol., AIME, New York, N.Y., 1: pp Flotation. A.M Woods, R., 1988, Flotation of Sulphide Minerals. Reagents in Mineral Technology. P Somasundaran and B. M. Moudgil, Eds., Marcel Dekker, Inc., New York, NY, USA. 2: pp Zachwieja, J. B., Walker, G. W. and Richardson, P. E., 1987, Electrochemical Flotation of Sulphides: The Born ite-ethylxa nthate System. Miner. Metal. Process., pp Zachwieja, J. B., McCarron, J.J., Walker,. W. and Buckley, A. N., 1989, Correlation Between the Surface Composition and Collectorless Flotation of Chalcopyrite, J. Coil. lnterf. Sci., 2: pp , 141

161 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Todi, PNG APPENDICES 142

162 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG APPENDIX #1 CHARACTERISTICS OF A TYPICAL CONCENTRATOR FEED BLEND 143

163 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedl, PNG UNIT #2 FLOTATION SURVEY DATA OF 14 FEBRUARY BULK ASSAYS AND TONNAGES Assays Stream TPH IF Cu [ % New Feed Scavenger (Final) Tailing RougherConcentrate Cleaner Feed Cleaner Concentrate Cleaner Tailing Recleaner Concentrate RecleanerTailing Column (Final) Concentrate ColumnTailing Stream TPH 1] New Feed Scavenger (Final) Tailing Rougher Concentrate Cleaner Feed Cleaner Concentrate Cleaner Tailing Recleaner Concentrate RecleanerTailing Column (Final) Concentrate Column Tailing Distribution ] Cu (%) Au (g/t) Au (g/t) ASCu (%) ASCu j Fe (%) Fe (%) j[ (%) S (%) S (%) CheckTail+Con=Feed *Typical mill throughput is 8 kilotonnes per day 144

164 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 1.2 MINERALOGICAL ANALYSIS BY QEM*SEM Species Chalcocite/Diginite Covellite Bornite/Fe-Digenite Chalcopyrite Cu Metal Cuprite CuFe Metal/Ox.8.3 Malachite CuFeOx/C Chrysocolla.1.1 Turquoise Other Cu Minerals Fe-Ox/C Flowrate Chalcocite/Diginite Covellite Bornite/Fe-Digenite Chalcopyrite Cu Metal Cuprite CuFe Metal/Ox Malachite CuFe OxjCO Chrysocolla Turquoise Other Cu Minerals Fe-Ox/C Scaled Combined Size % Fractions Chalcocite/Diginlte Covelllte Born ite/fe-digenite Chalcopyrlte Cu Metal.63.5 Cuprlte.8.7 CuFe Metal/Ox Malachite CuFe Ox/C Chrysocolla.2.1 Turquoise.. Other Cu Minerals Fe-Ox/C

165 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Size (pm) Wt (g) Wt (%) 1.3 SIZiNGS New Feed Assay (% Cu) Distribution (%) Mass Flow (tph) Cu Flow (tph) Total Final Tail Size Wt Wt Assay Distribution Mass Cu Flow Flow (pm) (g) (%) (% Cu) (%) (tph) (tph) Total _If Rougher Concentrate Size (pm) Total Wt (g) Wt (%) Assay (% Cu) Distribution (%) Mass Flow (tph) Cu Flow (tph) _

166 The Influence of Sodium Hydrogen on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG (ELm) Wt (g) Wt (%) Cleaner Feed Assay Distribution I (% Cu)] (%) Mass Flow (tph) Cu Flow (tph) Total Cleaner Concentrate Size Wt Wt Assay Distribution Mass Cu Flow Flow (g) (%) (% Cu) (%) (tph) (tph) Total CleanerTail Size Wt Wt Assay Distribution Mass Cu Flow Flow (g) (%) (% Cu) (%) (tph) (tph) Total

167 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Size Wt (g) Recleaner Concentrate Wt (%) Assay (% Cu) Distribution (%) Mass Flow (tph) Cu Flow (tph) Total ]j Recleaner Tail Size Wt Wt Assay ([ Distribution Mass Cu Flow Flow (sm) (g) (%) (% Cu) (%) (tph) (tph) Total Column Concentrate Size (sm) Total Wt (g) Wt (%) _- Assay (% Cu) Distribution (%) Mass Flow (tph) Cu Flow (tph)

168 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Size (llm) Wt (g) Wt (%) Column Tail Assay (% Cu) Distribution (%) Mass Flow (tph) j Cu Flow [jtph) Total

169 The Influence of Sodium Hydrogen on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 1.4 POINT COUNT DATA New Feed Mineral Mass%I! Adj Ternary Ternary Totals Mass% % Lib Cp Dg Rn Py NSG FeO Sulphide SuI+G Cp Dg Rn Py NSG ,4 1 FeO i&m Mineral % Lib Cp Dg Bn Py NSG Ternary FeO j[sulptiide Ternary SuI+G Totals Cp ( Dg, Rn Py NSG FeO C2 Mineral Mass% Adj Ternary Ter Totals Mass% % Lib Cp Og Rn Py NSG FeO Suiphide SuI+G Cp Dg,57, Bn, Py ,2 1 1 NSG FeO 1 -C2+C5 Mineral Mass% Adj Ternary Ternary Totals -. Cp 8.79 Mass% 2.62 % Lib 98.5 Cp Dg 1.3 Bn Py NSG.2 FeO jisulphldel[ SuI+G 1 Dg Rn Py NSG , FeO

170 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Rougher Concentrate +212gm Mineral Mass% Adj Ternary Ternary Totals Mass% % Libji Cp FeO Suiphide Sul+G Cp Dg Bn Py NSG FeO.47, i&m Mineral JJ Mass% Adj Mass% Cp JJ % Lib] I Cp Dg 3.36 Bn Py NSG.53 FeO.9 IL Ternary Sulphide.7 Ternary Sul-e-G.1 Totals 1 Dg , Bn Py , , NSG FeO C2 Mineral Mass% Adj Ternary Ternary Totals Cp 71. Mass% 23.5 % Lib Cp Dg 4.32 Bn.8 Py NSG FeO j Sulphide j Sul+G.8 1 Dg Bn Py NSG , FeC,. 1 -C2+C5 Mineral Mass% Adj if Ternary Ternary Totals Cp IL Mass% 24.6 % Lib Cp Dg Bn Py NSG FeO Suiphide Sul+G Og Bn 3, Py NSG ,76 1 FeC 1 151

171 . The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Final Concentrate +212pm Mineral Mass% Adj Ternary Ternary Totals Mass% % Lib Cp Dg Bn Py NSG FeO Suiphide Sul-'43 Cp Dg Bn Py NSG FeO Mineral Mass% Adj Mass% Cp If % Lib Cp 9646 Dg 2.45 Rn.2 j Py j NSG.76 FeO J Ternary Suiphide [ Ternary Sul+G.13 Totals 1 Dg Bn Py NSG FeO , Ill ii: -16+C2. =11 Mineral Mass% Adj Mass% Cp % Lib jf I[ Cp jf Dg Bn Py NSG FeO Ternary Sul G I[ Totals Dg Rn Py NSG FeO 1 Mineral Mass% Adj Ternary Ternary Mass% % Lib Cp Og Bn Py NSG FeC Suiphide Sul G [ Cp Dg Bn Py NSG FeO 1 152

172 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Final Tailing Mineral Mass% Adj Ternary Ternary Totals Cp IL Mass%.67 % Lib jj 2.7 Cp Dg Bn Py NSG FeO Suiphide IL Dg Bn Py NSG FeO III lO6iim Mineral Cp J Mass%.11 Adj Mass% % Lib Cp j Dg Rn Py [ [ j NSG 1 FeO Ternary Suiphide Ternary Totals 1 Dg, Rn. Py NSG FeO ii ii C2 Mineral Cp J Mass%.21 Adj Mass%.1 IL Lib 9.91 Cp 9.9 FeO [ if Ternary Suiphide Ternary Sul'G if [ Totals 1 Dg Bn. Py NSG FeO III -C2 +C5 Mineral Mass% Adj Mass% % Lib Cp Dg Rn Py NSG FeO Ternary Sulphide Ternary Totals SuliG j Cp Og Rn. Py NSG FeC II 153

173 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG C'eaner Feed Mass%II Adj flernary Ternary Totals Mass% % Lib Cp Dg FeO Suiphide Sul+G Cp Dg Bn Py NSG FeO Mineral Mass%1J Adj Ternary Ternary Totals % Lib Cp Dg Bn Py NSG FeO Suiphide Sul+G Cp Dg Bn Py NSG FeO C2 Mineral Mass% Adj % Lib Ternary Ternary Totals Mass% Cp Dg Bn Py NSG FeO Suiphide Sul+G Cp Dg Bn , Py NSG ,19 1 FeO C2+C5 Minerall Mass% Cp Adj Mass% 26.5 % Lib 98.1 Cp ][ Dg 1.3 Bn Py NSG FeC Ternary Ternary Q Sulphide If Sul+G Totals 1 Dg , Bn Py NSG FeO II 154

174 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Cleaner Concentrate +2l2itm Mineral Mass% Adj fi Ternary Ternary Totals Mass% % Lib Cp Dg Bn ] NSG FeO Sulphide SuI+G Cp Dg Bn Py NSG FeO gm Mineral Mass% Adj Ternary Ternary t1totals Mass% % Lib Cp Dg Bn Py NSG FeO Sulphide Sul-'-G Cp Dg , Bn Py ii iii ii iii_ii iii NSG FeO -16+C2 Mineral Mass% Adj Mass% % Lib Cp Dg Bn Py NSG FeO Ternary Sulphide Ternary SuIi-G Totals Cp Dg Bn Py NSG ii FeO iii iii II II II II (I C2+C5 (I II II II Mineral Mass% Adj Ternary Ternary Totals Mass% II %Lib II Cp Dg Bn Py NSG FeO ]1 Cp Dg Bn Py ii NSG iii FeO ii Ii liii 155

175 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Cleaner Tail +21 Mineral Mass% ({ Adj Mass% Cp % Lib Cp J{ Og j[ Bn Py NSG IL FeO Ternary Suiphide Ternary SuI+G jj Totals Dg Rn Py NSG FeO iii ii ii ' Mineral Mass%j Adj Mass% % Lib Cp Dg Bn Py NSG FeO Ternary Jf Ternary Sulphide Sul+G Totals Cp Dg Bn Py NSG T FeO T -16+C2 Mineral Mass% Adj Mass% Cp % Lib 94.9 Cp j Ternary Ternary Totals Dg Rn Py NSG FeO j Sulphideji SuI+G ,7 1 Dg Bn Py NSG FeO C2+C5 Mineral Mass% Adj Ternary Ternary Totals [Mass% % Lib Cp Dg Bn Py NSG FeO Suiphide Sul+G Cp Dg Bn Py NSG FeO , 1 156

176 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Recleaner Concentrate Mineral Mass% Adj [Mass% Cp % Lib Cp Dg Bn Py NSG FeO Ternary j[ Ternary Suiphide Sul+G IL Totals Dg Bn Py NSG FeO iii ii_iii Mineral Ternary Ternary Totals Mass% % Lib Cp Dg Bn Py NSG FeO Sulphideji SuI+G Cp Dg Bn Pt,, NSG FeO == -1 6+C2 Mineral Mass% Adj Ternary Ternary Totals Mass% % Lib Cp Dg Bn Py NSG FeO Sulphide Sul G Cp Og Bn Py NSG FeO lii ii iii -C2+C5 Mineral Cp Mass% Adj Q [Mass% % Lib Cp Dg 3.74 [ Bn NSG FeO If Ternary [Sulptlide Ternary Sul G Totals 1 Dg Bn Py NSG FeO 157

177 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 1.49 Recleaner Tail +212l1m Mineral Mass% Adj Binaiy Ternary Ternary Totals Mass% % Lib Cp Dg Bn Py NSG FeO Suiphide Sul-'-G Cp Dg Bn Py NSG FeO iii ii iii iii liii O6iim Mineral Mass% Adj Mass% % Lib Cp Dg Rn Py NSG FeO Ternary If Ternary Suiphide Sul+G Totals Cp Dg Bn Py ii NSG FeO iii if ii_iii iii -1 6+C2 Mineral Mass% Adj Ternary Ternary Totals Mass% % Lib Cp Dg Bn Py NSG FeO Suiphide SuI G Cp Dg Bn Py NSG FeO.31!L C2+C5 Mineral Mass% Adj Ternary Ternary Totals Mass% % Lib Cp Dg Bn Py NSG FeO Sulphide Su1'G Cp Dg Bn Py NSG FeO

178 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Column Tail Mineral Mass% Adj jj Mass% Cp % Lib Cp Dg Bn jj Py ] NSG JJ FeO Ternary Sulphide Ternary Sul+G Totals Dg Bn Py NSG FeO -212 Mineral Mass%O Adj Ternary Mass% % Lib Cp Dg Bn Py NSG FeO Sulphide Dg Bn Py NSG FeO iii iii 1 Ternary Sul G Totals b C2 Mineral Mass% Adl Ternary Ternary Totals Mass% % Lib Cp Dg Bn Py NSG FeO Sulphidejl Sul+G Cp Dg Bn Py NSG FeO C2+C5 Mineral Mass% Adj Mass% % Lib Cp Dg Bn Py NSG FeO Ternary 1] SulphideJl Ternary Sul+G Totals Cp Dg Bn Py 8.86 NSG 4.42 FeO.21 iii iii , iii

179 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 1.5 ROUGHER-SCAVENGER MINERAL RECOVERY Rougher Concentrate TPH TPH TPH TPH TPH TPH TPH TPH TPH TPH Mineral TPH Ternary Ternary Totals Lib Cp Dg Bn Py NSG FeO Suiphide Sul+G Cp Dg Bn 1. 1., Py NSG , FeO Final Tail Mineral TPH TPH TPH TPH TPH J) TPH TPH TPH Ternary TPH Ternary TPH Totals TPH Lib Cp Dg Bn Py NSG FeO Suiphide SuI+G Cp , 1. 1TT Dg 1.5.1, Bn Py ,, NSG , FeO Total l{ HER MINERA L RECOVERY Ternary Ternary Mineral Mass% Lib Cp Dg Bn Py NSG FeO Suiphide SuI+G Cp Dg Bn Py NSG FeO

180 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 1.7 TOTALPLANTMINERALRECOVERY Mineral TPH TPH TPH TPH TPH TPH TPH TPH TPH TPH TPH Ternary Ternary Totals Lib Cp Dg Bn Py NSG FeO Sulphide Sul+G Cp , Dg Bn Py NSG FeO, Recalculated Feed Mineral Mass% TPH j TPH TPH TPH TPH TPH TPH TPH Ternary TPH Totals Lib Cp Dg Bn Py NSG FeO Cp Dg Bn Py NSG FeO E Recovery Mineral Mass% Ternary Ternary Lib Cp Dg Bn Py NSG FeO Sulphide Sul G Cp öt 1.. Dg Bn Py NSG FeO

181 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG APPENDIX #2 CHARACTERISATION OF PORPHYRY ORE SAMPLES 162

182 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 2.1 MINERALS AND MINERAL GROUPINGS (Abstracted from The Aus. l.m.m. Field Geologist Manual, 1989, Monograph 9) quartz-rich granitoids Q quartzolite alkali feldspar granite Tonalite granodiorite alkali feldspar syenite Monzonite P foid gabrc Foid monzodiorite F Legend quartz A alkali feldspars (orthoclase, microline, perthite, anorthoclase, albite) P plagioclase, scapolite. F feldsparthoids or folds (leucite and pseudosite; nepheline, sodalite, nosean, hauynite, cancrinite, analcime etc..) 163

183 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 2.2 CHEMICAL ASSAYS OF PORPHYRY SAMPLES Assay Monzonite 'A' Monzodiorite 'A' Monzonite 'B' Monzodiorite 'B' Total Cu, % Acid soluble Cu, % Amm. acetate soluble Cu, % Silver nitrate soluble Cu, % Hydrofluoric soluble Cu, % Au, ppm Fe,% S, % Si2, ppm A Some similarities in the feed characteristics of monzonite and monzodiorite samples with the former having higher copper content than the latter. Note that chalcocite in both monzonite samples are very similar as determined by silver nitrate soluble copper assays. Acid soluble Cu minerals are dissolved by 4% H2S4 These are malachite, azurite, tenorite, chrysicolia, turquise and 5% of cuprite. Ammonium acetate soluble copper minerals are malachite, azurite and cuprite. Silver nitrate soluble copper minerals are chalcocite and native copper. Hydrofluoric acid dissolves acid soluble copper minerals and goethite copper. 164

184 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 2.3 STANDARD FLOTATION OF MONZONITE 'A' ph 6 Size (ILm) Feed Tailing Cu Rec Wt(g) Wt(%) %Cu Wt(g) Wt(%) %Cu Wt(g) Wt(%) %Cu Total ph 9 (%) Size (lim) Feed Wt(g) Wt(%) %Cu Tailing Wt(g) Wt(%) %Cu Wt(%) %Cu Cu Rec Total ph 11.5 (%) Size J{ (urn) l[ Feed Wt(g) Wt(%) %Cu Concentrate Wt(%) Tailing Wt(g) Wt(%) %Cu Cu Rec (%) , Total I[

185 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 2.4 STANDARD FLOTATION OF MONZODIORITE 'A' ph 6 Size Feed Tailing Cu Rec Wt(g) Wt(%) %Cu Wt(g) Wt(%) %Cu Wt(g) I{ Wt(%) %Cu ] , Total (%) 5.84 ph 9 Size (pm) Feed Concentrate Tailing Cu Rec Wt(g) l[ Wt(%) %Cu Wt(g) Wt(%) %Cu Wt(%) %Cu (%) Total ][ 147.M ph 11.5 Size (pm) Feed Concentrate Tailing Cu Rec %Cu Wt(g) Wt(%) Wt(g) Wt(%) , , Total

186 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 2.5 STANDARD FLOTATION OF MONZONITE 'B' ph 11.5 Size (pm) Feed Tailing Cu Rec Wt (g) WI (%) % Cu j Wt (g) Wt (%) % Cu (%) , , Total STANDARD FLOTATION OF MONZODIORITE 'B' ph 11.5 Size (I.Lm) Feed Tailing Cu Rec Wt (g) WI (%) % Cu WI (g) WI (%) % Cu (%) Total Jj

187 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 2.7 LIME ADDITION TO MILL - MONZODIORITE 'A' Monzodiorite ph 9, +24 mv (En) Product Weight, g % Cu % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative Rougher con Rougher con Rougher con Rougher con Rougher tail Rougher feed Monzodiorite ph 1.6, -36 mv Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Rougher con Roughercon Roughercon Rougher tail Ro feed Product Weight, g Monzodiorlte ph 11.5, -72 mv (Er.) I I % Cu % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative Rougher con Roughercon Roughercon Roughercon Rougher tail Rougherfeed

188 2.8 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG LIME ADDITION TO MILL MONZONITE 'A' Monzonite ph 9, -34 mv (E1,,) Product Weight, g % Cu % Cu Cumulative Rougher con Rougher con Roughercon Roughercon Rougher tail Rougher feed Cu Recovery % j Cu Recovery % Cumulative Monzonite ph 1.5, -36 mv Product Weight, g % Cu % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative ii Rougher con Roughercon Roughercon Rougher con Rougher tail Rougher feed Monzonite ph 11.5, -48 mv (Er.) Product Weight, g % Cu % Cu Cu Recovery Cu Recovery CumulatIve II % % Cumulative Rougher con 1 Rougher con 2 Rougher con 3 Rougher con 4 Rougher tail Rougherfeed

189 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG APPENDIX #3 SULPHIDISATION 17

190 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 3.1 CONTROLLED THROUGHOUT Monzodiorite ph 5, +155 mv (EpJ - Standard Product Weight, g % Cu % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative Rougher con Roughercon Rougher con Roughercon Rougher tail Rougher feed Monzodiorite ph 5, mv -49 g/t NaHS Product Weight, g % Cu % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative Rougher con Rougher con Roughercon Roughercon Rougher tail Rougher feed Monzodiorite ph 5, -2 mv (Er.) - 28 g/t NaHS Product ] Weight, g % Cu % Cu Cu Recovery Cu Recovery jj Cumulative % % Cumulative Rougher con Roughercon Rougher con Rougher con Rougher tail Rougher feed Monzodiorlte ph 5, -3 mv (Er.) - 44 g/t NaHS Product Weight, g % Cu % Cu [ Cu Recovery Cumulative % Cu Recovery % Cumulative Rougher con Roughercon Roughercon Roughercon Rougher tail Rougherfeed

191 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Monzodiorlte ph 9, +78 mv - Standard Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Roughercon Roughercon Roughercon Rougher tail Rougher feed Monzodiorite ph 9, mv (Er.) - 16 gil NaHS.1 I Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougherconl Rougher con Roughercon Roughercon Rougher tail Rougher feed Monzodiorite ph 9, -2 mv (E,,.) - 23 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % CumulatIve Rougher con Rougher con Roughercon Rougher con Rougher tail Rougher feed Monzodiorite ph 9, -3 mv (EpJ - 53 gil NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Jf Cumulative [ % % Cumulative Rougher con Roughercon Roughercon Rougher con Rougher tail Rougherfeed

192 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Monzodiorite ph 11.5, -74 mv - Product Weight, g % Cu % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative Rougher con Roughercon Roughercon Roughercon Rougher tail Rougher feed Monzodiorite ph 11.5, -2 mv (Er.) - 6 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery % Cu Recovery % Cumulative Rougher con Roughercon Rougher con Rougher con Roughertail Rougher feed J.24 Monzodiorite ph 11.5, -4 mv (EF,.) g/t NaHS Product Weight, g % Cu % Cu Cumulative Rougher con 1 Rougher con 2 Rougher con 3 Rougher con 4 Rougher tail Rougher feed Cu Recovery % Cu Recovery % Cumulative

193 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 3.2 SULPHIDISATION 'NOT' CONTROLLED THROUGHOUT 3.21 Monzodiorite 'B' Monzodiorite ph 5, +2 mv (Er.) - 9 g/t NaHS Product Weight, g % Cu % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative Rougher con Rougher con Rougher con Rougher con Rougher tail Rougher feed Monzodiorite ph 5, mv - 3 g/t NaHS Product Weight, g If % Cu L % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative Rougher con Roughercon Rougher con Rougher con Roughertail Rougher feed If.29 Monzodiorite ph 5, -2 mv (Er.) g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Jr Cu Recovery Cumulative % IL % Cumulative Rougher con Roughercon Rougher con Roughercon Rougher tail Rougher feed If.23 Monzodiorite ph 5, -3 mv g/t NaHS Product Weight, g If % Cu % Cu If Cu Recovery Cu Recovery.1 I IL j Cumulative % % Cumulative Rougherconi Roughercon Roughercon Rougher con Rougher tail Rougher feed

194 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Monzodiorite ph 9, mv - 9 g/t NaHS Product Weight, g % Cu % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative I.1 Rougher con Roughercon Roughercon Roughercon Rougher tail Rougher feed Monzodiorite ph 9, -2 my - 35 g/t NaHS Product Weight, g % Cu % Cu Cumulative Cu Recovery % Cu Recovery % Cumulative j Rougher con Roughercon Roughercon Roughercon Rougher tail Rougherfeed }J Monzodiorite ph 9, -3 mv (E,,.) - 14 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougherconl Rougher con Roughercon Rougher con Rougher tail Rougher feed Monzodiorite ph 11.5, -2 mv (Er.) - 19 g/t NaHS Product [ Weight, g % Cu % Cu Cu Recovery Cu Recovery L ]I Cumulative j % % Cumulative Rougher con Roughercon Rougher con Rougher con Rougher tail Rougher feed

195 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Monzodiorite ph 11.5, -3 mv (Er,) - 65 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery i I ii Cumulative % % Cumulative Rougherconi Rougher con Roughercon Roughercon Rougher tail Rougher feed JJ Monzonite 'B' Monzonite ph 5, +186 mv (Er.) - Standard Product Weight, g % Cu % Cu Cu Recovery Cu Recovery.1 I Cumulative % % Cumulative Roughercon Roughercon Roughercon Roughercon Roughertail Rougher feed Monzonite ph 5, mv (Er.) g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery.1 I Cumulative % % Cumulative Rougher con Roughercon Rougher con Roughercon Roughertail Rougherfeed ]J Monzonlte ph 5, -2 mv (Er,.) - 26 glt NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative II. Rougher con Roughercon Rougher con Roughercon Rougher tail Rougher feed

196 - The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Monzonite ph 5, -3 mv g/t NaHS Product Weight, g % Cu % Cu f[ Cu Recovery Cu Recovery j Cumulative [ % % Cumulative Rougher con Rougher con Rougher con Roughercon Rougher tail Rougher feed Monzonite ph 9, +16 mv (Em) - Standard Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative ] % % Cumulative Rougher con Roughercon Roughercon Rougher con Roughertail Rougherfeed Monzonite ph 9, mv -54 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery I Cumulative % IL % Cumulative Rougherconi Rougher con Roughercon Roughercon Rougher tail Rougherfeed Monzonite ph 9, -2 mv (Er.) g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Roughercon Rougher con Roughercon Rougher tail Rougherfeed

197 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Monzonite ph 9, -3 mv (Er.) - 26 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cumulative % Cu Recovery % Cumulative Rougher con Roughercon Roughercon Roughercon Rougher tail Rougherfeed Monzonite ph 11.5, +84 mv - Standard Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Roughercon Roughercon Roughercon Rougher tail Rougherfeed Monzonite ph 11.5, mv (Er,) - 28 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery ({ Cu Recovery Cumulative % % Cumulative Rougher con Roughercon Roughercon Roughercon Rougher tail Rougherfeed Monzonite ph 11.5, -2 mv g/t NaHS Product Weight, g % Cu % Cu Cu Recovery J{ Cu Recovery Cumulative % IL % Cumulative Rougher con Roughercon Roughercon Roughercon4 Rougher tail Rougherfeed J

198 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Monzonite ph 11.5, -3 mv g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Rougher con Roughercon Rougher con Roughertail Rougherfeed ] 3.3 SULPHIDISATION - NaHS ADDITION TO MILL Monzodiorite ph 7, +127 mv - 23 g/t NaHS Product Weight, g ]j % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative I Rougher con Rougher con Roughercon Roughercon Rougher tail Rougher feed Monzodiorite ph 7, +16 mv (Er.) - 47 g/t NaHS Product WeIght, g % Cu % Cu Cumulative Cu Recovery % Q Cu Recovery Cumulative Rougher con [ Rougher con Rougher con Roughercon Rougher tail Rougher feed Monzodiorite ph 7, -74 mv - 14 g/t NaHS Product Weight, g r % Cu I I % Cu Cumulative Cu Recovery JJ % j Cu Recovery % Cumulative Rougherconi Rougher con Roughercon Roughercon4 Rougher tail Rougher feed

199 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedl, PNG Monzodiorite ph 7, -77 mv g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery ii Cumulative % j % Cumulative Rougher con Roughercon Roughercon Rougher con Rougher tail Rougherfeed ]J Monzodiorite ph 9, +164 mv - 7 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative Rougher con Roughercon Rougher con Roughercon Rougher tail Rougher feed JJ Monzodiorite ph 9, +14 mv (Er.) - 47 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery.1I Cumulative % % Cumulative Rougherconi Rougher con Roughercon Rougher con Rougher tail Rougher feed Monzodiorite ph 9, +45 mv (Er,.) - 14 g/t NaNS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery II. Cumulative % % Cumulative Rougher con Roughercon Rougher con Rougher con Rougher tail Rougher feed Monzodiorite ph 9, +38 mv 233 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Rougher con Roughercon Roughercon4 Roughertail Rougherfeed

200 - The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Monzodiorite ph 11.5, +2 mv - 23 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Roughercon Roughercon Rougher con Rougher tail Rougherfeed Monzodiorite ph 11.5, +21 mv - 47 glt NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Roughercon Roughercon Roughercon Rougher tail Rougher feed Monzodiorite ph 11.5, +9 mv (Er.) - 14 g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Roughercon Rougher con Roughercon Rougher tail Rougher feed J Monzodiorite ph 11.5, +19 mv (Er) g/t NaHS Product Weight, g % Cu % Cu Cu Recovery Cu Recovery Cumulative % % Cumulative Rougher con Roughercon Rougher con Rougher con4 Rougher tail

201 2.44 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Suiphidisation - Monzonite 'A' Sample at ph 11.5 Size by Size Copper Recovery Size Feed Concentrate Tailing_ CuRec (pm) Wt (g) ]1 Wt (%) % Cu Wt (g) Wt (%) % Cu Wt (g) Wt (%) % Cu ] (%) Total 645. ]J_1. L_ [ioo.oo Suiphidisation - Monzodiorite 'A' Sample at ph 11.5 Size by Size Copper Recovery Size (pm) Feed Concentrate jj Tailing Cu Rec Wt(g) Wt(%) %Cu Wt(g) Wt(%) %Cu Wt(g) J[ Wt(%) %Cu (% Total 645. JJ Suiphidisation - Monzonite 'B' Sample at ph 11.5 Size by Size Copper Recovery Size Feed Cu Rec (pm) Wt (g) Wt (%) I[_% Cu Wt (g) Wt (%) % Cu (%) Total

202 The Influence of Sodium Hydrogen on Porphyry Sulphide Copper Recovery at Ok Tedi, PUG Sulphidisation - Monzodiorite 'B' Sample at ph 11.5 Size by Size Copper Recovery Size (urn) Feed Tailing Cu Rec Wt (g) Wt (%) % Cu Wt (g) Wt (%) % Cu , (%) Total }{

203 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG APPENDIX #4 PLANT TRIALS AND SURVEYS 184

204 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 4.1 PLANT NaHS TRIAL #3-28 JUNE TO 6 JULY 1996 (Abstracted from Lauder and Orwe, 1996) Copper Data NaHS On (% Cu) NaHS Off (% Cu) IRF IFC IRRT Rec 2RF 2FC 2R1 Rec IRF 1FC IRT Rec 2RF 2FC 2RT Rec ( , , , , , , , , , , , , ,877 34, , , , , ,641 4, , , ,787 34, , , , , , , , ,655 37, , ,44, ,718 36, , , , , , , , , ,617 36,

205 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Copper Data -Trial #3 (Continued) NaHS On (% Cu) NaHS Off (% Cu) IRF IFC 1RRT Ret 2RF 2FC 2RT Ret IRF 1FC 1RT Rec 2RF 2FC 2RT Ret , , , , , , , , , ,71, ,86 38, , , , , , , , , , , , , , , , , , , , , , Mean Italic type (bold) Standard deviation Regular type (bold) Where RF, FC and RT are Rougher feed, Final Concentrate and Rougher Tail respectively. 186

206 The Influence of Sodium Hydrogen Suiphlde on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 4.2 PLANT NaHS TRIAL #4 AT REDUCED ph - AUGUST, PLANT TRiAL ph 11.- Copper Data NaHS ON - ph 11.5(Regular type), ph 11. (Italic type) NaHS OFF ph 11.5 Date 1RFCu 1RTCu icurec 2RFCu 2CuRecI 1RFCu 1RTCu 1CuRec2RFCu 2RTCu 2CuRec l2aug , Aug l4aug AVERAGE COPPER RESULTS - PLANT TRIAL #4A Average, % ph 11. (Italic type) ph 11.5 (Unit #1) NaHSOn NaHS Off Feed, Cu Tail, Cu Recovery 84.6 II Copper recovery increase due to ph 11.5 = = 4.6% Effect of reduced ph with NaHS (ph 11.5 to 11.) = = 1.% 187

207 NaHS The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG PLANT TRIAL ph 11.- Gold Data NaHS ON ph 11.5(Regular type), ph 11. (Italic type) NaHS ph 11.5 Date 1RFAu 1RTAu laurec 2RFAu 2RTAu 2AuRec IRFAu 1RTAu laurec 2RFAu 2RTAu 2AuRec 12 Aug l3aug t Aug AVERAGE Gold RESULTS - PLANT TRIAL #4A Average l[ I ph 11. (Italic type) ph 11.5 (Unit #1) NaHS On Off Feed, Au (g/t) Tail, Au (g/t) Recovery (%) I{ Copper recovery increase due to ph 11.5 = = 4.2% Effect of reduced ph with NaHS (ph 11.5 to 11.) = =.4% 188

208 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG PLANT TRIAL Copper Data NaHS ON ph 11.5 (Regular type), ph 1.5 (Italic Type) NaHS ph 11.5 Date IRFCu 1RTCu ICuRec 2RFCu 2RTCu 2CuRec 1RFCu IRTCu 1CuRec2RFCu 2RTCu 2CuRec 19 Aug Aug Aug.598, , , , Aug , Aug , , , Sep ,

209 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Plant Trial #4B - Copper Data (continued) NaHS p (Regular type), ph 1.5 (Italic type) NaHS ph 11.5 Date IRFCu 1RTCu icurec 2RFCu 2RTCu 2CuRec 1RFCu 1RTCu 1CuRec2RFCu 2RTCu 2CuRec 11 Sep Sep Sep Mean StdDev

210 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG PLANT TRIAL #4B ph 1.5- Gold Data NaHS ON ph 11.5(Regular type), ph 1.5 (Italic type) NaHS OFF ph 11.5 Date 1RFAu 1RTAu laurec 2RFAu 2RTAu 2AuRec 1RFAu 1RTAu laurec 2RFAu 2RTAu 2AuRec 19 Aug Aug Aug Aug Aug Sep ,

211 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Plant Trial #4B - Gold Data (continued) NailS (ph 11.5 (Regular type), ph 1.5 (Italic type) NaHS OFF ph 11.5 Date 1RFAu 1RTAu laurec 2RFAu 2RTAu ZAuRec IRFAu IRTAu laurec 2RFAu 2RTAu 2AuRec 13 Sep Sep Mean StdDev

212 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG 4.3 FLOTATION SURVEY DATA -22 AUGUST, 1996 NaHS ON-OFF SURVEYS UNIT #2 FLOTATION SURVEY PULP CHEMICAL DATA Measurement Point ph Eh (mv) ORP Ball Mill Cyclone /F 1 Ball Mill Cyclone /F 2 Distribution Box Rougher Cell 1 Rougher Cell 3 RougherCell5 RougherCell7 Rougher Cell 9 Scavenger Cell 2 Scavenger Cell 4 ScavengerCell6 Distribution Box Rougher Cell 1 Rougher Cell 3 Rougher Cell5 Rougher Cell 7 Rougher Cell 9 Scavenger Cell 2 Scavenger Cell 4 Scavenger Cell NaH SOn NaH SOft Dissolved Temperature C

213 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG BULK ASSAYS AND TONNAGES NaHS Off Stream Weight Cu Assay % L Iph % actual adj Cu Rec % AS Cu % Act M ASCu Rec % Au Assay g,t NewRoufeed Combfeed Cell 3 tail , Con Cell 9 tail Con Scav tail Scavcon ,53 3,15 Cleanertail Final con NaHS On Act Adj Rec % Stream Weight Cu Assay % Cu Rec tph % actual adj % AS Cu % Act ASCu Rec % Au Assay g,t New Rou feed Combfeed Cell3tail Con Cell 9 tail Con Scav tail Scav con Cleanertail Final con Act Adj Au Rec % SIZE BY SIZE COPPER RECOVERY NaHS Off Size Feed (1 tph) Tail ( tph) Mass % Cu Mass Mass % % Cu Mass Recovery Total , %

214 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG NaHS On Size urn Feed (1 tph) Tail ( Iph) Mass % % Cu Mass Mass % % Cu J[ Mass , Recovery Total %

215 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG 4.4 STATISTICAL ANALYSIS OF PLANT TRIALDATA Compare NaHS on versus NaHS off taking the 'natural' difference into consideration using Trial #3 Copper Results (Method 1) When NaHS is used in Unit #2, the difference in Cu recovery (Unit #2-Unit #1) =(81.5% %) = 2.8%, thus when NaHS is not used in either Line, the difference in Cu recovery (Unit #2-Unit #1) = 8.6% % = -.6% The effect of NaHS is thus 3.4 % increase in copper recovery Test involving difference of means using Unit #1, (NaHS oft) and Unit #2 (NaHS on) using Plant Trial #3 Results. (Method 2) To test if there is a significant difference in copper recovery when NaHS is used, then it has to be decided between the following hypotheses at.5 and.1 level of significance. H: = and the difference is merely due to chance. H1 : and there is a significant difference in copper recovery when NaHS is used. Under the hypothesis H the mean and the standard deviation of the difference of the means are given by - = and a Ri - = (o12/n1 + o22/n2) 5 = ((7.342/42 + (5.672/42))5 = 1.43 where the sample standard deviations are used as estimates of and 2. Then z = - - = ( /1.43) = For a two-tailed test, the results are significant at a.5 level if z lies outside the range and Hence it can be concluded that at a.5 level, there is a significant difference in copper recovery when NaHS is used despite the fact that Unit #2 is naturally doing better than Unit #1 from Method 1 above. The same conclusion can be drawn at.1 level of significance since the observed value lies outside and Testing the differences of means using 'Student t' test, again considering Unit #1 and Unit #2 when NaHS was used in Unit #2 as in above. (Method 3) Thus, to test the hypothesis H that the samples come from the same population (i.e., = as well as = 2) then the t score is given by = ( - )/ o(1/n1-1/n2)5 where a = (N1s12 + N2s22/N1 + N2 - =((42 * * 5.672) / ( =

216 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG when N1 = 42, = 78.7, s1 = 7.34 and N2 = 42, x2 = 81.5, s2 = 5.67 then t = ( )/6.638* (1/42 + t = Test the hypotheses; H = and the difference is merely due to chance. H1 : and there is a significant difference in copper recovery when NaHS is used. Thus on the basis of a two tailed test at a.5 level of significance, we would reject H if t were outside -.95 and t which for (N1 + N2-2) = 82 degrees of freedom is the range tol.66. Thus, we accept H1. Further, the 95% confidence limits are given by ± t975(s/(n-1) 5) = 2.8 ± Since v = N - 1 = 42-1 = 41, we find t975 = 2.2. Then using the mean recovery difference of 2.8 and a standard deviation of 6.638, the required 95% confidence limits are 2.8 ± 2.2(6.6381(42- = 2.8 ± 2.1%. Thus, we can be 95% confident that the true mean lies between.7% ( ) and 4.9% ( ). It is clear from above that we can be 95% confident that NaHS will increase copper recovery by at least.7%. 4.5 ECONOMIC CONSIDERATIONS The financial gains to be realised by CPS is based on a 3% improved copper recovery by CPS of rougher feed using NaHS. The two economic scenarios are considered as follows: Case 1 : Assumes 1-2% skarn blend NaHS NaHS cost = US $1.25 per kilogram NaHS consumption = 25 g/t Production cost US $.31 per tonne ore Metallurgy.7% Cu per tonne of ore 7. kg Cu per tonne ore At 85% Cu recovery At 88% Cu recovery 5.95 kg Cu per tonne ore (Base Case) 6.16 kg Cu per tonne ore (Cu recovery due to NaHS) 197

217 The Influence of Sodium Hydrogen Sulphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG Recovery gain due to NaHS.21 kg Cu per tonne ore or.463 lb Cu per tonne ore. Benefit At break even Cu price of US $.8 per pound, Revenue = U S $.37 per tonne ore. Profit = Revenue - Cost = US $.37 - US $.31 US $.6 per tonne ore. At a nominal throughput rate of 85 k tonnes per day profit $ 5,1 per day. $ 153, per month(3 days) $ 1,836, per year(36 days) Case 2: Assumes separate porphyry and skarn treatment. Under this treatment regime, porphyry and skarn ores are treated alternately i.e, 5% of time on porphyry and 5% skarn of time with NaHS used exclusively on porphyry ores. NaHS NaHS cost = US $1.25 per kilogram NaHS consumption = (1-2 g/t), use average of 15 g/t. Production cost US $.15 per tonne ore Metallurgy.7% Cu per tonne of ore At 85% Cu recovery At 88% Cu recovery Recovery gain due to NaHS - 7. kg Cu per tonne ore 5.95 kg Cu per tonne ore (Base Case) 6.16 kg Cu per tonne ore (Cu recovery due to NaHS).21 kg Cu per tonne ore or.463 lb Cu per tonne ore. Benefit At break even Cu price of US $.8 per pound, Revenue = U S $.37 per tonne ore. Profit = Revenue - Cost = US$.37- US$.15 = US$.22 per tonne ore. At a nominal throughput rate of 85 k tonnes per day profit $ 18,7 per day $ 561, per month(3 days) 198

218 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG $ 3,366, per year(1 8 days) Overall, case 2 offers greater benefit than Case 1. Under both cases, approximately 3% decrease in frother is envisaged and gold recovery is expected to increase. Note that in both cases, any increase in feed grade, throughput and copper price will increase revenue resulting in reduced overall plant operating cost. Sulphidisation therefore improves metallurgical recoveries of copper and gold and offers partial environmental solution due to reduced copper into the Ok Tedi river system. 199

219 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG APPENDIX #5 PLANT NAHS SURVEY REPORT (Abstracted from OTML Internal Memorandum) 2

220 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG OKTEDI MINING LIMITED Mill Metallurgy - ---Inter-Office Memorandum To : Dave Lauder Senior Metallurgist Development Copy : Jon Glatthaar Chief Metallurgist Bill Blenkhorn Executive Manager Mill Glen Kuri Manager Mill Operations Rod Hanson Chief Chemist Brian Cornish Senior Metallurgist Flotation Karen McCaffery Senior Metallurgist Projects John Enge Acting Superintendent Mill Operations Stephen Grano University of South Australia Metallurgy File Metallurgical Laboratory File Date : l9august,1997 From : Danny Orwe Metallurgist Development Subject : Unit #2 NaHS On/Off Surveys on Porphyry Ore May, 1977 Situation Executive Summary Controlled potential suiphidisation (CPS) has been tested for a number of times on plant rougher feed which usually comprised a range of ore types, including skarn ores. The effect of NaHS on copper recovery from these trials have indicated anywhere between -1% reduced copper recovery and 5% increased copper recoveries. In contrast, the laboratory results on porphyry ores have consistently showed superior results over the results of plant trials and surveys. Complication Plant trials and surveys have shown that CPS may not be effective when the proportion of skarn in the feed blend increases. This is most likely due to the interactions occurring between floating and non-floating copper minerals and the gangue minerals, while low copper recovery on skarn 21

221 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG ores under the standard grind size (P8 15 is almost certainly due to poor mineral liberation. Objective To test the effect of NaHS by CPS of plant rougher feed treating porphyry ore and also to confirm previous laboratory results of CPS on porphyry ore samples. Conclusion Indeed, both copper and gold recoveries increased markedly with NaHS on a plant feed of porphyry ore. The increases were 7.4% and 13.2 % for copper and gold recoveries respectively. On a size by size basis, the increase in copper recovery occurred across the entire size range with significant increases observed for the ultrafines (-13 and the coarsest (+212 size fractions. 22

222 The Influence of Sodium Hydrogen Sulphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Introduction Controlled potential sulphidisation (CPS) using sodium hydrogen suiphide (NaHS) on rougher feed has demonstrated favourable results in plant trials and surveys at Ok Tedi. While laboratory results have shown increased copper recovery with CPS, this effect was not always observed in plant and if there was, the results were often lower than those obtained in laboratory tests. Based on extensive laboratory tests, it can be stated with little doubt that CPS on porphyry ore increases copper and gold recoveries. It was the aim of these surveys to determine the magnitude in which these recoveries can be improved in-plant by treating only porphyry ore. Plant Surveys Two surveys were conducted, one with 'NaHS On' and the other with 'NaHS Off'. These surveys were conducted when the plant was treating exclusively porphyry ore on May, During CPS, the rougher feed pulp potential was controlled in 'Cascade' meaning the NaHS solution flow was controlled by pulp ph to attain an set point of -25 mv measured by platinum electrode. When the change was made from 'NaHS On to NaHS Off', one hour was given for the circuit to stabilise. The samples for X-ray photoelectron spectroscopic (XPS) analysis for determining surface oxidation of copper minerals have also been taken but have not been analysed at the time of reporting. Only the samples collected for EDTA extractions were analysed and are reported here. It should be noted that copper species predominant at ph 11.5 are copper (II) hydroxides and carbonates, both of which are extractable by EDTA. The survey samples were prepared in a standard manner and submitted for Cu, ASCu, Au and F assays. These assays were then mass balanced. The effect of CPS on size by size copper recovery, was determined by mass balancing size by size data of rougher feed, final concentrate and final tailings. Results Mass Balanced Data The survey data in general was good given that only minor adjustments were made to actual measurements. The mass balanced data for the 'NaHS On/NaHS Off' situations are given in Table 1. The results in Table 1 show marked increases in Cu, ASCu and Au recoveries when NaHS was used. The recovery increases were 7.4%, 5.7% and 13.2% for Cu, ASCu and Au respectively. 23

223 The Influence of Sodium Hydrogen Suiphide on Porphyry Suiphide Copper Recovery at Ok Tedi, PNG The increase in copper recovery with NaHS was accompanied by a reduced copper concentrate grade from 34% Cu to 32% Cu. The gold grade was not affected. Mass Balanced Sizing Data There is no doubt that suiphidisation improved copper recovery across the entire size range. It is obvious from Figure 1 that marked contributions from the fine (- 31 and the coarse (+212 i.tm) size fractions increased total copper recovery. Full size by size copper data is contained in Table 2. EDTA Extraction of Pulp Samples The EDTA copper extraction results of NaHS On versus NaHS Off situations can be compared in Table 3. It is evident from the higher EDTA extractable Cu values for the NaHS Off situation (except for final tail) that oxidation of copper minerals was prevalent under the plant conditions during the survey period. The relatively high EDTA extractable Cu obtained for the final tail sample with the 'NaHS On' situation is expected, indicating rapid oxidation of copper minerals after aeration during the rougher/scavenger stage. This effect is possible for rapidly oxidising copper minerals such as digenite, covellite and bornite which are normally contained in the porphyry ores at Ok Tedi. Conclusion The results obtained from surveys conducted on May, 1997 confirm laboratory results and further reinforces that CPS using NaHS improves copper and gold recoveries from porphyry ores. DANNY ORWE 24

224 The Influence of Sodium Hydrogen Suiphide on Porphyry Sulphide Copper Recovery at Ok Tedi, PNG Stream Table 1 Mass Balance - NaHS On-Off Surveys - 23 May, Flow tph Meas % NaHS 'On' Case Copper Copper Gold Adi % Rec % Meas % Adj % Rec % Meas g/t Adj g/t Rec % Meas JJ ppm Rou Feed Rou Con Tail Rou Con Tail ScavCon Final Tail Final Con CleanerTail Stream Flow tph Meas % NaHS 'Off' Case Adj ppm Copper AS Coppe r Gold Fluorine Adj % Rec % Meas % Adj j{ Rec It.11 Rou Feed RouCon TailS RouCon Tailg Scav Con Final Tail Final Con CleanerTail Table 2 Size by Size Copper Recovery - NaHS On-Off Surveys - 23 May, 1997 ' NaHS On Size Feed Concentrate Tail Recovery % tph Cu tph 1 r Wt g J[ % Meas g/t Adj g/t Rec % Meas ppm tph % Cu Cu tph Wt g tph % Cu Cu tph , Total Size Feed Concentrate tph Cu tph 1[ Wt g tph % Cu NaHS Off Ads ppm Rec % Rec Tail Recovery % Cu tph Wt g tph % Cu Cu tph , Total 2. }J % 25