Metallurgical Improvements at Kagara s Mount Garnet Mine Through the Use of High Chrome Grinding Media

Metallurgical Improvements at Kagara s Mount Garnet Mine Through the Use of High Chrome Grinding Media J Kinal, C Greet and R Whittering ABSTRACT High chrome grinding media has been used in the mining industry for quite some time, as it often proves economical on a wear basis. However it is unusual for an operation to change to high chrome solely due to its metallurgical benefits. Kagara s Mount Garnet operation made the change from forged steel to high chrome media after laboratory testwork indicated that copper grades and recoveries would improve. The outcome was remarkable with positive changes in pulp chemistry throughout the circuit accompanied by marked improvements in copper, lead and zinc grades and recoveries. Reagent dosage rates were reduced, often by more than half, and the grinding media wear rate dropped to less than a third of the wear rate of the forged steel media. The economic analysis showed that out of the total increase of revenue and savings from metallurgical improvements and reagent and media consumption reductions the metallurgical improvements made up approximately 73 per cent, the reduced reagents saved 25 per cent and the savings through reduced media wear contributing by just over one per cent. This indicates that the popular view of high chrome media only being trialled in the plant for wear economics is outdated and the focus of operations should be shifted to using high chrome media for the metallurgical benefits. Authors Jessica Kinal Senior Metallurgist Magotteaux Australia Pty Ltd Suite 4, 83 Havelock Street, West Perth WA 6005 email: jessica.kinal@magotteaux.com Dr Christopher Greet Principal Metallurgist Magotteaux Australia Pty Ltd Suite 4, 83 Havelock Street, West Perth WA 6005 email: christopher.greet@magotteaux.com Richard Whittering Senior Metallurgist Kagara Zinc Ltd, Mount Garnet Operations 4 Zinc Street, Mount Garnet QLD 4872 email: richardw@mtgarnet.kagara.com.au 1

Metallurgical Improvements at Kagara s Mount Garnet Mine Through the Use of High Chrome Grinding Media J Kinal 1, C Greet 2 and R Whittering 3 1. Senior Metallurgist, Magotteaux Australia Pty Ltd, Suite 4, 83 Havelock Street, West Perth WA 6005. Email: jessica.kinal@magotteaux.com 2. Principal Metallurgist, Magotteaux Australia Pty Ltd, Suite 4, 83 Havelock Street, West Perth WA 6005. Email: christopher.greet@magotteaux.com 3. Senior Metallurgist, Kagara Zinc Ltd, Mount Garnet Operations, 4 Zinc Street, Mount Garnet QLD 4872. Email: richardw@mtgarnet.kagara.com.au ABSTRACT High chrome grinding media has been used in the mining industry for quite some time, as it often proves economical on a wear basis. However it is unusual for an operation to change to high chrome solely due to its metallurgical benefits. Kagara s Mount Garnet operation made the change from forged steel to high chrome media after laboratory testwork indicated that copper grades and recoveries would improve. The outcome was remarkable with positive changes in pulp chemistry throughout the circuit accompanied by marked improvements in copper, lead and zinc grades and recoveries. Reagent dosage rates were reduced, often by more than half, and the grinding media wear rate dropped to less than a third of the wear rate of the forged steel media. The economic analysis showed that out of the total increase of revenue and savings from metallurgical improvements and reagent and media consumption reductions the metallurgical improvements made up approximately 73 per cent, the reduced reagents saved 25 per cent and the savings through reduced media wear contributing by just over one per cent. This indicates that the popular view of high chrome media only being trialled in the plant for wear economics is outdated and the focus of operations should be shifted to using high chrome media for the metallurgical benefits. Theory The use of forged steel (high carbon, low alloy steel) grinding media to liberate valuable minerals prior to flotation is common practice due to the relatively low unit cost of this media compared to other forms. However from a wear and chemistry perspective, forged steels may not be the most cost effective proposition. It is known that total wear of grinding media is due to a combination of corrosive, abrasive and impact wear, but it is difficult to separate the contribution from each mechanism during wet grinding (Iwasaki et al, 1985). Despite this, investigations into wear mechanisms have been conducted (Natarajan and Iwasaki, 1984 and Iwasaki et al. 1985), and have reported that corrosive wear results in more than half of the total media wear and others report it is accelerated when in the presence of reactive sulfide minerals (Adam et al, 1984; Iwasaki et al, 1983; Isaacson, 1989). Besides the obvious consumable cost, the impact of corrosive grinding media wear on downstream processing is quite remarkable and has been studied for some time. Metallic 2

corrosion reactions in aqueous solutions are electrochemical in nature (Isaacson, 1989) which means that galvanic interactions occur in every grinding media-sulfide mineral system. In many reported cases, galvanic interactions have been found to adversely affect the flotation response of sulfide minerals by affecting their surface properties (Adam et al, 1984; Iwasaki et al, 1983; Natarajan and Iwasaki, 1984; Kocabag and Smith, 1985; Yelloji Rao and Natarajan, 1989a and b; Forssberg et al, 1993; Cheng et al, 1993; Yuan et al, 1996; Greet and Steinier, 2004, Greet et al, 2005). Electrochemical reactions are made up of the sum of two half reactions as one cathodic, or reduction, and the other anodic, or oxidation. In a grinding media - sulfide mineral system, due to the differences in rest potentials, complex galvanic cells are set up where the sulfide mineral can act as an anode or cathode, depending on its contact with other sulfide minerals, media and reagents (Cheng, Smith, Iwasaki, 1993). Generally, the forged steel balls act as anodes relative to the sulfide mineral cathode: Cathode (sulfide mineral): ½O 2 + H 2 O + 2e - 2OH - (1) Anode (grinding media): Fe Fe 2+ + 2e - (2) The dissolution of iron ions from the grinding media bonds with the hydroxyl species and forms hydroxyl complexes of iron which are hydrophilic and have been seen as coatings on the sulfide mineral surfaces (Adam et al, 1984; Natarajan and Iwasaki, 1984, Yelloji Rao and Natarajan, 1989a and b; Forssberg et al, 1992). These iron hydroxide surface coatings affect the floatability of the sulfide minerals, not only due to their hydrophilic nature but also by hindering effective collector adsorption. Interestingly, it has been noted that without a galvanic contact between the sulfide and the iron, the values of mixed potentials were in the vicinity of the xanthate/dixanthogen redox potential. However, when in contact with iron, the mixed potentials shifted towards a more negative value, making them too reducing for a xanthate collector to be adsorbed effectively (Adam et al 1984). One method of preventing these oxidation reactions occurring is to substitute inert grinding media into the system. As ceramics would be unsuitable in this situation and the expense of stainless steel media is prohibitive, high chrome white iron should be considered. High chrome grinding media initially rapidly corrodes to form a very hard chrome oxide layer which effectively then prevents the exchange of electrons and halts the corrosion process. This frees the oxygen in the system to oxidise the sulfide minerals such as pyrite and pyrrhotite and therefore inhibit the flotation of these minerals (Buckley and Woods 1985; Buckley and Woods 1987). The presence of oxygen is vitally important to assist in collector adsorption and mineral floatability (Gaudin, 1974). There have been many laboratory tests conducted comparing the effect of varying media types during grinding on flotation performance, and even pilot scale operations where the effect of changing the media type was not so clear, but minimal work has been conducted in full plant scale operations. This paper will demonstrate how changing the grinding media from forged steel to a high chromium alloy at Kagara Zinc s Mount Garnet operations effectively resulted in a statistical increase in copper, lead and zinc flotation performance. 3

Problem definition Kagara Zinc is the lowest cost zinc producer in Australia, with interests in Mungana/Red Dome, the Greenvale region and Admiral Bay. The company operates two concentrators located at Mt Garnet (105km south west of Cairns) treating polymetallic sulfide ores mined on its lease. The Surveyor ore proved difficult to treat, with the main problem being poor selectivity for chalcopyrite against pyrite. Table 1 clearly shows that the copper, lead and zinc minerals were misreporting into the wrong concentrate with approximately 26 per cent copper reporting to the lead and zinc concentrates, 19 per cent lead in the copper and zinc concentrates, and 9 per cent zinc in the copper and lead concentrates. Table 1: Copper, lead and zinc grades and recoveries for Mount Garnet, February and March 2004. Grade Recovery Cu, % Pb, % Zn, % Fe, % Cu, % Pb, % Zn, % Fe, % Feed 0.8 7.4 16.2 16.8 100 100 100 100 Cu Con Pb Con Zn Con Tailings 17.1 16.5 9.8 1.3 57.7 11.9 0.3 2.9 50.3 20.9 5.2 7.2 66.2 14.8 11.6 7.3 8.5 74.5 10.6 6.3 2.1 7.1 84.7 6.0 4.1 3.1 12.0 80.8 Initial site visit and laboratory testwork completed by OPTIMET Laboratories (Wong, 2003 a and b) demonstrated a strong relationship between grinding media type and pulp aeration with increased copper flotation kinetics and grades. Further laboratory tests by Magotteaux confirmed Wong s results and demonstrated the metallurgical advantages of high chrome grinding media (Kinal, 2004a and b). A plant survey was undertaken, highlighting that the Mount Garnet grinding and copper flotation circuits contained very low levels of dissolved oxygen and reasonably low Eh values which is conducive to pyrite flotation. It appeared that the oxygen was consumed during the grinding process, possibly through grinding media corrosion, and therefore not available to oxidise the pyrite to prevent its flotation. The amount of iron sulfide reporting to the copper concentrate was therefore quite high, averaging 10.60 per cent for the period measured. This, along with the problem of the valuable minerals misreporting to the wrong concentrates indicated that there was a massive problem with selectivity throughout each of the three circuits. Laboratory testing Laboratory grinding and flotation tests were conducted to compare the effects of grinding with forged and 30 per cent chrome media on copper flotation response. Pulp chemistry and EDTA extractable iron measurements were taken during the flotation tests. 4

Table 2 shows the mill discharge and flotation pulps became considerably more oxidising with the shift from forged to 30 per cent chrome grinding media. The more oxidising conditions observed when the 30 per cent chrome grinding media was employed were accompanied with an increase in dissolved oxygen levels in the mill discharge. There also appeared to be a decrease in ph which suggests that there may be more rapid oxidation of pyrite when the 30 per cent chrome grinding media was used. If this is true then it is expected that selectivity for chalcopyrite against pyrite should improve. Table 2: Pulp chemistry data for laboratory mill discharge and copper circuit for plant samples ground with forged and 30 per cent chrome media. Media Eh, mv (SHE) Mill Discharge ph DO, ppm Eh, mv (SHE) Flotation Feed ph DO, ppm Forged standard 67 7.01 0.00 58 6.79 0.00 30% Cr standard 354 6.52 4.26 204 6.36 0.00 The copper grade recovery curves (Figure 1) demonstrate that the forged standard test (no aeration) is bent over, indicating that another mineral is preferentially floating first, which is similar behaviour to that noted in the Mt Garnet plant. The flotation rate of the chalcopyrite is quite slow, and results in low concentrate grades. When the 30 per cent chrome grinding media is substituted for the forged media, the copper flotation performance markedly improves, with a faster flotation rate and higher grade of copper in the first concentrate. The improvement in copper grade when grinding with 30 per cent chrome media is due to better selectivity against galena, sphalerite, iron sulfides and non sulfide gangue (Table 3). 25.0 20.0 Forged 30% Cr Grade - Cu(%) 15.0 10.0 5.0 0.0 0.0 20.0 40.0 60.0 80.0 100.0 Recovery - Cu(%) Figure 1: Copper grade recovery curves for copper rougher tests completed on Surveyor ore comparing the effect of grinding with forged and 30 per cent chrome media. 5

Table 3: Copper and silver grades and silver and diluent recoveries at 66.2 per cent copper recovery for copper rougher tests completed on Surveyor ore comparing the effect of grinding with forged and 30 per cent chrome media. Grade Recovery Media Cu, % Ag, ppm Ag, % Pb, % Zn, % IS, % NSG, % Forged 14.35 604 15.54 4.62 2.93 2.60 1.78 30% Cr 18.96 750 14.90 2.65 1.62 1.87 0.91 Digital photographs were taken during these flotation tests and can be seen in Figures 2 and 3. The flotation rate of copper is clearly depicted in these photographs, with the 30 per cent chrome test obviously generating far superior copper metallurgy than when grinding with forged media despite the same flotation conditions. Figure 2 a,b,c,d: Photos of the first, second, third and forth concentrates of a copper roughing flotation test on Surveyor ore ground with forged media. Figure 3 a,b,c,d: Photos of the first, second, third and forth concentrates of a copper roughing flotation test on Surveyor ore ground with 30 per cent chrome media. Plant trial From the positive results generated from the site laboratory testwork, Mount Garnet personnel decided to undertake a plant trial, substituting 18 per cent chrome grinding media into the SAG mill. A series of pulp chemistry and EDTA surveys were conducted before and after changing the media charge. Figure 4 shows the Eh throughout the primary grinding circuit was much more oxidising than when measured previously while grinding with forged media. The ph (Figure 5) remained nominally the same as lime was added to a specific ph value. The dissolved oxygen profile saw the most dramatic change, with the dissolved oxygen levels when grinding with high chrome media up to over 3.5 parts per million in the cyclone overflow (Figure 6). The higher 6

levels of dissolved oxygen, along with more oxidising pulp potentials, are strong evidence that the change in grinding media from forged to high chrome involves a significant change in the corrosion mechanism. Further, as the grinding media was the only parameter that was consciously altered, the observed changes can be attributed directly to the high chrome grinding media. The EDTA extractable iron profile (Figure 7) supports this, with the levels of oxidised iron decreasing by almost a third in the cyclone overflow stream. 300 250 06-02-04 Forged 05-06-04 18% Cr Eh, mv (SHE) 200 150 100 50 0 Cyclone underflow SAG mill discharge Cyclone overflow Circuit Position Figure 5: Eh profiles through the grinding and flotation circuits of the Mount Garnet concentrator, comparing forged grinding media to 18 per cent chrome grinding media. Cu rougher Pb rougher Zn rougher Zn rougher tailing 12.0 11.0 10.0 9.0 ph 8.0 7.0 6.0 06-02-04 Forged 05-06-04 18% Cr 5.0 4.0 Cyclone underflow SAG mill discharge Cyclone overflow Circuit Position Figure 6: ph profiles through the grinding and flotation circuits of the Mount Garnet concentrator, comparing forged grinding media to 18 per cent chrome grinding media. Cu rougher Pb rougher Zn rougher Zn rougher tailing 7

8.0 7.0 06-02-04 Forged 05-06-04 18% Cr 6.0 DO (ppm) 5.0 4.0 3.0 2.0 1.0 0.0 Cyclone underflow SAG mill discharge Cyclone overflow Circuit Position Cu rougher Pb rougher Zn rougher Zn rougher tailing Figure 7: Dissolved oxygen profiles through the grinding and flotation circuits of the Mount Garnet concentrator, comparing forged grinding media to 18 per cent chrome grinding media. 0.35 0.30 06-02-04 Forged 05-06-04 18% Cr EDTA Extractable Fe % 0.25 0.20 0.15 0.10 0.05 0.00 Cyclone underflow SAG mill discharge Circuit Position Cyclone overflow Cu rougher Pb rougher Zn rougher Final tailing Figure 8: EDTA extractable iron profiles through the grinding and flotation circuits of the Mount Garnet concentrator, comparing forged grinding media to 18 per cent chrome grinding media. 8

Metallurgical performance Monitoring the shift data continued for five months after the high chrome media was substituted into the SAG mill. In this time the process water was diluted with a higher ratio of raw water in order to continue along the path of cleaning the system to promote better copper, lead and zinc metallurgy. Therefore the following improvement in shift performance can not be attributed solely to the grinding media, rather a combination of the high chrome media and cleaner water, as well as any other operational factors. Figure 9 plots the copper circuit performance over seven months. The forged period has been taken from after the copper circuit collector was changed and before the 18 per cent chrome was added to the SAG mill. The high chrome period was taken from after the 18 per cent chrome was added to the SAG mill and has been cleaned to remove periods such as shutdowns and out of the ordinary reagent usage. The lead and zinc circuit performances were treated in a similar fashion, but the data is not shown. 50.0 45.0 40.0 Replaced RTD13 with DSP009 18% Cr in SAG Raw Water 100.0 90.0 80.0 35.0 70.0 Grade, % 30.0 25.0 20.0 60.0 50.0 40.0 Recovery, % 15.0 30.0 10.0 5.0 Ore change, very low grade and high throughput 20.0 10.0 0.0 10 11 12 123456789 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 3123456789 10 11 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 3123456789 10 11 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29123456789 10 11 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 3123456789 10 11 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30123456789 10 11 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 3123456789 10 11 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30123456789 10 11 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 0.0 December, 2003 January, 2004 February, 2004 March, 2004 April, 2004 May, 2004 June, 2004 July, 2004 Cu grade Cu recovery Figure 9: Copper circuit performance for the Mount Garnet concentrator for the period from December 2003 to July 2004, showing the effect of changing grinding media from forged to high chrome. Clean data was extracted from the shift performance and comparisons made between the periods when grinding with forged and high chrome media. Table 4 shows that there was a noticeable difference in copper, lead and zinc performance when the grinding media changed, however other factors such as head grade and tonnage were also different. 9

Table 4: Difference between circuit performance parameters comparing forged to 18 per cent chrome media. Head Grade Parameter Forged 18% Cr Difference Cu (%) Pb (%) Zn (%) 0.82 7.44 16.23 0.87 6.97 17.21 + 0.05-0.47 + 0.98 Feed Rate DMT (24 hr) 825 734-91 Copper Concentrate Lead Concentrate Zinc Concentrate recovery (%) grade (%) tonnage (24 hr) recovery (%) grade (%) tonnage (24 hr) recovery (%) grade (%) tonnage (24 hr) 67.13 17.26 28.66 74.67 57.96 79.36 85.49 50.27 227.30 73.32 21.24 22.56 80.07 60.40 68.18 88.11 51.17 217.68 + 6.19 + 3.98-6.10 + 5.40 + 2.44-11.18 + 2.62 + 0.90-9.62 To compare the test condition (high chrome grinding media), a multiple variable regression model can be used. If there is a significant difference between the two cases, then the process can be said to have been altered by the test condition (Napier-Munn, 2005). Using the cleaned data, tonnage and grade along with dummy variables of zero for forged and one for high chrome were tabulated against recovery and modelled using the multiple linear least squares regression model from Excel. The confidence values show that in the copper, lead and zinc circuits, the grinding media type is highly significant with respect to change in metallurgical performance. The standard errors showed that there is a fair amount of scatter in the forged media data and it is obvious from the time series chart in Figure 9 that the plant was noticeably more stable when high chrome media was implemented. The coefficients of the on/off variable give the difference in recovery between the on (high chrome) and off (forged) cases. Table 5 lists these differences and the statistical confidence that accompanies these figures. 10

Table 5: Difference between copper, lead and zinc circuit performance parameters comparing forged to 18 per cent chrome media. Copper Concentrate Lead Concentrate Zinc Concentrate Parameter Recovery (%) Grade (%) Recovery (%) Grade (%) Recovery (%) Grade (%) Difference (18% Cr Forged) +5.65 % +4.07 % +5.37 % +2.16 % +3.60 % +0.97 % Confidence values (%) >99.99% >99.99% >99.99% 99.89% >99.99% 99.84% As grinding media plant trials occur over extended periods of time to generate wear data, it is very difficult to design the trial such that all other factors which potentially influence recovery (e.g. tonnage, grade, mineralogy and operational changes) are removed. Therefore although there has been a low level of statistical analysis completed on this data, the calculated change in recoveries should be viewed with caution. Further, as the economic analysis is based on the calculated recovery improvements, it follows that caution should be maintained when studying the revenue increases. Economic analysis Increasing recovery at the same or better grade effectively means an increase in revenue earned. Using an average throughput rate of 800 tonnes per day with an availability of 90 per cent, the increase in concentrate production from the change to high chrome (including other factors) can be calculated. Then, using the copper, lead and zinc prices from August 2004, a dollar value equating to revenue increase can be demonstrated. Table 6 demonstrates that a total of $A 3.91 M in revenue has potentially been earned directly from the improvements in recovery. This does not take into account benefits in improved concentrate grade as the terms of concentrate sale are confidential. However, it is known that a higher grade concentrate will attract fewer penalties. Table 5: Increase in revenue due to increased recovery assuming set head grades. Metal Copper Lead Zinc Metal Price (LME 27/08/2004) AUD $ 3,990 AUD $ 1312 AUD $ 1377 Recovery Change (%) + 5.65 + 5.37 + 3.60 Revenue Increase (AUD) $ 485,803 $ 1,377,547 $ 2,107,853 Total $ 3,91,203 11

Apart from the metallurgical benefits documented in this case study, it should be pointed out that there has been considerable saving through a reduction in the consumption of consumables, i.e. grinding media and reagents (Table 7). It is widely known that high chrome grinding media has superior wear rates to that of forged media, which in some instances is sufficient to justify a change in media. The consumption of grinding media at Mount Garnet dropped by approximately 68 per cent due to the change from forged to 18 per cent chrome media in the SAG mill. This change was enough to offset the higher cost of high chrome grinding media as well as increasing revenue (approx A$56 576 pa). The usage rates of most of the reagents also dropped by a remarkable amount, ranging from 46 to 68 per cent reductions. Only the frother saw an increase in use, which is likely due to the addition of raw water to the circuit. The reduction in the collectors were expected, as the collector-mineral reactions are electrochemical in nature and are therefore influenced by the oxidation state of minerals, galvanic reactions and dissolved ions in the pulp (Ekmekçi, et al, 2005). Surface coatings of iron hydroxides as well as low dissolved oxygen levels as a result of grinding with forged media creates a barrier to reagent attachment, so to reduce reagent usage, cleaner surfaces and higher dissolved oxygen concentrations is necessary. This is achievable through grinding with high chrome media. Table 7: Change in reagent usage for the Mount Garnet concentrator, comparing forged to 18 per cent chrome media, removing the effect of throughput variations. Reagent Change (%) Grinding Media -68.17 Antiscalent DSP009 Copper Sulfate Cyanide Frother Lime SMBS Xanthate Zinc Sulfate -66.86-66.48-46.61-48.65 +101.06-68.80-66.73-59.38-62.35 Table 8 lists the estimated saving Mount Garnet made by reducing media and reagent consumption rates, and the revenue earned by improving metallurgical performance after swapping forged media to 18 per cent chrome media using the assumptions given above. It is 12

very clear that the greatest increase in revenue was due to the improved metallurgical performance (73 per cent of total). However, conventional thinking has been that grinding media should be justified on reduced wear alone. This narrow criteria needs to be reviewed, to take into account pulp chemical changes that often result in reductions in reagent consumption and improvements in metallurgy. This example provides significant evidence that far greater improvements can be made when grinding media is used with the downstream process in mind. Table 8: Increases in revenue due to improvements in metallurgy and decreases in media and reagent consumption rates. Parameter Est. original Plant Budget ($A per annum) Saving/Revenue ($A per annum) Per cent of Total Saving/Revenue Media $161 500 $ 56 576 1.05 % Reagents $2 200 000 $ 1 369 116 25.37 % Metallurgy $74 400 000 $ 3 971 203 73.58 % Total $76 660 000 $ 5 396 895 100 % Conclusions The Mount Garnet copper-lead-zinc plant demonstrated poor metallurgical performance with misreporting of the valuable minerals and poor selectivity for chalcopyrite against pyrite. The pulp chemistry showed low pulp potentials and dissolved oxygen levels in most streams, along with high EDTA extractable iron levels. After laboratory tests indicated that metallurgical improvements could be found by changing to a more inert grinding media, 18 per cent chrome media was loaded into the SAG mill for a plant trial. The resulting changes included improved pulp chemistry with more oxidising Eh and dissolved oxygen values, along with lower EDTA extractable iron percentages. The metallurgical changes were impressive, with increased grades and recoveries of copper, lead and zinc with a corresponding reduction in grinding media consumption as well as reagent dosage rates. It is estimated that the change from forged to high chrome grinding media contributed to an increase in revenue of almost A$5.4 million per annum. Of this, metallurgical improvements accounted for around 73 per cent of the increase. It must be noted that the improvements in metallurgy were due to a variety of factors, including grinding media change, cleaner water, and other operational factors. This case study challenges conventional thinking which dictates that a change in grinding media must be justified by a decrease in media consumption alone. The grinding circuit (and the media 13

used) is the primary conditioner and does have a significant impact on downstream processing. So, it is imperative that these aspects be taken into account in any plant trial. Further to this, studies investigating the most appropriate grinding media should be included in the design and feasibility stage of all new ore body developments. The Mt Garnet ore feasibility testwork did include grinding media effects and these did show a marked copper circuit performance. Acknowledgements The authors would like to acknowledge Kagara Zinc and Magotteaux Australia for the permission to publish this paper. References Adam K, Natarajan K A and Iwasaki I (1984), Grinding media wear and its effect on the flotation of sulphide minerals, International Journal of Mineral Processing, 12, pp 39 to 54. Buckley A N and Woods R (1985), X-ray photoelectron spectroscopy of oxidised pyrrhotite surfaces, Applications of Surface Science, 22/23, pp 280 to 287. Buckley A N and Woods R (1987), The surface oxidation of pyrite, Applied Surface Science, 27, pp 437 to 452. Cheng X, Smith K A and Iwasaki I (1993), Electrochemistry of chalcopyrite-pyrrhotite-mild steel interactions and its relevance to the flotation of complex sulphide ores, in the proceedings of the Paul E Queneau International Symposium: Extractive Metallurgy of Copper, Nickel and Cobalt (Edited by: R G Reddy and R N Weizenback), Volume I: Fundamental Aspects, pp 971 to 991 (The Minerals, Metals and Materials Society: New York). Ekmekci Z, Buswell M A, Bradshaw D J, Harris P J (2005), The value and limitations of electrochemical measurements in flotation of precious metal ores, Minerals Engineering, 18, pp 825 to 831. 14

Forssberg K S E, Subrahmanyam T V and Nilsson L K (1993), Influence of grinding method on complex sulphide ore flotation: a pilot plant study, International Journal of Mineral Processing, 38, pp 157 to 175. Gaudin A M (1974), The role of oxygen in flotation, Journal of Colloid and Interface Science, 47 (2), pp 99 to 114. Greet CJ and Steinier P (2004), Grinding the primary conditioner, in the Proceedings of the Metallurgical Plant Design and Operating Strategies Conference, pp 319 to 336 (The Australasian Institute of Mining and Metallurgy: Melbourne). Greet C J, Kinal J and Steinier P (2005), Grinding media - Its effect on pulp chemistry - Fact or fiction?, in the Proceedings of the Centenary of Flotation 2005 Symposium, pp 967 to 972 (The Australasian Institute of Mining and Metallurgy: Brisbane). Isaacson A E (1989), Effect of sulphide minerals on ferrous alloy grinding media corrosion, United States Bureau of Mines Report 9244. Iwasaki I, Natarajan K A, Riemer S C, and Orlich J N (1985), Corrosive and Abrasive Wear in Ore Grinding, Wear, 103, pp 253 to 262. Iwasaki I, Reid K J, Lex H A, and Smith K A, (1983) Effect of Autogenous and Ball Mill Grinding on Sulphide Flotation, Mining Engineering, 35, pp 1184 to 1190. Kinal J (2004a), DP 3, Mount Garnet: Investigating the effects of high chrome grinding media on copper, lead and zinc flotation, Magotteaux Australia. Kinal J (2004b), DP16, Mount Garnet: Effect of 18 percent chrome grinding media on copper, lead and zinc flotation, Magotteaux Australia. 15

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