Redbook. Mining Solutions

Transcription

1 Redbook Mining Solutions

2 2 Content 1. Introduction 2. Solvent Extraction 3. Copper Extraction from Acidic Sulfate Solution 3.1 Chemistry of Copper Extraction 3.2 Development of a Cu SX Process Flow Sheet 3.3 Laboratory Development of an SX Circuit 4. Copper Extraction from Ammoniacal Solution 5. Nickel Extraction from Ammoniacal Solution 6. BASF Alamine and Aliquat Reagents 7. Extraction of Uranium 8. Extraction of Molybdenum and Vanadium 9. LIX Reagents Additional Applications 10. Appendices 10.1 Isocalc Computer Modeling Software 10.2 Test Procedures 10.3 SX Extractants and Process Auxilliaries 10.4 Mixer Settlers 10.5 Diluents for Metal Solvent Extraction Applications 10.6 Typical Properties of Reagents 11. Footnotes

3 3 1. Introduction The 20th century saw a marked expansion in the requirements for various metals and global need grew rapidly. Development of nations such as China and India as well as advances in metal application technologies has fueled increased demand for metals. To meet the needs of modern society for metals in general and higher purity metals in particular, the mining industry has had to find more effective and efficient methods for processing ores and recovering the metal values to overcome the challenges associated with decreasing ore grades and increasingly stringent environmental regulations. The development of hydrometallurgical processing has played a significant role in helping to overcome these challenges and will provide many of the new processes required to meet the challenges of the future. Solvent extraction (SX) technology will play an integral role in many of these new processes. The first example of the use of liquid-liquid solvent extraction to recover and purify a metal can be traced back to the extraction of uranyl nitrate into ethyl ether by Peligot in The analytical chemistry literature contains thousands of references to the use of solvent extraction to isolate, purify and concentrate materials to facilitate analysis. This work in analytical chemistry has resulted in the development of a large pool of fundamental knowledge with regards to solution chemistry and organic based extractants 2. Starting in the 1950 s, solvent extraction was applied on a commercial scale to the recovery of uranium, vanadium and molybdenum 3. The Mining Solutions business of BASF, which traces at least a part of its roots to the former General Mills Chemicals, developed Alamine 336 and introduced it in 1957 for the recovery of uranium 4. Alamine 336 remains the reagent of choice to this day for the solvent extraction of uranium. The introduction of Alamine 336 to the mining industry was followed by the development and introduction of LIX 64 for the recovery of copper by solvent extraction. The first successful application of the leach-solvent extraction-electrowinning process for the recovery of copper was marked by the startup of the Ranchers Bluebird Mine copper solvent extraction plant (Design = 5,000 tonnes Cu / yr) in This was quickly followed by the commissioning of the Cyprus Bagdad copper solvent extraction plant (Design= 6,600 tonnes Cu / yr) in The Bagdad copper solvent extraction plant is now part of Freeport McMoRan and is the oldest operating solvent extraction plant in the world 6. This was followed by the commissioning of the Nchanga Tailings Leach Plant (Design = 54,000 tonnes Cu / yr) in Since it s earliest beginnings, the Mining Solutions group has been committed to and remains committed to the development of solvent extraction technology and solvent extraction reagents. The use of copper solvent extraction has grown dramatically since the late 1960 s. There are a total of more than 119 copper solvent extraction plants currently operating around the world producing an estimated 3.7 MM tons of copper in Given that total copper production in 2012 was estimated to be approximately MM tons 8, copper SX represented 22 % of the global copper production.

4 4 The Mining Solutions group s dedication to improving solvent extraction technology has led to a number of industry firsts : Developed tertiary amines (Alamine reagents) and quaternary amines (Aliquat reagents) for metal extraction 4 Conceptualized leaching-solvent extraction-electrowinning for copper 4,7 Developed first commercially successful phenolic oxime reagents (LIX reagents) for extraction of copper and nickel. 7,9 Developed first alcohol modified aldoxime blend for copper extraction 7 Conceptualized and developed the Picket Fence 10 Introduced Clay Treatment 11 and scrubbing processes for cleaning of contaminated circuit organics Developed non-modified aldoxime / ketoxime blends 12,13 Conceptualized and developed use of wash stage technology in copper solvent extraction 14 Conceptualized and developed precipitation / releach flow sheet for recovery of nickel and cobalt from laterite ores 15,16 Conceptualized and developed improved flowsheets Modified Series Parallel Optimum Series Parallel 17 Split Circuit 18 Sequential Circuit 19 The goal of this book is to familiarize the reader with the fundamental concepts of solvent extraction technology as well as with the LIX, Alamine and Aliquat solvent extraction reagents and their applications. This booklet will also introduce other reagents, systems and services provided by the Mining Solutions business of BASF. More detailed information about specific reagents, metals, or process systems is available on request. LIX, Alamine, Aliquat and Isocalc * are registered trademarks of BASF SE. * Isocalc is a registered trademark in Brazil, Canada, Mexico, Peru and the US

5 5 2. Solvent Extraction Solvent extraction (SX) as used in this booklet refers to a liquid-liquid extraction process for separating species in solution by their distribution between two immiscible solvents 1. In the metal recovery operations of interest, the SX process involves a chemical reaction of the metal species of interest with an organic extractant in an organic diluent such as a petroleum distillate cut similar to kerosene. The reaction of the metal species with the organic extractant results in a hydrocarbon soluble metal complex. The chemistry involves equillibria as a result transfer of the metal species into (extraction) and out of (stripping) the hydrocarbon phase can be controlled by altering conditions such as the ph of the aqueous. As part of a metal recovery process, solvent extraction using BASF extractants has three primary objectives: Purification of the metals from unwanted impurities. Extract desired metal(s) away from impurities. Extract impurities away from desired metal(s). Concentration of the metal values to reduce downstream processing costs. Conversion of the metal values to a form which simplifies final recovery. In any given solvent extraction process, one, two, or all three objectives may be necessary. A key point for the reader to understand is illustrated in Figure 1. Solvent extraction is only one unit process in a series of unit processes in going from the metal bearing ore to the final metal product. The leaching process delivers a metal bearing solution whose nature will vary depending on the actual ore and the conditions required to achieve effective solubilization of the metal values. The solvent extraction process must be able to efficiently transfer the metal values from this incoming leach solution into the organic phase. The final metal recovery step will determine the conditions under which the metal values will be transferred from the metal loaded organic to generate a concentrated and purified aqueous metal solution. Leaching / SX / metal recovery are interlocking processes whose overall success is dependent on the effectiveness of each step. To develop an effective metal recovery process, it is critical to know the nature of the leach solution that is to be treated and the recovery process that will be used to produce the desired metal product. Each sets criteria within which the solvent extraction process must operate. The solvent extraction process is conceptually simple: The metal bearing leach solution (Pregnant Leach Solution, PLS) is fed into a mixer along with an immiscible hydrocarbon solution of a metal extractant (Barren Organic) where the two solutions are intimately mixed. The resultant emulsion overflows from the extraction mixer into the settler. As it progresses down the settler, the solutions separate to give a metal loaded organic (LO) solution on top and a metal depleted aqueous solution (raffinate) on the bottom. The raffinate is discharged via an underflow weir and recycled to leaching. The LO passes over a weir and flows to a second mixer where it is intimately mixed with a strip solution. The resultant emulsion overflows from the strip mixer into the corresponding settler where it separates into a metal barren organic (BO) which is returned to extraction and a concentrated aqueous solution (Pregnant Strip Solution) of the desired metal in a form from which it can be readily recovered. Figure 2 illustrates a copper solvent extraction plant consisting of 2 stages of countercurrent extraction and 2 stages of countercurrent stripping. Formula 1 2RH (Organic) + Cu +2 (Aqueous) Extract Strip R 2 Cu (Organic) + 2H + (Aqueous)

6 6 Figure 1: Generalized Metal Recovery Flowsheet Incorporating Solvent Extraction with BASF Reagents. Recycled Leach Solution Metal Leaching Stripped LIX Reagent Aqueous Strip Solution Metal Extraction Metal Stripping Pure Metal Product Each mixer-settler represents one stage of extraction or stripping. In conventional circuit flowsheets, E1 designates the stage into which the PLS is introduced and S1 designates the stage into which the loaded organic is introduced. In some cases, wash or scrub stages may be required to prevent or reduce the transfer of unwanted species on the organic phase from extraction to strip or vice versa. The combination of proper reagent choice, ability to use a variable number of mixer-settler stages, adjust flow rates, and use of wash stages allows a great deal of flexibility in designing a plant to meet the requirements for a given metal recovery problem. Impure Metal Leach Solution Leaching Process Metal Loaded LIX Solvent Extraction Reagent Concentrated & Purified Metal Solution Final Metal Recovery To develop a successful flow sheet for the recovery of a metal, it is important to know the composition of the aqueous feed solution in terms of the metal species and other species including anions that are present. With respect to metals, the extractable species can be classified into 4 types: Figure 2: Copper Continuous Solvent Extraction Unit 1. Metal cations, for example Cu 2+, Ni 2+, Co 2+, Zn Complex metal anions such as UO 2 (SO 4 ) 3 4-, Mo 8 O 26 4-, H 2 V 6 O 17 2-, CoCl Complex metal cations such as MoO Neutral metal species such as UO 2 (NO 3 ) 2 E1 Partially Loaded Organic E2 PLS Raffinate Surge Tank Loaded Organic S1 Barren Organic S2 Pregnant Strip Soln Lean Strip Soln

7 7 The metal species listed above have all been recovered commercially in solvent extraction plants at one time or another. It represents only a small sample of the many extractable chemical species that may be present. Metal extractants are divided up into five separate classes dependent upon the structure of the extractant, the mechanism of extraction and nature of the metal species extracted: Chelating extractants. Ion pairing extractants. Organic acids. Extractants that function by ligand substitution. Extractants that function by solvation. BASF markets chelating reagents and ion pairing reagents. Chelating reagents function by forming chemical bonds with a cationic metal ion at two sites similar to grasping an object between the ends of one s thumb and index finger. The LIX reagents based on the phenolic oximes are examples of chelating reagents. Ion pairing extractants function by forming an organic soluble ion pair between an organic soluble cationic species and a complex anionic metal species. The Alamine and Aliquat reagents are examples of ion pairing extractants. The Alamine reagents are based on tertiary amines having long alkyl chains. They accept a proton from acid solutions to form a cationic ammonium ion which can then pair with an anion in the organic phase. Aliquat reagents are based on quaternary amine salts. The Aliquat reagents function similarly to the Alamine reagents; the difference being that the quaternary amine is always positively charged. Since there is no need to form a cation by protonation, the Aliquat reagents can also extract anionic species from alkaline aqueous solutions. Successful reagent selection requires matching the chemical characteristics of the extractant with those of the metal species present in the incoming aqueous feed solution. While chemists have identified metal extractants for carrying out chemical separations of just about all metals in one form or another, the number of extractants available to carry out commercially viable large scale metal recovery processes is relatively small. In order to be commercially successful, a metal extractant must meet the following criteria at least in part: 1. Have a cost conducive to good process economics. 2. Extract the desired metal(s) with some degree of selectivity from the aqueous feed solution. 3. Strip the metal values from the loaded organic into an aqueous solution which facilitates final metal recovery. 4. Be stable to the operating conditions through many cycles of extraction and stripping. 5. Load and strip metal at a rate fast enough to permit use of economical mixing times. 6. Exhibit good phase separation properties. 7. Be nonflammable with low toxicity, non-carcinogenic, etc. 8. Soluble both as the extractant and as the metal complex in an inexpensive organic diluent. 9. Avoid transfer of species from stripping to extraction that might interfere with extraction. While no extractant meets 100 % of each of these criteria, successful reagents possess a good balance of all the properties in the list. BASF reagents possess this balance of properties. Reagent selectivity is often an issue. Very few, if any, extractants demonstrate selectivity for only one metal over a broad range of conditions. Many extractants, however, are reasonably selective for one metal over another under a certain set of conditions. The selectivity is dependent on the conditions and the challenge is to match the conditions associated with the given leach solution with the selectivity characteristics of the available reagents. A perfect match is seldom achieved. One either settles for a reagent that performs reasonably well or one tries to alter the leaching process to produce a leach solution which will allow an extractant to be more selective. To do this successfully, one needs a very good understanding of the chemistry of the leaching process as well as the chemistry of the extraction process. A BASF technical representative can help to provide the necessary understanding of the chemistry.

8 8 3. Copper Extraction from Acidic Sulfate Solution 3.1 Chemistry of Copper Extraction All modern commercial copper solvent extraction reagents are based on phenolic oxime type molecules. They can be classified into two general types, aldoximes and ketoxime. H H In the process of forming a complex, two hydrogen ions are released into the aqueous solution for every copper ion that is extracted. The chemistry is summarized in the following equation where RH represents the extractant (Formula 1). H O N O H O N O H O H R O N H CH 3 Cu N O R R R H O H R Aldoxime Ketoxime C 9 H 19 C9 Aldoxime, 5-Nonylsalicylaldoxime Ketoxime, 5-Nonyl-2- hydroxyacetophenone Oxime A key parameter in controlling the equilibrium position of this reaction is the acid content of the aqueous phase. Low concentrations of acid in the aqueous favor extraction and high acid concentrations favor stripping. This behavior can be represented graphically as a ph isotherm. Typical ph isotherms for ketoxime and C9 aldoxime are represented in Figures 1 and 2. Figure 1: ph Isotherms for Several Metals with Ketoxime C 12 H 25 C12 Aldoxime, 5-Dodecylsalicylaldoxime Cu Mo Ni Co They form a complex (I) with copper by loss of the phenolic hydrogen as a proton and formation of chemical bonds from the phenolic oxygen (dark red) to the copper ion and from the nitrogen (dark blue) of the oxime to the copper ion. The complex is very non-polar and hydrocarbon soluble. They belong to a group of molecules described as bidentate chelating agents since they grasp the copper ion between the two sites in a pincer like fashion. The R group is typically a highly branched hydrocarbon chain consisting of either 9 or 12 carbon atoms. Extraction % Fe 3+ Mn ph Zn Formula 1 Extract 2RH (Organic) + Cu +2 (Aqueous) Strip R 2 Cu (Organic) + 2H + (Aqueous)

9 9 These ph isotherms can be used to predict the extraction characteristics of a reagent under a variety of conditions. For example, it is apparent that copper(ii) is strongly extracted by both reagents at a ph of 2.0 and that the C9 aldoxime extracts copper(ii) more strongly than the ketoxime. Ferric iron at a ph of 2.0 is only slightly extracted and nickel(ii), cobalt(ii), zinc(ii) and manganese(ii) are not extracted. With the ketoxime at a ph of 5.0, copper(ii), iron(iii), nickel(ii) and cobalt(ii) are all potentially strongly extracted. From a practical standpoint, extraction of iron(iii) at a ph of 5.0 is not important since iron(iii) is only slightly soluble at a ph of 5.0. Figure 2: ph Isotherms for Several Metals with C9 Aldoxime any extracted Mo(VI) can be removed from the organic if necessary. In most cases, only Fe(III) presents a potential problem with regard to preparing a pure copper solution from a normal copper leach solution at ph = 2.0 in agreement with the ph isotherms in Figures 1 and 2. Table 1: Relative Extraction Power of Ketoxime and Aldoxime for Metals at ph Cu Ni Metal Relative Extractive Power 80 Mo Co Zn Cu(II) Very strongly extracted Extraction % Fe(III) Mo(VI) 1) Slightly extracted Moderately extracted 20 0 Fe Mn V(V) 1) Zn(II) Sn(II) Slightly extracted Nil Nil ph Ca(II) Nil From a comparison of Figures 1 and 2, one can conclude that the C9 aldoxime extracts all of the metals with the exception of manganese(ii) more strongly than does the ketoxime. In making comparisons of ph isotherms for two different reagents with the same metal or for two different metals with the same reagent, the ph isotherms must be determined under exactly the same conditions. A summary of the general relative extraction behavior for a wide range of metals with ketoxime and C9 aldoxime is summarized in Table 1. Mg(II) As(III) Al(III) Fe(II) Nil Nil Nil Nil While the data in Figures 1 and 2 suggest that Mo(VI) could be a problem in a copper solvent extraction circuit using either a ketoxime, an aldoxime, a blend of a ketoxime with an aldoxime or a modified aldoxime. It typically is not a problem for two reasons. Copper is more strongly extracted than Mo(VI) by the oximes and readily displaces any extracted Mo(VI) from the organic. If excess copper is present, Mo(VI) will not be significantly extracted. Even if Mo(VI) is extracted by the oximes, it is not readily stripped by an aqueous solution of sulfuric acid and is therefore not transferred to the copper electrolyte. In addition, Mo(VI) strips readily on the alkaline side so Si(IV) Nil Co(II) Nil Ni(II) Nil Mn(II) Nil 1) The chemistry of Mo(VI) and V(V) on the acid side is quite complex. They do not normally present a problem in copper solvent extraction circuits.

10 10 Consideration of extraction isotherms and selectivity data allow the metallurgist to develop metal separation schemes. Where such data is not available for a particular system, one can develop the required information by screening the reagent against the metals most likely to be found in the aqueous feed solutions of interest under conditions similar to those expected in the solvent extraction process. The resultant selectivity data holds only at the conditions under which it is determined. Small changes in the test conditions can result in significant shifts in the extraction isotherms and selectivity. These conditions include: The nature of the reagent. The nature of the anions present in the aqueous solution. The metal and reagent concentrations. The oxidation state of the metal. The ph of the aqueous feed solution. The temperature at which extraction occurs. The organic-aqueous contact time. Modern metallurgists have a broad spectrum of copper extractant formulations based on the aldoximes and ketoxime available to aid them in developing effective recovery schemes for copper from a broad range of leach solutions. As can be seen from a comparison of the Cu ph isotherms in Figures 1 and 2, the aldoximes by themselves are much stronger copper extractants than is the ketoxime. While their extractive strength is a potential advantage, it is also a problem. The aldoximes do not readily give up the extracted copper when contacted with typical lean electrolyte solutions that are generated by standard copper tank house operations. As a result, only a relatively small percentage of the overall loading capacity is utilized in the transfer of copper from extraction to stripping (Net Transfer). Figure 3: Effect of Increasing LIX 84-I Content on Stripping of Cu and Cu Net Transfer with Non-modified Aldoxime / Ketoxime Blends* Cu Conc (g / L) Net Transfer@ ph 2.0 Increasing Ketoxime Content: Weaker Extractant, More readily Stripped, Higher Net Transfer Net Transfer@ ph 1.5 Stripped Organic LIX 860N-I LIX 973N LIX 984N LIX 937N LIX 84-I * Solutions of the reagents were prepared in a hydrocarbon diluent and the concentrations adjusted to give a Cu max load of 5.6 g/l copper under the conditions of the BASF Oxime QC procedure. The organics were then contacted twice with an aqueous strip solution containing 35 g/l Cu and 160 g/l sulfuric acid at an O/A =1 by shaking for 15 minutes. The resultant stripped organics were assayed for copper content and then contacted with aqueous solutions containing 6 g/l Cu at ph s of 2.0 and 1.5 at an O/A = 1 by shaking for 15 minutes to yield loaded organics. The copper contents of the loaded organics were determined. The Cu Net Transfer was then determined by subtracting the copper concentration of the stripped organic from that of the corresponding loaded organic. Table 2: Proportions of LIX 84-I and LIX 860N-I in Standard Non-modified Reagents Two approaches have been utilized to increase the net transfer of reagents formulated with aldoximes. One approach is to combine the aldoxime, either C9 or C12, with ketoxime. The aldoxime and ketoxime form a synergistic mixture, i.e. the combination strips more readily than one would expect based on a simple combination of the properties of the two components 1,2. Blending the two components results in no significant impact on copper loading capacity in extraction while greatly improving stripping. This translates into an increase in copper net transfer capability relative to an aldoxime by itself. As illustrated in Figure 3 and Table 2, increasing the proportion of ketoxime relative to aldoxime results in increased ease of stripping (lower residual copper on the stripped organic) consistent with a decrease in extractive strength. The decrease in extractive strength is also reflected in the fact that the net transfer capability falls off faster as the acid concentration increases (lower ph). Reagent % v/v LIX 84-I % v/v LIX 860N-I LIX 84-I 1) LIX 937N LIX 984N LIX 973N LIX 860N-I 2) ) Ketoxime dissolved in a hydrocarbon diluent. 2) C9 aldoxime dissolved in a hydrocarbon diluent.

11 11 By blending the aldoxime and ketoxime in varying proportions, BASF Mining Solutions can tailor a reagent to fit the specific extraction and stripping requirements of a particular application. Formulations consisting of mixtures of an aldoxime with ketoxime are classified as non-modified reagents or blends. Figure 4: Effect of Increasing Ester Modifier Content on Stripping of Cu and Cu Net Transfer with Modified Aldoxime Reagents* Net Transfer@ ph 2.0 The second approach takes advantage of the fact that the aldoxime will form complexes by hydrogen bonding with a wide variety of chemical compounds 3,4. The most commonly used classes of compounds in commercial formulations are alkyl phenols as well as higher molecular weight alcohols and esters. These materials are commonly referred to as thermodynamic modifiers in this application. Increasing the relative amount of the thermodynamic modifier results in a shift in performance similar to that observed with the ketoxime as illustrated in Figure 4 where LIX 860N-I represents no modifier and Increasing Ester Content: the level of modifier, an ester, increases as one progresses from LIX 0.5 Weaker Extractant, More readily Stripped, Higher Net Transfer 654N-LV to LIX 684N-LV, the most heavily modified formulation in the series. Formulations consisting of a mixture of a thermodynamic modifier with an aldoxime are classified as modified reagents or 0 LIX 860N-I LIX 654N-LV LIX 664N-LV modified aldoximes. * Procedure was identical to that described for Figure 3. Cu Conc (g / L) 4 Net Transfer@ ph 1.5 Stripped Organic LIX 674N-LV LIX 684N-LV Table 3: Comparison of Properties for Reagents based on Ketoximes, Aldoximes, Non-modified Blends and Modified Aldoximes Property Ketoxime Aldoxime Non-Modified Blend Modified Aldoxime Extractive Strength Moderate Very Strong Customized Customized Stripping Very Good Poor Customized Customized Cu / Fe Selectivity Excellent Excellent Excellent Excellent Extraction Kinetics Very Good Very Fast Fast Very Fast 1) Phase Separation Fast Fast Fast Fast Stability Very Good Very Good Very Good Very Good 2) Crud Generation 3) Low Low Low Variable 4) 1) Formulations based on C9 aldoximes tend to be slightly faster than those based on C-12 aldoxime. 2) Dependent on the particular thermodynamic modifier used in the formulation. 3) Dependent on the composition of the leach liquor and the modifier. 4) In many cases, the presence of thermodynamic modifiers increases crud formation.

12 12 One can also blend thermodynamic modifiers with mixtures of aldoxime with ketoxime to form a third class of extractant formulations, modified aldoxime / ketoxime blends. BASF Mining Solutions has the capability of offering all three classes of extractant formulations. A general comparison of the copper extraction characteristics of ketoxime, aldoximes, non-modified blends and modified aldoximes is summarized in Table 3. Presents the operators of copper solvent extraction plants with a wide choice of reagents from which to choose. The availability of: Pure aldoxime based extraction reagents LIX 860-I, a C12 aldoxime based formulation and LIX 860N-I, a C9 aldoxime based formulation Modified aldoxime reagents LIX 622N, and the ester based series: LIX 654N-LV, LIX 664N-LV, LIX 674N-LV and LIX 684N-LV Pure ketoxime based extraction reagents LIX 84-I and LIX 8180 Non-modified aldoxime / ketoxime blends LIX 973N, LIX 984N, and LIX 937N Modified aldoxime / ketoxime blends LIX 1552N-LV Since ketoxime based reagents are moderately strong copper extractants, they operate best when the ph of the leach solution is relatively high (above ph 1.8) and the solution is relatively warm (20 C or higher). Since they strip very well, they can effectively be used with only one strip stage and they can be used efficiently when the amount of acid in the lean electrolyte exiting the copper tank house is relatively low (less than 160 g/l H 2 SO 4 ). They have also been effectively used in cases where the leach solution contains nitrate which will degrade modified aldoximes 5. Modified aldoxime reagents have excellent metallurgical properties even at low temperatures, low ph s or when the copper content of the leach liquor is very high and high copper recoveries are needed. However, in many cases, the use of a modified aldoxime formulation carries with it higher entrainment rates and / or greater crud generation resulting in increased carryover of impurities to the electrolyte and higher reagent consumption per ton of copper produced 6,7,8. The non-modified aldoxime / ketoxime mixtures also operate well at lower ph s, lower temperatures, and with leach liquors having a higher copper content. They tend to be slightly slower kinetically at lower temperatures depending on the ketoxime content of the formulation as compared to modified aldoxime formulations. They also tend to be slightly less selective for copper over iron as compared to an ester modified aldoxime formulation. In terms of physical performance under a wide variety of conditions, they tend to give more stable mixer continuities, lower entrainment of aqueous in the loaded organic and generate less crud than modified aldoxime formulations. Some of these physical advantages can be attributed to the fact that these reagents are the lowest density and lowest viscosity copper solvent extraction reagents available. Clearly there is not a single reagent of choice for the extraction of copper from sulfuric acid leach liquors. Your BASF Mining Solutions technical representative can help you decide on the best reagent for your needs.

13 Development of a Cu SX Process Flow Sheet Factors for Consideration When developing a process for recovery of copper by solvent extraction, there are a number of factors to consider: Type of leach and nature of the ore Composition of the pregnant leach solution Nature of the final copper product and process required to produce it Operational philosophy The primary commercial application for modern phenolic oxime based copper solvent extraction reagents has been recovery of copper from dilute sulfuric acid leach solutions. These solutions result from leaching of copper oxide and / or secondary sulfide ores using various leaching technologies including dump, heap, in-situ, thin layer, vat, and agitation 1,2,3. The choice of methodology is dependent on the nature of the ore and the ore grade. A variety of technologies are currently being investigated for the leaching of primary copper sulfide concentrates 4,5,6,7. Since leaching is a critical step in the overall process of Leach-SX-EW, BASF strongly recommends that one thoroughly investigate the leaching characteristics of their ore 8,9,10,11. If you cannot bring the copper into solution effectively, it cannot be extracted. Money spent on up front leaching studies typically proves to be a wise investment. Depending on the leaching technology and ore grade, pregnant leach solutions may contain from less than 1 g/l copper up to about 50 g/l of copper over a ph range of < 1.0 to 3.0. the composition of typical sulfuric acid leach solutions that have been treated by solvent extraction are summarized in Table 1. Table 1: Typical Sulfuric Acid Leach Solutions Leach Type Cu (g/l) ph Dump, Heap, In-situ < 1 to to 2.2 Ferric Cure, Thin Layer 3 to to 2.2 Vat 5 to to 2.0 Agitation 1 to to 2.0 Concentrate 25 to 80 < 1.0 to > 2.0 In addition to copper, leach solutions may contain other metals such as iron (ferric and ferrous), molybdenum, manganese, aluminum, magnesium, sodium, and potassium. In addition to sulfate, it may contain anions such as chloride and nitrate. The concentration of these impurities will vary widely depending on the ore, available water sources and evaporation rate. Certain ore bodies in Chile contain nitrate. Since nitrate is readily leached, the concentration of nitrate in the resultant leach solutions may be up to g/l. Due to the lack of fresh water, some operations successfully operate using sea water for leaching resulting in up to 90 g/l of chloride in the leach solution. While the presence of nitrate and chloride can cause problems in SX- EW, methods have been developed to successfully deal with them 12. The nature of the leach, the ore type and climatic conditions may play a role in the temperature of the pregnant leach solution delivered to solvent extraction which in turn will determine the operating temperatures in extraction and stripping. A typical heap leach solution will range in temperature from about 20 C to about 30 C but may drop to C during harsh winter conditions and / or high elevations. Colder temperatures will shift the extraction equilibrium to the left (weaker extraction), affect the extraction kinetics and the solution viscosities impacting overall extraction efficiencies and physical performance of the extraction circuit. Vat, agitation and concentrate leach solutions can be quite warm resulting in temperatures in extraction of up to 45 C. While the higher temperatures will result in shifting the extraction isotherm to the left 13, increasing kinetics and lowering solution viscosities, hydrolytic degradation of the reagent may become more of an issue depending on reagent type. Copper is typically recovered as copper cathode but has also been recovered as copper sulfate crystal 14,15,16. Most copper EW tank houses which produce high quality copper cathode operate so that the lean electrolyte exiting the cell contains from 32 to 40 g/l of copper and 150 to 185 g/l of sulfuric acid. Improvements in technology have allowed current densities to be increased from about 160 amps/m 2 to well over 400 amps/m 2 in today s modern tank houses. To insure high copper quality at these high current densities, the level of copper in the electrolyte exiting the cells is typically maintained at levels greater than 35 g/l of copper and at times greater than 40 g/l of copper. Based on experience in some tank houses, slightly higher quality copper is obtained when plating from sulfuric acid concentrations at the lower end of the acid concentration range 17. The tank house parameters in terms of copper and acid in the exiting spent electrolyte and incoming rich electrolyte are determined in part by the operating philosophy of the plant manager. These parameters combined with the strip staging and nature of the oxime copper extractant will impact how completely the loaded organic is stripped and how much free reagent will be available to carry out extraction.

14 14 Along with the evolutions in leaching technologies, reagent technologies and tank house operations, there have been significant developments in the understanding of the interaction of reagent and circuit staging which can result in lower costs and more efficient copper production 18,19,20,21. A listing of circuit configurations that have been used in commercial operations over the years is summarized in Table 2. Table 2: Commercial Solvent Extraction Circuit Configurations Circuit Type Configuration* Stages per Train Series 4E x 3S 7 Series 4E x 2S 6 Series 3E x 2S 5 Series 2E x 2S 4 Series 2E x 1S 3 1E x 1S 2 Series Parallel 2E x 1EP x 1S 4 Series Parallel 2E x 1EP x 2S 5 Cross Flow 1E x 1EP x 1EP x 1S 4 them to use a series parallel flow scheme or some other combination of stages to be able to treat the required additional flow. Making allowance for potential plant alterations during the planning stages will provide the plant with the flexibility to meet future requirements 27. When treating a leach solution containing significant amounts of chloride, nitrate, iron, or manganese, the addition of a loaded organic wash stage should also be considered to minimize the transfer of these impurities to the tank house 28. BASF Mining Solutions produces three oximes, C9 aldoxime (LIX 860N-I), C12 aldoxime (LIX 860-I) and ketoxime (LIX 84-I), which serve as the basis for formulation of a wide range of modified and non-modified copper extractants. Deciding on the best reagent choice for a given application requires having an understanding of the inherent properties of these oximes 29,30. For example in circuits operating at higher temperatures in extraction, one might want to use LIX 84-I, mixtures of LIX 84-I with LIX 860-I or a modified C12 aldoxime to take advantage of their stability. The relative stability of the oximes is: ketoxime > C12 aldoxime > C9 aldoxime. When dealing with a leach solution containing nitrate, LIX 84-I has proven to be the most resistant to degradation. In cases where one is faced with a leach solution containing high levels of copper, recovery will be limited by the corresponding increase in acid concentration in the aqueous as the copper is extracted. The logical choice would be a reagent formulation containing higher levels of an aldoxime or a less modified aldoxime. Work has shown however that a combination of a weaker extractant such as LIX 84-I in a circuit having 3 stages of extraction in series and 1 strip stage can also be effectively used 31,32. When considering reagent choices, contact your local BASF Mining Solutions technical representative who has the knowledge of the reagents and experience to assist you in making the best reagent selection for your individual application. * E represents extraction stage, EP refers to a parallel extraction stage, and S refers to a strip stage Figure 1: Sequential Circuit The most common circuit configurations in use today are 2E x 2S, 2E x 1S, and 2E x 1EP x 1S. More recent developments include the use of the Split Circuit concept and Sequential Circuit (Figure 1) concept to reduce acid consumption and increase copper recoveries in agitation leach circuits 22,23,24,25,26. While many plants opt to employ a simple circuit consisting of 2 stages of extraction in series and 1 or 2 stages of stripping in series to minimize capital cost, they may find their production capacity limited at some point as the grade of the incoming pregnant leach solution declines due to a drop in ore grade. To maintain production, they must be able to treat more leach solution. This may require modifying the piping or adding additional extraction stages to allow Acid Milled Ore Solids Water Leach 1 S/L 1 Leach 2 SX 1 CCD S/L 2 SX 3 SX 2 Tails Co Recovery Neut Tails

15 Laboratory Development of an SX Circuit Given a pregnant leach solution (PLS), how does one develop a process for recovering the metals of interest? The first step is to determine if the solution is typical of what would be expected in normal operation. Work carried out on a non-typical solution is often wasted effort. The composition of the solution with regard to metals, metal concentration, ph, presence of ammonia and its concentration, presence of chloride or nitrate and their concentrations, etc., must be determined. Given the composition, one can then begin to make judgments with regard to which metals can be separated based on available extraction isotherms. If the data for some of the metals is not available, the extractant(s) being considered should be screened against these metals. Given this information, one can then determine a strategy for recovering commercially viable metals by solvent extraction under the given set of conditions. With this background, circuit development work can now begin keeping in mind that all parts of the total metal recovery process must fit together in a workable manner. As an example, consider development of a copper solvent extraction circuit to treat a copper heap leach solution containing 2.5 g/l of Cu and 1.30 g/l of total Fe at a ph of Assume also that you want a copper recovery of 90 %. Extraction and Strip Isotherms While a variety of extractants can be used, LIX 984N, a widely used non-modified blend of aldoxime and ketoxime, is particularly well suited to treat the leach solution under discussion. Based on previous experience with similar solutions, one can expect LIX 984N to transfer g/l Cu per 1 % v/v in a circuit consisting of 2 stages of extraction and 1 stage of stripping, a common choice in modern plants. Since the ph is 1.80, we will assume that the copper transfer will be somewhere in the middle to lower end of the range (0.26 g/l of copper/1 % v/v LIX 984N). Using the following equation, one can then calculate the approximate reagent concentration required to meet the stated goal of 90 % recovery. Equation 1 [2.50 g/l Cu x (0.90)] / 0.26 g/l Cu per % v/v = 8.7 % v/v LIX 984N To determine the extraction and strip isotherms, a solution containing 8.7 % v/v LIX 984N was prepared in a suitable diluent and used in a series of shakeouts with the leach solution and the expected strip solution. The organic was first contacted at an organic to aqueous volume ratio (O/A) of about 1 with the leach solution by vigorous shaking in a separatory funnel for about 3 minutes. The aqueous phase is discarded after the phases have separated. A portion of the resultant copper loaded organic (LO) is then contacted with vigorous shaking three times with fresh rich electrolyte (RE) at an O/A = 1. Rich electrolyte is the aqueous acid strip solution that is expected to exit the strip stage. In this exercise, we will assume that the RE contains 50 g/l Cu and 160 g/l of sulfuric acid. The resultant organic will closely approximate a stripped organic (SO) one would expect to generate in a continuous circuit having one strip stage. This process serves not only to generate a SO for the isotherm determination but also serves to wash out any low molecular weight impurities from the manufacturing process. The extraction isotherm is then determined as follows: Vigorously contact the freshly prepared SO with leach solution for 3 10 minutes at various O/A ratios (Typically 10/1 to 1/5). Typically requires 6 7 points for a good isotherm. Contacting can be carried out in separatory funnels or by stirring in BASF QC mixer boxes. (When using separatory funnels, longer contact times are recommended to insure that true equilibrium is achieved.) If the temperature in extraction is expected to be warm due to the temperature of the incoming leach solution, contacting should be carried out in jacketed vessels at the expected temperature and samples of organic and aqueous must be collected at the expected temperature. For further information, contact your BASF technical representative. After allowing the phases to separate, samples of the respective organic and aqueous samples are collected, filtered and saved for analysis. The organic is analyzed for copper (and perhaps iron) while the aqueous is analyzed solely for copper. The data is summarized in Table 1 and is plotted in Figure 1. Accurate measurement of the organic and aqueous volumes used for each shakeout will allow one to calculate a mass balance for each point. Mass balances should be very good for O/A ratios in the range of 5:1 to 1:5. If the mass balance is poor for one point, the retained samples corresponding to that shakeout should be re-analyzed. Mass balances at the extremes of O/A (10/1, 1/10) are typically less precise. For copper extraction with a phenolic oxime type extractant, the plot should result in a smooth curve similar to that shown in Figure 1. One should also check how the various points are distributed along the curve. For the best results, it is important to carefully define the area around the bow in the curve as accurately as possible. If need be, additional shakeouts might be required at O/A ratios that will generate points in the desired area of the curve. These samples should be analyzed in a block along with the previous samples to eliminate analytical variations.

16 16 Figure 1: Extraction Isotherm Figure 2: Strip Isotherm Organic g/l Copper Aqueous g/l Copper Aqueous g/l Copper Organic g/l Copper Table 1: Equilibrium Isotherm Extraction Data Table 2: Equilibrium Isotherm Stripping Data O/A Organic (g/l Cu) Aqueous (g/l Cu) O/A Organic (g/l Cu) Aqueous (g/l Cu) 10/ / / / / / / SO / / / / / / LO 3.90 SE 30.7 Leach Solution 2.50

17 17 The strip isotherm is then determined as follows: LO is contacted at various O/A s (Typically 10/1 to 1/4) with a typical copper electrolyte from an electrowinning tankhouse. This is known as strip electrolyte (SE) or lean electrolyte (LE). In our example, we have taken a LE containing 30.7 g/l Cu and 190 g/l sulfuric acid. The organic and aqueous phase are contacted by vigorous shaking or mixing. The temperature in stripping is typically higher than in extraction, C, so contacts should be carried out in temperature controlled jacketed vessels. After equilibration, the phases are allowed to settle, samples of each phase taken and filtered, and then analyzed for copper. The data is summarized in Table 2 and plotted in Figure 2. Isotherms are specific for the conditions under which they are determined. Changing one of the parameters, i.e., the reagent concentration, the copper concentration of the aqueous phase, the ph of the leach solution, the acid concentration of the strip solution, temperature 1, etc., will result in a different isotherm. In most cases, small changes in one or two of the parameters result in such small changes that it would not necessitate generating a second isotherm. McCabe-Thiele Diagrams Properly generated extraction and stripping isotherms represent equilibrium conditions and, as such, predict the best extraction and stripping which can be obtained. These isotherms can be used to establish the performance that can be expected with a given staging. As an example, consider the extraction isotherm in Figure 1 and assume: steps representing the staging. Draw a horizontal line from the point where the operating line intersects the vertical leach solution line to the extraction isotherm and then draw a vertical line down from the intersection point of the horizontal line with the isotherm to the operating line creating a step. Repeat the process by adding another horizontal line and another vertical line as illustrated in Figure 3 to create a second step which completes the McCabe-Thiele diagram for a two stage extraction circuit. Each step represents a single stage of extraction. This diagram would predict that it is possible to achieve a raffinate of 0.22 g/l of Cu and a LO containing 4.30 g/l of Cu (Figure 3) with two stages of extraction. Figure 3 does not represent a McCabe-Thiele diagram at true equilibrium. If the diagram represented true equilibrium, the operating line would intersect with the SO line and the isotherm line at the point where the isotherm line intersects the SO line. The construction of a McCabe-Thiele diagram at true equilibrium is an iterative process. Assuming that the O/A flow ratio remains unchanged, one would draw a new operating line parallel to the first operating line starting from a point approximately one half the distance from the isotherm line to the raffinate line. One would then draw in the steps as described above. In this particular case, the second iteration step is all that is required to produce a McCabe-Thiele diagram (Figure 4) that is essentially at equililbrium. It predicts a raffinate of 0.15 g/l of Cu and a LO of 4.17 g/l of Cu. Figure 3: McCabe-Thiele Extraction Isotherm First Approximation The SO entering the last extraction stage contains 1.80 g/l Cu. The leach solution contains 2.50 g/l of Cu. The advance flow rates of both SO and leach solution are equal (O/A = 1). Draw a horizontal line which intercepts the Y axis at 1.80 g/l Cu representing the Cu content of the stripped organic and then a vertical line intercepting the X axis at 2.50 g/l of Cu representing the Cu content of the aqueous leach solution. Next add the operating line. The operating line has a slope which is the inverse of the organic / aqueous flow rate. In this case, the slope of the operating line is 1. Add the operating line by drawing a line with a slope of 1 from the point where the extraction isotherm intersects the horizontal SO line until it intersects the vertical line representing the copper content of the leach solution. One can then begin to draw in the Organic g/l Copper LO Raff. = 0.22 SO Aqueous g/l Copper Feed = 2.50 g/l Cu

18 18 Figure 4: McCabe-Thiele Extraction Isotherm Iterative Process Organic g/l Copper 5.0 LO SO Feed = 2.50 g/l Cu A line vertical to the x axis is drawn representing the LO. A vertical line is then drawn from the y axis at 51 g/l of Cu representing the RE to intersect with the LO line. A vertical line is then dropped from the point where the RE line intersects the strip isotherm line to the x axis. This line represents the expected SO (1.77 g/l Cu). A third line is then added representing the SE. The operating line is then drawn from the point where the SO line intersects the SE line to the intersection points of the LO and RE lines. This is the operating line. (See Figure 5) The slope of the operating line (20.3 / 2.13 = 9.50) is equal to the ratio of the advance organic flow to advance aqueous flow needed across stripping to obtain the desired RE. A two stage McCabe-Thiele strip diagram is constructed in a fashion similar to that described for the two stage McCabe-Thiele extraction diagram. It predicts a SO of 1.12 g/l of Cu when building a RE of 51 g/l of Cu and operating at an O/A flow ratio of 7.3/1. Raff. = 0.15 Aqueous g/l Copper Number of Extraction / Strip Stages Required The construction of an equilibrium McCabe-Thiele diagram for one stage of stripping is very simple. Consider the stripping isotherm in Figure 2 and assume: The LO contains 3.90 g/l of Cu. The desired rich electrolyte (RE) contains 51 g/l of Cu. The strip electrolyte (SE) contains 30.7 g/l of Cu. Figure 5: McCabe-Thiele Strip Isotherm Single Stage Aqueous g/l Copper RE SO = Organic g/l Copper SE Loaded Organic = 3.90 g/l Cu An important decision in developing a design for an SX plant is to decide on the staging requirements. The capital cost of a stage must be weighed against the potential benefits that the stage provides. Consider the use of one stage of stripping versus two stages of stripping in the example above: Two strip stages will give a SO containing 1.12 g/l of Cu which will translate into a net copper transfer on the organic of 2.78 g/l of copper (LO = 3.90 g/l Cu minus SO = 1.12 g/l Cu). One strip stage will give a SO containing 1.77 g/l of Cu which in turn leads to a net copper transfer of 2.13 g/l Cu. Due to differences in net copper transfer, a circuit operating with one strip stage will require a reagent concentration approximately 1.3 times higher than in the case of a circuit with two strip stages in order to achieve equivalent performance in terms of copper recovery in extraction. The expected reagent losses will be about 1.3 times higher for the 1 strip stage plant as compared to the 2 strip stage plant. Comparison of the capital costs for the additional strip stage versus the increased operating costs due to the increased reagent usage allow one to make a purely economic decision on the strip stage requirements. The increased reagent concentration needed with one strip stage compared to having two strip stages will depend on the nature of the leach liquor, the desired copper recovery and the particular reagent under consideration.

19 19 Continuous Copper SX Circuit With the development of modern reagent technology, most companies elect to treat dump leach liquors in SX plants consisting of two stages of extraction and one stage of stripping (2E-1S plants). To determine how such a plant might actually function, a 2E-1S circuit was set up in the laboratory and operated at the advance O/A determined in the McCabe-Thiele diagrams in Figure 4 and Figure 5. A mixer retention time of 2.6 minutes was selected simply because most copper SX plants operate with 2 3 minutes of mixer retention depending on the leach solution conditions, the mixer design, and the company operating philosophy. To achieve good metallurgical results and maximize the amount of information collected, several things are important: Flow rates must be accurately set and continually monitored. Small changes result in fluctuations in the circuit performance requiring additional time to achieve equilibrium. Proper mixing requires that mixer dispersions be maintained at an O/A near 1. Recycles should be employed where necessary to maintain the appropriate mixer dispersions. Mixer turbines must turn fast enough to maintain good mixing and pumping action but slow enough to avoid causing heavy entrainment. The circuit should be sampled frequently and the samples must be rapidly and accurately analyzed shortly after collection. This allows the operator to closely monitor the circuit and observe changes in circuit behavior as operating parameters are changed. After changes in an operating parameter, the circuit should be allowed to run until overall equilibrium is once again achieved. A circuit is at equilibrium when there is a good metal balance and a good metal-acid balance across the whole circuit as well as across each stage: At equilibrium in extraction, the metal extracted from the aqueous phase in an extraction stage in a given amount of time is equal to the acid equivalent gained by that same aqueous phase in the given amount of time and the amount of metal loaded by the organic in that stage in the same given amount of time. At equilibrium in stripping, the metal stripped from the organic phase in a given amount of time is equal to the metal gained and the acid equivalent lost by the strip aqueous phase in that stage in the same given amount of time. When at equilibrium, the analysis for copper and acid do not change as the circuit runs so long as the flows, the composition of the leach solution, the composition of the SE, and the nature of the organic phase do not change. In order to balance metal and acid values, accurate solution analyses and solution flow rates have to be known. In addition, solution samples should be taken from the rear of the respective settler for that stage. When possible, it is best to pull the samples at those points easiest to access and least likely to upset the circuit. The circuit behavior will reflect the interdependence of the extraction and stripping operations. For example, a loss of stripping efficiency will result in a higher copper content on the stripped organic which in turn will result in less available reagent for extraction and which will lead to higher raffinates. To compensate for a loss in stripping efficiency, one must operate the circuit with either a slightly higher reagent concentration or a slightly higher organic to aqueous advance ratio in extraction in order to maintain copper recovery. Alternatively, one must accept a slightly lower copper recovery. Metal transfer in an extraction stage is typically between 85 % to 95 % of theoretical while metal transfer in a strip stage is usually > 95 % of theoretical in modern plants due to the improvements in mixer design. As a result, the values predicted by equilibrium McCabe-Thiele diagrams for the aqueous and organic phases exiting a given stage are seldom achieved in an operating plant. As an example, compare the organic and aqueous values predicted by the McCabe-Thiele diagram in Figure 3 with the values generated in a continuous laboratory circuit using the same aqueous feed solution, organic solution and SE solution (Table 3, Figure 6). The circuit achieved a raffinate of 0.28 g/l Cu and a loaded organic of 4.08 g/l Cu as compared to the raffinate of 0.22 g/l Cu and a loaded organic of 4.24 g/l Cu as predicted by the first iteration McCabe-Thiele extraction diagram (Figure 3). The stripped organic of 1.80 g/l Cu is close to the 1.77 g/l Cu predicted by the McCabe- Thiele strip diagram (Figure 5).

20 20 This brings up a critical point. If the circuit gives different results from those predicted by the McCabe-Thiele diagram at 100 % of equilibrium, why should one do all of the work required to generate the McCabe-Thiele diagram in the first place? There are a number of good reasons: Generating an isotherm helps to develop a feel for the system. The isotherm will usually reflect any unusual metallurgical behavior characteristics of the system. While not typically observed in Cu systems, the overall shape of the isotherm may be more S shaped than the smooth curve shown when extracting other species with extractants such as amines. For example, this may reflect changes in the nature of the extracted species depending on changes in the composition of the aqueous depending on degree of extraction. In addition, a good idea of the actual circuit results can be obtained by drawing in the operating line as previously described for Figure 3. Instead of drawing in the horizontal and vertical lines to represent 100 % of equilibrium, draw the horizontal lines in to represent only 95 % efficiency as shown in Figure 6. The resultant McCabe-Thiele two stage extraction diagram predicts a raffinate of 0.28 g/l Cu, a value identical to that achieved in the circuit run. The feed chosen for the above example is typical of the leach solution generated by many copper leach operations and represents one of the simplest feeds to treat. Copper recovery is very good, selectivity for copper over iron is high (A copper to iron of about 1,100/1 on a transfer basis was achieved in the circuit.) and there is little tramp metal contamination. More complicated feed solutions are evaluated in a similar fashion as described in the above example. The extraction and strip isotherms as well as the circuit staging can, however; be significantly more complex. With complex metal extraction systems, the initial circuit may have to be modified several times before the best recovery scheme is worked out. Figure 6: McCabe-Thiele Extraction Isotherm Circuit Data Organic g/l Copper 5.0 LO Table 3: Circuit Profile Data with 8.7 % v/v LIX 984N in Escaid 110 Sample Organic Aqueous Extraction Stage 1 Extraction Stage Raff. = 0.28 SO Aqueous g/l Copper g/l Cu g/l Fe g/l Cu g/l Fe Feed = 2.50 g/l Cu Strip Stage 1.80 N.D LE Aqueous Leach

21 21 4. Copper Extraction from Ammoniacal Solution The use of ammonia as a leaching agent for copper has been practiced on a commercial scale since the early 1900 s. In 1916, Kennecott Copper Company and Hecla Mining Company began to recover copper from gravity plant tailings using an ammoniacal leach. The copper was recovered as a copper oxide precipitate after stripping the ammonia from the solution with steam. Ammonia has been used to leach copper from native copper ores, copper oxide ores and copper sulfide ores including chalcopyrite 1,2,3. The use of ammonia for the leaching of copper from ores has a number of advantages: It is more selective. Metals such as iron and manganese are not soluble in the leach liquor. It can be used to treat ores containing high levels of acid consuming gang and is less corrosive than acid leach systems. It is also well suited for recovery of copper from secondary sources such as scrap copper wire, consumer electronics such as printed circuit boards, copper drosses, and smelter flue dusts 1,4,5,6. Due to the volatile nature of ammonia, leaching is typically carried out in closed vats to minimize ammonia losses 1,3. Recent developments in use of ammonia for heap leaching suggest that it may become practical as well 7. Increasing the ammonia concentration in the aqueous shifts the equilibrium to the right. Ammonia competes with the reagent for the metal ion. As illustrated by the ammonia isotherms, extraction decreases as the ammonia concentration increases. This suggests that under some circumstances one might be able to strip the metal from the loaded reagent with high concentrations of ammonia. The ammonia isotherms in Figure 1 show that copper(ii) is more strongly extracted from an ammoniacal solution than is nickel (II) suggesting that it should be possible to selectively extract copper away from the nickel. The feasibility of such a separation was demonstrated using LIX 65N 8. An alternative separation scheme is suggested by considering the LIX 84-I ammonia isotherms and ph isotherms. While copper and nickel are relatively strongly extracted from ammonia by LIX 84-I, the corresponding ph isotherms show that nickel is readily stripped at a ph of where copper is strongly extracted. Co-extraction of nickel and copper with the same organic stream followed by a ph controlled wash to remove small amounts of co-extracted ammonia and then selectively stripping the nickel and copper loaded organic using ph control to give a copper free, nickel-rich solution and a copper rich solution containing a small amount of nickel 9,10. Figure 1: Metal Extraction by LIX 84-I as a Function of Total Ammonia Concentration General Mills Mining Chemicals division (now a part of BASF Mining Solutions) demonstrated that copper could be extracted from ammoniacal leach solutions using LIX 63 and introduced it to the industry in LIX 63, an alpha hydroxy oxime, was quickly supplanted by LIX 65N, a hydroxy benzophenone oxime, which in turn has been replaced by LIX 84-I, a acetophenone oxime (Ketoxime). The variation in extractive behavior for LIX 84-I with copper, nickel and zinc as a function of total ammonia concentration is summarized in Figure 4. The general equation for extraction of a metal ion(m) in the +2 state from an ammoniacal solution with LIX 84-I (RH) is shown below (Formula 1). Metal Extraction ( %) Zn Ni Cu Ammonia g/l (NH 3 / NH 4 +1 = 2 / 1) Formula 1 M(NH 3 ) 4 +2 (Aqueous) + 2 RH (Organic) R 2 M (Organic) + 2 NH 3(Aqueous) + 2 NH 4 + (Aqueous)

22 22 While the study of ph isotherms, selectivity data and ammonia isotherms allows the conceptualization of a metal separation flowsheet, it does not provide one with the specific details on how to most effectively carry out the separation in the most efficient, costwise manner. Laboratory work is still required to determine the precise extraction and stripping conditions, circuit staging requirements, etc. The manufacture of printed circuit boards (PCB) involves selectively etching copper from the board leaving the desired circuit. Ammoniacal etchants based on either ammonium chloride or ammonium sulfate are typically used. As the concentration of copper in the etchant increases, the efficiency of the etching process decreases. Typically, at about 140 g/l of copper, the etchant is considered to be spent. The spent etchant can then be regenerated for reuse by extraction of the copper. This can be carried out on-site or the spent etchant can be sent off to a central treatment facility. The recovery of copper and regeneration of the spent etchant by solvent extraction with LIX 84-I has been practiced commercially for a number of years and BASF has had previous experience with a number of these operations globally. A typical layout for a PCB spent etchant copper solvent extraction plant is shown in Figure 2. Two wash stages are employed to minimize or prevent transfer of impurities between extraction and stripping. Due to the high concentrations of ammonia and ammonium ion in the aqueous feed solution, co-extraction of ammonia by LIX 84-I will occur. In addition to the co-extracted ammonia, the loaded organic will contain small amounts of entrained aqueous. This will result in transfer of ammonia and chloride to the strip circuit leading to the buildup of ammonium sulfate and chloride in the strip solution. Both of these chemical species are undesirable. The excess ammonium sulfate must be disposed of and high chloride levels can lead to chlorine gas formation in the electrowinning tankhouse. The stripped organic can also transfer sulfuric acid to extraction by entrainment leading to undesirable buildup of ammonium sulfate in the regenerated etchant. Typically, the aqueous phase in the wash stages would be a dilute acid stream. By coupling the two wash stages as illustrated, a weak acid solution can be generated by scrubbing the stripped organic in W2 to remove the entrained acid and the resultant weakly acidic W2 aqueous can then be fed to W1 where it contacts the loaded organic. Scrubbing with dilute acid removes the ammonia from the loaded organic. The resultant W1 aqueous can then return to W2. This arrangement results in an efficient use of fresh water for washing and reduces reagent consumption 11,12. Extraction reagents based on ketoxime such as LIX 84-I and LIX 84-IT are favored for the recovery of copper from ammoniacal solutions. Copper is strongly extracted by ketoxime from an ammoniacal solution and is readily stripped with acid resulting in very high net transfer. The high extractive strength of aldoxime based formulations is not required to achieve high recoveries and they are not as readily stripped with acid so net transfers are lower. LIX 84-IT is based on ketoxime modified with a small amount of an ester modifier. Addition of a small amount of modifier reduces ammonia co-extraction 13. Figure 2: Basic Layout of a PCB Spent Etchant Cu SX Circuit Raffinate Loaded Organic W1 Aqueous E1 E3 S1 W1 E2 W2 S2 Spent Etchant Spent Electrolyte Strong Electrolyte W2 Aqueous

23 23 5. Nickel Extraction from Ammoniacal Solution Use of ammonia to leach nickel sulfide ores was first proposed around the beginning of the 20th century. The first commercial application of ammonia to the leaching of nickel however was the use of the Caron Process to treat nickel oxide ores in Nicaro, Cuba starting in This was followed by the startup in the mid-1950 s of the Sherritt Gordon plant in Fort Saskatchewan, Alberta which used a high pressure ammonia leach to recover nickel from a sulfide concentrate 1,2. In 1970 following the development of LIX 65N, a flowsheet was developed by BASF for the recovery of copper and nickel from an electro-refining tank house bleed stream. After recovery of the copper, the aqueous copper raffinate was neutralized with ammonia followed by extraction of the nickel. SEC Corporation adopted the technology and operated a plant successfully for a number of years 3. During this same time frame, BASF published a series of investigations to refine the recovery of nickel from ammoniacal solutions 4,5,6. Queensland Nickel commissioned the first large scale plant to recover nickel from an ammoniacal leach liquor in 1989 using LIX 87QN, a modified ketoxime specifically developed for this application 7,8. Figure 1: Production of base metal hydroxide intermediate Ore pretreatment Gravity concentration / cyclone / scrubbing H 2 SO 4 Sulfur, steam Autoclave acid leaching Fe(SO 4 ) 2 disproportionates to Fe 2 O 3 and H 2 SO 4, Ni, Cu, Co and Zn leach as sulfates. Cr is Cr 2+. Tails S L CCD Air CaO or MgO Hydroxide precipitation ph 5.0 Precipitation and removal of iron Reject or recycle to leach S L MgO or CaO Hydroxide precipitation ph 9.0 MgO is the preferred alkali as it permits use of an ammonium carbonate leach. CaO requires an ammonium sulfate leach. Rejection of Mn 2+, SO 4 2+, Cr 2+ S L Belt filter Base metal hydroxide filter cake intermediate To ammonia leach and SX-EW

24 24 With the increased interest in the recovery of nickel from laterite ores and drawing on its experience in extraction of nickel from ammoniacal solutions, BASF conceptualized a flowsheet for the recovery of nickel from laterite ores. This flowsheet was further developed and implemented by Cawse Nickel Operations 9. The basic elements of the front half of the Cawse process (Figure 1) are: High Pressure Acid Leaching (HPAL) of the laterite ore. Solid-Liquid separation. ph adjustment to remove iron. Further adjustment of ph to precipitate the base metals (Ni, Cu, Co, Zn) as crystalline hydroxides. The refinery portion (Figure 2) of the process includes: Re-leach of the Mixed Metal Hydroxide Precipitate (MHP) with ammonia under oxidizing conditions. Solvent extraction of the nickel with a ketoxime, LIX 84-INS. Recovery of nickel cathode. Recovery of cobalt from nickel raffinate by precipitation of cobalt sulfide which can be further refined into high purity cobalt metal. Figure 2: Ammonia Re-Leach-LIX 84-INS Nickel SX-Electrowinning Base metal hydroxide filter cake intermediate Air / O 2 NH 3 / CO 2 Ammonia leaching To acid leach S L Steam / air Steam stripping and oxidation Steam stripping to remove free ammonia and to help oxidize Mn and Co Reject or return to acid leach Peroxide to oxidize all Co 2+ to Co 3+ S L Clarification to remove MnO and other suspended solids Raffinate to Co recovery H 2 S PPT Nickel SX extraction with LIX 84-INS Nickel electrowinning Loaded organic wash Zn and NH 3 removal Nickel stripping Organic bleed to Co and Cu strip and reoximation Stripped organic wash

25 25 The Cawse flowsheet possesses a number of advantages relative to other proposed flowsheets for treatment of laterite ores 9. They include: Process has been industrially proven having produced 8,000 ton/year of nickel cathode. The MHP can either be sold to other nickel producers or further treated to produce high purity nickel cathode and cobalt sulfide. The MHP can be stockpiled allowing a steady feed to the nickel refinery portion of the plant when the HPAL is not operating. The combination of the hydroxide precipitation step followed by ammonia re-leach is largely selective for Ni, Co, Cu, and Zn while rejecting troublesome Mn and Cr. Use of MgO for the hydroxide precipitation minimizes gypsum formation downstream from the re-leach of the MHP. The nickel concentration of the ammonia leach solution can be controlled (Typically g/l Ni) to minimize the size of the nickel SX plant. Final products are readily marketable high purity nickel cathode or nickel sulfate and cobalt sulfide. Ammonia is recycled resulting in low ammonia consumption per ton of nickel produced. Overall metal recovery is very high due to recycling of intermediates Process employs only one SX circuit and one extractant type removing the potential for cross contamination of the circuit organics. A schematic of the Cawse SX plant is shown in Figure 3 9. The chemistry of extraction and stripping is summarized in the following equations (Formula 1). Figure 3: Schematic of Cawse SX plant PLS E1 Raffinate E2 E3 SOW LOW 1 LOW 2 Dil. acid wash Aq. S1 S2 S3 S4 Nickel Electrowinning Wash Aq Formula 1 Extraction 2 RH (Organic) + Ni(NH 3 ) 4 +2 (Aqueous) R 2 Ni (Organic) + 2 NH 3(Aqueous) + 2 NH 4 + (Aqueous) Stripping R 2 Ni (Organic) + H 2 SO 4 (Aqueous) Ni +2 (Aqueous) + SO 4-2 (Aqueous) + 2 RH (Organic)

26 26 Successful operation of an ammoniacal nickel SX circuit must take into consideration a number of factors: As nickel is extracted, the concentration of ammonia and ammonium ion in the aqueous phase increases, effectively limiting nickel transfer into the organic phase. Copper, zinc, cobalt and manganese are typically present in the MHP ammoniacal re-leach liquor and will co-extract with the nickel. Cobalt(+2) and manganese(+2) will be converted to higher oxidation states on the organic making them difficult to strip and resulting in a buildup in concentration over time poisoning the organic. Due to the nature of the organic and ammoniacal solutions, the interfacial tension is quite low relative to the interfacial tensions observed when extracting copper from acidic sulfate solutions. Nickel electrowinning limits the ph of the incoming rich electrolyte to Ammonia and ammonium ion can be transferred to strip by both entrainment and chemical loading Potential for formation of metal amine sulfate salts which may precipitate in lines or alter chemistries in some fashion. Nickel stripping kinetics are slow. Choice of MHP re-leach solution impacts extraction kinetics. Use conservative settler design, settler flux of 3 4 m 3 / m 2 /hr in extraction and 3 5 m 3 /m 2 /hr in stripping, with aqueous continuous mixing in all stages. Use S1 to consume excess acid in aqueous and control ph of rich electrolyte at Use wash stages to remove ammonia / ammonium ion from the loaded organic and entrained acid from the stripped organic. Use 5 7 minute mixer retention times in stripping and operate at C. Increase extraction mixer retention times slightly when using ammonia / ammonium sulfate leach conditions. Analytical methodology for measurement of ammonia transfer on loaded organic, determination of cobalt(+2) concentration in leach liquor, and determination of the concentration of sodium lauryl sulfate in electrolyte. The treatment of ammoniacal leach solutions containing higher copper concentrations than those normally seen in laterite processing such as those generated by autoclave leaching of nickel sulfide concentrates has been proposed 9. Use of ph controlled selective stripping of nickel and copper have shown in the laboratory that a high purity nickel strip solution containing up to g/l of nickel could be obtained 13,14. The technology developed by BASF to address these points with regard to nickel recovery from ammoniacal leach solutions includes 9,10,11,12 : Control MHP leaching to generate a solution containing g/l nickel followed by steam stripping to reduce the ammonia content to g/l. Depending on copper concentration, treat bleed stream of stripped organic to control copper level on organic or alternatively use ph controlled selective strip to recover both high purity copper and nickel 13,14. Maintain oxidizing conditions in leach to maintain cobalt and manganese in higher oxidation states which will not load on organic. Employ reductive strip to remove cobalt and manganese from organic phase coupled with re-oximation to re-generate oxime hydrolyzed under reductive strip conditions. For further information concerning the extraction of nickel from ammoniacal solutions contact your nearest BASF Mining Solutions representative.

27 27 6. BASF Alamine and Aliquat Reagents BASF offers a series of tertiary amines (Alamine reagents) and a quaternary amine (Aliquat 336) (Table 1) for metal extraction. The R groups are alkyl hydrocarbon chains which may be branched or straight chain and which may contain differing numbers of carbon atoms. Tertiary amines are basic due to the presence of a lone pair of electrons on the central nitrogen atom. While other types of amines are known, the tertiary amines find the widest use in metal recovery processing by solvent extraction. BASF currently offers three Alamine reagents for metal solvent extraction applications but has the capability to produce other tertiary amines if the need should arise. Aliquat 336 is derived from quaternization of Alamine 336 with methyl chloride. Table 1: Alamine and Aliquat Extractants Alamine Reagents Alamine 308 R = Iso octyl (Highly Branched C8 Chain) Alamine 336 R = Mixed C8 and C10 (Straight Chain) Alamine 304 R = C12 (Straight Chain) Tertiary amines have the general formula: Aliquat 336 has the general formula: R R Aliquat Reagent R N R N + CH 3 CI R R Aliquat 336 R = Mixed C8 and C10 (Straight Chain) The tertiary amines and quaternary amine are examples of the ion pair class of extractants. Protonation of the tertiary amine results in formation of an organic ammonium cation which then forms a hydrocarbon soluble ion pair with an anion as illustrated in the following equations (Formula 1). The extent to which the protonated amine will exchange one anion for another is dependent on the relative affinity of the two anions for the organic ammonium cation and the relative stability of the two anions in the aqueous phase (Formula 2). Typically, extraction favors larger anions having a low charge density over smaller anions which Formula 1 R 3 N (Organic) + HA (Aqueous) R 3 NH + A - (Organic) Formula 2 R 3 NH + A - (Organic) + B - (Aqueous) R 3 NH + B - (Organic) + A - (Aqueous) Formula 3 2 R 3 NH + B - (Organic) + Na 2 CO 3 (Aqueous) 2 R 3 N (Organic) + 2 NaB (Aqueous) + CO 2 + H 2 O

28 28 have a high charge density. The selectivity of extraction will also be influenced to some extent by the relative amounts of the two anions in the aqueous solution. While the choice of stripping agent depends on the overall recovery process, there are two approaches that can be used to recover the extracted anion from the organic phase when using amines. The first is to crowd the desired anion off the organic phase by contacting the organic with a concentrated aqueous solution of another anion such as chloride. Alternatively and most typical, the amine is deprotonated by contacting it with an aqueous solution of a base such as sodium carbonate as illustrated in Formula 3. Stripping with a base typically results in the best stripping and in the fewest number of strip stages. In some cases, changes in ph will result in changes in the nature of the extracted anionic species making stripping more favorable. For example, polymolybdates which are strongly extracted on the acid side are converted to molybdate at ph s greater than 8.0, which is much less strongly extracted than the polymolybdate. The chemistry of extraction and stripping with Aliquat 336 differs from that of the tertiary amines due to the fact that the quaternary amine functionality is always positively charged. While the same considerations of anion size and relative charge determine the relative ease of extraction of different anions, extraction of anions is not ph dependent as it is with the tertiary amines. This can be used to advantage in some instances such as recovery of a metal from a basic leach solution. The biggest disadvantage to using a quaternary amine type extractant is that it will not deprotonate so it is necessary to use crowding with high concentrations of another anion as a stripping strategy. Alamine 308 is a tri-isooctyl amine. Its primary application is: Separation of cobalt from nickel in acidic chloride systems 1,2 Recovery of zinc from spent electrolyte solution 3 Alamine 336 is a tri(n-c8, C10 alkyl) amine. Principle applications are: Recovery of uranium from acidic sulfate leach solutions Recovery of molybdenum from acidic sulfate leach liquors Recovery of vanadium(+5) from acidic leach liquors Extraction of tungsten from acidic liquors 4 Separation of molybdenum and rhenium 5 Recovery of gallium from acidic chloride solutions 6 Extraction of gold from acidic thiocyanate leach liquors 7 Alamine 304 is tridodecyl amine. Its major applications are: Recovery of molybdenum from acidic sulfate leach liquors Extraction of organic acids such as citric acid from fermentation broths 8 Aliquat 336 is tri(n-c8, C10 alkyl) methyl ammonium chloride. Its uses include: Recovery of molybdenum from acidic sulfate leach liquors Recovery of vanadium(+5) from acidic leach liquors Rare earth separations 9 Removal of arsenic from copper refinery electrolytes 10 In general, any metal capable of forming an anionic complex in an aqueous solution is a candidate for extraction by tertiary or quaternary amines. Figure 1 summarizes some extraction data for Alamine 336 and / or similar amines for a wide variety of metal aqueous systems 11. Oak Ridge National Laboratory has carried out an extensive series of studies with regard to the effect of chloride concentration and ph on extraction of various elements as their chloride complexes by amines or quaternary amines 12. Figure 1 summarizes the extraction isotherms for a number of metals as a function of chloride concentration in the aqueous at ph 2 and 40 C. Figure 1: Extraction Isotherms for Alamine 336 as a Function of Choride Concentration (ph = 2, 40 C). Extraction % Zn Mo Cu Fe 3+ Fe 2+ Sn Mn Co [CL ], g / L. Ni, Cr

29 29 Figure 2: Survey of Extraction by High Molecular Weight Tertiary Amines Li Be B C N O F Na Mg Al Si P S Cl K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br IV V VI III II II II b c bk b b b bh Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I III IV V VI VII IV I hj vc bcdg c abcdlm b bh CS Ba La* Hf Ta W Re Os Ir Pt Au Hg TI Pb Bi Po At III IV V III IV h bc cg b b Fr Ra Ac * Elements Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu III III III III III III III h h h h h h Elements Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No 103 IV V VI VI VI III III III III III abcdh abcd ab ab ab ab ab abf hj hj hj hj hj cd ef gi Key Blocked elements are strongly extracted by one contact with 0.1 M amine from the acid systems shown below: a HNO 3 d H 3 PO 4 g COOH 2 j NH 4 SCN l HBr b HCI e HF h LiCI, LiCI, LiCI HCI, CsCI k H 2 CrO 4 m HI c H 2 SO 4 f CH 3 COOH i various organic acids (a) Taken from Standard Methods of Chemical Analysis, Volume II A, Sixth Edition, page 190. Van Nostrand Reinhold Company, 1963.

30 30 Development of a Separation Process While development of a separation process based on chelating reagents such as the LIX oximes is somewhat straight forward due to the constraints imposed by the chelation chemistry, amine systems tend to be more complicated due to: The large number of aqueous anionic systems where an amine extractant might be applicable. Protonated amines and quaternary amines must be paired with an anion to maintain charge neutrality in the organic phase which often results in poor selectivity depending on the relative amounts of amine or quaternary amine relative to the targeted species. The large number of potential stripping agents as compared to copper loaded oximes where stripping with sulfuric acid is the standard. The ph, the metal oxidation state and the effects of concentration of the anionic complexing agent all have an impact on the chemical behavior of the system. Development of amine systems can be more of an art form rather than a science. Any investigation of a potential separation process should start with a laboratory program whose goal is to develop the best conditions for extraction, stripping and final product recovery consistent with the overall metallurgical flowsheet. The development of a separation process for cobalt, iron and nickel from an acid chloride solution illustrate the importance of the factors cited above. Figure 1 shows that nickel(+2) is only slightly extracted at greater than 200 g/l chloride ion while cobalt(+2) and iron(+3) are extracted at chloride ion concentrations of g/l. Furthermore, iron(+3) is still strongly extracted at 50 g/l chloride ion. Given these points, one can expect to develop an excellent separation of these metals by first dissolving the mixture into a concentrated hydrochloric acid solution, oxidizing the iron to the +3 state, coextracting the cobalt(+2) and iron(+3) with an amine while leaving the nickel(+2) in the original aqueous solution. The cobalt can then be selectively stripped off the loaded organic by water. This flowsheet has been studied in a BASF laboratory. Several slightly different flowsheets for this separation have also been reported 13,14. The best choice of flowsheet is dependent upon the relative amounts of cobalt, nickel and iron present. Often, the complex of the protonated amine or quaternary amine cation with the extracted anion may have only limited solubility in a typical hydrocarbon diluent resulting in the formation of a third phase and / or phase separation problems. A third phase is a viscous layer that typically collects at the interface. It is primarily composed of the precipitated complex. Due to the ionic nature of the complex, the third phase is highly polar which makes it a very good solvent for polar materials such as the free amine or quaternary amine. The free extractant (amine or quaternary amine) will distribute from the hydrocarbon diluent into the third phase resulting in a rapid loss of loading capacity and net transfer. Addition of a solvation modifier (phase modifier) such as a long chain alcohol, e. g., isodecanol, isotridecanol; to the organic phase is normally employed to prevent third phase formation and / or phase separation problems. Replacement of at least a portion of the hydrocarbon diluent with a high aromatic diluent may also be employed. For additional information regarding BASF amines and quaternary amine reagents, contact your local BASF Mining Solutions technical representative.

31 31 7. Extraction of Uranium In 1957, the Mining Solutions unit of BASF (which in part originated from the General Mills Mining Chemicals Division) introduced Alamine 336, tri(octyl, decyl) amine, to the mining industry for the recovery of uranium by solvent extraction from acidic sulfate leach liquors. Alamine 336 was quickly accepted by the industry with the first application occurring in 1958 with the startup of the Kerr McGee uranium mill at Grants, New Mexico, USA 1. At the peak of the uranium industry in the late 70 s, approximately 80 % of the production in the USA used the Alamine 336 solvent extraction flowsheet. It was this ongoing involvement in the uranium industry that eventually led to the conceptualization and development of the phenolic oximes for the recovery of copper from acidic leach liquors. The hydrometallurgical processing of uranium has been extensively reviewed 2,3,4,5. The general chemistry for the processing of uranium through leaching with dilute sulfuric acid, solvent extraction and precipitation to yield high grade U 3 O 8 is summarized in Figure 1. Sulfuric acid leaching of uranium ores is carried out under oxidizing conditions at a redox potential of mv relative to a saturated calomel electrode. While ferric ion is the primary oxidant, oxidants such as manganese dioxide, sodium perchlorate or hydrogen peroxide are employed to convert ferrous ion to ferric ion. Under these conditions, uranium is converted to the +6 valence state and is solubilized as the anionic uranyl di-sulfate or tri-sulfate complexes. After clarification to remove residual solids, the leach solution is contacted with an organic phase consisting of Alamine 336, an alcohol such as isodecanol or isotridecanol as a solvation modifier, and a suitable hydrocarbon diluent. The alcohol is typically present at about 50 % of the concentration of the amine. Often, prior to extraction, the organic phase is contacted with a dilute solution of sulfuric acid to preprotonate the amine and load the organic with sulfate or bisulfate. This ensures that the amine will be protonated in extraction, the ph of the aqueous phase will remain approximately constant since no acid extraction will occur, and will help to maximize selectivity for uranium. In extraction, the sulfate / bisulfate anion is exchanged for an anionic uranyl sulfate complex. Uranium extraction is an anion exchange process. Depending on a variety of factors, there is the potential for competitive extraction by other anions present in the leach liquor. To achieve the desired uranium purity, a number of scrubbing stages as illustrated in Figure 2 may be employed in the solvent extraction circuit to remove these unwanted anions from the organic phase and prevent their transfer to stripping. Stripping of the loaded organic can be carried out with ammonia, strong sulfuric acid solutions, sodium chloride or nitrate solutions. The use of ammonia / ammonium sulfate is a preferred option 6,7,8,9. Stripping is carried out by ph controlled addition of ammonia gas or ammonium hydroxide solution to each strip stage 10,11. Careful control Figure 1: General Chemistry of Uranium Processing H 2 SO 4 LEACHING Solvent Extraction (SX) Yellowcake Production UO 2 + Fe 3+ UO Fe 2+ UO H 2 SO 4 UO 2 (SO 4 ) H + Pre-protonation 2 R 3 N (Organic) : + H 2 SO 4(Aqueous) ( R 3 NH + ) 2 S0 4-2 (Organic) Extraction UO 2 ( SO 4 ) ( R 3 NH + ) 2 SO 4-2 ( R 3 NH + ) 4 UO 2 ( SO 4 ) 3-4 (Organic) + 2 S0 4-2 (Aqueous) Stripping ( R 3 NH + ) 4 UO 2 ( SO 4 ) 3-4 (Organic) + 4 NH 4 OH (Aqueous) 4 R 3 N (Organic) + ( NH 4 ) 2 UO 2 ( S0 4 ) 2(Aqueous) + ( NH 4 ) 2 S0 4(Aqueous) + 4 H 2 O Precipitation 2 ( NH 4 ) 2 UO 2 (SO 4 ) NH 4 OH ( NH 4 ) 2 U 2 O ( NH 4 ) 2 SO H 2 O Calcination (Heat > 580 C) (NH 4 ) 2 U 2 O 7 + heat 2U 3 O 8 of ammonia addition is required. The presence of excess ammonia will result in the precipitation of ammonium diuranate in the mixers resulting in crud formation and operational problems. After stripping, additional ammonia is added to the pregnant strip solution to precipitate the uranium as ammonium diuranate (ADU). After filtration and drying, the ADU is calcined to produce high purity (99 % or greater) U 3 O 8. The process described above involving direct solvent extraction of the uranium from the dilute acid leach solution is often described as the Amex process (Figure 3) or the Purlex process. An alternative flowsheet involves pre-concentration of uranium by use of an ion exchange resin followed by extraction of the uranium from the resin eluate solution with an amine. This is referred to as the Eluex process (Figure 4) (Bufflex process in South Africa). The Eluex process takes advantage of the use of relatively non-selective ion exchange resins to treat very dilute solutions to generate a much more concentrated solution of uranium and then use of the more selective amine solvent extraction process to recover a purer uranium concentrate 1,12.

32 32 Figure 2: Typical Uranium SX circuit for Recovery from Acidic Sulfate Leach Liquors 12,13 Uranium Extraction PLS Raffinate E1 E2 E3 E4 Organic scrubbing Loaded organic to PLS or leach Sc1 H 2 O Sc2 H 2 SO 4 Sc3 NH 3 /(NH 4 ) 2 SO 4 Sc4 H 2 O Uranium Stripping S4 ph 4.8 S3 ph 4.0 S2 ph 3.8 S1 ph 3.3 NH 3 Barren strip liquor L S ADU precipitation HX C Liquor to calciner Na 2 CO 3 / NaOH regeneration ph ~ 11.0 H 2 SO 4 protonation ph ~ 1.0 Barren organic Each uranium leach, ion exchange and / or solvent extraction operation is somewhat unique due to differences in the pregnant leach solution stemming from the ore and gangue mineralogy, site water quality, and site specific water balance issues. These differences can give rise to a variety of operational challenges 13,14,15,16 : Crud Formation Typical solvent extraction plant design specifications target less than 20 ppm of solids in the incoming pregnant leach liquor. Incoming solids can interact with the organic phase in the mixer to form a solid stabilized emulsion, crud. Depending on the level, 100 s to 1000 s of ppm, and nature of the solids, some crud will be formed. In cases where crud formation is mild, it may be responsible for transfer of impurities to final product. In severe cases, it may result in the need to shut down the plant and clean out the accumulated crud and solids. The presence of dissolved species such as silica may also contribute to crud formation. The soluble silica can be converted to insoluble silica precipitates due to changes in the chemical nature of the aqueous solution at the organic-aqueous interface triggering polymerization of the soluble silica to higher molecular weight silica species. In addition to reducing the incoming solids / soluble silica levels, operating the plant using organic continuous mixing will help to minimize crud formation. In extreme cases where high levels of solids or soluble silica is present in the incoming feed, the plant operators may elect to by-pass or shut down the solvent extraction process until the pregnant leach solution returns to normal. BASF offers a broad product range of floculants and coagulants as well as technical expertice to assist plant operators in solving pregnant leach liquor clarification issues as well as reduce soluble silica levels. Poor phase disengagement Poor phase disengagement can arise from a number of sources. Many uranium ore deposits contain a range of organic substances such as humic acids. Under the oxidative conditions of the leach, these materials can be converted to

33 33 carboxylic acids and organic sulfates which are surfactant-like in nature, distribute into the organic phase and build up in concentration in the organic phase over time resulting in longer phase disengagement times. Carboxylic acids have also been generated by bio-oxidation of the alcohol solvation modifier and the hydrocarbon diluent. Carboxylic acid contamination of the organic may also result in a reduction of uranium from extraction to strip either by reacting with the amine to reduce extraction capacity or by transferring uranium from stripping back to extraction. The overall level of these organic contaminants can be reduced by scrubbing a bleed stream of the stripped organic phase with a strongly alkaline aqueous carbonate solution (i.e., ph ~ 11 12). Chemical transfer of impurities from extraction to strip. Under the typical ph of the leach solution, molybdenum will be present as a polymolybdate anion which is also readily extracted by tertiary amines such as Alamine 336. Under the conditions of the ammonia strip, the molybdenum will also strip and will report to the final uranium product. Depending on the ph of the leach solution, its redox potential, and the presence of other anions such as phosphate, silicate, arsenate, etc., molybdenum can be present in a number of reduced polymolybdate or heteropolymolybdate (i.e., containing Mo 5+ ) species which tend to form complexes with the amine extractant that are poorly soluble in the organic phase and tend to form sticky third phases or goo which collect in the settlers at the interface and in the bottoms of the settlers reducing settling volume. These precipitates may be orange, yellow, green, blue, or gray in color. The color being dependent on the oxidation state of the molybdenum and heteroatoms present. If the formation of these insoluble molybdenum third phases is a problem, BASF recommends the use of Alamine The use of diluents having a high aromatic content, higher concentrations of alcohol solvation modifiers, and operating at a redox potential high enough to insure that molybdenum is all present in the +6 oxidation state will also help to prevent third phase formation. Where sufficient molybdenum is present, one can selectively strip the uranium using an acidified chloride solution and then strip the molybdenum off the organic using a sodium carbonate solution. If vanadium is present, one can selectively recover it by controlling the redox potential of the aqueous. Vanadium(+4) is not extracted by tertiary amines from sulfate solutions while the vanadium(+5) forms a polyvanadate which is readily extracted. At redox potentials below about 600 mv (against standard calomel electrode), vanadium is present only in the +4 oxidation state and the uranium can be extracted away from the vanadium. Once the uranium is recovered, one can adjust the redox potential of the raffinate to about 720 mv at which point all of the vanadium will be present in the +5 oxidation state and can be extracted as the polyvanadate. However, the polyvanadate species are strong oxidants and will cause degradation of the amine. Zirconates will also be co-extracted along with uranium by tertiary amines. Careful control of the scrub stage ph between as well as use of a bit of uranium to crowd the zirconates off the organic will minimize its transfer to strip. Other contaminants common to uranium circuits can also be controlled using appropriate strategies. A thorough understanding of the components in the leach solution is critical to operating a uranium recovery plant. Amine degradation Nitrate is problematic for a couple of reasons. It is preferentially extracted over the uranyl sulfate species by tertiary amines and thus suppresses uranium extraction. Under certain conditions, the presence of nitrates in the leach solution can lead to a high redox potential ( mv against standard calomel electrode). Under these conditions, the tertiary amine undergoes very rapid attack by the nitrate and is converted to the corresponding di-alkyl nitrosamine resulting in loss of loading capacity and increased phase disengagement problems. This problem has been most frequently observed in Eluex circuits where the uranium is first concentrated by use of an ion-exchange column. The uranium is then further purified and concentrated by solvent extraction with a tertiary amine. The solution has been to control the redox potential to below 510 mv by addition of iron wire to the aqueous weirs in extraction 17,18. Tertiary amines are stable to most process conditions such as acidity and alkalinity at typical temperatures. At temperatures over about 90 C, protonated amines will slowly degrade by a Hoffman elimination type mechanism. Contact with strong oxidants such as vanadium(+5), hydrogen peroxide, etc., will result in oxidative degradation of amines. Acid consuming ores are leached with alkaline carbonate solutions to generate the uranyl tricarbonate complex. While the uranyl tricarbonate complex can be extracted with Aliquat 336, this approach has not been pursued commercially to any large extent 14,19. Recovery of uranium from copper solvent extraction raffinates by solvent extraction with Alamine 336 has also been practiced at BHP Billiton s Olympic Dam Operations and at Anamax Twin Buttes 20,21.

34 34 Figure 3: Amex Process Figure 4: Eluex Process Sulfuric Acid Ore Oxidant Sulfuric Acid Ore Oxidant Leaching Water Leaching Water Solids to tailings S/L Separation Uranium Rich Solution SX Barren Solution Ammonium Sulfate Solids to tailings Ammonium Sulfate S/L Separation Uranium Solution SX CIX Sulfuric Acid Barren Solution Ammonia Precipitation Uranium Rich Solution Barren Acid Filtration Ammonia Precipitation Tailings Filtration Tailings Yellowcake Yellowcake

35 35 8. Extraction of Molybdenum and Vanadium Molybdenum The primary sources of molybdenum are concentrates derived as by-products from flotation of copper sulfide ores or directly from molybdenum ores. These concentrates are typically roasted to produce a crude molybdenum oxide and a flue dust, which also has a high molybdenum content. Both can be leached with sulfuric acid to produce leach solutions from which molybdenum can be recovered via solvent extraction to produce a high purity molybdenum oxide product. Since rhenium is often associated with molybdenum, the option to recover rhenium using solvent extraction exists as well. Molybdenum sulfide concentrates can also be effectively leached using high pressure oxidative leach techniques to produce a feed solution amenable to processing by solvent extraction. Molybdenum can also be successfully leached from spent hydrocarbon cracking catalysts and recovered using solvent extraction. Solvent extraction can also provide routes to recover molybdenum from non-traditional sources such as acidic heap and dump copper leach solutions 1. The solvent extraction of molybdenum can be a challenging undertaking due to molybdenum s complicated and unique chemistry. An understanding of the aqueous solution chemistry and solvent extraction chemistry of molybdenum is necessary to successfully operate a molybdenum solvent extraction plant. BASF through its predecessor companies has been supplying solvent extraction technology for the recovery of molybdenum since the late 1950 s and the chemical expertise to understand the unique problems faced by plant operators when dealing with molybdenum 2. Molybdenum Chemistry Molybdenum can be present as a wide variety of species in an aqueous solution 3. The oxidation potential of the solution, the nature of the other anions and metals that are present as well as their concentration, the ph of the solution and the concentration of molybdenum all play a role in determining which molybdenum species are in equilibrium with one another in a given leach liquor. While molybdenum can exist in a number of oxidation states, it is predominantly found in the +6 oxidation state in leach liquors derived from pressure oxidation of concentrates or molybdenum oxide. Figure 1: Distribution of molybdenum(+6) species as function of ph Isopolymolybdates Mo 7 O 24 6, Mo 8 O 26 4 MoO 4 2 A simplified picture of the primary molybdenum (+6) species of interest and the ph range over which they form is shown in Figure 1. As the ph increases from zero to about 1.5, the concentration of the molybdenyl cation decrease and the isopolymolybdates become more important. Between about ph 1.0 to ph 6.0, the Mo 7 and the Mo 8 species are of the most interest. At ph s greater than 7.0, the simple molybdate ion predominates. The picture can be further complicated by the presence of Mo (+5) in the leach liquors. The presence of other heteroatoms such as P, As, Si, Ti, Zr, and Ge in the solution can also complicate the chemistry further due to the potential to form a vast number of heteropolymolybdate species. Cationic MoO ph

36 36 Molybdenum Extraction Molybdenum is typically recovered from acidic (ph ) sulfate solutions by extraction with a tertiary amine such as Alamine 336 or Alamine 304. The chemistry is outlined in Formula 1. Formula 1 Extraction R 3 N (Org) + H 2 SO 4(Aq) [R 3 NH + HSO 4- ] (Org) Mo 8 O 26-4 (Aq) + 4 [R 3 NH + HSO 4- ] (Org) [(R 3 NH + ) 4 Mo 8 O 26-4 ] (Org) + 4 HSO 4 - (Aq) Stripping [(R 3 NH + ) 4 Mo 8 O 26-4 ] (Org) + 12 OH - (Aq) 8 MoO R 3 N (Org) + 8 H 2 O (Aq) Due to the fact that polymolybdates are strongly extracted from acidic sulfate leach liquors by tertiary amines allowing one to operate at very high percentages of molybdenum maximum loading, recoveries are typically very high in 2 to 3 counter current stages of extraction. Stripping is accomplished by contacting the loaded organic with ammonia. Very high concentrations of molybdenum, up to 100 g/l, can be achieved in the strip liquor in 1 to 2 stages of stripping using a concentrated ammonia solution and maintaining the ph in stripping between 9.0 to 9.5. The results of a mini plant circuit run in a BASF laboratory is shown in Figure 2. The feed solution was derived from leaching a flue dust with sulfuric acid to generate a feed containing 5.56 g/l of molybdenum and g/l of free residual acid. The organic phase consisted of 2 % w/v Alamine 336 in Aromatic 150, a 100 % aromatic diluent. Note that 97.3 % recovery of molybdenum was achieved in E1 and 99.1 % recovery overall indicating that no more than 2 stages of extraction are required in this case. Stripping was highly efficient with 99.4 % stripping achieved in S1. Figure 2: Mini plant circuit Wash Water Spent Wash 0.06 g/l W1 ph 1.5 LO Surge Feed 5.56 g/l 6.21 g/l Rich Strip Liquor 78.2 g/l p H g/l 6.28 g/l 0.04 g/l 0.03 g/l S1 S2 W g/l 0.69 g/l 0.54 g/l NH 3 Strip Soln 65 g/l 0.07 g/l E1 E2 E3 p H 9.35 Wash Water Washed SO 0.03 g/l Raffinate 0.05 g/l Spent Wash 1.3 g/l

37 37 Molybdenum Solvent Extraction Technical Challenges One of the more prevalent problems that molybdenum solvent extraction plant operators face is the formation of third phases 4,5. These third phases tend to be very thick oils that collect in the organic phase, at the organic / aqueous interface, and in some instances even on the sides and bottom of the settler. Depending on their chemical composition, they may range from a yellow / green to a dark blue / green in color. If a small proportion of the molybdenum is present in the +5 oxidation state, the molybdenum amine complex tends to have limited solubility in the organic phase, especially if the diluent is predominantly aliphatic in character. The resultant third phase tends to be a very dark blue in color, hence it is commonly referred to as the blue goo. When operating circuits in BASF laboratories, the formation of the blue goo has been noted in stripping. Addition of a small amount of hydrogen peroxide to the strip solution has been used to eliminate it. If the molybdenum in the feed solution has not been completely converted to the +6 oxidation state, the solution may be a light blue to dark blue in appearance as seen in Figure 3. The bottle on the left is a sample of leach solution containing some molybdenum(+5), a drop of 35 % hydrogen peroxide has been added to the top of the leach solution in the center bottle, and the bottle on the right was mixed thoroughly after addition of a couple of drops of 35 % hydrogen peroxide. Note the change in color from a dark blue to a light yellow / green. Adjustment of the redox potential to mv (vs SCE) was required to insure complete conversion of the molybdenum(v) to the molybdenum(vi) in the BASF laboratory. As noted earlier, heteropolymolybdic acids will form species such as in the case of phosphorus, PMo 12 O 40-3, in solution. The amine complexes of these heteropolymolydates tend to vary in color and have limited solubility in the organic phase. A yellow green crystalline material has been isolated from a uranium plant and characterized as (R 3 NH) 3 [PMo 12 O 4 0] 3(R 3 NHCl). Figure 4 shows a sample of a yellow green goo obtained from a molybdenum solvent extraction plant. This material had collected on the bottom of the settlers. Figure 4: Figure 3: Based on past experience, one sign that third phase formation may be occurring is the loss of extractive strength due to the loss of amine as third phase from the circuit organic. This can be quite rapid. Where the formation of third phases is a problem, BASF recommends the use of Alamine 304 as the reagent. The alkyl groups of Alamine 304 are 12 carbons in length as compared to the 8 and 10 carbon chains found in Alamine 336 resulting in improved solubility of the molybdenum amine complexes 6. The use of a diluent having more aromatic character is also recommended. Rhenium Molybdenum is often associated with rhenium and flowsheets for the separation and recovery of molybdenum and rhenium have been developed 7,8,9. For additional information contact your local BASF Mining Solutions representative.