Process for producing a concentrate

Abstract

A process for producing a concentrate from a feed material containing a first metal-containing phase and a second metal-containing phase is disclosed. The process includes contacting the feed material with an alkaline solution containing a lixiviant comprising an amino acid, or derivative thereof, and forming a leachate containing the second metal (and optionally the first metal) and a leach residue containing the first metal. The process also includes subjecting the leach residue to flotation and producing a first metal concentrate and a tailings fraction.

Description

[0001] PROCESS FOR PRODUCING A CONCENTRATE

[0002] TECHNICAL FIELD

[0003] A process is disclosed for the production of a concentrate. The process may be used in the production of a metal concentrate from ores, ore concentrates or tailings, or from other metal containing materials including jewellery, electronic scrap, and other scrap materials. Also disclosed is a metal extraction method that includes the process for the production of a metal concentrate. The metal extraction method is particularly applicable to the recovery of precious metals and / or base metals from an ore material (including an ore concentrate) and discussion will therefore focus on such metals. However, it is to be understood that the process is not limited to such recovery.

[0004] BACKGROUND ART

[0005] The recovery of metal values from ore minerals generally includes a number of common unit operations including comminution (crushing and grinding), separation of ore from gangue (e,g by gravity and flotation), metal extraction (e,g leaching) and metal recovery (e,g SX, IX, precipitation, activated carbon, EW). Leaching is a method where the feed material (such as ore, concentrate or tailings) is contacted with an aqueous solution containing a lixiviant to solubilise a target metal into the solution phase. Flotation is a method of separating the target metal rich component (such as ore minerals) from the target metal poor component (such as gangue) of a ground ore or ore concentrate by exploiting respective differences in hydrophobicity of the two components. The difference in hydrophobicity is enhanced by using a collector. In the case of flotation of sulphide ores, the collector is typically a xanthate. An aqueous slurry of the particles treated with the collector is aerated in flotation cells to produce bubbles. The hydrophobic particles attach to the air bubbles and are then skimmed off the top or overflow into a launder to produce a concentrate of the metal values.

[0006] In the case of processing metal-containing ores (such as copper and precious metal ores), currently the industry uses flotation to produce a concentrate fraction that comprises metal sulphide minerals (e.g., pyrite, chalcocite, covellite, chalcopyrite, bornite, millerite, pentlandite, sphalerite, cattierite, linnaeite, galena or sphalerite) and a tailings fraction. The precious metals mostly (around 50 to 90%, depending on mineralogy) report to the concentrate fraction, with the remainder reporting to the tailings fraction. The tailings fraction may be subjected to a cyanide leach to recover the remaining precious metals. However, in many cases it is not economical to treat the tailings fraction with cyanide to recover the precious metals because the residual sulphides and chalcophile minerals consume high quantities of cyanide with undesirable production of WADs (weak acid dissociable cyanide) which would need subsequent detoxification to allow water recycling. Further, because of the difficulty in economically removing precious metals from the concentrate fraction, there can be a high percentage of precious metal impurities remaining in the final mineral concentrate.

[0007] There is accordingly a need for an alternative, economic, metal recovery process that enables the control of the precious metals (and other unwanted metal phases) levels in mineral concentrates.

[0008] The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the apparatus and method as disclosed herein.

[0009] SUMMARY OF THE DISCLOSURE

[0010] According to the present disclosure, there is provided a process for producing a concentrate from a feed material containing a first metal-containing phase and a second metal-containing phase, said process including:

[0011] (i) contacting the feed material with an alkaline solution containing a lixiviant comprising an amino acid, or derivative thereof, in order to form a leachate containing the second metal (and optionally the first metal) and a leach residue containing the first metal; and

[0012] (ii) subjecting the leach residue to flotation to produce a first metal concentrate and a tailings fraction.

[0013] The inventors have surprisingly discovered that the level of a metal phase (which may be desirable, such as a precious metal or undesirable, such as an impurity phase) in a metal concentrate may be effectively controlled by using a two-stage process in which the leaching and flotation steps are reversed from the conventional order. Reversal of the leaching and flotation steps is facilitated by using a leaching solution that includes an amino acid lixiviant, which may be in the presence of a leach enhancer, to treat the feed material. It has been observed that use of an amino acid as the primary lixiviant allows enhanced extraction of precious metals without the prior problems associated with using cyanide as the primary lixiviant discussed above. Moreover, amino acids lixiviants are generally more environmentally and / or cost-wise advantageous as compared with other lixiviants such as thiosulfate, thiourea, halides and mercury.

[0014] Leaching first can facilitate recovery of the high paying precious metals without some of it ending up in the concentrate where payability is low. Moreover, if the resulting leachate includes elevated levels of metals derived from the metal sulfides (such as copper) the consequences are not as problematical when amino acid is used as the primary lixiviant because those metals in solution may be readily recovered, such as by precipitation with a sulfide source to form metal sulfides that can be subsequently floated. The sulfide source may comprise a hydrosulfide (e,g NaHS).

[0015] The use of an amino acid lixiviant has the additional surprising advantage that the effectiveness of a subsequent flotation step is enhanced. Without wishing to be limited by theory, it is believed that amino acid retained in the leach residue ("ripios") produced in step (i) enhances the adsorption of a collector on ore particles and improves the floatability of ore minerals in step (ii). Accordingly, the first metal containing fraction is more efficiently separated from gangue during the flotation step. This further improves the purity of the final first metal containing concentrate.

[0016] The feed material may comprise an ore, an ore concentrate, a process by-product or a waste product such as a flotation tailings fraction. The feed material may also or instead comprise other metal containing materials including jewellery, electronic scrap, and other scrap materials.

[0017] In an embodiment, the feed material may include one or more sulfides of the first metal. The first metal may comprise a chalcophile metal (as defined herein) and discussion herein will accordingly focus on chalcophile metals- although it is to be understood that the process is not limited to such metals. In another embodiment, the feed material may include one or more metal sulfides selected from pyrite, chalcocite, covellite, chalcopyrite, bornite, millerite, pentlandite, sphalerite, cattierite, linnaeite, galena or sphalerite. The first metal may instead or additionally be present as a native metal. As used herein, the term "native metal" means a metal that is present in the feed material in its elemental form either as an alloy or in its pure form.

[0018] A more comprehensive list of examples of first metal containing phases are set out below:

[0019] Cobalt Minerals

[0020] Linnaeite

[0021] Carrolite

[0022] Cattierite Smaltite

[0023] Cobaltite

[0024] Skutterudite

[0025] Saffordite

[0026] Glaucodite

[0027] Heazlewoodite

[0028] Copper Minerals

[0029] Native Copper

[0030] Copper arsenide's, tellurides, and selenides

[0031] Chalcocite

[0032] Djurleite

[0033] Cubanite

[0034] Covellite

[0035] Bornite

[0036] Chalcopyrite

[0037] Tetrahedrite

[0038] Tennantite

[0039] Enargite

[0040] Stannite

[0041] Lead Minerals

[0042] Native Lead

[0043] Galena

[0044] Nickel Minerals

[0045] Pentlandite

[0046] Millerite

[0047] Niccolite

[0048] Violarite

[0049] Cobalt Nickel Pyrite

[0050] Gersdorfitte

[0051] Zinc Minerals

[0052] Sphalerite

[0053] Wurtzite (High Fe ZnS)

[0054] Cadmium Minerals

[0055] Greenockite The second metal containing phase may comprise a metal value, such as precious metal (e,g gold silver and / or PGMs). Alternatively, or in addition, the second metal containing phase may comprise an impurity phase such as a metal oxide. The metal oxide may be an oxide of the first metal, for example, a chalcophile metal oxide. An example of a chalcophile metal oxide is a copper oxide such as malachite. The chalcophile metal oxide may be a secondary mineral phase produced by the oxidation or weathering of the primary sulfide mineral. The presence of such impurity phases in the feed material can be problematic in conventional flotation processes as they do not report to the concentrate fraction during flotation and therefore may end up in tailings, resulting in reduced recovery of the chalcophile metals.

[0056] A more comprehensive list of examples of second metal (namely precious metal) containing phases are set out below:

[0057] Gold

[0058] Native Gold

[0059] Gold Tellurides

[0060] Gold Bisthmuides

[0061] Silver

[0062] Native Silver

[0063] Argentite

[0064] Platinum Minerals

[0065] Native Platinum

[0066] Sperrylite

[0067] As used herein, the term "lixiviant" refers to a specific active chemical of a leaching solution that complexes with and enables the extraction or dissolution of target elements from a feed material (e.g., ore). A "primary lixiviant" is the primary (or main) active chemical in the leaching solution that complexes with and enables the extraction or dissolution of target elements from the feed material. Accordingly, the "primary lixiviant" may mean (i) the sole lixiviant present in a leaching solution, or (ii) in the case of a leaching solution containing more than one lixiviant, the lixiviant that is present in solution in the highest concentration. In the case of the present disclosure, the primary lixiviant comprises an amino acid, or derivative thereof, such as an amino acid salt. As used herein, the term "amino acid" means an organic compound containing both a carboxyl (- COOH) and an amino (-NH2) functional group. In many cases, the amino acid contains a -CHR or CH2group. In most cases the amino (-N H2) group and the carboxyl (-COOH) group connects to the same - CHR or -CH2connecting group and are referred to as primary alpha-amino-acids. The "R" group in the -CHR connecting group can take on any organic structure, such as aliphatic hydrocarbon groups to complex organic structures including aromatic groups, heterocyclic groups, and poly-nuclear groups or various other organic groups. In its simplest form, the R-group is only hydrogen, in which case the molecule reverts to the simplest primary alpha-amino-acid, called glycine.

[0068] As used herein, the term "amino acid salt" includes an alkali metal salt, for example, a sodium or potassium glycinate. Alternatively, the amino acid salt may be an alkaline earth salt (for example its calcium salt).

[0069] The alkaline solution may additionally include a leach enhancer which may enhance the leaching function of the amino acid or its derivative and / or may reduce the temperature requirements for the leaching process. As used herein, the term "leach enhancer" refers to an aqueous species that facilitates the function of the lixiviant to enhance the leaching process. The leach enhancer may have a catalyst function on the extraction. Thus, the primary lixiviant is still the amino acid or its derivative or salt. The leach enhancer may comprise one or more of the following species: iodine and / or iodide mixtures, bromine and / or bromide mixtures, ammonia, thiourea, copper salts, and cyanide in its various salts, or mixtures of these species. In one embodiment, the leach enhancer comprises a cyanide salt (such as sodium cyanide). In another embodiment, the leach enhancer is the sparsely soluble copper glycinate (Cu(Gly)2) which catalyses the leaching of the feed material. The leach enhancer may particularly increase the rate of leaching of precious metals, as well as chalcophile base metals from the feed material. The leach enhancer may be present in solution at a concentration of 2 molar or less. In an embodiment, the leach enhancer has a concentration of 1.5 molar or less. In another embodiment, the leach enhancer has a concentration of 1 molar or less. In an embodiment, the leach enhancer has a concentration of 0.5 molar or less. In an embodiment, the leach enhancer has a minimum concentration of 1.5 molar or less. In another embodiment, the leach enhancer has a minimum concentration of 0.1 molar. In another embodiment, the leach enhancer has a minimum concentration of 0.2 molar. In another embodiment, the leach enhancer has a minimum concentration of 0.3 molar. The step of contacting the material with an alkaline solution containing a lixiviant comprising an amino acid, may comprise the selective leaching process disclosed in WO 2016 / 141438 Al, the entire disclosure of which is incorporated herein by reference. In that process, a material containing at least one Chalcophile Group Element ("CPM") as herein defined and one or more non Chalcophile Group Elements ("NCE") as herein defined is contacted with an alkaline solution containing a lixiviant comprising an amino acid or derivative thereof in order to selectively leach the CPM from the material to produce a CPM containing leachate and a NCE containing residue. The CPM is then recovered from the leachate such as by using conventional methods familiar with those skilled in the art.

[0070] As discussed in WO 2016 / 141438 Al, the CPMs comprise: Co, Ni, Cu, Zn, Ga, Ge, Rh, Pd, Ag, Cd, In, Sn, Ir, Pt, Au, Hg, Tl, Pb and Bi. In an embodiment, the CPMs may comprise: Co, Ni, Zn, Ga, Ge, Rh, Pd, Ag, Cd, In, Sn, Ir, Pt, Hg, Tl, Pb and Bi. In another embodiment, the CPMs may comprise: Co, Ni, Zn, Ga, Ge, Rh, Pd, Cd, In, Sn, Ir, Pt, Hg, Tl, Pb and Bi. In a further embodiment, the CPMs may comprise Co, Ni, Zn, Ga, Ge, Cd, In, Sn, Hg, Tl, Pb, Bi. In another embodiment, the CPMs may exclude Pb.

[0071] The NCEs comprise all elements that are not members of the CPMs.

[0072] Where the leach enhancer is added, the weight ratio of amino acid to the leach enhancer in solution during contact with the feed material is greater than 2:1 (conversely, the leach enhancer preferably does not make up more than 33 weight% of the combined mass of amino acid and leach enhancer). The weight ratio of amino acid to the leach enhancer may be greater than 3:1. However, typically the ratio of amino acid (e.g. glycine) to the leach enhancer is higher, such as a minimum of 10:1. In an embodiment, the minimum weight ratio of amino acid to leach enhancer is 100:1. The weight ratio may be as high as 1000:1, particularly where high ratios of CPM base metals (e.g. Ni, Cu, Co, Zn, Pb) to CPM precious 30 metals (Au, Ag Pt, Pd, Rh, Ir) are present.

[0073] The amino acid concentration in solution may vary from 0.1 to 240 grams per litre. The amino acid concentration may be a minimum of 3.75 grams per litre and in an embodiment may be a minimum of 16 grams per litre. The maximum amino acid concentration may be 60 grams per litre and in another embodiment, the amino acid concentration is a maximum of 37.8 grams per litre.

[0074] The leaching step (i) is conducted under alkaline conditions. In an embodiment, the leaching step is conducted using a moderately alkaline solution having a pH above 7. In one embodiment, the pH is at least 8. In another embodiment, the pH is at least 8.5. In another embodiment, the pH is at least 9. In another embodiment, the pH is at least 9.5. In another embodiment, the pH is at least 9.5. In another embodiment, the pH is at least 10. In another embodiment, the pH is a maximum of 13. In another embodiment, the pH range is a maximum of 11.5. In another embodiment, the pH is a maximum of 10.

[0075] In step (ii) of the process, the chalcophile metal containing leach residue is subjected to flotation to produce a chalcophile metal concentrate and a tailings fraction. In an embodiment, the leach residue contains one component that is rich in a target metal and another component that is poor in the target metal. For example, the component that is rich in a target metal may largely comprise metal sulfides and the component that is poor in the target metal may largely comprise gangue minerals. The flotation step may comprise forming an aqueous slurry of particles of the leach residue which is treated with a collector (such as a xanthate) and aerated in flotation cells to produce bubbles. As noted above, it is believed that the presence of retained amino acid in the leach residue enhances the effectiveness of the flotation step by improving adsorption of the collector onto ore particles and thereby improving their floatability.

[0076] The flotation step may include treatment of the leach residue in a rougher- scavenger cell and / or a cleaner cell and / or a cleaner- scavenger cell.

[0077] The process flowsheet for producing the concentrate may include multiple steps that include at least one step of leaching a feed material followed by a step of flotation of the leach residue. These steps may occur at any suitable point in the flowsheet.

[0078] In an embodiment, the feed material for step (i) comprises comminuted run of mine ore.

[0079] In another embodiment, the feed material for step (i) comprises an ore concentrate produced from a separation step, such as by gravity separation or flotation.

[0080] In an embodiment, the feed material for step (i) comprises a rougher- scavenger concentrate. The rougher-scavenger concentrate may be the product of flotation of ground run of mine ore. In this embodiment, the leach residue from step (ii) is subjected to flotation in a cleaner cell and / or a cleaner- scavenger cell. The leach reside may undergo grinding prior to flotation in step (ii).

[0081] The process of the present disclosure may include one or more of the following additional steps: 1) subjecting the chalcophile metal concentrate produced in step (ii) to a further leaching step to produce a further leachate containing the second metal (and optionally the chalcophile metal) and a further leach residue containing the chalcophile metal. The further leach residue may be subjected to a further flotation step to produce a further chalcophile metal concentrate and a further tailings fraction.

[0082] 2) treating the chalcophile metal concentrate and / or any further chalcophile metal concentrate to recover the chalcophile metal.

[0083] 3) treating the leachate and any further leachate to recover the second metal and any chalcophile metal / s.

[0084] According to the present disclosure, there is further provided a process for producing a concentrate of a target metal from a feed material containing one component that is relatively rich in the target metal and another component that is relatively poor in the target metal, the feed material having been leached with an alkaline solution containing a lixiviant comprising an amino acid, wherein the process includes:

[0085] (i) subjecting an aqueous slurry of the feed material to flotation and producing a metal concentrate fraction and a tailings fraction;

[0086] (ii) recovering the metal concentrate fraction.

[0087] Step (i) may comprise processing the leached feed material in a flotation circuit.

[0088] Step (i) may comprise subjecting an aqueous slurry of the feed material to flotation whilst being aerated in order to produce the metal concentrate fraction and the tailings fraction

[0089] According to the present disclosure, there is also provided a process for recovering a first metal from a feed material containing said first metal containing phase and a second metal containing phase, said process including:

[0090] (i) contacting the feed material with an alkaline solution containing a lixiviant comprising an amino acid, or derivative thereof, and forming a leachate containing the second metal (and optionally the first metal) and a leach residue containing the first metal;

[0091] (ii) subjecting the first metal containing leach residue to flotation and producing a metal concentrate and a tailings fraction;

[0092] (iii) leaching the first metal concentrate produced in step (ii) and producing a further leachate containing the second metal (and optionally the first metal) and a further leach residue containing the chalcophile metal; (iv) subjecting the further leach residue to a further flotation step and producing a further first metal concentrate and a further tailings fraction;

[0093] (v) treating the first metal concentrate and / or the further first metal concentrate and recovering the first metal; and

[0094] (vi) treating the leachate and / or the further leachate and recovering the second metal and any first metal / s.

[0095] Step (ii) and / or step (iv) may comprise processing the first metal containing leach residue in a flotation circuit and producing the first metal concentrate and the tailings fraction.

[0096] The metal / s may be recovered by one or more methods including solvent extraction (SX), ion exchange (IX), precipitation, adsorption, electrowinning, etc.

[0097] Advantageously the metal may be recovered by adsorption.

[0098] The adsorbent may advantageously be activated carbon which is inexpensive and often readily available.

[0099] Alternatively, the adsorbent may be an ion-exchange resin. The ion-exchange resin may comprise an insoluble polymer matrix containing a backbone of cross-linked styrene or methacrylic acid polymers that are cross-linked with divinylbenzene containing side chains of ion-active functional groups to exchange anions or cations from solution. These "functional groups" contain either positively- charged ions (to absorb cations) or negatively-charged ions (to absorb anions). The two most common commercial resins are made of polystyrene sulfonate, followed by polyacrylate.

[0100] Polyacrylates are formed by reaction of polyacrylic acid with sodium acrylate forming an anionic polyelectrolyte with negatively charged carboxylic groups in the main chain. It is a polymer made up of chains of acrylate compounds where sodium acrylate is the salt of acrylic acid. It contains sodium, which gives it the ability to absorb large amounts of water.

[0101] Ion-exchange resins may be acrylic-based or epoxy-based. Acrylic resins can be repeatedly heated and shaped being strong, durable, and resistant to UV damage. Epoxy resin create hard and durable castings where once the mixture is set, it cannot be remoulded or reshaped. Epoxy resins are very strong and resistant to chemicals, electrical damage, and heat. This makes them ideal for use in high-stress environments and applications requiring strength and durability. Epoxy resins are also more prone to breakage due to this hardness then acrylic resins.

[0102] The adsorbent may be present during the leaching process, for example as carbon-in-leach (CIL) or resin-in leach (RIL). Accordingly, the metal extracted during the leaching process is adsorbed onto the adsorbent (activated carbon particles or resin) within the leach solution. In another embodiment the adsorbent is contacted with the leachate after separation from the leach residue.

[0103] Advantages of at least some embodiments of the present disclosure include:

[0104] • Significant improvement in purity and amount of recovered metal concentrates as compared with prior art methods.

[0105] • Higher recovery of the second metal, particularly recovery of precious metals (e.g., greater than 75 % recovery of gold).

[0106] • Lower residence time of feed material in leach solution enabling higher throughput.

[0107] • Improved effectiveness of flotation with enhanced floatability of concentrate and better separation from tailings.

[0108] • Effectiveness to scavenge lost chalcophile and precious metals from tailings.

[0109] BRIEF DESCRIPTION OF THE DRAWINGS

[0110] Notwithstanding any other forms which may fall within the scope of the processes as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

[0111] Figure 1 is a flowsheet of a conventional (prior art) process for production of a copper concentrate and precious metals from a copper-precious metal ore.

[0112] Figure 2 is a flowsheet of a first embodiment of a process for production of a copper concentrate.

[0113] Figure 3 is a flowsheet of a second embodiment of a process for production of a copper concentrate.

[0114] Figure 4 is a flowsheet of a conventional (prior art) process for recovery of precious metals from an ore material containing iron sulfides, precious metal, and a relatively low concentration of copper sulfides (typically less than 0.1% copper). Figure 5 is a flowsheet of a conventional (prior art) process for recovering precious metal from an ore material containing iron sulfides, precious metal, and a relatively high concentration of copper sulfides (typically contain greater than 0.1% copper).

[0115] Figure 6 is a third embodiment of the present process and is a modification of the flowsheet shown in Figure 4.

[0116] Figure 7 is a fourth embodiment of the present process and is a modification of the flowsheet shown in Figure 5.

[0117] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0118] Figures 1, 4 and 5 are flowsheets of conventional (prior art) processes whereas Figures 2, 3, 6 and 7 are flowsheets showing embodiments of the present disclosed process. Each of Figures 2, 3, 5 and 7 includes multiple steps in the flowsheets and these multiple steps include at least one leach step that produces a leach residue followed by a flotation step on the leach residue. Accordingly, the leach step followed by the flotation step on the leach residue can be conducted at any suitable point in the flowsheet.

[0119] Figure 1 shows a flowsheet (10) of a conventional (prior art) process for production of a copper concentrate and precious metals from a copper-precious metal ore. The ore (12) is comminuted in crushing (14) and grinding (16) stages, then undergoes gravity separation (18). The concentrate (20) from the gravity separation is processed in an elution and electrowinning step (22) and then in pyrometallurgy step to produce dore (a semi-pure alloy of gold and silver) (24). The gravity tails (26) undergo flotation in rougher- scavenger cells (28) and the flotation concentrate (30) is subjected to further grinding and gravity separation (32). Tails (34) from the further gravity separation step undergo flotation in cleaner (36) and cleaner-scavenger (38) cells to produce the final copper concentrate (40). Flotation tails (42) from the cleaner-scavenger flotation are then treated with a cyanide carbon in leach (CIL) leach (44) to extract gold which is recovered onto activated carbon and then recovered in the elution and electrowinning step (22).

[0120] Figure 2 shows a flowsheet of a first embodiment of a process (110) for production of a copper concentrate (140) and dore (124) from a copper-precious metal ore (112). In Figure 2 similar reference numerals represent similar features / steps of the prior art process in Figure 1. The following discussion will therefore focus on the features that differ from Figure 1. The flotation concentrate (130) from the rougher- scavenger cells (128) comprises feed material to a leaching stage (146). The flotation concentrate (130) is leached with an alkaline aqueous solution containing a lixiviant comprising an amino acid (glycine) and a leach enhancer comprising cyanide. In this embodiment, the leach (146) is conducted as a carbon-in-leach (CIL) process in which precious metal extracted from the concentrate (130) is adsorbed onto activated carbon particles within the leach solution. The extracted precious metal is then recovered in the elution and electrowinning step (122) to produce dore (124). The leach residue (148) is subjected to further grinding and gravity separation (132). Tails (134) from the further gravity separation step undergo flotation in cleaner (136) and cleanerscavenger (138) cells to produce the final copper concentrate (140). Flotation tails (142) from the cleaner-scavenger flotation (138) are then subjected to a second leaching stage (150) in which the flotation tails (142) are leached with an alkaline aqueous solution containing a lixiviant comprising an amino acid (e,g glycine) and a leach enhancer comprising cyanide. The leach (150) is also conducted as a carbon in leach (CIL) process in which precious metal extracted from the concentrate (130) is adsorbed onto carbon particles and the extracted precious metal is then recovered in the elution step (122) to produce dore (124).

[0121] Figure 3 shows a flowsheet of a second embodiment of a process (210) for production of a copper concentrate (240) and dore (224) from a copper-precious metal ore (212). In Figure 3 similar reference numerals represent similar features / steps of the prior art process in Figure 1 and the flowsheet of Figure 2. The following discussion will therefore focus on the features that differ from Figures 1 and 2. The concentrate (220) from the gravity separation (218) is processed in an elution step (222) to produce dore (224). The gravity tails (226) comprise feed material to a leaching stage (246). The gravity tails (226) are leached with an alkaline aqueous solution containing a lixiviant comprising an amino acid (glycine) and a leach enhancer comprising cyanide. In this embodiment, the leach (246) is also conducted as a carbon-in-leach (CIL) process in which precious metal extracted from the gravity tails (226) is adsorbed onto carbon particles within the leach solution. The extracted precious metal is then recovered in the elution step (222) to produce dore (224). The leach residue (248) is subjected to flotation in rougher- scavenger cells (228). A sulfide source (252), such as NaHS, is added to the flotation slurry to precipitate out any chalcophile metals co-leached with the precious metals and the precipitated chalcophile sulfides report to the flotation concentrate. The flotation concentrate (230) is subjected to further grinding and gravity separation (232). Tails (234) from the further gravity separation step undergo flotation in cleaner (236) and cleaner-scavenger (238) cells. Flotation tails (242) from the cleaner-scavenger flotation (238) are then subjected to a second leaching stage (250) in which the flotation tails (242) are leached with an alkaline aqueous solution containing a lixiviant comprising an amino acid (glycine) and a leach enhancer comprising cyanide.

[0122] The leach (250) is also conducted as a CIL process in which precious metal extracted from the flotation tails (242) is adsorbed onto carbon particles and the extracted precious metal is then recovered in the elution step (222) to produce dore (224).

[0123] Figure 4 is a flowsheet of a conventional process for recovering precious metal from an ore material containing iron sulfides (e,g pyrite and possibly pyrrhotite), precious metal and a relatively low concentration of copper sulfides (e,g chalcopyrite and possibly chalcocite, bornite, etc). The ore material (312) would typically contain less than 0.1% copper. Again, similar reference numerals refer to similar features. The ore (312) is comminuted in crushing (314) and grinding (316) stages, then undergoes gravity separation (318). The concentrate (320) from the gravity separation is processed in an elution and electrowinning step (322) to produce dore (a semi-pure alloy of gold and silver) (324). The gravity tails (326) undergo flotation in rougher- scavenger cells (328) and the flotation concentrate (330) is subjected to ultrafine grinding (332). The ground concentrate is then subjected to an intensive cyanide leach (336). Tails from both the intensive cyanide leach (336) and from the flotation stage (328) undergo further cyanide leaching (344). The leachate is processed in the elution and electrowinning step (322).

[0124] Figure 5 is a flowsheet of a conventional process for recovering precious metal from an ore material containing iron sulfides (e,g pyrite and possibly pyrrhotite), precious metal and a relatively high concentration of copper sulfides (e,g chalcopyrite and possibly chalcocite, bornite, etc). The ore material (412) would typically contain greater than 0.1% copper. Again, similar reference numerals refer to similar features. The ore (412) is comminuted in crushing (414) and grinding (416) stages, then undergoes gravity separation (418). The concentrate (420) from the gravity separation is processed in an elution and electrowinning step (422) to produce dore (a semi-pure alloy of gold and silver) (424). The gravity tails (426) undergo flotation in rougher- scavenger cells (428) and the flotation concentrate (430) is subjected to ultrafine grinding (432). The ground concentrate is then subjected to an intensive cyanide leach (436) followed by counter current decantation (440). The CCD leachate is then subjected to a Merrill Crowe process stage (430) to precipitate precious metal from solution by zinc cementation which is then recovered in the elution stage (422). The cyanide containing tails from the Merrill Crowe process stage (430) must then undergo a SART (sulfidization, acidification, recycling and thickening) process (438) in order to manage and recycle the cyanide in the tails. The copper is recovered as copper product (450) and recovered cyanide (434) is recycled to the intensive cyanide leaching step (436).

[0125] Figure 6 is a third embodiment of the present process and is a modification of the flowsheet shown in Figure 4. Similar reference numerals relate to similar features and discussion of the third embodiment will therefore focus on the differences between it and Figure 4. In Figure 6, the flotation concentrate (530) is subjected to ultrafine grinding (532). The ground concentrate is then leached (536) with an alkaline aqueous solution containing a lixiviant comprising an amino acid (glycine) and a leach enhancer comprising cyanide (referred to herein as "GlyCat™"). Tails from both the GlyCat™ leach (536) and from the flotation stage (528) undergo further cyanide leaching (544). The leachate from the leach step (544) is processed in the elution and electrowinning step (522), while the leach residue is subjected to flotation in cleaner cells (554). A sulfide source (552), such as NaHS, is added to the flotation slurry to precipitate out any copper metals co-leached with the precious metals and the precipitated copper sulfides report to the flotation concentrate which is recovered as copper concentrate (550).

[0126] Figure 7 is a fourth embodiment of the present process and is a modification of the flowsheet shown in Figure 5. Similar reference numerals relate to similar features and discussion of the fourth embodiment will therefore focus on the differences between it and Figure 5. In Figure 7, the ground concentrate from the ultrafine grinding (632) step is then subjected to a GlyCat™ leach (636) followed by counter current decantation (640). The CCD leachate is then subjected to a Merrill Crowe process stage (630) to precipitate precious metal from solution by zinc cementation which is then recovered in the elution stage (622). Because there is no intensive cyanide leach step (as in Figure 5), there is no requirement for a subsequent SART step to manage and recycle cyanide, leading to considerable cost savings. The CCD tails are treated in a second GlyCat™ leach step (644) and the leachate therefrom is treated in the elution and electrowinning step (622) to produce dore. The leach tails are subjected to flotation in cleaner cells (654). A sulfide source (652), such as NaHS, is added to the flotation slurry to precipitate out copper metals co-leached with the precious metals and the precipitated copper sulfides report to the flotation concentrate which is recovered as copper concentrate (650).

[0127] Whilst a number of specific process embodiments have been described, it should be appreciated that the process may be embodied in many other forms. In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" and variations such as "comprises" or "comprising" are used 10 in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.

Claims

CLAIMS1. A process for producing a concentrate from a feed material containing a first metal containing phase and a second metal containing phase, said process including:(i) contacting the feed material with an alkaline solution containing a lixiviant comprising an amino acid, or derivative thereof, and forming a leachate containing the second metal (and optionally the first metal) and a leach residue containing the first metal; and(ii) subjecting the leach residue to flotation and producing a first metal concentrate and a tailings fraction.

2. The process of claim 1, wherein the feed material comprises one or more of an ore, a concentrate of an ore, a by-product of a process, a waste product, jewellery, electronic scrap, and other scrap materials.

3. The process of claim 1 or 2, wherein the first metal is present in the feed material as one or more sulfides and / or as a native metal.

4. The process of any preceding claim, wherein the first metal comprises a chalcophile metal (as defined herein).

5. The process of claim 3 wherein the feed material includes one or more metal sulfides selected from pyrite, chalcocite, covellite, chalcopyrite, bornite, millerite, pentlandite, cattierite, linnaeite, galena or sphalerite.

6. The process of any preceding claim, wherein the second metal containing phase includes a precious metal such as gold, silver and / or a platinum group element.

7. The process of any preceding claim, wherein the second metal containing phase includes an impurity phase such as a metal oxide.

8. The process of claim 7, wherein the metal oxide is an oxide of the first metal, for example, a copper oxide such as malachite.

9. The process of claim 7, wherein the metal oxide is produced by the oxidation or weathering of a primary sulfide mineral.

10. The process of any preceding claim, wherein the alkaline solution additionally includes a leach enhancer to enhance the leaching function of the amino acid or its derivative and / or to reduce the temperature requirements for the process.

11. The process of claim 10, wherein the leach enhancer comprises one or more of the following species: iodine and / or iodide mixtures, bromine and / or bromide mixtures, ammonia, ammonium, thiourea, copper salts, and cyanide salts and mixtures of these species.

12. The process of claim 11, wherein the leach enhancer is copper glycinate (Cu(Gly)2).

13. The process of any one of claims 10 to 12, wherein the leach enhancer is present in solution at a concentration of 2 molar or less.

14. The process of any one of claims 10 to 13, wherein the weight ratio of amino acid (or derivative) to the leach enhancer is greater than 2:1, such as greater than 3:1 in the solution.

15. The process of any preceding claim, wherein the amino acid concentration in solution may vary from 0.1 to 240 grams per litre.

16. The process of any preceding claim, wherein pH of the alkaline solution is at least 8.

17. The process of any preceding claim, including leaching the first metal concentrate produced in step (ii) and producing a further leachate containing the second metal (and optionally the first metal) and a further leach residue containing the first metal.

18. The process of claim 17, including processing the first leach residue in a flotation circuit and producing a further metal concentrate and a further tailings fraction.

19. The process of claim 17 or 18, wherein the first metal concentrate and / or any further metal concentrate to recover the first metal.

20. The process of any one of claims 17 to 19, including treating the leachate and any further leachate and recovering the second metal and any first metal / s.

21. The process of any preceding claim, including recovering the first metal and / or second metal by one or more methods including solvent extraction (SX), ion exchange (IX), precipitation, adsorption and electrowinning.

22. The process of claim 21, including recovering the first metal and / or second metal by adsorption using activated carbon.

23. A process for producing a concentrate of a target metal from a feed material containing one component that is relatively rich in the target metal and another component that is relatively poor in the target metal, the feed material having been leached with an alkaline solution containing a lixiviant comprising an amino acid, wherein the process includes:(i) subjecting an aqueous slurry of the feed material to flotation and producing a metal concentrate fraction and a tailings fraction; and(ii) recovering the metal concentrate fraction.

24. A process for recovering a first metal from a feed material containing said first metal containing phase and a second metal containing phase, said process including:(i) contacting the feed material with an alkaline solution containing a lixiviant comprising an amino acid, or derivative thereof, and forming a leachate containing the second metal (and optionally the first metal) and a leach residue containing the first metal;(ii) subjecting the first metal containing leach residue to flotation and producing a first metal concentrate and a tailings fraction;(iii) subjecting the first metal concentrate produced in step (ii) to a further leaching step and producing a further leachate containing the second metal (and optionally the first metal) and a further leach residue containing the first metal;(iv) subjecting the further leach residue to a further flotation step and producing a further first metal concentrate and a further tailings fraction;(v) treating the first metal concentrate and / or the further first metal concentrate and recovering the first metal; and (vi) treating the leachate and / or the further leachate and recovering the second metal and any first metal / s.

25. A concentrate produced by a process of claim 1 or 23.

26. A metal produced by the process of claim 24.

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