CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is an international PCT application which claims priority to United States Provisional Patent Application Serial No. 61/746,710 filed on 28 December 2012.

BACKGROUND

[0002] Many of the world's metal containing ores contain only small amounts (e.g. , by percent weight) of desirable metals. In order to make such ores commercially viable, it is often necessary to leach (i.e. , extract) the metal from the ore and concentrate it prior to further processing.

[0003] For example, over 90% the world's mine copper is currently obtained from copper sulfide ore processing. The most important copper sulfide species present in ores are chalcopyrite, bornite chalcosite, covellite, tenantite and enargite, of which chalcopyrite is the species found in most relative abundance and, therefore, the one of greatest economic interest. High-grade copper ores may only contain about 2% copper by weight and low-grade ores, which may be commercially viable nonetheless, may contain less than 1% copper by weight.

[0004] Copper sulfide ore processing is sustained by technologies based on physical and chemical processes associated with mineral crushing, grinding and flotation, followed by fusion-conversion of concentrates and electrolytic refining of metal. In practice, over 70% of copper is produced through the described route - known as the conventional route - which is limited to high and medium grade ores, according to the specific characteristics of deposits and of ore processing plants. [0005] On the other hand, ores in which copper is present in the form of oxide species (easily soluble in acid) are processed by means of acid leaching processes, followed by solvent extraction processes and electro- winning of the metal, in what is known as copper winning through hydrometallurgy. This route is very attractive due to its lower operation and investment costs when compared to conventional technologies, as well as to its lower environmental impact. Nevertheless, applications of this technology are limited to oxide ores, or to copper sulfide mixed ores in which metal is present in the form of secondary sulfides (chalcosite and covellite) that are acid soluble in the presence of an energetic oxidizing agent catalyzed by microorganisms.

[0006] As an alternative to the processes described above, leaching of minerals may be accomplished in the presence of micro-organisms that enhance the leaching kinetics. However, the leaching environments are difficult for microorganisms due to the low pH, high ionic strength, and high temperatures. In fact, all hydro metallurgical processing conditions can be incredibly harsh to microorganisms. In some instances, extremophiles (i.e. , bacteria that thrive under extreme conditions) may be used in bioleaching. Nevertheless, bioleaching is inherently inefficient because, for example, much of the organisms' energy must be expended by the organisms in life processes unrelated to mineral recovery, the organisms must be supplied with nutrients, many of which are incompatible with mineral processing and recovery, and leaching may tend to kill microorganisms or suppress their growth due to harsh environments (e.g. , low pH, high ionic strength, high temperatures, etc.). SUMMARY

[0007] Described herein are enzyme-based leaching agents that can be used to leach metals from metal-containing ores. Methods for recovering metals from metal- containing ores using such enzyme-based leaching agents are also described. Enzymes that are active under leaching conditions (e.g. , low pH, high ionic strength, high temperatures) may be isolated from microorganisms that are able to thrive under such conditions. In addition, the activity of enzymes that are identified as being active under leaching conditions may be improved through protein engineering techniques such as, but not limited to, random mutagenesis, site directed mutagenesis, directed evolution, combinatorial techniques, and the like.

[0008] In an embodiment, a leaching agent for recovering a metal from a metal- containing ore is described. The leaching agent includes an acid and at least one enzyme associated with the acid and capable of promoting (e.g. , enhancing) leaching metal from the metal-containing ore. For example, the leaching agent may be substantially abiotic. In one embodiment, the at least one enzyme may include a native enzyme or a recombinant enzyme that is isolated from or derived from a microorganism.

[0009] In another embodiment, a method of recovering a metal from a metal- containing ore is described. The method includes (1) contacting the ore with a leaching agent that includes at least one enzyme, wherein the leaching agent is substantially abiotic, (2) performing a leaching process with the leaching agent to leach the metal from the metal-containing ore, (3) producing at least one of a solid or liquid leachate from the leaching process, wherein the leachate includes the metal from the metal- containing ore, and (4) recovering the metal from the leachate. [0010] In a more specific embodiment, the method may include a method of recovering copper from a copper sulfide-containing ore. Such a method includes (1) contacting the copper sulfide-containing ore with an acidic, substantially abiotic leaching agent that includes Fe(III) and at least one enzyme capable of oxidizing Fe(II) to Fe(III), (2) performing a leaching process to leach the copper from the copper sulfide-containing ore, (3) producing at least one of a solid or liquid leachate from the leaching process, wherein the leachate includes the copper from the copper sulfide- containing ore, and (4) recovering copper metal from the leachate.

[0011] In one embodiment, the at least one enzyme may include at least one of rusticyanin or cytochrome C442. In one embodiment, the copper sulfide-containing ore may include at least one of copper sulfide (chalcocite and covellite) or copper iron sulfide (chalcopyrite and bornite). Other metals that can be recovered using the methods described herein include, but are not limited to, molybdenum, gold, silver, and nickel.

[0012] In an embodiment, a screening assay may be performed to identify the at least one enzyme that is suitable for leaching the metal. In an embodiment, crystalline nano-scale mineral particles may be pre-synthysized that represents, or otherwise approximate a composition of the metal-containing ore. In an embodiment, the composition of the crystalline nano-scale mineral particles may be approximately about 0.001 μιη to about 0.1 μιη in diameter. In some embodiments, the screening assay may further include subjecting the crystalline nano-scale mineral particles to a solution to form a plurality of homogenous test assays, and separately combining the test assays with different enzymes to identify the at least one enzyme. In some embodiments, the different enzymes used may be previously subjected to random or site-specific mutagenesis.

[0013] In an embodiment, the screening assay further includes identifying colorometric, fluorometric, or calorimetric changes within any of the test assays. For example, the solution may be include one or more of the following for identifying colorometric changes: a) ferrozine if the metal contains iron, copper, or cobalt; b) cuprizone if the metal contains copper; or c) PAR if the metal contains zinc, nickel, cobalt, or copper. In an embodiment, the solution may include one or more of the following for identifying fluorometric changes: a) monobromobimane if the metal contains thiols; or b) Fura-2 if the metal contains manganese, cobalt, zinc, copper, nickel, or cadmium. For example, colorometric changes may be identified with a photoelectric colorimeter or color standard comparison; fluorometric changes may be identified with a flurometer; and calorimetric changes may be identified using thermocouples or calorimeters.

[0014] In a further embodiment, contacting the metal-containing ore with a leaching agent may include providing at least one non-biocatalyst. For example, the at least one non-biocatalyst comprises light waves, microwaves, or radiowaves.

[0015] Features from any of the disclosed embodiments may be used in combination with one another, without limitation. In addition, other features and advantages of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the following detailed description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To further clarify the above and other advantages and features of embodiments of the present invention, a more particular description will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only illustrated embodiments of the invention and are therefore not to be considered limiting of its scope. Various embodiments of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0017] Figure 1 illustrates a flow diagram for a biohydrometallurgy process according to an embodiment that may employ any of the leaching agents disclosed herein;

[0018] Figure 2 illustrates a flow diagram for a biohydrometallurgy leaching process according to an embodiment that may employ any of the leaching agents disclosed herein; and

[0019] Figure 3 illustrates a flow diagram for a biohydrometallurgy process for recovering copper from a copper sulfide-containing ore according to an embodiment that may employ any of the leaching agents disclosed herein.

DETAILED DESCRIPTION

[0020] Described herein are enzyme-based leaching agents that can be used to leach metals from metal-containing ores. Methods for recovering metals from metal- containing ores using such enzyme-based leaching agents are also described. Enzymes that are active under leaching conditions (e.g. , low pH, high ionic strength, high temperatures) may be isolated from microorganisms that are able to thrive under such conditions. In addition, the activity of enzymes that are identified as being active under leaching conditions may be improved through protein engineering techniques such as, but not limited to, random mutagenesis, site directed mutagenesis, directed evolution, combinatorial techniques, and the like.

I. LEACHING AGENTS

[0021] In an embodiment, a leaching agent for recovering a metal from a metal- containing ore is described. The leaching agent includes at least one enzyme capable of leaching at least one metal or a metal-containing species from the metal-containing ore. Preferably, the leaching agent is substantially abiotic. As used herein, the term "abiotic" refers to a leaching agent that is substantially free of bacteria, fungi, and other living organisms that are capable of self-replication. One will appreciate that while the materials (e.g. , metal containing ores) that the leaching agent is applied to may include microorganisms that can proliferate under leaching conditions, the leaching agent itself is substantially abiotic.

[0022] In one embodiment, the leaching agent includes an acid to which a metal- containing ore may be exposed, such as by immersion in a leaching tank or percolation as occurs in heap leaching. In another embodiment, the leaching agent may be a dry material that is added to the metal-containing ore. For instance, the leaching agent may include a lyophilized enzyme and any optional additives. Such a dry leaching agent may, for example, be activated by rehydrating the leaching agent in hydrated leach pile. The leaching agent may have an enzyme concentration sufficient to allow the concentration of enzyme in the leach agent to be about 1 ppm to about 1000 ppm or any concentration therebetween, such as about 5 ppm to about 100 ppm, or about 10 ppm to about 25 ppm.

[0023] In an embodiment, the enzyme may be added in a lyophilized state. The most concentrated is in mM range. The solution may be buffered to leach condition pH. In some embodiments, detergents or fatty organics should not be added that are mobile in the leach pile. Detergents/ polymers may be used to get higher E solubilities for transport. In an embodiment, PEGylation of the enzyme and immobilization of enzymes on a surface may be performed. This surface may be used to line leach vessels or be a media (such as beads) that is larger than the crushed ore and readily separated by screening after mixing with the ore slurry. The leaching agent may contain a redox agent to keep the enzyme in an active redox state prior to addition to the ore.

[0024] In one embodiment, the leaching agent further includes at least one of Fe(III) or a silver ion. For instance, in the recovery of copper from copper sulfide ores, Fe(III) may be used to convert insoluble copper sulfide species to soluble Cu ²⁺ ions. For example, the reaction formula below illustrates this process:

CuS + 8 Fe ³⁺ + 4 H ₂ 0→ Cu ²⁺ + 8 Fe ²⁺ + S0 ₄ ^2~ + 8 H ⁺ Formula 1

Recovery of copper from copper-iron-sulfide ores (e.g. , chalcopyrite) can be accomplished by a similar chemical process. Likewise, similar chemistry can be used for recovery of metals such as lead, nickel, and zinc from sulfide-containing ores. However, in order to maintain the process, it is necessary to either begin the process with an excess of Fe(III), replenish the Fe(III) by continuing to add more as the leaching progresses, or convert the Fe(II) back to Fe(III).

[0025] Starting with an excess of Fe(III) and/or continually adding Fe(III) to the leach are expensive and impractical. This can be appreciated by reviewing Formula 1 above: 8 moles of Fe(III) is needed in order to recover 1 mole of Cu ²⁺ from CuS. Other copper sulfides require even more Fe(III). However, in one embodiment, the enzyme(s) included in the leaching agent may be selected to be capable of converting Fe(II) to Fe(III). Such an enzyme can continually recycle Fe(II) to Fe(III) and keep the leaching reaction going forward.

[0026] In one embodiment, the leaching agent may include a native enzyme or a recombinant enzyme that is isolated from or derived from a microorganism. In one embodiment, the enzyme is derived from an organism selected from the group consisting of acidophiles, thermophiles, halophiles, and combinations thereof. For example, Acidithiobacillus ferrooxidans is a bacterium that is able to thrive in acidified sulfate soils, mine drainage effluents, and other mining areas. A. ferrooxidans naturally produces enzymes that can be used in enzyme-based leaching agents described herein. Such enzymes can be isolated as native enzymes from A. ferrooxidans or a similar organism or recombinant enzymes can be produced and isolated from other organisms (e.g., E. coli) using recombinant DNA technology.

[0027] In one embodiment, the enzyme includes at least one of a cupredoxin, a cytochrome, an iron- sulfur protein, or another enzyme that is capable of participating in one or more redox reactions involved in leaching metal(s) from metal-containing ores. For example, the enzyme may be at least one of rusticyanin or cytochrome C442. In one embodiment, rusticyanin is particularly preferred. Rusticyanin is a bacterial enzyme that is, in its native context, involved in electron- transfer. Rusticyanin is a copper- containing enzyme and a strong oxidant that can, for example, catalyze the conversion of Fe(II) to Fe(III). Overexpression and purification of the rusticyanin protein from A. ferrooxidans in E. coli is described in "Gene Synthesis, High-Level Expression, and Mutagenesis of Thiobacillus ferrooxidans Rusticyanin: His 85 Is a Ligand to the Blue Copper Center," Casimiro et al., Biochemistry 1995, 34, 6640-6648, the entirety of which is incorporated herein by reference.

[0028] In one embodiment, the leaching agent may further include one or more of a chaperone, a detergent, a polymer additive (e.g., PEO, PVP, or combinations thereof), or an electron transfer dye in an amount of about 1-100 ppm. Such additives may, for example, increase the stability and/or activity of the enzyme included in the leaching agent. For example, the structure of the ore may prevent access by the enzyme to the metal-containing species or the ore may develop a crust in the leaching process that likewise prevents access by the enzyme to the metal-containing species. In such a case, the electron transfer dye may be added to the leaching agent to shuttle electrons between the enzyme and the ore. Suitable examples of electron transfer dyes include, but are not limited to, methyl viologen (redox potential of about -660 mV (SHE)), patent blue, curcumin (redox potential of about 0.8-1 (SHE)), methylene blue (redox potential of 100-500 mV (SHE)), diphenylamine (redox potential of about 760 mV (SHE)), bromophenol blue, and the like.

[0029] In addition to the foregoing, enzymes having identified activity under leaching conditions can be selectively engineered to increase their activity, increase pH stability, resistance to high ionic strength, high temperatures, and the like. Proteins may be re-engineered to alter their activity and/or their stability using a number of techniques. For instance, enzyme activity, stability, and the like may be improved through protein engineering techniques such as, but not limited to, random mutagenesis, site directed mutagenesis, directed evolution, combinatorial techniques, combinations thereof, and the like. Referring specifically to rusticyanin, the high-resolution three- dimensional structure of rusticyanin is known. This high-resolution three-dimensional structure can be used to identify candidate residues for mutagenesis in order to improve enzyme activity, stability, and the like.

[0030] For example, redox potentials may be tuned by altering the secondary sphere of an enzyme' s active site while pH stability may be increased by blocking solvent access to enzymes active site via steric interactions and hydrophobic amino acids. Altering the amino acid sequence of proteins can negatively impact the enzyme's activity (i.e. , how well it functions chemically). Nevertheless, high-throughput mutagenesis and analysis processes can be used to quickly identify successful mutants by producing a large number and screening them for activity under the harsh conditions of mineral processing. Those enzymes that remain active may then be sequenced and subjected to further study. In this way, a natural enzyme can be altered in order to yield an enzyme that is easily overexpressed and purified as well as being highly active and stable under leaching conditions.

[0031] For instance, the activity and/or the stability of a natural enzyme may be altered so that the enzyme is active for recovering a metal from a metal-containing ore at under conditions such as, but not limited to, a pH in a range of 0-4 (e.g., 0-2, or 0-3), a high ionic strength up to and including a saturation point of one or more metals (e.g. , copper ions) from the metal-containing ore, or a temperature up to about 80 °C. In contrast to natural and genetically modified organisms that may be used in bioleaching, these altered proteins are not subject to any special environmental regulations and, because they cannot self-replicate, they are therefore seen as catalysts opposed to biological reagents.

[0032] Further discussion of such techniques and examples of their use for altering the activity of proteins can be found in "Enhancement of pH stability and activity of glycerol dehydratase from Klebsiella pneumoniae by rational design," Qi X et al., Biotechnol Lett. 2012 Feb;34(2):339-46; "Improvement in the alkaline stability of subtilisin using an efficient random mutagenesis and screening procedure," Cunningham et al., Protein Eng. (1987) 1 (4): 319-325; "Structure-based replacement of methionine residues at the catalytic domains with serine significantly improves the oxidative stability of alkaline amylase from alkaliphilic Alkalimonas amylolytica," Yang et al., Biotechnology Progress, Volume 28, Issue 5, pages 1271-1277, September/October 2012; "Modulating the Redox Potential and Acid Stability of Rusticyanin by Site-Directed Mutagenesis of Ser86," Hall et al., Biochemistry, 1998, 37 (33), pp 11451-11458; "Rationally tuning the reduction potential of a single cupredoxin beyond the natural range," Marshall et al., Nature 462, 113-116 (5 November 2009); "A combination of weakly stabilizing mutations with a disulfide bridge in the a-helix region of Trichoderma reesei endo-l,4-P-xylanase II increases the thermal stability through synergism," Turunena et al., Journal of Biotechnology, Volume 88, Issue 1, 1 June 2001, Pages 37-46; "Engineering of a Cold- Adapted Protease by Sequential Random Mutagenesis and a Screening System," Taguchi et al., Appl. Environ. Microbiol. February 1998 vol. 64 no. 2 492-495; "Tuning the activity of an enzyme for unusual environments: sequential random mutagenesis of subtilisin E for catalysis in dimethylformamide," Chen et al., PNAS June 15, 1993 vol. 90 no. 12 5618- 5622; and "Optimising enzyme function by directed evolution," Dalby et al., Current Opinion in Structural Biology, Volume 13, Issue 4, August 2003, Pages 500-505, the entireties of which are incorporated herein by reference.

II. METHODS OF RECOVERING A METAL FROM A METAL- CONTAINING ORE

[0033] Referring now to Figure 1, a flow diagram for a biohydrometallurgy process 100 is illustrated according to an embodiment, which may employ any of the leaching agents disclosed herein. The biohydrometallurgy process 100 includes a step 110 of mining and/or receiving the metal-containing ore. Most copper ores contain only a small percentage of copper metal, with the remainder of the ore being unwanted rock or waste minerals, typically silicate minerals or oxide minerals for which there is often no value. The average grade of copper ores in the 21st century is below 1% copper, with a proportion of economic ore minerals (including copper) being less than 2% of the total volume of the ore rock. A key objective in the metallurgical treatment of any ore is the separation of ore minerals from the waste materials within the rock.

[0034] Following mining of the ore 110, the ore is subjected to a process called comminution 120. Comminution is a process in which solid materials are reduced in size, by crushing, grinding and other processes. There are several methods of comminution. Comminution of solid materials requires different types of crushers and mills depending on the feed properties such as hardness at various size ranges and application requirements such as throughput and maintenance. The most common machines for the comminution of coarse feed material are the jaw crusher (lm > P80 > 100 mm), cone crusher (P80 > 20 mm) and hammer crusher. Primary jaw crusher product in intermediate feed particle size ranges (100mm > P80 > 20mm) can be ground in autogenous or semi-autogenous mills depending on feed properties and application requirements. For comminution of finer particle size ranges (20mm > P80 > 30 μιη) machines like the ball mill, vertical roller mill, hammer mill, roller press or high compression roller mill, vibration mill, jet mill and others may be used.

[0035] Following comminution 120, the metal-containing ore may be subjected to flotation 130 prior to leaching 140. Flotation 130 is essentially a concentration process. Flotation 130 is particularly effective for concentrating copper obtained from copper- containing ores. Remember that it is likely that less than 1% (e.g. , about 0.6%) of the ore is copper. In such cases, it may be desirable to concentrate the proportion of copper in the ore prior to further processing.

[0036] In such a case, the ore from the comminution process 120 may be combined with water to form a slurry and the slurry is mixed with milk of lime (simply water and ground-up limestone) to give a basic pH, an oil (e.g. , pine oil) to make bubbles, an alcohol to strengthen the bubbles, and a flotation reagent - e.g. , potassium amyl xanthate or a peptide flotation reagent.

[0037] The xanthates or the peptides are added to the slurry in relatively small quantities. The xanthates or peptides are long chain molecules. In one embodiment, one end of the chain is polar and sticks to sulfide minerals while the other end is nonpolar and is attracted to the nonpolar hydrocarbon pine oil molecules.

[0038] Raising the pH causes the polar end to ionize more and to preferentially stick to sulfide minerals (e.g. , chalcopyrite (CuFeS ₂ ) or chalcocite (Cu ₂ S)). Air is blown into the tanks and agitated like a giant blender, producing a foamy froth. The sulfide mineral grains become coated with the flotation reagent with their hydrophobic ends waving around trying desperately to get out of the water.

[0039] The hydrophobic tails attach themselves to the oily air bubbles which become coated with chalcopyrite grains as they rise to the surface and flow over the edge of the tank. In this manner through a series of steps the ore is concentrated. For example, copper ore can be concentrated from about 0.6% to an eventual value of about 30% copper. Waste rock particles do not adhere to the bubbles and drop to the bottom of the tank.

Following either comminution 120 or flotation 130, the ground and/or concentrated ore may be subjected to a leaching process 140 to liberate the metal form the metal- containing ore. Leaching is an extraction process used to extract precious metals, copper, uranium, and other metals from ore via a series of chemical reactions that absorbs specific minerals and then re-separate them after their division from other earth materials. In one embodiment, the leaching 140 may be a heap leaching process. In heap leaching, the ore is piled on a lined bed and then leaching chemicals are percolated through the pile to leach metal from the ore. In the case of heap leaching, the enzyme- based leaching processes described herein may be preferable to known bioleaching processes that use bacterial consortia because the heap leaching process can generate a great deal of heat that can kill living cells; however, enzymes may be unaffected.

Furthermore, enzymes do not require nutrients or battle with existing heap components and become altered in the activity. For example, bacteria compete for nutrients and eventually die off.

[0040] In another embodiment, the leaching 140 may include a tank leaching process where the ore and the leaching chemical are combined in a tank and stirred to promote separation of metal from the ore. In the case of stirred reactor or agitated leach vessel, the enzyme-based methods described herein may be further preferable to known bioleaching processes that use bacterial consortia in that the mixing processes may actually tend to physically rupture cells by grinding them or smashing them between the ore material.

[0041] Referring now to Figure 2, the leaching process 140 is illustrated in greater detail according to an embodiment. The leaching process includes a step 210 of contacting the ore with a substantially abiotic leaching agent that includes at least one enzyme. In one embodiment, the at least one enzyme has a concentration in the leaching agent of a lower concentration of about 1 ppm, 5 ppm, 10 ppm, 15 ppm, 20 ppm, 30 ppm, 50 ppm, 75 ppm, 100 ppm, 150 ppm, 200 ppm, 300 ppm, 400 ppm, or about 500 ppm; an upper concentration of about 1000 ppm, 900 ppm, 800 ppm, 700 ppm, 600 ppm, 550 ppm, 500 ppm, 450 ppm or about 400 ppm, and any combination of the recited lower and upper concentration values, such as about 1 ppm to about 1000 ppm (e.g., 5-10 ppm, 1-5 ppm, or 5-15 ppm).

[0042] The leaching 140 further includes a step 220 of performing a leaching process to leach the metal from the metal-containing ore. As explained in greater detail herein above, the at least one enzyme in the leaching agent is capable of participating in one or more chemical reactions that separate the metal from the metal containing ore. In one embodiment, the enzyme may be an iron oxidizing enzyme. For example, rusticyanin is oxidizing enough to oxidize chalcopyrite.

[0043] For example, the leaching process may include converting Fe(III) to Fe(II) to yield a soluble metal species from the metal-containing ore and the leaching process may then further include enzymatically converting the Fe(II) produced in the leaching process back to Fe(III). In one embodiment, the enzyme may be at least one of a cupredoxin, a cytochrome, or an iron-sulfur protein. Suitable examples of enzymes include, but are not limited to rusticyanin or cytochrome C442.

[0044] The leaching 140 further includes a step 230 of producing at least one of a solid or liquid leachate from the leaching process, wherein the leachate includes the metal from the metal-containing ore.

[0045] Referring again to Figure 1, following the leaching process 140, the metal(s) may be recovered from the leachate in steps 150- 170. In step 150, the leachate is treated to remove impurities from the leachate. For example, impurities may be removed with the use of ion exchange resins, molecular recognition, microfibers (e.g., carbon nanomaterial), or by biorecognition.

[0046] In step 160, the metal is extracted from the leachate by solvent extraction. For example, copper is typically extracted acidic leachate by adding phenolic oxime compounds to the leachate that selectively complex with copper. The copper complexed with oxime can be recovered from the leachate. The oxime is recycled and the copper is sent to further processing.

[0047] In step 170, the metal(s) from the solvent extraction step 160 are purified by electrowinning. Electro winning, also called electroextraction, is an electrodeposition process where metals in solution are electrodeposited on an electrode surface. Electrowinning uses electroplating on a large scale - the resulting metals are said to be electrowon. The metal is deposited on the cathode (either in solid or in liquid form), while the anodic reaction is usually oxygen evolution. The most common electrowon metals are lead, copper, gold, silver, zinc, aluminium, chromium, cobalt, manganese, and the rare-earth and alkali metals. For aluminium, this is the only production process employed.

[0048] Referring now to Figure 3, a specific embodiment of a method 300 for extracting copper from a copper sulfide-containing ore is illustrated. Such a method 300 includes a step 310 of providing a copper sulfide-containing ore. In one embodiment, the copper sulfide-containing ore may include the copper sulfide- containing ore includes at least one of copper sulfide (chalcocite and covellite) or copper iron sulfide (chalcopyrite and bornite).

[0049] Method 300 further includes a step 320 of contacting the copper sulfide- containing ore with an acidic, substantially abiotic leaching agent that includes Fe(III) and at least one enzyme capable of oxidizing Fe(II) to Fe(III). In one embodiment, the enzyme may be at least one of rusticyanin or cytochrome C442. A suitable example of such an enzyme is rusticyanin. In one embodiment, the enzyme has a concentration in the leaching process of about 1 ppm to about 1000 ppm. In one embodiment, the leaching solution further comprising one or more of a chaperone, a detergent, a polymer additive, or an electron transfer dye.

[0050] In one embodiment, the leaching agent may include silver ions in addition to Fe(III). Silver ions are capable of participating in chemical reactions to liberate copper from copper sulfate ore similarly to iron. In addition, because silver is highly toxic to most living organisms, the enzyme based processes described herein can use silver, whereas processes that uses bacterial consortia cannot use silver because the silver could kill some or all of the organisms in the consortia.

[0051] The method 300 further includes a step 330 of performing a leaching process wherein the enzyme is allowed to participate in one or more chemical reactions to recover copper from the copper sulfate ore. The leaching process 330 produces a leachate in step 340 that includes copper recovered from the ore. The method 300 finally includes a step 350 of recovering copper metal from the leachate. The metal may, for example, be recovered from the leachate according to steps 150-170 described in reference to Figure 1.

[0052] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.