Systems and methods including electrochemically regenerated, oxidative leaching of target materials from sulfide minerals with nitrates

Abstract

An electrochemically mediated, hydrometallurgical method is provided for extraction of nickel, zinc, lead, silver, molybdenum, and / or copper from sulfide minerals. These metal concentrates, such as pentlandite, pyrrhotite, pyrite, sphalerite, galena, Ag2S, MoS2, etc., are contacted with nitric acid and cerium(IV) nitrates, cerium(IV) methanesulfonate, and / or cerium(IV) sulfate, as oxidative leaching agents to preferentially leach the target metals contained therein. The strong oxidizing capacity of cerium(IV) enables rapid dissolution of metal sulfides under ambient conditions. Cerium(IV) can be electrochemically regenerated and recycled for treatment of additional sulfide minerals. Target metal products can be extracted via processes such as solvent extraction and precipitation, enabling complete recovery, e.g., of nickel from pentlandite.

Description

Attorney Docket No.: 105054-201SYSTEMS AND METHODS INCLUDING ELECTROCHEMICALLY REGENERATED, OXIDATIVE LEACHING OF TARGET MATERIALS FROM SULFIDE MINERALS WITH NITRATESCROSS REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the benefit of U.S. Provisional Application Nos. 63 / 921,377, filed November 20, 2025, and 63 / 722,657, filed November 20, 2024, which is incorporated by reference as if disclosed herein in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0002] This invention was made with government support under DE-AR0001706 awarded by the U.S. Department of Energy. The government has certain rights in the invention.BACKGROUND

[0003] The increasing demand for nickel, driven by widespread adoption of battery technologies, necessitates more sustainable extraction methods. Nickel is a critical material due to its extensive use in stainless steel production, super alloys, and lithium-ion batteries, especially within nickelmanganese-cobalt (NMC) batteries, which are widely employed in electric vehicles due to their superior energy density. Current forecasts suggest global nickel demands will increase by 215- 350% by 2050, and in the short term, lead to an estimated shortfall of approximately one million tons by 2040. Addressing this shortfall sustainably and economically necessitates advanced nickel- mineral processing technologies that reduce and account for environmental and human health impacts while minimizing production costs.

[0004] Nickel primarily occurs in two distinct mineral forms: laterites and sulfides, accounting for roughly 65% and 35% of global reserves, respectively. Although lateritic deposits are more abundant, their extraction and processing are typically energy-intensive and environmentally challenging. In contrast, nickel sulfides are amenable to conventional flotation concentration techniques, offering potential advantages in economic viability and environmental impact. The declining availability of high-grade nickel laterite deposits has sparked renewed interest inAttorney Docket No.: 105054-201 processing lower-grade nickel sulfide resources due to their strategic locations in politically stable regions and lower carbon footprints.

[0005] Pentlandite ((Fe,Ni)9Ss) is the predominant terrestrial nickel sulfide mineral and serves as the primary ore in major nickel-producing regions such as Sudbury, Canada, and Kambalda, Australia. Current industrial extraction processes predominantly employ pyrometallurgical techniques, where nickel matte, an intermediate product containing 30% to 60% nickel, is produced at temperatures of about 1350°C. However, these conventional processes are characterized by high energy consumption and substantial emissions of greenhouse gases and sulfur dioxide. Conventional processing of nickel sulfide ores relies on smelting that results in significant unrealized environmental and human-health costs. Alternative processes involving solid-state selective reduction, roasting, and hydrogen-based reduction have also been explored but remain economically challenging due to severe operating conditions.

[0006] Hydrometallurgical methods, such as leaching at or near ambient temperatures using reagents including ammonia, chloride, nitric acid, and sulfuric acid, have been investigated as cleaner alternatives. Recent studies report that ambient-pressure and low-temperature hydrometallurgical methods deliver low nickel recovery (less than about 40%) and are frequently slowed by sulfur passivation, while bioleaching at a controlled pH environment shows elemental sulfur layer formation that limits nickel extraction kinetics. These factors collectively mean that more extreme conditions are usually employed to achieve economically viable recovery from nickel sulfide feedstocks.SUMMARY

[0007] Aspects of the present disclosure are directed to methods of leaching target materials from sulfide minerals. In some embodiments, the method includes providing a composition including a metal concentrate, the metal concentrate including concentrations of one or more target metals; contacting the metal concentrate with a solution including one or more chemical oxidizers, the chemical oxidizers including cerium(IV); oxidizing at least a portion of the target metal within the metal concentrate via reaction with the one or more chemical oxidizers; isolating a target-metal- containing product from the composition; and isolating a product from the target-metal-containing product that includes a concentration of the target metal. In some embodiments, the target metal includes nickel, zinc, lead, silver, molybdenum, copper, or combinations thereof. In someAttorney Docket No.: 105054-201 embodiments, the metal concentrate includes pentlandite, pyrrhotite, pyrite, sphalerite, galena, Ag2S, M0S2, or combinations thereof. In some embodiments, the method includes pretreating the metal concentrate with one or more acids before contacting the metal concentrate with the solution.

[0008] In some embodiments, the one or more chemical oxidizers include cerium nitrates, cerium sulfates, cerium sulfonates, or combinations thereof. In some embodiments, the chemical oxidizers include cerium(IV) methanesulfonate, cerium(IV) sulfate, cerium(IV) nitrate, cerium(IV) ammonium nitrate, or combinations thereof.

[0009] In some embodiments, the method includes electrochemically converting a concentration of cerium(III) to cerium(IV) and contacting the cerium(IV) with the composition. In some embodiments, the method includes recovering a solid component from the target-metal-containing product; electrochemically converting the target-metal-containing product to obtain a second solution containing a concentration of recycled chemical oxidizers, the chemical oxidizers including cerium(IV); contacting at least a portion of the second solution with the solid component in a secondary oxidation reactor; and recycling the second solution from the secondary oxidation reactor to contact the composition. In some embodiments, the method includes obtaining a first portion and at least a second portion of the target-metal-containing product; electrochemically converting the first portion of the target-metal-containing product to obtain a concentration of recycled chemical oxidizers, the chemical oxidizers including cerium(IV); contacting the recycled chemical oxidizers with the composition; and extracting a solid cerium product from the second portion, wherein the product is isolated from the second portion. In some embodiments, the method includes electrochemically converting the target-metal-containing product to obtain a second solution containing a concentration of recycled chemical oxidizers, the chemical oxidizers including cerium(IV); contacting at least a first portion of the second solution with the composition; obtaining at least a second portion of the second solution; and extracting a solid cerium product from the second portion of the second solution, wherein the product is isolated from the second portion of the second solution.

[0010] In some embodiments, the step of isolating a product from the target-metal -containing product includes an electrochemically converting process, a precipitation process, a solvent extraction process, or combinations thereof. In some embodiments, the step of isolating a product from the target-metal-containing product includes contact with a concentration of: copper; one or more bases; sodium bisulfate and sulfuric acid, or combinations thereof.Attorney Docket No.: 105054-201

[0011] In some embodiments, the concentration of metal concentrate loaded into the solution is between about 5 g / L and about 100 g / L. In some embodiments, the concentration of cerium(IV) in the solution is between about 0.1 M and about 2.5 M. In some embodiments, the solution includes HNO3 at an about 1 : 1 to about 6: 1 ratio with the cerium(IV).

[0012] Aspects of the present disclosure are directed to a system for leaching target materials from sulfide minerals. In some embodiments, the system includes a source of target metal concentrate; an oxidation reactor in communication with the source of target metal concentrate, the oxidation reactor including a solution including one or more chemical oxidizers, the chemical oxidizers including cerium(IV); a target-metal-containing product outlet stream in fluid communication with the oxidation reactor; an electrolyzer in fluid communication with the target-metal-containing product stream, the electrolyzer producing a recycled chemical oxidizer stream in fluid communication with the oxidation reactor; and a product that includes a concentration of the target metal from the targetmetal-containing product stream, the target metal including nickel, zinc, lead, silver, molybdenum, copper, or combinations thereof. In some embodiments, the system includes a stream splitter positioned to: direct a first portion of the target-metal-containing product outlet stream to the electrolyzer and a second portion of the target-metal-containing product outlet stream to a targetmetal recovery reactor; direct a first portion of the recycled chemical oxidizer stream to the oxidation reactor and a second portion of the recycled chemical oxidizer stream to a target-metal recovery reactor, or combinations thereof. In some embodiments, the target-metal recovery reactor is in communication with a source of recovery compounds, the recovery compounds including: copper; one or more bases; sodium bisulfate and sulfuric acid, or combinations thereof.

[0013] Aspects of the present disclosure are directed to a method of leaching target materials from sulfide minerals. In some embodiments, the method includes preparing a medium in an oxidation reactor. In some embodiments, the medium includes concentrations of a nitrate compound; a cerium compound including cerium(IV) methanesulfonate, cerium(IV) nitrate, cerium(IV) sulfate, cerium(IV) ammonium nitrate, or combinations thereof, and metal concentrates including pentlandite, pyrrhotite, pyrite, sphalerite, galena, Ag2S, M0S2, or combinations thereof. In some embodiments, the medium includes between about 5 g / L and about 100 g / L metal concentrate, between about 0.1 M and about 2.5 M cerium compound, and between about 1 : 1 to about 6:1 ratio of nitrate compound to cerium(IV).Attorney Docket No.: 105054-201

[0014] In some embodiments, the method includes oxidizing at least a portion of target metal within the metal concentrate via reaction with cerium(IV) in the medium; isolating a target-metal- containing product from the oxidation reactor; precipitating a cerium product from the target-metal- containing product; electrochemically recycling cerium(III) from the target-metal-containing product to a concentration of cerium(IV); recycling a portion of the cerium(IV) to the oxidation reactor; and isolating a product including target metal from the target-metal-containing product via an electrolysis process, a solvent extraction process, precipitation process, or combinations thereof. In some embodiments, the concentration of target metal in the product is higher than in the metal concentrates.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings show embodiments of the disclosed subject matter for the purpose of illustrating the invention. However, it should be understood that the present application is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

[0016] FIGs. 1A-1D are charts of methods for leaching target materials from sulfide minerals according to embodiments of the present disclosure;

[0017] FIG. 2 is a chart of a method for leaching silver from silver sulfide according to embodiments of the present disclosure;

[0018] FIG. 3 is a chart of a method of leaching target materials from sulfide minerals according to embodiments of the present disclosure;

[0019] FIGs. 4A-4B portray systems for leaching target materials from sulfide minerals according to embodiments of the present disclosure;

[0020] FIG. 5 is a graph showing percent of nickel and iron released from acid-pretreated nickel- bearing pentlandite as a function of time according to embodiments of the present disclosure;

[0021] FIG. 6 is a graph showing percent of nickel extracted from acid-pretreated nickel-bearing pentlandite as a function of time using nitrates and sulfates according to embodiments of the present disclosure;Attorney Docket No.: 105054-201

[0022] FIG. 7Ais a graph showing percent of nickel extracted from acid-pretreated nickel-bearing pentlandite as a function of time at various pentlandite loadings according to embodiments of the present disclosure;

[0023] FIG. 7B is a graph showing percent of nickel extracted from acid-pretreated nickel-bearing pentlandite as a function of time at various nitric acid concentrations according to embodiments of the present disclosure;

[0024] FIG. 7C is a graph showing percent of nickel extracted from acid-pretreated nickel-bearing pentlandite as a function of time at various cerium(IV) concentrations according to embodiments of the present disclosure;

[0025] FIG. 7D is a graph showing percent of nickel extracted from acid-pretreated nickel-bearing pentlandite as a function of time at various temperatures according to embodiments of the present disclosure;

[0026] FIG. 8 is a graph showing x-ray diffraction (XRD) patterns of acid-pretreated nickel-bearing pentlandite according to embodiments of the present disclosure;

[0027] FIG. 9Ais a graph showing percent of nickel and iron extracted from the as-delivered raw pentlandite concentrate according to embodiments of the present disclosure; and

[0028] FIG. 9B is a graph showing concentration of nickel and iron in a pregnant leach solution following leaching of the as-delivered raw pentlandite concentrate according to embodiments of the present disclosure.DETAILED DESCRIPTION

[0029] Referring now to FIG. 1A, some embodiments of the present disclosure are directed to a method 100A of leaching target materials from sulfide minerals. In some embodiments, the target materials include one or more target metals. In some embodiments, the sulfide materials include metal concentrates including concentrations of the target metals. As used herein, the term “metal concentrate” refers to a medium including a concentration of the target metal, the extraction of which is desired. In some embodiments, the metal concentrate is a metal-containing mineral or combination of metal-containing minerals. In some embodiments, the target metal includes nickel, zinc, lead, silver, molybdenum, copper, or combinations thereof. In some embodiments, the metalAttorney Docket No.: 105054-201 concentrate includes pentlandite, pyrrhotite, pyrite, sphalerite, galena, Ag2S, M0S2, or combinations thereof. The exemplary embodiments of the present disclosure described above will demonstrate leaching and recovery of particular combinations of target metals from corresponding metal concentrates, however the present disclosure is not necessary limited to these exemplary embodiments, as one of ordinary skill in the art would be able to identify compositions of available sulfide minerals and the target metals available for leaching and recovery therefrom.

[0030] At 102A, a composition including the metal concentrate is provided. The composition and / or metal concentrate can be from any suitable source, e.g., naturally occurring material, industrial waste materials, etc., or combinations thereof. In some embodiments, the composition and / or metal concentrate is pretreated. In some embodiments, this pretreatment includes contact of the composition and / or metal concentrate with one or more acids. In some embodiments, the one or more acids includes H2SO4.

[0031] At 104A, the metal concentrate is contacted with a solution including one or more chemical oxidizers. In some embodiments, the chemical oxidizers include oxidizing ions, a compound including oxidizing ions, or combinations thereof. In some embodiments, the chemical oxidizers include cerium(IV). In some embodiments, the cerium(IV) chemical oxidizers are generated via electrochemical conversion of a concentration of cerium(III) to cerium(IV), which can then subsequently be contacted 104A with the composition / metal concentrates.

[0032] In some embodiments, the chemical oxidizers include cerium nitrates, cerium sulfonates, cerium sulfates, or combinations thereof. In some embodiments, the chemical oxidizer compounds include cerium(IV) methanesulfonate, cerium(IV) sulfate, cerium(IV) nitrate, cerium(IV) ammonium nitrate, or combinations thereof. In some embodiments, the concentration of cerium(IV) in the solution contacted 104A with the metal concentrate is between about 0.1 M and about 2.5 M.

[0033] Cerium(IV) is a strong oxidizing agent. With nitric acid as a supporting electrolyte, cerium(IV) has a redox potential of 1.61V. In some embodiments, the solution further contains nitrate ions, a compound including nitrate ions, or combinations thereof. In some embodiments, the solution includes HNO3. In some embodiments, the solution includes HNO3 at an about 1 : 1 to about 6: 1 ratio with the cerium(IV). In some embodiments, the solution is contacted 104 with the metal concentrate for about 5 minutes, about 10 minutes, about 20 minutes, about 30 minutes, about 40 minutes, about 50 minutes, about 60 minutes, about 70 minutes, about 80 minutes,Attorney Docket No.: 105054-201 about 90 minutes, about 100 minutes, about 110 minutes, about 120 minutes, etc. In some embodiments, the solution is contacted 104 with the metal concentrate at a temperature below about 80°C, about 70°C, about 60°C, about 50°C, about 40°C, etc. In some embodiments, the solution is contacted 104A with the metal concentrate at about room temperature.

[0034] At 106A, at least a portion of the target metal within the metal concentrate is oxidized via reaction with the one or more chemical oxidizers, as will be discussed in greater detail below.

[0035] At 108A, a target-metal-containing product is isolated from the composition. The targetmetal-containing product can be isolated by any suitable process, e.g., filtration, decanting, etc., or combinations thereof. In some embodiments, the target-metal-containing product is a liquid including leachate from the composition. In some embodiments, the target-metal-containing product includes concentrations of target metal from the metal concentrates, e.g., nickel, zinc, lead, silver, molybdenum, copper, or combinations thereof. In some embodiments, the target-metal- containing product includes concentrations of target metal ions. In some embodiments, the target- metal-containing product also includes concentrations of reduced chemical oxidizer, unreacted chemical oxidizer, unreacted metal concentrate, inerts, etc., or combinations thereof. In some embodiments, the target-metal-containing product is provided to a subsequent oxidation reactor for additional leaching with additional chemical oxidizers. In some embodiments, the target-metal- containing product is subjected to 1 or more serially performed oxidative leaching processes consistent with those described in the present disclosure.

[0036] At 110A, a product is isolated from the target-metal-containing product. In some embodiments, the product includes a concentration of the target metal. In some embodiments, isolation 110A includes an electrolysis process, a precipitation process, a solvent extraction process, or combinations thereof. In some embodiments, isolation 110A includes contact with a concentration of copper; one or more bases; sodium bisulfate and sulfuric acid, or combinations thereof.

[0037] Referring now to FIG. IB, some embodiments of the present disclosure are directed to a method 100B of leaching target materials from sulfide minerals. In some embodiments, as discussed above, at 102B, a composition including the metal concentrate is provided. At 104B, the metal concentrate is contacted with a solution including one or more chemical oxidizers. At 106B, at least a portion of the target metal within the metal concentrate is oxidized via reaction with theAttorney Docket No.: 105054-201 one or more chemical oxidizers. At 108B, a target-metal-containing product is isolated from the composition.

[0038] In some embodiments, at HOB, a solid component is recovered from the target-metal- containing product. In some embodiments, the recovered solid component includes unreacted composition from step 102B. At 112B, the target-metal-containing product is electrochemically converted to obtain a second solution containing a concentration of recycled chemical oxidizer compounds including cerium(IV). In some embodiments, at 114B, at least a portion of the second solution is contacted with the solid component, e.g., in a secondary oxidation reactor. In some embodiments, at least a portion of the second solution is recycled for use in step 104B, e.g., in a primary oxidation reactor. In some embodiments, at 116B, second solution from the secondary oxidation reactor is recycled to contact the composition in step 104B, again, e.g., in a primary oxidation reactor. At 118B, the product is isolated from the target-metal-containing product.

[0039] Referring now to FIG. 1C, some embodiments of the present disclosure are directed to a method 100C of leaching target materials from sulfide minerals. In some embodiments, as discussed above, at 102C, a composition including the metal concentrate is provided. At 104C, the metal concentrate is contacted with a solution including one or more chemical oxidizers. At 106C, at least a portion of the target metal within the metal concentrate is oxidized via reaction with the one or more chemical oxidizers. At 108C, a target-metal-containing product is isolated from the composition.

[0040] In some embodiments, at 110C, a first portion and at least a second portion of the target- metal-containing product are obtained. At 112C, the first portion of the target-metal-containing product is electrochemically converted, obtaining a concentration of recycled chemical oxidizers including cerium(IV). At 114C, the recycled chemical oxidizers are contacted with the composition. In some embodiments, at 116C, a solid cerium product is extracted from the second portion. At 118C, the product is isolated from the second portion.

[0041] Referring now to FIG. ID, some embodiments of the present disclosure are directed to a method 100D of leaching target materials from sulfide minerals. In some embodiments, as discussed above, at 102D, a composition including the metal concentrate is provided. At 104D, the metal concentrate is contacted with a solution including one or more chemical oxidizers. At 106D, at least a portion of the target metal within the metal concentrate is oxidized via reaction with theAttorney Docket No.: 105054-201 one or more chemical oxidizers. At 108D, a target-metal-containing product is isolated from the composition.

[0042] In some embodiments, at HOD, the target-metal-containing product is electrochemically converted to obtain a second solution containing a concentration of recycled chemical oxidizer compounds including cerium(IV). At 112D, at least a first portion of the second solution is recycled back and contacted with the composition. At 114D, at least a second portion of the second solution is obtained. At 116D, a solid cerium product is extracted from the second portion of the second solution. At 118D, the product is isolated from the second solution.

[0043] The leaching kinetics of various metal concentrations in cerium-containing reactants were examined, e.g., pentlandite in cerium(IV) nitrate, with emphasis on the influence of electrolyte composition, concentrate loading, acid concentration, and temperature on dissolution efficiency. Through characterizing the leached product, the oxidation reactions were identified and the electron consumption was quantitatively determined. Additionally, the selective leaching study was conducted on mineral concentrate containing a substantial amount of pyrrhotite, demonstrating the preferential dissolution of pentlandite.

[0044] In an exemplary embodiment of the present disclosure, an amount of nickel concentrate such as pentlandite (Fe4.5Ni4.5Ss) can be leached, e.g., at oxidation reaction step 106A, 106B, 106C, or 106D above, according to reactions 1 and 2 below:Fe45Ni45Sa+ 22.5Ce4+4.5Fe3++ 8S° + 4.57Vi2++ 22.5Ce3+(Reaction 1)Fe45Ni45Sg+ 70.5Ce4++ 32H2O -> 4.5Fe3++ 8SO^~ + 4.5JVi2++ 70.5Ce3++ 64H+(Reaction 2)

[0045] In the exemplary embodiment wherein pentlandite is included in the composition, Ce(IV) is reduced to a concentration of Ce(III), producing a pregnant leach solution (PLS) rich in Ce(III) and Ni(II). As discussed above, in some embodiments, the pentlandite is pretreated, e.g., via contact with one or more acids including sulfuric acid, which results in removal of pyrrhotite and improved nickel recovery.

[0046] In some embodiments, sodium bisulfate and sulfuric acid is added to the PLS, causing cerium to precipitate out as NaCe(SC>4)2. Additional treatments of the PLS with bases suchAttorney Docket No.: 105054-201 as NaOH can further remove iron compounds and generate a high-purity mixed hydroxide precipitate product enriched with nickel from the pentlandite.

[0047] In an exemplary embodiment of the present disclosure, an amount of sphalerite (ZnS) metal concentrate can be leached, e.g., at oxidation reaction step 106A, 106B, 106C, or 106D above, according to reactions 3 and 4 below:ZnS + 2Ce4+Zn2++ S°s)+ 2Ce3+(Reaction 3)ZnS + 8Ce4++ 4H2O Zn2++ 5042" + 8Ce3++ 8H4(Reaction 4)In the exemplary embodiment wherein ZnS is included in the composition, Ce(IV) is reduced to a concentration of Ce(III), causing Zn(II) to leach out and leaving behind solid elemental sulfur.

[0048] Referring now to FIG. 2, in an exemplary embodiment of the present disclosure, an amount of silver sulfide (Ag2S) can be leached, e.g., at oxidation reaction step 106A, 106B, 106C, or 106D above. In the exemplary embodiment wherein Ag?S is included in the composition, Ce(IV) is reduced to a concentration of Ce(III), causing silver to leach out as silver nitrate and leaving behind solid elemental sulfur. Subsequent addition of copper to the to the silver nitrate results in the formation of copper nitrate and a silver product that can be isolated therefrom. X-ray diffraction (XRD) analysis following leaching with IM cerium(IV) nitrate and cementation with copper showed that this exemplary embodiment of the present disclosure resulted in pure metallic silver products.

[0049] In an exemplary embodiment of the present disclosure, an amount of molybdenite (M0S2) can be leached, e.g., at oxidation reaction step 106A, 106B, 106C, or 106D above, according to reactions 5 and 6 below:MOS2+ 18Ce4++ 12H2O -> MoO42~ + 2SO42~ + 18Ce3++ 24H+Reaction 5MOS2+ 6Ce4++ 4H2O -> Mo042~ + 2S° + 6Ce3++ 8H+Reaction 6Attorney Docket No.: 105054-201 In the exemplary embodiment wherein M0S2 is included in the composition, Ce(IV) is reduced to a concentration of Ce(III), producing a PLS rich in Ce(III) and Mo(VI).

[0050] In some embodiments, base such as NaOH or NH4OH is added to the PLS, causing Mo to precipitate out in the form of Ce2(MoC>4)3 combined with Ce(OH)3 as by-products. Further separation of Mo from cerium can be achieved by washing the precipitate with NaOH. With stirring, the Mo in the precipitate redissolves while cerium stays in solid form.

[0051] In some embodiments, sodium bisulfate and sulfuric acid is added to the PLS, causing cerium to precipitate out as NaCe(SO4)2. This cerium precipitate can be converted to cerium(III) hydroxide and dissolved in acid to regenerate cerium(IV) electrochemically. In the exemplary embodiment described above with M0S2, as substantially all Mo remains in the PLS, the NaCe(SO4)2 can be filtered out and the Mo product isolated and recovered.

[0052] Referring now to FIG. 3, some embodiments of the present disclosure are directed to a method 300 of leaching target materials from sulfide minerals. At 302, a medium is prepared in an oxidation reactor. In some embodiments, the medium includes concentrations of a nitrate, e.g., nitrate compounds; cerium, e.g., a cerium compound; and metal concentrates. As discussed above, in some embodiments, the nitrate includes nitric acid (HNO3). In some embodiments, the cerium includes cerium nitrates, cerium sulfonates, cerium sulfates, or combinations thereof. In some embodiments, the cerium includes cerium(IV) methanesulfonate, cerium(IV) sulfate, cerium(IV) nitrate, cerium(IV) ammonium nitrate, or combinations thereof. In some embodiments, the metal concentrates includes pentlandite, pyrrhotite, pyrite, sphalerite, galena, Ag2S, M0S2, or combinations thereof.

[0053] In some embodiments, the medium includes between about 5 g / L and about 100 g / L metal concentrate. In some embodiments, the medium includes between about 0.1 M and about 2.5 M cerium. In some embodiments, the medium includes between about 1 : 1 to about 6: 1 ratio of nitrate to cerium(IV).

[0054] At 304, at least a portion of target metal within the metal concentrate is oxidized via reaction with cerium(IV) in the medium. At 306, a target-metal-containing product is isolated from the oxidation reactor. In some embodiments, the isolated target-metal-containing product is added to a second, third, etc. reactor for additional oxidation, e.g., contact with additional fresh media.Attorney Docket No.: 105054-201

[0055] In some embodiments, at 308, a cerium product is precipitated from the target-metal- containing product. In some embodiments, at 310, at least a portion of the cerium(III) from the target-metal-containing product is electrochemically recycled to a concentration of cerium(IV). In some embodiments, at 312, a portion of the cerium(IV) is recycled to the oxidation reactor.

[0056] At 314, a product including a concentration of target metal is isolated from the target-metal- containing product. As discussed above, in some embodiments, the target metal includes nickel, zinc, lead, silver, molybdenum, copper, or combinations thereof. The product can be isolated 314 via any suitable process, including via an electrolysis process, a solvent extraction process, precipitation process, or combinations thereof. In some embodiments, the concentration of target metal in the product is higher than in the metal concentrates.

[0057] Referring now to FIGs. 4A-4B, some embodiments of the present disclosure are directed to a system 400 for leaching target materials from sulfide minerals. In some embodiments, system 400 includes a source 402 of target metal concentrate. In some embodiments, the metal concentrate includes pentlandite, pyrrhotite, pyrite, sphalerite, galena, Ag?S, M0S2, or combinations thereof. In some embodiments, source 402 is naturally occurring material, industrial waste materials, etc., or combinations thereof.

[0058] In some embodiments, system 400 includes an oxidation reactor 404 in communication with source 402 of target metal concentrate. In some embodiments, oxidation reactor 404 is two or more reactors arranged in series, parallel, or combinations thereof, for facilitating a multi-stage leaching of target metals from the metal concentrates. Oxidation reactor 404 includes a solution 406. As discussed above, in some embodiments, solution 406 includes one or more chemical oxidizers. In some embodiments, the chemical oxidizers include cerium(IV). As discussed above, the one or more chemical oxidizers includes cerium nitrates, cerium sulfonates, cerium sulfates, or combinations thereof. In some embodiments, the chemical oxidizers include cerium(IV) methanesulfonate, cerium(IV) sulfate, cerium(IV) nitrate, cerium(IV) ammonium nitrate, or combinations thereof.

[0059] In some embodiments, the solution includes between about 0.1 M and about 2.5 M cerium. In some embodiments, the solution includes an additional concentration of nitrates, e.g., HNO3. In some embodiments, the solution includes between about 1 : 1 to about 6: 1 ratio of a nitrate toAttorney Docket No.: 105054-201 cerium(IV). In some embodiments, the concentration of metal concentrate loaded into the solution is between about 5 g / L and about 100 g / L.

[0060] Still referring to FIG. 4A, system 400 includes a target-metal-containing product outlet stream 408. As discussed above, outlet stream 408 includes target-metal-containing product, but can also include concentrations of reduced chemical oxidizer, unreacted chemical oxidizer, unreacted metal concentrate, inerts, etc., or combinations thereof. In some embodiments, outlet stream 408 is in fluid communication with oxidation reactor 406, e.g., to remove target-metal-containing product, etc. from oxidation reactor 406 and recover components, e.g., a target metal product, therefrom.

[0061] In some embodiments, system 400 includes an electrolyzer 410. In some embodiments, outlet stream 408 is in fluid communication with electrolyzer 410. In some embodiments, electrolyzer 410 produces a recycled chemical oxidizer stream 412 that is in fluid communication with oxidation reactor 404.

[0062] In some embodiments, system 400 includes a target-metal recovery reactor 414. In some embodiments, recovery reactor 414 is configured to output a product outlet stream 416 including one or more products. As discussed above, in some embodiments, the product includes a concentration of the target metal from outlet stream 408. In some embodiments, the target metal includes nickel, zinc, lead, silver, molybdenum, copper, or combinations thereof.

[0063] In some embodiments, recovery reactor 414 is in fluid communication with outlet stream 408. In some embodiments, recovery reactor 414 is in communication with a source 418 of recovery compounds. As discussed above, in some embodiments, the recovery compounds include copper; one or more bases; sodium bisulfate and sulfuric acid; etc. or combinations thereof. The recovery compounds enable recovery of target metals, e.g., via solvent extraction, precipitation, etc.

[0064] In some embodiments, system 400 includes a stream splitter 420. In some embodiments, stream splitter 420 can direct up to 100% of outlet stream 408 and / or recycled chemical oxidizer stream 412 to a desired system component. Specifically referring to FIG. 4A, in some embodiments, stream splitter 420 is positioned to direct a first portion 408' of outlet stream 408 to electrolyzer 410 and a second portion 408" of outlet stream 408 to recovery reactor 414. In some embodiments, stream splitter 420 directs between about 10% and about 90% of outlet stream 408 as first portion 408' to electrolyzer 410. In some embodiments, stream splitter 420 directs about 90% of outlet stream 408 as first portion 408' to electrolyzer 410.Attorney Docket No.: 105054-201

[0065] Referring now to FIG. 4B, in some embodiments, stream splitter 420 is positioned to direct a first portion 412' of recycled chemical oxidizer stream 412 to oxidation reactor 404 and a second portion 412" of recycled chemical oxidizer stream 412 to target-metal recovery reactor 414. In some embodiments, stream splitter 420 directs between about 10% and about 90% of recycled chemical oxidizer stream 412 as first portion 412' to oxidation reactor 404. In some embodiments, stream splitter 420 directs about 90% of recycled chemical oxidizer stream 412 as first portion 412' to oxidation reactor 404.EXAMPLES

[0066] Referring now to FIG. 5, the leaching kinetics of pentlandite in cerium(IV) nitrate were examined, with emphasis on the influence of electrolyte composition, concentrate loading, acid concentration, and temperature on dissolution efficiency. Additionally, the selective leaching study was conducted on mineral concentrate containing a substantial amount of pyrrhotite, demonstrating the preferential dissolution of pentlandite.

[0067] Raw nickel concentrate was obtained from the Tamarack, MN resource from Talon Metals Corp. The chemical assays determined by X-ray fluorescence (XRF) are shown in Table 1 below. Quantitative analysis shows that pentlandite, the primary nickel-bearing phase, makes up 46% of the concentrate by weight. XRD Rietveld refinement analysis was conducted to confirm these results. The result indicates that the concentrate comprises 53% pentlandite and 47% pyrrhotite.

[0068] Cerium (III) nitrate (Sigma-Aldrich) was dissolved in IM HNO3 to produce a IM Ce(NO3)a electrolyte solution. A lOOmL divided batch cell was used for the electrochemical oxidation of Ce(III) to Ce(IV). The cell included mesh-type platinum anode and cathode, separated by a Nafion 117 membrane. The catholyte compartment contained IM HNO3 solution. A constant current of 0.8A (corresponding to a current density of 40 mA / cm2) was applied using an Ivium-n- Stat potentiostat. The conversion of Ce(III) to Ce(IV) was verified through potentiometric titration with lM Fe(SO4)2 solution.

[0069] The leaching experiments were conducted in a batch setup. Nickel concentrate was added into IM H2SO4 at a solid loading of 50g / L. The resulting slurry was then heated to 80°C and stirred for 2 hours to remove most of the pyrrhotite from the concentrate. The acid-treated concentrate was then added into Ce(NO3)4 solution and stirred for 1 hour. The effects of mass loading (10-40g / L), Ce(IV) concentration (0.5-2M), acid concentration (1-3M), and temperature (25-55°C) wereAttorney Docket No.: 105054-201 investigated. Each leaching experiment was performed in duplicate, and the average conversion values are reported. In some experiments, the nickel concentrate was directly introduced into Ce(NC>3)4 solution without acid pretreatment and allowed to react for 2 hours. After the reaction, the solid product was filtered and dried in air prior to characterization.

[0070] Liquid samples of 250 pL were taken from the leach solution at time intervals of 0, 5, 10, 20, 40, and 60 min through a 0.45 pm syringe filter. The samples were then diluted using 2% HNO3 to appropriate concentration and measured using inductively coupled plasma-optical emission spectroscopy (ICP-OES, HORIBA Scientific) for nickel and iron concentration.

[0071] The electrochemical behavior of the mineral concentrate during leaching was measured via the construction of mineral electrodes. By mass, an 8: 1 : 1 mineral concentrate :PVDF binder: carbon- black mixture was mixed with N-Methyl-2-Pyrrolidone, slurry cast to 150pm on grade 2 titanium substrate, and dried for 24 hours. 12mm disks were die punched from the sheet and these disks were contact welded to titanium leads. These electrodes were used as working electrodes in a three- electrode cell setup with an AgCl reference electrode and platinum wire counter electrode. All tests were performed on an Autolab M204 Multichannel PGSTAT.

[0072] The as-delivered raw nickel concentrate and acid-pretreated concentrate were analyzed by energy-dispersive XRF (EDX-7200, SHIMSDZU) to determine the iron, nickel, copper, cobalt and sulfur content. The mineral phase was characterized by XRD (Panalytical X’Pert3) with Cu Ku radiation (40 kV, 40 mA). The samples were scanned in the range of 10-100° with a step size of 0.01° and 128s counting time at each step. XRD software HighScore Plus (Malvern Panalytical) was used to perform Rietveld refinements to quantify the phases in the concentrate and products.

[0073] To investigate the leaching behavior of nickel -bearing pentlandite, pyrrhotite was selectively removed from the concentrate through leaching in IM H2SO4 for 2 hours at 80°C at a mass loading of 50g / L. Experimental results show that about 70% iron and about 2% nickel in the concentrate were leached, indicating that pyrrhotite was dissolved into the acid while pentlandite remained largely unreacted. The composition of the acid-pretreated nickel concentrate by XRF is presented in Table 1. The weight percentages of iron and nickel are similar, suggesting that the concentrate was predominantly pentlandite. The pretreated concentrate was subsequently subjected to leaching with cerium(IV) nitrate to examine its dissolution behavior.Attorney Docket No.: 105054-201Table 1 : Weight fraction of selected elements in raw and acid-pretreated nickel concentrate.

[0074] FIG. 5 presents the extraction kinetics of nickel and iron in IM Ce(NC>3)4 electrolyte at a mass loading of 20g / L, which was generated through electrolytic oxidation of IM Ce(NOa)3 in IM HNO3. The amount of nickel extracted increased rapidly in the initial 10 minutes, achieving 66% recovery, followed by a gradual slowdown. After 2 hours of leaching, 89% of the nickel was extracted from the concentrate, with iron dissolving concurrently. Approximately 10% of the copper was detected in the leach solution, suggesting the low reactivity of chalcopyrite. To achieve complete nickel extraction from pentlandite, extended leaching was conducted, resulting in 98.5% leached after 6 hours. A double-leaching process was also tested. Specifically, the acid pretreated nickel concentrate was initially leached in IM Ce(NC>3)4 for 30 minutes, after which the solid residue was filtered and dried before it was reacted again with fresh IM Ce(NO3)4for another hour. The results show that 65.6% of nickel was extracted during the first leach, while an additional 32.8% was extracted in the second leach, yielding a 99.4% extraction efficiency. These findings collectively demonstrate that nearly complete nickel recovery from pentlandite can be achieved through cerium(IV) leaching. A control experiment using IM HNO3 as the leaching medium suggests that a negligible amount of nickel and iron (<1%) was leached after 2 hours, suggesting that the fast kinetics were attributed to the oxidizing capacity of cerium(IV).

[0075] Referring now to FIG. 6, the nickel extraction percentages achieved in 0.5M Ce(SO4)4 dissolved in 0. IM H2SO4 and in 0.5M Ce(NCh)4 solution under identical loading of acid-pretreated concentrate were investigated. The leaching kinetics of pentlandite were also investigated in cerium(IV) sulfate media.

[0076] A reduced cerium(IV) concentration was used, considering the solubility constraints of cerium(IV) sulfate. As shown in the plot, the leaching kinetics in nitrate media are significantly faster than in sulfate media, with nickel extraction reaching 78% within one hour in the nitrate system, while cerium(IV) sulfate used approximately 8 hours of reaction time to achieve a similar recovery. To quantify the leaching rates of pentlandite in cerium(IV) nitrate and cerium(IV) sulfate media, an exponential model was applied to fit the experimental data. The derived kinetic rate constants indicate that leaching in cerium(IV) nitrate proceeds 12 times faster than in cerium(IV)Attorney Docket No.: 105054-201 sulfate media. Furthermore, a shrinking core model used to describe the oxidative leaching of sulfide mineral was fitted, with a similar conclusion that leaching is approximately 10-times faster in nitrate.

[0077] Referring now to FIG. 7A-7D, the effect of feedstock loading on nickel extraction efficiency was evaluated using IM Ce(NOs)4 as the oxidizing agent. The results indicate that the fraction of nickel leached decreased as more concentrate was loaded. At a mass loading of 10 g / L, the nickel conversion reached 92% within one hour of leaching.

[0078] The effect of nitric acid concentration on the dissolution kinetics was also investigated. The starting cerium(III) electrolytes were prepared with varying HNO3 concentrations ranging from IM to 3M. The electrochemically generated cerium(IV) was reacted with acid-pretreated nickel concentrate, with results shown in FIG. 7B. The concentration of nitric acid had a negligible impact on the leaching rates, with consistent nickel recoveries of about 83% observed across all concentrations after one hour. From a process perspective, lower nitric acid concentrations can be preferable, due to reducing the base consumption for downstream neutralization processes and minimizing risks associated with nitrate loss.

[0079] The relationship between cerium(IV) concentration and nickel extraction efficiency is presented in FIG. 7C. The results show that increasing the cerium(IV) concentration from IM to 2M improves the nickel recovery from 82% to 95%, whereas a reduction to 0.5M decreases leaching conversion and rate. Under fixed mass loading conditions, increasing the cerium(IV) concentration led to more complete recovery and thereby increasing nickel concentration in the PLS.

[0080] Temperature effects on leaching were evaluated between 25°C and 55°C (see FIG. 7D). While leaching conversions remained unchanged from 25°C to 35°C, a slight decrease was observed at 45°C, with similar conversions persisting at 55°C. At the end of leaching at 55°C, 74.5% of the nickel was extracted, compared to 82% at 25°C. Typically, increasing temperature improves the leaching kinetics and recovery of sulfide minerals, as it can mitigate passivation through accelerating the diffusion across the product layers. Without wishing to be bound by theory, the observed decrease of nickel leached might be related to the hydrolysis of cerium(IV) species at elevated temperature, forming insoluble CeCh nanoparticles and consequently reducing the concentration of available oxidant species in the leach solution.Attorney Docket No.: 105054-201

[0081] Referring now to FIG. 8, XRD patterns of the acid-pretreated nickel concentrate and cerium(IV) leached residues are displayed. The results reveal that the most prominent diffraction peaks in the pre-leach concentrate, observed at 20 angles of 29.5° and 51.5°, correspond to pentlandite. This indicates that pentlandite is the primary mineral phase within the concentrate prior to oxidative leaching. Following a one-hour reaction with cerium(IV), a notable reduction in pentlandite peak intensities was observed, accompanied by the emergence of characteristic peaks attributable to elemental sulfur. The quantitative analysis was conducted through Rietveld refinement, with results shown in Table 2 below. The results show that the acid-pretreated concentrate contains predominantly pentlandite with a minor amount of elemental sulfur. The presence of elemental sulfur can be attributed to the leaching of pyrrhotite during the acid pretreatment process. Post-leaching residue analysis indicates that elemental sulfur constitutes the majority component, with residual unreacted pentlandite. Without wishing to be bound by theory, the observed increase in chalcopyrite weight percentage may be attributed to its relative inertness during the cerium(IV) leach, resulting in its concentration within the residue.Table 2: Mineral composition of the pre-leach and post-cerium(IV) leach concentrate determined from Rietveld refinement of the XRD results.

[0082] Referring now to FIGs. 9A-9B, selective leaching of pentlandite from pyrrhotite containing feedstocks was demonstrated. As discussed above, pyrrhotite constitutes the second major mineral phase alongside pentlandite in the raw nickel concentrate. Understanding the selectivity between these two mineral phases during cerium(IV) leaching helps process design. FIG. 9A presents the extraction percentages of nickel and iron from the raw nickel concentrate over a 2-hour period during reaction with 1 M Ce(NCh)4 solution. The results demonstrate that the nickel extraction increases rapidly to 57.7% within the first 10 minutes, and plateaus. Iron followed similar leaching behavior, but plateaued at a significantly lower extraction percentage (23.7%). Upon completion of the leaching process, 82.7% nickel and 37.5% iron were extracted from the concentrate. Based on the weight percentages of iron and nickel in the raw concentrate (Table 1) and the stoichiometric atomic ratios of these elements in pentlandite, mass balance calculations indicate that approximately 35% of the total iron content resides within pentlandite, while the remaining 65% isAttorney Docket No.: 105054-201 associated with pyrrhotite. Therefore, iron extraction is predominantly attributed to pentlandite leaching, with pyrrhotite remaining relatively inert during the leaching process. The leach residue was characterized by XRD to validate the selectivity during the leaching. The XRD spectra, along with Rietveld refinement analysis, revealed that the solid residue contains 74% pyrrhotite, 24% elemental sulfur, and 1% pentlandite. These results confirm the selective dissolution of pentlandite from the raw nickel concentrate after two hours of oxidative leaching, with pyrrhotite being retained in the solid residue.

[0083] FIG. 9B illustrates the concentrations of iron and nickel in the PLS after 120 minutes of leaching with 1 M Ce(NOs)4 under various solid loading conditions. At a concentrate loading of 20 g / L, iron and nickel concentrations were approximately equivalent, indicating that the leaching process is governed by pentlandite dissolution. The concentration differential between these elements becomes increasingly pronounced as mass loading increased. At 80 g / L loading, nickel and iron concentrations in the PLS reached 4.9 g / L and 7.4 g / L, respectively. This enhanced iron extraction suggests that more pyrrhotite was leached at higher concentrate loadings. Without wishing to be bound by theory, this may be attributed to galvanic interactions between pentlandite and pyrrhotite, with these interactions becoming more significant as solid content increases within the system.

[0084] Systems and methods of the present disclosure advantageously provide an electrochemically mediated, hydrometallurgical method for target metal extraction from sulfide minerals, e.g., nickel extraction from pentlandite-bearing nickel feedstocks, using cerium(IV) nitrate as an oxidative leaching agent. Selective leaching studies with pyrrhotite-containing feedstocks reveals a preferential dissolution of pentlandite, with most of the pyrrhotite remaining in the solid residue.

[0085] Cerium(IV) serves as a redox mediator that can be electrochemically regenerated and recycled. The strong oxidizing capacity of cerium(IV) enables rapid dissolution of metal sulfides under ambient conditions. The conversion demonstrates inverse relationships with both mass loading and cerium(IV) concentration. Advantageous metal recovery efficiencies, including complete nickel recovery, is attainable through embodiments of the present disclosure.

[0086] Although the invention has been described and illustrated with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing andAttorney Docket No.: 105054-201 various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention.

Claims

Attorney Docket No.: 105054-201CLAIMSWhat is claimed is:

1. A method of leaching target materials from sulfide minerals, comprising: providing a composition including a metal concentrate, the metal concentrate including concentrations of one or more target metals; contacting the metal concentrate with a solution including one or more chemical oxidizers, the chemical oxidizers including cerium(IV); oxidizing at least a portion of the target metal within the metal concentrate via reaction with the one or more chemical oxidizers; isolating a target-metal-containing product from the composition; and isolating a product from the target-metal-containing product that includes a concentration of the target metal, wherein the one or more chemical oxidizers includes cerium nitrates, cerium sulfonates, cerium sulfates, or combinations thereof.

2. The method according to claim 1, wherein the chemical oxidizers include cerium(IV) methanesulfonate, cerium(IV) sulfate, cerium(IV) nitrate, cerium(IV) ammonium nitrate, or combinations thereof.

3. The method according to claim 1, wherein the target metal includes nickel, zinc, lead, silver, molybdenum, copper, or combinations thereof.

4. The method according to claim 3, wherein the metal concentrate includes pentlandite, pyrrhotite, pyrite, sphalerite, galena, Ag2S, M0S2, or combinations thereof.

5. The method according to claim 1 , wherein contacting the metal concentrate with a solution including one or more chemical oxidizers includes: electrochemically converting a concentration of cerium(III) to cerium(IV), and contacting the cerium(IV) with the composition.Attorney Docket No.: 105054-2016. The method according to claim 1, further comprising: recovering a solid component from the target-metal-containing product; electrochemically converting the target-metal-containing product to obtain a second solution containing a concentration of recycled chemical oxidizers, the chemical oxidizers including cerium(IV); contacting at least a portion of the second solution with the solid component in a secondary oxidation reactor; and recycling the second solution from the secondary oxidation reactor to contact the composition.

7. The method according to claim 1, further comprising: obtaining a first portion and at least a second portion of the target-metal-containing product; electrochemically converting the first portion of the target-metal-containing product to obtain a concentration of recycled chemical oxidizers, the chemical oxidizers including cerium(IV); contacting the recycled chemical oxidizers with the composition; and extracting a solid cerium product from the second portion, wherein the product is isolated from the second portion.

8. The method according to claim 1, further comprising: electrochemically converting the target-metal-containing product to obtain a second solution containing a concentration of recycled chemical oxidizers, the chemical oxidizers including cerium(IV); contacting at least a first portion of the second solution with the composition; obtaining at least a second portion of the second solution;Attorney Docket No.: 105054-201 extracting a solid cerium product from the second portion of the second solution, wherein the product is isolated from the second portion of the second solution.

9. The method according to claim 1, wherein the step of isolating a product from the targetmetal-containing product includes an electrolysis process, a precipitation process, a solvent extraction process, or combinations thereof.

10. The method according to claim 9, wherein the step of isolating a product from the targetmetal-containing product includes contact with a concentration of: copper; one or more bases; sodium bisulfate and sulfuric acid, or combinations thereof.

11. The method according to claim 1, further comprising pretreating the metal concentrate with one or more acids before contacting the metal concentrate with the solution.

12. The method according to claim 1, wherein the concentration of metal concentrate loaded into the solution is between about 5 g / L and about 100 g / L.

13. The method according to claim 1, wherein the concentration of cerium(IV) in the solution is between about 0.1 M and about 2.5 M.

14. The method according to claim 1, wherein the solution includes HNO3 at an about 1 : 1 to about 6: 1 ratio with the cerium(IV).

15. A system for leaching of target materials from sulfide minerals, the system comprising: a source of target metal concentrate; an oxidation reactor in communication with the source of target metal concentrate, the oxidation reactor including a solution including one or more chemical oxidizers, the chemical oxidizers including cerium(IV);Attorney Docket No.: 105054-201 a target-metal-containing product outlet stream in fluid communication with the oxidation reactor, an electrolyzer in fluid communication with the target-metal-containing product stream, the electrolyzer producing a recycled chemical oxidizer stream in fluid communication with the oxidation reactor; a product that includes a concentration of the target metal from the target-metal- containing product stream, the target metal including nickel, zinc, lead, silver, molybdenum, copper, or combinations thereof, wherein the one or more chemical oxidizers includes cerium nitrates, cerium sulfonates, cerium sulfates, or combinations thereof.

16. The system according to claim 15, wherein the chemical oxidizers include cerium(IV) methanesulfonate, cerium(IV) sulfate, cerium(IV) nitrate, cerium(IV) ammonium nitrate, or combinations thereof.

17. The system according to claim 15, wherein: the metal concentrate includes pentlandite, pyrrhotite, pyrite, sphalerite, galena, Ag2S, M0S2, or combinations thereof.

18. The system according to claim 17, further comprising a stream splitter positioned to: direct a first portion of the target-metal-containing product outlet stream to the electrolyzer and a second portion of the target-metal-containing product outlet stream to a target-metal recovery reactor; direct a first portion of the recycled chemical oxidizer stream to the oxidation reactor and a second portion of the recycled chemical oxidizer stream to a target-metal recovery reactor, or combinations thereof.

19. The system according to claim 15, wherein the target-metal recovery reactor is in communication with a source of recovery compounds, the recovery compounds comprising:Attorney Docket No.: 105054-201 copper; one or more bases; sodium bisulfate and sulfuric acid, or combinations thereof.

20. A method of leaching target materials from sulfide minerals, comprising: preparing a medium in an oxidation reactor, wherein the medium includes concentrations of: a nitrate compound; a cerium compound including cerium(IV) methanesulfonate, cerium(IV) sulfate, cerium(IV) nitrate, cerium(IV) ammonium nitrate, or combinations thereof, and metal concentrates including pentlandite, pyrrhotite, pyrite, sphalerite, galena, Ag2S, M0S2, or combinations thereof, wherein the medium includes: between about 5 g / L and about 100 g / L metal concentrate, between about 0.1 M and about 2.5 M cerium compound, and between about 1 : 1 to about 6: 1 ratio of nitrate compound to cerium(lV), oxidizing at least a portion of target metal within the metal concentrate via reaction with cerium(IV) in the medium; isolating a target-metal-containing product from the oxidation reactor; precipitating a cerium product from the target-metal-containing product;Attorney Docket No.: 105054-201 electrochemically recycling cerium(III) from the target-metal-containing product to a concentration of cerium(IV); recycling a portion of the cerium(IV) to the oxidation reactor; and isolating a product including target metal from the target-metal-containing product via an electrolysis process, a solvent extraction process, precipitation process, or combinations thereof, wherein the concentration of target metal in the product is higher than in the metal concentrates, wherein the target metal includes nickel, zinc, lead, silver, molybdenum, copper, or combinations thereof.

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