Metallic iron extraction from iron ores using reductive leach

Abstract

Included herein are methods and systems for electrolytically producing metallic iron from a feedstock having solid ferric species, such as one or more ferric-containing iron oxides, using acidic leaching and concurrently chemical non-electrolytic reduction of ferric ions in the presence of one or more reductants such as pyrite material(s) to make a ferrous-rich aqueous acidic solution, optionally followed by impurity removal of non-iron impurities and electroplating of metallic iron.

Description

Leydig Ref. 340515: 3-25 WO METALLIC IRON EXTRACTION FROM IRON ORES USING REDUCTIVE LEACH CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U. S. Provisional Patent Application Serial No. US 63 / 746,753, filed January 17, 2025, and to U. S. Provisional Patent Application Serial No. 63 / 773,140, filed March 17, 2025, each of which is incorporated herein by reference in its entirety for all purposes.BACKGROUND

[0002] Systems and methods herein address challenges associated with difficult-to-dissolve iron oxide feedstock compounds, such as hematite, and address challenges associated with feedstocks or ores having substantial fractions of impurities, such as Al and P. Thermal roasting and / or thermal reduction of ore may facilitate dissolution of ore using an acid, such as sulfuric acid, to form an acidic iron-salt solution and ultimately make a ferrous-rich aqueous acidic solution from which metal iron can be electroplated in a separate electrolytic plating cell. In some applications or world regions, however, there may be cost and / or energy-intensiveness benefits in making the thermal roasting and / or reduction of feedstock milder or incomplete and / or in avoiding electrochemical cells other than iron electroplating cells. Various aspects and embodiments disclosed herein address related challenges in order to ultimately leach iron oxide feedstocks and electroplate metal iron therefrom.SUMMARY

[0003] Aspects disclosed herein include methods for producing metallic iron comprising: reductively leaching an iron source material with an aqueous acid and one or more reductants to produce a ferrous-rich acidic aqueous solution; wherein the iron source material comprises magnetite; wherein the step of reductive leaching comprises leaching the iron source material with the aqueous acid thereby forming dissolved ferric ions and, concurrently in a same reductive leach reactor, non-electrolytically reducing the dissolved ferric ions via the one or more reductants; wherein the one or more reductants comprise one or more pyrite materials, one or more metal sulfide materials, or a combination thereof; wherein the produced ferrous-rich aqueous acidic solution is characterized by a ratio of dissolved ferrous ion concentration to total dissolved iron ion concentration greater than 0.50 (optionally greater than or equal to 0.80); raising a pH of the produced ferrous-rich acidic aqueous solution to remove at least a portion of non-Leydig Ref. 340515: 3-25 WO iron impurities thereby forming a treated ferrous-rich solution; and electroplating metallic iron by electrochemically reducing dissolved ferrous ions from the treated ferrous-rich solution at a plating cathode of an iron electroplating cell.

[0004] Aspects disclosed herein include systems for producing metallic iron comprising: a reductive leach reactor configured to reductively leach an iron source material with an aqueous acid and one or more reductants to produce a ferrous-rich acidic aqueous solution; wherein the iron source material comprises magnetite; wherein the reductive leach reactor is configured to (a) leach the iron source material with the aqueous acid to thereby form dissolved ferric ions and concurrently (b) non-electrolytically reduce the dissolved ferric ions via the one or more reductants at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm; wherein the one or more reductants comprise one or more pyrite materials, one or more metal sulfide materials, or a combination thereof; and wherein the ferrous-rich aqueous acidic solution is characterized by a ratio of dissolved ferrous ion concentration to total dissolved iron ion concentration greater than 0.50 (optionally greater than or equal to 0.80); an impurity removal subsystem configured to receive the produced ferrous-rich acidic aqueous solution and raise its pH to thereby remove at least a portion of non-iron impurities and produce a treated ferrous-rich solution; and an iron electroplating cell configured to electroplate metallic iron at a plating cathode via an electrochemical reduction of dissolved ferrous ions from the treated ferrous-rich solution.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a schematic process flow diagram illustrating an example system, and associated methods, for reductive leaching of a feedstock comprising iron oxide, removal of non-iron impurities, and electroplating of metal iron.

[0006] FIG. 2A is a schematic process flow diagram illustrating an example system, and associated methods, for reductive leaching of a feedstock comprising iron oxide, removal of non-iron impurities, and electroplating of metal iron, in which an optional pretreatment, such as thermal reduction, is performed on the feedstock prior to reductive leach.

[0007] FIG. 2B is a schematic process flow diagram illustrating an example system, and associated methods, for reductive leaching of a feedstock comprising iron oxide, removal of non-iron impurities, and electroplating of metal iron, in which an optional pre-Leydig Ref. 340515: 3-25 WO treatment, such as thermal reduction, is performed on the feedstock prior to reductive leach and further an optional reductant generation is performed to generate the one or more reductants.

[0008] FIG. 2C is a schematic process flow diagram illustrating an example system, and associated methods, for reductive leaching of a feedstock comprising iron oxide, removal of non-iron impurities, and electroplating of metal iron, in which: an optional pretreatment, such as thermal reduction, is performed on the feedstock prior to reductive leach; and an optional reductant generation is performed to generate the one or more reductants, where further optionally iron powder is electrochemically generated for use as a reductant in the reductive leach.

[0009] FIG. 2D is a schematic process flow diagram illustrating an example system, and associated methods, for reductive leaching of a feedstock comprising iron oxide, removal of non-iron impurities, and electroplating of metal iron, in which: an optional pretreatment, such as thermal reduction, is performed on the feedstock prior to reductive leach; an optional reductant generation is performed to generate the one or more reductants, where further optionally iron powder is electrochemically generated for use as a reductant in the reductive leach; and further an electrochemical acid regenerator cell is used to reduce aqueous ferric ions from at least a portion of the plating anolyte prior to recycling the anolyte to the reductive leach.

[0010] FIG. 3A is a schematic process flow diagram illustrating an example system, and associated methods, leaching and chemical reduction of a feedstock comprising iron oxide, removal of non-iron impurities, and electroplating of metal iron, the system having a leach step or leach reactor separate from or in sequence with a chemical (non-electrolytic) ferric reduction step or ferric reduction reactor. The system optionally includes a feedstock pre-treatment, such as a thermal reduction of at least a portion of the feedstock iron oxides to magnetite. The system further optionally includes a reductant generation subsystem or step to generate the one or more reductants used for the chemical reduction, where a reductant is optionally iron powder, which is optionally electrochemically generated from a treated ferrous-rich solution. In this system, and associated methods, according to various aspects herein, at least a portion of electrolyte from the iron electroplating cell is optionally recycled back to the chemical (non-electrolytic) ferric reduction reactor or step. In this system, and associated methods,Leydig Ref. 340515: 3-25 WO according to various aspects herein, the anodic reaction of the iron electrochemical cell may be an electrochemical oxidation of dissolved ferrous to dissolved ferric, in which case at least some of the used / spent anolyte, having generated dissolved ferric compared to fresh anolyte, may be recycled back to the chemical ferric reduction reactor or step.

[0011] FIG. 3B is a schematic process flow diagram illustrating an example system, and associated methods, leaching and chemical reduction of a feedstock comprising iron oxide, removal of non-iron impurities, and electroplating of metal iron, the system having a leach step or leach reactor separate from or in sequence with a chemical (non-electrolytic) ferric reduction step or ferric reduction reactor. The system optionally includes a feedstock pre-treatment, such as a thermal reduction of at least a portion of the feedstock iron oxides to magnetite. The system further optionally includes a reductant generation subsystem or step to generate the one or more reductants used for the chemical reduction, where a reductant is optionally iron powder, which is optionally electrochemically generated from a treated ferrous-rich solution. In this system, and associated methods, according to various aspects herein, at least a portion of electrolyte from the iron electroplating cell is optionally recycled back to the leach reactor or step. In this system, and associated methods, according to various aspects herein, the anodic reaction of the iron electrochemical cell may be an electrochemical oxidation of water and evolution of oxygen gas, in which case at least a portion of the acidified used / spent anolyte, may be recycled back to the leach reactor or step to facilitate leaching.

[0012] FIG. 4 is a schematic illustration showing a three-phase reaction point at which a solid catalyst, a gaseous reactant, and an aqueous solution meet.

[0013] FIG. 5A is a schematic illustration of a ferric reduction reactor configured to reduce aqueous ferric ions to ferrous ions by oxidation of hydrogen gas.

[0014] FIG. 5B is a schematic illustration of a reductive leach reactor configured to reductively leach solid iron ore particles in a slurry along with an aqueous electrolyte and optional conductive and / or catalytic additive particles (e.g., carbon).

[0015] FIG. 6 is a schematic illustration of an acid regeneration fuel cell in which hydrogen is oxidized to protons at a hydrogen reduction anode while ferric ions areLeydig Ref. 340515: 3-25 WO reduced to ferrous ions at a cathode separated from the anode by a separator membrane.

[0016] FIG. 7 is a schematic process flow diagram illustrating a process for reductively leaching iron ore, removing impurities, and electroplating iron from the purified leach solution.

[0017] FIG. 8 is a schematic process flow diagram illustrating a process for reductively leaching iron ore, removing impurities, and electroplating iron from the purified leach solution, and further including a ferric polishing reactor.

[0018] FIG. 9A and FIG. 9B are each a schematic process flow diagram illustrating a process for leaching and chemically (non-electrolytically) reducing aqueous ferric, removing impurities, and electroplating iron from the purified leach solution. These systems, and associated methods, according to various aspects herein, include a leach tank separate from or in sequence with a chemical (non-electrolytic) ferric reduction reactor for reducing dissolved ferric ions to dissolved ferrous ions. These systems, and associated methods, further include an optional thermal pre-treatment reactor to pre-process (e.g., reduce at least some iron oxides to magnetite) feedstock prior to leaching. In some aspects, the electroplating cell may perform an anodic reaction of electrochemical oxidation of water and oxygen gas evolution, in which case at least some of the used / spent anolyte, being acidified compared to fresh anolyte, may be recycled back to the leach tank to facilitate continued leaching (FIG. 9A). In some aspects, the electroplating cell may perform an anodic reaction of electrochemical oxidation of dissolved ferric ions to dissolved ferrous ions, in which case at least some of the used / spent anolyte, comprising anodically generated ferric ions compared to fresh anolyte, may be recycled back to the chemical ferric reduction reactor (FIG. 9B).

[0019] FIG. 10 is a schematic process flow diagram illustrating a process for reductively leaching iron ore, removing impurities, and electroplating iron from the purified leach solution, including disposition of various products and recycling streams.

[0020] FIG. 11 is a schematic process flow diagram illustrating a process for reductively leaching iron ore, removing impurities, and electroplating iron from the purified leach solution, including electroplating vs an oxygen evolution reaction.Leydig Ref. 340515: 3-25 WO

[0021] FIG. 12 is a schematic diagram illustrating an example process for reducing iron oxides in iron ore to ferrous oxide using sulfur dioxide optionally produced by combustion of sulfur in air.

[0022] FIG. 13 is a schematic diagram illustrating an example process for reducing iron oxides in iron ore to ferrous oxide by direct reduction with sulfur, then leaching the ferrous oxide into a leach solution, removing impurities from the leach solution, and electroplating metallic iron from the leach solution.

[0023] FIG. 14 is a schematic diagram illustrating an example process for reducing iron oxides in iron ore to magnetite (Fe₃O₄) using sulfur as a direct reducing agent, reductively leaching the magnetite into a leach solution while contacting the leach solution with a reducing gas (e.g., sulfur dioxide and / or another reducing gas), removing impurities from the leach solution, and electroplating metallic iron from the leach solution. In the FIG. 14 process, a sulfur trioxide byproduct of ore reduction and of reductive leaching may be made into a sulfuric acid coproduct.

[0024] FIG. 15 is a schematic diagram illustrating an example process for reducing iron oxides in iron ore to magnetite (Fe₃O₄) using sulfur as a direct reducing agent, reductively leaching the magnetite into a leach solution while contacting the leach solution with a reducing gas (e.g., sulfur dioxide and / or another reducing gas), removing impurities from the leach solution, and electroplating metallic iron from the leach solution. In the FIG. 14 process, a sulfur trioxide byproduct of ore reduction and of reductive leaching may be made into a sulfuric acid coproduct. In the process of FIG.15, direct reduction of ore with sulfur produces a sulfur dioxide byproduct instead of a sulfur trioxide byproduct. The sulfur dioxide byproduct may be combined with sulfur dioxide (or other reducing gas) from another source in the reductive leaching step.

[0025] FIG. 16 is a schematic diagram illustrating generic equipment for performing various processes described herein. FIG. 16 includes a first reduction reactor for reducing hematite to magnetite, a second reduction reactor for reducing magnetite to ferrous oxide (FeO, also known as wüstite). The reduced iron oxide(s) may be leached in a cascade of leaching tanks. Impurities may be removed from a final leaching tank, and the purified iron-rich leach solution may be direct to electrowinning cells for electroplating metallic iron from the purified iron-rich leach solution.Leydig Ref. 340515: 3-25 WO

[0026] FIG. 17 is a schematic diagram illustrating a generic process for extracting metallic iron from iron ore using thermal reduction, reductive leaching, and electroplating. In the process of FIG. 17, iron oxides in iron ore may be reduced to one or more reduced states, the reduced ore may be reductively leached to produce a ferrous iron salt solution (ferrous sulfate is suggested as a nonlimiting example) by contacting the leach solution with one or more reducing gases, impurities may be removed from the ferrous iron salt solution, and metallic iron may be cathodically electroplated from the ferrous iron salt solution while anodically oxidizing water to oxygen or other anodic oxidation reaction.

[0027] FIG. 18 is a schematic flow diagram illustrating an example process and system including non-electrolytic reduction of dissolved ferric and / or non-dissolved ferric to ferrous ions using one or more reductants comprising one or more pyrite materials.

[0028] FIG. 19 is a schematic flow diagram illustrating another example process and system including non-electrolytic reduction of dissolved ferric and / or non-dissolved ferric to ferrous ions using one or more reductants comprising one or more pyrite materials.

[0029] FIG. 20 is a schematic flow diagram illustrating another example process and system including non-electrolytic reduction of dissolved ferric and / or non-dissolved ferric to ferrous ions using one or more reductants comprising one or more pyrite materials.STATEMENTS REGARDING CHEMICAL COMPOUNDS AND NOMENCLATURE

[0030] In general, the terms and phrases used herein have their art-recognized meaning, which can be found by reference to standard texts, journal references and contexts known to those skilled in the art. The following definitions are provided to clarify their specific use in the context of this disclosure.

[0031] This application and Applicant’s U. S. Patent 11,753,732 (hereinafter, 732 patent), which is incorporated herein by reference in its entirety, include methods and systems for electroplating iron metal from a starting feedstock, such as iron ore, which includes iron oxides.

[0032] As used herein, the terms “pure iron” and “high purity iron” are used in a relative sense to refer to a metallic iron material that is more pure than an iron source material, and contains an acceptably low quantity of one or more impurities. In some aspects, pure iron is at least 98 at.% Fe, at least 98.5 at.% Fe, at least 99.0 at.% Fe, atLeydig Ref. 340515: 3-25 WO least 99.5 at% Fe, at least 99.9 at.% Fe, at least 99.95 at.% Fe, at least 99.99 at.% Fe, at least 99.995 at.% Fe, or at least 99.999 at.% Fe.

[0033] As used herein, the terms “iron source material,” “iron feedstock” or simply “feedstock” are used to refer to iron-containing materials that may be used as inputs into the various systems and methods described herein. “Iron source materials” and “feedstocks” may include iron in any form, such as one or more iron oxides, one or more iron hydroxides, one or more iron oxyhydroxides, one or more iron carbonates, iron one or more sulfides, iron one or more silicates, one or more iron-based metals, one or more other iron metal or iron-containing materials that are products of ironmaking or steelmaking processes (e.g., slags, dusts, off-fall, scrap, pickling liquors, etc), and / or one or more other iron-containing compounds, ores, rocks or minerals, including any mixtures thereof, in naturally-occurring states, man-made states, and / or beneficiated or purified states. The term “iron ore” is intended to be consistent with the term as it is known in the art of iron or steel manufacturing and includes any naturally-occurring material (whether or not processed, refined, or beneficiated) that contains one or more forms of iron oxide and / or other materials containing substantial quantities (such as but not limited to at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, at least 35 wt.%, at least 40 wt.%, at least 45 wt.%, at least 50 wt.%, at least 55 wt.%, at least 60 wt.%, at least 65 wt.%, at least 70 wt.%, at least 75 wt.%, at least 80 wt.%, at least 85 wt.%, at least 90 wt.%, or at least 95 wt.%) of iron compounds (iron oxides, iron carbonates, iron silicates, etc.). The term “iron-containing ore” or simply “iron ore” may include materials recognized, known, or referred to in the art as iron ore(s), rock(s), natural rock(s), sediment(s), natural sediment(s), mineral, and / or natural mineral(s), whether in naturally-occurring states or in beneficiated or otherwise purified or modified states. As used herein, an iron ore comprises one or more iron oxides, such as but not limited to, one or more phases of hematite, one or more iron oxide-hydroxides such as goethite or limonite, magnetite, Fe₄O₅, Fe₅O₆, Fe₅O₇, Fe₂₅O₃₂, Fe₁₃O₁₉, wüstite, or combinations thereof. As used herein, the term “oxide” is intended to be inclusive of hydroxides and hydrated oxides. Some embodiments of processes and systems described herein may be particularly useful for iron feedstocks comprising, consisting of, or consisting essentially of one or more iron ores (or blends of iron ores) including hematite, goethite, magnetite, limonite, siderite (FeCO₃), ankerite, turgite, bauxite, pyrite, fayalite, or any combination thereof. Optionally, an iron source material or iron feedstock may furtherLeydig Ref. 340515: 3-25 WO comprise an iron metal material, such as, but not limited to, iron dust (e.g., fine particulate produced as a byproduct of ironmaking or steelmaking processes in blast furnaces, oxygen furnaces, electric arc furnaces, etc.), iron powder, scrap steel, mill scale (as the term is known in the art), and / or scrap iron such as scrap wrought or cast iron. Feedstocks may comprise various other non-iron materials, which are generally referred to herein as “impurities” or “non-iron impurities.”

[0034] As used herein, the term “impurity” refers to an element or compound other than a desired final product material (e.g., iron). In various embodiments, depending on the intended end-use of a product material, a given element or compound may or may not be considered an “impurity.” In some cases, one or more elements or compounds that may be impurities to one process or sub-process may be isolated or purified, collected, and sold as a secondary product material (also referred to as “co-products” or “by-products”).

[0035] As used herein, the term “pyrite” is intended to be inclusive of any naturally-occurring or synthetically-produced materials or minerals containing one or more iron sulfides in any quantity, ratio, or mixture, including those containing elements in addition to Fe and S, and having any crystal structure. As used herein, the term “pyrite material” includes any material being or comprising at least 5 wt.% (optionally at least 10 wt.%, optionally at least 15 wt.%, optionally at least 20 wt.%, optionally at least 25 wt.%, optionally at least 30 wt.%, optionally at least 40 wt.%, optionally at least 50 wt.%, optionally at least 60 wt.%, optionally at least 70 wt.%, optionally at least 75 wt.%, optionally at least 80 wt.%, optionally at least 90 wt.%, optionally at least 95 wt.%) one or more forms of pyrite, including but not limited to synthetic and / or naturally-occurring FeS2, FeS, Fe2S, Fe₉S₁₁, Fe₃S₄, one or more non-stoichiometric forms thereof, non-stoichiometric iron sulfides such as but not limited to pyrrhotite Fe(1-x)S (x = 0 to 0.125), mixed metal iron sulfides such as but not limited to copper sulfides such as but not limited to chalcopyrite (CuFeS2), mixed metal iron sulfides such as but not limited to nickel sulfides such as but not limited to pentlandite ((Fe,Ni)₉S₈), any allotrope(s) thereof, and any combination(s) and mixture(s) thereof. Additional information, including chemical structures and interactions, and examples of pyrite materials are provided in “Chemistry of Iron Sulfides” by David Rickard and George W. Luther, ACS Vol 102, issue 2, Jan. 30, 2007 (DOI / 10.1021 / cr0503658). Sources of pyrite materials mayLeydig Ref. 340515: 3-25 WO include naturally-occurring pyrite, mine wastes, mining residues, mine tailings (wet or dry), waste materials from industrial processes such as copper electrowinning, among others. Prior to use as a reductant, pyrite materials or pyrite-bearing materials may be processed, such as separation, comminution, rinsing, gangue separation, or other processes to produce a pyrite reductant material.

[0036] As used herein, the term “metal sulfide material” refers to any material being or comprising at least 5 wt.% (optionally at least 10 wt.%, optionally at least 15 wt.%, optionally at least 20 wt.%, optionally at least 25 wt.%, optionally at least 30 wt.%, optionally at least 40 wt.%, optionally at least 50 wt.%, optionally at least 60 wt.%, optionally at least 70 wt.%, optionally at least 75 wt.%, optionally at least 80 wt.%, optionally at least 90 wt.%, optionally at least 95 wt.%) one or more metal sulfides, including synthetic and / or naturally-occurring metal sulfides, such as but not limited to Na₂S, K₂S, MgS, CaS, TiS, TiS₂, Ti₂S₃, VS, VS₂, V₂S₃, V₂S₅, MnS, MnS₂, NiS, Ni₃S₂, Cu₂S, CuS, ZnS, MoS₂, Mo₂S₃, Mo₃S₄, Mo₆S₈, W₂S₃, WS₂, any non-stoichiometric form(s) thereof, any allotrope(s) thereof, and any combination(s) thereof.

[0037] The term “iron-based metal” refers to a metal or metallic material, such as an alloy, characterized by a composition having greater than 50 at.% Fe. Optionally, in aspects herein, an iron-based metal is a metal or metallic material, such as an alloy, characterized by a composition having at least 60 at.% Fe, optionally at least 70 at.% Fe, optionally at least 80 at.%, optionally at least 90 at.% Fe, optionally at least 95 at.% Fe, optionally at least 97 at.% Fe, optionally at least 98 at.% Fe, optionally at least 98.5 at.% Fe, optionally at least 99.0 at.% Fe, optionally at least 99.5 at.% Fe, optionally at least 99.9 at.% Fe, optionally at least 99.95 at.% Fe, optionally at least 99.99 at.% Fe. Iron-based metals include, but are not limited to, metallic iron or iron metal, steel materials, silicon steel, silicon iron, electrical steel, electrical iron, cast iron, gray iron, white iron, ductile iron, malleable iron, wrought iron, any iron-carbon alloy characterized by greater than 50 at.% Fe (optionally at least 60 at.% Fe, optionally at least 70 at.% Fe, optionally at least 80 at.%, optionally at least 90 at.% Fe, optionally at least 95 at.% Fe), and any combinations thereof.

[0038] As used herein, the terms “steel” and “steel material” are inclusive of any material known in the art as “steel”, such as, but not limited to, stainless steels, carbonLeydig Ref. 340515: 3-25 WO steels, tool steels, crucible steels, spring steels, alloy steels, maraging steels, highspeed steels, weathering steels, and any variations and grades thereof.

[0039] The term “iron-containing metal” refers to a metal or metallic material containing iron in a metallic, Fe°, state, including iron metals or iron-containing alloys, such as steels, pig iron, ferroalloys, or others, with more than a de-minimus quantity of iron (e.g., greater than approximately 5 atomic %).

[0040] As used herein, the term “oxidation state” carries its normal meaning in the context of chemistry and refers to a number assigned to an element which represents the number of electrons lost (if the number is positive) or gained (if negative) by an atom of that element in a chemical compound or aqueous ionic state. The oxidation number is generally denoted as a superscript such as the “2+” in Fe2+(ferrous iron), but may also be denoted by parenthetical roman numerals such as Fe(ll).

[0041] As used herein, the term “net iron oxidation state” refers to a molar average of the oxidation states of individual iron atoms in a material. For example, a material that is a mixture of FeO (ferrous oxide or wüstite), of which the iron atoms have an oxidation state of +2, and iron metal (Fe°), such as iron powder, of which the iron atoms have an oxidation state of 0, will have a net iron oxidation state somewhere between 0 and 2 depending on the ratio of moles of FeO to the moles of Fe°.

[0042] The net iron oxidation state may be determined by determining the relative amounts of different phases or species of elements or compounds in the material (also referred to as the “phase composition” of the material). Phase composition of a material may be determined by any suitable method, such as X-ray diffraction (XRD) optionally employing a reference intensity ratio (RIR) analysis, thermogravimetric analysis (TGA), or a combination of these and then assigning an oxidation state for each detected phase. The net iron oxidation state may then be calculated based on the oxidation state defined by each detected phase and the relative quantities of each phase detected in the material. Another method of determining a net iron oxidation state of a material is to digest the material in a non-oxidizing acid while measuring hydrogen gas evolved and then determining a quantity of ferrous (Fe2+) and ferric (Fe3+) iron ions in solution. The quantity (or ratio) of ferrous and ferric ions in the solution, resulting from digestion of the materia, may be measured via electrochemical techniques known in the art (e.g., coulometric titration, oxidation-reduction potential measurements, or others), viaLeydig Ref. 340515: 3-25 WO chemical titration, and / or other useful techniques known in the art. In some cases, a combination of these methods or other methods may be used to determine the net iron oxidation state of a material. For example, leaching tests may be used to measure reduction of ferric in the resulting leachate solution, the final ferrous / ferric ratio in solution, total Fe recovery, and leaching kinetics and quantitation of absolute iron ion concentration in solution may be determined coulometric titration.

[0043] In various embodiments herein, various compositions, compounds, or solutions may be substantially “isolated” or “purified” to a degree sufficient for the purposes described herein. In various embodiments, a substantially purified composition, compound or formulation (e.g., ferrous iron solutions, ferric iron solutions, or plated metallic iron) may have a chemical purity of 90% (e.g., by molarity of ionic concentrations or by weight) or more. For various applications, a material may be “pure” if it has a chemical purity of 95%, 99%, 99.9%, 99.99%, or 99.999% pure.

[0044] Reference made herein to a “tank” is intended to include any vessel suitable for containing liquids, such as highly acidic or caustic aqueous solutions if needed. In some embodiments, such a vessel may include additional features or components to assist or improve mixing of solid and / or liquid contents of the vessel. For example, a dissolution tank may include passive or actively operated structures or features for agitating a solution or solid / liquid mixture, such as baffles, stirrers, etc. A dissolution tank or other tank useful in the systems and methods herein may also include features to allow for sparging a gas into or through solid and / or liquid contents of the tank to increase gas contact with solid and / or liquid materials within the tank. Various tanks may also include baskets, sieves, pans, filters, or other structures to collect and separate solids from liquids. In some embodiments, a tank may be configured to direct liquid or gas flow through the tank in such a way as to agitate the mixture therein (e.g., flowdirecting structures, pumps, impellers, baffles, impellers, stir-bars, stir blades, vibrators, cyclonic flow channels, etc.).

[0045] The term “iron electroplating” (or “iron plating” as used synonymously herein) refers to a process by which dissolved iron is electrochemically reduced to metallic iron on a cathodic surface. Equivalent terms “electrodeposition,” “electroforming,” and “electrowinning” are also used herein synonymously with “iron electroplating.” The shape or form-factor of the electroplated iron need not be a “plate” by any definition ofLeydig Ref. 340515: 3-25 WO that term. For example, electroplated iron may take any shape or form and may be deposited on any suitable cathodic surface as described in various embodiments herein. Examples of possible physical forms of “electroplated” iron include chips, flakes, coins, crowns, powder, strips, or other shapes. In some embodiments, a cathodic surface material may be selected for a degree to which deposited iron adheres to the cathodic surface. For example, if a desired electroplated product is a powder, a cathodic surface with a low iron adhesion may be desired. Examples of materials with high and low iron adhesion properties are described herein, and additional examples will be clear to those skilled in the art. In various embodiments, some regions of a cathode may be masked prior to electroplating for producing electroplated material in a desired shape or formfactor, for example as described in US Patent 4,139,430, which is incorporated herein by reference to the extent not inconsistent herewith.

[0046] As used herein, any reference to a “PEM” or “proton exchange membrane” may be interpreted as also including a “CEM” or “cation exchange membrane”, both terms may include any available membrane material that selectively allows passing positively charged cations and / or protons. The abbreviation “AEM” is used to refer to anion exchange membranes selective to negatively-charged aqueous ions and includes any available anion-selective membrane.

[0047] As used herein, electrochemically generated ions, such as electrochemically generated protons and electrochemically generated iron ions (e.g., Fe2+, Fe3+), refer to ions that are generated or produced in an electrochemical reaction. For example, electrochemical oxidation of water at an anode may electrochemically generate protons and electrochemically generate oxygen. For example, aqueous ferrous (Fe2+) ions in an anolyte may be electrochemically oxidized an anode to aqueous ferric (Fe3+) ions. As used herein, the term “anodically generated” ions refers to ions generated by electrochemically oxidation at an anode. As used herein, the term “anodically generated” ions refers to ions generated by electrochemically reduction at a cathode.

[0048] As used herein, aqueous protons and electrochemically generated protons are intended to be inclusive of aqueous protons and aqueous hydronium ions.

[0049] As used herein, unless otherwise specified, the terms “ferric iron solution” or “ferric solution” may refer to an aqueous solution that contains dissolved iron that is at least predominantly (i.e., between 50 mol.% and 100 mol.%) in the Fe3+(i.e., “ferric”)Leydig Ref. 340515: 3-25 WO ionic state with the balance of dissolved iron being in the “ferrous” Fe2+state. Similarly the term “ferric ion” refers to one or more ions in the ferric (Fe3+) state. Either “ferric solutions” or “ferrous solutions” may also contain other dissolved ions or colloidal or particulate materials, including impurities.

[0050] The term “dissolved” in reference to ions, such as dissolved ferric ions or dissolved ferrous ions, refers to ions dissolved and thereby solvated by a solvent such as water or an aqueous solution. As used herein, the term “aqueous ions”, such as aqueous ferric ions or aqueous ferrous ions, refers to ions dissolved in water. The term “non-dissolved” refers to a solid undissolved non-solvated species. The term “nondissolved ferric” and “solid ferric” refer to any one or more solid compositions or materials in which ferric (Fe3+or Fe(lll)) exists in a non-dissolved solid, such as, for example, ferric in solid particles or pieces of hematite. As an illustrative example, reduction of solid hematite to solid magnetite comprises the reduction of non-dissolved (solid) ferric to non-dissolved (solid) ferrous. The term “non-dissolved ferrous” and “solid ferrous” refer to any one or more solid compositions or materials in which ferrous (Fe2+or Fe(ll)) exists in a non-dissolved solid, such as, for example, ferrous in solid particles or pieces of magnetite or wüstite. Likewise, the term “solid ions”, such as “solid iron ions”, refers to ions bound in a solid and undissolved composition.

[0051] As used herein, the term “thermally reducing” refers to a thermal treatment at an elevated temperature in the presence of one or more reductants and / or in the presence of one or more reductant precursors (e.g., solid(s) or liquid(s)) capable of producing one or more reductants (e.g., gaseous reductants) at the process temperature. Thermal reduction is also referred to in the art as reduction roasting.Optionally, thermal reduction is performed at a temperature selected from the range of approximately 200 °C. and 1000 °C, such as optionally selected from the range of approximately 400 °C to 1000 °C or optionally selected from the range of 200 °C to 600 °C. Optionally, the reductant is a gas comprising hydrogen (H2) gas. Additional description and potentially useful embodiments of thermal reduction may be found in the following reference, which is incorporated herein by reference to the extent not inconsistent herewith: “Hydrogen reduction of hematite ore fines to magnetite ore fines at low temperatures”, Hindawi, Journal of Chemistry, Volume 2017, Article ID 1919720.Leydig Ref. 340515: 3-25 WO

[0052] As used herein, a reductant is a reagent material capable of chemically reducing another material or composition, such as solid ferric or dissolved ferric. Herein, the terms “reductant” and “reducing agent” have the same meaning and are used interchangeably. A reductant can be a gas, a solid, or a liquid. Example, non-limiting, reductants useful herein include H₂ gas, H₂S gas, SO₂ gas, CO gas, methane gas, solid sulfur, an iron-based metal (such as but not limited to iron metal, optionally >99.0% purity Fe), one or more pyrite materials (as defined herein), one or more metal sulfide materials (as defined herein), metallic copper, an inorganic electron shuttle or redox mediator material, an organic electron shuttle or redox mediator material, a plurality thereof, or any combination thereof. As used herein, an “electron shuttle” or “redox mediator” is a material that can be reversibly oxidized and reduced and is capable of reducing Fe3+ions dissolved in an acidic aqueous solution to Fe2+ions. Electron shuttles useful herein, according to some aspects, include metal ions (or salts thereof, such as sulfate salts) that may be stable in a plurality of oxidation states in an aqueous acidic solution under relevant conditions herein, such as but not limited to approximately 1 atm and a temperature between approximately 30 °C and 85 °C. Electron shuttle materials useful herein include copper metal, a copper oxide, a copper sulfate, other copper salt(s), tin metal, a tin oxide, a tin sulfate, other tin salt(s), titanium metal, a titanium oxide, a titanium sulfate, other titanium salt(s), vanadium metal, a vanadium oxide, a vanadium sulfate, other vanadium salt(s), various organic compounds, and any combinations thereof. Electron shuttle materials useful herein include tin-containing material(s) or compound(s) capable of being a Sn2+ / Sn4+electron shuttle in an acidic aqueous solution according to aspects herein, vanadium-containing material(s) or compound(s) capable of being a V3+ / V4+electron shuttle in an acidic aqueous solution according to aspects herein, titanium-containing material(s) or compound(s) capable of being a Ti3+ / Ti4+electron shuttle in an acidic aqueous solution according to aspects herein, copper-containing material(s) or compound(s) capable of being a Cu / Cu2+and / or a Cu+ / Cu2+electron shuttle in an acidic aqueous solution according to aspects herein, and any combinations thereof. As used herein, a reducing gas (or, “gaseous reductant”) may be but is not limited to hydrogen gas, forming gas, natural gas, reformed natural gas, carbon monoxide, methane, one or more other natural or reformed hydrocarbon gas, hydrogen sulfide gas, sulfur dioxide, one or more other gases known in the art as reducing gas(es), or any combination thereof. Without wishing to be bound by anyLeydig Ref. 340515: 3-25 WO particular theory, it is believed that providing or adding certain composition(s) as reductant(s) may involve in-situ chemical reaction(s) that generate one or more different chemical species, in trace, minor, or more significant concentrations, where the in-situ generated species may behave as reductant(s) in-situ. It is intended that any such in-situ generated species acting as reductants are within the scope of the reductants described herein.

[0053] As used herein, the terms “chemical reduction” and “non-electrolytic reduction” are used herein interchangeably to refer to a reduction reaction, such as but not limited to ferric-to-ferrous, that is performed or occurs without or in the absence of an applied voltage or current to initiate or drive the reaction. Chemical reduction, or non-electrolytic reduction, may be spontaneous, galvanic and / or promoted or accelerated by a catalyst.

[0054] The term “ferric reduction reactor” is used herein to refer to a tank or reactor for performing chemical (non-electrolytic) ferric-to-ferrous reduction, which may include chemical reduction of solid undissolved ferric (e.g., ferric oxide), chemical reduction of dissolved ferric ions, or a combination thereof. The term “aqueous ferric reduction reactor” is used herein to refer to a tank or reactor for performing chemical (non-electrolytic) reduction of aqueous dissolved ferric ions to aqueous dissolved ferrous ions, generally but not necessarily in the absence of solid or undissolved particulates of iron oxide. In some aspects, FIG. 2D, FIG. 3A, FIG. 3B, FIG. 5A, FIG. 6, FIG. 7, FIG. 8, FIG. 9A, and FIG. 9B include or illustrate a ferric reduction reactor or aqueous ferric reduction reactor.

[0055] The term “reductive leach” and grammatical variations thereof such as “reductive leaching”, “reductively leaching”, and “reductively leach” are used to refer to concurrent acidic leaching of a feed (such as an iron source material or iron feedstock) and chemical (non-electrolytic) reduction of one or more species to lower oxidation state(s) of one or more constituent species (in a solid or aqueous state) in the feed material. Leaching refers to the dissolution of one or more solid species in a feed to form one or more dissolved species. Therefore, in aspects herein, reductively leaching an iron-containing feedstock or iron source material having one or more iron oxide materials refers to a process in which (a) one or more (solid) iron oxides, from the iron-containing feedstock or iron source material, are dissolved to form dissolved speciesLeydig Ref. 340515: 3-25 WO such as dissolved ferrous ions, dissolved ferric ions, or a combination thereof, and in which (b) iron in a ferric or iron(lll) state is chemically (non-electrolytically) reduced to iron in a ferrous or iron(ll) state. In aspects herein, chemical / non-electrolytic reduction includes reduction of iron in a ferric or iron(lll) state to dissolved ferrous ions. In aspects herein, chemical / non-electrolytic reduction includes reduction of dissolved ferric ions to dissolved ferrous ions. In aspects herein, reductive leach occurs in a slurry containing particulates of one or more solid (non-dissolved) iron oxide species for at least a portion of the duration of the reductive leach. One or more reductants (as defined herein) are used to facilitate chemical reduction. As such, reductive leaching may be performed with one or more reductants provided in the presence of or in contact with the species to be reduced, such as dissolved ferric ions. As used herein, reductive leaching may be performed in a slurry comprising an aqueous acid, one or more iron oxide species, and one or more reductants. As used herein, the term “reductive leach reactor” refers to a reactor, vessel, or tank (as defined herein) performing or configured to perform reductive leach as defined herein. In some aspects, figures including but not limited to, FIG. 1 -FIG. 2D, FIG. 5B, FIG. 7, FIG 8, FIG. 10, FIG. 11, FIG. 12, FIG. 14, FIG. 15, FIG. 16, FIG. 17, FIG. 19, and FIG. 20 include or illustrate a reductive leach reactor.

[0056] Reductive leach reactors and chemical ferric reduction reactors may include any suitable hardware configuration suitable for the combination of feedstock, acidic solution, and reductant, including solid / liquid reactors, solid / solid reactors, solid / gas reactors, liquid / gas reactors, or solid / liquid / gas reactors. Example reactor types may include fluidized bed reactors, packed bed reactors, static bed reactors, continuously-stirred reactors, plug flow reactors, sparging reactors, bubble column reactors, trickle bed reactors, catalytic reactors, or reactors with combinations of these or other features for mixing feedstocks, reductants, and leaching solutions.

[0057] As used herein, the term “air roasting” refers to a thermal treatment performed at an elevated temperature in the presence of air or other oxygen-containing atmosphere. Air roasting of ore, such as iron-containing ore, can break down or decrease average particle size of an ore. Optionally, air roasting is performed at temperature selected from the range 300° C. and 500° C. Additional description and potentially useful embodiments of air roasting may be found in the following reference, which is incorporated herein by reference to the extent not inconsistent herewith: “StudyLeydig Ref. 340515: 3-25 WO of the calcination process of two limonitic iron ores between 250° C. and 950° C.”, Revista de la Facultad de Ingeneria, p. 33 (2017).

[0058] In various embodiments, any acid or mix of acids can be used for dissolution of iron ores (and / or other feedstock materials), including but not limited to hydrochloric acid, sulfuric acid, a sulfonic acid, phosphoric acid, nitric acid, acetic acid, oxalic acid, citric acid, boric acid, perboric acid, carbonic acid, methanesulfonic acid, or any mixture or combination of these or other acids. In various embodiments, “iron ore” can include any iron oxide such as, but not limited to, hematite (Fe2O3), maghemite, ferrihydrite, magnetite (Fe3O4), or hydroxides such as geothite (FeOOH), akaganite, lepidocrocite, ferrihydrite, limonite, or any combinations of these or other iron-containing ores.

[0059] As used herein, the terms “acid regenerator” and “acid regeneration cell” are used interchangeably. In aspects herein, an acid regeneration cell may incorporate or by characterized by one or more aspects thereof in the 732 patent. In various aspects herein, an acid regeneration cell is generally consistent with aspects thereof and use of the term in the ’732 patent, and includes an electrolytic cell in which a cathodic reaction includes the reduction of ferric iron to ferrous iron and the anodic reaction comprises oxidation of an anodic reactant such as water (resulting in the evolution of oxygen gas) or chloride ions (resulting in the evolution of chlorine gas), or other oxidizable reactants.

[0060] As used herein, the term “material” is inclusive of pure materials and mixtures of a plurality of different materials or species.

[0061] As used herein, the term “wt.%” or “wt%” refers to a weight percent, or a mass fraction represented as a percentage by mass. The term “at.%” or “at%” refers to an atomic percent, or an atomic ratio represented as a percentage of a type of atom with respect to total atoms in a given matter, such as a molecule, compound, material, nanoparticle, polymer, dispersion, etc. The term “mol.%” refers to molar percent or percent by moles. The term “vol.%” refers to volume percent.

[0062] As used herein, the term “and / or” is used herein, in the description and in the claims, to refer to a single element alone or any combination of elements from the list in which the term and / or appears. In other words, a listing of two or more elements having the term “and / or” is intended to cover embodiments having any of the individual elements alone or having any combination of the listed elements. For example, theLeydig Ref. 340515: 3-25 WO phrase “element A and / or element B” is intended to cover embodiments having element A alone, having element B alone, or having both elements A and B taken together. For example, the phrase “element A, element B, and / or element C” is intended to cover embodiments having element A alone, having element B alone, having element C alone, having elements A and B taken together, having elements A and C taken together, having elements B and C taken together, or having elements A, B, and C taken together.

[0063] As used herein, the term “±” refers to an inclusive range of values, such that “X±Y,” wherein each of X and Y is independently a number, refers to an inclusive range of values selected from the range of X-Y to X+Y. In the cases of “X±Y” wherein Y is a percentage (e.g., 1.0±20%), the inclusive range of values is selected from the range of X-Z to X+Z, wherein Z is equal to X*(Y / 100). For example, 1.0±20% refers to the inclusive range of values selected from the range of 0.8 to 1.2.

[0064] The term “predominantly” is used herein to refer to a property, condition, or value being greater than 50%. In specific instances, the term “predominantly” may indicate a property, condition, or value being greater than 60%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, greater than 98%, greater than 99%, greater than 99.5%. For example, a material mixture characterized as “predominantly wüstite” is more than 50 mol.% wüstite, or in other instances at least 60 mol.% wüstite, at least 70 mol.% wüstite, at least 80 mol.% wüstite, at least 90 mol.% wüstite, at least 95 mol.% wüstite, at least 98 mol.% wüstite, at least 99 mol.% wüstite, at least 99.5 mol.% wüstite, with the balance being other compositions, such as but not limited to hematite, magnetite, iron metal, and / or impurities.

[0065] The terms “substantially” and “approximately” are used interchangeably and refer to a property, condition, or value that is equivalent to or is within a reasonable variance from a stated property, condition, or value. For example, a property, condition, or value described as “substantially” or “approximately” X (X being a number for purpose of this paragraph) may include properties, conditions, or values that are within 20%, within 10%, within 5%, within 1%, or within 0.1% of said X. Examples of such uses include phrases such as “substantially equal”, “substantially equivalent”, “substantially unchanged”, “approximately”, and “approximately equal to.”Leydig Ref. 340515: 3-25 WO

[0066] As used herein, the terms “aqueous iron ion” and “aqueous dissolved iron ion” are used interchangeably. It will be understood that aqueous ions, such as aqueous iron ions, are ions that are dissolved in an aqueous solution. The term “aqueous iron ions” refers to dissolved iron ions of any and all possible oxidation states in the respective or referenced solution under its conditions, including but not necessarily limited to, dissolved ferric (Fe3+) and ferrous (Fe2+) ions. The term “aqueous ferrous ions” refers to aqueous dissolved ferrous (Fe2+) ions in a solution. The term “aqueous ferric ions” refers to aqueous dissolved ferric (Fe3+) ions in a solution.

[0067] As used herein, when referring to a compound or ions being aqueous, the term “aqueous” refers to said compound or ions, respectively, being dissolved or solvated by water. An “aqueous solution” refers to a solution that comprises water as solvent and one or more solute species dispersed, dissolved, or otherwise solvated by the water. Optionally, but not necessarily, an aqueous solution or an aqueous solvent includes 20 vol.% or less, optionally 15 vol.% or less, optionally 10 vol.% or less, preferably 5 vol.% or less, of a non-water liquid.

[0068] The term “electronic communication” refers to the arrangement of two or more materials or items such that electrons can be transported to, past, through, and / or from one material or item to another. Electronic communication between two materials or items can be direct, such as via physical contact between the two materials or items. Electronic communication between two materials or items can be indirect, or via / through one or more other materials or items, for example, such as, but not limited to, two materials being in electronic communication with each other as a result of both contacting another electrically conductive material. Generally, at least one or all of materials or items in electronic communication are electrically conducting or semiconducting.

[0069] The term “ionic communication” refers to the arrangement of two or more materials or items such that ions can be transported to, past, through, and / or from one material or item to another. Generally, ions can pass through one or more ionically conducting materials or media, such as but not limited to ionically conducting liquids, such as water, and solid ionic conductors. Optionally, but not necessarily exclusively, as used herein, transport or conduction of ions refers to transport or conduction of ions in / via an aqueous solution. For example, in some embodiments two materials or itemsLeydig Ref. 340515: 3-25 WO are in ionic communication with one another if a path of ion flow is provided directly between the two materials or items. In some embodiments, two materials or items are in ionic communication with one another if an ion flow path is provided indirectly between the two materials or items, such as by including one or more other materials or items or ion flow paths between the two materials or items. In one embodiment, two materials or items are not necessarily in ionic communication with one another unless ions from a first material or item are transferred to, past and / or through a second material or item, such as along an ion flow path. Generally, for example, an iron-based metal and a reduction-catalyst, such as a graphite textile, that are both concurrently in contact with an aqueous solution, are in ionic communication because aqueous iron ions may pass between the iron-based metal and reduction-catalyst via the aqueous solution.

[0070] As used herein, an “iron-rich” aqueous solution is an aqueous solution having ions dissolved therein wherein aqueous iron ions (including ferric and ferrous ions) are more than 50 mol.% (optionally more than 60 mol.%, optionally more than 70 mol.%, optionally more than 80 mol.%, optionally more than 90 mol.%, optionally more than 95 mol.%, optionally more than 98 mol.%, optionally more than 99 mol.%) of all aqueous cation species in said solution.

[0071] As used herein, a “ferrous-rich” aqueous solution, such as a ferrous-rich aqueous leachate and a treated ferrous-rich aqueous solution, is an aqueous solution having iron ions dissolved therein wherein the concentration ratio of ferrous ions to all iron ions in said solution is greater than 0.50 (optionally greater than 0.60, optionally greater than 0.70, optionally greater than 0.80, optionally greater than 0.90, optionally greater than 0.95, optionally greater than 0.98, optionally greater than 0.99, optionally greater than 0.995, optionally greater than 0.999). In some aspects herein, the ferrous-rich leachate is characterized by a ratio of concentrations of Fe3+ions to Fe2+ions being less than or equal to approximately 0.01, optionally less than or equal to approximately 0.009, optionally less than or equal to approximately 0.0075, optionally less than or equal to approximately 0.005, optionally less than or equal to approximately 0.0025, optionally less than or equal to approximately 0.001, or optionally the ratio can be greater than or equal to 0.0075, 0.005, 0.0025, or 0.001 and such values can be combined in any manner to form a range, such as 0.001 to 0.01.Leydig Ref. 340515: 3-25 WO

[0072] As used herein, a “ferric-rich” aqueous solution is an aqueous solution having iron ions dissolved therein wherein the concentration ratio of ferric ions to all iron ions in said solution is greater than 0.50 (optionally greater than 0.60, optionally greater than 0.70, optionally greater than 0.80, optionally greater than 0.90, optionally greater than 0.95, optionally greater than 0.98, optionally greater than 0.99).

[0073] The term “total iron ion concentration” refers to the concentration of all aqueous iron ions, including but not limited to ferrous and ferric ions, in a referenced aqueous solution. The term “ferric ion concentration” refers to the concentration of all aqueous ferric ions in a referenced aqueous solution. The term “ferrous ion concentration” refers to the concentration of all aqueous ferrous ions in a referenced aqueous solution.

[0074] As used herein, the term “material” is inclusive of pure materials and mixtures or composites of a plurality of different materials or species.

[0075] The term “mean residence time” refers to the term as would be known to one skilled in the art. Generally, the residence time of a fluid refers to the residence time of a fluid parcel, or an infinitesimal volume of fluid, being the total time that the parcel has spent inside a control volume or at a specified / referenced location or surface. The residence time of a set of fluid parcels is quantified in terms of the frequency distribution of the residence time in the set, which is known as residence time distribution (RTD), or in terms of its average, known as mean residence time.

[0076] As used herein, the term “textile” refers to any fiber-based material(s). A felt is an example of a textile.

[0077] As used herein, the term “supporting salt” and “supporting ion” refers to a salt and ion, respectively, corresponding to or serve as a supporting electrolyte or which form, at least partially, a supporting electrolyte when dissolved in order to increase a conductivity of a host solution. In some embodiments, for example, the electrolytes and solutions in either the dissolution subsystem and the plating subsystem may contain dissolved iron species, acid, and additionally inert salts serving as supporting electrolyte to enhance the electrolyte conductivity, which may be particularly beneficial at low ferrous concentrations, wherein the inert salts serving as supporting electrolyte to enhance conductivity may be referred to as supporting salts. Supporting salts mayLeydig Ref. 340515: 3-25 WO include any electrochemically inert salt such as sodium chloride, potassium chloride, ammonium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, sodium chloride, potassium chloride, ammonium chloride or others, or combinations of salts. The concentration of the supporting salts in the solution, if used, may range from approximately 0.1 to approximately 1 M, for example.

[0078] As used herein, the term “precipitation pH” refers to a pH at which the referenced one or more ions or salts are thermodynamically favored or expected to precipitate out of the host aqueous solution. Generally, the solubility of ions and salts dissolved in an aqueous solution may depend on the pH of the aqueous solution. As pH increases in the acidic region, many metallic ions form metal hydroxides which tend to precipitate out of the host solution due to decreasing solubility. The precipitation pH is defined herein as the pH corresponding to a point where solubility of a given ion or salt is below a concentration threshold. The precipitation pH may be an upper boundary beyond which the solubility of a given ion or salt is less than 1 mM, optionally less than 0.1 mM.

[0079] As used herein, the terms “steady state” and “steady-state” generally refer to a condition or a set of conditions characterizing a process, a method step, a reaction or reactions, a solution, a (sub)system, etc., that are true longer than they are not true during operation or performance of the process, method step, reaction or reactions, solution, (sub)system, etc. For example, dissolution of an ore or feedstock may be characterized by a steady state condition, wherein the steady state condition is true during at least 50%, optionally at least 60%, optionally at least 70%, optionally at least 80%, optionally at least 90%, optionally at least 95% of a time during which the dissolution is occurring. For example, a steady state condition may be exclusive of conditions characterizing the transient start-up and shut-down phases of a process such as dissolution of a feedstock.

[0080] The term “cathodic chamber” refers to a region, compartment, vessel, etc. comprising a cathode, or at least a portion or surface thereof, and a catholyte. The term “anodic chamber” refers to a region, compartment, vessel, etc. comprising an anode, or at least a portion or surface thereof, and an anolyte.Leydig Ref. 340515: 3-25 WO

[0081] As used herein, the term “ore dissolution subsystem” may also be referred to as the “dissolution subsystem”, “first subsystem”, and “STEP 1.” The “dissolution subsystem” comprises the “acid regenerator” described herein.

[0082] As used herein, the term “iron-plating subsystem” may also be referred to as the “second subsystem” and “STEP 2.”

[0083] As used herein, the term “in the presence of” generally refers to the two or more species or constituents being present in a mixture or medium such that they may chemically, physically, electrically, electrochemically, and / or otherwise interact with one another and / or with other constituents of the mixture or medium. For example, the mixture may be a solution of one or more solutes in a solvent or solvent mixture or mixture may be a slurry comprising a solution and one or more solid (non-dissolved) particulates dispersed therein. For example, the two or more species may comprise a solute and a solvent or solvent mixture, two or more solutes and a solvent or solvent mixture, one or more non-dissolved species and a solvent or solvent mixture, one or more non-dissolved species and one or more dissolved species and a solvent or solvent mixture, etc. For the example, the interaction may be a chemical reaction involving at least one of the one or more species in the mixture. For example, a first solute being chemically reduced in the presence of a first solvent refers to a chemical reduction reaction occurring in a mixture (e.g., solution) comprising the first solute and the solvent, wherein the first solute is a reagent being chemically reduced in the chemical reaction, but wherein other reagents may participate in said chemical reaction, and wherein the solvent may or may not be a reagent in the chemical reaction. For example, a first nondissolved species provided in the presence of a second dissolved species and a solvent refers to a mixture where said first species, said second species, and said solvent are available to interact (chemically, physically (e.g., come in contact), electrically, electrochemically, or otherwise) with each other, regardless of whether a chemical reaction actually occurs directly involving any of said species or solvent. The term “in the presence of” may allow for but does not require that any interaction or chemical reaction occur, nor that any particular species participate in a reaction if one occurs. Generally, species in presence of each other may be in direct physical contact with each other at or for some time(s) within the mixture thereof.Leydig Ref. 340515: 3-25 WO DETAILED DESCRIPTION

[0084] In the following description, numerous specific details of devices, device components and methods are set forth to provide a thorough explanation of the precise nature of the various inventions described herein. It will be apparent, however, to those of skill in the art that the various inventions can be practiced without these specific details. Without wishing to be bound by any particular theory, there may be discussion herein of beliefs or understandings of underlying principles relating to the devices and methods disclosed herein. It is recognized that regardless of the ultimate correctness of any mechanistic explanation or hypothesis, an embodiment of devices and methods may nonetheless be operative and useful.Overview of Example Systems and Methods:

[0085] In the electrowinning of metallic iron from aqueous solutions, excess acid in the electroplating solution leads to substantial parasitic hydrogen evolution, but raising pH of the electroplating solution increases the risk of precipitating ferric compounds, which diminishes the quality and quantity of electroplated iron. Therefore, it is important to minimize a concentration of ferric ions (Fe3+) in the electroplating solution or plating catholyte in order to efficiently produce high quality electrodeposited iron.

[0086] The present disclosure provides, in various aspects and embodiments, systems and methods for chemically reducing ferric to ferrous in aqueous solutions and / or in solid materials. The aspects and embodiments herein provide systems and methods for achieving such reduction while minimizing the consumption of energy (electrical or otherwise) by utilizing one or more chemical reductants in gaseous, solid, liquid, or aqueous form. The aspects and embodiments herein for effecting reduction of ferric to ferrous prior to electroplating are broadly divided into two categories. Reductive leach methods and systems perform ferric-to-ferrous reduction concurrently with leaching of (predominantly solid) iron feedstock materials, while using chemical reducing agents (or, reductants) to obtain leach solutions rich with dissolved iron predominantly in the ferrous state. The second category includes systems and methods in which ferric reduction is performed in the absence, in various aspects, of solid ore in a ferric reduction reactor. In such cases, leaching (e.g., in a leach tank) of a feedstock is performed separately from or in sequence with aqueous ferric reduction (e.g., in an aqueous ferric reduction reactor). Chemical ferric-to-ferrous reduction is performedLeydig Ref. 340515: 3-25 WO using chemical reducing agents (or, reducing agents) as distinguished from electrolytic reduction methods that consume electrical energy. Reactors for performing chemical reduction of aqueous ferric ions to ferrous ions are variously referred to herein as “aqueous ferric reduction reactors,” “ferric reduction reactors,” “ferric-to-ferrous reactors,” “chemical (non-electrolytic) ferric-to-ferrous reduction reactors”

[0087] Systems and methods disclosed herein include electroplating iron from an aqueous acidic solution that is ferrous-rich, wherein at least a majority of dissolved iron ions are dissolved ferrous ions, with minimal or none of impurities such as, but not limited to, Al and P, which can be deleterious to electroplating and / or for subsequent applications of the electroplated iron, such as steel production. The systems and methods disclosed herein are compatible with a wide range of feedstock materials having iron ore or iron oxides. The initial feedstock, therefore, can present challenges to obtaining the desired ferrous-rich solution. For example, Applicant previously found that hematite (Fe2O3) or its hydrated form, goethite (FeOOH), dissolved in acid significantly slower than magnetite (Fe3O4). Yet, commonly, ores contain lots of hematite / goethite, sometimes exclusively. High temperature thermal reduction may be used to convert difficult-to-dissolve iron oxides, such as hematite, to easier-to-dissolve materials, such as magnetite. However, in some applications and regions, the requirements of thermal reduction may be prohibitive, whether due to cost, clean fuel scarcity, carbon emissions, or any combination of these and other reasons.

[0088] Various aspects and embodiments herein address this challenge. Applicant discovered a variety of approaches employing chemical, or non-electrolytic, reduction, at low or mild temperatures, that facilitate leaching of difficult-to-dissolve iron oxides and facilitate formation of ferrous-rich acidic aqueous solutions from a variety of iron oxidecontaining feedstocks. Particularly, systems and methods disclosed herein include aspects pertaining to reduction ferric — aqueous / dissolved ferric ions in an aqueous solution, non-dissolved solid ferric such as ferric bound with an oxygen atom in a solid iron oxide particulate, or a combination thereof. Systems and methods disclosed herein include leaching and chemical (or, non-electrolytic) reduction. In some aspects, leaching and chemical reduction are performed at the same time, which is referred to herein as reductive leaching. In some aspects, leaching and chemical reduction are performed as separate steps, optionally sequentially, optionally in different vessels. One skilled in theLeydig Ref. 340515: 3-25 WO art will recognize that use of reductive leaching or separate steps of leaching and chemical reduction, both of which and variations thereof are disclosed herein, depends on factors including, but not limited to, available or preferred reductant(s), feedstock composition, energy cost, and capital costs.

[0089] Some steps, features, reactors, reactions, conditions, compositions, parameters, explanations, etc., such as certain aspects with respect to impurity removal and iron electroplating, are described in additional detail in Applicant’s other patent publications. In particular, various aspects and embodiments useful or related to the systems and methods disclosed herein are found in International Patent Publication WO2022204391, International Patent Publication W02024064061, International Patent Publication WO2024072741, and International Patent Publication WO2022197954, all of which are incorporated herein in their entireties.

[0090] Example, non-limiting, systems and methods according to various aspects disclosed herein are illustrated in FIG. 1, FIG. 2A, FIG. 2B, FIG. 2C, FIG. 2D, FIG. 3A, and FIG. 3B. In particular, FIG. 1, FIG. 2A, FIG. 2B, FIG. 2C, and FIG. 2D represent non-limiting systems, and associated methods, according to various aspects herein, having a reductive leach reactor, wherein acid leaching of a feedstock and chemical (non-electrolytic) ferric-to-ferrous reduction (in dissolved states and / or in solid undissolved states) occur together concurrently, generally in the same vessel or tank. FIG. 3A and FIG. 3B represent non-limiting systems, and associated methods, according to various aspects herein, having a leach tank and an aqueous ferric reduction reactor, such that acidic leach of a feedstock is performed separate from or in sequence with a chemical (non-electrolytic) ferric-to-ferrous reduction reactor.and Methods with a Reductive Leach Reactor:

[0091] With reference to each of FIG. 1, FIG. 2A, FIG. 2B, FIG. 2C, and FIG. 2D, a feedstock 102 (202) is provided to a reductive leach reactor 110 (210). Reductive leach reactor 110 (210) performs reductive leach of the provided feedstock 102 (202) in the presence one or more reductants 104 (204) and an aqueous acid. Feedstock 102 (202) comprises one or more iron oxides, optionally in the form of raw iron ore(s), pre-processed iron ore(s) (e.g., thermally reduced ore), or a combination thereof. The one or more reductants 104 (204), in the form added to a ferric reduction reactor or reductive leach reactor 110 (210), is one or more solid reductants, one or more gaseousLeydig Ref. 340515: 3-25 WO reductants, one or more liquid reductants, one or more oxidizable aqueous species, or a combination thereof. In some aspects, for example, a solid metal salt powder may be added as reductant 104 (204), which when added to an aqueous acidic solution dissolves and dissociates and where an aqueous ion of the salt, such as the dissolved aqueous metal ion thereof, is capable of being oxidized and reducing aqueous Fe3+ions to aqueous Fe2+ions. For example, one or more reductants 104 (204) can be H₂ gas, H₂S gas, SO₂ gas, CO gas, methane gas, solid sulfur, an iron-based metal (such as but not limited to iron metal, optionally >99.0% purity Fe), a pyrite material, a metal sulfide material, metallic copper, an inorganic electron shuttle or redox mediator material, an organic electron shuttle or redox mediator material, a plurality thereof, or any combination thereof. Electron shuttle materials useful herein include various copper salts, tin salts, titanium salts, vanadium salts (such as metal sulfate salts), various organic compounds, and combinations thereof. Reductive leach reactor 110 (210) may have a slurry therein, the slurry comprising the aqueous acid, particulates of the provided solid feedstock being leached and reduced, and optionally particulates of a solid reductant. If a gaseous reductant is used, such as H₂S gas, it is optionally captured and recycled — gas recycle 106 (206) — back to reductive leach reactor 110 (210). For example, a gaseous reductant, such as H₂S gas, may be bubbled through the slurry in reductive leach reactor 110 (210), collected, and recycled back into the reactor 110 (210) to bubble through the slurry again. Optionally, chemical reduction is further in the presence of a catalyst, and further optionally in the presence of a conductivity enhancer, which are described in further detail elsewhere herein. In some aspects, metallic iron, optionally in the form of iron powder, iron flakes, iron chunks, or any combination thereof, is used as a reductant 104 (204) in reductive leach reactor 110 (210). In some aspects, the metallic iron as a reductant comprises a portion of the electroplated iron metal 142 (242). In some aspects, the iron as a reductant comprises metallic iron powder formed in an electrochemical iron-powder cell 245, which may be a separate cell from iron electroplating cell 140 (240). In some aspects, one or more pyrite materials are used as the one or more reductants 104 (204) in reductive leach reactor 110 (210). In some aspects, one or more metal sulfide materials are used as the one or more reductants 104 (204) in reductive leach reactor 110 (210). In some aspects, a combination of one or more pyrite materials and one or more metal sulfide materials are used as the one or more reductants 104 (204) in reductive leach reactor 110 (210).Leydig Ref. 340515: 3-25 WO Reductive leach reactor 110 (210) may be operated in continuous mode or batch mode. In various aspects, certain discussion and aspects herein pertaining to reductive leach reactor 110 or 210, such as but not limited to composition of the one or more reductants 104 (204), conditions and parameters in reductive leach reactor 110 or 210 (such as pH, temperature, pressure, residence time, and / or concentrations), input(s) to reductive leach reactor 110 or 210 (such as but not limited to feedstock or iron source material composition and form factor, acid composition, input solution pH), and / or output(s) of reductive leach reactor 110 or 210 (such as but not limited to concentration of dissolved ferrous, concentration of dissolved ferric, and / or pH of the ferrous-rich aqueous leachate) likewise may pertain independently to each of reductive leach reactor 810 (FIG. 8), 1010 (FIG. 10), 1110 (FIG. 11), 1410 (FIG. 14), 1510 (FIG. 15), 1710 (FIG. 17), 1908 (FIG. 19), and 2008 (FIG. 20) and the respective embodiments or aspects.

[0092] Parameters such as, but not limited to, solution pH, solution temperature, gas pressure, relative concentrations or amounts of reagents or reaction participants (e.g., reductant, solid ferric, dissolved ferric, catalyst), composition of feedstock, and residence or reaction time both affect and may be tuned to effect the reductive leach. In some aspects, reductive leach is performed in solution with pH selected from the range of approximately 0.2 to approximately 5. In some aspects, reductive leach is performed with a solution temperature of less than approximately 120 °C, such as selected from the range of approximately 60 °C to approximately 80 °C, and under a gas pressure of less than approximately 2 atm. In some aspects, higher pressures and temperatures are used to accelerate the reaction or obviate the use of a catalyst, such as a solution temperature selected from the range of approximately 80 °C to approximately 250 °C and a gas pressure selected from the range of approximately 1 atm to approximately 40 atm. In some aspects, reductive leach is performed with a mean residence time of fluid selected from the range of 2 minutes to 48 hours.

[0093] In some aspects, an initial or starting feedstock, having iron oxides, is pretreated or pre-processed 215. Feed pre-treatment subsystem 215 may be a thermal reduction or a roasting process. For example, thermal reduction may be performed on at least a portion of a starting feedstock to thermally reduce at least a portion of iron oxides therein, such as to reduce hematite and / or goethite to magnetite, thereby increasing a fraction of magnetite in the feedstock and / or lowering a net iron oxidation state of theLeydig Ref. 340515: 3-25 WO feedstock. Feedstock 102 (202), which is provided to reductive leach reactor 110 (210), may consist essential of or may comprise the pre-treated feed or thermally reduced feed, optionally in combination with other ore or iron oxide-containing materials, such as a raw ore.

[0094] In some aspects, the system includes a reductant generation subsystem 225 to produce, re-produce I regenerate, and / or isolate one or more of reductant(s) 104 (204). For example, in some aspects, H₂S gas, for use as a reductant 104 (204), may be generated at reductant generation subsystem 225 by any process known in the art, such as by reacting H₂ gas with solid or molten sulfur. For example, in some aspects, H₂ gas, for use as a reductant 104 (204), may be generated at reductant generation subsystem 225 by any process known in the art, such as via water electrolysis, steam methane reformation, mixing metallic iron with an acid, or other methods. For example, in some aspects, SO₂ gas, for use as a reductant 104 (204), may be generated at reductant generation subsystem 225 by any process known in the art, such as by combustion of sulfur or combusting a sulfur-containing composition (e.g., as described further herein). For example, in some aspects FeS (iron(ll) sulfide) may be generated at reductant generation subsystem 225 such that reductant(s) 204 comprises the generated FeS.

[0095] In some aspects, external heat may be applied to reductive leach reactor 110 (210) and / or reductive leach involves exothermic reaction(s). In some aspects, reductive leach is performed with mild temperature and pressure conditions, such as with a liquid temperature being less than approximately 120 °C and the gas pressure in the reactor 110 (210) being less than approximately 2 atm. In some aspects, reductive leach is performed with a liquid temperature selected from the range of approximately 20 °C to less than approximately 100 °C and under a gas pressure of approximately 1 atm.

[0096] The reductive leach forms a ferrous-rich aqueous acidic solution (or, “ferrous-rich aqueous leachate”), while there may also be undissolved or precipitated solids, such as silica and / or quartz, which do not dissolve under the conditions in reductive leach reactor 110 (210). The undissolved solids may be separated from the solution, such as by precipitation and / or filtration, and removed as stream 114. In some aspects, the formed ferrous-rich aqueous leachate has a pH of less than approximately 2 or in some aspects less than or equal to approximately 0.7. In some aspects, a concentration of solid particulates of an average diameter selected from the range of approximately 1Leydig Ref. 340515: 3-25 WO pm to approximately 10 pm in the ferrous-rich aqueous leachate as it exits reductive leach reactor and / or as it is provided to impurity removal subsystem 130 (230) is sufficiently low enough to be undetectable above noise by dynamic light scattering (DLS). In some aspects, a concentration of solid (undissolved) particulates of an average diameter selected from the range of approximately 5 pm to approximately 10 mm in the ferrous-rich aqueous leachate as it exits reductive leach reactor and / or as it is provided to impurity removal subsystem 130 (230) is less than 1 mg / L.

[0097] In some aspects, systems and methods herein comprise a step of raising a pH of the ferrous-rich aqueous leachate, such as but not limited to leachate 112, 212, 312, 1812, 1912, 2012, or corresponding leachate of FIG. 7, FIG. 8, FIG. 9A, FIG. 9B, FIG. 10, FIG. 11, FIG. 12, FIG. 13, FIG. 14, FIG. 15, or 17. In some aspects, a leachate pH is raised via addition of one or more iron oxide materials or addition of one or more iron oxide material in combination with one or more iron-based metals or metallic iron. In some aspects, after a reductive leach step or reductive leach reactor, the resulting solution’s pH is raised via addition of one or more iron oxide materials or one or more iron oxide material in combination with one or more iron-based metals or metallic iron. The ferrous-rich aqueous leachate 112 (212), generally free of solids such as described in the preceding paragraph, may be removed from reductive leach reactor 110 (210) and provided to an impurity removal subsystem 130 (230). Impurity removal subsystem 130 (230) precipitates one or more non-iron impurities from the ferrous-rich aqueous leachate 112 (212) by up-shifting or raising the pH of the solution to a pH or pH range at which one or more non-iron impurities precipitate out of the solution resulting, such as described in the ’732 patent. In some aspects, for example, the solution pH is increased to within the range of approximately 2 to approximately 7, or in some aspects up to a pH of approximately 12, for the purpose of precipitating one or more impurities. For example, solubility of aluminum hydroxide (Al(OH)3) decreases significantly as pH increases above 3 (e.g., 6 orders of magnitude solubility drop between pH 3 and 5), while iron (II) hydroxide (Fe(OH)2, or “ferrous” hydroxide) has a higher solubility in this pH range. Thus, aluminum hydroxide may be precipitated without substantial precipitation of ferrous ions by raising the pH above 3 until approximately 5, where the ferrous-rich leachate pH may be less than approximately 2 prior to starting the impurity removal. Likewise phosphates salts, such as aluminum phosphates, silica, and titanium hydroxide may be precipitated. The pH upshifting may be performed in a single step orLeydig Ref. 340515: 3-25 WO in a plurality of steps, wherein a determined amount of a base is added to reach a determined pH based on which impurity or impurities are desired to precipitate out. For example, multiple steps of pH upshifting may be performed to precipitate different impurities at different pH levels. The removed non-iron impurities 234 are thereby precipitated and removed or separated out (e.g., filtration) in one or a plurality of steps or continuously. In some aspects, the added base is or comprises an iron-based metal, such as metal iron, optionally in the form of a powder. At least some of removed noniron impurities 134 (324) may be co-products of the process, optionally with further processing depending on industry needs. Generally, throughout impurity removal, the solution may be maintained at conditions (e.g., pH and temperature) such that ferrous ions remain soluble and dissolved therein. It is generally desired to precipitate impurities, such as Al, P, Ti, Mg, Ca, and / or Mn compounds, while precipitating minimal-to-no ferrous, thereby maintaining ferrous ions in the solution. Optionally, iron metal added in the impurity removal subsystem is iron electrochemically produced in the system or method itself, such as iron electroplated in iron electroplating cell 140 (240). In some aspects, impurity removal is performed with a liquid temperature selected from the range of approximately 20 °C to approximately 100 °C. At the end of impurity removal, the solution pH may be adjusted to a range desired for iron electroplating, such as less than approximately 3.1 or selected from the range of approximately 2 to approximately 3. Impurity removal subsystem 130 (230) produces a treated-ferrous rich acidic aqueous solution 132 (232) which is provided to iron electroplating cell 140 (240).

[0098] In some aspects, a portion of the treated-ferrous rich acidic aqueous solution 132 (232) may be provided to a non-electrolytic iron-product subsystem. For example, the non-electrolytic iron-product subsystem may produce an iron salt, such as ferrous sulfate or ferrous chloride, by precipitation and / or crystallization. The iron salt may then be a co-product of the system, according to some aspects herein.

[0099] Iron electroplating cell 140 (240) comprises a plating cathode in the presence of a plating catholyte, an anode (also referred to herein as plating anode) in the presence of an anolyte (also referred to herein as a plating anolyte), and optionally a separator separating the plating catholyte from the plating anolyte. Further descriptions of example electroplating cell configurations are provided below.Leydig Ref. 340515: 3-25 WO

[0100] In some aspects, a concentration of solid particulates of an average diameter selected from the range of approximately 1 pm to approximately 10 pm in the catholyte of electroplating cell 140 (240) is sufficiently low enough to be undetectable above noise by dynamic light scattering (DLS). In some aspects, a concentration of solid (undissolved) particulates of an average diameter selected from the range of approximately 5 pm to approximately 10 mm in the catholyte of electroplating cell 140 (240) is less than approximately 1 mg / L.

[0101] The treated-ferrous-rich solution 132 (232) is provided to the catholyte or cathode chamber of iron electroplating cell 140 (240). In iron electroplating cell 140 (240), dissolved ferrous ions are electrochemically reduced to iron metal at the plating cathode. Electroplated iron metal 142 (242) is removed as a product. In some aspects, a portion of treated-ferrous-rich solution 132 (232) is also provided, as a separate stream, directly or indirectly to the plating anolyte or anode chamber of iron electroplating cell 140 (240). In some aspects, the anodic reaction at the plating anode is electrochemical oxidation of ferrous ions to ferric ions, the oxidized ferrous ions being ferrous ions directly or indirectly from the treated-ferrous-rich solution 132 (232). In some aspects, the anodic reaction at the plating anode is water oxidation and evolution of oxygen gas. In systems and methods having a reductive leach reactor 110 (210), used / spent plating anolyte 244 may be recycled to reductive leach reactor 110 (210).

[0102] In some aspects, the predominant anodic reaction at the anode(s) of the iron electroplating cell(s), such as but not limited to iron electroplating cell 140, 240, 340, 740, 840, 940, 1240, 1340, 1440, 1540, 1740, 1820, 1920, or 2020, is water oxidation and oxygen evolution, also referred to as an oxygen evolution reaction (OER).

[0103] In some aspects wherein the anodic reaction at the plating anode is ferrous to ferric oxidation, the used / spent plating anolyte, having electrochemically generated dissolved ferric ions, is optionally provided to a catholyte or cathode chamber of an electrochemical acid regenerator cell 250 (or any other aqueous ferric reduction reactor), wherein at least a portion of dissolved ferric ions are electrochemically reduced to dissolved ferrous ions. At least a portion of the acid regenerator’s (AR’s) processed catholyte 252 may then be provided to reductive leach reactor 110 (210). This is optional because the used / spent plating anolyte with dissolved ferric ions may instead be recycled to reductive leach reactor 110 (210) to reduce those ferric ions (in whichLeydig Ref. 340515: 3-25 WO case, the acid regenerator may optionally be omitted from the system). In some aspects, at least a portion of AR’s processed catholyte 252, after electrochemical ferric reduction therein, may be provided directly to impurity removal subsystem 130 (230), bypassing the reductive leach reactor 110 (210), if the dissolved ferric ions concentration is sufficiently low. In some aspects, if the ferric concentration and impurity concentration is sufficiently low in the AR’s processed catholyte 252, after the cell is operated, at least a portion of AR’s processed catholyte 252 may optionally be provided to the plating catholyte.

[0104] Not shown but optionally present in any of the systems and methods described here is a water management subsystem. The water management subsystem may perform any of a plurality of functions, including evaporation, condensation, crystallization, heating, cooling, etc. For example, if iron electroplating cell 140 (240) is a divided cell, wherein the plating catholyte and plating anolyte are separated by a proton or anion exchange membrane, then as the treated ferrous-rich aqueous solution is added to the catholyte, to replenish ferrous ion concentration during plating, the total volume of catholyte continues to increase. To manage this, plating catholyte may be periodically or continuously removed and water may be removed therefrom (e.g., evaporation) to make a concentrated used / spent plating catholyte. In aspects wherein the anodic reaction is water oxidation and oxygen gas evolution at the plating anode of the iron electroplating cell 140 (240), water removed from the (used / spent) plating catholyte may be collected (e.g., condensed) and recycled to the plating anolyte.

[0105] In some aspects, the used / spent plating catholyte or concentrated used / spent plating catholyte may recycled to reductive leach reactor 110 (210). This may be done to manage accumulation of impurities in the plating catholyte. Optionally, some used / spent plating catholyte or concentrated used / spent plating catholyte is bled from iron electroplating cell 140 (240) to manage accumulation of impurities.Pyrite Material(s) and / or Metal Sulfide Material(s) as Reductant(s):

[0106] In various aspects herein, such as but not limited to those corresponding to FIG. 1, FIG. 2A, FIG. 2B, FIG. 2C, FIG. 2D, FIG. 18, FIG. 19, and FIG. 20 and associated descriptions, the one or more reductants may comprise one or more pyrite materials (as defined herein) and / or one or more metal sulfide materials (as defined herein).Leydig Ref. 340515: 3-25 WO

[0107] Pyrite materials such as FeS2 are abundant naturally occurring minerals found to rapidly reduce aqueous Fe3+to aqueous Fe2+while producing sulfuric acid according to Equation 41 below.FeS2+ 7 Fe2(SO4)3+ 8 H2O 15 FeSO4+ 8 H2SO4(41)

[0108] Millions of tons of pyrite materials are mined annually as part of the mining of sulfide ores, including zinc, copper, nickel and refractory gold ores. Pyrite is a gangue (i.e., an un-desired naturally occurring component) present in these ores, typically finely ground along with the rest of the ore and then removed in the concentrators (e.g., by gravity, flotation, or other methods), and discarded as tailings. Producing each ton of concentrate (i.e., processed ore-based material with an increased concentration of a desired mineral or element) requires processing many tons of ore, the volumes of pyriterich tailings currently produced in the mining industry are large and commensurate with iron-production at the scale of millions of tons of iron per year.

[0109] Pyrite materials and other sulfides are a significant concern for tailings storage, because once finely ground and exposed to air, they produce Acid Mine Drainage (AMD). Over long periods of time, this AMD creates acid that makes its way into groundwater and surface water, and enables dissolution of toxic metals that would otherwise remain in the rock. As such, tailings management programs take complex and expensive steps to slow this oxidation or neutralize this acid, such as mixing the pyrite with lime or limestone, or sealing the pyrite behind barriers and membranes that prevent oxygen from reaching it.

[0110] Therefore, by using pyrite material(s) to reduce ferric iron and produce acid, this problematic mine waste can be put to beneficial use in the electrowinning of iron from ore-based feedstocks. The use of pyrite material(s) as a ferric reductant is particularly useful in a sulfate-based leaching and electrowinning system, but can also be used in systems with other acid chemistries (e.g., HCI, methanesulfonic acid, or others), either as a mixed acid or by using different acids for different process steps. While the examples provided herein are described with reference to sulfate systems for simplicity, any other acid salt or salts may be used instead of or in addition to sulfuric acid.Leydig Ref. 340515: 3-25 WO

[0111] Using pyrite material(s) for ferric reduction in an iron electrowinning system is not without its challenges. Although the process of ferric reduction with pyrite is very “electron efficient” (14 electrons are released per mole of pyrite leached), pyrite also adds sulfur to the process, resulting in a buildup of sulfate. At some point, according to some aspects, excess sulfate may need to be removed to prevent its accumulation to unacceptable levels.

[0112] One option for removing sulfate is to use a bleed stream and lime to neutralize the bleed residue. This may involve increasing the size of a bleed stream (relative to a system using an electrochemical AR) to purge the excess sulfate from the system. A “bleed stream” is a hydrometallurgical method for maintaining impurities below a threshold concentration by continuously removing a small volume of solution from the system, removing all salts from the bleed stream, and optionally returning the water to the system. A bleed stream sufficient to remove excess sulfate in this case may be as high as 10% or more of the electrolyte flowing to the plating anodes in each “cycle.” If iron is discarded with other elements in such a bleed stream, it would constitute a significant loss (although iron could be recaptured from the bleed stream by other methods). Lime or limestone may be used to neutralize the bleed stream waste and / or to cause precipitation of one or more solids.

[0113] Another option for removing excess sulfate is to use the sulfate bleed stream described above, and treat it with lime to precipitate gypsum, but then redissolve the iron hydroxides from the resulting slurry and then return the re-dissolved iron solution to the electrowinning system so that the iron is not lost. In some embodiments, gypsum precipitation and iron hydroxide re-dissolution is done anaerobically so that predominantly ferrous hydroxide is precipitated and re-dissolved with minimal ferric hydroxide.

[0114] Another method is for the excess sulfur to leave the process as sulfuric acid. This can be done by precipitating gypsum as above and roasting the gypsum to make SO2, which could be converted to H2SO4 similar to a traditional acid plant. Conversion of SO2 to H2SO4 may involve temperatures of over 1200 °C.

[0115] Another alternative is to remove the sulfate as jarosite (e.g., as natrojarosite: NaFe3(SO4)2(OH)6). Before pyrite is added, and while the concentration of Fe3+ions is high, the spent plating anolyte may be pH-adjusted and heated to precipitate jarosite.Leydig Ref. 340515: 3-25 WO Jarosite is well-studied in zinc hydrometallurgy, and is a preferred way to remove iron from zinc electrowinning systems because it is very filterable and tends to take other impurities with it (e.g., arsenic, lead, potassium, etc), natrojarosite also generates acid as it precipitates, which is good for leaching but can also make process control (e.g., pH control) complex.

[0116] Another option is to produce H2SO4 from ferrous sulfate. To achieve this, the sulfate bleed stream may be evaporated to dryness, leaving primarily FeSO4, with small amounts of other sulfates. This could then be roasted at approximately 700-800 °C to make hematite (Fe2O3) and SO2. The SO2 may be used to make H2SO4 by conventional methods, and the hematite may be returned to the electrowinning process as a feedstock along with fresh hematite, goethite, magnetite, and / or wüstite ore.

[0117] Still another option is to produce FeSO4as a co-product along with plated iron. If a bleed stream is evaporated, the first thing to crystallize will be FeSO4·7H2O. FeSO4may be crystallized as a relatively pure ferrous sulfate salt. Ferrous sulfate is commonly used in the manufacture of lithium-iron-phosphate batteries among other things.

[0118] Another challenge is that many sulfide ores such as those containing pyrite material(s) also tend to contain notable amounts of transition metals (e.g., Zn, Cu, Cd, Ni) as well as toxic impurities, particularly arsenic. To the extent these impurities do not enter the leachate, they can simply be removed as solids. However, some sulfides leach well in Fe3+ion solutions, and these sulfides would still contribute to the reduction of ferric. Ferric ion is an extremely good lixiviant for breaking down these types of ores. However, the transition metal ions would likely remain in solution, and may need to be removed (e.g., by precipitation, solvent extraction, electrowinning, or other methods) or held to a low concentration via a bleed stream.

[0119] As an example, arsenic may be removed as scorodite (FeAsO4·2H2O), a mineral formed from Fe3+and As5+. However, this would need to be performed before converting or removing all Fe3+from the leach solution. Cementation with Fe powder may also be used to remove elements such as Cu, Ni, Pb, Cd, and other transition metals found in sulfide ores from the leachate. The produced cementates may be further valorized and / or sold as co-products rather than discarded.Leydig Ref. 340515: 3-25 WO

[0120] Depending on the makeup of a pyrite source material, magnetic separation may be used to separate magnetite (Fe3O4) and magnetic pyrrhotite from any nonmagnetic impurities. While FeS2 is not magnetic, it may be sufficiently associated with magnetic FeS (or pyrrhotite) particles that the pyrite material(s) is separated as well.

[0121] An alternative to removing impurities may be to produce pyrite and / or pyrrhotite (a non-stoichiometric variant of FeS) from metallic iron and elemental sulfur in a thermal process.

[0122] In various embodiments described herein, pyrite material(s), such as FeS2, is used to reduce aqueous ferric ions to ferrous ions while producing acid as described above with reference to EQ1. This reaction can also be leveraged in reductively leaching magnetite (Fe3O4) according to Equation 42 below:FeS2+ Fe2(SO4)3+ 2Fe3O417 FeSO4(42)

[0123] Magnetite may be produced from hematite (Fe2O3) and / or goethite FeO(OH) by thermal reduction in a suitable reductive environment as described in various examples in the ‘604 patent. Pyrite material(s) can also be used to reduce aqueous ferric ions produced by air oxidation of ferrous ions, or ferric ions produced by dissolution of hematite and / or goethite. In some embodiments, a thermal reduction step may be omitted. For example, in embodiments in which an iron feedstock produces predominantly ferrous ions when leached in acid, or in which a rate of leaching ferric ions is acceptable, a thermal reduction step may be omitted.

[0124] It is believed that pyrite material(s) may also be used in a reductive leach of hematite and / or goethite by rapidly reducing leached ferric ions to ferrous ions while producing acid. In some embodiments, such reductive leach of hematite and / or goethite may be accelerated by using a high surface area of pyrite material relative to the volume of acidic leach solution, and / or by performing the reductive leach under elevated temperature and / or pressure, or by providing a suitable catalyst for accelerating the rate of ferric reduction. A reductive leach of hematite may proceed according to Equation 43 below.3FeS2+ 13Fe2(SO4)3+ 8 Fe2O345 FeSO4(43)

[0125] FIG. 18 illustrates one example of a process 1800 in which a pyrite leach reactor 1802 is used to contact pyrite material(s) 1801 with spent anolyte 1810Leydig Ref. 340515: 3-25 WO containing a high concentration of ferric ions produced in an anode chamber 1822 of an iron electrowinning cell 1820 (also referred to as a “plating cell” 1820). In the example of FIG. 18, an iron feedstock material 1804 is optionally thermally reduced at 1806 (if needed) from a naturally occurring or as-supplied state (e.g., goethite, hematite, etc.) to produce a material in which iron is predominantly in an iron II (ferrous or Fe(ll)) state). For example, material exiting the thermal reduction step may comprise primarily FeO (wüstite) or a mixture of FesCM (magnetite), FeO, and metallic iron, which will predominantly produce aqueous Fe2+when leached at 1808. In some embodiments, an iron feedstock may comprise at least some material in a hematite and / or goethite (predominantly Fe(lll)) state in addition to or instead of material in an Fe(ll) state. In some embodiments, the thermal reduction step is omitted or performed on only a portion of the feedstock.

[0126] In some aspects, systems and methods herein may include providing one or more pyrite materials, as defined herein, to a reductant generation subsystem (e.g., 225, 325) to generate FeS (iron(ll) sulfide) such that the one or more reductants provided to a reductive leach reactor comprises the generated FeS.

[0127] The leachate 1812 exiting the leaching step 1808 may be directed to an Impurity Removal step 1830 in which impurities (e.g., alumina, silica, phosphorous) are precipitated following a pH shift driven by the addition of a base material such as but not limited to one or more iron-based metals (e.g., metallic iron), one or more iron oxides, iron (II) hydroxide, lime, sodium hydroxide, another metal hydroxide, ora combination thereof. Residues 1842 and 1844 from the leach and precipitation steps may be stored, discarded, or valorized as co-products. The impurity removal step 1830 may comprise processes, materials, and equipment as described in the ‘604 patent.

[0128] The solution 1832 exiting the impurity removal step 1830 which contains iron predominantly (i.e., between 50% and 100%, optionally at least 90%, at least 95%, or at least 99%) in a ferrous (Fe2+) state, may be split into an anolyte 1834 directed into an anode half-cell 1822 and a catholyte 1836 directed into a cathode half-cell 1824 of a divided plating cell 1820 as described in the ‘604 patent. Iron metal is electroplated from the plating catholyte 1836, the plated iron being subsequently removed as a metallic iron product 1838 as described in the ‘604 patent. In some embodiments, spent plating catholyte 1811 may be concentrated in a distillation reactor 1850 by evaporating excessLeydig Ref. 340515: 3-25 WO water 1852 and the concentrated electrolyte 1854 may be returned to the plating cathode chamber 1824 for further iron electroplating.

[0129] In some embodiments described in the ‘604 patent, the reaction in the anode half-cell 1822 of the iron plating cell 1820 includes oxidation of Fe2+to Fe3+. In such embodiments in the ‘604 patent, the produced Fe3+in the spent anolyte is reduced to Fe2+in an acid regeneration cell. In the system of FIG. 18, the spent anolyte 1810 containing Fe3+exiting the plating cell 1820 is reduced to Fe2+using pyrite 1801 in a pyrite reactor 1802. The pyrite-reduced solution 1814, which will also contain an increased concentration of sulfuric acid (according to Equation 41 above), may then be returned to the leach reactor 1808 for subsequent leaching of iron feedstock material(s). In embodiments in which the pyrite material(s) in the pyrite reactor 1802 includes insoluble elements or compounds, any solid residue 1846 may be removed from the pyrite reactor 1802 and discarded or valorized. In some embodiments, dissolved impurities from the pyrite 1801 may be removed in the impurity removal step 1830 using any of the methods described in the ‘604 patent.

[0130] As described above, in some embodiments excess sulfate 1860 produced in the reaction of Equation 41 may be removed from the electrolyte via a bleed stream 1862 by one or more methods or treatments such as crystallization, precipitation, or others.

[0131] As indicated by the dashed line 1870, an optional electrolyte conduit may be provided to allow for circulation of the leachate between an ore leach reactor 1808 and a pyrite reactor 1802 in order to reduce any ferric produced in the leach reactor 1808 either by air oxidation or by dissolution of feedstock materials containing iron (III).

[0132] FIG. 19 illustrates an alternative embodiment in which a first pyrite material(s) 1902a may be added directly into a reductive leach reactor 1908 and a second pyrite material(s) 1901b may be added to a separate pyrite reactor 1902. This configuration may be beneficial in systems in which the feedstock material contains substantial quantities of feme-producing iron (III) to be reduced prior to performing impurity removal and / or iron electroplating. Alternatively or in addition, any number of pyrite reactors 1902 and feedstock leach reactors 1908 may be arranged in a cascade or seriesconfiguration.Leydig Ref. 340515: 3-25 WO

[0133] FIG. 20 illustrates an example process 2000 in which pyrite material(s) 2001, spent anolyte 2010, and iron feedstock material 2004 are all reacted in a common reductive leach reactor 2008. The configuration of FIG. 20 simplifies equipment, but may involve more complex management of pyrite and feedstock additions to the leach reactor 2008.

[0134] Electroplating cell 2020, with reference to FIG. 20, is characterized by the predominant the anodic reaction being an oxygen evolution reaction (OER). If the plating anode 2022 primarily performs oxygen evolution then the spent anolyte 2010 will tend to contain a relatively low concentration of ferric ions, but will tend to contain more acid due to the production of acid in the water splitting oxygen evolution reaction.Therefore, a separate pyrite reactor may not be needed, and spent anolyte 2010 may be directed to the leach reactor 2308 where the pyrite can be used to reduce ferric produced in the dissolution of feedstock materials 2004 containing Fe(lll) such as magnetite or hematite.

[0135] Without wishing to be bound by any particular theory of operation, it is believed that providing or adding certain composition(s) as reductant(s) may include in-situ chemical reaction(s) that generate one or more different chemical species, in trace, minor, or more significant concentrations, where the in-situ generated species may behave as reductant(s) in-situ. For example, it is believed that providing FeS2, as a reductant for a reductive leach may facilitate reaction(s) generating in-situ FeS, optionally including non-stoichiometric variations thereof, where the FeS may behave as a chemical reductant during the reductive leach. Further, for example, without wishing to be bound by any particular theory, FeS, whether present in the as-provided composition and / or whether generated in-situ, may, under certain conditions, react with another species or decompose to facilitate generating in-situ H2S, which may behave as an in-situ reductant during reductive leach.Example Systems and Methods with an Aqueous Ferric Reduction Reactor:

[0136] FIG. 3A and FIG. 3B represent non-limiting systems, and associated methods, according to various aspects herein, having a leach tank and an aqueous ferric reduction reactor, such that acidic leach of a feedstock is performed separate from or in sequence with a chemical (non-electrolytic) ferric-to-ferrous reduction reactor. Generally, descriptions, features, considerations, parameters, and conditions associatedLeydig Ref. 340515: 3-25 WO with (sub)systems, components, materials, etc., in FIG. 1 - FIG. 2D are likewise applicable to same or like (sub)systems, components, materials, etc., respectively, in FIG. 3A- FIG. 3B. For example, generally, descriptions, features, considerations, parameters, and conditions described elsewhere herein pertaining to the one or more reductants 104 & 204, reductant generation 225, iron powder electrochemical cell 245, feedstock 202, feed pre-treatment 215, reductant gas recycle 106 & 206, ferrous-rich aqueous leachate 112 & 212, undissolved solids 114 & 214, impurity removal subsystem 130 & 230, removed non-iron impurities 134 & 234, treated aqueous ferrous-rich solution 132 & 232, iron electroplating cell 140 & 240, used / spent plating electrolyte 144 & 244, and electroplated metal iron 142 & 242 also apply, in various aspects herein, to the one or more reductants 304, reductant generation 325, iron powder electrochemical cell 345, feedstock 302, feed pre-treatment 315, reductant gas recycle 306, ferrous-rich aqueous leachate 312, undissolved solids 314, impurity removal subsystem 330, removed non-iron impurities 334, treated aqueous ferrous-rich solution 332, iron electroplating cell 340, used / spent plating electrolyte 344, and electroplated metal iron 342, respectively.

[0137] The systems illustrated in FIG. 3A and FIG. 3B include a leach subsystem (e.g., leach tank) 310 and a ferric reduction reactor 320, which is optionally an aqueous ferric reduction reactor. A feedstock 302 is provided to leach tank 310. Feedstock 302 comprises iron oxide(s). Feedstock 302 may comprise raw iron ore(s), thermally reduced iron ore(s) (formed at thermal pre-treatment subsystem 315), or a combination thereof. Leach tank 310 comprises a slurry of the provided feedstock 302 and an aqueous acid, such as but not limited to H2SO4. An aqueous leachate is formed in leach tank 310. Undissolved or precipitated solids, such as silica and / or quartz, may also be present in the slurry. The aqueous leachate is separated / removed from the slurry and provided to ferric reduction reactor 320 as aqueous leachate 311 (which may be referred to as “first leachate” in discussions elsewhere herein). Aqueous leachate 311 is optionally substantially free of solids. Aqueous leachate 311 comprises aqueous dissolved ferric ions, aqueous dissolved ferrous ions, or a combination thereof.

[0138] Reductant(s) in ferric reduction reactor 320 chemically (non-electrolytically) reduces aqueous dissolved ferric ions, such as those from aqueous leachate 311, to aqueous dissolved ferrous ions in the presence of one or more reductants 304.Leydig Ref. 340515: 3-25 WO Optionally, chemical reduction is further in the presence of a catalyst, such as platinumgroup metal(s), and further optionally in the presence of a conductivity enhancer, which are described in further detail below. In some aspects, a concentration of solid (undissolved) particulates of an average diameter selected from the range of approximately 5 pm to approximately 10 mm in the aqueous solution in ferric reduction reactor 320 is less than 1 mg / L.

[0139] Parameters such as, but not limited to, solution pH, solution temperature, gas pressure, relative concentrations or amounts of reagents or reaction participants (e.g., reductant, solid ferric, dissolved ferric, catalyst), composition of feedstock, and residence or reaction time both affect and may be tuned to effect the ferric reduction in ferric reduction reactor 320. In some aspects, ferric reduction is performed in solution with pH selected from the range of approximately 0.5 to approximately 5. In some aspects, ferric reduction is performed with a solution temperature of less than approximately 120 °C, such as selected from the range of approximately 60 °C to approximately 80 °C, and under a gas pressure of less than approximately 2 atm. In some aspects, higher pressures and temperatures are used to accelerate the reaction or obviate the use of a catalyst, such as a solution temperature selected from the range of approximately 80 °C to approximately 250 °C and a gas pressure selected from the range of approximately 1 atm to approximately 40 atm. In some aspects, ferric reduction is performed with a residence time of fluid selected from the range of 2 minutes to 48 hours.

[0140] One or more reductants 304 is provided to ferric reduction reactor 320.Descriptions herein with respect to one or more reductants 204 apply to one or more reductants 304, including example reductants.

[0141] In some aspects, ferric reduction reactor 320 is substantially free of solid undissolved ferric species. In some aspects, ferric reduction reactor 320 is substantially free of solid undissolved particulates or substantially free of a slurry. Ferric reduction reactor 320 produces a ferrous-rich aqueous acidic solution 312 (or, ferrous-rich aqueous leachate 312), which is provided to impurity removal subsystem 330.

[0142] In some aspects, the ferrous-rich aqueous acidic solution 312 has a pH of less than 2 or in some aspects less than or equal to 0.7. In some aspects, a concentration of solid particulates of an average diameter selected from the range ofLeydig Ref. 340515: 3-25 WO approximately 1 pm to approximately 10 pm in the ferrous-rich aqueous acidic solution 312 provided to impurity removal subsystem 330 is sufficiently low enough to be undetectable above noise by dynamic light scattering (DLS). In some aspects, a concentration of solid (undissolved) particulates of an average diameter selected from the range of approximately 5 pm to approximately 10 mm in the ferrous-rich aqueous acidic solution 312 provided to impurity removal subsystem 330 is less than 1 mg / L.

[0143] Iron electroplating cell 340 comprises a plating cathode in the presence of a plating catholyte, an anode (also referred to herein as plating anode) in the presence of an anolyte (also referred to herein as a plating anolyte), and optionally a separator separating the plating catholyte from the plating anolyte. Further descriptions of example electroplating cell configurations are provided below.

[0144] The treated-ferrous-rich solution 332 is provided to the catholyte or cathode chamber of iron electroplating cell 340). In iron electroplating cell 340, dissolved ferrous ions are electrochemically reduced to iron metal at the plating cathode. Electroplated iron metal 342 is removed as a product. In some aspects, a portion of treated-ferrous-rich solution 323 is also provided, as a separate stream, directly or indirectly to the plating anolyte or anode chamber of iron electroplating cell 340. In some aspects, the anodic reaction at the plating anode is electrochemical oxidation of ferrous ions to ferric ions, the oxidized ferrous ions being ferrous ions directly or indirectly from the treated-ferrous-rich solution 332. In some aspects, the anodic reaction at the plating anode is water oxidation and evolution of oxygen gas. In various aspects, used / spent electrolyte 344 from iron electroplating cell 340 may be recycled to leach tank 310, ferric reduction reactor 320, or a combination of both.

[0145] In some aspects, a concentration of solid particulates of an average diameter selected from the range of approximately 1 pm to approximately 10 pm in the catholyte of electroplating cell 340 is sufficiently low enough to be undetectable above noise by dynamic light scattering (DLS). In some aspects, a concentration of solid (undissolved) particulates of an average diameter selected from the range of approximately 5 pm to approximately 10 mm in the catholyte of electroplating cell 340 is less than 1 mg / L.

[0146] In some aspects, the anodic reaction at the plating anode is electrochemical oxidation of dissolved ferrous ions to dissolved ferric ions, in which case used / spent plating anolyte, having electrochemically generated ferric ions and a higherLeydig Ref. 340515: 3-25 WO concentration of ferric ions than in the treated ferrous-rich solution 332, may be recycled to ferric reduction reactor 320, wherein the electrochemically generated dissolved ferric ions are re-reduced to dissolved ferrous ions.

[0147] In some aspects, the anodic reaction at the plating anode is electrochemical oxidation of water and evolution of oxygen gas, in which case used / spent plating anolyte, which may have a lower pH than treated ferrous-rich solution 332. Similarly, in aspects in which the anodic reaction at the plating anode is electrochemical oxidation of hydrogen gas, the pH of the spent anolyte will be lower than the treated ferrous-rich solution 332 due to production of aqueous protons in the anolyte. In either case, the spent plating anolyte may be recycled back to leach tank 310 to further facilitate the acidic leach of feedstock 302.

[0148] Not shown but optionally present in any of the systems and methods described here is a water management subsystem. The water management subsystem may performed any of a plurality of functions, including evaporation, condensation, crystallization, heating, cooling, etc. For example, if iron electroplating cell 340 is a divided cell, wherein the plating catholyte and plating anolyte are separated by a proton or anion exchange membrane, then as the treated ferrous-rich aqueous solution is added to the catholyte, to replenish ferrous ion concentration during plating, the total volume of catholyte continues to increase. To manage this, plating catholyte may be periodically or continuously removed and water may be removed therefrom (e.g., evaporation) to make a concentrated used / spent plating catholyte. In aspects wherein the anodic reaction is water oxidation and oxygen gas evolution at the plating anode of the iron electroplating cell 340, water removed from the (used / spent) plating catholyte may be collected (e.g., condensed) and recycled to the plating anolyte. In some aspects, the used / spent plating catholyte or concentrated used / spent plating catholyte may recycled to ferric reduction reactor 320. This may be done to manage accumulation of impurities in the plating catholyte. Optionally, some used / spent plating catholyte or concentrated used / spent plating catholyte is bled from iron electroplating cell 340 to manage accumulation of impurities.

[0149] In some aspects, other processes in addition to electroplating or instead of electroplating may be used to extract iron from the treated ferrous-rich aqueous solution, such as but not limited to, recrystallization, cementation, and / or other methods known inLeydig Ref. 340515: 3-25 WO the art. For example, in some aspects herein, FeSCM or FeCl2 may be crystallized, as a co-product useful for some applications, from the treated ferrous-rich aqueous solution, instead of electroplating or in addition to electroplating iron.

[0150] It will be understood that any tank, reactor, or electrochemical cell illustrated in schematics herein, such as those described above, may be implemented as a plurality of tanks, reactor(s), or electrochemical cells, optionally connected in parallel and / or in series by configurations known in the art.Example Iron Electroplating Cell Configurations:

[0151] Various configurations of an iron electroplating cell, such as 140, 240, and 340 above, are described in in International Patent Publication WO2022204391, International Patent Publication W02024064061, International Patent Publication WO2024072741, and International Patent Publication WO2022197954, all of which are incorporated herein in their entireties.

[0152] The iron electroplating cells (140, 240, 340) may generally be configured similarly to any other electrowinning or electroplating cell bath, including anodes and cathodes alternatingly arranged in a bath, with anodes separated from cathodes by separators. In some aspects, plating catholyte is prevented from mixing with plating anolyte within the plating cell by a separator membrane and / or other structures. For example, in some aspects, the iron electroplating cell has a proton exchange membrane (PEM), an anion exchange membrane (AEM), a microporous separator, or a diaphragm separating the plating catholyte from the plating anolyte. In some aspects, the anodic reaction at the plating cell’s anode is an electrochemical oxidation of aqueous dissolved ferrous ions to aqueous dissolved ferric ions. In various other aspects, the anodic reaction at the plating cell’s anode is an electrochemical oxidation of water and evolution of oxygen gas. In other aspects, the anodic reaction at the plating cell’s anode is an oxidation of a gaseous reactant, such as hydrogen gas.

[0153] In various aspects, the iron electroplating cell may be configured as a cathode-to-anode flow cell. In a cathode-to-anode flow plating cell, the electrolyte flows into the bath at a cathode region, then flows from the cathode region(s) into the anode region(s) and then out of the plating cell. For example, the electrolyte may be flowed through a suitable structure such as highly porous flow-through separator or throughLeydig Ref. 340515: 3-25 WO one or more conduits while generally being prevented from flowing back towards the cathode(s). In some aspects, the separator may be a diaphragm or highly porous material or conduit that facilitates electrolyte flow from cathode(s) to anode(s) with minimal or no electrolyte flow in the opposite direction. This directional control facilitates extraction of ferric ions generated at the anode and minimizing or avoiding flow of those anodically generated ferric ions back to the cathode region of the bath.

[0154] In some aspects, a plating cell configured in a cathode-to-anode flow configuration has an individual separator surrounding each anode in the plating bath such that the anode chambers are defined as the interior of the bags. Such a configuration may be referred to in the art as a “bagged anode” (an example of which is provided in US Patent 4,201,653 to O’Neill, et al., which incorporated here by reference the extent not inconsistent herewith). In other aspects, separators may be sealed to a frame or to bath side-walls to separate cathode chambers from anode chambers. Flow of electrolyte from the cathode chambers into the anode chambers may be provided for by selection of a suitably porous separator material or by additional flow structures such as conduits (e.g., as described in US Patent 4159232 to Bacon et. al., which incorporated here by reference the extent not inconsistent herewith) or overflow dams (e.g., as described in US Patent 2,810,868 to Bodamer et. al., which incorporated here by reference the extent not inconsistent herewith). Electrolyte may be removed from a cathode-to-anode flow cell plating cell from the anode chambers. In some aspects, two or more separators may be used to separate anodes from cathodes while providing for uni-directional cathode-to-anode flow of electrolyte. For example, in some aspects anodes and cathodes may each be surrounded by bag-shaped separators as shown in US Patent 4,087,339 to Elliott, et al, which incorporated here by reference the extent not inconsistent herewith.

[0155] The electrolyte in a cathode-to-anode flow cell may be a ferrous-rich aqueous solution, such as an impurity-treated ferrous-rich solution described herein. The electrolyte is directed into the cathode region(s) of the cell where it operates as catholyte. The electrolyte then flows through the separator to an anode region where it operates as an anolyte. In various aspects, reactions at the anode may include oxygen evolution and / or oxidation of aqueous dissolved ferrous ions to aqueous dissolved ferric ions. In some aspects, oxygen evolution may be avoided by selecting an anode materialLeydig Ref. 340515: 3-25 WO that readily promotes ferrous oxidation without catalyzing oxygen evolution. Examples of such materials include plates, sheets, felts, wools, meshes (woven or unwoven) or other structures of carbon, graphite, graphene, or conductive polymers. Alternatively, if an oxygen evolution reaction is acceptable or desired, the anodes may comprise materials such as lead oxide, tin oxide, and / or platinum group metal oxides (referred to as “mixed metal oxide anodes” or “dimensionally stable anodes” in the field of electrochemistry).

[0156] In aspects described throughout herein comprising an iron electroplating or electrodeposition cell with an anodic reaction of aqueous dissolved ferrous ion oxidation to aqueous dissolved ferric ion, the respective cell may optionally be configured as cathode-to-anode flow cell.Additional Iron Electroplatinq Cell Considerations:

[0157] In various aspects, the electroplating cell is configured to electroplate metallic iron from the Fe2+ions at the cathode(s), for example in the form of a plated Fe metal sheet. In some aspects, the electroplating cell is configured to electrochemically generate iron powder at the cathode(s). Whether iron metal is produced as a plated shape (plates, coins, crowns, sheet, etc.) on the cathode or as a powder may be controlled via, for example, the operating current density, where higher current densities, such as greater than or equal to approximately 0.2 A / cm2(such as optionally selected from the range of 0.2 A / cm2to 0.5 A / cm2or higher) will prefer to form Fe metal powder, whereas lower current densities result in a preference for denser Fe metal plates (or other shapes) on the cathode. Regardless of the form factor, the resulting electrochemically generated Fe metal is highly pure, in various aspects being at least 99 wt.% Fe.

[0158] In some aspects wherein Fe metal is electroplated onto the cathode in the form of a plate, sheet, crowns, coins, or other plated shapes, it may be desirable for the cathode material, or a surface material thereof, to have sufficient adhesion with the electroplated iron to avoid premature delamination of the deposited iron while potentially allowing for mechanical removal of the iron. Cathodic materials with surfaces having such adhesion properties may include iron, mild steel, stainless steel (e.g., stainless 304, stainless 316, or other grades of stainless steel), or other metals (e.g., zinc or copper if a multi-layered structure is desired). In various embodiments, a re-usable cathode may be treated prior to electroplating iron and after removal of deposited iron.Leydig Ref. 340515: 3-25 WO In various embodiments, some regions of a cathode may be masked prior to electroplating for producing electroplated material in a desired shape or form-factor, for example as described in US Patent 4,139,430, which is incorporated herein by reference to the extent not inconsistent herewith. Electrowinning systems according to embodiments and aspects herein may comprise any number of plating cells, cell baths, or other configurations, any of which may be optimized for producing iron in any desired form -factor.

[0159] When it is desired that iron powder is produced at the cathode in an iron electroplating cell, cathodic surface materials or mechanical properties may be selected to promote and or facilitate powder generation at the cathode and / or removal of powder from the cathode. For example, in some aspects, a vibrating belt cathode may be used to facilitate the separation of the Fe powder from the cathode and subsequent removal from the iron plating cell. In some aspects, the cathode surface material may be selected for low iron adhesion to facilitate the iron powder separation and subsequent removal. Some example low iron adhesion cathode surface material may include aluminum, graphite, lead, nickel, conductive polymer(s), graphene, titanium, ora combination of these or other materials with a tendency for low adhesion of electrodeposited iron.

[0160] Alternatively or in addition to selecting a low-adhesion cathode surface, the plating catholyte may be circulated intensely through a cathodic region of a plating cell to help loosen electrodeposited powder, thereby further facilitating removal of electrochemical generated iron powder.

[0161] Optionally, electrochemically generated iron powder is harvested with the aid of one or more hydrocyclone(s) in series and / or using permanent magnets installed at the underflow of the hydrocyclone(s). Optionally, the electrochemically generated iron powder is rinsed with slightly acidic water to remove traces of catholyte, and optionally further passivated with nitric acid and dried in an inert (e.g., nitrogen gas) atmosphere. Additional details of various systems and methods for electrolytical ly producing iron powder are provided in the art, including: U. S. Patent Publication 2011 / 0089045 (Cardarelli); U. S. Patent 3,969,207 (Kerti, et al.); and UK Patent Publication GB899028A (Montan Union Handelsges M B H).Leydig Ref. 340515: 3-25 WO Chemical Reduction and Reductive

[0162] As also provided in the 732 patent, it is possible to oxidize hydrogen gas at the acid regeneration cell (AR) anode (and / or at a plating cell anode) instead of oxidizing water. Because hydrogen oxidation at a catalyst is a spontaneous energyproducing reaction when coupled with ferric reduction, such a cell can be described as an acid regeneration fuel cell (or AR fuel cell). The hydrogen may be supplied from an alkaline or PEM water electrolyzer or any other source of hydrogen gas. The 732 patent also describes coupling the AR with a leach tank such that the electrochemical reduction in the AR supports leaching of iron or in the leach tank. This can be done by recirculating electrolyte / leach solution between the AR and the leach tank.

[0163] In various aspects, by effectively combining functions of an AR fuel cell and a leach tank into a single reactor, Applicant has discovered that it is possible to perform a reductive leach of solid hematite iron ore using a hydrogen fuel cell reactor. While not wishing to be bound by any theory of operation, it is believed that in some aspects, the fuel cell anode oxidizes gaseous hydrogen to aqueous protons while the cathode reduces solid-state Fe(lll) to Fe(ll) (e.g., by reducing hematite or goethite to magnetite) in addition to aqueous reduction of ferric (Fe3+) to ferrous (Fe2+) ions. In various aspects, the process is facilitated by the iron ore being in electrical contact with the hydrogen reduction catalyst (anode), such as through the use of a conductive additive material (e.g., carbon particles, metal particles, conductive polymers, or others). In various aspects, the reactor may be configured as an energy-generating fuel cell (e.g., having an external circuit through which produced electrical current may be stored or applied to an electrical load), or as a short-circuited fuel cell from which energy is not collected. Various other or additional aspects are disclosed herein.

[0164] Without wishing to be bound by any particular theory, it is believed that some reduction occurs in a solid state (e.g., reduction of Fe2Os or FeOOH to FesCM or FeO) and some reduction occurs in an aqueous state (e.g., reduction of aqueous Fe3+ions to Fe2+ions). In some aspects, reactors may be optimized for either solid-state reduction, for aqueous state reduction, or combinations of the two. For example, in some embodiments, a first reductive leach reactor may be optimized primarily for solid-state reduction and a second reductive leach reactor may be optimized primarily for aqueous state reduction of ferric ions with a hydrogen gas bubbled or sparged through the liquid.Leydig Ref. 340515: 3-25 WO

[0165] When H2gas is used as a reductant, the reductive leach reactor (e.g., reductive leach reactor of FIG. 7 or FIG 8 or reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D) may comprise a hydrogen oxidation catalyst on a support and an iron ore slurry made up of iron ore particles mixed with an acidic aqueous solution (although in some embodiments, alkaline solutions may be used instead of acidic aqueous solution). In some embodiments, in order to increase conductivity of the aqueous portion of the slurry, it may also comprise a supporting electrolyte containing one or more dissolved salts that are substantially inert in the reactions described herein. In various aspects, the reductive leach reactor may benefit from the iron ore being in electrical contact with the catalyst, such as via a conductive current collector and / or a conductive additive material (e.g., carbon particles) mixed with the slurry. The reactor may be configured as an energy-generating fuel cell (in which generated energy may be captured through an external circuit), or as a short-circuited fuel cell from which energy is not collected.

[0166] Applicant has discovered that hematite-containing iron ore can be leached relatively quickly (in a matter of hours) and relatively completely (up to ~95% Fe leached) in a reductive leaching process utilizing both protons and electrons released by catalytic oxidation of hydrogen gas with an acidic electrolyte. Any acid can be used, including sulfuric, hydrochloric, or others (or mixtures of acid salts).

[0167] Oxidation of hydrogen gas produces protons and electrons according to Equation 1:H2(g)→ 2H+(aq)+ 2e−[1]

[0168] It is believed that by catalytically oxidizing hydrogen gas at an electrode in contact with an aqueous acidic solution and in electrical contact with iron ore particles submerged in the acidic solution, the produced electrons participate in the solid-phase reduction of iron oxide compounds (e.g., reduction of hematite (Fe2O3) to magnetite (Fe3O4)) while the produced protons replace acid consumed by leaching the ore (leaching may occur before, after, or concurrent with any solid-state reduction). Because magnetite leaches more readily than hematite, the magnetite produced in the reduction is believed to dissolve very quickly. Because magnetite dissolves to both ferric (2 / 3) and ferrous (1 / 3), some of the electrons produced by hydrogen oxidation will be consumed in reducing the aqueous ferric to ferrous while also producing acid according to Equation 2 below.Leydig Ref. 340515: 3-25 WO Fe3+reduction produces acid: H2+ Fe2(SO4)3→ H2SO4+ 2FeSO4[2]Ore Reduction Solid Phase only: H2+ 3Fe2O3→ 2Fe3O4+ H2O [3] Leach: Fe3O4+ 4‘H2S 04— > F e2(^SO4)3+ FeS04+ 4‘H2O [4]Ferric Reduction: H2+ Fe2(SO4)3→ H2SO4+ 2FeSO4[2]Ore Reduction Net: H2+ Fe2O3+ 2H2SO4→ 3H2O + 2FeSO4[5]

[0169] As shown in the Ore Reduction Net equation (5), reductive leach consumes acid, and acid is decreasing.

[0170] In some embodiments, “used” or “spent” plating anolyte having an increased concentration of ferric (as described in the 732 patent) may also be directed to the reductive leach reactor so as to reduce ferric produced in the plating anolyte back to ferrous for use in subsequent plating operations. In such cases, the net reaction proceeds according to Equation 6:Net Reaction: 3H2+ Fe2O3+ 2Fe2(SO4)3→ 6FeSO4+ 3H2O [6]

[0171] Note that this net reaction doesn’t involve acid, meaning in some embodiments, a reductive leach reactor may be started without acid (or with only a small quantity of acid), provided the aqueous solution contains enough supporting electrolyte to provide a desired degree of conductivity.

[0172] Cathodic half reactions:Fe3+(aq)+ e-→ Fe2+(aq)[7] 3Fe2O3(s)+ 2e−+ 2H+(aq)→ 2Fe3O4(s)+ H2O(l)[8] Fe3O4(s)+ 8H+(aq)+ 2e−→ 3Fe2+(aq)+ 4H2O(l)[9] FFe2O3(s)+ 6H+(aq)+ 2e−→ 2Fe2+(aq)+ 3H2O(l)

[0010]

[0173] In some embodiments, the electrolyte (aqueous solution) in the reductive leach reactor (e.g., reductive leach reactor of FIG. 7 or FIG 8 or reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D) may also contain ferric and / or ferrous iron from a used or spent electroplating anolyte and / or catholyte.

[0174] Reductive leaching may allow for elimination of (or substantially decreased need for) thermal reduction of hematite ore, which would decrease thermal energyLeydig Ref. 340515: 3-25 WO requirements and carbon emissions. However, in some embodiments, it may be desirable to roast iron ore in air at a temperature of approximately 200 °C to approximately 400 °C in order to dehydrate constituents such as goethite and / or to burn out organic materials in the ore prior to introducing ore into a reductive leach reactor.

[0175] Other advantages of reductive leaching over thermal reduction include elimination of any thermal energy penalty from heating impurity mass in high-impurity ores; decreased need for iron or other base material for consuming residual acid prior to electroplating; decreased impurity dissolution leading to less energy spent regenerating acid consumed in dissolution of impurities; potential elimination (or at least decrease) in colloidal silica, among other benefits.

[0176] In some aspects, in order to achieve the catalytic oxidation of hydrogen gas, a triple phase boundary condition is maintained such that a reaction zone exists at the interface 400 between the liquid electrolyte 402, the gaseous hydrogen 404, and the solid catalyst 406 as illustrated in FIG. 4. In the configuration of FIG. 4, the interface 400 is shown at a surface of the liquid 402. When gaseous hydrogen is sparged through the liquid (either injected via a tube from above or though a sparger below), an interface 400 may occur at any point within the liquid volume where the gas, catalyst, and liquid meet.

[0177] In various aspects, hydrogen (gas) contacts the hydrogen oxidation catalyst (solid) to perform the hydrogen oxidation reaction (HOR) and the resulting protons are able to get into the electrolyte liquid. The reaction occurs where all three phases meet. Reductive leach reactors may be designed such that a triple phase boundary exists at a range of liquid levels, liquid flow conditions, and / or gas flow conditions.

[0178] For example, some reactors may be configured with a hydrogen oxidation electrode configured in a heat exchanger type design using tubes (e.g., concentric tubes submerged in electrolyte and containing one or more gas flow channels through which they hydrogen may flow) to increase the surface area where reaction can occur. Using a tube material that would allow H2diffusion but not liquid ingress would take advantage of hydrogen’s high diffusion. Examples of such tube materials may include hydrophobic polymers such as PTFE, or others.

[0179] Hydrogen oxidation catalysts may include any catalysts suitably used in hydrogen fuel cell applications including platinum, platinum and / or other platinum groupLeydig Ref. 340515: 3-25 WO metals (“PGMs” e.g., Pd, Rh, Ru, Os, Fr, Ir). Platinum group metals may be loaded onto carbon (e.g., platinum on carbon particles “Pt / C”) or on other materials, particles, meshes, or substrates. For example, platinum group metal(s) may be loaded in a resin or similar matrix. Alternatively, non-PGM HOR catalysts such as alloys of metals such as nickel, chromium, tungsten, molybdenum, copper, etc. Some examples include Ni-Mo alloys, Mo alloys (e.g., MoS2) Cr-Ni alloys, Ni-W alloys, Ni-Cu alloys, doped carbon materials (e.g., nitrogen-doped carbon) or others either loaded onto particles, including carbon particles, conductive polymer particles, non-conductive polymer particles, ion exchange resin particles, ceramic particles, or other conductive or non-conductive particles, or loaded onto any other surface, sheet, mesh, foam, or substrate made of such materials.

[0180] In some embodiments, a reductive leach reactor (e.g., reductive leach reactor of FIG. 7 or FIG 8 or reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D) may be configured to achieve heterogenous reactions by dispersing a hydrogen oxidation catalyst (e.g., Pt / C), optionally on a support or other substrate, throughout a reactor and sparging micro and / or nano sized H2bubbles through the ore-acid slurry. In some embodiments, such a reactor may comprise or be configured similarly to a fluidized bed reactor.

[0181] In some aspects, reductive leach reactors (e.g., reductive leach reactor of FIG. 7 or FIG 8 or reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D) operate under mild conditions of liquid temperature (of the acidic solution) being less than 120 °C, optionally less than 100 °C, and under a gas pressure of less than 2 atm, optionally approximately 1 atm.

[0182] In some aspects, reductive leach reactors (e.g., reductive leach reactor of FIG. 7 or FIG 8 or reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D) can also be designed to operate at elevated temperature and / or pressure (e.g., temperatures of 200 °C or more and / or pressure above 10 bar up to approximately 50 bar). Operating the hydrogen oxidation reaction at elevated temperature and / or pressure may enable use of less expensive catalysts including non-PGM catalysts such as those listed above.

[0183] In some embodiments, a reductive leach reactor (e.g., reductive leach reactor of FIG. 7 or FIG 8 or reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D) operating at elevated pressure may be operated in limit-cycle mode. In such embodiments,Leydig Ref. 340515: 3-25 WO hydrogen may be driven into a reactor enclosure until pressure in the enclosure reaches a maximum set point. As hydrogen is consumed in the reductive leaching reaction, the pressure will fall. Once the pressure reaches a minimum set point, hydrogen can again be driven into the reactor until the maximum set point is reached again. In some embodiments, initiation of driving hydrogen into the reactor may include starting hydrogen production with a water electrolyzer, and stopping the hydrogen flow may comprise stopping the water electrolyzer. Alternatively or in addition, starting and / or stopping hydrogen flow may comprise operating one or more valves, pumps, pressure regulators, or other flow control devices.

[0184] Reductive leach reactors can be designed in a “short-circuit” arrangement in which electrons electrochemically generated at the hydrogen oxidizing anode may be conducted into the ore slurry (which may act as the cathode) rather than through an external circuit.

[0185] In some embodiments, the ore-acid slurry in a reductive leach reactor (e.g., reductive leach reactor of FIG. 7 or FIG 8 or reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D) may also include a conductive additive to promote conduction of electrons throughout the iron ore particles. Ideal conductive additives may include materials that are electrically conductive but otherwise non-reactive (or minimally-reactive) in the acidic slurry. For example, the conductive additive may comprise carbon and / or graphite particles similar in size or smaller than the iron ore particles. In other examples, other metals, alloys, or conductive metal oxides, or conductive polymers (or polymers with conductive additives) that are insoluble or very sparingly soluble in the chosen acid may be used as a conductive additive. For example, such conductive additive materials may comprise stainless steel or titanium, among others. In yet other examples, a redox mediator or electron shuttle (e.g., ascorbic acid) capable of supporting aqueous oxidation and reduction reactions may be used in place of or in addition to a solid conductive additive. An example short-circuited reductive leach reactor is shown in FIG.5B.

[0186] FIG. 5A illustrates a ferric reduction reactor, also referred to as a “direct Fe3+reduction reactor,” 500 which comprises a vessel 502 containing an aqueous solution 504 containing ferric ions. In some aspects, ferric reduction reactor 500 is an example of ferric reduction reactor 320 of FIG. 3A or FIG. 3B or of aqueous ferric feduction reactorLeydig Ref. 340515: 3-25 WO of FIG. 9A or FIG. 9B. A hydrogen injection tube or sparger 505 may inject hydrogen gas 507 either into the head space above the solution 504, or bubbled into the solution 504 below the liquid (or optionally from the bottom of the vessel 502). A hydrogen oxidation catalyst 506 may be supported on a conductive substrate 508 such as a graphite or carbon plate, rod, sheet, foam, mesh, etc. Hydrogen oxidized at the catalyst 506 may produce protons which enter the solution 504 while produced electrons may be conducted to the solution 504 via the conductive substrate 508, where they drive reduction of ferric ions to ferrous in the solution 504. In some embodiments, the aqueous ferric reduction reactor 500 of FIG. 5A may include a stirrer 510 or other agitation mechanism to promote mass transport.

[0187] As shown in FIG. 5B, a direct Fe3+reduction reactor may form the basis for a reductive leach reactor 550 which includes an ore slurry 552 comprising an aqueous electrolyte 554, iron ore particles 556 and conductive particles 558. Similarly to the ferric reduction reactor 500, the reductive leach reactor 550 may also include a hydrogen introduction structure such as an injection tube or sparger 562 for introducing hydrogen gas 560 below the surface of the electrolyte 554. The reductive leach reactor may comprise a hydrogen oxidation catalyst 566 supported on a conductive support 568. Alternatively or in addition, the conductive particles 558 may also support a hydrogen oxidation catalyst material (e.g. platinum or other platinum group metals may be deposited onto or into particles of carbon, graphite, polymer, ion exchange resin or other other materials). In some aspects, reductive leach reactor 550 is an example of the reductive leach reactor of FIG. 7 or FIG 8 or of reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D.

[0188] Reductive leach reactors (e.g., reductive leach reactor of FIG. 7 or FIG 8 or reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D) can also be designed in energyproducing configurations (also referred to as “fuel cell” configurations) by directing generated electrons through an external circuit which can be connected to an electrical load. An example fuel cell reductive leach reactor is shown in FIG. 6.

[0189] As shown in FIG. 6, an acid regeneration fuel cell 600 may be configured to oxidize hydrogen gas as described herein. As shown, a hydrogen oxidation catalyst such as platinum on carbon or “Pt / C” may be deposited onto or otherwise combined with a gas diffusion layer (GDL) 604 which may be layered onto or placed adjacent to an ionLeydig Ref. 340515: 3-25 WO conductive separator membrane 606 such as a proton exchange membrane or other cation exchange membrane. The separator membrane 606 separates the hydrogen oxidation catalyst anode 604 from a cathode 608 made of a porous conductive material such as carbon or graphite felt or any other suitable conductive material. In operation, hydrogen is oxidized to protons at the anode 604 while ferric ions are reduced to ferrous ions at the cathode 608, thereby driving an electron through the external circuit 610, and may be applied to an electric load 612.

[0190] Short-circuit and / or fuel cell reductive leach reactors may be designed to accommodate a flowing ore-acid slurry in electrical contact with the hydrogen oxidation anode. Alternatively, a solid / liquid reactor may be used instead of a flowing slurry. For example, any reactor in which the aqueous acidic electrolyte contacts a bed of the solid ore and (optionally) conductive additive particles, such as a packed bed reactor or a fluidized bed reactor.

[0191] A reductive leach reactor (e.g., reductive leach reactor of FIG. 7 or FIG 8 or reductive leach reactor 110 or 210 of FIG. 1 - FIG. 2D) may be incorporated into a two-step iron electroplating system in place of an acid regenerator as shown in the example of FIG. 7. In such cases, a reductive leach reactor can also be used to reduce ferric iron from a used or spent electroplating anolyte back to the ferrous state for subsequent electroplating cycles. In some cases, a first hydrogen oxidizing reactor (i.e., a reductive leach reactor that omits solid-phase ore and only contains a ferric / ferrous acidic electrolyte) may be used for reducing ferric iron in used / spent plating anolyte to ferrous, and a second hydrogen oxidizing reductive leach reactor may be used for reductively leaching solid ore.

[0192] With reference to FIG. 8, in some embodiments, an AR, AR fuel cell or other aqueous ferric reduction reactor (e.g., a metallic iron packed bed) may be used for “polishing” remaining ferric (Fe3+) ions from the leach solution by reducing those ferric ions to ferrous prior to an impurity removal step. A ferric polishing reactor may include any type of aqueous ferric reduction reactor described herein, although optionally sized for a smaller quantity or lower rate of ferric reduction compared to some other ferric reduction reactors herein. In cases in which impurity removal is performed using a base other than metallic iron, a polishing reactor may decrease loss of iron to precipitation of ferric compounds.Leydig Ref. 340515: 3-25 WO

[0193] In aspects where a thermal roasting step is needed or desired, which may depend on ore composition, such as to achieve iron leaching within a desired timeframe, a reductive leach reactor may be incorporated into a 2-step iron electroplating system (e.g., as shown and described in the 732 patent) that also includes a thermal reduction step (e.g., a magnetization roast, air-only roast, natural gas reduction roast, hydrogen reduction roast, or other thermal reduction process), such as presented by treatment 215 or 315 in FIG. 2A- FIG. 3B.

[0194] FIG. 7 illustrates an example embodiment of a two-step iron production system such as those described in the 732 patent, but incorporating a reductive leach reactor in place of an acid regeneration cell.

[0195] FIG. 9A illustrates a system, according to various aspects herein, of an iron production system incorporating a leach tank and an aqueous ferric reduction reactor (labeled “Aq. Ferric Reduction Reaction”), such as the system of FIG. 3B, wherein H2 gas is used as reductant to chemically (non-electrolytically) reduce aqueous dissolved ferric ions to aqueous dissolved ferrous ions, such as discussed above. In the system of FIG. 9A, the anodic reaction in the iron electroplating cell may be water oxidation and oxygen gas evolution (oxygen evolution reaction, OER). Used / spent electrolyte, comprising used / spent anolyte and / or used / spent catholyte, may be recycled back to the leach tank.

[0196] FIG. 9B illustrates a system, according to various aspects herein, of an iron production system incorporating a leach tank and an aqueous ferric reduction reactor (labeled “Aq. Ferric Reduction Reactor”), such as the system of FIG. 3A, wherein H2 gas is used as reductant to chemically (non-electrolytically) reduce aqueous dissolved ferric ions to aqueous dissolved ferrous ions, such as discussed above. In the system of FIG.9B, the anodic reaction in the iron electroplating cell may be electrochemical (anodic) oxidation of aqueous dissolved ferrous ions to aqueous dissolved ferric ions. Used / spent plating anolyte, comprising anodically-generated ferric ions, may be recycled back to the aqueous ferric reduction reactor for re-reduction of the generated ferric ions.Reductive Leachinq of Ores with Reducinq Gas:

[0197] In some embodiments a reductive leaching process may be performed at low temperatures, by contacting iron ore with an aqueous acid solution (e.g., sulfuric acid,Leydig Ref. 340515: 3-25 WO hydrochloric acid, or other acids or acid mixtures) to leach ore components into the solution. During such leaching, the acid solution (optionally in a slurry with ore particles) may be contacted with a reducing gas such as natural gas, reformed natural gas, carbon monoxide, methane, any other natural or reformed hydrocarbon gas, hydrogen gas, forming gas, sulfur dioxide gas, hydrogen sulfide gas, or mixtures of any of these or other reducing gases. In some embodiments, the iron ore may be of a type containing goethite and / or hematite components. In other embodiments, the iron ore may contain at least some magnetite, whether naturally-occurring or produced by reduction of geothite or hematite.

[0198] In various embodiments, a reducing gas may be bubbled through (or otherwise contacted with) a leach solution in a leaching vessel (e.g., while the acid leaching solution is in contact with the ore; such as a reductive leach reactor described throughout herein or illustrated in FIG. 1 - FIG. 2D, FIG. 5B, FIG. 7, FIG 8, FIG. 10, FIG.11, FIG. 12, FIG. 14, FIG. 15, or FIG. 17) and / or in a separate gas-liquid contactor in the absence of ore (such as an aqueous ferric reduction reactor described elsewhere herein or illustrated in FIG. 3A, FIG. 3B, FIG. 5A, FIG. 9A, or FIG. 9B). In some embodiments, a recirculating system may be used in which an acid solution is contacted with an ore material (e.g., in a dissolution tank, vessel, heap, or other leaching configuration), followed by directing a pregnant leach solution with the reducing gas in a separate gasliquid contactor, thereby reducing aqueous ions to a lower oxidation state (e.g., reducing aqueous ferric to ferrous). The thus-reduced leach solution may then be returned to contact with the ore for further leaching. Alternatively (or following a desired number of leach / reduction cycles), the reduced leach solution may be directed to an impurity removal step and / or an electroplating step as described elsewhere herein.

[0199] In various embodiments, such “low temperature” reductive leaching may be performed at temperatures of between approximately 50 °C and approximately 90 °C, in some embodiments approximately 60 °C to approximately 80 °C, and in various specific embodiments, at approximately 60 °C, at approximately 70 °C, or at approximately 80

[0200] In some example embodiments, reductive leaching of iron ore using a reducing gas such as sulfur dioxide gas (SO2(g)) may comprise multiple steps, optionally including the following reactions:Leydig Ref. 340515: 3-25 WO

[0201] Dissolution of iron ore (e.g., hematite, goethite) in sulfuric acid:FFe2O3(s)+ 3H2SO4→ Fe2(SO4)3+ 3H2O (11)

[0202] Reduction of aqueous ferric ions to ferrous ions:2Fe3++ 3SO42’ + SO2(g) + 2H2O 2Fe2++ 4SO42’ + 4H+(12)Equivalently: Fe2(SO4)3+ SO2+ 2H2O 2FeSO4+ 2H2SO4(13)

[0203] The Overall reaction of steps 11 and 12 above may be written as:FFe2O3(s) + SO2(g) + H2SO4→ 2FeSO4+ H2O (14)

[0204] Sulfur dioxide for use in the above example reactions may be obtained by various methods. For example, in some embodiments, sulfur dioxide may be obtained by combusting elemental sulfur in an oxygen rich environment such as air.

[0205] Sulfur combustion in air proceeds according to the equation:S(s) + O2(g) → SO2(g) + Heat (-296.8 kJ / mol) (15)

[0206] It is believed that reductive leaching using a reducing gas such as sulfur dioxide gas (or others) may accelerate leaching kinetics for hematite and other difficult-to-dissolve naturally occurring iron ores. In some embodiments, the heat released by sulfur combustion may be productively used for other processes, such as evaporative water removal, ore roasting, thermal reduction of ores, electrical power generation (which power may be used to drive electrochemical plating cells or for other purposes), or other steps including various heat-consuming steps.

[0207] Deleterious impurities, such as alumina, phosphorous, silica, titania, or others (whether present as dissolved species or as colloidal suspensions) may be removed from the aqueous leach solution by precipitation and / or crystallization processes, optionally driven by a pH shift, referred to throughout herein as impurity removal. Such a pH shift may be driven by addition of iron metal or other proton-donor (or materials containing a net excess of soluble proton-donor materials relative to proton-acceptors) such as limestone, lime, slaked lime, dololime, steel slags, ferrous oxide, magnesium oxides, calcium oxides, ammonia, ammonium hydroxide, or others.Leydig Ref. 340515: 3-25 WO

[0208] In various embodiments, metallic iron may be cathodically electroplated in an electrolytic (or “electrowinning”, “electroplating”) cell with an anodic reaction such as oxygen gas evolution, chlorine gas evolution, ferrous oxidation (i.e., oxidation of aqueous Fe2+ions to Fe3+ions), or other electrochemical oxidation reactions.Thermal Reduction of Iron Ores Using Reducing Gases:

[0209] In some embodiments, iron ores containing highly oxidized iron oxides such as goethite or hematite may be thermally reduced to lower oxidation state minerals by contacting the ore with a reducing gas at an elevated temperature for sufficient time to produce a desired reduced mineral form. For example, hematite (Fe2O3or ferric oxide) may be reduced to magnetite (Fe3O4), which may be reduced to ferrous oxide (FeO), which may be reduced to iron metal (Fe). Some aspects of thermal reduction described hereafter are optionally, in some aspects, performed as part of the “Pre Treatment” in FIG. 2A, FIG. 2B, FIG. 3A, or FIG. 3B, the “Thermal Reactor” in FIG. 9A or 9B, or the “Ore Reduction” in FIG. 12, FIG. 13, FIG. 14, FIG. 15, or FIG. 17.

[0210] In some example embodiments, hematite components in an iron ore may be reduced to magnetite using a reducing gas such as sulfur dioxide at a temperature of approximately 400 °C (e.g., approximately 350 °C to approximately 450 °C). Such a process may involve the following steps and equations:

[0211] In some embodiments, sulfur dioxide gas may be produced by combustion of sulfur in air as described above with reference to Equation 15.

[0212] Reduction of hematite to magnetite at approximately 400 °C may proceed according to the equation:3Fe2O3(s) + SO2(g) 2FesO4(s) + SO3(g) (16)

[0213] The sulfur trioxide (SO3) gas produced in Equation 16 may be combined with water to form sulfuric acid according to the equation:SO3(g) + H2O(I) H2SO4(l)(ΔH = -130.2 kJ / mol) (17)

[0214] In various embodiments, the thermal energy exothermically released by formation of sulfuric acid according to Equation 17 may be transferred and used in any other part of the iron extraction process as described herein.Leydig Ref. 340515: 3-25 WO

[0215] In some embodiments, the reduced ore produced by the sulfur thermal reduction of Equation 16 may be leached in a sulfuric acid solution. Optionally, the ore leaching may include a reductive leaching step using sulfur dioxide (and / or another reducing gas). Such reductive leaching may comprise the following reactions:

[0216] Dissolution of magnetite:Fe3O4(s) + 4H2SO4→ Fe2(SO4)3+ FeSO4+ 4H2O (18)

[0217] Reduction of ferric to ferrous:2Fe3++ 3SO42−+ SO2(g)+ 2H2O → 2Fe2++ 4SO42−+ 4H+(19A) Equivalently: Fe2(SO4)3+ SO2(g)+ 2H2O → 2FeSO4+ 2H2SO4(19B) Overall: Fe3O4(s) + 2H2SO4+ SO2(g) 3FeSO4 + 2H2O (20)

[0218] Any impurities may then be removed, and metallic iron may be electroplated from the solution as described herein. For example, in some embodiments iron may be electroplated against an oxygen-evolution anode (optionally, an OER anode may be separated from the plating cathode by an anion exchange membrane) according to the equation:FeSO4+ H2O → Fe + H2SO4+ 1 / 2O2(g)(21)

[0219] For an overall system equation of:Fe3O4(s) + 2H2SO4+ SO2(g)+ H2O → 3FeSO4+ 3H2O → 3Fe + 3H2SO4+ 3 / 2O2(g)(22A)Equivalently: Fe3O4(s) + SO2(g)+ H2O → 3Fe + H2SO4+ 3 / 2O2(g)(22B)

[0220] The overall equation starting from a hematite-containing ore is:3Fe2O3(s) + 3SO2(g) + 3H2O → 6Fe + 3H2SO4+ 3O2(g) (23)

[0221] In the process represented by Equations 16 to 23, three moles of excess acid will be generated per six moles of metallic iron. One mole of that excess acid will be in the form of concentrated acid from Equation 17 and two moles of acid will be produced as more dilute acid from the oxygen evolution reaction of Equation 21.

[0222] The process represented by Equations 16 to 23 will also consume approximately 0.5 mole of sulfur for each mole of metallic iron produced, orLeydig Ref. 340515: 3-25 WO approximately 0.29 tonnes of sulfur per tonne of metallic iron produced. With approximately one mole of sulfuric acid generated per 2 moles of metallic iron produced (or approximately 0.875 tonnes H2SO4 per tonne of Fe produced, or approximately 3 tonnes of sulfuric acid per tonne of sulfur consumed), the process of Equations 6 to 13 offers a substantial opportunity to produce sale-able sulfuric acid as a byproduct or coproduct along with iron production.

[0223] Heat generated from the formation of sulfuric acid in Equation 17 can be transferred and used for any other process within the system, such as to remove water from a diluted acid stream via mechanical vapor recompression and / or multiple effect evaporation (MVR / MEE), or other methods.

[0224] In some embodiments, the heat from the combustion of sulfur (e.g., in a furnace) may be used to thermally reduce ore components such as hematite to magnetite as described herein. If sufficient energy is available from the combustion of sulfur for the degree of thermal reduction needed for a particular material, then external heating may not be needed.

[0225] The process represented in Equation 23 produces magnetite which Applicant has found to be relatively easy to leach in systems and methods disclosed herein. If the ferric (Fe3+) portion of dissolved magnetite (Fe3O4) is reduced to ferrous (Fe2+) using sulfur dioxide gas (SO2), then an acid regeneration cell may be omitted from the system. This means that such a system may comprise a dissolution system incorporating gasliquid contactor to contact the reducing gas (e.g., sulfur dioxide) with the iron-rich acidic solution, an impurity removal subsystem for removing impurities, and an electroplating cell configured to electroplate iron metal from the ferrous solution on cathodes paired with anodes configured to perform either oxidation of (oxygen-evolution) or oxidation of ferrous iron to ferric iron. In the latter case, the used / spent anolyte solution containing ferric (Fe3+) iron ions may be returned to reducing gas reduction step.Thermal reduction of Iron Ore to FeO using SO2:

[0226] In some embodiments, rather than dissolving iron feedstock materials such as hematite or magnetite containing iron in the ferric (iron (III) or Fe3+) state, the solid iron ore feedstock material may be reduced to a ferrous (iron (II) or Fe2+) state prior to leaching. This may have the combined benefit of promoting relatively easy dissolution,Leydig Ref. 340515: 3-25 WO in systems and methods disclosed herein, and may simplify plant design by omitting the need for electrochemical acid regeneration cells and / or reducing gas-liquid contactors.

[0227] In some embodiments, iron ores containing goethite, hematite, and / or magnetite may be reduced to ferrous oxide (FeO) using a reducing gas such as sulfur dioxide or other reducing gases referenced herein, which may be obtained by combustion of sulfur in air or any method described herein or other methods. In various embodiments, reduction to ferrous oxide may comprise producing a reduced ore material in which at least 90%, 95%, 99%, 99.9%, or more of the iron oxide is reduced to the form of ferrous oxide (FeO). One example of such an iron extraction process is illustrated in FIG. 12. As shown in FIG. 12, sulfur and air may be input to a combustion reactor (e.g. a furnace) to produce gaseous sulfur dioxide (SO2(g)) which may then be contacted with iron ore in an ore reduction reactor at sufficient temperature and for sufficient time to reduce the ore to ferrous oxide (FeO). In various embodiments, an ore reduction reactor may comprise a rotary kiln, fluidized bed, shaft furnace, moving grate furnace, or any other suitable furnace or reactor. The sulfur trioxide (SO3) byproduct may be dissolved in water to produce sulfuric acid (H2SO4). Meanwhile, the ferrous oxide may be leached in an acidic leach solution (sulfuric acid in the illustrated example, but alternatively HCI or other acids or acid mixtures). The iron-rich leach solution, which should contain substantially only ferrous iron ions (notwithstanding any ferric iron ions that may be produced by incidental oxidation such as by contact with air) may then be passed to an impurity removal step at which deleterious impurities may be removed by precipitation, solvent extraction, or other methods. The purified ferrous iron solution may then be directed to a plating cell (or “electrowinning” cell) which may be configured to electroplate metallic iron on cathodes paired with oxygen evolution anodes.Alternatively, the plating cell anodes may be configured to oxidize any other species as described elsewhere herein.

[0228] It is believed that thermal reduction of iron oxides at a temperature of at least 570 °C may produce stable ferrous oxides which may be further processed as described herein, particularly if such subsequent processing is performed shortly after reduction. In some embodiments, produced ferrous oxide may be quenched, cooled and / or stored in oxygen-free environments (e.g., in containers under vacuum or with gas blankets of inert gas such as nitrogen, argon, etc.) to prevent or minimize oxidation. In someLeydig Ref. 340515: 3-25 WO embodiments, thermal reduction of iron ore to produce ferrous oxide may include addition of water vapor, optionally at a concentration ranging from 1 to 50 vol%, or from 10 to 50 vol% to humidify the reducing gas (or gas mixture) during thermal reduction.

[0229] An example process such as that illustrated in FIG. 12 may involve the following steps and equations:

[0230] Reduction of hematite to FeO (e.g., at > 570 °C):Fe2O3(s) + SO2(g) 2FeO(s) + SO3(g) (24)

[0231] Formation of sulfuric acid:SO3(g)+ H2O(l)→ H2SO4(l)(ΔH = -130.2 kJ / mol) (17)

[0232] Leaching of FeO in sulfuric acid:FeO(s) + H2SO4→ FeSO4+ H2O (25)

[0233] Plating of metallic iron vs OER:H2O(l)+ FeSO4→ Fe + H2SO4+ 1 / 2O2(g)(21)

[0234] Overall reaction in this example:Fe2O3(s) + SO2(g)+ H2O → 2Fe + H2SO4+ O2(g)(26)

[0235] The process represented by Equations 24-26 may consume 0.5 mole of sulfur for each mole of metallic iron (Fe) produced, or approximately 0.29 tonnes of sulfur per tonne of metallic iron produced. Approximately 1 mole of sulfuric acid is generated per 2 moles of Fe produced, or approximately 0.875 tonnes of H2SO4 per tonne of iron produced.

[0236] In some embodiments, the acid used for leaching may be regenerated in the electroplating cell anodic chamber. Therefore, the process need not consume acid. Any make-up acid needed may be supplied by the acid produced in Equation 17.Thermal Reduction of Iron Ores to FeO Using Sulfur:

[0237] In some embodiments, rather than combusting sulfur in air to produce sulfur dioxide gas in a first furnace and then contacting the sulfur dioxide with iron ore in a separate reactor, the combustion furnace may be configured to include the iron ore inLeydig Ref. 340515: 3-25 WO the sulfur conduction furnace to perform combustion, sulfur dioxide production, and ore reduction in a single reactor.

[0238] Alternatively, instead of (or in addition to) directing air into the sulfur combustion furnace, sulfur may be used to directly reduce iron oxides such as goethite, hematite, magnetite (or others) to ferrous oxide in a sulfur direct ore reduction reactor. An example of such a process is illustrated in FIG. 13, which shows an example sulfur direct reduction process in which the ore is added to a sulfur direct reduction reactor along with sulfur (e.g., in a powder or granular form) and optionally air. The sulfur direct reduction reactor (or furnace) may be heated to a temperature of approximately 400 °C to approximately 800 °C (preferably at least 570 °C in some embodiments) to reduce iron oxides in the ore to ferrous oxide (FeO). FIG. 13 also shows an optional catalytic oxidation reactor for oxidizing residual sulfur dioxide to sulfur trioxide, a dissolution reactor to make sulfuric acid from the residual sulfur trioxide, a leaching reactor to leach the FeO into an acidic leach solution, an impurity removal reactor in which impurities may be removed by any suitable method including by precipitating impurity compounds (e.g., by a pH shift or other methods), and an electro-plating (or “electrowinning”) reactor in which metallic iron may be plated on cathodes while anodically oxidizing water, ferrous iron, or any other oxidizable species. Acid produced in the anolyte of the plating cell may be returned to the leaching reactor.

[0239] It is believed that, in the absence of sufficient gaseous oxygen to support combustion of sulfur, combustion may be driven by reduction of oxides in the ore when the reactor is at sufficient temperature (e.g., 570 °C to 700 °C). For example, direct reduction of hematite to ferrous oxide may proceed according to the equation:Fe2O3(s) + 1 / 3S → 2FeO(s) + 1 / 3SO3(g)(27)

[0240] The sulfur trioxide produced in the above reaction may be used to form sulfuric acid according to Equation 17 above. The ferrous oxide thus produced may be leached to form an iron-rich leach solution, impurities may be removed, and iron may be electroplated according to any of the examples or embodiments described elsewhere herein. The overall reaction for iron extraction by direct reduction of hematite with sulfur may be written as:Fe2O3(s) + 1 / 3S + 1 / 3H2O → 2Fe + 1 / 3H2SO4+ O2(g)(28)Leydig Ref. 340515: 3-25 WO

[0241] Alternatively, in some cases at least some of the sulfur may not be fully oxidized to sulfur trioxide (SO3), but instead may remain as sulfur dioxide (SO2) as shown in the equation:Fe2O3(s) + 1 / 2S → 2FeO(s) + 1 / 2SO2(g)(29)

[0242] In such cases, the sulfur dioxide may be catalytically oxidized to sulfur trioxide according to the equation:SO2(g)+ 1 / 2O2→ SO3(g)(30)

[0243] The sulfur trioxide may then be combined with water to form sulfuric acid according to Equation 17. Nonetheless, the ferrous oxide produced in Equation 29 may be leached to form an iron-rich leach solution, impurities may be removed, and iron may be electroplated according to any of the examples or embodiments described elsewhere herein.

[0244] The overall reaction for iron extraction by direct reduction of hematite with sulfur including catalytic oxidation of sulfur dioxide may be written as:Fe2O3(s) + 1 / 2S + 1 / 4O2+ 1 / 2H2O → 2Fe + 1 / 2H2SO4+ O2(g)(31)Thermal Reduction of Iron Ores to Fe3O4Using Sulfur:

[0245] In some embodiments, sulfur may be used to reduce iron ores containing goethite or hematite to formation of magnetite (Fe3O4) instead of driving thermal reduction all the way to ferrous oxide (FeO). This may be advantageous in the case of ores which prove to be difficult to reduce to FeO, or to reduce the need for tight temperature controls. In some embodiments, ores containing goethite or hematite may be directly reduced with sulfur to form magnetite (Fe3O4) as described herein, and then the magnetite (which is magnetic) may be magnetically separated from non-magnetic impurities such as silica and alumina. In various embodiments, reduction to magnetite may comprise producing a reduced ore material in which at least 90%, 95%, 99%, 99.9%, or more of the iron oxide is reduced to the form of magnetite (Fe3O4).

[0246] FIG. 14 illustrates an example process for extracting iron from ores by thermally reducing the ores to magnetite before leaching. As shown, sulfur may be combusted in a combustion reactor (or furnace) to produce sulfur dioxide that may beLeydig Ref. 340515: 3-25 WO directed to a reductive leaching reactor. The iron ore may be directly reduced with sulfur as described above, but with the objective of substantially stopping reduction at magnetite formation. Reduction may be stopped at magnetite by maintaining the sulfur direct ore reduction reactor at a temperature of preferably more than approximately 570 °C. The magnetite may then optionally be subjected to a magnetic separation step where the magnetic phase (magnetite) material is separated from non-magnetic materials. The magnetite may then be leached in a reductive leaching process such as those described herein above to produce an iron-rich leach solution containing iron in substantially only the ferrous form. Impurities may be removed from the iron rich leach solution to produce a purified iron leach solution. Metallic iron may then be electroplated from the purified iron rich leach solution according to any of the examples or embodiments described herein.

[0247] As in above examples, sulfur trioxide produced as byproducts of sulfur direct reduction of ore and reductive leaching may be combined with water to make a sulfuric acid byproduct.

[0248] Sulfur direct reduction of iron ore to magnetite may proceed according to the equation:33Fe2O3(s) + 1 / 3S → 2Fe3O4(s) + 1 / 3SO3(g)(32)

[0249] An example reaction using a system such as that shown in FIG. 14 may be:Fe3O4(s) + 2H2SO4+ SO2(g)→ 3FeSO4+ 2H2O (33)

[0250] In some cases, during sulfur direct reduction of iron ore, at least some of the sulfur may not be fully oxidized to sulfur trioxide, but may remain as sulfur dioxide. In some embodiments, the remaining sulfur dioxide may be catalytically oxidized to sulfur trioxide as described above.

[0251] Alternatively, as shown in FIG. 15, if the sulfur direct ore reduction predominantly produces sulfur dioxide instead of sulfur trioxide, then the exhaust gases (i.e., predominantly SO2) from the sulfur direct reduction reactor may be directed to the reductive leaching step along with sulfur dioxide produced by air-combustion of sulfur. In this case, less sulfur combustion may be required to produce SO2 for the reductive leaching step.Leydig Ref. 340515: 3-25 WO

[0252] An overall reaction for the example process of FIG. 15 may be written as:3Fe2O3(s) + 1 / 2S + 3 / 2SO2(g)+ 2H2O → 6Fe + 2H2SO4+ 3O2(g)(34)

[0253] In any of the above embodiments, instead of producing sulfur dioxide by aircombustion of sulfur, sulfur dioxide may be regenerated by thermally decomposing sulfuric acid (e.g., by heating it to a temperature above 700°C) to form sulfur dioxide, water, and oxygen, according to the equation:H2SO4→ SO2(g)+ H2O(g)+ 1 / 2O2(g)(35)

[0254] In such embodiments, sulfur dioxide may be regenerated from sulfuric acid formed by combining water with sulfur trioxide (e.g., produced as a byproduct of reductive leaching or sulfur direct reduction of ore). In this way, overall consumption of sulfur and water may be minimized. However, the energy required for the endothermic thermal decomposition of sulfuric acid would need to be supplied from a different source. In various embodiments, the energy for H2SO4 thermal decomposition may be provided as electrical energy, solar energy including solar thermal energy, geothermal energy, or by combustion of fossil fuels, biomass, or other fuels.

[0255] In various embodiments, in addition to combustion of sulfur, sulfur dioxide may also (or alternatively) be produced by various other methods. In one example, sulfur dioxide may be produced via combustion of hydrogen sulfide (H2S) according to:2H2S(g) + 3O2(g) 2SO2(g) + 2H2O(g) + Heat (-518kJ / mol) (36)

[0256] Sulfur dioxide may also be produced or obtained from autogenous smelting or roasting of sulfide base metal minerals such as sphalerite ((Zn, Fe)S), galena (PbS), petlandite ((Ni, Fe)9S8), copper sulfide ores such as chalcopyrite (CuFeS2), bornite (CusFeS4), covellite (CuS), and chalcocite (Cu2S), sulfide minerals of iron such as pyrite (FeS2) and pyrrhotite (FeS), and other pyrite materials or sulphur based compounds such as sulphates that can be decomposed to SO2. Alternatively, sulfur dioxide may be obtained from synthetic materials, waste materials, or other materials containing sulfide compounds such as iron sulfide (FeS), pyrite (FeS2), zinc sulfide (ZnS), lead sulfide (PbS), or others. Example equations may include:2FeS(s) + 7 / 2O2(g) Fe2O3(s) + 2SO2(g) (37) 2FeS2(s) + 11 / 2O2(g) → Fe2O3(s) + 4SO2(g) (38)Leydig Ref. 340515: 3-25 WO ZnS + 3 / 2O2(g) ZnO(s) + SO2(g) (39) PbS + 3 / 2O2(g) → PbO(s) + SO2(g) (40)

[0257] FIG. 16 illustrates an example system configuration that may be used in connection with any of the reduction, leaching, and electrowinning (or electro plating) methods described herein. In the illustrated system, an ore containing hematite may be reduced in a first reduction reactor to form magnetite. In some embodiments, the ore may be transferred to a second reactor in which magnetite is reduced to ferrous oxide. The ferrous oxide (and / or magnetite if desired) may be transferred to one or more leach vessels for acid leaching of the ore. The leach solution may then be transferred to an electrowinning bath in which iron may be electroplated from the leach solution. The system comprises reduction reactors (which may be fluidized bed reactors, rotary kilns, shaft furnace, moving grate furnace, or any other furnace or reactor suitable for contacting a reducing gas with the ore), leach vessels (which may comprise stirred or static tanks or other vessels suitable for acid leaching of solids), and one or more electrowinning baths of any construction suitable for electrowinning (or electro plating) of iron from the leach solution.Certain Aspects and Embodiments:

[0258] Various aspects are contemplated and disclosed herein, a plurality of which is set forth in the paragraphs below. It is explicitly contemplated and disclosed that any aspect or portion thereof can be combined to form an aspect. In addition, it is explicitly contemplated and disclosed that: any reference to Aspect A1 includes reference to Aspects A1a, A1b, A1c, Aid, A1e, A1f, A1g, A1h, A1i, A1j, A1k, and any combination thereof; any reference to Aspect A8 includes reference to Aspects A8a, A8b, A8c, and A8d; and so on (any reference to an aspect includes reference to that aspect’s lettered versions). Moreover, the terms “any preceding aspect” and “any one of the preceding aspects” means any aspect that appears prior to the aspect that contains such phrase (for example, the sentence “Aspect A4: The method or system of any one of the preceding Aspects...” means that any Aspect prior to Aspect A4 is referenced, including letter versions, including aspects A1 a through A3). For example, it is contemplated and disclosed that, optionally, any method, any step, any system, any subsystem, any composition, etc., according to any of the below aspects may be useful with or combined with any other aspect(s) provided below. Further, for example, it is alsoLeydig Ref. 340515: 3-25 WO contemplated and disclosed that any embodiment or aspect described above may, optionally, be combined with any of the below listed aspects.

[0259] Aspect A1a: A method of producing metallic iron from a feedstock (e.g., 102, 202, 302, 702, 802, 901, 902, 1002, 1102, 1401, 1501, or 1701 ) having one or more iron oxides, the method comprising:leaching at least a portion of the one or more iron oxides from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with an aqueous acid; andnon-electrolytically reducing dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of one or more reductants and an aqueous acidic solution at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm; wherein:the dissolved and the non-dissolved ferric are from the one or more iron oxides;the step of non-electrolytically reducing comprises chemically reducing dissolved ferric ions to dissolved ferrous ions, chemically reducing at least a portion of the one or more iron oxides from the feedstock, or a combination thereof;the steps of leaching and non-electrolytically reducing result in formation of a ferrous-rich acidic aqueous solution (e.g., ferrous-rich aqueous solution 112, 212, or 312) having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; wherein the method further comprises:treating (e.g., impurity removal 130, 230, 330, 730, 830, 930, 1030, 1130, 1230, 1330, 1430, 1530, or 1730) the ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution (e.g., treated ferrous-rich aqueous solution 132, 232, or 332); andelectroplating iron from the treated ferrous-rich solution in an iron electroplating cell (e.g., iron electroplating cell 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740).

[0260] Aspect A1 b: A method of producing metallic iron from a feedstock (e.g., 102, 202, 302, 702, 802, 901, 902, 1002, 1102, 1401, 1501, or 1701 ) having solid ferric, the method comprising:Leydig Ref. 340515: 3-25 WO leaching at least a portion of the solid ferric from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with an aqueous acid; andnon-electrolytically reducing dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of one or more reductants and an aqueous acidic solution at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm; wherein:the dissolved and the non-dissolved ferric are from the solid ferric of the feedstock; the step of non-electrolytically reducing comprises chemically reducing dissolved ferric ions to dissolved ferrous ions, chemically reducing at least a portion of the solid ferric from the feedstock, or a combination thereof;the steps of leaching and non-electrolytically reducing result in formation of a ferrous-rich acidic aqueous solution (e.g., ferrous-rich aqueous solution 112, 212, or 312) having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; wherein the method further comprises:treating (e.g., impurity removal 130, 230, 330, 730, 830, 930, 1030, 1130, 1230, 1330, 1430, 1530, or 1730) the ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution (e.g., treated ferrous-rich aqueous solution 132, 232, or 332); andelectroplating iron from the treated ferrous-rich solution in an iron electroplating cell (e.g., iron electroplating cell 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740).

[0261] Aspect A1c: A system for producing metallic iron from a feedstock (e.g., 102, 202, 302, 702, 802, 901, 902, 1002, 1102, 1401, 1501, or 1701 ) having one or more iron oxides, the system comprising:a leach tank (e.g., 310 or 910) and a ferric reduction reactor (e.g., 320, 500, or 920); or a reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710);wherein:Leydig Ref. 340515: 3-25 WO the leach tank is configured to leach at least a portion of the one or more iron oxides from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with an aqueous acid;the ferric reduction reactor is configured to non-electrolytically reduce dissolved ferric ions to dissolved ferrous ions in the presence of one or more reductants (e.g., 104, 204, or 304) and an aqueous acidic solution at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm, thereby producing a ferrous-rich aqueous acidic solution (e.g, 312);the reductive leach reactor is configured to (a) leach at least a portion of the one or more iron oxides from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with the aqueous acid and (optionally concurrently) (b) non-electrolytically reduce dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants, the one or more iron oxides, and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm, thereby producing the ferrous-rich aqueous acidic solution (e.g., 112 or 212); andthe dissolved and the non-dissolved ferric are from the one or more iron oxides; and wherein the system further comprises:an impurity removal subsystem (e.g., 130, 230, 330, 730, 830, 930, 1030, 1130, 1230, 1330, 1430, 1530, or 1730) to remove at least a portion of non-iron impurities from the produced ferrous-rich aqueous acidic solution, thereby forming a treated ferrous-rich solution; andan iron electroplating cell (e.g., 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740) configured to electroplate iron metal at a plating cathode by electrochemically reducing aqueous ferrous ions.

[0262] Aspect Aid: A system for producing metallic iron from a feedstock (e.g., 102, 202, 302, 702, 802, 901, 902, 1002, 1102, 1401, 1501, or 1701 ) having solid ferric, the system comprising:a leach tank (e.g., 310 or 910) and a ferric reduction reactor (e.g., 320, 500, or 920); orLeydig Ref. 340515: 3-25 WO a reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710);wherein:the leach tank is configured to leach at least a portion of the solid ferric from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with an aqueous acid;the ferric reduction reactor is configured to non-electrolytically reduce dissolved ferric ions to dissolved ferrous ions in the presence of one or more reductants (e.g., 104, 204, or 304) and an aqueous acidic solution at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm, thereby producing a ferrous-rich aqueous acidic solution (e.g, 312);the reductive leach reactor is configured to (a) leach at least a portion of the solid ferric from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with the aqueous acid and (optionally concurrently) (b) non-electrolytically reduce dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants, the solid ferric, and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm, thereby producing the ferrous-rich aqueous acidic solution (e.g., 112 or 212); andthe dissolved and the non-dissolved ferric are from the solid ferric of the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702);and wherein the system further comprises:an impurity removal subsystem (e.g., 130, 230, 330, 730, 830, 930, 1030, 1130, 1230, 1330, 1430, 1530, or 1730) to remove at least a portion of non-iron impurities from the produced ferrous-rich aqueous acidic solution, thereby forming a treated ferrous-rich solution; andan iron electroplating cell (e.g., 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740) configured to electroplate iron metal at a plating cathode by electrochemically reducing aqueous ferrous ions.

[0263] Aspect A1e: A method of producing metallic iron, the method comprising:Leydig Ref. 340515: 3-25 WO providing an iron source material in the presence of an aqueous acid and one or more reductants;wherein the iron source material comprises one or more iron oxides comprising solid ferric;non-electrolytically reducing dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm;treating the ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution; and electroplating iron from the treated ferrous-rich solution in an iron electroplating cellwherein:the dissolved and the non-dissolved ferric are from the solid ferric of the one or more iron oxides;the step of non-electrolytically reducing results in formation of a ferrous- rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; and the step of treating comprises raising a pH of the ferrous-rich acidic aqueous solution.

[0264] Aspect A1f: A system for producing metallic, the system comprising:a reductive leach reactor configured to provide an iron source material in the presence of an aqueous acid and one or more reductants, wherein the iron source material comprises one or more iron oxides comprising solid ferric; wherein the reductive leach reactor is further configured to non-electrolytically reduce dissolved ferric, nondissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm and thereby produce ferrous-rich aqueous acidic solution; wherein the dissolved and the non-dissolved ferric are from the one or more iron oxides;an impurity removal subsystem to remove at least a portion of non-iron impurities from the produced ferrous-rich aqueous acidic solution and thereby form a treated ferrous-rich solution; andLeydig Ref. 340515: 3-25 WO an iron electroplating cell configured to electroplate iron metal at a plating cathode by electrochemically reducing aqueous ferrous ions.

[0265] Aspect A1 g: The system of Aspect A1f, wherein the reductive leach reactor is configured to both leach at least a portion of the one or more iron oxides and non-electrolytically reduce dissolved ferric, non-dissolved ferric, or a combination thereof.

[0266] Aspect A1 h: A system for producing metallic, the system comprising:a leach tank configured to leach at least a portion of one or more iron oxides from an iron source material and produce a first acidic leachate;a ferric reduction reactor configured to provide an iron source material in the presence of the first acidic leachate and one or more reductants to non- electrolytically reduce dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm and thereby produce ferrous-rich aqueous acidic solution; wherein the dissolved and the non-dissolved ferric are from the one or more iron oxides;an impurity removal subsystem to remove at least a portion of non-iron impurities from the produced ferrous-rich aqueous acidic solution and thereby form a treated ferrous-rich solution; andan iron electroplating cell configured to electroplate iron metal at a plating cathode by electrochemically reducing aqueous ferrous ions.

[0267] Aspect A1 i: The system of Aspect A1f, A1g, or A1 h, wherein the impurity removal subsystem is configured to provide one or more iron oxide materials in contact with the produced ferrous-rich aqueous acidic solution.

[0268] Aspect A1j: The system of Aspect A1f, A1g, or A1h, wherein the impurity removal subsystem is configured to provide one or more iron oxide materials and one or more iron-based metals in contact with the produced ferrous-rich aqueous acidic solution.

[0269] Aspect A1 k: A method of producing metallic iron, the method comprising:providing an iron source material in the presence of an aqueous acid and one or more reductants;Leydig Ref. 340515: 3-25 WO wherein the iron source material comprises one or more iron oxides comprising solid ferric;reductively leaching the one or more iron oxides, the step of reductively leaching comprising non-electrolytically reducing dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm;treating the ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution; and electroplating iron from the treated ferrous-rich solution in an iron electroplating cellwherein:the dissolved and the non-dissolved ferric are from the solid ferric of the one or more iron oxides;the step of non-electrolytically reducing results in formation of a ferrous- rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; and the step of treating comprises raising a pH of the ferrous-rich acidic aqueous solution.

[0270] Aspect A2: The method or system of Aspect A1, wherein the steps of leaching and non-electrolytically reducing are performed concurrently and in the presence of each other in a first acidic leachate.

[0271] Aspect A3: The method or system of Aspect 1 or 2, wherein the steps of leaching and non-electrolytically reducing are performed in the same vessel (e.g., reductive leach reactor 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710).

[0272] Aspect A4: The method or system of any one of the preceding Aspects, wherein the step of reducing comprises chemically reducing aqueous ferric ions to ferrous ions in the first acidic leachate in the presence of the one or more reductants (e.g., one or more reductants 104, 204, or 304).

[0273] Aspect A5a: The method or system of any one of the preceding Aspects, wherein the step of reducing comprises chemically reducing at least a portion of the one or more solid iron oxides from the feedstock in the first acidic leachate. Aspect A5b: TheLeydig Ref. 340515: 3-25 WO method or system of any one of the preceding Aspects, wherein the step of reducing comprises chemically reducing at least a portion of the solid ferric from the feedstock in the first acidic leachate.

[0274] Aspect A6a: The method or system of any one of the preceding Aspects, wherein the step of non-electrolytically reducing comprises reducing ferric in the one or more oxides to ferrous. Aspect A6b: The method or system of any one of the preceding Aspects, wherein the step of non-electrolytically reducing comprises reducing the solid ferric to solid ferrous.

[0275] Aspect A7a: The method or system of any one of the preceding Aspects, wherein the one or more iron oxides comprises hematite and / or goethite and wherein the step of reducing comprises reducing the hematite and / or goethite to magnetite, wüstite, iron metal, or a combination thereof in the first acidic leachate. Aspect A7b: The method or system of any one of the preceding Aspects, wherein the step of reducing comprises reducing solid ferric to solid ferrous in the first acidic leachate.

[0276] Aspect A8: The method or system of any one of the preceding Aspects, wherein the step of reducing comprises reducing dissolved ferric ions to dissolved ferrous ions in the presence of a slurry comprising solid iron oxide particles, the first acid leachate having the dissolved ferric ions, and the one or more reductants.

[0277] Aspect A9: The method or system of Aspect A1 (i.e., any of A1a-A1d), wherein the step of leaching is performed separately from the step of chemically reducing.

[0278] Aspect A10: The method or system of Aspect A9, wherein the steps of leaching and chemically reducing are performed in different vessels (e.g., leach tank 310 or 910 and ferric reduction reactor 320, 500, or 920, respectively).

[0279] Aspect A11: The method or system of Aspect 9 or 10, wherein the step of leaching (e.g., in leach tank 310 or 910) forms a first aqueous leachate (e.g., 311) comprising dissolved ferric ions which are chemically reduced to dissolved ferrous ions in the step of non-electrolytically reducing (e.g., in ferric reduction reactor 320, 500, or 920) thereby forming the ferrous-rich acidic solution (e.g., 312).

[0280] Aspect A12a: The method or system of any one of Aspects 9-11, wherein the step of non-electrolytically reducing comprises chemically reducing aqueous ferric ionsLeydig Ref. 340515: 3-25 WO to aqueous ferrous ions in the absence of the one or more iron oxides. Aspect A12b: The method or system of any one of Aspects 9-11, wherein the step of non-electrolytically reducing comprises chemically reducing aqueous ferric ions to aqueous ferrous ions in the absence of the solid ferric.

[0281] Aspect A13: The method or system of any one of Aspects 9-12, wherein the step of leaching comprises forming a first aqueous leachate and undissolved solids, separating the undissolved solids and at least a portion of the first aqueous leachate, and providing at least a portion of the separated first aqueous leachate to the separate step of non-electrolytically reducing.

[0282] Aspect A14: The method or system of any one of the preceding Aspects, wherein the step of non-electrolytically reducing is performed in the further presence of a catalyst.

[0283] Aspect A15: The method or system of Aspect 14, wherein the catalyst is provided on an electrically conductive substrate.

[0284] Aspect A16: The method or system of any one of Aspects 14-15, wherein the catalyst is provided on and / or in particles, one or more meshes, one or more sheets, one or more foams, or a combination thereof.

[0285] Aspect A17: The method or system of any one of Aspects 14-16, wherein the catalyst is provided on carbon particles, conductive polymer particles, non-conductive polymer particles, ion exchange resin particles, ceramic particles, or any combination thereof.

[0286] Aspect A18: The method or system of any one of Aspects 14-17, wherein the catalyst is a hydrogen oxidation catalyst and the one or more reductants comprises H₂ gas.

[0287] Aspect A19: The method or system any one of Aspects 14-18, wherein the catalyst comprises one or more platinum-group metals, nickel, chromium, tungsten, molybdenum, copper, carbon materials, doped carbon materials, one or more alloys thereof, or any combination thereof.

[0288] Aspect A20: The method or system of any one of Aspects 14-19, wherein the step of reducing is performed in further presence of a conductivity enhancer.Leydig Ref. 340515: 3-25 WO

[0289] Aspect A21: The method or system of Aspect 20, wherein the conductivity enhancer is one or more allotropes of carbon.

[0290] Aspect A22: The method or system of any one of the preceding Aspects being free of electrochemical reduction of ferric to ferrous between the steps of non-electrolytically reducing and treating.

[0291] Aspect A23: The method or system of any one of the preceding Aspects, wherein the one or more reductants is one or more solid reductants, one or more gaseous reductants, one or more dissolved aqueous reductants, or a combination thereof.

[0292] Aspect A24: The method or system of any one of the preceding Aspects, wherein the one or more reductants comprises H₂ gas, H₂S gas, SO₂ gas, CO gas, methane gas, solid sulfur, an iron-based metal, an iron metal of at least 99 at.% purity, one or more pyrite materials, one or more metal sulfide materials, copper metal, a copper oxide, a copper salt, tin metal, a tin oxide, a tin salt, titanium metal, a titanium oxide, a titanium salt, vanadium metal, a vanadium oxide, a vanadium salt, an inorganic redox mediator, an organic redox mediator, a plurality thereof, or any combination thereof.

[0293] Aspect A25: The method or system of any one of the preceding Aspects, wherein the one or more reductants comprises H₂ gas and the method comprises producing the H₂ gas by reacting metallic iron with an acid, by a water electrolyzer, or a combination thereof.

[0294] Aspect A26: The method or system of any one of the preceding Aspects, wherein the one or more reductants comprises SO₂ gas and the method comprises producing the SO₂ gas by combusting solid sulfur in the presence of oxygen.

[0295] Aspect A27: The method or system of any one of the preceding Aspects, wherein the one or more reductants comprises H₂S gas and the method comprises producing the H₂S gas by reacting hydrogen gas and sulfur.

[0296] Aspect A28: The method or system of any one of the preceding Aspects, wherein the one or more reductants comprises metallic iron and the method comprises producing the metallic iron electrochemically, the step of producing the metallic ironLeydig Ref. 340515: 3-25 WO electrochemically being separate from the step of electroplating iron (e.g., in Fe powder cell 245 or 345).

[0297] Aspect A29: The method or system of any one of the preceding Aspects, wherein the step of non-electrolytically reducing comprises providing one or more solid reductants which dissolve in the acidic solution to form aqueous reducing reactants for reducing aqueous ferric ions.

[0298] Aspect A30: The method or system of any one of the preceding Aspects, wherein the one or more reductants comprises one or more gaseous reductants, and wherein the gas atmosphere in the step of non-electrolytically reducing is 0.5 vol.% to 100 vol.% the one or more gaseous reductants.

[0299] Aspect A31: The method or system of any one of the preceding Aspects, wherein the one or more reductants comprises one or more solid reductants provided to the step of non-electrolytically reducing according to a molar ratio of reductant to ferric being at least 1.

[0300] Aspect A32a: The method or system of any one of the preceding Aspects further comprising thermally reducing (e.g., Feed Pre Treatment 215 or Thermal Pre Treatment 315) the one or more iron oxides of the feedstock at a temperature greater than 120 °C and in the presence of a gaseous thermal reductant, thereby forming a thermally reduced feedstock; wherein the step of leaching is performed on the thermally reduced feedstock. Aspect A32b: The method or system of any one of the preceding Aspects further comprising thermally reducing (e.g., Feed Pre Treatment 215 or Thermal Pre Treatment 315) the solid ferric of the feedstock at a temperature greater than 120 °C and in the presence of a gaseous thermal reductant, thereby forming a thermally reduced feedstock; wherein the step of leaching is performed on the thermally reduced feedstock.

[0301] Aspect A33: The method or system of Aspect 32, wherein the step of non-electrolytically reducing is performed in the presence of the thermally reduced feedstock.

[0302] Aspect A34: The method or system of Aspect 32 or 33, wherein the step of thermally reducing comprises reducing hematite and / or goethite to magnetite.Leydig Ref. 340515: 3-25 WO

[0303] Aspect A35: The method or system of any one of the preceding Aspects further comprising air roasting the feedstock, wherein the step of leaching is performed on the air roasted feedstock.

[0304] Aspect A36: The method or system of Aspect 35, wherein the step of non-electrolytically reducing is performed in the presence of the air roasted feedstock.

[0305] Aspect A37: The method or system of any one of the preceding Aspects, wherein the step of electroplating comprises reducing aqueous ferrous ions to metallic iron at a plating cathode in the presence of a catholyte of the electroplating cell (e.g., iron electroplating cell 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740).

[0306] Aspect A38: The method or system of any one of the preceding Aspects, wherein the step of electroplating further comprises oxidizing aqueous ferrous ions to ferric ions at an anode in the presence of an anolyte of the electroplating cell (e.g., iron electroplating cell 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740).

[0307] Aspect A39: The method or system of any one of Aspects 1 -37, wherein the step of electroplating further comprises oxidizing water and evolving oxygen gas at an anode in the presence of an anolyte of the electroplating cell (e.g., iron electroplating cell 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740).

[0308] Aspect A40: The method or system of any one of the preceding Aspects, wherein the step of treating (e.g., impurity removal 130, 230, 330, 730, 830, 930, 1030, 1130, 1230, 1330, 1430, 1530, or 1730) comprises increasing a pH of the ferrous-rich acidic aqueous solution from initial pH thereby precipitating the one or more impurities from the solution.

[0309] Aspect A41: The method or system of any one of the preceding Aspects, wherein an electrolyte from the electroplating cell (e.g., 144, 244, or 344) is provided directly or indirectly to the step of leaching, the step of non-electrolytically reducing, or both.

[0310] Aspect A42: The method or system of any one of the preceding Aspects, wherein an anolyte, a catholyte, or a combination thereof (e.g., 144, 244, or 344) from the electroplating cell is provided to a vessel in which the step of leaching (e.g., leachLeydig Ref. 340515: 3-25 WO tank 310 or 910), the step of non-electrolytically reducing (e.g., ferric reduction reactor 320, 500, or 920), or both (e.g., reductive leach reactor 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710) are being performed.

[0311] Aspect A43: The method or system of any one of the preceding Aspects, wherein an anolyte, a catholyte, or a combination thereof (e.g., 144, 244, or 344) from the electroplating cell is provided to a catholyte of an electrochemical acid regenerator for electrochemically reducing dissolved ferric ions to dissolved ferrous ions.

[0312] Aspect A44: The method or system of any one of the preceding Aspects, wherein a portion of the catholyte (e.g., 252) of the electrochemical acid regenerator (e.g., 250) is provided to a vessel in which the step of leaching (e.g., leach tank 310 or 910), the step of non-electrolytically reducing (e.g., ferric reduction reactor 320, 500, or 920), or both (e.g., reductive leach reactor 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710) are being performed.

[0313] Aspect A45: The method or system of any one of the preceding Aspects, wherein a vessel in which the step of leaching (e.g., leach tank 310or 910), the step of non-electrolytically reducing (e.g., ferric reduction reactor 320, 500, or 920), or both (e.g., reductive leach reactor 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710) are being performed is not connected to an external electrical circuit capable of driving an electrochemical reaction.

[0314] Aspect A46: The method or system of any one of the preceding Aspects, wherein the ferrous-rich aqueous acidic solution is characterized by a ratio of ferrous ion concentration to total iron ion concentration greater than or equal to 0.80.

[0315] Aspect A47: The method or system of any one of the preceding Aspects, wherein the ferrous-rich aqueous acidic solution has a concentration of dissolved ferric ions less than or equal to 3 mM.

[0316] Aspect A48: The method or system of any one of the preceding Aspects, wherein the aqueous acid comprises H₂SO₄.

[0317] Aspect A49: A system for producing metallic iron from a feedstock (e.g., 102, 202, 302, 702, 802, 901, 902, 1002, 1102, 1401, 1501, or 1701 ) having one or more iron oxides (or solid ferric), the system comprising:a leach tank (e.g., 310 or 910) and a ferric reduction reactor (e.g., 320, 500, or 920); orLeydig Ref. 340515: 3-25 WO a reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710);wherein:the leach tank is configured to leach at least a portion of the one or more iron oxides (or solid ferric) from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with an aqueous acid;the ferric reduction reactor is configured to non-electrolytically reduce dissolved ferric ions to dissolved ferrous ions in the presence of one or more reductants (e.g., 104, 204, or 304) and an aqueous acidic solution at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm, thereby producing a ferrous-rich aqueous acidic solution (e.g, 312);the reductive leach reactor is configured to (a) leach at least a portion of the one or more iron oxides (or solid ferric)from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with the aqueous acid and (optionally concurrently) (b) non-electrolytically reduce dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants, the one or more iron oxides(or solid ferric), and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm, thereby producing the ferrous-rich aqueous acidic solution (e.g., 112 or 212); andthe dissolved and the non-dissolved ferric are from the one or more iron oxides (or solid ferric);and wherein the system further comprises:an impurity removal subsystem (e.g., 130, 230, 330, 730, 830, 930, 1030, 1130, 1230, 1330, 1430, 1530, or 1730) to remove at least a portion of non-iron impurities from the produced ferrous-rich aqueous acidic solution, thereby forming a treated ferrous-rich solution; andan iron electroplating cell (e.g., 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740) configured to electroplate iron metal at a plating cathode by electrochemically reducing aqueous ferrous ions.Leydig Ref. 340515: 3-25 WO

[0318] Aspect A50: The system of Aspect 49 comprising the reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710).

[0319] Aspect A51 a: The system of Aspect 50, wherein the reductive leach reactor is configured to concurrently (a) leach at least a portion of the one or more iron oxides from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with the aqueous acid and (b) non-electrolytically reduce dissolved ferric, nondissolved ferric, or a combination thereof. Aspect A51b: The system of Aspect 50, wherein the reductive leach reactor is configured to concurrently (a) leach at least a portion of the solid ferric from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with the aqueous acid and (b) non-electrolytically reduce dissolved ferric, non-dissolved ferric, or a combination thereof.

[0320] Aspect A52: The system of any one of Aspects 49-51, wherein the reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710) is configured to non-electrolytically reduce dissolved ferric ions to dissolved ferrous ions.

[0321] Aspect A53: The system of any one of Aspects 49-52, wherein the reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710) is configured to non-electrolytically reduce dissolved ferric ions to dissolved ferrous ions and non-electrolytically reduce non-dissolved ferric; wherein the non-dissolved ferric is in the form of one or more iron oxides.

[0322] Aspect A54: The system of Aspect 49 comprising the leach tank (e.g., 310 or 910) and the ferric reduction reactor (e.g., 320, 500, or 920).

[0323] Aspect A55: The system of Aspect 54, wherein the leach tank (e.g., 310 or 910) and the ferric reduction reactor (e.g., 320, 500, or 920) are separate vessels; wherein the leach tank produces a first aqueous leachate (e.g., 311) which is then provided to the ferric reduction reactor for non-electrolytic reduction of ferric ions dissolved in the first aqueous leachate to dissolved ferrous ions, thereby producing the ferrous-rich acidic solution (e.g., 312).

[0324] Aspect A56: The system of Aspect 54, wherein the first aqueous leachate (e.g., 311) is free of suspended solid particulates.Leydig Ref. 340515: 3-25 WO

[0325] Aspect A57: The system of any one of Aspects 49-56, wherein the produced ferrous-rich aqueous solution (e.g., 112, 212, or 312) is free of suspended solid particulates.

[0326] Aspect A58: The system of any one of Aspects 49-57, wherein the ferrous-rich acidic solution (e.g., 112, 212, or 312) is provided to the impurity removal subsystem (e.g., 120, 130, or 330).

[0327] Aspect A59: The system of any one of Aspects 49-58, wherein the treated ferrous-rich aqueous solution (e.g., 132, 232, or 332) is free of suspended solid particulates.

[0328] Aspect A60: The system of any one of Aspects 49-59 wherein the treated ferrous-rich aqueous solution (e.g., 132, 232, or 332) is provided to the plating catholyte or cathodic chamber of the iron electroplating cell (e.g., 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740).

[0329] Aspect A61: The system of any one of Aspects 49-60, wherein the iron electroplating cell (e.g., 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740) comprises a plating catholyte in the presence of a plating cathode configured to electrolytically reduce dissolved ferrous ions to metal iron at the plating cathode.

[0330] Aspect A62: The system of any one of Aspects 49-61, wherein the iron electroplating cell (e.g., 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740) comprises a separator separating the plating catholyte from a plating anolyte; wherein the separator is a proton exchange membrane (PEM), an anion exchange membrane (AEM), a microporous separator, a diaphragm, or a combination thereof.

[0331] Aspect A63: The system of any one of Aspects 49-62, wherein the separator is a proton exchange membrane (PEM) or an anion exchange membrane (AEM).

[0332] Aspect A64: The system of any one of Aspects 49-62, wherein the separator is a microporous separator, a diaphragm, or a combination thereof.

[0333] Aspect A65: The system of any one of Aspects 49-62 or 64, wherein the iron electroplating cell (e.g., 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740) is a cathode-to-anode flow cell.Leydig Ref. 340515: 3-25 WO

[0334] Aspect A66: The system of any one of Aspects 49-63, wherein the iron electroplating cell (e.g., 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740) is not a cathode-to-anode flow cell.

[0335] Aspect A67: The system of any one of Aspects 49-66 further comprising an acid regenerator cell (e.g., 250) configured to electrolytically reduce dissolved ferric ions to dissolved ferrous ions.

[0336] Aspect A68: The system of any one of Aspects 49-67, wherein the iron electroplating cell (e.g., 140, 240, 340, 740, 840, 940, 1040, 1140, 1240, 1340, 1440, 1540, or 1740) comprises a plating anolyte in the presence of a plating anode configured to electrolytically oxidize dissolved ferrous ions to dissolved ferric ions.

[0337] Aspect A69: The system of any one of Aspects 49-68, wherein the system comprises the leach tank (e.g., 310 or 910) and the ferric reduction reactor (e.g., 320, 500, or 920); wherein at least a portion of the plating anolyte, having electrolytically-generated dissolved ferric ions, is provided (e.g., as 344) to the ferric reduction reactor; and wherein at least a portion of the electrolytically-generated dissolved ferric ions are non-electrolytically reduced to dissolved ferrous ions in the ferric reduction reactor.

[0338] Aspect A70: The system of any one of Aspects 49-68, wherein the system comprises the reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710); wherein at least a portion of the plating anolyte, having electrolytically-generated dissolved ferric ions, is provided (e.g., as 144 or 244) to the reductive leach reactor; and wherein at least a portion of the electrolytically-generated dissolved ferric ions are non-electrolytically reduced to dissolved ferrous ions in the reductive leach reactor.

[0339] Aspect A70: The system of any one of Aspects 49-70 further comprising an acid regenerator cell (e.g., 250); wherein at least a portion of the plating anolyte, having electrolytically-generated dissolved ferric ions, is provided (e.g., as 144 or 244) to the acid regenerator cell (e.g., 250); and wherein at least a portion of the electrolytically-generated dissolved ferric ions are electrolytically reduced to dissolved ferrous ions at a cathode of the acid regenerator cell.Leydig Ref. 340515: 3-25 WO

[0340] Aspect A72: The system of any one of Aspects 49-70 being free of an acid regenerator cell configured to electrolytically reduce dissolved ferric ions to dissolved ferrous ions.

[0341] Aspect A73: The system of any one of Aspects 49-67, wherein the iron electroplating cell comprises a plating anolyte in the presence of a plating anode configured to electrolytically oxidize water and evolve oxygen gas.

[0342] Aspect A74: The system of any one of Aspects 49-73 further comprising a thermal pre-treatment subsystem (e.g., 215 or 315) configured to thermally reduce, air roast, or a combination thereof the feedstock; wherein the leach tank (e.g., 310 or 910) or the reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710), whichever is present, receives the pre-treated feedstock.

[0343] Aspect A75: The system of Aspect 74, wherein the thermal pre-treatment subsystem (e.g., 215 or 315) is configured to thermally reduce at least a portion of solid ferric in the feedstock to solid ferrous.

[0344] Aspect A76a: A method of producing metallic iron from a feedstock having one or more iron oxides, the method comprising:non-electrolytically reducing (e.g., in reactor 1315, 1415, or 1515) at least a portion of the one or more iron oxides from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) by contacting the one or more iron oxides with sulfur at a temperature selected from the range of 100 °C to 500 °C in the absence of an aqueous solution, thereby producing a reduced feedstock;leaching (e.g., in leach tank 1310, 1410, or 1510) at least a portion of the reduced feedstock with an aqueous acid to form a ferrous-rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions;treating (e.g., in impurity removal subsystem 1330, 1430, or 1530) the ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution; andelectroplating iron (e.g., in cell 1340, 1440, or 1540) from the treated ferrous-rich solution in an iron electroplating cell.Leydig Ref. 340515: 3-25 WO

[0345] Aspect A76b: A method of producing metallic iron from a feedstock having solid ferric, the method comprising:non-electrolytically reducing at least a portion of the solid ferric from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) by contacting the solid ferric with sulfur at a temperature selected from the range of 100 °C to 500 °C in the absence of an aqueous solution, thereby producing a reduced feedstock; leaching (e.g., in leach tank 1310, 1410, or 1510) at least a portion of the reduced feedstock with an aqueous acid to form a ferrous-rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions;treating (e.g., in impurity removal subsystem 1330, 1430, or 1530) the ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution; andelectroplating iron (e.g., in cell 1340, 1440, or 1540) from the treated ferrous-rich solution in an iron electroplating cell.

[0346] Aspect A76c: A system for producing metallic iron from a feedstock having one or more iron oxides (or solid ferric), the method comprising:a reactor (e.g., 1315, 1415, or 1515) configured to contact the one or more iron oxides (or solid ferric) of the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with sulfur at a temperature selected from the range of 100 °C to 500 °C in the absence of an aqueous solution to non-electrolytically reduce at least a portion of the one or more iron oxides (or solid ferric) from the feedstock(e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702), thereby producing a reduced feedstock;a leach tank (e.g., 1310, 1410, or 1510) configured to leach at least a portion of the reduced feedstock with an aqueous acid to form a ferrous-rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; an impurity removal subsystem (e.g., 1330, 1430, or 1530) configured to remove at least a portion of non-iron impurities from the ferrous-rich acidic aqueous solution, thereby forming a treated ferrous-rich solution; andLeydig Ref. 340515: 3-25 WO an iron electroplating cell (e.g., 1340, 1440, or 1540) configured to electroplate iron from the treated ferrous-rich solution at a plating cathode.

[0347] Aspect A77: The method or system of Aspect 76 wherein the step of non-electrolytically reducing is performed in the further presence of one or more gaseous reductants.

[0348] Aspect A78: The method or system of Aspect 76 or 77, wherein the one or more gaseous reductants comprises H₂ gas, H₂S gas, SO₂ gas, CO gas, methane gas, or a combination thereof.

[0349] Aspect A79a: The method or system of any one of Aspects 76-78, wherein the step of non-electrolytically reducing comprises reducing ferric in the one or more oxides to ferrous. Aspect A79b: The method or system of any one of Aspects 76-78, wherein the step of non-electrolytically reducing comprises reducing ferric in the solid ferric to ferrous.

[0350] Aspect A80: The method or system of any one of Aspects 76-79, wherein the step of non-electrolytically reducing comprises reducing hematite and / or goethite to magnetite, wüstite, iron metal, or a combination thereof.

[0351] Aspect A81: A system for producing metallic iron from a feedstock having one or more iron oxides (or solid ferric), the method comprising:a reactor (e.g., 1315, 1415, or 1515) configured to contact the one or more iron oxides (or solid ferric) of the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with sulfur at a temperature selected from the range of 100 °C to 500 °C in the absence of an aqueous solution to non-electrolytically reduce at least a portion of the one or more iron oxides (or solid ferric) from the feedstock(e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702), thereby producing a reduced feedstock;a leach tank (e.g., 1310, 1410, or 1510) configured to leach at least a portion of the reduced feedstock with an aqueous acid to form a ferrous-rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; an impurity removal subsystem (e.g., 1330, 1430, or 1530) configured to remove at least a portion of non-iron impurities from the ferrous-rich acidic aqueous solution, thereby forming a treated ferrous-rich solution; andLeydig Ref. 340515: 3-25 WO an iron electroplating cell (e.g., 1340, 1440, or 1540) configured to electroplate iron from the treated ferrous-rich solution at a plating cathode.

[0352] Aspect A82a: A method of producing metallic iron from a feedstock having one or more iron oxides (or solid ferric), the method comprising:reductively leaching (e.g., in reactor 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710) at least a portion of the one or more iron oxides (or solid ferric) from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) by providing a slurry having particles of the one or more iron oxides (or solid ferric), an aqueous acid, and a conductivity enhancer in the presence of a hydrogen oxidation catalyst and a hydrogen gas thereby forming a ferrous-rich aqueous acidic solution; wherein the step of reductively leaching comprises:dissolving iron oxide in the aqueous acid to form dissolved ferric ions; andproviding the hydrogen gas in contact with both the catalyst and the slurry thereby reducing the dissolved ferric ions to dissolved ferrous ions; andwherein the ferrous-rich acidic aqueous solution has a greater concentration of dissolved ferrous ions than of dissolved ferric ions.

[0353] Aspect A82b: A system for producing metallic iron from a feedstock having one or more iron oxides (or solid ferric), the method comprising:a reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710) configured to reductively leach at least a portion of the one or more iron oxides (or solid ferric) from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702); wherein the reductive leach reactor comprises a slurry having particles of the one or more iron oxides (or solid ferric), an aqueous acid, and a conductivity enhancer in the presence of a hydrogen oxidation catalyst and a hydrogen gas thereby forming a ferrous-rich aqueous acidic solution;wherein:at least a portion of the one or more iron oxides (or solid ferric) is dissolved in the aqueous acid to form dissolved ferric ions; andthe hydrogen gas is in contact with both the catalyst and the slurry to facilitate reduction of the dissolved ferric ions to dissolved ferrous ions; andLeydig Ref. 340515: 3-25 WO the ferrous-rich acidic aqueous solution has a greater concentration of dissolved ferrous ions than of dissolved ferric ions.

[0354] Aspect A83: The method or system of Aspect 82, wherein the hydrogen oxidation catalyst is provided on an electrically conductive substrate in contact with the slurry.

[0355] Aspect A84: The method or system of Aspect 82 or 83, wherein chemical reduction of dissolved ferric ions to dissolved ferrous ions occurs at a three-phase interface of hydrogen gas, catalyst, and the aqueous acid having dissolved ferric ions.

[0356] Aspect A85: The method or system of any one of Aspects 82-84 further comprising treating the ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution.

[0357] Aspect A86: The method or system of any one of Aspects 82-85 further comprising electroplating iron from the treated ferrous-rich solution in an iron electroplating cell.

[0358] Aspect A87: The method or system of any one of Aspects 82-86, wherein the step of reductively leaching is non-electrolytic.

[0359] Aspect A88: The method or system of any one of Aspects 82-87, wherein the step of reductively leaching is performed at a liquid temperature of less than 120 °C and under a gas pressure less than 2 atm.

[0360] Aspect A89: The method or system of any one of Aspects 82-88, wherein the conductivity enhancer comprises solid particles of an electrically conductive material.

[0361] Aspect A90: The method or system of any one of Aspects 82-89, wherein the conductivity enhancer comprises a conductive metal or metal oxide that is insoluble or sparingly soluble in the aqueous acid.

[0362] Aspect A91: The method or system of any one of Aspects 82-90, wherein the conductivity enhancer comprises carbon or graphite particles.

[0363] Aspect A92: The method or system of any one of Aspects 82-91, wherein the conductivity enhancer comprises a redox mediator.

[0364] Aspect A93: The method or system of Aspect 92, wherein the redox mediator is ascorbic acid.Leydig Ref. 340515: 3-25 WO

[0365] Aspect A94: A system for producing metallic iron from a feedstock having one or more iron oxides (or solid ferric), the method comprising:a reductive leach reactor (e.g., 110, 210, 550, 710, 810, 1010, 1110, 1410, 1510, or 1710) configured to reductively leach at least a portion of the one or more iron oxides (or solid ferric) from the feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702); wherein the reductive leach reactor comprises a slurry having particles of the one or more iron oxides (or solid ferric), an aqueous acid, and a conductivity enhancer in the presence of a hydrogen oxidation catalyst and a hydrogen gas thereby forming a ferrous-rich aqueous acidic solution;wherein:at least a portion of the one or more iron oxides (or solid ferric) is dissolved in the aqueous acid to form dissolved ferric ions; andthe hydrogen gas is in contact with both the catalyst and the slurry to facilitate reduction of the dissolved ferric ions to dissolved ferrous ions; andthe ferrous-rich acidic aqueous solution has a greater concentration of dissolved ferrous ions than of dissolved ferric ions.

[0366] Aspect A95: A method of producing metallic iron from a feedstock having one or more iron oxides (or solid ferric), the method comprising:thermally reducing at least a portion of solid ferric in the feedstock to solid ferrous to form a reduced feedstock;leaching at least a portion of the reduced feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702) with an aqueous acid to form a first aqueous leachate; andnon-electrolytically reducing dissolved ferric ions in the first aqueous leachate to dissolved ferrous ions in the presence of hydrogen gas, a conductivity enhancer, and a hydrogen oxidation catalyst to form a ferrous-rich aqueous acidic solution;wherein the ferrous-rich acidic aqueous solution has a greater concentration of dissolved ferrous ions than of dissolved ferric ions.

[0367] Aspect A96: A system for producing metallic iron from a feedstock having one or more iron oxides (or solid ferric), the method comprising:Leydig Ref. 340515: 3-25 WO a thermal reactor configured to reduce at least a portion of solid ferric in the feedstock to solid ferrous to form a reduced feedstock (e.g., 102, 202, 302, 702, 802, 902, 1002, 1102, 1202, 1402, 1502, or 1702);a leach tank (e.g., 310 or 910) configured to leach at least a portion of the reduced feedstock with an aqueous acid to form a first aqueous leachate having dissolved ferric ions and dissolved ferrous ions; anda ferric reduction reactor (e.g., 320, 500, or 920) configured to non-electrolytically reduce at least a portion of the dissolved ferric ions in the first aqueous leachate to dissolved ferrous ions in the presence of a conductivity enhancer, a hydrogen oxidation catalyst, and a hydrogen gas to form a ferrous-rich aqueous acidic solution; wherein:the ferrous-rich acidic aqueous solution has a greater concentration of dissolved ferrous ions than of dissolved ferric ions.

[0368] Aspect A97a: The method or system of any one of the preceding Aspects, wherein the aqueous acid (a) is or (b) comprises: hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, citric acid, oxalic acid, boric acid, or any combination thereof. Aspect A97b: The method or system of any one of the preceding claims, wherein each of the first aqueous leachate, the ferrous-rich aqueous acidic solution, the treated ferrous-rich aqueous acidic solution, and the plating catholyte comprises: hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, citric acid, oxalic acid, boric acid, or any combination thereof. Aspect A97c: The method or system of any one of the preceding claims, wherein each of the first aqueous leachate, the ferrous-rich aqueous acidic solution, the treated ferrous-rich aqueous acidic solution, and the plating catholyte comprises sulfuric acid.

[0369] Aspect A98: The method or system of any one of the preceding Aspects, wherein the ferrous-rich aqueous acidic solution has a pH selected from the range of approximately -1 to approximately 2, wherein any value and range therebetween inclusively is contemplated herein, such as but not limited to 0 to approximately 2, approximately 0.7 to approximately 2, approximately 0.5 to approximately 2, or approximately 0.5 to approximately 1.5.Leydig Ref. 340515: 3-25 WO

[0370] Aspect A99a: The method or system of any one of the preceding Aspects, wherein the treated ferrous-rich aqueous acidic solution has a pH selected from the range of approximately 2 to approximately 12 prior to being provided to the iron electroplating cell, wherein any value and range therebetween inclusively is contemplated herein. Aspect A99b: The method or system of any one of the preceding Aspects, wherein the treated ferrous-rich aqueous acidic solution is adjusted to a plating pH prior to being provided to the iron electroplating cell, the plating pH being selected from the range of approximately 2 to approximately 3.1, wherein any value and range therebetween inclusively is contemplated herein, optionally less than 3.1.

[0371] Aspect A100: The method or system of any one of the preceding Aspects, wherein the plating catholyte is characterized by a pH selected from the range of approximately 2 to approximately 3.1, wherein any value and range therebetween inclusively is contemplated herein, optionally less than 3.1.

[0372] Aspect A101: The method or system of any one of the preceding Aspects, wherein the plating catholyte is characterized by a temperature selected from the range of approximately 55 °C to approximately 90 °C, wherein any value and range therebetween inclusively is contemplated herein, such as a temperature selected from the range of approximately 60 °C to approximately 85 °C, or a temperature selected from the range of approximately 60 °C to approximately 80 °C.

[0373] Aspect A102: The method or system of any one of the preceding Aspects, wherein reductive leaching (e.g., in any reductive leach reactor disclosed herein) is performed with a liquid temperature selected from the range of approximately 20 °C to less than approximately 100 °C, wherein any value and range therebetween inclusively is contemplated herein, such as a liquid temperature selected from the range of approximately 20 °C to approximately 80 °C, or a liquid temperature selected from the range of approximately 60 °C to approximately 80 °C.

[0374] Aspect A103: The method or system of any one of the preceding Aspects, wherein non-electrolytic reduction (e.g., in any ferric reduction reactor disclosed herein) is performed with a liquid temperature selected from the range of approximately 20 °C to less than approximately 100 °C, wherein any value and range therebetween inclusively is contemplated herein, such as a liquid temperature selected from the range ofLeydig Ref. 340515: 3-25 WO approximately 20 °C to approximately 80 °C, or a liquid temperature selected from the range of approximately 60 °C to approximately 80 °C.

[0375] Aspect A104: The method or system of any one of the preceding Aspects, wherein leaching (e.g., in any leach tank disclosed herein) is performed with a liquid temperature selected from the range of approximately 20 °C to less than approximately 100 °C, wherein any value and range therebetween inclusively is contemplated herein, such as a liquid temperature selected from the range of approximately 20 °C to approximately 80 °C, or a liquid temperature selected from the range of approximately 60 °C to approximately 80 °C.

[0376] Aspect A105: The method or system of any one of the preceding Aspects, wherein reductive leaching (e.g., in any reductive leach reactor disclosed herein) is performed under a gas pressure selected from the range of approximately 0.9 atm to approximately 2 atm, wherein any value and range therebetween inclusively is contemplated herein, such as a gas pressure selected from the range of approximately 1 atm to approximately 1.5 atm, or a gas pressure of approximately 1.

[0377] Aspect A106: The method or system of any one of the preceding Aspects, wherein non-electrolytic reduction (e.g., in any ferric reduction reactor disclosed herein) is performed under a gas pressure selected from the range of approximately 0.9 atm to approximately 2 atm, wherein any value and range therebetween inclusively is contemplated herein, such as a gas pressure selected from the range of approximately 1 atm to approximately 1.5 atm, or a gas pressure of approximately 1.

[0378] Aspect A107: The method or system of any one of the preceding Aspects, wherein leaching (e.g., in any leach tank disclosed herein) is performed under a gas pressure selected from the range of approximately 0.9 atm to approximately 2 atm, wherein any value and range therebetween inclusively is contemplated herein, such as a gas pressure selected from the range of approximately 1 atm to approximately 1.5 atm, or a gas pressure of approximately 1.

[0379] Aspect A108: The method or system of any one of the preceding Aspects, wherein reductive leaching (e.g., in any reductive leach reactor disclosed herein) is performed with a pH of the aqueous solution therein being selected from the range ofLeydig Ref. 340515: 3-25 WO approximately 0.5 to approximately 5, wherein any value and range therebetween inclusively is contemplated herein.

[0380] Aspect A109: The method or system of any one of the preceding Aspects, wherein non-electrolytic reduction (e.g., in any ferric reduction reactor disclosed herein) is performed with a pH of the aqueous solution therein being selected from the range of approximately 0.5 to approximately 5, wherein any value and range therebetween inclusively is contemplated herein.

[0381] Aspect A110a: The method or system of any one of the preceding Aspects, wherein a mean residence time of fluid in the leach tank, in the ferric reduction reactor, or in the reductive leach reactor is selected from the range of approximately 30 seconds to approximately 48 hours, wherein any value and range therebetween inclusively is contemplated herein, such as approximately 1 minute to approximately 48 hours, approximately 2 minutes to approximately 48 hours, approximately 30 seconds to approximately 36 hours, approximately 30 seconds to approximately 24 hours, approximately 30 seconds to approximately 12 hours, approximately 30 seconds to approximately 6 hours, approximately 30 seconds to approximately 3 hours, approximately 30 seconds to approximately 2 hours, approximately 30 seconds to approximately 1 hour, approximately 30 seconds to approximately 30 minutes. Aspect A110b: The method or system of any one of the preceding Aspects, wherein a mean residence time of fluid in the leach tank and / or in the ferric reduction reactor is selected from the range of approximately 30 seconds to approximately 48 hours, wherein any value and range therebetween inclusively is contemplated herein, such as approximately 1 minute to approximately 48 hours, approximately 2 minutes to approximately 48 hours, approximately 30 seconds to approximately 36 hours, approximately 30 seconds to approximately 24 hours, approximately 30 seconds to approximately 12 hours, approximately 30 seconds to approximately 6 hours, approximately 30 seconds to approximately 3 hours, approximately 30 seconds to approximately 2 hours, approximately 30 seconds to approximately 1 hour, approximately 30 seconds to approximately 30 minutes. Aspect A110c: The method or system of any one of the preceding Aspects, wherein a mean residence time of fluid in the reductive leach reactor is selected from the range of approximately 30 seconds to approximately 48 hours, wherein any value and range therebetween inclusively isLeydig Ref. 340515: 3-25 WO contemplated herein, such as approximately 1 minute to approximately 48 hours, approximately 2 minutes to approximately 48 hours, approximately 30 seconds to approximately 36 hours, approximately 30 seconds to approximately 24 hours, approximately 30 seconds to approximately 12 hours, approximately 30 seconds to approximately 6 hours, approximately 30 seconds to approximately 3 hours, approximately 30 seconds to approximately 2 hours, approximately 30 seconds to approximately 1 hour, approximately 30 seconds to approximately 30 minutes.

[0382] Aspect A111 a: The method of any one of the preceding Aspects, wherein the step of leaching, the step of non-electrolytically reducing, or the step of reductively leaching is characterized by a mean residence time of fluid selected from the range of approximately 30 seconds to approximately 48 hours, wherein any value and range therebetween inclusively is contemplated herein, such as approximately 1 minute to approximately 48 hours, approximately 2 minutes to approximately 48 hours, approximately 30 seconds to approximately 36 hours, approximately 30 seconds to approximately 24 hours, approximately 30 seconds to approximately 12 hours, approximately 30 seconds to approximately 6 hours, approximately 30 seconds to approximately 3 hours, approximately 30 seconds to approximately 2 hours, approximately 30 seconds to approximately 1 hour, approximately 30 seconds to approximately 30 minutes. Aspect A111 b: The method of any one of the preceding Aspects, wherein the step of leaching and / or the step of non-electrolytically reducing is characterized by a mean residence time of fluid selected from the range of approximately 30 seconds to approximately 48 hours, wherein any value and range therebetween inclusively is contemplated herein, such as approximately 1 minute to approximately 48 hours, approximately 2 minutes to approximately 48 hours, approximately 30 seconds to approximately 36 hours, approximately 30 seconds to approximately 24 hours, approximately 30 seconds to approximately 12 hours, approximately 30 seconds to approximately 6 hours, approximately 30 seconds to approximately 3 hours, approximately 30 seconds to approximately 2 hours, approximately 30 seconds to approximately 1 hour, approximately 30 seconds to approximately 30 minutes. Aspect A111c: The method of any one of the preceding Aspects, wherein the step of reductively leaching is characterized by a mean residence time of fluid selected from the range of approximately 30 seconds to approximately 48 hours, wherein any value and range therebetween inclusively is contemplated herein,Leydig Ref. 340515: 3-25 WO such as approximately 1 minute to approximately 48 hours, approximately 2 minutes to approximately 48 hours, approximately 30 seconds to approximately 36 hours, approximately 30 seconds to approximately 24 hours, approximately 30 seconds to approximately 12 hours, approximately 30 seconds to approximately 6 hours, approximately 30 seconds to approximately 3 hours, approximately 30 seconds to approximately 2 hours, approximately 30 seconds to approximately 1 hour, approximately 30 seconds to approximately 30 minutes.

[0383] Aspect A112a: The method or system of any one of the preceding Aspects, wherein the anode of the iron electroplating cell has a composition comprising carbon or any one or more allotropes of carbon such as graphite, lead, lead oxide, one or more mixed metal oxides, or any combination of these. Aspect A112b: The method or system of any one of the preceding Aspects, wherein the anode of the iron electroplating cell has a composition comprising any one or more allotropes of carbon such as graphite, lead, lead oxide, or any combination of these.

[0384] Aspect B1: A method of reducing and leaching an iron ore into a solution, the method comprising:placing a slurry in a reductive leach reactor, the slurry comprising iron ore particles, a conductivity enhancer, and an aqueous electrolyte;wherein the reductive leach reactor comprises a hydrogen oxidation catalyst on an electrically conductive substrate, the electrically conductive substrate being in electrical contact with the slurry;directing a flow of hydrogen gas into the reductive leach reactor such that the hydrogen gas contacts the catalyst and at least the aqueous electrolyte of the slurry at a three-phase triple point such that the hydrogen gas is reduced at the catalyst thereby producing electrons that are conducted by the substrate to the slurry including the conductivity enhancer and the iron ore particles; and removing an iron-rich aqueous solution from the reductive leach reactor.

[0385] Aspect B2: The method of Aspect B1, wherein the aqueous electrolyte is acidic.

[0386] Aspect B3: The method of Aspect B1, wherein iron in the iron-rich aqueous solution is predominantly in the form of ferric (Fe2+) ions.Leydig Ref. 340515: 3-25 WO

[0387] Aspect B4: The method of Aspect B1, B2 or B3, wherein the iron ore contains iron predominantly in the form of hematite and / or goethite.

[0388] Aspect B5: The method of Aspect B4, wherein the hydrogen gas is electrochemically reduced at a three-phase point at which the catalyst, the aqueous electrolyte, and the hydrogen gas are all in contact with one another, and wherein said electrochemical reduction releases electrons that are conducted by the substrate.

[0389] Aspect B6: The method of any of the preceding Aspects B1 -B5, wherein the conductivity enhancer comprises solid particles of an electrically conductive material.

[0390] Aspect B7: The method of Aspect B6, wherein the conductivity enhancer comprises a conductive metal or metal oxide that is insoluble or sparingly soluble in the aqueous electrolyte

[0391] Aspect B8: The method of Aspect B6, wherein the conductivity enhancer comprises carbon or graphite particles.

[0392] Aspect B9: The method of any of Aspects B1 -B5, wherein the conductivity enhancer comprises a redox intermediary.

[0393] Aspect B10: The method of Aspect B9, wherein the redox intermediary is ascorbic acid.

[0394] Aspect B11: The method of any of the preceding Aspects B1-B12, further comprising raising pH of the aqueous electrolyte sufficiently to cause precipitation of impurities, wherein impurities comprise elements other than iron (Fe).

[0395] Aspect B12: The method of any of the preceding Aspects B1-B12, further comprising transferring the iron-rich aqueous solution to an electrolyte reduction reactor in which remaining ferric (Fe3+) ions are reduced to ferrous (Fe2+) ions.

[0396] Aspect B13: The method of any of the preceding Aspects B1-B12, further comprising transferring the iron-rich aqueous solution to an electroplating cell, electroplating iron on a cathode of the electroplating cell, and removing the plated iron from the electroplating cell.

[0397] Aspect B14: The method of Aspect B13, wherein a portion of the iron-rich aqueous solution is used as an anolyte (anode solution) in an anode chamber of theLeydig Ref. 340515: 3-25 WO electroplating cell, wherein the anode chamber is separated from the cathode by a membrane.

[0398] Aspect B15: The method of Aspect B14, further comprising returning a spent anolyte solution to the reductive leach reactor, wherein the spent anolyte is which is depleted in ferrous ions relative to the iron-rich aqueous solution having been oxidized at the anode of the electroplating cell.

[0399] Aspect B16: The method of any of the preceding Aspects B1-B15, further comprising collecting, via an external circuit, energy generated in the ore reduction reactor.

[0400] Aspect B17: The method of any of Aspects B1-B15, wherein the ore reduction reactor is not connected to an external circuit.

[0401] Aspect B18: The method of any of the preceding Aspects B1-B17, further comprising flowing the slurry through a cathode chamber of the reductive leach reactor.

[0402] Aspect B19: The method of any of Aspects B1-B17, further comprising operating the reductive leach reactor in a batch mode, comprising adding a batch of iron ore to the slurry, and removing a batch of undissolved solids after each of a plurality of reaction batches.

[0403] Aspect B20: The method of any of the preceding Aspects B1-B219 further comprising directing the iron-rich aqueous solution through a second reactor in which aqueous ferric (Fe3+) ions are reduced to ferrous (Fe2+) ions.

[0404] Aspect B21: The method of Aspect B20, wherein the second reactor is an acid regeneration (AR) fuel cell reactor in which ferrous ions are electrochemically reduced to ferric ions at a cathode of the AR fuel cell while hydrogen gas is oxidized at an anode of the AR fuel cell, while also producing electrical energy through an external circuit.

[0405] Aspect B22: The method of any of the preceding Aspects B1 -B21, wherein at least a portion of the hydrogen gas is provided from a water electrolyzer.

[0406] Aspect B23: The method of any of the preceding Aspects B1-B22, wherein at least a portion of the hydrogen gas is provided from a source other than a water electrolyzer.Leydig Ref. 340515: 3-25 WO

[0407] Aspect B24: The method of any of the preceding Aspects B1-B23, further comprising removing undissolved solids from the reductive leach reactor.

[0408] Aspect B25: The method of any of the preceding Aspects B1-B24, further comprising increasing pH of the aqueous electrolyte sufficiently that at least one impurity compound is precipitated from the aqueous electrolyte, and removing the impurity compound from the reductive leach reactor along with the undissolved solids.

[0409] Aspect B26: The method of any of the preceding Aspects B1-B25, further comprising directing the iron-rich aqueous solution to an impurity removal reactor in which impurity compounds are precipitated from the iron-rich aqueous solution by increasing pH of the iron-rich aqueous solution.

[0410] Aspect B27: The method of Aspect B26, wherein pH of the iron-rich aqueous solution is increased by addition of a base.

[0411] Aspect B28: The method of Aspect B27, wherein the base comprises metallic iron.

[0412] Aspect B29: A reductive leach reactor apparatus for simultaneously reducing and leaching an iron ore into an aqueous solution, the reactor comprising:an ore slurry region at least temporarily containing a quantity of a slurry comprising iron ore particles, a conductivity enhancer, and an aqueous electrolyte;a gas region containing hydrogen gas; anda hydrogen oxidation catalyst on an electrically conductive substrate; wherein at least a portion of the conductive substrate is in electrical contact with the slurry.

[0413] Aspect B30: The apparatus of Aspect B29, wherein the ore slurry region has an inlet and an outlet configured to allow slurry to flow through the ore slurry region.

[0414] Aspect B31: The apparatus of Aspect B29 or B30, wherein the reductive leach reactor comprises an anode chamber through which the hydrogen gas flows, wherein the anode chamber is separated from the cathode chamber by a separator membrane.

[0415] Aspect B32: The apparatus of any of Aspects B29-B31, wherein the gas region contains substantially only hydrogen gas.Leydig Ref. 340515: 3-25 WO

[0416] Aspect B33: The apparatus of any of Aspects B29-B31, further comprising a gas delivery outlet submerged in the aqueous electrolyte for bubbling hydrogen gas through the ore slurry.

[0417] Aspect B34: The apparatus of Aspect B33, wherein the gas delivery outlet is sized to produce micro-scale and / or nano-scale bubbles.

[0418] Aspect B35: The apparatus of any of Aspects B29-B34, wherein the ore slurry region is configured for batch mode operation in which a batch of ore is added to the ore slurry region, reductively leached, and then undissolved solids are removed.

[0419] Aspect B36: The apparatus of any of Aspects B29-B35, further comprising an external circuit for capturing electrical energy produced by the apparatus.

[0420] Aspect B37: The apparatus of any of Aspects B29-B35, wherein the apparatus does not include an external circuit.

[0421] Aspect B38: The apparatus of any of Aspects B29-B37, wherein the reactor is further configured as a pressure vessel capable of operating at an internal pressure of at least 10 bar up to 30 bar.

[0422] Aspect B39: The apparatus of Aspect B38, wherein the reactor also comprises a heater capable of heating the vessel to a temperature of at least 200 °C.

[0423] Aspect C1: A method of extracting metallic iron from an iron ore containing one or more iron oxides, the method comprising:first reductively leaching the iron ore in an aqueous acidic leach solution to produce a ferrous iron-rich leach solution in which iron is substantially entirely in a ferrous (Fe2+) oxidation state (or dissolved iron consists essentially of Fe2+iron ions);wherein reductively leaching comprises contacting the aqueous acidic leach solution with a first reducing gas before, during, or after contacting the leach solution with the iron ore;removing impurities from the ferrous iron-rich leach solution by (optionally) shifting pH of the ferrous iron-rich leach solution and precipitating impurity compounds; andLeydig Ref. 340515: 3-25 WO directing the ferrous iron-rich leach solution to an electrochemical plating cell, and cathodically electroplating metallic iron while (optionally) anodically oxidizing water to evolve oxygen gas or anodically oxidizing ferrous iron to ferric iron.

[0424] Aspect C2: The method of Aspect C1, further comprising, prior to the first reductively leaching, thermally reducing at least some of the iron oxides in the iron ore to form a reduced iron oxide by contacting the iron ore with a second reducing gas at a temperature of between about 350 °C to about 1,000 °C or more.

[0425] Aspect C3: The method of Aspect C1 or Aspect C2, further comprising directly reducing at least some of the iron oxides in the iron ore by heating the iron ore and elemental sulfur in a direct reduction reactor to a temperature of between about 350 °C to about 800 °C.

[0426] Aspect C4: The method of Aspect C3, further comprising directing an oxygencontaining gas (which may optionally be air) into the direct reduction reactor during the directly reducing.

[0427] Aspect C5: The method of any of Aspects C2, C3, or C4, wherein the reduced iron oxide is magnetite (Fe3O4).

[0428] Aspect C6: The method of any of Aspects C2, C3, or C4, wherein the reduced iron oxide is ferrous oxide (FeO).

[0429] Aspect C7: The methods of any of the previous Aspects C1-C6 in which the first or second reducing gas is sulfur dioxide.

[0430] Aspect C8: The method of Aspect C7, wherein the sulfur dioxide is produced by combusting elemental sulfur in an oxygen-containing gas (which may optionally be air).

[0431] Aspect C9: The method of Aspect C8, further comprising contacting a sulfur trioxide byproduct with water to form sulfuric acid.

[0432] Aspect C10: The method of Aspect C8 or C9, wherein heat produced from combustion of elemental sulfur is used to thermally reduce the iron ore.Leydig Ref. 340515: 3-25 WO

[0433] Aspect C11: The method of Aspect C8, C9 or C10, wherein heat produced from combustion of elemental sulfur is used to evaporate water from an acidic salt solution (optionally a spent ferrous iron-rich leach solution after cathodic electroplating).

[0434] Aspect C12: The method of any of the preceding Aspects C1 -C11, wherein the anodic reaction during electroplating is oxygen evolution from water oxidation, and wherein acid is produced in an anode chamber of the electrochemical plating cell during the cathodic electroplating; and returning the produced acid to a subsequent reductive leaching step.

[0435] Aspect C13: The method of Aspect C12, wherein the acid produced in the anode chamber of the electrochemical plating cell is sulfuric acid, and further comprising removing a portion of the sulfuric acid from the plating cell, thermally decomposing the removed portion of sulfuric acid to produce sulfur dioxide, water, and oxygen.

[0436] Aspect C14: The method of Aspect C13, further comprising using the sulfur dioxide made by thermal decomposition in a subsequent reductive leaching step.

[0437] Aspect C15: The method of any of Aspects C1 – C6, wherein the first orsecond reducing gas is or comprises hydrogen gas.

[0438] Aspect C16: The method of any of Aspects C1 – C6, wherein the first orsecond reducing gas is at least one member of the group consisting of natural gas, reformed natural gas, carbon monoxide, methane, another natural or reformed hydrocarbon gas, forming gas, and hydrogen sulfide gas.

[0439] Aspect C17: The method of any of Aspects C1-C11, C15, or C16, wherein the anodic reaction during electroplating is anodically oxidizing ferrous iron ions to ferric iron ions, and further comprising reducing the anodically-produced ferric ions by contacting the ferrous ions with the first reducing gas.

[0440] Aspect C18: The method of any of the preceding Aspects C1 -C17, further comprising generating electrical energy from heat released by producing the first or second reducing gas, and using the generated electrical energy to power the electroplating cells.

[0441] Aspect C19: A method of extracting metallic iron from an iron ore containing one or more iron oxides, the method comprising:Leydig Ref. 340515: 3-25 WO thermally reducing at least some of the iron oxides in the iron ore to form a ferrous oxide iron ore (optionally at least 90%, 95%, 99%, 99.9%, or more of the iron oxide is reduced the form of ferrous oxide, FeO) by contacting the iron ore with a first reducing gas at a temperature of at least 570 °C; leaching the reduced iron ore in an aqueous acidic leach solution to produce a ferrous iron-rich leach solution in which iron is substantially entirely in a ferrous (Fe2+) oxidation state (or dissolved iron consists essentially of Fe2+iron ions);removing impurities from the ferrous iron-rich leach solution by (optionally) shifting pH of the ferrous iron-rich leach solution and precipitating impurity compounds;directing the ferrous iron-rich leach solution to an electrochemical plating cell, and cathodically electroplating metallic iron while (optionally) anodically oxidizing water to evolve oxygen gas or anodically oxidizing ferrous iron to ferric iron

[0442] Aspect C20: The method of Aspect C19, in which the first reducing gas is sulfur dioxide.

[0443] Aspect C21: The method of Aspect C20, wherein the sulfur dioxide is produced by combusting elemental sulfur in an oxygen-containing gas (which may optionally be air).

[0444] Aspect C22: The method of Aspect C21, further comprising contacting a sulfur trioxide byproduct with water to form sulfuric acid.

[0445] Aspect C23: The method of Aspect C21 or C22, wherein heat produced from combustion of elemental sulfur is used to thermally reduce the iron ore.

[0446] Aspect C24: The method of Aspect C21, C22, or C23, wherein heat produced from combustion of elemental sulfur is used to evaporate water from an acidic salt solution (optionally a spent ferrous iron-rich leach solution after cathodic electroplating).

[0447] Aspect C25: The method of any of Aspects C19-C24, wherein the anodic reaction during electroplating is oxygen evolution from water oxidation, and wherein acidLeydig Ref. 340515: 3-25 WO is produced in an anode chamber of the electrochemical plating cell during the cathodic electroplating; and returning the produced acid to a subsequent reductive leaching step.

[0448] Aspect C26: The method of Aspect C25, wherein the acid produced in the anode chamber of the electrochemical plating cell is sulfuric acid, and further comprising removing a portion of the sulfuric acid from the plating cell, thermally decomposing the removed portion of sulfuric acid to produce sulfur dioxide, water, and oxygen.

[0449] Aspect C27: The method of Aspect C26, further comprising using the sulfur dioxide made by thermal decomposition in a subsequent reductive leaching step.

[0450] Aspect C28: The method of any of Aspects C19 – C27, wherein the firstreducing gas is hydrogen gas.

[0451] Aspect C29: The method of any of Aspects C19– C27, wherein the first reducing gas is at least one member of the group consisting of natural gas, reformed natural gas, carbon monoxide, methane, another natural or reformed hydrocarbon gas, forming gas, and hydrogen sulfide gas.

[0452] Aspect C30: The method of any of Aspects C19-C29, wherein the anodic reaction during electroplating is anodically oxidizing ferrous iron ions to ferric iron ions, and further comprising reducing the anodically-produced ferric ions by contacting the ferrous ions with the first reducing gas.

[0453] Aspect C31: The method of any of Aspects C19-C29, further comprising generating electrical energy from heat released by producing the first reducing gas, and using the generated electrical energy to power the electroplating cells.

[0454] Aspect C32: The method of any of Aspects C19-C31, further comprising reductively leaching the iron ore in an aqueous acidic leach solution to produce a ferrous iron-rich leach solution in which iron is substantially entirely in a ferrous (Fe2+) oxidation state (or dissolved iron consists essentially of Fe2+iron ions); wherein reductively leaching comprises contacting the aqueous acidic leach solution with a second reducing gas before, during, or after contacting the leach solution with the iron ore; wherein the second reducing gas is the same or different from the first reducing gas.

[0455] Aspect C33: A method of extracting metallic iron from an iron ore containing one or more iron oxides, the method comprising:Leydig Ref. 340515: 3-25 WO thermally reducing at least some of the iron oxides in the iron ore to form a magnetite iron ore (optionally at least 90%, 95%, 99%, 99.9%, or more of the iron oxide is reduced to the form of magnetite, Fe3O4) by contacting the iron ore with a first reducing gas at a temperature of between about 350 °C to about 700 °C;leaching the reduced iron ore in an aqueous acidic leach solution to produce a ferrous iron-rich leach solution in which iron is substantially entirely in a ferrous (Fe2+) oxidation state (or dissolved iron consists essentially of Fe2+iron ions);removing impurities from the ferrous iron-rich leach solution by (optionally) shifting pH of the ferrous iron-rich leach solution and precipitating impurity compounds;directing the ferrous iron-rich leach solution to an electrochemical plating cell, and cathodically electroplating metallic iron while (optionally) anodically oxidizing water to evolve oxygen gas or anodically oxidizing ferrous iron to ferric iron.

[0456] Aspect C34: The method of Aspect C33, in which the first reducing gas is sulfur dioxide.

[0457] Aspect C35: The method of Aspect C34, wherein the sulfur dioxide is produced by combusting elemental sulfur in an oxygen-containing gas (which may optionally be air).

[0458] Aspect C36: The method of Aspect C35, further comprising contacting a sulfur trioxide byproduct with water to form sulfuric acid.

[0459] Aspect C37: The method of Aspect C35 or C36, wherein heat produced from combustion of elemental sulfur is used to thermally reduce the iron ore.

[0460] Aspect C38: The method of any of Aspects C34-C37, wherein heat produced from combustion of elemental sulfur is used to evaporate water from an acidic salt solution (optionally a spent ferrous iron-rich leach solution after cathodic electroplating).

[0461] Aspect C39: The method of any of Aspects C33-C38, wherein the anodic reaction during electroplating is oxygen evolution from water oxidation, and wherein acidLeydig Ref. 340515: 3-25 WO is produced in an anode chamber of the electrochemical plating cell during the cathodic electroplating; and returning the produced acid to a subsequent reductive leaching step.

[0462] Aspect C40: The method of Aspect C39, wherein the acid produced in the anode chamber of the electrochemical plating cell is sulfuric acid, and further comprising removing a portion of the sulfuric acid from the plating cell, thermally decomposing the removed portion of sulfuric acid to produce sulfur dioxide, water, and oxygen.

[0463] Aspect C41: The method of Aspect C40, further comprising using the sulfur dioxide made by thermal decomposition in a subsequent reductive leaching step.

[0464] Aspect C42: The method of any of Aspects C33-C38, wherein the first reducing gas is hydrogen gas.

[0465] Aspect C43: The method of any of Aspects C33-C41, wherein the first reducing gas is at least one member of the group consisting of natural gas, reformed natural gas, carbon monoxide, methane, another natural or reformed hydrocarbon gas, forming gas, and hydrogen sulfide gas.

[0466] Aspect C44: The method of any of Aspects C33-C43, wherein the anodic reaction during electroplating is anodically oxidizing ferrous iron ions to ferric iron ions, and further comprising reducing the anodically-produced ferric ions by contacting the ferrous ions with the fist reducing gas.

[0467] Aspect C45: The method of any of Aspects C33-C43, further comprising generating electrical energy from heat released by producing the first reducing gas, and using the generated electrical energy to power the electroplating cells.

[0468] Aspect C46: The method of any of Aspects C33-C45, wherein said leaching further comprises reductively leaching, comprising contacting the aqueous acidic leach solution with a second reducing gas before, during, or after contacting the leach solution with the iron ore; wherein the second reducing gas is the same or different from the first reducing gas.

[0469] Aspect C47: A method of extracting metallic iron from an iron ore containing one or more iron oxides, the method comprising:Leydig Ref. 340515: 3-25 WO directly reducing at least some of the iron oxides in the iron ore to form a ferrous oxide iron ore by contacting the iron ore with elemental sulfur at a temperature of at least 570 °C;leaching the reduced iron ore in an aqueous acidic leach solution to produce a ferrous iron-rich leach solution in which iron is substantially entirely in a ferrous (Fe2+) oxidation state (or dissolved iron consists essentially of Fe2+iron ions);removing impurities from the ferrous iron-rich leach solution by (optionally) shifting pH of the ferrous iron-rich leach solution and precipitating impurity compounds;directing the ferrous iron-rich leach solution to an electrochemical plating cell, and cathodically electroplating metallic iron while (optionally) anodically oxidizing water to evolve oxygen gas or anodically oxidizing ferrous iron to ferric iron.

[0470] Aspect C48: The method of Aspect C47, in which the reducing gas is sulfur dioxide.

[0471] Aspect C49: The method of Aspect C48, wherein the sulfur dioxide is produced by combusting elemental sulfur in an oxygen-containing gas (which may optionally be air).

[0472] Aspect C50: The method of Aspect C49, further comprising contacting a sulfur trioxide byproduct with water to form sulfuric acid.

[0473] Aspect C51: The method of Aspect C49 or C50, wherein heat produced from combustion of elemental sulfur is used to thermally reduce the iron ore.

[0474] Aspect C52: The method of any of Aspects C49-C51, wherein heat produced from combustion of elemental sulfur is used to evaporate water from an acidic salt solution (optionally a spent ferrous iron-rich leach solution after cathodic electroplating).

[0475] Aspect C53: The method of any of Aspects C47-C52, wherein the anodic reaction during electroplating is oxygen evolution from water oxidation, and wherein acid is produced in an anode chamber of the electrochemical plating cell during the cathodic electroplating; and returning the produced acid to a subsequent reductive leaching step.Leydig Ref. 340515: 3-25 WO

[0476] Aspect C54: The method of Aspect C53, wherein the acid produced in the anode chamber of the electrochemical plating cell is sulfuric acid, and further comprising removing a portion of the sulfuric acid from the plating cell, thermally decomposing the removed portion of sulfuric acid to produce sulfur dioxide, water, and oxygen.

[0477] Aspect C55: The method of Aspect C54, further comprising using the sulfur dioxide made by thermal decomposition in a subsequent reductive leaching step.

[0478] Aspect C56: The method of any of Aspects C47-C55, wherein the reducing gas is hydrogen gas.

[0479] Aspect C57: The method of any of Aspects C47-C55, wherein the reducing gas is at least one member of the group consisting of natural gas, reformed natural gas, carbon monoxide, methane, another natural or reformed hydrocarbon gas, forming gas, and hydrogen sulfide gas.

[0480] Aspect C58: The method of any of Aspects C47-C57, wherein the anodic reaction during electroplating is anodically oxidizing ferrous iron ions to ferric iron ions, and further comprising reducing the anodically-produced ferric ions by contacting the ferrous ions with the reducing gas.

[0481] Aspect C59: The method of any of Aspects C47-C58, further comprising generating electrical energy from heat released by producing the reducing gas, and using the generated electrical energy to power the electroplating cells.

[0482] Aspect C60: A method of extracting metallic iron from an iron ore containing one or more iron oxides, the method comprising:directly reducing at least some of the iron oxides in the iron ore to form a magnetite iron ore by contacting the iron ore with elemental sulfur at a temperature of between about 350 °C to about 569 °C;leaching the reduced iron ore in an aqueous acidic leach solution to produce a ferrous iron-rich leach solution in which iron is substantially entirely in a ferrous (Fe2+) oxidation state (or dissolved iron consists essentially of Fe2+iron ions);Leydig Ref. 340515: 3-25 WO removing impurities from the ferrous iron-rich leach solution by (optionally) shifting pH of the ferrous iron-rich leach solution and precipitating impurity compounds;directing the ferrous iron-rich leach solution to an electrochemical plating cell, and cathodically electroplating metallic iron while (optionally) anodically oxidizing water to evolve oxygen gas or anodically oxidizing ferrous iron to ferric iron.

[0483] Aspect C61: The method of Aspect C60, in which the reducing gas is sulfur dioxide.

[0484] Aspect C62: The method of Aspect C61, wherein the sulfur dioxide is produced by combusting elemental sulfur in an oxygen-containing gas (which may optionally be air).

[0485] Aspect C63: The method of Aspect C62, further comprising contacting a sulfur trioxide byproduct with water to form sulfuric acid.

[0486] Aspect C64: The method of Aspect C62 or C63, wherein heat produced from combustion of elemental sulfur is used to thermally reduce the iron ore.

[0487] Aspect C65: The method of any of Aspects C62-C64, wherein heat produced from combustion of elemental sulfur is used to evaporate water from an acidic salt solution (optionally a spent ferrous iron-rich leach solution after cathodic electroplating).

[0488] Aspect C66: The method of any of Aspects C60-C65, wherein the anodic reaction during electroplating is oxygen evolution from water oxidation, and wherein acid is produced in an anode chamber of the electrochemical plating cell during the cathodic electroplating; and returning the produced acid to a subsequent reductive leaching step.

[0489] Aspect C67: The method of Aspect C66, wherein the acid produced in the anode chamber of the electrochemical plating cell is sulfuric acid, and further comprising removing a portion of the sulfuric acid from the plating cell, thermally decomposing the removed portion of sulfuric acid to produce sulfur dioxide, water, and oxygen.

[0490] Aspect C68: The method of Aspect C67, further comprising using the sulfur dioxide made by thermal decomposition in a subsequent reductive leaching step.Leydig Ref. 340515: 3-25 WO

[0491] Aspect C69: The method of any of Aspects C60-C68, wherein the reducing gas is hydrogen gas.

[0492] Aspect C70: The method of any of Aspects C60-C68, wherein the reducing gas is at least one member of the group consisting of natural gas, reformed natural gas, carbon monoxide, methane, another natural or reformed hydrocarbon gas, forming gas, and hydrogen sulfide gas.

[0493] Aspect C71: The method of any of Aspects C60-C70, wherein the anodic reaction during electroplating is anodically oxidizing ferrous iron ions to ferric iron ions, and further comprising reducing the anodically-produced ferric ions by contacting the ferrous ions with the reducing gas.

[0494] Aspect C72: The method of any of Aspects C60-C70, further comprising generating electrical energy from heat released by producing the reducing gas, and using the generated electrical energy to power the electroplating cells.

[0495] Aspect C73: The method of any of Aspects C60-C72, wherein said leaching further comprises reductively leaching, comprising contacting the aqueous acidic leach solution with a second reducing gas before, during, or after contacting the leach solution with the iron ore; wherein the second reducing gas is the same or different from the first reducing gas.

[0496] Aspect D1a: A method of producing metallic iron, the method comprising:providing an iron source material in the presence of an aqueous acid and one or more reductants;wherein the iron source material comprises one or more iron oxides comprising solid ferric;non-electrolytically reducing dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm;treating the ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution; and electroplating iron from the treated ferrous-rich solution in an iron electroplating cellLeydig Ref. 340515: 3-25 WO wherein:the dissolved and the non-dissolved ferric are from the solid ferric of the one or more iron oxides;the step of non-electrolytically reducing results in formation of a ferrous- rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; and the step of treating comprises raising a pH of the ferrous-rich acidic aqueous solution.

[0497] Aspect D1b: A system for producing metallic iron, the system comprising:a reductive leach reactor configured to provide an iron source material in the presence of an aqueous acid and one or more reductants, wherein the iron source material comprises one or more iron oxides comprising solid ferric; wherein the reductive leach reactor is further configured to non-electrolytically reduce dissolved ferric, nondissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm and thereby produce ferrous-rich aqueous acidic solution; wherein the dissolved and the non-dissolved ferric are from the one or more iron oxides;an impurity removal subsystem configured to remove at least a portion of noniron impurities from the produced ferrous-rich aqueous acidic solution and thereby form a treated ferrous-rich solution; andan iron electroplating cell configured to electroplate iron metal at a plating cathode by electrochemically reducing aqueous ferrous ions.

[0498] Aspect D1c: The system of Aspect D1b, wherein the reductive leach reactor is configured to both leach at least a portion of the one or more iron oxides and non-electrolytically reduce dissolved ferric, non-dissolved ferric, or a combination thereof.

[0499] Aspect Did: A system for producing metallic iron, the system comprising:a leach tank configured to leach at least a portion of one or more iron oxides from an iron source material and produce a first acidic leachate;a ferric reduction reactor configured to provide an iron source material in the presence of the first acidic leachate and one or more reductants to non- electrolytically reduce dissolved ferric, non-dissolved ferric, or a combinationLeydig Ref. 340515: 3-25 WO thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm and thereby produce ferrous-rich aqueous acidic solution; wherein the dissolved and the non-dissolved ferric are from the one or more iron oxides;an impurity removal subsystem configured to remove at least a portion of noniron impurities from the produced ferrous-rich aqueous acidic solution and thereby form a treated ferrous-rich solution; andan iron electroplating cell configured to electroplate iron metal at a plating cathode by electrochemically reducing aqueous ferrous ions.

[0500] Aspect Die: The system of Aspect D1b, D1c, or Did, wherein the impurity removal subsystem is configured to provide one or more iron oxide materials in contact with the produced ferrous-rich aqueous acidic solution.

[0501] Aspect D1f: The system of Aspect D1b, D1c, or Did, wherein the impurity removal subsystem is configured to provide one or more iron oxide materials and one or more iron-based metals in contact with the produced ferrous-rich aqueous acidic solution.

[0502] Aspect Dig: A method of producing metallic iron, the method comprising:providing an iron source material in the presence of an aqueous acid and one or more reductants;wherein the iron source material comprises one or more iron oxides comprising solid ferric;reductively leaching the one or more iron oxides, the step of reductively leaching comprising non-electrolytically reducing dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm;treating the ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution; and electroplating iron from the treated ferrous-rich solution in an iron electroplating cellwherein:Leydig Ref. 340515: 3-25 WO the dissolved and the non-dissolved ferric are from the solid ferric of the one or more iron oxides;the step of non-electrolytically reducing results in formation of a ferrous- rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; and the step of treating comprises raising a pH of the ferrous-rich acidic aqueous solution.

[0503] Aspect D1 h: A method of producing metallic iron, the method comprising:providing an iron source material in the presence of an aqueous acid and one or more reductants; wherein the iron source material comprises one or more iron oxides comprising solid ferric;non-electrolytically reducing dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm; wherein the step of non-electrolytically reducing results in formation of a ferrous-rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; wherein the dissolved and the non-dissolved ferric are from the solid ferric of the one or more iron oxides;treating the produced ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution; wherein the step of treating comprises raising a pH of the ferrous-rich acidic aqueous solution; andelectroplating iron from the treated ferrous-rich solution in an iron electroplating cell.

[0504] Aspect D1 i: A method of producing metallic iron, the method comprising:leaching an iron source material in the presence of an aqueous acid and one or more reductants; wherein the iron source material comprises one or more iron oxides comprising solid ferric;non-electrolytically reducing dissolved ferric, non-dissolved ferric, or a combination thereof in a mixture comprising the iron source material, the one or more reductants, and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm;Leydig Ref. 340515: 3-25 WO wherein the steps of leaching and non-electrolytically reducing are performed concurrently and in a same reductive leach reactor;wherein the step of non-electrolytically reducing results in formation of a ferrous-rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; andwherein the dissolved and the non-dissolved ferric are from the solid ferric of the one or more iron oxides;treating the produced ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution; wherein the step of treating comprises raising a pH of the ferrous-rich acidic aqueous solution; andelectroplating iron from the treated ferrous-rich solution in an iron electroplating cell.

[0505] Aspect D2: The method or system of Aspect D1, wherein the step of non-electrolytically reducing comprises chemically reducing dissolved ferric ions to dissolved ferrous ions, chemically reducing at least a portion of the one or more iron oxides, or a combination thereof.

[0506] Aspect D3: The method or system of Aspect D1 or D2, comprising leaching at least a portion of the iron source material with the aqueous acid.

[0507] Aspect D4: The method or system of any one of Aspects D1 -D3, wherein the steps of leaching and non-electrolytically reducing are performed concurrently and in the presence of each other in a first acidic leachate to produce the ferrous-rich acidic aqueous solution.

[0508] Aspect D5: The method or system of Aspect D4, comprising a step of reductively leaching the iron source material with the aqueous acid; wherein the step of reductively leaching comprises the steps of leaching and non-electrolytically reducing.

[0509] Aspect D6: The method or system of Aspect D3, D4, or D5, wherein the steps of leaching and non-electrolytically reducing are performed in the same vessel.

[0510] Aspect D7: The method or system of Aspect D6, wherein the step of reductively leaching is performed in a reductive leach reactor.Leydig Ref. 340515: 3-25 WO

[0511] Aspect D8: The method or system of any one of Aspects D3-D7, wherein the step of reducing comprises chemically reducing aqueous ferric ions to ferrous ions in the presence of the one or more reductants.

[0512] Aspect D9: The method or system of any one of Aspects D3-D8, wherein the step of reducing comprises chemically reducing at least a portion of the one or more solid iron oxides.

[0513] Aspect D10: The method or system of any one of Aspect D1-D9, wherein the step of non-electrolytically reducing comprises reducing ferric in the one or more iron oxides to ferrous.

[0514] Aspect D11: The method or system of any one of Aspect D1 -D10, wherein the one or more iron oxides comprises hematite and / or goethite and wherein the step of reducing comprises reducing the hematite and / or goethite to magnetite, wüstite, iron metal, or a combination thereof.

[0515] Aspect D12: The method or system of any one of Aspect D1-D11, wherein the step of reducing comprises reducing dissolved ferric ions to dissolved ferrous ions in the presence of a slurry comprising solid iron oxide particles.

[0516] Aspect D13: The method or system of any one of Aspect D1-D12 being free of electrochemical reduction of ferric to ferrous between the steps of non-electrolytically reducing and treating.

[0517] Aspect D14: The method or system of any one of Aspect D1-D13, wherein the one or more reductants is one or more solid reductants, one or more gaseous reductants, one or more dissolved aqueous reductants, or a combination thereof.

[0518] Aspect D15: The method or system of any one of Aspect D1-D14, wherein the step of non-electrolytically reducing comprises providing one or more solid reductants which dissolve in the acidic solution to form aqueous reducing reactants for reducing aqueous ferric ions.

[0519] Aspect D16: The method or system of any one of Aspect D1-D15, wherein the one or more reductants comprises H₂ gas, H₂S gas, SO₂ gas, CO gas, methane gas, solid sulfur, an iron-based metal, an iron metal of at least 99 at.% purity, one or more pyrite materials, one or more metal sulfide materials, copper metal, a copper oxide, a copper salt, tin metal, a tin oxide, a tin salt, titanium metal, a titanium oxide, a titaniumLeydig Ref. 340515: 3-25 WO salt, vanadium metal, a vanadium oxide, a vanadium salt, an inorganic redox mediator, an organic redox mediator, a plurality thereof, or any combination thereof.

[0520] Aspect D17: The method or system of any one of Aspect D1-D16, wherein the one or more reductants comprises one or more pyrite materials.

[0521] Aspect D18: The method or system of any one of Aspect D1 -D17, wherein the one or more reductants comprises one or more metal sulfide materials.

[0522] Aspect D19: The method or system of any one of Aspect D1 -D18, wherein the one or more reductants comprises one or more solid reductants provided to the step of non-electrolytically reducing according to a molar ratio of reductant to ferric being at least 1.

[0523] Aspect D20: The method or system of any one of Aspect D1 -D19, wherein the iron source material comprises an iron ore or a combination of a plurality of iron ores.

[0524] Aspect D21: The method or system of any one of Aspect D1 -D20, wherein the iron source material comprises one or more iron ores, one or more thermally reduced iron ores, or a combination thereof.

[0525] Aspect D22: The method or system of any one of Aspect D1 -D21 further comprising thermally reducing an initial feedstock having one or more iron ores at a temperature greater than 120 °C and in the presence of a gaseous thermal reductant, thereby forming a thermally reduced feedstock; wherein the step of leaching and / or non-electrolytically reducing is performed on the thermally reduced feedstock.

[0526] Aspect D23: The method or system of Aspect D22, wherein the step of non-electrolytically reducing is performed in the presence of the thermally reduced feedstock.

[0527] Aspect D24: The method or system of Aspect D22 or D23, wherein the step of thermally reducing comprises reducing hematite and / or goethite to magnetite.

[0528] Aspect D25: The method or system of any one of Aspect D1 -D24 further comprising air roasting the feedstock, wherein the step of leaching and / or non-electrolytically reducing is performed on the air roasted feedstock.

[0529] Aspect D26: The method or system of Aspect D25, wherein the step of non-electrolytically reducing is performed in the presence of the air roasted feedstock.Leydig Ref. 340515: 3-25 WO

[0530] Aspect D27: The method or system of any one of Aspect D1-D26, wherein the step of electroplating comprises reducing aqueous ferrous ions to metallic iron at a plating cathode in the presence of a catholyte of the electroplating cell.

[0531] Aspect D28: The method or system of any one of Aspect D1 -D27, wherein the step of electroplating further comprises oxidizing aqueous ferrous ions to ferric ions at an anode in the presence of an anolyte of the electroplating cell.

[0532] Aspect D29: The method or system of any one of Aspect D1 -D27, wherein the step of electroplating further comprises oxidizing water and evolving oxygen gas at an anode in the presence of an anolyte of the electroplating cell.

[0533] Aspect D30: The method or system of any one of Aspect D1 -D29, wherein the step of raising the pH of the ferrous-rich acidic aqueous solution comprises providing one or more iron oxide materials in contact with said ferrous-rich acidic aqueous solution.

[0534] Aspect D31: The method or system of any one of Aspect D1 -D30, wherein the step of raising the pH of the ferrous-rich acidic aqueous solution comprises providing a combination of one or more iron oxide materials and one or more iron-based materials.

[0535] Aspect D32: The method or system of any one of Aspect D1 -D31, wherein an electrolyte from the electroplating cell is provided directly or indirectly to the step of leaching, the step of non-electrolytically reducing, or both.

[0536] Aspect D33: The method or system of any one of Aspect D1 -D32, wherein an anolyte, a catholyte, or a combination thereof from the electroplating cell is provided to a vessel in which the step of leaching, the step of non-electrolytically reducing, or both are being performed.

[0537] Aspect D34: The method or system of any one of Aspect D1 -D33, wherein a vessel in which the step of leaching, the step of non-electrolytically reducing, or both are being performed is not connected to an external electrical circuit capable of driving an electrochemical reaction.

[0538] Aspect D35: The method or system of any one of Aspect D1 -D34, wherein the ferrous-rich aqueous acidic solution is characterized by a ratio of ferrous ion concentration to total iron ion concentration greater than or equal to 0.80.Leydig Ref. 340515: 3-25 WO

[0539] Aspect D36: The method or system of any one of Aspect D1 -D35, wherein the ferrous-rich aqueous acidic solution has a concentration of dissolved ferric ions less than or equal to 3 mM.

[0540] Aspect D37: The method or system of any one of Aspect D1 -D35, wherein the aqueous acid comprises H₂SO₄.

[0541] Aspect D38: A system for producing metallic iron, the system comprising:a reductive leach reactor configured to provide an iron source material in the presence of an aqueous acid and one or more reductants, wherein the iron source material comprises one or more iron oxides comprising solid ferric; wherein the reductive leach reactor is further configured to non-electrolytically reduce dissolved ferric, nondissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm and thereby produce ferrous-rich aqueous acidic solution; wherein the dissolved and the non-dissolved ferric are from the one or more iron oxides;an impurity removal subsystem configured to remove at least a portion of noniron impurities from the produced ferrous-rich aqueous acidic solution and thereby form a treated ferrous-rich solution; andan iron electroplating cell configured to electroplate iron metal at a plating cathode by electrochemically reducing aqueous ferrous ions.

[0542] Aspect D39: The system of Aspect 38, wherein the reductive leach reactor is configured to both leach at least a portion of the one or more iron oxides and non-electrolytically reduce dissolved ferric, non-dissolved ferric, or a combination thereof.

[0543] Aspect D40: A system for producing metallic iron, the system comprising:a leach tank configured to leach at least a portion of one or more iron oxides from an iron source material and produce a first acidic leachate;a ferric reduction reactor configured to provide an iron source material in the presence of the first acidic leachate and one or more reductants to non- electrolytically reduce dissolved ferric, non-dissolved ferric, or a combination thereof in the presence of the one or more reductants and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atmLeydig Ref. 340515: 3-25 WO and thereby produce ferrous-rich aqueous acidic solution; wherein the dissolved and the non-dissolved ferric are from the one or more iron oxides;an impurity removal subsystem configured to remove at least a portion of noniron impurities from the produced ferrous-rich aqueous acidic solution and thereby form a treated ferrous-rich solution; andan iron electroplating cell configured to electroplate iron metal at a plating cathode by electrochemically reducing aqueous ferrous ions.

[0544] Aspect D41: The system of Aspect 38, 39, or 40, wherein the impurity removal subsystem is configured to provide one or more iron oxide materials in contact with the produced ferrous-rich aqueous acidic solution.

[0545] Aspect D42: The system of Aspect 38, 39, or 40, wherein the impurity removal subsystem is configured to provide one or more iron oxide materials and one or more iron-based metals in contact with the produced ferrous-rich aqueous acidic solution.

[0546] Aspect D43: A method of producing metallic iron, the method comprising:leaching an iron source material in the presence of an aqueous acid and one or more reductants; wherein the iron source material comprises one or more iron oxides comprising solid ferric;non-electrolytically reducing dissolved ferric, non-dissolved ferric, or a combination thereof in a mixture comprising the iron source material, the one or more reductants, and the aqueous acid at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm;wherein the steps of leaching and non-electrolytically reducing are performed concurrently and in a same reductive leach reactor;wherein the step of non-electrolytically reducing results in formation of a ferrous-rich acidic aqueous solution having a greater concentration of dissolved ferrous ions than of dissolved ferric ions; andwherein the dissolved and the non-dissolved ferric are from the solid ferric of the one or more iron oxides;treating the produced ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities, thereby forming a treated ferrous-rich solution; wherein the step of treating comprises raising a pH of the ferrous-rich acidic aqueous solution; andLeydig Ref. 340515: 3-25 WO electroplating iron from the treated ferrous-rich solution in an iron electroplating cell.

[0547] Aspect D44: The method of Aspect D43 being free of electrochemical reduction of ferric to ferrous between the steps of non-electrolytically reducing and treating.

[0548] Aspect D45: The method of Aspect D43, wherein the one or more reductants comprises H₂ gas, H₂S gas, SO₂ gas, CO gas, methane gas, solid sulfur, an iron-based metal, an iron metal of at least 99 at.% purity, one or more pyrite materials, one or more metal sulfide materials, copper metal, a copper oxide, a copper salt, tin metal, a tin oxide, a tin salt, titanium metal, a titanium oxide, a titanium salt, vanadium metal, a vanadium oxide, a vanadium salt, an inorganic redox mediator, an organic redox mediator, a plurality thereof, or any combination thereof.

[0549] Aspect D46: The method of Aspect D45, wherein the one or more reductants comprises one or more pyrite materials.

[0550] Aspect D47: The method of Aspect D45, wherein the one or more reductants comprises one or more metal sulfide materials.

[0551] Aspect D48: The method of Aspect D43, wherein the iron source material comprises an iron ore or a combination of a plurality of iron ores.

[0552] Aspect D49: The method of Aspect D43, wherein the iron source material comprises one or more iron ores, one or more thermally reduced iron ores, or a combination thereof.

[0553] Aspect D50: The method of Aspect D49, wherein the step of non-electrolytically reducing is performed in the presence of the thermally reduced feedstock.

[0554] Aspect D51: The method of Aspect D43, wherein the step of electroplating comprises (a) reducing aqueous ferrous ions to metallic iron at a plating cathode in the presence of a catholyte of the electroplating cell and (b) the step of electroplating further comprises oxidizing water and evolving oxygen gas at an anode in the presence of an anolyte of the electroplating cell.

[0555] Aspect D52: The method of Aspect D51, wherein an electrolyte from the electroplating cell is provided to the steps of leaching and non-electrolytically reducing.Leydig Ref. 340515: 3-25 WO

[0556] Aspect D53: The method of Aspect D43, wherein the step of raising the pH of the ferrous-rich acidic aqueous solution comprises providing one or more iron oxide materials in contact with said ferrous-rich acidic aqueous solution.

[0557] Aspect D54: The method of Aspect D43, wherein the step of raising the pH of the ferrous-rich acidic aqueous solution comprises providing a combination of one or more iron oxide materials and one or more iron-based materials.

[0558] Aspect D55: The method of Aspect D43, wherein the reductive leach reactor is not connected to an external electrical circuit capable of driving an electrochemical reaction.

[0559] Aspect D56: The method of Aspect D43, wherein the ferrous-rich aqueous acidic solution is characterized by a ratio of ferrous ion concentration to total iron ion concentration greater than or equal to 0.80; and wherein the ferrous-rich aqueous acidic solution has a concentration of dissolved ferric ions less than or equal to 3 mM.

[0560] Aspect D57: The method of any one of Aspects D43-45, wherein the aqueous acid comprises H₂SO₄.

[0561] Aspect E1a: A method for producing metallic iron, the method comprising:reductively leaching an iron source material with an aqueous acid and one or more reductants to produce a ferrous-rich acidic aqueous solution;wherein the iron source material comprises magnetite;wherein the step of reductive leaching comprises leaching the iron source material with the aqueous acid thereby forming dissolved ferric ions and, concurrently in a same reductive leach reactor, non-electrolytically reducing the dissolved ferric ions via the one or more reductants; wherein the one or more reductants comprise one or more pyrite materials, one or more metal sulfide materials, or a combination thereof;wherein the produced ferrous-rich aqueous acidic solution is characterized by a ratio of dissolved ferrous ion concentration to total dissolved iron ion concentration greater than 0.50 (optionally greater than or equal to 0.60, optionally at least 0.75, optionally at least 0.80, optionally at least 0.82, optionally at least 0.84, optionally at least 0.85, optionally at leastLeydig Ref. 340515: 3-25 WO 0.86, optionally at least 0.87, optionally at least 0.88, optionally at least 0.89, optionally at least 0.90, optionally at least 0.91, optionally at least 0.92, optionally at least 0.93, optionally at least 0.94, optionally at least 0.95, optionally at least 0.96, optionally at least 0.97, optionally at least 0.98, optionally at least 0.99);raising a pH of the produced ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities thereby forming a treated ferrous-rich solution; andelectroplating metallic iron by electrochemically reducing dissolved ferrous ions from the treated ferrous-rich solution at a plating cathode of an iron electroplating cell.

[0562] Aspect E1 b: A method for producing metallic iron, the method comprising:reductively leaching an iron source material with an aqueous acid and one or more reductants to produce a ferrous-rich acidic aqueous solution;wherein the iron source material comprises magnetite;wherein the step of reductive leaching comprises leaching the iron source material with the aqueous acid thereby forming dissolved ferric ions and, concurrently in a same reductive leach reactor, non-electrolytically reducing the dissolved ferric ions via the one or more reductants; wherein the one or more reductants comprise one or more pyrite materials, one or more metal sulfide materials, or a combination thereof;wherein the produced ferrous-rich aqueous acidic solution is characterized by a ratio of dissolved ferrous ion concentration to total dissolved iron ion concentration greater than 0.50 (optionally greater than or equal to 0.60, optionally at least 0.75, optionally at least 0.80, optionally at least 0.82, optionally at least 0.84, optionally at least 0.85, optionally at least 0.86, optionally at least 0.87, optionally at least 0.88, optionally at least 0.89, optionally at least 0.90, optionally at least 0.91, optionally at least 0.92, optionally at least 0.93, optionally at least 0.94, optionally at least 0.95, optionally at least 0.96, optionally at least 0.97, optionally at least 0.98, optionally at least 0.99);andLeydig Ref. 340515: 3-25 WO removing iron or iron-containing salt(s) from the ferrous-rich solution.

[0563] Aspect E1c: The method of Aspect E1b further comprising raising a pH of the produced ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities thereby forming a treated ferrous-rich solution.

[0564] Aspect E1d: The method of Aspect E1b or E1c, wherein the step of removing iron comprises electroplating metallic iron by electrochemically reducing dissolved ferrous ions from the ferrous-rich solution at a plating cathode of an iron electroplating cell

[0565] Aspect E2a: The method of Aspect E1, wherein the iron source material is predominantly magnetite (by weight) or wherein the iron source material contains iron predominantly in an iron(ll) state. Aspect E2b: The method of Aspect E1, wherein the iron source material contains iron predominantly in an iron(ll) state. Aspect E2c: The method of Aspect E1, wherein the iron source material is predominantly magnetite (by weight).

[0566] Aspect E3a: The method of Aspect E1 or E2, wherein the iron source material comprises iron metal. Aspect E3b: The method of Aspect E1 or E2, wherein the iron source material comprises iron in an iron(O) state.

[0567] Aspect E4a: The method of any one of Aspects E1-E3 comprising thermally reducing at least a portion (optionally a majority, by weight) of hematite and / or goethite in an iron-containing feedstock to magnetite, wüstite, or a combination of both thereby forming a thermally reduced ore; wherein the iron source material comprises the thermally reduced ore. Aspect E4b: The method of any one of Aspects E1-E3 comprising thermally reducing at least a portion (optionally a majority, by weight) of and / or goethite in an iron-containing feedstock to magnetite, wüstite, or a combination of both thereby forming a thermally reduced ore; wherein the iron source material comprises the thermally reduced ore; and wherein the thermally reduced ore is predominantly magnetite (by weight). Aspect E4c: The method of any one of Aspects E1-E3 comprising thermally reducing at least a portion (optionally a majority, by weight) of hematite and / or goethite in an iron-containing feedstock to magnetite, wüstite, or a combination of both thereby forming a thermally reduced ore; wherein the iron source material comprises the thermally reduced ore; and wherein the thermally reduced ore isLeydig Ref. 340515: 3-25 WO predominantly magnetite (by weight); and wherein the iron-containing feedstock is predominantly hematite and / or goethite (by weight).

[0568] Aspect E5: The method of Aspect E4, wherein the iron-containing feedstock comprises an iron ore or a combination of a plurality of iron ores.

[0569] Aspect E6a: The method of any one of the preceding E Aspects, wherein the iron source material comprises one or more iron ores. Aspect E6b: The method of any one of the preceding E Aspects, wherein the iron source material comprises one or more iron ores and a thermally reduced ore. Aspect E6c: The method of any one of the pre...

Claims

Leydig Ref. 340515: 3-25 WO We claim:

1. A method for producing metallic iron, the method comprising:reductively leaching an iron source material with an aqueous acid and one or more reductants to produce a ferrous-rich acidic aqueous solution;wherein the iron source material comprises magnetite;wherein the step of reductively leaching comprises leaching the iron source material with the aqueous acid thereby forming dissolved ferric ions and, concurrently in a same reductive leach reactor, non- electrolytically reducing the dissolved ferric ions via the one or more reductants;wherein the one or more reductants comprise one or more pyrite materials, one or more metal sulfide materials, or a combination thereof;wherein the produced ferrous-rich aqueous acidic solution is characterized by a ratio of dissolved ferrous ion concentration to total dissolved iron ion concentration greater than 0.50;raising a pH of the produced ferrous-rich acidic aqueous solution to remove at least a portion of non-iron impurities thereby forming a treated ferrous-rich solution; andelectroplating metallic iron by electrochemically reducing dissolved ferrous ions from the treated ferrous-rich solution at a plating cathode of an iron electroplating cell.

2. The method of claim 1, wherein the iron source material is predominantly magnetite or wherein the iron source material contains iron predominantly in an iron(ll) state.

3. The method of claim 1 or 2, wherein the iron source material comprises iron metal.

4. The method of any one of the preceding claims comprising thermally reducing at least a portion of hematite and / or goethite in an iron-containing feedstock to magnetite, wüstite, or a combination of both thereby forming a thermally reduced ore; wherein the iron source material comprises the thermally reduced ore.Leydig Ref. 340515: 3-25 WO 5. The method of claim 4, wherein the iron-containing feedstock comprises an iron ore or a combination of a plurality of iron ores.

6. The method of any one of the preceding claims, wherein the iron source material comprises one or more iron ores.

7. The method of any one of the preceding claims, wherein the one or more reductants is the one or more pyrite materials.

8. The method of any one of the preceding claims, wherein the one or more pyrite materials comprise FeS2.

9. The method of any one of the preceding claims, wherein the step of electroplating comprises (a) reducing dissolved ferrous ions to metallic iron at a plating cathode in contact with a catholyte of the electroplating cell, and (b) oxidizing water and evolving oxygen gas at an anode in contact with an anolyte of the electroplating cell.

10. The method of any one of the preceding claims comprising withdrawing a portion of an electrolyte from the iron electroplating cell and providing the withdrawn electrolyte as a lixiviant to the step of reductive leaching.

11. The method of any one of the preceding claims, wherein the withdrawn and provided electrolyte has a concentration of dissolved ferric ions less than or equal to 0.15 M.

12. The method of any one of the preceding claims, wherein the step of raising the pH comprises providing one or more iron oxide materials in contact with said ferrous-rich acidic aqueous solution.

13. The method of claim 12, wherein the step of raising the pH comprises providing a combination of the one or more iron oxide materials and one or more iron-based metals.

14. The method of any one of the preceding claims, wherein the ferrous-rich aqueous acidic solution has a concentration of dissolved ferric ions less than or equal to 10 mM.

15. The method of any one of the preceding claims being free of electrochemical reduction of ferric to ferrous between the steps of reductive leaching and raising.Leydig Ref. 340515: 3-25 WO 16. The method of any one of the preceding claims, wherein the reductive leach reactor is not connected to an external electrical circuit capable of driving an electrochemical reaction.

17. The method of any one of the preceding claims, wherein the aqueous acid comprises H₂SO₄.

18. The method of any one of the preceding claims, wherein the step of reductive leaching is performed at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm.

19. The method of any one of the preceding claims, wherein the produced ferrous- rich aqueous acidic solution is characterized by the ratio of dissolved ferrous ion concentration to total dissolved iron ion concentration greater than or equal to 0.80.

20. A system for producing metallic iron, the system comprising:a reductive leach reactor configured to reductively leach an iron source material with an aqueous acid and one or more reductants to produce a ferrous- rich acidic aqueous solution;wherein the iron source material comprises magnetite;wherein the reductive leach reactor is configured to (a) leach the iron source material with the aqueous acid to thereby form dissolved ferric ions and concurrently (b) non-electrolytically reduce the dissolved ferric ions via the one or more reductants at a liquid temperature less than 120 °C and under a gas pressure less than 2 atm;wherein the one or more reductants comprise one or more pyrite materials, one or more metal sulfide materials, or a combination thereof; andwherein the ferrous-rich aqueous acidic solution is characterized by a ratio of dissolved ferrous ion concentration to total dissolved iron ion concentration greater than 0.50;an impurity removal subsystem configured to receive the produced ferrous- rich acidic aqueous solution and raise its pH to thereby remove at least a portion of non-iron impurities and produce a treated ferrous-rich solution; andLeydig Ref. 340515: 3-25 WO an iron electroplating cell configured to electroplate metallic iron at a plating cathode via an electrochemical reduction of dissolved ferrous ions from the treated ferrous-rich solution.

21. The system of claim 20, wherein the iron source material is predominantly magnetite or wherein the iron source material contains iron predominantly in an iron(ll) state.

22. The system of claim 20 or 21, wherein the iron source material comprises iron metal.

23. The system of any one of claims 20-22 comprising a thermal reduction reactor configured to thermally reduce at least a portion of hematite and / or goethite in an iron-containing feedstock to magnetite, wüstite, or a combination of both, thereby forming a thermally reduced ore; wherein the iron source material comprises the thermally reduced ore.

24. The system of claim 23, wherein the iron-containing feedstock comprises an iron ore or a combination of a plurality of iron ores.

25. The system of any one of claims 20-24, wherein the iron source material comprises an iron ore or a combination of a plurality of iron ores.

26. The system of any one of claims 20-25, wherein the one or more reductants is the one or more pyrite materials.

27. The system of any one of claims 20-26, wherein the one or more pyrite materials comprise FeS2.

28. The system of any one of claims 20-27, wherein the step of electroplating comprises (a) reducing dissolved ferrous ions to metallic iron at a plating cathode in contact with a catholyte of the electroplating cell, and (b) oxidizing water and evolving oxygen gas at an anode in contact with an anolyte of the electroplating cell.

29. The system of any one of claims 20-28 comprising withdrawing a portion of an electrolyte from the iron electroplating cell and providing the withdrawn electrolyte as a lixiviant to the step of reductive leaching.

30. The system of any one of claims 20-29, wherein the withdrawn and provided electrolyte has a concentration of dissolved ferric ions less than or equal to 0.15 M.Leydig Ref. 340515: 3-25 WO 31. The system of any one of claims 20-30, wherein the step of raising the pH comprises providing one or more iron oxide materials in contact with said ferrous- rich acidic aqueous solution.

32. The system of claim 31, wherein the step of raising the pH comprises providing a combination of the one or more iron oxide materials and one or more iron-based metals.

33. The system of any one of claims 20-32, wherein the ferrous-rich aqueous acidic solution has a concentration of dissolved ferric ions less than or equal to 10 mM.

34. The system of any one of claims 20-33 being free of electrochemical reduction of ferric to ferrous between the steps of reductive leaching and raising.

35. The system of any one of claims 20-34, wherein the reductive leach reactor is not connected to an external electrical circuit capable of driving an electrochemical reaction.

36. The system of any one of claims 20-35, wherein the aqueous acid comprises H₂SO₄.

37. The system of any one of claims 20-36, wherein the reductive leach reactor is operated at a liquid temperature less than 120 °C and a gas pressure less than 2 atm.

38. The system of any one of claims 20-37, wherein the produced ferrous-rich aqueous acidic solution is characterized by the ratio of dissolved ferrous ion concentration to total dissolved iron ion concentration greater than or equal to 0.80.

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