Iron production by direct electrolysis of iron ore

Abstract

An iron electrolysis system (200) can include an anode chamber (210) containing an aqueous anolyte (212), a cathode chamber (220) containing an aqueous catholyte (222), and a cation-exchange membrane (230) separating the anode chamber from the cathode chamber. The catholyte can include an iron ion (238). The cation-exchange membrane can be in contact with the anolyte and the catholyte and can allow transfer of the iron ion through the cation-exchange membrane. An anode (214) can be in contact with the anolyte and a cathode (224) can be in contact with the catholyte. The anolyte, catholyte, or both can include magnesium salt, calcium salt, or a combination thereof.

Description

[0001] IRON PRODUCTION BY DIRECT ELECTROLYSIS OF IRON ORE

[0002] CROSS REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Application No. 63 / 649,671, filed May 20, 2024, which is hereby incorporated herein by reference.

[0004] STATEMENT REGARDING FEDERALLY SPONSORED

[0005] RESEARCH OR DEVELOPMENT

[0006] This invention was made with government support under DE-SC0023947 awarded by the U.S. Department of Energy. The government has certain rights in the invention.

[0007] NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

[0008] Not applicable.

[0009] INCORPORATION BY REFERENCE STATEMENT

[0010] Not applicable.

[0011] BACKGROUND

[0012] Iron (Fe) occurs naturally as iron ores such as hematite, magnetite, goethite, limonite, wustite, pyrite, and others which are made up iron oxides such as Fe2C>3, FeiCh. FeO and iron sulfides such as FeS2, FeS, FesS4, etc. In iron metal and steel production, iron oxides are typically reduced to form iron metal. A majority (about 71%) of global crude steel production currently utilizes a reduction process known as blast furnace-basic oxygen furnace (BF- BOF). This process usually uses carbon (such as coke) as a reductant. The carbon binds oxygen in the iron ore and generates carbon dioxide (CO2). Thus, the most common process for producing iron and steel produces a significant amount of carbon dioxide. In fact, iron and steel production as a whole currently accounts for about 7% of total industry carbon dioxide production.

[0013] Some other processes have been used to directly reduce iron ore to iron metal sponge via a solid-state process using a reducing gas. However, the reducing gas used in such processes typically originates from reformed natural gas, syngas, or coal, which also have a heavy carbon footprint. Therefore, the most common processes currently used to produce iron and steel also produce a significant amount of carbon dioxide, which can be harmful to the environment.

[0014] SUMMARY

[0015] Iron electrolysis systems and methods of producing iron by direct electrolysis of iron ore are described. In one example, an iron electrolysis system can include an anode chamber containing an aqueous anolyte, a cathode chamber containing an aqueous catholyte comprising an iron ion, and a cation-exchange membrane separating the anode chamber from the cathode chamber. The cation-exchange membrane can be in contact with the anolyte and the catholyte and can allow transfer of the iron ion through the cation-exchange membrane. The system can also include an anode in contact with the anolyte and a cathode in contact with the catholyte. The anolyte, catholyte, or both can comprise magnesium salt, calcium salt, or a combination thereof.

[0016] An example method of producing iron by direct electrolysis of iron ore can include reducing a pH of an aqueous anolyte by electro-oxidation of water at an anode in contact with the anolyte. A cation-exchange membrane can separate the anolyte from an aqueous catholyte. The anolyte, catholyte, or both can comprise magnesium salt, calcium salt, or a combination thereof. The method can further include introducing iron ions into one or both of the anolyte and the catholyte, and reducing the iron ions to form iron metal at a cathode in contact with the catholyte.

[0017] There has thus been outlined, rather broadly, features of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from the following detailed description of the invention, taken with the accompanying drawings and claims, or may be learned by the practice of the invention.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a flowchart illustrating an example method of producing iron by direct electrolysis of iron ore, in accordance with the present disclosure. FIG. 2 is a side cross-sectional schematic view of an example iron ore electrolysis system, in accordance with the present disclosure.

[0020] FIGs. 3A and 3B are side cross-sectional schematic views of another example iron ore electrolysis system, in accordance with the present disclosure.

[0021] FIG. 4 is a side cross-sectional schematic view of an example iron ore electrolysis system, in accordance with the present disclosure.

[0022] FIG. 5 is a side cross-sectional schematic view of another example iron ore electrolysis system, in accordance with the present disclosure.

[0023] FIG. 6 is a side cross-sectional schematic view of yet another example iron ore electrolysis system, in accordance with the present disclosure.

[0024] FIG. 7 is a side cross-sectional schematic view of another example iron ore electrolysis system, in accordance with the present disclosure.

[0025] FIG. 8 is a side cross-sectional schematic view of still another example iron ore electrolysis system, in accordance with the present disclosure.

[0026] FIG. 9 is a flowchart illustrating an example method of producing iron, in accordance with the present disclosure.

[0027] FIG. 10 is a graph of voltage vs. current density in an example iron electrolysis system, in accordance with the present disclosure.

[0028] FIG. 11 is graph of efficiency and voltage in an example iron electrolysis system, in accordance with the present disclosure.

[0029] FIG. 12 is a graph of efficiency and voltage in another example iron electrolysis system, in accordance with the present disclosure.

[0030] FIG. 13 is a graph of efficiency and voltage in another example iron electrolysis system, in accordance with the present disclosure.

[0031] FIG. 14 is a graph of efficiency and voltage in another example iron electrolysis system, in accordance with the present disclosure.

[0032] FIG. 15 is an EDX analysis of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.

[0033] FIG. 16 is a SEM image of iron obtained in an example iron electrolysis system, in accordance with the present disclosure. FIG. 17 is an XRD analysis of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.

[0034] FIG. 18 is a graph of efficiency vs. current density in an example iron electrolysis system, in accordance with the present disclosure.

[0035] FIG. 19 is a graph of efficiency and voltage vs. time in an example iron electrolysis system, in accordance with the present disclosure.

[0036] FIG. 20 is an XRD analysis of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.

[0037] FIG. 21 is an EDX analysis of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.

[0038] FIG. 22 is a SEM image of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.

[0039] FIG. 23 is a graph of anolyte pH and efficiency vs. time in an example iron electrolysis system, in accordance with the present disclosure.

[0040] FIG. 24 is an XRD analysis of iron obtained in another example iron electrolysis system, in accordance with the present disclosure.

[0041] FIG. 25 is an EDX analysis of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.

[0042] FIG. 26 is a SEM image of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.

[0043] FIG. 27 is a graph of anolyte pH and efficiency vs. time in an example iron electrolysis system, in accordance with the present disclosure.

[0044] These drawings are provided to illustrate various aspects of the invention and are not intended to be limiting of the scope in terms of dimensions, materials, configurations, arrangements or proportions unless otherwise limited by the claims.

[0045] DETAILED DESCRIPTION

[0046] While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. Thus, the following more detailed description of the embodiments of the present invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the present invention, to set forth the best mode of operation of the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the present invention is to be defined solely by the appended claims.

[0047] Definitions

[0048] In describing and claiming the present invention, the following terminology will be used.

[0049] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a salt” includes reference to one or more of such materials and reference to “the membrane” refers to one or more of such membranes.

[0050] As used herein, “faradaic efficiency” can also be called “Faraday efficiency” or “faradic efficiency.” This refers to the fraction of electric current that flows through an electrochemical cell that effects a desired electrochemical reaction. The remaining fraction of the electric current, which does not contribute to the desired electrochemical reaction, can be consumed by faradaic losses such as unwanted side reactions and heat generation.

[0051] As used herein with respect to an identified property or circumstance, “substantially” refers to a degree of deviation that is sufficiently small so as to not measurably detract from the identified property or circumstance. The exact degree of deviation allowable may in some cases depend on the specific context.

[0052] As used herein, “adjacent” refers to the proximity of two structures or elements. Particularly, elements that are identified as being “adjacent” may be either abutting or connected. Such elements may also be near or close to each other without necessarily contacting each other. The exact degree of proximity may in some cases depend on the specific context.

[0053] As used herein, the term “about” is used to provide flexibility and imprecision associated with a given term, metric or value. The degree of flexibility for a particular variable can be readily determined by one skilled in the art. However, unless otherwise enunciated, the term “about” generally connotes flexibility of less than 2%, and most often less than 1%, and in some cases less than 0.01%.

[0054] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[0055] As used herein, the term “at least one of’ is intended to be synonymous with “one or more of.” For example, “at least one of A, B and C” explicitly includes only A, only B, only C, or combinations of each.

[0056] Numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited limits of 1 to about 4.5, but also to include individual numerals such as 2, 3, 4, and subranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as “less than about 4.5,” which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described.

[0057] Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. Means-plus-function or step-plus- function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) “means for” or “step for” is expressly recited; and b) a corresponding function is expressly recited. The structure, material or acts that support the means-plus function are expressly recited in the description herein. Accordingly, the scope of the invention should be determined solely by the appended claims and their legal equivalents, rather than by the descriptions and examples given herein. Methods of Producing Iron Metal by Electrolysis of Iron Ore and Iron Electrolysis Systems

[0058] The present disclosure describes processes for producing iron metal from iron ore through electrolysis. The major products of the processes can be iron metal and oxygen. Carbon is not involved in any of the chemical reactions that occur in this process, and no carbon dioxide is produced. If the electricity used for electrolysis is supplied from renewable resources such as solar or wind power, then the entire iron production process can be carbon- emission-free.

[0059] Electrolysis of iron ore can break iron ore directly into iron metal and oxygen gas. Due to its simplicity and potential carbon-emission-free nature, electrolysis has received attention in recent years. Among different electrolysis processes, molten oxide electrolysis (MOE) is the most studied because it enables the direct production of iron metal in the liquid state from iron oxide feedstock. This produces liquid iron metal that can be easily separated from the molten oxide electrolyte, and the high solubility of iron oxide in the electrolyte enables high operation current, such as 1 A / cm2. However, the high operation temperature (often greater than 1,538 °C) can result in significant energy inefficiency due to heat loss. The MOE reactor can also suffer from severe corrosion due to the oxygen-rich environment, high temperature, the presence of ceramic-solubilizing molten oxide, and the presence of metal -solubilizing molten metal. Moreover, MOE has a low faradaic efficiency (34-46%) due to the corrosion of cathode. Using molten salt electrolyte (such as halide or carbonate) can significantly reduce the operating temperature to 750-900 °C, but the reaction rate is limited by the sluggish solid-state reduction of iron oxide and / or the diffusion of the dissolved iron oxide in the electrolyte. In addition, it is difficult to separate the produced solid iron from the molten salt.

[0060] Electrolysis in aqueous electrolyte can significantly lower the operating temperature to below 150 °C. This can allow for simpler reactor design and reduce the energy consumption compared to the generation and maintaining of high temperature in the MOE process. Electrowinning, i.e., the electrolysis of suspended iron ore particles in alkaline solutions can be performed at 100-120 °C. In the electrowinning process, a solid-state shrinking-core conversion of iron oxide to iron metal occurs when iron ore particles pass by the cathode in the stirred electrolyte. However, the reaction rate is restricted to about 0.1 A / cm2, due to the limited reaction area (electrode-particle contact surface) and the slow electron / oxygen anion transport in the iron oxide particles. Oxygen bubbles formed on the cathode can be trapped due to the high viscosity of the suspension. The trapped bubbles can block the electrode surface and further compromise the reaction rate. Additionally, the formed product is usually a mixed-phase solid particle containing both iron metal and iron oxide, making it difficult to separate the iron metal.

[0061] Electrolysis in acidic electrolyte can potentially address the above issues. Electrolysis in acidic electrolyte can be performed at much lower temperature than MOE. Iron ore can dissolve into the acidic electrolyte and form iron ions (i.e. Fe3+and / or Fe2+ions). The reduction of Fe3+and / or Fe2+ions to Fe metal, i.e., electrochemical deposition of Fe, is a liquid-solid two-phase reaction that can be much more facile than the solid-state reaction in an alkaline electrolyzer. The high solubility of Fe3+and Fe2+in acidic electrolyte (>3.5M) also allows a high rate of operation with good mass transfer. The acidic electrolyte can also have much lower viscosity than a suspension electrolyte used in an alkaline electrolyzer. Additionally, the obtained precipitate from the acidic electrolyte is pure Fe metal, typically with no, or substantially no, Fe oxide in the bulk deposited Fe metal.

[0062] Despite these positive features of electrolysis in acidic electrolyte, the electrolysis of Fe ore in acidic electrolyte presents challenges. One challenge is that there is a large amount of H+present in acidic electrolyte. The reduction of H+is both thermodynamically and kinetically more favorable than the reduction of Fe3+and Fe2+. Therefore, electrolysis in acidic electrolyte tends to favor the reduction of H+to produce hydrogen gas over the reduction of Fe3+and Fe2+. This side reaction leads to a low faradic efficiency during Fe deposition as well as the corrosion of formed Fe. As H+ions are reduced, the pH of the electrolyte increases and Fe3+ions may precipitate as hydroxide.

[0063] The methods of producing iron metal described herein involve electrolyzing iron ore in acidic electrolyte. However, the methods described herein can have much higher faradaic efficiency than other electrolysis methods. This can be achieved by minimizing the hydrogen evolution reaction (HER) that occurs as a side reaction at the cathode, in which H+is reduced instead of Fe3+or Fe2+. The methods described herein can continuously convert Fe ore into Fe metal and oxygen at low temperatures, such as in the range of 25-80 °C. In some examples, the methods can use an electrochemical reactor having two compartments separated by a cation exchange membrane. The compartments can be referred to as an “anode chamber” and a “cathode chamber.” Both chambers can be filled with electrolyte, which may be two different electrolytes or the same electrolyte in some examples. The electrolyte in the anode chamber can be referred to as the “anolyte,” and the electrolyte in the cathode chamber can be referred to as the “catholyte.” One or both of the anolyte and the catholyte can include magnesium salt, calcium salt, lithium salt, or a combination thereof. In some cases, the magnesium salt can include magnesium chloride, magnesium sulfate, magnesium perchlorate, magnesium nitrate, or combinations thereof. In other cases, the calcium salt can include calcium chloride, calcium sulfate, calcium perchlorate, calcium nitrate, or a combination thereof. In the anode chamber, water can be oxidized to form O2 gas and H+ions at an anode. This can reduce the pH of the anolyte. Iron ions, including Fe3+and / or Fe2+ions, can be introduced into the cathode chamber. The iron ions can be reduced at the cathode to form iron metal. In various examples, the iron ions can be produced from iron ore in various ways. For example, iron ore can be leached by acidic anolyte in the anode chamber, or iron ore can be leached by acidic anolyte in a separate leaching vessel, or iron ore can be leached using another acid to prepare a solution containing iron ions ahead of time. In some examples, the iron ions can be transferred from the anolyte to the catholyte across the cation exchange membrane, while in other examples a solution of iron ions can flow directly into the cathode chamber. These and other examples are described in more detail below.

[0064] The chemical reactions involved in this process, using Fe2O3as an example feedstock, are shown below.

[0065] H2O -* 2H++ 2e + 0.5O2(g) (I)

[0066] Fe2O3+ 6H+— 2Fe3++ 3H2O (II)

[0067] Fe3 1+ 3e‘ — > Fe(s) (III)

[0068] Equations (I) through (III) show the individual chemical reactions that can take place in the methods described herein. Reaction (I) can take place at the anode, where water is oxidized to form H+ions and oxygen gas. Reaction (II) can take place when iron ore is contacted with an acid, which can be in the anode chamber or in a separate leaching vessel. The acid can be supplied by anolyte after reaction (I) has reduced the pH of the anolyte. Reaction (III) can occur at the cathode, where the Fe3+ions are reduced to form Fe solid metal. The overall reaction that occurs in the electrochemical reactor is shown as Equation (IV) below:

[0069] Fe2O3— 2Fe(s) + 1.5O2(g) (IV)

[0070] Thus, the iron oxide in the ore can be the sole reactant and the only products are iron metal and oxygen gas, in this example. The materials in the aqueous electrolytes and the anode and cathode are also not consumed by the reaction. Therefore, the process of producing iron metal from iron ore can be performed with no net consumption of any materials other than the iron ore.

[0071] As mentioned above, electrolysis of iron ore in acidic electrolyte can be challenging because of the hydrogen evolution reaction (HER) that competes with the reduction of Fe3+and / or Fe2+at the cathode. This challenge is addressed by the methods and systems described herein. First, the design of the electrochemical reactor creates a pH gradient from the anode to the cathode. The local pH is very low near the anode because the of oxygen evolution reaction that occurs at the anode. The H+ions formed at the anode can be used to react with iron ore to form Fe3 1ions. At the cathode, the concentration of H1ions can be lower than at the anode and the concentration of Fe3ions can be higher than at the anode. Although some H+ions may migrate through the cation exchange membrane into the cathode chamber, the concentration of H+in the cathode chamber can be much lower because most of the H+ions have already been consumed by the reaction with iron ore. The pH at the cathode can be higher, such as in the range of 1 to 5, and in some cases 4 to 5. This pH range can suppress HER and favor the reduction of Fe3+ions. Additionally, in some examples, the cathode chamber can contain a specific type of electrolyte that can further suppress HER. In some examples, this electrolyte can include a salt of magnesium or calcium or lithium, in particular magnesium chloride or calcium chloride or lithium chloride. However, other salts can be suitable. For example, magnesium chloride, magnesium sulfate, magnesium perchlorate, magnesium nitrate, calcium chloride, calcium sulfate, calcium perchlorate, calcium nitrate, lithium chloride, lithium sulfate, lithium perchlorate, lithium nitrate, and the like can be used. Use of perchlorate salts can provide production of oxygen. The characteristics of this electrolyte are described in more detail below. With the pH gradient and the HER- suppressing electrolyte, the methods described herein can be used to make iron metal with high faradaic efficiency, such as greater than 90%, greater than 95%, or greater than 99%.

[0072] With this description in mind, FIG. 1 is a flowchart illustrating one example method 100 of producing iron by direct electrolysis of iron ore. The method includes reducing a pH of an aqueous anolyte by electro-oxidation of water at an anode in contact with the anolyte, wherein a cation-exchange membrane separates the analyte from an aqueous catholyte, wherein the anolyte, catholyte, or both comprises magnesium salt, calcium salt, or a combination thereof 110; introducing iron ions into one or both of the anolyte and the catholyte 120; and reducing the iron ions to form iron metal at a cathode in contact with the catholyte 130.

[0073] The methods described herein can be performed using an iron electrolysis system that includes the components described in the method. In some examples, the iron electrolysis system can include an anode chamber that contains an aqueous anolyte and a cathode chamber that contains an aqueous catholyte. The anolyte, catholyte, or both can include magnesium salt, calcium salt, or a combination thereof. The catholyte can also include an iron ion. A cation-exchange membrane can separate the anode chamber from the cathode chamber. An anode can be in contact with the anolyte and a cathode can be in contact with the catholyte.

[0074] An example iron electrolysis system 200 is shown in FIG. 2. This system includes an anode chamber 210 that contains an aqueous anolyte 212 and a cathode chamber 220 that contains an aqueous catholyte 222. A cation exchange membrane 230 separates the anode chamber from the cathode chamber. The cation exchange membrane is in contact with both the anolyte and the catholyte. This can allow cations, such as iron ions, to move from the anolyte to the catholyte and vice versa. An anode 214 is positioned in the anode chamber in contact with the anolyte. A cathode 224 is positioned in the cathode chamber in contact with the catholyte. When the system is operating, the anode is positively charged, which causes negatively charged anions to be attracted to the anode. Conversely, the cathode is negatively charged, causing positively charged cations to be attracted to the cathode. In this example, the aqueous anolyte includes magnesium chloride, which dissolves to form Mg2+ions 232 and Cl’ ions 234. The anolyte also includes H+236 ions, which are formed at the anode by electro-oxidation of water. As a general rule, aqueous anolytes can be chosen to form non- oxidizable ions and avoid production of oxidizable anions (e.g. ClOf, SO42', etc ). The catholyte also includes Mg2+ions and Cl’ ions. The catholyte also includes Fe3+ions 238. These iron ions are reduced at the cathode to form iron metal. The combination of the anode chamber, anolyte, anode, cation exchange membrane, cathode chamber, catholyte, and cathode can be referred to collectively as an electrolytic cell. In this example, the electrolytic cell represents the entire system, but in other examples the system can include additional components.

[0075] The example shown in FIG. 2 has an anode chamber and cathode chamber with an open top. This type of system can be made using an open-top vessel and adding a cation exchange membrane to divide the vessel into two chambers. Alternately, an open-top electrolytic cell can be made with two open-top half-cell vessels that are joined together with the cation exchange membrane between the two half-cell vessels. This is merely one example of the structure of the electrolytic cell, and a variety of other structures can also be used, including closed chambers, microfluidic chambers, and others.

[0076] Furthermore, the example shown in FIG. 2 shows that anode and cathode partially submerged in the anolyte and catholyte, respectively. This is merely one example, and in other examples the anode and cathode can be fully submerged in the anolyte and the catholyte, respectively. The anode and cathode can have a variety of structural forms, include plates, wires, rods, mesh, and others. In some examples, the anode and / or cathode can be positioned partially within the anode chamber and the cathode chamber, respectively. In other examples, the anode and / or cathode can be positioned fully enclosed within the anode chamber and cathode chamber, respectively. In still further examples, the anode and / or cathode can be affixed to, embedded in, or can make up a wall of the anode chamber and cathode chamber, respectively. Any arrangement of the anode and cathode can be used as long as the anode has at least one surface in contact with the anolyte, and as long as the cathode has at least one surface in contact with the catholyte. The anode and cathode can alternatively have two surfaces, three surfaces, or any other number of surface in contact with the anolyte and catholyte, respectively.

[0077] FIG. 3A shows another example iron electrolysis system 300. In this example, iron ore 302 is introduced, in particulate form, directly into the anolyte 312 in the anode chamber 310. This figure shows the system in operation, and as such the figure shows electrons 304 flowing into the cathode 324 and out of the anode 314. An electro-oxidation reaction of water occurs at the anode, which converts water to oxygen gas 316 and H+ions 336. In this example system, the anode chamber includes an oxygen gas outlet 340 above the anode to allow the oxygen gas to escape from the anode chamber. The anode chamber also includes an iron ore inlet 342 configured to receive the iron ore. The iron ore is added to the anolyte, where the iron ore is leached by the anolyte. In particular, the H+ions that are formed at the anode can react with iron oxide in the iron ore to produce iron ions 338 (Fe3+or Fe2+or mixtures thereof, depending on the ore source material,) and water. In the case of Fe3+ions, the Fe3+ions can migrate through the cation exchange membrane 330 to the catholyte 322 in the cathode chamber 320. There, the Fe3+ions can be reduced to iron metal (Fe) 306 at the cathode. These same mechanisms would apply if the iron ore source produced Fe2+ions. The iron metal can form as a plating / coating layer on the cathode or as iron particles, or a combination thereof. As in the previous example, the catholyte and the anolyte also include Mg2+ions 332 and Cl' ions 334.

[0078] While the iron electrolysis system is running, there can be gradient in pH between the anode and the cathode. The pH gradient can be present in the anolyte and the catholyte, starting with a relatively low pH at the anode and increasing to a relatively high pH at the cathode. FIG. 3B shows the example system 300 of FIG. 3A with shading in the anolyte 312 and the catholyte 322 to indicate the pH gradient. The anolyte closest to the anode 314 can have the lowest pH, indicated by dark shading 350. The pH can then gradually increase at positions moving closer and closer to the cathode 324. In this figure, the pH is shown to increase through multiple zones 352, 354, 356, 358, until reaching a maximum pH at the cathode, which is represent by the non-shaded area 360. The low pH at the anode can be useful because in this area the anolyte is acidic, which allows it to leach iron ore and convert iron oxide to Fe3+ions. The higher pH at the cathode can be useful because the hydrogen evolution reaction is less favorable at high pH. Therefore, this unwanted side reaction can be minimized when the pH is higher at the cathode. The increase in pH can be explained by H+ions reacting with iron ore to form Fe3+. This reaction consumes the H+ions, and accordingly the concentration of H+decreases more and more at locations farther from the anode. The iron ore particles and various ions are not shown in FIG. 3B in order to show the pH gradient more clearly. In some examples, the methods of producing iron by direct electrolysis of iron ore can be performed as batch processes. For example, the system shown in FIGs. 3A and 3B can be used in a batch process. In one example, a batch of iron ore can be loaded all at once into the anode chamber. The electrolytic cell can then run for a sufficient time to generate acid in the anolyte to leach the iron ore, forming Fe3+ions, and to reduce the Fe3+ions at the cathode to form iron metal. The electrolytic cell can run until all iron oxide in the iron ore is converted to iron metal, or until a desired fraction of the iron oxide is converted to iron metal. After the system has run for the sufficient time, the iron metal that was produced in the cathode chamber can be recovered and any insoluble solids left over from the iron ore can be removed and discarded or sent to further processing. The anolyte and catholyte can be reused for a subsequent batch, or discarded, or sent to further processing.

[0079] In another example, a method of producing iron by direct electrolysis of iron ore can be performed as a semi -continuous process. Using the system shown in FIGs. 3A and 3B, iron ore can be fed into the anode chamber continuously or periodically. If the iron ore contains insoluble impurities or other insoluble solids, these solids can be removed from the anode chamber either continuously or periodically. When the electrolytic cell is running, iron metal can continuously form at the cathode. As mentioned above, the iron metal can be plated on the cathode surface as a coating, or the iron metal may form particles that are not connected to the cathode. The particles can collect at the bottom of the cathode chamber. The iron metal can be periodically recovered from the cathode chamber. In certain examples, recovering the iron metal can include removing the cathode having iron metal plated on the surface. A new cathode can then be placed into the cathode chamber to replace the iron plated cathode. The anolyte and catholyte are not consumed during the process.

[0080] FIG. 4 shows another example iron electrolysis system 400 that can also be used for batch processes or continuous processes. This system includes an electrolytic cell 401 including an anode chamber 410 fdled with an anolyte 412 and a cathode chamber 420 filled with a catholyte 422. An anode 414 is on one wall of the anode chamber, and a cathode 424 is on one wall of the cathode chamber. A cation exchange membrane 430 separates the anode chamber from the cathode chamber. In this example, iron ore is not loaded into the anode chamber. Instead, a feedstock catholyte storage vessel 440 contains Fe3+ions pre-dissolved in catholyte solution. This feedstock catholyte flows into the cathode chamber, where the Fe3+ions can be reduced to form iron metal 404, e.g. typically coated on the cathode. Used catholyte that has been depleted of Fe3+ions then flows out to a used catholyte storage vessel 442. At the same time, an anolyte storage vessel 444 contains a supply of anolyte solution. The anolyte solution flows into the anode chamber where the pH of the anolyte is reduced by electro-oxidation of water at the anode. This makes the anolyte more acidic. The acidic anolyte is then stored in an acidic anolyte storage vessel 446. In some cases, the acidic anolyte that is stored can subsequently be used to leach iron ore to prepare a solution of Fe3+ions that can be used as the feedstock in a subsequent batch. Additionally, the stored used catholyte can be used as the fresh anolyte in a subsequent batch, in examples where the catholyte and anolyte have the same composition. In this particular example, the anolyte and catholyte both include calcium chloride, which dissolves to from Ca2+ions 432 and Cl’ ions 434, with formation of Ch at the anode (e g. in which case H+is also not generated). In other examples, at least one of the anolyte or the catholyte can include calcium salt, magnesium salt, or combination thereof. In various examples, the anolyte and catholyte can include the same dissolved salts or different dissolved salts, i.e., calcium chloride, magnesium chloride, or other salts.

[0081] In some cases, it can be useful to store acidic anolyte as shown in FIG. 4 and then use the stored acidic anolyte to leach iron ore in a separate process. The leachate can then be used as a feedstock for the electrolysis system shown in FIG. 4. The process of reducing of reducing iron ions to make iron metal may proceed at a different rate than the process of leaching iron ore to make the iron ions. Therefore, when iron ore is leached simultaneously with reducing the iron ions to make iron metal, the overall rate of the process may be limited by leaching or reduction. When the leaching and reduction processes are separated, each process can proceed at its own rate. This can increase overall speed and efficiency in some cases. However, an integrated process that simultaneously leaches iron ore and reduces iron ions can also be useful because of its simplicity and reduced utilization of equipment.

[0082] FIG. 5 illustrates another example iron electrolysis system 500. This example includes a feedstock catholyte storage vessel 540 that provides a catholyte solution 522 containing Fe3+ions to the cathode chamber 520 of an electrolytic cell 501. As in previous examples, a cathode 524 is in contact with the catholyte in the cathode chamber. In this particular example, the cathode is positioned along one wall of the cathode chamber. The Fe3+ions are reduced at the cathode to form iron metal 506. The used catholyte, which has been at least partially depleted of Fe3ions, flows out of the cathode chamber and then is recycled to the anode chamber 510 to be used as anolyte 512. In this example, the catholyte and anolyte can include magnesium chloride or calcium chloride, or a combination thereof. The concentration of the magnesium chloride or calcium chloride can be equivalent in the catholyte and the anolyte, making them usable interchangeably as catholyte and anolyte. As in previous examples, H+ions are produced at the anode 514 by electrooxidation of water. Alternatively, the catholyte and the anolyte can be magnesium sulfate or calcium sulfate in a similar manner. In either case, this reduces the pH of the anolyte, making the anolyte acidic. The acidic anolyte then flows out of the anode chamber into an acidic anolyte storage vessel 546. As in previous examples, a cation exchange membrane 530 separates the anode chamber from the cathode chamber. This membrane can allow cations, such as the Fe3+ions, to cross over the membrane. As in the example of FIG. 4, this example can be used to store acidic anolyte that can be used to leach iron ore. The leachate can then be used as the feedstock catholyte containing iron ions in a subsequent batch.

[0083] FIG. 6 shows another example iron electrolysis system 600 that involves leaching iron ore 602 simultaneously with reducing the iron ions to form iron metal 606. The iron ore is loaded into a leaching vessel 650 that is separate from the electrolytic cell 601. An anolyte 612 is circulated from the anode chamber 610 to the leaching vessel and the back to the anode chamber. While the anolyte is in the anode chamber, the anode 614 reduces the pH of the anolyte by electro-oxidation of water in the anolyte. Thus, the anolyte that flows out of the anode chamber has a lower pH than the anolyte flowing into the anode chamber. The acidic anolyte flows to the leaching vessel, where the acid reacts with iron oxide to form Fe3+ions 638. This reaction also increases the pH of the anolyte. The anolyte flowing out of the leaching vessel has a higher pH and contains Fe3+ions, and this anolyte stream is recycled to the anode chamber. In this example, the Fe3+ions diffuse through the cation exchange membrane 630 into the catholyte 622 in the cathode chamber 620. The Fe3+ions are then reduced at the cathode 624 to form iron metal. This system also includes a waste solids stream 652 that removes insoluble solids that are left over after the iron oxide has been converted to Fe3+ions. A similar example iron electrolysis system 700 is shown in FIG. 7 having anode 714, cathode 724, acidic anolyte 712, catholyte 722, and cation exchange membrane 730 separating the anolyte from the catholyte. This system also includes a leaching vessel 750. The leaching vessel is loaded with iron ore 702 as in the previous example. Acidic anolyte 712 flows into the leaching vessel to convert iron oxide to Fe3+ions 738. This reaction raises the pH of the anolyte. The anolyte with dissolved Fe3+ions then flows out of the leaching vessel to a separate filter unit 760. The filter unit removes undissolved solids from the anolyte and the solids are disposed of in a waste solids stream 752. In other examples, the solids can be processed for other recoverable materials such as other metals. After the anolyte with dissolved Fe3+ions has been filtered, the stream flows directly into the cathode chamber 720. Thus, the anolyte is also used as the catholyte. While in the cathode chamber, the Fe3+ions are reduced to iron metal 706. The catholyte, which has been at least partially depleted of Fe3+ions, is then recycled to the anode chamber and the catholyte is used as the anolyte. If Fe3 1remain in the anolyte, they are able to migrate across the cation exchange membrane 730 into the cathode chamber. In the anode chamber 710, the anolyte again becomes acidic because the H+ions 736 formed at the anode. This process can be run as a continuous process if iron ore is continuously loaded in the leaching vessel.

[0084] Another example iron electrolysis system 800 is shown in FIG. 8. This example includes a feedstock catholyte storage vessel 840 that is connected to the cathode chamber 820. A catholyte 822 having pre-dissolved Fe3+ions 838 flows from the feedstock catholyte storage vessel into the cathode chamber. The Fe3+are reduced at the cathode 824 to form iron metal 806. The catholyte is then recycled to the storage vessel 840. This cycle can continue running as long as Fe3+ions remain in the catholyte. In some examples, the Fe3+ions can be replenished periodically or continuously. While the catholyte flows through the cathode chamber, an anolyte 812 flows through the anode chamber 810. The anolyte becomes more acidic because of the electro-oxidation reaction of water at the anode 814. The acidic anolyte flows out of the anode chamber to a neutralizer 870. The neutralizer increases the pH of the anolyte back to neutral or close to neutral pH. The anolyte is then recycled back to the anode chamber. As in the previous examples, a cation exchange membrane 830 separates the cathode chamber from the anode chamber. In some examples, it can be useful to agitate the anolyte and / or catholyte to increase the mass transfer of Fe3+ions from the anode chamber to the cathode. The agitation can include stirring, shaking, laminar flow, turbulent flow, or other suitable methods of moving the liquid electrolytes. In several of the examples described above, recycle lines carry flowing anolyte or catholyte and continuously recycle these electrolytes. This flowing motion can provide sufficient agitation in some examples. Additionally, the anolyte can be pumped directly into the cathode chamber in some examples, and this can ensure that the Fe3+ions in the anolyte can reach the cathode.

[0085] The cation exchange membranes used in the systems described herein can be positioned in contact with both the anolyte and the catholyte so that ions can migrate from the first electrolyte to the second electrolyte. The cation exchange membrane can also block transfer of some other materials, such as iron ore particles and iron metal particles. In some examples, the cation exchange membrane can be a NAFION cation exchange membrane (available from The Chemours Company, USA) or a DARAMIC porous membrane (available from DARAMIC, USA) which can be useful if the catholyte and anolyte are the same.

[0086] In further detail regarding the anode, the anode can be made from a conductive material that can resist corrosion and oxidation at low pH levels. In some examples, the anode can be made of a metal such as one or more of platinum, gold, silver, copper, zinc, bismuth, tin, copper, indium, lead, stainless steel, nickel, titanium, aluminum, tungsten, or alloys thereof. In other examples, oxidation resistant anode materials can be formed of one or more of platinum, gold, silver, stainless steel, nickel, titanium, aluminum, tungsten, or alloys thereof. Carbon-based materials can also be used, such as glassy carbon, graphite, carbon felt, carbon cloth, carbon paper, porous carbon, activated carbon, or others. The anode can also include a catalyst for the oxygen evolution reaction (i.e., oxidation of water to form oxygen gas). In certain examples, the catalyst can include nickel, platinum, cobalt, ruthenium, palladium, or alloys thereof, or manganese oxide, lead oxide, ruthenium oxide, cobalt oxide, nickel oxide, iron oxide, and iridium oxide or a combination. The combination of anode material and catalyst (if used) can be selected to provide a lower overpotential for the oxygen evolution reaction and good corrosion resistance in the acidic electrolyte. The cathode can also be made of a conductive material. The pH level at the cathode is usually higher than the pH at the anode. However, the pH at the cathode can be slightly acidic, such as in the range of 4 to 5. In some examples, it can be useful to use a cathode material that does not bond to iron metal or form alloys with iron. This can allow iron metal particles formed on the cathode surface to easily detach from the cathode. When the iron metal forms and alloy with the material of the cathode or otherwise bonds to the surface of the cathode, then the iron can build up and form a coating on the cathode that can be difficult to remove. However, in some examples this type of cathode can be used and the iron metal can be removed from the surface of the cathode later by various methods. An iron cathode can be used in some cases, and the electrolysis process can deposit additional iron metal onto the iron cathode. In certain examples, the cathode can be made of a glassy carbon material that does not bond to iron metal. In further examples, the cathode can be made of graphite, carbon felt, carbon cloth, carbon paper, porous carbon, activated carbon, or other carbonbased materials. The cathode can also be made of metal, such as one or more of platinum, gold, silver, copper, zinc, bismuth, tin, indium, lead, stainless steel, nickel, titanium, aluminum, tungsten, or alloys thereof.

[0087] In further examples, the cathode can include iron oxide, and the iron oxide of the cathode can be reduced to iron metal as part of the electrolysis process. In some examples, the cathode can include iron oxide in the form of Fe2O3 or FesCri. The cathode can also include an additive to increase the conductivity of the cathode. For example, the cathode can include carbon mixed with the iron oxide. In certain examples, a ratio of iron oxide to carbon in the cathode can be from about 99: 1 to about 1 : 1, or about 10: 1. The cathode can also include a binder to hold iron oxide and carbon particles together. In certain examples, the binder can include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), NAFION (perfluorosulfonic acid polymer) powder, and the like.

[0088] The cathode surface area can affect the rate at which Fe3+and / or Fe2+ions are reduced to form iron metal. Therefore, the size and surface are of the cathode can be selected depending on the desired rate of iron metal production. In some examples, the cathode can have a reaction area from about 0.01 m2to about 10 m2, or from about 0.1 m2to about 5 m2, or from about 0.2 m2to about 2 m2, or from about 0.5 m2to about 1 m2. The reaction area can be the area of the cathode that is in contact with the catholyte, where Fe3+and / or Fe2+ions can be reduced to iron metal.

[0089] The production rate of the iron electrolysis system can range from about 100 grams of iron metal per day to about 100 kg per day, or from about 1 kg per day to about 50 kg per day, or from about 5 kg per day to about 20 kg per day, in some examples. The desired rate of production of iron metal can also affect the amount of electric current that will be used. In some examples, the methods of producing iron metal can consume a current from about 10 A to about 2,000 A, or from about 100 A to about 1,500 A, or from about 200 A to about 1,000 A, or from about 500 A to about 700 A.

[0090] The methods described herein can also include controlling the pH in the anode chamber and in the cathode chamber. As mentioned above, the pH can be very low near the anode, where the oxygen evolution reaction occurs. For example, the pH at the anode can be less than 1, less than 0, less than -1, or even less than -2. The acidic anolyte that is formed at the anode can have a pH from -2 to 0 in some examples. In examples where fresh anolyte flows into the anode chamber and acidic anolyte flows out of the anode chamber, the acidic anolyte stream can have a pH from about -2 to about 0 and the fresh anolyte stream can have a pH from about 4 to about 6 in some examples. The catholyte can have a higher pH. In some examples, the catholyte can have a pH from about 4 to about 5. In some cases, a pH gradient can exist between the anode and the cathode. The local pH of the anolyte can be lower near the anode and higher near the cation exchange membrane. Similarly, the local pH of the catholyte can be lower near the cation exchange membrane and higher closer to the cathode. The design and operation of the electrolysis reactor can ensure that the pH in the cathode chamber stays in the appropriate range. If the pH is too high, then precipitation of Ca(OH)2 and Fe(OH)s may occur. A low pH can reduce the faradaic efficiency of the iron deposition reaction. To maintain a stable pH in the cathode chamber, any H+that is consumed in the cathode chamber can be replenished by H+migrating from the anode chamber. This can be achieved by balancing H+consumption rate in the cathode chamber, which can be controlled by adjusting the operation current, with H+flux through the membrane, which can be controlled by adjusting pH in the anode chamber and the thickness and / or selectivity of the membrane. In further detail regarding the anolyte and catholyte, in some examples the anolyte and catholyte can be aqueous electrolytes. At least one of the anolyte or the catholyte can include a chloride salt selected from magnesium chloride and calcium chloride, or a combination thereof. In certain examples, both the anolyte and the catholyte can include the same chloride salt. In other examples, the anolyte or catholyte can include a different salt. For example, in some cases the anolyte can include a perchlorate. The perchlorate is an anion that can be paired with a cation to form a salt. In various examples, the anolyte can include a salt such as sodium perchlorate, lithium perchlorate, calcium perchlorate, magnesium perchlorate, manganese perchlorate, or other salts. Other anions include sulfate, nitrate, phosphate, tetraboron fluoride, bis(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, bis(oxalate)borate, bis(fluorosulfonyl(imide, and difluoro(oxalate)borate. The concentration of salt in the anolyte can be from about 0.5 mol / L to about 10 mol / L, or from about 1 mol / L to about 6 mol / L, or from about 3 mol / L to about 5 mol / L. In further examples, the anolyte can also include a buffer agent such as sodium citrate. This can help regulate the pH in the anode chamber.

[0091] The catholyte in the cathode chamber can help to suppress the hydrogen evolution reaction at the cathode. The chloride salt selected from magnesium chloride, calcium chloride, manganese chloride, lithium chloride, sodium chloride, potassium chloride or combinations thereof can be included to help suppress the hydrogen evolution reaction. In some examples, the chloride salt can be present at a concentration such that the cation of the co-salt (e.g., Mg2+, Ca2+, etc.) is at a concentration from about 3 mol / L to about 5 mol / L. In further examples, the concentration of the co-salt cation can be from about 3.5 mol / L to about 5 mol / L, or from about 4 mol / L to about 4.5 mol / L, or from about 4.5 mol / L to about 5 mol / L, or from about 4.3 mol / L to about 4.7 mol / L. The anolyte can also include a chloride salt (the same salt or a different salt than in the catholyte) at a concentration within these ranges.

[0092] In further examples, the catholyte and / or anolyte can also include a salt having an anion such as bromide, iodide, or a multiatomic anion, such as sulfate, perchlorate, nitrate, phosphate, bis(trifluoromethanesulfonimide), trifluoromethanesulfonate, acetate, tetraboron fluoride, or a combination thereof. In further examples, the multiatomic anion can include a multi-dentate anion. For example, multi-dentate anions can be used such as, but not limited to, oxalate(C2O42'), sulfate (SCL2-), mesylate (CHsSQf), and the like. In further examples, the catholyte can also include a buffer agent such as one or more of sodium citrate, sodium malonate, sodium ascorbate, sodium acetate, and the like. This can help to regulate the pH in the cathode chamber. In another example, one or both of the anolyte and catholyte can consist essentially of water, iron ions, and the chloride salt selected from magnesium chloride, calcium chloride, or a combination thereof.

[0093] In some examples, the anolyte and catholyte can be at a relatively low temperature while the iron metal is being produced (much lower than the high temperatures used to melt iron and iron ore in some other production methods). The temperature of the first and second electrolytes can be from about 0 °C to about 150 °C in some examples, from 25 °C to 150 °C in some examples, or from about 25 °C to about 90 °C, or from about 25 °C to about 50 °C, or from about 50 °C to about 90 °C in other examples. In some cases, using higher temperatures, such as around 90 °C can increase the dissolution rate of iron ore and the rate of diffusion of ions in the electrolysis cell. On the other hand, heating the materials to a higher temperature can also increase the energy consumption of the process. However, the relatively low temperatures used in the methods described herein can save a significant amount of energy compared to other processes. By comparison, the blast furnace process and the molten oxide electrolysis process both utilize temperatures over 1500 °C. Direct reduction of iron processes often uses temperatures from about 800 °C to about 1200 °C. Thus, the methods described herein use much lower temperatures and this can save significantly on energy costs.

[0094] The faradaic efficiency of the process described herein can be from about 80% to about 99.9%, or from about 90% to about 99.9%, or from about 95% to about 99.9%, or from about 95% to about 99%, in some examples. These levels of faradaic efficiency can be higher than other processes that utilize electricity to reduce iron. Electrowinning processes have had a faradaic efficiency in the range of about 86% to about 97%. Molten oxide electrolysis processes have had even lower faradaic efficiency in the range of about 34% to about 46%. Therefore, the methods described herein also save costs of electricity and reduce undesired side reactions that would lower the faradaic efficiency.

[0095] The experimental results described below utilized an operating current of around 50 mA / cm2, referring to the total electric current divided by the surface area of the cathode on which the iron reduction reaction occurred. However, the operating current can be increased in scaled-up processes. In some examples, the operating current used in the methods described herein can be from about 100 mA / cm2to about 1,000 mA / cm2or from about 500 mA / cm2to about 1,000 mA / cm2. The operating current can be proportionate to the rate at which iron metal is produced. In some examples, the rate of mass transfer of Fe3+and / or Fe2+ions to the cathode can also affect the rate of iron production. The methods can include controlling the rate of Fe3+and / or Fe2+ions mass transfer to the cathode so that this rate matches the rate at which the Fe3+and / or Fe2+ions is reduced (which is controlled by the operating current). As explained above, this can involve adjusting the dissolution rate of iron ore in the anode chamber, agitating the electrolytes, selecting the cation exchange membrane thickness, and other parameters.

[0096] The total energy cost of producing iron metal using the methods described herein can be lower than many previous processes. The theoretical minimum energy needed to produce iron metal from Fe2C>3 (a common iron ore) is about 1.84 kWh / kg. This is based on the free energy different between Fe20a and Fe metal. In practice, the methods described herein can have an energy cost from about 2 kWh / kg to about 10 kWh / kg, or from about 2.5 kWh / kg to about 5 kWh / kg, or from about 2.5 kWh / kg to about 3 kWh / kg, or less than 2.7 kWh / kg in some examples. By comparison, the blast furnace process uses about 4.98 kWh / kg of iron metal; the direct reduction of iron process uses about 3.5 to 5.5 kWh / kg of iron metal; the molten oxide electrolysis process uses about 2.78 to about 4.63 kWh / kg of iron metal; and electrowinning process uses about 3.6 kWh / kg.

[0097] In the methods described herein, the energy cost can be affected by the distance between the anode and cathode, as well as the overpotential of the anode for the oxygen evolution reaction. Resistance between the anode and cathode can be reduced by moving the anode and cathode closer together, increasing the conductivity of the electrolytes, and increasing operation temperature. The overpotential of the anode can be reduced by increasing the anode surface area, selecting effective anode catalysts, and increasing the operating temperature. As an example, the wherein the anode and cathode can be separated by a distance from about 0.1 cm to about 10 cm, 2 cm to about 10 cm, or from 0.1 cm to 2 cm, or from 10 cm to 50cm.

[0098] The types of iron ore used as feedstock for the methods described herein can include any iron-oxide-containing ore or iron-sulfide-containing ore. Several examples include hematite, magnetite, goethite, limonite, siderite, wustite, pyrite, or a combination thereof. Iron oxide compounds in the ore can include FezCh, Fe(OH)O, FeaC , FeO, and others. Iron sulfide compounds in ore can include FeS, FeS2, FesS4, and others. Many iron ores include a small fraction (3.9-6.0%) of non-Fe impurities. Typical Fe ore contains the oxide of K, Ti, P, Al, Mn, Si, Cu, Mg, and Ca as impurities. Among them, the oxide of Al and Si (i.e., alumina and silica) are resistant to the corrosion of acid. Therefore, they can be removed from the system by periodically separating the insoluble solids, which can be done by including a flowing channel to the anode chamber to allow any solid particles to be flushed out and collected. The oxide of Ca can dissolve into the electrolyte and produce Ca2+, but the Ca2ions are not likely to affect the process, especially when the electrolyte includes calcium salt already. The oxide of Mn can dissolve and produce Mn ions. Since the reduction potential of Mn2+(-1.18 V vs SHE) is much lower than that of Fe2+(-0.44V vs SHE), it is unlikely that Mn will be reduced together with Fe. It is expected that Ca2+, Mg2+and Ti3+would exhibit similar properties. However, upon long-duration operation, an increasing amount of Mn2+can build up and may increase electrolyte viscosity and decrease conductivity. Therefore, these ions can be removed from the electrolyte. This can be accomplished by periodically precipitating Mn2+by adding base (such as NaOH), organic ligands (such as bipyridine) or natural zeolite. The oxide of phosphorous can dissolve into the electrolyte and form phosphoric acid, which will can gradually increase the pH of the electrolyte and reduce the faradic efficiency. The phosphoric acid can be removed from the electrolyte by adding Ca2, which can precipitate the phosphate anion as calcium phosphate.

[0099] The iron ore can be introduced into the anode chamber or a separate leaching vessel as particles. In various examples, the iron ore can have an average particle size from about 1 micrometer to about 5 mm, or from about 1 micrometer to about 1 mm, or from about 10 micrometers to about 1 mm, or from about 100 micrometers to about 1 mm, or from about 10 micrometers to about 100 micrometers. As a guideline, the raw iron ore can be mechanically ground to the desired particle size. The particle size can be tuned to match the dissolution rate of iron ore with the iron deposition rate. The rate at which the iron ore particles are fed can depend on the size of the reactor and the desired rate of iron production. In some examples, the iron ore can be fed into the electrolysis reactor at a rate from about 5 kg / day to about 100 kg / day, or from about 10 kg / day to about 100 kg / day. If the process is a continuous process, then iron ore particles can be introduced continuously or semi- continuously into the system. The methods described herein can also be performed as a batch process. A batch of a desired amount of iron ore can be loaded in the anode chamber or leaching vessel and then the entire batch can be converted to iron metal over an operating time period. As a general guideline, the iron ore can have a mole fraction of iron oxide of 90% to 95%, or 80% to 95%, or 60-95%.

[0100] The iron metal forming at the cathode can form as an iron coating on the cathode or solid particles that separate from the cathode. In some examples, the average particle size of the iron metal can be from about 1 micrometer to about 5 mm, or from about 1 micrometer to about 1 mm, or from about 10 micrometers to about 1 mm, or from about 100 micrometers to about 1 mm, or from about 10 micrometers to about 100 micrometers.

[0101] Certain methods of producing iron metal can also include a bioleaching step. Bioleaching can involve utilizing microorganisms to extract iron ions from minerals. For example, bacteria can be used to extract iron from iron ore. In certain examples, the iron ore can include pyrite (FeSz), and the bioleaching step can include using bacteria to convert the pyrite to Fe2+and / or Fe3+ions, while the sulfur can be converted to sulfuric acid. The Fe2+and Fe3+ions extracted in this way can then be reduced to form iron metal using electrolysis as described above.

[0102] In further examples, additional steps can be performed in the method, such as prereducing Fe3+ions to Fe2+ions before introducing the Fe2+ions into the electrolysis cell. This pre-reduction can be accomplished, in certain examples, by adding additional iron ore to a leach solution containing Fe3+ions. Other steps that may be performed in the method can include pre-treatment to remove impurities before electrolysis and post-treatment to remove impurities after electrolysis.

[0103] One example method of producing iron 900 is illustrated in FIG. 9. In this method, pyrite (FeS2) is fed to a bio-leaching step. In this step, air, carbon dioxide, and water are also present and bacteria can grow and extract Fe3+ions from the pyrite. This step produces a leaching solution comprising the Fe3+ions, H+ions, SO42-ions, and impurities. The leaching solution is then subjected to a pre-reduction step in which the Fe3+ions are reduced to Fe2+ions. The leaching solution is then subject to a pre-treatment step to remove a portion of impurities. In this example, copper is removed in the pre-treatment step. The leaching solution is then subjected to electrolysis using any of the systems or methods described above. The electrolysis step converts the Fe2+ions to iron metal. The process also produces sulfuric acid and the remaining solution can be post-treated to remove additional impurities. In this example, the additional impurities include zinc and manganese. These steps can be performed in separate reaction vessels in some examples. In other examples, one or more of these steps can be performed together in a single vessel. These steps can be performed continuously or in a batch configuration.

[0104] Example 1: Electrochemical Reactor

[0105] A test reactor was constructed with two glass chambers. Similar to the configuration of FIG. 5, the first chamber was filled with an aqueous anolyte and an anode was partially submerged in the anolyte. The anolyte included calcium perchlorate (Ca(C104)2) at a concentration of 4.5 mol / L. The anode was a platinum wire. The second glass chamber was filled with an aqueous catholyte and a cathode was partially submerged in the catholyte. The catholyte included FeCL salt at a concentration of 0.1 mol / L and CaCL salt at a concentration of 4.5 mol / L. The cathode was titanium foil. The distance between the anode and the cathode was about 6 cm. The glass chambers were separated by a NAFION cation exchange membrane (available from The Chemours Company, USA), with the anolyte in contact with the cation exchange membrane on one side and the catholyte in contact with the cation exchange membrane on the opposite side.

[0106] Iron ore powder was added to the anode chamber. Initially, the anolyte in the anode chamber was clear and the catholyte in the cathode chamber was yellow due to the presence of Fe3+ions in the catholyte. An electrolysis reaction was then started using a potentiostat connected to the anode and cathode. The electric current used for electrolysis was about 50 mA per square centimeter of cathode area. The temperature in the reactor during electrolysis was about 25 °C. After 4 hours of electrolysis, oxygen bubbles formed on the anode and the anolyte had become slightly yellow due to the formation of Fe3+ions from dissolving the iron ore. The catholyte had changed color to slightly greenish, due to the formation of iron metal and Fe2+ions by reducing Fe3+ions. After 24 hours of electrolysis, the anolyte had become very yellow. The catholyte had become mostly clear, except for a slight yellow color near the cation exchange membrane. Black iron metal powder covered the cathode and additional iron powder settled to the bottom of the cathode chamber. This indicates that Fe3+ions formed by dissolving the iron ore were migrating through the cation exchange membrane, and then being converted to iron metal at the cathode. In this experiment, the iron ore was converted to iron metal with a faradaic efficiency of 80-90%. It is noted that this is much higher than the faradaic efficiency of electrolysis of iron in an acidic electrolyte (such as a common Fe2(SO4)3 electrolyte, which usually has a faradaic efficiency of 2-8% with hydrogen evolution reaction dominating the cathodic reaction. The black powder formed on the titanium foil cathode was confirmed to be iron by X-ray diffraction.

[0107] Example 2: Bench-top electrolysis system in batch mode

[0108] A bench-top electrolysis system is constructed with dimensions of 10 cm* 10 cm *4 cm, with two cylindrical chambers of 5 cm in diameter and 1.4 cm in length. The interelectrode distance can be adjusted from 4 mm to 23 mm using a 3D-printed electrode holder. The body of the electrolyzer is made of acrylic and the cell is held together by two aluminum end plates. Electrolysis in batch and continuous modes using different feedstocks, including reagent-grade Fe oxide and two different Fe ores, is studied. In the baseline experiment of the batch-mode operation, 0.3 M Fe3+was pre-dissolved into the electrolyte as the feedstock. Electrolysis was performed at 30 mA / cm2for 1 hour, corresponding to 25% utilization of the total dissolved Fe3+. The cell voltage showed an initial nucleation bump, and then the voltage gradually stabilizes to about 3.2 V. The catholyte pH decreases to -0.35, and the anolyte changes from near neutral to acidic (pH = -1) due to the H+produced from OER. A dense deposit was observed on the Ti cathode, which was confirmed to be highly pure Fe (> 99%) by XRD. Based on the weight of the deposited Fe, the faradic efficiency and the energy consumption can be calculated. For the baseline experiment (Bl), the faradic efficiency and energy consumption are 98.9% and 4.6 kWh / kg-Fe, respectively.

[0109] In the baseline system, 4.5 M MgCE is added into the catholyte to enable an electrolyte with a very large C17Fe3+ratio far exceeding three, the stoichiometry of FeCh. Such electrolytes are termed anion-rich electrolytes herein. Such anion-rich electrolytes can suppress HER, promote Fe deposition reaction, and significantly increase Fe deposition efficiency to >99%. Experimental results suggest that 4.5 M Mg or Ca salts show the best enhancement among these tested support salts. A control experiment using a regular electrolyte with 1 M NaCl support salt was performed to highlight the role of the anion-rich electrolyte. Under the same electrolysis condition, the faradic efficiency of this control system is poor (only 41.5%) due to the substantial HER reaction. Such a remarkable difference in efficiency highlights the role of the anion-rich electrolyte in achieving high efficiency ironmaking in acidic electrolytes.

[0110] In the electrolysis process, the applied current density determines both the throughput per electrode size (thus scalability) and energy consumption. A higher current generally results in more reactions per unit of time, leading to increased Fe production and elevating energy consumption. Additionally, mass transfer of Fe3+can become limiting at high currents, resulting in more side reactions and consequent reduced efficiency. Here, the current effect is examined in a range of 3.3 to 1000 mA / cm2. By reducing the current density to 3.3 mA / cm2(B3), the voltage reduces to 1.62 V. For a net reaction, 4FeCl3+6H2O=4Fe+3O2+12HCl (4Fe3++6H2O=4Fe+3O2+12H+), the standard electromotive force (EMF) has been calculated as 1.65 V. This suggests that at such a low current, the overpotential (reaction overpotential, ohmic overpotential and concentration overpotential) is negligible and the system is close to thermodynamic equilibrium. Consequently, the energy consumption is 2.7 kWh / kg-Fe, only 14% more than the thermodynamic limit (2.36 kWh / kg-Fe). However, at such a low current, the faradaic efficiency reduces to 86.1%, likely a result of the comproportionating reaction between the deposited Fe and Fe3+in the solution (2Fe3++Fe=3Fe2+).

[0111] On the other hand, when increasing the current to 1000 mA / cm2, the voltage rises to about 12 V. Meanwhile, efficiency increases to 100.5%, suggesting that the high current results in a high local pH and, consequently, the precipitation of Fe(OH)3. This is evidenced by the orange precipitation observed on the Fe deposit and further confirmed by XRD. As a result, the purity of the Fe deposits decreases to 86%. In addition, unlike the compact morphology obtained at 30 mA / cm2, the deposited Fe shows a much more porous morphology. To prevent Fe(OH)3precipitation, Ca salt is employed as the supporting salt instead of Mg salt because its solution has a lower pH and a higher conductivity. The image of the deposit and XRD confirm that with Ca support salt, electrolysis can be done at 1000 mA / cm2with a highly pure Fe deposit (>99%) with no Fe(OH)3. The efficiency is slightly reduced to 95.7%, which could be explained by the powdery Fe deposit that tends to fall off, thus leading to an underestimate of the Fe deposit weight. Meanwhile, the energy consumption increases to 17.1 kWh / kg-Fe due to the high voltage (with Mg salt). These results demonstrate that the methods described herein can produce high purity Fe with very good efficiency (>95%).

[0112] For any ironmaking process to be practical, a factor is its tolerance to impurities in Fe ores. Natural Fe ores contain various impurities that can alter the system's chemistry and potentially cause the process to fail. The effect of highly soluble impurities, such as K+, Na+, and Ca2+, is examined in the batch mode experiment because they are most prone to dissolve into the electrolyte with high concentration during Fe ore leaching. The effect of other possible impurities will be examined in the continuous mode experiment. In a control experiment, 10 mM of K+, Na+, and Ca2+are added to the electrolyte. The efficiency slightly decreases to 97.3%, possibly due to the error caused by scale, and the voltage remains unchanged. The Fe deposit does not adhere to the Ti substrate as effectively as in the baseline experiment B 1. XRD confirms that the bulk of the deposit consists of only Fe with no alloys of Na, K, Mg, or Ca. The energy dispersive X-ray spectroscopy (EDX) shows a small fraction of Mg and Cl (less than 1 atom%) due to surface adsorption. These results suggest that highly soluble alkali and alkaline earth metal impurities do not co-deposit with Fe and enter the deposited product.

[0113] In summary, in the batch-mode electrolysis, it was demonstrated that (1) by using the anion-rich electrolyte, the iron electrolysis system shows lower energy consumption and better efficiency than state-of-the-art (SOA) acid system (98.9 %@ 30 mA / cm2, 4.6 kWh / kg- Fe); (2) the energy consumption can be as low as 2.7 kWh / kg-Fe by reducing the current to 3.3 mA / cm2; (3) it can support very high electrolysis current (1000 mA / cm2) with high efficiency (>95%) and high Fe deposit purity (>99%); and (4) it can still produce highly pure Fe deposit (>99%) with the presence of alkali and alkali earth impurities.

[0114] Example 3: Bench-top electrolysis system in continuous mode

[0115] Commercial scalability is particularly useful for ironmaking processes. Continuous operation can be used to achieve good scalability. Therefore, the electrolysis system was tested in a continuous mode. The batch-mode experiment demonstrates that after one hour of electrolysis, H+accumulates in the anolyte, which reduces the anolyte pH to -1 — 2. During long-term operation, H+in the anolyte gradually migrates into the cathode chamber, which reduces the catholyte pH and compromises the Fe deposition Faradaic efficiency. At the near 100% efficiency shown in the baseline experiment, three moles of H+are generated in the anolyte for every mole of Fe deposited. By using the produced H+to leach Fe ore in real-time in a continuous operation, it is possible to achieve three aims simultaneously: (1) preventing H+from accumulation in the system, thus avoiding the consequent enhancement of HER side reaction at the cathode; (2) liberating Fe3+from Fe ore, replenishing the consumed Fe3+, and therefore sustaining the Fe deposition reaction during extended electrolysis; and (3) intensifying the process by integrating leaching with electrowinning. During the leaching process, the acid-insoluble impurities like Si O2 can be filtered out after electrolysis, and acidsoluble impurities (e g., AI2O3, MgO) will stay in the electrolyte and can be treated for further use after electrolysis. The anolyte is continuously circulated into a mixer-settler during electrolysis, where it is mixed with Fe ore particles. The mixer-settler acts as a leaching vessel. In the mixer-settler, H+reacts with Fe ore and liberates Fe3+(3H++ 0.5 Fe2O3=Fe3++1.5H2O). The H+depleted stream is then returned to the anode chamber to supply Fe3+into the electrolyzer.

[0116] In the baseline experiment, no Fe oxide is added into the mixer-settler so that all the Fe3+in the catholyte is pre-dissolved. Electrolysis was performed at 10 mA / cm2for 1 hour, corresponding to 100% utilization of the pre-dissolved Fe3+. Since Fe deposition consumes Fe3+in the catholyte, Fe3+concentration in the electrolyte gradually decreases. Meanwhile, the anolyte pH decreases significantly from 6.35 to -1.37 after 1 hour, and the migration of H+into the cathode chamber reduces the catholyte pH from 0.95 to 0.61. Due to the reduced pH and gradually depleted Fe3+, the cathode reaction selectivity shifts toward HER, resulting in a low faradaic efficiency of 47.9%.

[0117] Introducing Fe2Os particles into the mixer-settler significantly mitigates the drop in anolyte pH, ensuring it remains above -1 throughout the entire five-hour electrolysis period. This also leads to a lower cell voltage due to the reduced overpotential of OER at higher pH levels. Unlike the baseline experiment, the catholyte pH gradually increases to ~3.5 due to HER. Consequently, the first-hour average efficiency is 90.9%, much higher than the baseline. After three hours of electrolysis, the average efficiency drops to 84.2%. This is likely a result of Fe3+depletion because the Fe oxide dissolution rate is slower than the Fe deposition rate. Nevertheless, an average efficiency of more than 84.0% is maintained throughout the five-hour electrolysis. The anolyte pH decreases during electrolysis but stabilizes around -0.7. Based on the weight of the Fe deposit and the pre-dissolved Fe3+in the electrolyte, 74.5% of Fe in the deposit comes from Fe2Ch, indicating the successful conversion of Fe2Os to Fe metal.

[0118] Next, two types of real Fe ores are used as feedstock: a Fe ore concentrate and a Utah Fe ore. The former consists mainly of magnetite, and the latter consists of hematite and goethite. The acid-soluble components in these ores are identified by inductively coupled plasma atomic emission spectroscopy (ICP-AES), and insoluble components are identified by XRD. The main impurities in Fe ore concentrate are EU2O3 and MgO, and AI2O3 and SiCE in Utah Fe ore. After one hour of electrolysis using these Fe ores as the feedstock, the pH of the anolyte is higher than that of the baseline, suggesting the consumption of Hldue to Fe ore dissolution. The average faradaic efficiency of the first hour exceeds that of the baseline, implying that Fe3+from the Fe ores compensates for the consumption of Fe3+. The anolyte pH remains lower than that observed when reagent-grade Fe2O3 was added, indicating a much slower dissolution rate of the actual Fe ores compared to reagent-grade Fe2O3. In contrast to experiments with reagent-grade Fe2Oi, the voltage increases and the efficiency drops to 34-38% after five-hour electrolysis, suggesting the depletion of Fe3+during extended electrolysis. The low efficiency indicates significant HER, which is consistent with the pH increase in the catholyte. Despite the fact that the leaching of Fe ore is much slower than the electro-reduction of Fe3+from the electrolyte, the anolyte pH never drops below -2, confirming that Fe ore can curtail pH drop in the anolyte. The Fe deposits show only very thin layers of Fe on Ti compared to the experiment with reagent-grade Fe2C .

[0119] In summary, by integrating Fe deposition with Fe ore leaching, the in-situ generated H+from OER can be harvested to dissolve Fe ore and produce Fe3+, which not only sustains the electrolysis reaction during long-duration operation but also prevents the generated H+from crossing over into the catholyte and reduces faradaic efficiency. However, the leaching rate is slower than the electro-reduction rate of Fe3+under the test condition, especially for real Fe ores. As a result, integrating leaching with Fe deposition only slows down the efficiency deterioration but does not prevent it. This can be addressed by decoupling leaching from electrodeposition, as discussed in the next example.

[0120] Example 4: Continuous ironmaking using pre-prepared leach solution as the feed

[0121] To address the mismatch between the slow leaching rate and the electrodeposition rate observed in the previous example, continuous-mode operation was conducted using preprepared leach solution of the Fe ores as the feedstock. The Fe ore is first leached in a continuous-stirring reactor. Any acid-insoluble impurities were filtered after leaching and then the leach solution was fed into the cathode chamber of the electrolyzer. The electrolyzer produces Fe in the cathode chamber, and O2 and H+in the anode chamber. The in-situ generated acid can be recirculated back to the leaching step, thereby closing the chemical loop. This experiment focuses on the electrolysis step, in which the pre-prepared leach solution is stored in an external container and pumped into the electrolyzer as a catholyte. In the meantime, the anolyte is circulated into the electrolyzer from an external tank, where the produced H+ is collected and stored for Fe ore leaching. In the baseline experiment, an impurity -free leach solution from reagent-grade Fe2Ch was used as the feedstock and electrolysis was conducted at 30 mA / cm2for 5 hours. The anolyte pH decreases significantly from near neutral to below -2 upon electrolysis due to the continuous production of H+, resulting in increasing cell voltage due to the higher OER overpotential. Meanwhile, the catholyte pH first increases due to HER and peaks after three hours of electrolysis then starts to decrease due to H+cross-over from the anolyte. The efficiency increases from 81.4% gradually to close to 100% in the first 5 hours, which is attributed to the increasing pH. A highly pure Fe deposit (>99%) is obtained.

[0122] Electrolysis at a higher current was performed to test the scalability. At 100 mA / cm2, the catholyte pH decreases to -1.2 V gradually. Meanwhile, a small amount of brown precipitate can be observed on the surface of the deposited Fe, which is confirmed to be Fe(OH)3 by XRD. As a result, the purity of the Fe deposit decreases to 88%. Since Fe(OH)3 forms at pH>2, higher than the observed average pH (-1.4), the Fe(OH)3 formation is due to the high local pH around the cathode. Further increasing the current to 300 mA / cm2, a similar phenomenon is observed with a Fe deposit purity of 85%. By increasing the catholyte flow rate to 150 ml / min to enhance the mass transfer in the catholyte, such local pH gradient can be minimized so that the precipitation of Fe(OH)a can be avoided. Consequently, a high efficiency of 91-99% is achieved with a highly pure Fe deposit (>98%).

[0123] Impurity tolerance was studied by using the aforementioned two different Fe ores. They are first dissolved in acid to create the leach solution, which is then used in continuous ironmaking. The pH of both the anolyte and catholyte exhibited a more gradual decline compared to those observed in the baseline experiment and the experiments with increased current above, which could be attributed to the residual solid in the leaching solution that can continuously react with H+. A lower cell voltage and a higher faradaic efficiency are observed, resulting in lower energy consumption. Overall, no significant effect of impurities on Fe deposition was observed. SiO2 in the Fe ores is insoluble in acid. Therefore, they do not enter the electrolyte and pose any influence on Fe deposition. Acid-soluble impurities, such as Eu, Mg, and Al, were not observed in the deposits, as evidenced by the XRD result, which can be explained by the fact that the reduction potentials of Eu, Mg, Ca, and Al are significantly lower than that of Fe. Highly pure Fe deposit was obtained (> 99%) with a high efficiency of 90-99.7%.

[0124] In summary, using a leach solution of Fe ore as feedstock, it was demonstrated that (1) the iron electrolysis system can continuously produce Fe with a high efficiency of close to 100%; (2) electrolyte pH management is useful to maintain the high efficiency and high purity of Fe deposits. Long-duration operation leads to a very high concentration of H+in the anolyte, which tends to migrate into the cathode chamber, steers reaction selectivity toward HER and reduces faradaic efficiency. High-current operation tends to create a high local pH at the cathode, leading to hydroxide precipitation, which can be solved by increasing the flow rate; and (3) the efficiency, energy consumption and purity of Fe deposits are not affected by the impurities (SiCh, AI2O3, MgO, EU2O3, ThCh and CaO) in the Fe ores.

[0125] Example 5: Electrolyte design

[0126] The previous examples mainly discuss how process parameters (current, flow rate, the types of feedstocks) affect the ironmaking performance (voltage, efficiency, energy consumption). This example includes experiments related to the composition of the anolyte and catholyte. The composition of the electrolytes can affect their conductivity and pH and governs the faradaic efficiency of Fe deposition. In acidic electrolytes, the cathodic reaction can be dominated by HER with a low Fe deposition efficiency (41.5%) when using regular electrolytes. Adding 4.5 M MgCh / CaCh into the catholyte can significantly suppress HER and the efficiency can be boosted to >98%.

[0127] The use of perchlorate and chloride were compared in the anolyte. In Example 1, ClOf salt was is used in the anolyte to ensure the anode reaction is OER. OER is kinetically difficult in acidic electrolytes, leading to large overpotential and high energy consumption. In a control experiment, chloride salt is used in the anolyte so that chlorine evolution reaction (CER) occurs as the anode reaction. Due to the more facile kinetics of CER in an acidic solution, the average voltage decreases from 3.2V to 2.3V and the efficiency slightly increases to 99.7% due to higher pH in both catholyte and anolyte (CER does not produce protons), which reduces the energy consumption to 3.2 kWh / kg-Fe.

[0128] Chloride was compared to sulfate in the catholyte. In the electro-metallurgy industry, sulfate electrolyte is more commonly used due to its lower corrosivity compared to chloride. Switching both the catholyte and anolyte to a sodium sulfate system results in an efficiency of 30.1% and a voltage of 3.1. With 2.5M MgSO4 as the support salt, the efficiency increases to 81.4% and the voltage decreases to 4.3V. Due to the low solubility of MgSO4, it is impossible to increase the supporting salt concentration further. A control experiment in a chloride system with 2.5M MgCh shows that the chloride system has a higher efficiency of 94.1% and a lower voltage of 3.2V, suggesting Cl’ better suppresses HER and promotes Fe deposition.

[0129] The concentration of the salt in the anolyte and catholyte can affect the Faradaic efficiency. Efficiency increases from 81.4% with 2.5M CaCE to 99.3% for 4.5M CaCE, while voltage only increases slightly from 2.9 V by 14.7% to 3.3V.

[0130] Example 6: Batch reaction comparisons

[0131] A series of electrolysis experiments were run in batch mode using Fe2<93 as a feedstock, leached with acid to form a leaching solution. In a first experiment, the electrolysis was run at varying voltage and current density using an anolyte comprising Ca(C104)2 to directly produce O2 from the anode. This experiment was repeated with an anolyte comprising CaCh to directly produce Ch from the anode as an alternative pathway. The relationship between voltage and current density for both of these experiments is shown in FIG. 10.

[0132] To test the effect of changing the concentration of calcium in the electrolyte, experiments were performed with two different concentrations of the calcium salts in the electrolyte. The efficiency and voltage that were recorded in the experiments with the low calcium concentration and the high calcium concentration are shown in the graph of FIG. 11. In this case, a low Ccameans 2.5M CaCh catholyte and 2.5M Ca(C104)2 anolyte, while a high Cca is 4.5M where the catholyte and anolyte have different salts but same concentration to maintain the balance of osmotic pressure.

[0133] Experiments were also performed with the normal electrolyte and then repeated with an electrolyte having impurities dissolved therein. FIG. 12 shows a graph of the efficiency and voltage obtained using the normal (baseline) electrolyte and the electrolyte with dissolved impurities.

[0134] To compare cathode materials, an experiment was performed using a titanium cathode and then the experiment was repeated with a stainless steel cathode. The efficiency and voltage achieved in these experiments are shown in the graph of FIG. 13.

[0135] The separator material was also varied. An experiment was run with a NAFION™ membrane, and the experiment was repeated with a filter paper membrane. The efficiency and voltage achieved in these experiments are shown in the graph of FIG. 14.

[0136] Additionally, FIG. 15 shows an EDX analysis of the iron deposits obtained in the test with the dissolved impurities. FIG. 16 shows an SEM image of the iron deposits. FIG. 17 shows an XRD analysis of the iron deposits.

[0137] Example 7: Continuous operation using low-grade ore as feedstock

[0138] A continuous system was set up similar to the system shown in FIG. 8. A low-grade ore was leached to form a leaching solution, which was placed in a catholyte storage tank. The ore included 63.3 mass% Fe, 32 mass% O, 4 mass% Si, 0.84 mass% Al, and 0.02 mass% other elements. An anolyte was placed in an anolyte storage tank. The continuous process was run for 1 hr at a time at different current densities. This experiment was repeated, once with a regular electrolyte (1 M support salt concentration) and once with an anion-rich electrolyte (4.5 M support salt concentration). The relationship between efficiency and current density of these experiments is shown in the graph of FIG. 18. The same system was then run for 5 hours with the anion-rich electrolyte in constant-current electrolysis at 30 mA / cm2. FIG. 19 shows a graph of the efficiency vs. time and voltage vs. time during the 5 hours. The average efficiency was 97.6%. The iron produced after 5 hours was 99.5 mass% Fe and 0.5 mass% other elements.

[0139] Example 8: Comparison of voltage and current density

[0140] Two experiments were run with different voltages and current densities. The first was run at 4.4 V with a current density of 100 mA / cm2. The second was run at 1.6 V with a current density of 30 mA / cm2. The first experiment (4.4 V) produced iron with a purity greater than 99%, with an efficiency of 91%-99% (varying over the 5-hour run time). The total energy used was 6.7 kWh / kg-Fe. FIG. 20 shows an XRD analysis of the iron produced in the first experiment. FIG. 21 shows an EDX analysis of the iron produced in the first experiment. FIG. 22 shows a SEM image of the iron produced in the first experiment. FIG. 23 shows a graph of efficiency and the pH of the anolyte vs. time during the first experiment. In the second experiment (1.6 V), the purity of the iron produced was also greater than 99%. the efficiency was greater than 98%. The total energy used was 1.62 kWh / kg-Fe. FIG. 24 shows an XRD analysis of the iron produced in the second experiment. FIG. 25 shows an EDX analysis of the iron produced in the second experiment. FIG. 26 shows a SEM image of the iron produced in the second experiment. FIG. 27 shows a graph of efficiency and the pH of the anolyte vs. time during the second experiment.

[0141] Example 9: FesC cathode

[0142] An electrolysis cell was constructed with a cathode made from a 10:1 mixture of Fe3<D4 and Ketjenblack (Kej) Carbon with a PTFE binder. The anode in the cell was platinum. The catholyte included 4.5 M CaCh and the anolyte included 4.5 M Ca(C104)2. The current used was 50 mA and the voltage was about 20 V. The Kej Carbon increased the conductivity of the FesO4, but voltage was still very high. The reaction kinetics were slow, and the reaction was continued for 24 hrs. Example 10: FezO; cathode

[0143] Another electrolysis cell was consutructed similar to Example 9, but with a cathode made from a 10: 1 mixture of FezCh and Kej Carbon with a PTFE binder. This cell was run for 24 hrs at about 20 V with a current of 50 mA. After the reaction, the catholyte had a pH of -0.87 and the anolyte had a pH of -1.65. In this experiment, it was found that the dissolution rate of FezCh was fast. It is unknown whether the FezCE dissolves first and then the iron ions are reduced to make iron metal, or if the FezCh is directly reduced without dissolving. It is also possible that the FezCh dissolves and is reduced at the same time. In any case, the FezC cathode was able to be converted to Fe metal in this cell. A white precipitate was found after the reaction, which could be Ca(OH)z or PTFE.

[0144] Additional Examples

[0145] The technology described herein can include the following enumerated examples:

[0146] 1. An iron electrolysis system, comprising: an anode chamber containing an aqueous anolyte; a cathode chamber containing an aqueous catholyte comprising an iron ion; a cation-exchange membrane separating the anode chamber from the cathode chamber, wherein the cation-exchange membrane is in contact with the anolyte and the catholyte and allows transfer of the iron ion through the cation-exchange membrane; an anode in contact with the anolyte; and a cathode in contact with the catholyte, wherein the anolyte, catholyte, or both comprises magnesium salt, calcium salt, or a combination thereof.

[0147] 2. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anolyte and catholyte both comprise the magnesium salt, calcium salt, or combination thereof.

[0148] 3. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the magnesium salt is magnesium chloride, magnesium sulfate, magnesium perchlorate, magnesium nitrate, or combinations thereof, and the calcium salt is calcium chloride, calcium sulfate, calcium perchlorate, calcium nitrate, or a combination thereof. 4. The system of claim 3, wherein the anolyte, catholyte, or both comprises the magnesium chloride, magnesium perchlorate, calcium chloride, calcium perchlorate, or combination thereof at a concentration of 3 molar to 5 molar based on cation concentration.

[0149] 5. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anolyte comprises magnesium perchlorate, calcium perchlorate, or a combination thereof and wherein the catholyte comprises magnesium chloride, calcium chloride, lithium chloride, or a combination thereof.

[0150] 6. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anode chamber further comprises an iron ore inlet configured to receive iron ore to be leached by the anolyte in the anode chamber.

[0151] 7. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising an acidic anolyte storage vessel connected to an outlet of the anode chamber.

[0152] 8. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising a leaching vessel connected to anode chamber or the cathode chamber, the leaching vessel having an iron ore inlet and a leaching acid inlet.

[0153] 9. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the leaching acid inlet is connected to an outlet of the anode chamber to receive acidic anolyte from the anode chamber for use as the leaching acid.

[0154] 10. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising a recycle line connecting an outlet of the leaching vessel to an inlet of the anode chamber to recycle iron -ion-containing anolyte from the leaching vessel to the anode chamber. 11. The system of any of examples 1 -19 or the method of any of examples 20-41, further comprising a feedstock line connecting an outlet of the leaching vessel to an inlet of the cathode chamber to input iron-ion-containing anolyte into the cathode chamber for use as the catholyte.

[0155] 12. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising a filter connected to an outlet of the leaching vessel to filter solid particles from a leach solution flowing out of the leaching vessel.

[0156] 13. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising a leach solution vessel connected to an inlet of the cathode chamfber to input pre-prepared leach solution containing an iron ion into the cathode chamber for use as the catholyte.

[0157] 14. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising a neutralizer having an inlet connected to an outlet of the anode chamber to receive acidic anolyte and an outlet connected to an inlet of the anode chamber to recycle neutralized anolyte from the neutralizer to the anode chamber.

[0158] 15. The system of any of examples 1-19 or the method of any of examples 20-41, wherein a pH gradient is present in the cathode chamber and the anode chamber during operation, wherein a pH of the anolyte at the anode is from -2 to 0 and wherein a pH of the catholyte at the cathode is from 1 to 5.

[0159] 16. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anode comprises a metal selected from the group consisting of: platinum, lead, and combinations thereof.

[0160] 17. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the cathode comprises a metal selected from the group consisting of: titanium, stainless steel, and combinations thereof. 18. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the cathode comprises iron oxide.

[0161] 19. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anode chamber further comprises an oxygen gas outlet.

[0162] 20. A method of producing iron by direct electrolysis of iron ore, comprising: reducing a pH of an aqueous anolyte by electro-oxidation of water at an anode in contact with the anolyte, wherein a cation-exchange membrane separates the anolyte from an aqueous catholyte, wherein the anolyte, catholyte, or both comprises magnesium salt, calcium salt, or a combination thereof; introducing iron ions into one or both of the anolyte and the catholyte; and reducing the iron ions to form iron metal at a cathode in contact with the catholyte.

[0163] 21. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anolyte and catholyte both comprise the magnesium salt, calcium salt, or combination thereof.

[0164] 22. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the magnesium salt is magnesium chloride, magnesium sulfate, magnesium perchlorate, magnesium nitrate, or combinations thereof, and the calcium salt is calcium chloride, calcium sulfate, calcium perchlorate, calcium nitrate, or a combination thereof.

[0165] 23. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anolyte, catholyte, or both comprises the magnesium chloride, magnesium perchlorate, calcium chloride, calcium perchlorate, or combination thereof at a concentration of 3 molar to 5 molar based on cation concentration.

[0166] 24. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anolyte comprises magnesium perchlorate, calcium perchlorate, or a combination thereof and wherein the catholyte comprises magnesium chloride, calcium chloride, or a combination thereof

[0167] 25. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the iron ions are introduced into the anolyte by leaching iron ore in the anolyte.

[0168] 26. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anolyte is contained in an anode chamber and the iron ore is loaded directly into the anode chamber.

[0169] 27. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the method is performed as a batch process.

[0170] 28. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anolyte is contained an anode chamber and a leaching vessel connected to the anode chamber, wherein the iron ore is loaded into the leaching vessel to leach the iron ore in the leaching vessel.

[0171] 29. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising pumping the anolyte having the reduced pH from the anode chamber into the leaching vessel.

[0172] 30. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising pumping the anolyte having leached iron ions therein from the leaching vessel into the anode chamber.

[0173] 31. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising pumping the anolyte having leached iron ions therein from the leaching vessel into a cathode chamber for use as the catholyte. 32. The system of any of examples 1 -19 or the method of any of examples 20-41, further comprising filtering the anolyte having leached iron ions therein from the leaching vessel.

[0174] 33. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising pumping the anolyte having the reduced pH into a storage vessel and storing the anolyte before leaching the iron ore.

[0175] 34. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the iron ions are introduced into the catholyte by transferring the iron ions from the anolyte to the catholyte through the cation-exchange membrane.

[0176] 35. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the iron ions are introduced into the catholyte by pumping a pre-prepared leach solution contain an iron ion into a cathode chamber for use as the catholyte.

[0177] 36. The system of any of examples 1-19 or the method of any of examples 20-41, further comprising pumping the anolyte having the reduced pH from an anode chamber to a neutralizer to neutralize the anolyte, and recycling the neutralized anolyte from the neutralizer to the anode chamber.

[0178] 37. The system of any of examples 1-19 or the method of any of examples 20-41, wherein a pH gradient is present between the cathode and the anode, wherein a pH of the anolyte at the anode is from -2 to 0 and wherein a pH of the catholyte at the cathode is from 1 to 5.

[0179] 38. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the method comprises substantially no net consumption of material other than iron ore.

[0180] 39. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the anolyte and the catholyte have a temperature from 20 °C to 90 °C. 40. The system of any of examples 1 -19 or the method of any of examples 20-41, wherein the iron metal is produced at an energy cost from 2.7 kWh / kg Fe to 5 kWh / kg Fe.

[0181] 41. The system of any of examples 1-19 or the method of any of examples 20-41, wherein the cathode comprises iron oxide and wherein the method further comprises reducing the iron oxide of the cathode to form iron metal.

[0182] While the flowcharts presented for this technology may imply a specific order of execution, the order of execution may differ from what is illustrated. For example, the order of two more blocks may be rearranged relative to the order shown. Further, two or more blocks shown in succession may be executed in parallel or with partial parallelization. In some configurations, one or more blocks shown in the flow chart may be omitted or skipped.

[0183] Reference was made to the examples illustrated in the drawings and specific language was used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the technology is thereby intended. Alterations and further modifications of the features illustrated herein and additional applications of the examples as illustrated herein are to be considered within the scope of the description.

[0184] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more examples. In the preceding description, numerous specific details were provided, such as examples of various configurations to provide a thorough understanding of examples of the described technology. It will be recognized, however, that the technology may be practiced without one or more of the specific details, or with other methods, components, devices, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the technology.

[0185] Although the subject matter has been described in language specific to structural features and / or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements may be devised without departing from the spirit and scope of the described technology.

Claims

CL IMSWhat is claimed is:

1. An iron electrolysis system, comprising: an anode chamber containing an aqueous anolyte; a cathode chamber containing an aqueous catholyte comprising an iron ion; a cation-exchange membrane separating the anode chamber from the cathode chamber, wherein the cation-exchange membrane is in contact with the anolyte and the catholyte and allows transfer of the iron ion through the cation-exchange membrane; an anode in contact with the anolyte; and a cathode in contact with the catholyte, wherein the anolyte, catholyte, or both comprises magnesium salt, calcium salt, or a combination thereof.

2. The system of claim 1, wherein the anolyte and catholyte both comprise the magnesium salt, calcium salt, or combination thereof.

3. The system of claim 1, wherein the magnesium salt is magnesium chloride, magnesium sulfate, magnesium perchlorate, magnesium nitrate, or combinations thereof, and the calcium salt is calcium chloride, calcium sulfate, calcium perchlorate, calcium nitrate, or a combination thereof.

4. The system of claim 3, wherein the anolyte, catholyte, or both comprises the magnesium chloride, magnesium perchlorate, calcium chloride, calcium perchlorate, lithium chloride, or combination thereof at a concentration of 3 molar to 5 molar based on cation concentration.

5. The system of claim 3, wherein the anolyte comprises magnesium perchlorate, calcium perchlorate, or a combination thereof and wherein the catholyte comprises magnesium chloride, calcium chloride, or a combination thereof.

6. The system of claim 1, wherein the anode chamber further comprises an iron ore inlet configured to receive iron ore to be leached by the anolyte in the anode chamber.

7. The system of claim 1, further comprising an acidic anolyte storage vessel connected to an outlet of the anode chamber.

8. The system of claim 1, further comprising a leaching vessel connected to anode chamber or the cathode chamber, the leaching vessel having an iron ore inlet and a leaching acid inlet.

9. The system of claim 8, wherein the leaching acid inlet is connected to an outlet of the anode chamber to receive acidic anolyte from the anode chamber for use as the leaching acid.

10. The system of claim 9, further comprising a recycle line connecting an outlet of the leaching vessel to an inlet of the anode chamber to recycle iron-ion-containing anolyte from the leaching vessel to the anode chamber.

11. The system of claim 9, further comprising a feedstock line connecting an outlet of the leaching vessel to an inlet of the cathode chamber to input iron-ion-containing anolyte into the cathode chamber for use as the catholyte.

12. The system of claim 8, further comprising a filter connected to an outlet of the leaching vessel to filter solid particles from a leach solution flowing out of the leaching vessel.

13. The system of claim 1, further comprising a leach solution vessel connected to an inlet of the cathode chamber to input pre-prepared leach solution containing an iron ion into the cathode chamber for use as the catholyte.

14. The system of claim 1, further comprising a neutralizer having an inlet connected to an outlet of the anode chamber to receive acidic anolyte and an outlet connected to an inlet of the anode chamber to recycle neutralized anolyte from the neutralizer to the anode chamber.

15. The system of claim 1, wherein a pH gradient is present in the cathode chamber and the anode chamber during operation, wherein a pH of the anolyte at the anode is from -2 to 0 and wherein a pH of the catholyte at the cathode is from 1 to 5.

16. The system of claim 1, wherein the anode comprises a metal selected from the group consisting of: platinum, lead, and combinations thereof.

17. The system of claim 1, wherein the cathode comprises a metal selected from the group consisting of: titanium, stainless steel, and combinations thereof.

18. The system of claim 1, wherein the cathode comprises iron oxide.

19. The system of claim 1, wherein the anode chamber further comprises an oxygen gas outlet.

20. A method of producing iron by direct electrolysis of iron ore, comprising: reducing a pH of an aqueous anolyte by electro-oxidation of water at an anode in contact with the anolyte, wherein a cation-exchange membrane separates the anolyte from an aqueous catholyte, wherein the anolyte, catholyte, or both comprises magnesium salt, calcium salt, or a combination thereof; introducing iron ions into one or both of the anolyte and the catholyte; and reducing the iron ions to form iron metal at a cathode in contact with the catholyte.

21. The method of claim 20, wherein the anolyte and catholyte both comprise the magnesium salt, calcium salt, lithium salt, or combination thereof.

22. The method of claim 20, wherein the magnesium salt is magnesium chloride, magnesium sulfate, magnesium perchlorate, magnesium nitrate, or combinations thereof, and the calcium salt is calcium chloride, calcium sulfate, calcium perchlorate, calcium nitrate, or a combination thereof.

23. The method of claim 22, wherein the anolyte, catholyte, or both comprises the magnesium chloride, magnesium perchlorate, calcium chloride, calcium perchlorate, or combination thereof at a concentration of 3 molar to 5 molar based on cation concentration.

24. The method of claim 22, wherein the anolyte comprises magnesium perchlorate, calcium perchlorate, or a combination thereof and wherein the catholyte comprises magnesium chloride, calcium chloride, or a combination thereof25. The method of claim 20, wherein the iron ions are introduced into the anolyte by leaching iron ore in the anolyte.

26. The method of claim 25, wherein the anolyte is contained in an anode chamber and the iron ore is loaded directly into the anode chamber.

27. The method of claim 26, wherein the method is performed as a batch process.

28. The method of claim 25, wherein the anolyte is contained an anode chamber and a leaching vessel connected to the anode chamber, wherein the iron ore is loaded into the leaching vessel to leach the iron ore in the leaching vessel.

29. The method of claim 28, further comprising pumping the anolyte having the reduced pH from the anode chamber into the leaching vessel.

30. The method of claim 28, further comprising pumping the anolyte having leached iron ions therein from the leaching vessel into the anode chamber.

31. The method of claim 28, further comprising pumping the anolyte having leached iron ions therein from the leaching vessel into a cathode chamber for use as the catholyte.

32. The method of claim 28, further comprising filtering the anolyte having leached iron ions therein from the leaching vessel.

33. The method of claim 25, further comprising pumping the anolyte having the reduced pH into a storage vessel and storing the anolyte before leaching the iron ore.

34. The method of claim 20, wherein the iron ions are introduced into the catholyte by transferring the iron ions from the anolyte to the catholyte through the cation-exchange membrane.

35. The method of claim 20, wherein the iron ions are introduced into the catholyte by pumping a pre-prepared leach solution contain an iron ion into a cathode chamber for use as the catholyte.

36. The method of claim 20, further comprising pumping the anolyte having the reduced pH from an anode chamber to a neutralizer to neutralize the anolyte, and recycling the neutralized anolyte from the neutralizer to the anode chamber.

37. The method of claim 20, wherein a pH gradient is present between the cathode and the anode, wherein a pH of the anolyte at the anode is from -2 to 0 and wherein a pH of the catholyte at the cathode is from 1 to 5.

38. The method of claim 20, wherein the method comprises substantially no net consumption of material other than iron ore.

39. The method of claim 20, wherein the anolyte and the catholyte have a temperature from 20 °C to 90 °C.

40. The method of claim 20, wherein the iron metal is produced at an energy cost from 2.7 kWh / kg Fe to 5 kWh / kg Fe.

41. The method of claim 20, wherein the cathode comprises iron oxide and wherein the method further comprises reducing the iron oxide of the cathode to form iron metal.

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