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WO2025245086A1 - Production de fer par électrolyse directe de minerai de fer - Google Patents

Production de fer par électrolyse directe de minerai de fer

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Publication number
WO2025245086A1
WO2025245086A1 PCT/US2025/030158 US2025030158W WO2025245086A1 WO 2025245086 A1 WO2025245086 A1 WO 2025245086A1 US 2025030158 W US2025030158 W US 2025030158W WO 2025245086 A1 WO2025245086 A1 WO 2025245086A1
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WO
WIPO (PCT)
Prior art keywords
anolyte
iron
catholyte
cathode
anode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/US2025/030158
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English (en)
Inventor
Tao Gao
Jing Liu
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University of Utah Research Foundation Inc
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University of Utah Research Foundation Inc
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Filing date
Publication date
Application filed by University of Utah Research Foundation Inc filed Critical University of Utah Research Foundation Inc
Publication of WO2025245086A1 publication Critical patent/WO2025245086A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21B—MANUFACTURE OF IRON OR STEEL
    • C21B15/00—Other processes for the manufacture of iron from iron compounds
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C1/00—Electrolytic production, recovery or refining of metals by electrolysis of solutions
    • C25C1/06—Electrolytic production, recovery or refining of metals by electrolysis of solutions or iron group metals, refractory metals or manganese
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/02—Electrodes; Connections thereof

Definitions

  • Iron 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.
  • 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).
  • BF- BOF blast furnace-basic oxygen furnace
  • Some other processes have been used to directly reduce iron ore to iron metal sponge via a solid-state process using a reducing gas.
  • 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.
  • 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.
  • 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.
  • 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.
  • FIGs. 3A and 3B are side cross-sectional schematic views of another example iron ore electrolysis system, in accordance with the present disclosure.
  • FIG. 4 is a side cross-sectional schematic view of an example iron ore electrolysis system, in accordance with the present disclosure.
  • FIG. 5 is a side cross-sectional schematic view of another example iron ore electrolysis system, in accordance with the present disclosure.
  • FIG. 6 is a side cross-sectional schematic view of yet another example iron ore electrolysis system, in accordance with the present disclosure.
  • FIG. 7 is a side cross-sectional schematic view of another example iron ore electrolysis system, in accordance with the present disclosure.
  • FIG. 8 is a side cross-sectional schematic view of still another example iron ore electrolysis system, in accordance with the present disclosure.
  • FIG. 9 is a flowchart illustrating an example method of producing iron, in accordance with the present disclosure.
  • FIG. 10 is a graph of voltage vs. current density in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 11 is graph of efficiency and voltage in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 12 is a graph of efficiency and voltage in another example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 13 is a graph of efficiency and voltage in another example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 14 is a graph of efficiency and voltage in another example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 15 is an EDX analysis of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.
  • 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.
  • FIG. 18 is a graph of efficiency vs. current density in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 19 is a graph of efficiency and voltage vs. time in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 20 is an XRD analysis of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 21 is an EDX analysis of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 22 is a SEM image of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 23 is a graph of anolyte pH and efficiency vs. time in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 24 is an XRD analysis of iron obtained in another example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 25 is an EDX analysis of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 26 is a SEM image of iron obtained in an example iron electrolysis system, in accordance with the present disclosure.
  • FIG. 27 is a graph of anolyte pH and efficiency vs. time in an example iron electrolysis system, in accordance with the present disclosure.
  • “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.
  • 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.
  • 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.
  • 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%.
  • 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.
  • 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 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.
  • 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.
  • 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/cm 2 .
  • the high operation temperature (often greater than 1,538 °C) can result in significant energy inefficiency due to heat loss.
  • 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.
  • molten salt electrolyte such as halide or carbonate
  • Using molten salt electrolyte 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.
  • 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.
  • the reaction rate is restricted to about 0.1 A/cm 2 , 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.
  • 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.
  • 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. Fe 3+ and/or Fe 2+ ions). The reduction of Fe 3+ and/or Fe 2+ 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 Fe 3+ and Fe 2+ 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.
  • the methods of producing iron metal described herein involve electrolyzing iron ore in acidic electrolyte.
  • 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 Fe 3+ or Fe 2+ .
  • 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.
  • 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.
  • the magnesium salt can include magnesium chloride, magnesium sulfate, magnesium perchlorate, magnesium nitrate, or combinations thereof.
  • the calcium salt can include calcium chloride, calcium sulfate, calcium perchlorate, calcium nitrate, or a combination thereof.
  • 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 Fe 3+ and/or Fe 2+ 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.
  • 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.
  • 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.
  • 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 Fe 3+ ions are reduced to form Fe solid metal.
  • Equation (IV) The overall reaction that occurs in the electrochemical reactor is shown as Equation (IV) below:
  • 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.
  • 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 Fe 3 1 ions.
  • the concentration of H 1 ions can be lower than at the anode and the concentration of Fe 3 ions can be higher than at the anode.
  • 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 Fe 3+ ions.
  • the cathode chamber can contain a specific type of electrolyte that can further suppress HER.
  • this electrolyte can include a salt of magnesium or calcium or lithium, in particular magnesium chloride or calcium chloride or lithium chloride.
  • other salts can be suitable.
  • 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.
  • 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%.
  • 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.
  • the methods described herein can be performed using an iron electrolysis system that includes the components described in the method.
  • 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.
  • FIG. 2 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.
  • the anode 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.
  • the aqueous anolyte includes magnesium chloride, which dissolves to form Mg 2+ ions 232 and Cl’ ions 234.
  • the anolyte also includes H + 236 ions, which are formed at the anode by electro-oxidation of water.
  • aqueous anolytes can be chosen to form non- oxidizable ions and avoid production of oxidizable anions (e.g. ClOf, SO4 2 ', etc ).
  • the catholyte also includes Mg 2+ ions and Cl’ ions.
  • the catholyte also includes Fe 3+ 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.
  • the electrolytic cell represents the entire system, but in other examples the system can include additional components.
  • 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.
  • 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.
  • FIG. 2 shows that anode and cathode partially submerged in the anolyte and catholyte, respectively.
  • the anode and cathode can have a variety of structural forms, include plates, wires, rods, mesh, and others.
  • the anode and/or cathode can be positioned partially within the anode chamber and the cathode chamber, respectively.
  • the anode and/or cathode can be positioned fully enclosed within the anode chamber and cathode chamber, respectively.
  • 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.
  • FIG. 3A shows another example iron electrolysis system 300.
  • 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.
  • 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.
  • the H + ions that are formed at the anode can react with iron oxide in the iron ore to produce iron ions 338 (Fe 3+ or Fe 2+ or mixtures thereof, depending on the ore source material,) and water.
  • the Fe 3+ ions can migrate through the cation exchange membrane 330 to the catholyte 322 in the cathode chamber 320. There, the Fe 3+ ions can be reduced to iron metal (Fe) 306 at the cathode.
  • the iron metal can form as a plating/coating layer on the cathode or as iron particles, or a combination thereof.
  • the catholyte and the anolyte also include Mg 2+ ions 332 and Cl' ions 334.
  • 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.
  • 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 Fe 3+ 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 Fe 3+ .
  • the methods of producing iron by direct electrolysis of iron ore can be performed as batch processes.
  • the system shown in FIGs. 3A and 3B can be used in a batch process.
  • 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 Fe 3+ ions, and to reduce the Fe 3+ 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.
  • a method of producing iron by direct electrolysis of iron ore can be performed as a semi -continuous process.
  • 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.
  • iron metal can continuously form at the cathode.
  • 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.
  • 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.
  • 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
  • a cathode 424 is on one wall of the cathode chamber.
  • a cation exchange membrane 430 separates the anode chamber from the cathode chamber.
  • iron ore is not loaded into the anode chamber. Instead, a feedstock catholyte storage vessel 440 contains Fe 3+ ions pre-dissolved in catholyte solution.
  • This feedstock catholyte flows into the cathode chamber, where the Fe 3+ ions can be reduced to form iron metal 404, e.g. typically coated on the cathode.
  • Used catholyte that has been depleted of Fe 3+ ions then flows out to a used catholyte storage vessel 442.
  • 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.
  • the acidic anolyte that is stored can subsequently be used to leach iron ore to prepare a solution of Fe 3+ ions that can be used as the feedstock in a subsequent batch.
  • 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.
  • the anolyte and catholyte both include calcium chloride, which dissolves to from Ca 2+ ions 432 and Cl’ ions 434, with formation of Ch at the anode (e g. in which case H + is also not generated).
  • At least one of the anolyte or the catholyte can include calcium salt, magnesium salt, or combination thereof.
  • the anolyte and catholyte can include the same dissolved salts or different dissolved salts, i.e., calcium chloride, magnesium chloride, or other salts.
  • 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.
  • 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 Fe 3+ ions to the cathode chamber 520 of an electrolytic cell 501.
  • a cathode 524 is in contact with the catholyte in the cathode chamber.
  • the cathode is positioned along one wall of the cathode chamber. The Fe 3+ ions are reduced at the cathode to form iron metal 506.
  • the used catholyte which has been at least partially depleted of Fe 3 ions, flows out of the cathode chamber and then is recycled to the anode chamber 510 to be used as anolyte 512.
  • 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.
  • H + ions are produced at the anode 514 by electrooxidation of water.
  • 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.
  • a cation exchange membrane 530 separates the anode chamber from the cathode chamber. This membrane can allow cations, such as the Fe 3+ ions, to cross over the membrane.
  • 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.
  • 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.
  • 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 Fe 3+ 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 Fe 3+ ions, and this anolyte stream is recycled to the anode chamber.
  • the Fe 3+ ions diffuse through the cation exchange membrane 630 into the catholyte 622 in the cathode chamber 620.
  • the Fe 3+ 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 Fe 3+ ions.
  • FIG. 7 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 Fe 3+ ions 738. This reaction raises the pH of the anolyte.
  • the anolyte with dissolved Fe 3+ 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.
  • the solids can be processed for other recoverable materials such as other metals.
  • the stream flows directly into the cathode chamber 720.
  • the anolyte is also used as the catholyte.
  • the Fe 3+ ions are reduced to iron metal 706.
  • the catholyte which has been at least partially depleted of Fe 3+ ions, is then recycled to the anode chamber and the catholyte is used as the anolyte.
  • Fe 3 1 remain 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.
  • FIG. 8 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 Fe 3+ ions 838 flows from the feedstock catholyte storage vessel into the cathode chamber.
  • the Fe 3+ 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 Fe 3+ ions remain in the catholyte. In some examples, the Fe 3+ 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.
  • 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 Fe 3+ 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.
  • recycle lines carry flowing anolyte or catholyte and continuously recycle these electrolytes. This flowing motion can provide sufficient agitation in some examples.
  • the anolyte can be pumped directly into the cathode chamber in some examples, and this can ensure that the Fe 3+ ions in the anolyte can reach the cathode.
  • 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.
  • 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.
  • the anode can be made from a conductive material that can resist corrosion and oxidation at low pH levels.
  • 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.
  • 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).
  • 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.
  • the pH at the cathode can be slightly acidic, such as in the range of 4 to 5.
  • 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.
  • the cathode can be made of a glassy carbon material that does not bond to iron metal.
  • 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.
  • 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.
  • 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.
  • the cathode can include carbon mixed with the iron oxide.
  • 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.
  • the binder can include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), NAFION (perfluorosulfonic acid polymer) powder, and the like.
  • the cathode surface area can affect the rate at which Fe 3+ and/or Fe 2+ 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.
  • the cathode can have a reaction area from about 0.01 m 2 to about 10 m 2 , or from about 0.1 m 2 to about 5 m 2 , or from about 0.2 m 2 to about 2 m 2 , or from about 0.5 m 2 to about 1 m 2 .
  • the reaction area can be the area of the cathode that is in contact with the catholyte, where Fe 3+ and/or Fe 2+ ions can be reduced to iron metal.
  • 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.
  • 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.
  • the methods described herein can also include controlling the pH in the anode chamber and in the cathode chamber.
  • the pH can be very low near the anode, where the oxygen evolution reaction occurs.
  • 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.
  • 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.
  • the catholyte can have a pH from about 4 to about 5.
  • 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.
  • 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.
  • 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.
  • 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.
  • both the anolyte and the catholyte can include the same chloride salt.
  • the anolyte or catholyte can include a different salt.
  • the anolyte can include a perchlorate.
  • the perchlorate is an anion that can be paired with a cation to form a salt.
  • the anolyte can include a salt such as sodium perchlorate, lithium perchlorate, calcium perchlorate, magnesium perchlorate, manganese perchlorate, or other salts.
  • anions include sulfate, nitrate, phosphate, tetraboron fluoride, bis(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, bis(oxalate)borate, bis(fluorosulfonyl(imide, and difluoro(oxalate)borate.
  • 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.
  • the anolyte can also include a buffer agent such as sodium citrate. This can help regulate the pH in the anode chamber.
  • 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.
  • the chloride salt can be present at a concentration such that the cation of the co-salt (e.g., Mg 2+ , Ca 2+ , etc.) is at a concentration from about 3 mol/L to about 5 mol/L.
  • 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.
  • 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.
  • the multiatomic anion can include a multi-dentate anion.
  • multi-dentate anions can be used such as, but not limited to, oxalate(C2O4 2 '), sulfate (SCL 2- ), mesylate (CHsSQf), and the like.
  • 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.
  • 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.
  • 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.
  • heating the materials to a higher temperature can also increase the energy consumption of the process.
  • the relatively low temperatures used in the methods described herein can save a significant amount of energy compared to other processes.
  • 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.
  • the methods described herein use much lower temperatures and this can save significantly on energy costs.
  • 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.
  • the experimental results described below utilized an operating current of around 50 mA/cm 2 , referring to the total electric current divided by the surface area of the cathode on which the iron reduction reaction occurred.
  • the operating current can be increased in scaled-up processes.
  • the operating current used in the methods described herein can be from about 100 mA/cm 2 to about 1,000 mA/cm 2 or from about 500 mA/cm 2 to about 1,000 mA/cm 2 .
  • the operating current can be proportionate to the rate at which iron metal is produced.
  • the rate of mass transfer of Fe 3+ and/or Fe 2+ ions to the cathode can also affect the rate of iron production.
  • the methods can include controlling the rate of Fe 3+ and/or Fe 2+ ions mass transfer to the cathode so that this rate matches the rate at which the Fe 3+ and/or Fe 2+ 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.
  • 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 is about 1.84 kWh/kg. This is based on the free energy different between Fe20a and Fe metal.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the oxide of Al and Si i.e., alumina and silica
  • the oxide of Ca can dissolve into the electrolyte and produce Ca 2+ , but the Ca 2 ions 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.
  • Mn 2+ (-1.18 V vs SHE) is much lower than that of Fe 2+ (-0.44V vs SHE)
  • base such as NaOH
  • organic ligands such as bipyridine
  • 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 Ca 2 , which can precipitate the phosphate anion as calcium phosphate.
  • the iron ore can be introduced into the anode chamber or a separate leaching vessel as particles.
  • 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.
  • 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.
  • 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.
  • the iron ore can have a mole fraction of iron oxide of 90% to 95%, or 80% to 95%, or 60-95%.
  • the iron metal forming at the cathode can form as an iron coating on the cathode or solid particles that separate from the cathode.
  • 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.
  • Certain methods of producing iron metal can also include a bioleaching step.
  • Bioleaching can involve utilizing microorganisms to extract iron ions from minerals.
  • bacteria can be used to extract iron from iron ore.
  • the iron ore can include pyrite (FeSz), and the bioleaching step can include using bacteria to convert the pyrite to Fe 2+ and/or Fe 3+ ions, while the sulfur can be converted to sulfuric acid.
  • the Fe 2+ and Fe 3+ ions extracted in this way can then be reduced to form iron metal using electrolysis as described above.
  • additional steps can be performed in the method, such as prereducing Fe 3+ ions to Fe 2+ ions before introducing the Fe 2+ ions into the electrolysis cell.
  • This pre-reduction can be accomplished, in certain examples, by adding additional iron ore to a leach solution containing Fe 3+ 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.
  • FIG. 9 One example method of producing iron 900 is illustrated in FIG. 9.
  • pyrite FeS2
  • FeS2 pyrite
  • air, carbon dioxide, and water are also present and bacteria can grow and extract Fe 3+ ions from the pyrite.
  • This step produces a leaching solution comprising the Fe 3+ ions, H + ions, SO4 2- ions, and impurities.
  • the leaching solution is then subjected to a pre-reduction step in which the Fe 3+ ions are reduced to Fe 2+ ions.
  • the leaching solution is then subject to a pre-treatment step to remove a portion of impurities.
  • 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 Fe 2+ ions to iron metal.
  • the process also produces sulfuric acid and the remaining solution can be post-treated to remove additional impurities.
  • the additional impurities include zinc and manganese.
  • 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.
  • NAFION cation exchange membrane available from The Chemours Company, USA
  • 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 Fe 3+ 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 Fe 3+ ions from dissolving the iron ore.
  • the catholyte had changed color to slightly greenish, due to the formation of iron metal and Fe 2+ ions by reducing Fe 3+ 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 Fe 3+ 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%.
  • Example 2 Bench-top electrolysis system in batch mode
  • 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 Fe 3+ was pre-dissolved into the electrolyte as the feedstock. Electrolysis was performed at 30 mA/cm 2 for 1 hour, corresponding to 25% utilization of the total dissolved Fe 3+ .
  • the cell voltage showed an initial nucleation bump, and then the voltage gradually stabilizes to about 3.2 V.
  • 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.
  • 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 Fe 3+ can become limiting at high currents, resulting in more side reactions and consequent reduced efficiency.
  • the current effect is examined in a range of 3.3 to 1000 mA/cm 2 . By reducing the current density to 3.3 mA/cm 2 (B3), the voltage reduces to 1.62 V.
  • 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.
  • the iron electrolysis system shows lower energy consumption and better efficiency than state-of-the-art (SOA) acid system (98.9 %@ 30 mA/cm 2 , 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/cm 2 ; (3) it can support very high electrolysis current (1000 mA/cm 2 ) 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.
  • SOA state-of-the-art
  • Example 3 Bench-top electrolysis system in continuous mode
  • 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.
  • the H + depleted stream is then returned to the anode chamber to supply Fe 3+ into the electrolyzer.
  • the anolyte pH decreases during electrolysis but stabilizes around -0.7. Based on the weight of the Fe deposit and the pre-dissolved Fe 3+ in the electrolyte, 74.5% of Fe in the deposit comes from Fe2Ch, indicating the successful conversion of Fe2Os to Fe metal.
  • a Fe ore concentrate 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 H l due to Fe ore dissolution.
  • the average faradaic efficiency of the first hour exceeds that of the baseline, implying that Fe 3+ from the Fe ores compensates for the consumption of Fe 3+ .
  • 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.
  • the voltage increases and the efficiency drops to 34-38% after five-hour electrolysis, suggesting the depletion of Fe 3+ during extended electrolysis.
  • the low efficiency indicates significant HER, which is consistent with the pH increase in the catholyte.
  • the in-situ generated H + from OER can be harvested to dissolve Fe ore and produce Fe 3+ , 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.
  • the leaching rate is slower than the electro-reduction rate of Fe 3+ under the test condition, especially for real Fe ores.
  • 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.
  • Example 4 Continuous ironmaking using pre-prepared leach solution as the feed
  • 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.
  • the anolyte is circulated into the electrolyzer from an external tank, where the produced H+ is collected and stored for Fe ore leaching.
  • an impurity -free leach solution from reagent-grade Fe2Ch was used as the feedstock and electrolysis was conducted at 30 mA/cm 2 for 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.
  • 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.
  • 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
  • Acid-soluble impurities such as Eu, Mg, and Al
  • 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%.
  • 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.
  • 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.
  • 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%.
  • Example 2 The use of perchlorate and chloride were compared in the anolyte.
  • 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.
  • 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.
  • Chloride was compared to sulfate in the catholyte.
  • 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.
  • 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.
  • 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.
  • a series of electrolysis experiments were run in batch mode using Fe2 ⁇ 93 as a feedstock, leached with acid to form a leaching solution.
  • 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.
  • a low Cc a means 2.5M CaCh catholyte and 2.5M Ca(C104)2 anolyte
  • a high Cca is 4.5M where the catholyte and anolyte have different salts but same concentration to maintain the balance of osmotic pressure.
  • FIG. 12 shows a graph of the efficiency and voltage obtained using the normal (baseline) electrolyte and the electrolyte with dissolved impurities.
  • the separator material was also varied. An experiment was run with a NAFIONTM 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.
  • 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.
  • Example 7 Continuous operation using low-grade ore as feedstock
  • 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.
  • 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.
  • 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.
  • 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.
  • 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
  • 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.
  • 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.
  • magnesium salt is magnesium chloride, magnesium sulfate, magnesium perchlorate, magnesium nitrate, or combinations thereof
  • the calcium salt is calcium chloride, calcium sulfate, calcium perchlorate, calcium nitrate, or a combination thereof.
  • 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.
  • 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.
  • 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.
  • magnesium salt is magnesium chloride, magnesium sulfate, magnesium perchlorate, magnesium nitrate, or combinations thereof
  • the calcium salt is calcium chloride, calcium sulfate, calcium perchlorate, calcium nitrate, or a combination thereof.
  • 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.

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Abstract

Un système d'électrolyse de fer (200) peut comprendre une chambre anodique (210) contenant un anolyte aqueux (212), une chambre cathodique (220) contenant un catholyte aqueux (222), et une membrane échangeuse de cations (230) séparant la chambre anodique de la chambre cathodique. Le catholyte peut comprendre un ion fer (238). La membrane échangeuse de cations peut être en contact avec l'anolyte et le catholyte et peut permettre le transfert de l'ion fer à travers la membrane échangeuse de cations. Une anode (214) peut être en contact avec l'anolyte et une cathode (224) peut être en contact avec le catholyte. L'anolyte, le catholyte ou les deux peuvent comprendre un sel de magnésium, un sel de calcium ou une combinaison de ceux-ci.
PCT/US2025/030158 2024-05-20 2025-05-20 Production de fer par électrolyse directe de minerai de fer Pending WO2025245086A1 (fr)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100044243A1 (en) * 2006-09-21 2010-02-25 Qit-Fer & Titane Inc. Electrochemical process for the recovery of metallic iron and chlorine values from iron-rich metal chloride wastes
US20130189592A1 (en) * 2010-09-09 2013-07-25 Farshid ROUMI Part solid, part fluid and flow electrochemical cells including metal-air and li-air battery systems
US9045841B1 (en) * 2006-10-30 2015-06-02 Novellus Systems, Inc. Control of electrolyte composition in a copper electroplating apparatus
US20210002742A1 (en) * 2014-09-09 2021-01-07 MetOx PTE.LTD System, apparatus, and process for leaching metal and storing thermal energy during metal extraction
US20210230759A1 (en) * 2017-02-24 2021-07-29 Vanadiumcorp Resources Inc. Metallurgical And Chemical Processes For Recovering Vanadium And Iron Values From Vanadiferous Titanomagnetite And Vanadiferous Feedstocks
US20230364590A1 (en) * 2018-06-29 2023-11-16 Illinois Institute Of Technology Transition metal mxene catalysts for conversion of carbon dioxide to hydrocarbons

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100044243A1 (en) * 2006-09-21 2010-02-25 Qit-Fer & Titane Inc. Electrochemical process for the recovery of metallic iron and chlorine values from iron-rich metal chloride wastes
US9045841B1 (en) * 2006-10-30 2015-06-02 Novellus Systems, Inc. Control of electrolyte composition in a copper electroplating apparatus
US20130189592A1 (en) * 2010-09-09 2013-07-25 Farshid ROUMI Part solid, part fluid and flow electrochemical cells including metal-air and li-air battery systems
US20210002742A1 (en) * 2014-09-09 2021-01-07 MetOx PTE.LTD System, apparatus, and process for leaching metal and storing thermal energy during metal extraction
US20210230759A1 (en) * 2017-02-24 2021-07-29 Vanadiumcorp Resources Inc. Metallurgical And Chemical Processes For Recovering Vanadium And Iron Values From Vanadiferous Titanomagnetite And Vanadiferous Feedstocks
US20230364590A1 (en) * 2018-06-29 2023-11-16 Illinois Institute Of Technology Transition metal mxene catalysts for conversion of carbon dioxide to hydrocarbons

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