METAL PRODUCTION FROM HALIDE-BASED MOLTEN SALT ELECTROLYSIS PROCESS

Abstract

An electrolysis reactor for electrolytically generating one or more metal cathode product(s) includes a dimensionally stable anode (DSA) and a cathode positioned in a molten salt electrolyte containing fused salts, wherein the DSA includes a graphite substrate and a non-ceramic, transition metal oxide coating on the substrate and wherein during electrolysis the one or more metal cathode product(s) are produced at the cathode.

Claims

1. An electrolysis reactor for electrolytically generating one or more metal cathode product(s) comprising: a dimensionally stable anode (DSA) and a cathode positioned in a molten salt electrolyte containing fused salts, wherein the DSA includes a graphite substrate and a non-ceramic, transition metal oxide coating on the substrate and wherein during electrolysis the one or more metal cathode product(s) are produced at the cathode.

2. The electrolysis reactor of claim 1, wherein the non-ceramic, transition metal oxide coating includes RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, CuO, or binary mixtures thereof.

3. The electrolysis reactor of claim 1, wherein the non-ceramic, transition metal oxide coating includes a 30:70 wt. % to 60:40 wt. % binary mixture of two of RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, or CuO.

4. The electrolysis reactor of claim 1, the non-ceramic, transition metal oxide coating has a thickness of about 1 m to about 1000 m.

5. The electrolysis reactor of claim 1, wherein the molten salt electrolyte includes a molten mixture of at least 50 mol % chloride containing fused salts.

6. The electrolysis reactor of claim 5, wherein balance of the fused salt comprises a single electrolyte or mixture of electrolytes where the anion is a carbonate, sulfate, phosphate, fluoride, bromide, iodide, or hydroxide.

7. The electrolysis reactor of claim 5, wherein the molten salt electrolyte includes a metal salt of the one or more metal cathode product(s), the one or metal cathode product(s) including at least one of Fe, Al, Mg, Ti, Li, Na, Dy, Nd, NdPr, La, or Ce.

8. The electrochemical cell electrolysis reactor of claim 7, wherein the metal salt includes at least one of FeX.sub.2, FeX.sub.3, AlX.sub.3, NdX.sub.3, MgX.sub.2, TiX.sub.3, TiX.sub.4, LiX, NaX, DyX.sub.2, DyX.sub.3, NdPrX.sub.6, LaX.sub.3, CeX.sub.2, or CeX.sub.3, where X is a halogen.

9. The electrolysis reactor of claim 8, wherein the molten salt electrolyte includes a eutectic of the metal salt and at least one of LiCl, KCl, NaCl, CsCl, MgCl.sub.2, BaCl.sub.2, SrCl.sub.2, or CaCl.sub.2 and the molten salt electrolysis is conducted at a temperature of about 400 C. to about 1200 C.

10. The electrolysis reactor of claim 8, wherein the molten salt electrolyte includes a eutectic of FeX.sub.2 and/or FeX.sub.3, where X is a halogen, and at least one of LiCl, KCl, NaCl, CsCl, MgCl.sub.2, BaCl.sub.2, SrCl.sub.2, or CaCl.sub.2 and the molten salt electrolysis is conducted at a temperature of about 400 C. to about 1200 C.

11. The electrolysis reactor of claim 1, wherein electrolysis is conducted at a current density of about 50 mA/cm.sup.2 to about 10 A/cm.sup.2.

12. A system for production of iron from iron oxides and/or iron ore containing iron compounds and/or aqueous spent pickle liquor containing iron halide, the system comprising: an electrolysis reactor for molten salt electrolysis of iron halide feedstock to iron and halogen(s), wherein the electrolysis reactor includes a dimensionally stable anode (DSA) and a cathode positioned in a molten salt electrolyte containing fused salts, the DSA includes a graphite substrate and a non-ceramic, transition metal oxide coating on the substrate, and during electrolysis iron is produced at the cathode from the iron halide feed stock and halogen gas is produced at the anode.

13. The system of claim 12, wherein the non-ceramic, transition metal oxide coating includes RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, CuO, or binary mixtures thereof.

14. The system of claim 12, wherein the non-ceramic, transition metal oxide coating includes a 30:70 wt. % to 60:40 wt. % binary mixture of two of RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, or CuO.

15. The system of claim 12, wherein the molten salt electrolyte includes a molten mixture of at least 50 mol % chloride containing fused salts.

16. The system of claim 12, wherein the molten salt electrolyte includes a eutectic of FeX.sub.2 and/or FeX.sub.3, where X is a halogen, and at least one of LiCl, KCl, NaCl, CsCl, MgCl.sub.2, BaCl.sub.2, SrCl.sub.2, or CaCl.sub.2 and the molten salt electrolysis is conducted at a temperature of about 400 C. to about 1200 C.

17. The system of claim 12, wherein electrolysis is conducted at a current density of about 50 mA/cm.sup.2 to about 10 A/cm.sup.2.

18. The system of claim 12, further comprising a halogenation reactor configured for non-carbothermic reacting of the iron oxides and/or iron ore containing iron compounds with halogen acids to form the iron halide feedstock and/or a dehydration reactor for dehydrating an aqueous spent pickle liquor containing iron halide to form the iron halide feedstock.

19. The system of claim 18, where the halogenation reactor includes a halogen acid or leaching acid converted from the generated halogen at molarity effective to convert the iron oxide to the iron halide feedstock.

20. The system of claim 18, wherein the iron ore comprises at least one of taconite, hematite, siderite, ironstone, magnetite ore, limonite, or goethite; and/or the aqueous spent pickle liquor comprises a product from a pickling bath used in the production of steel.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1 is a schematic illustration of a dimensionally stable anode in accordance with an embodiment.

[0036] FIG. 2 is a schematic illustration of an electrochemical cell that includes a dimensionally stable anode in accordance with an embodiment.

[0037] FIG. 3 is a schematic illustration of an electrochemical reactor for the continuous production of molten rare earth elements or rare earth element-containing alloys.

[0038] FIG. 4 is an image of a dimensionally stable anode that includes RuO.sub.2 on a graphite substrate (Ru loading about 0.4 mg/cm.sup.2).

[0039] FIG. 5 illustrates a schematic flow diagram of a process for iron metal production using molten salt electrolysis (MSE).

[0040] FIG. 6 illustrates a schematic diagram of a system for performing the molten salt electrolysis of FIG. 5.

[0041] FIG. 7 illustrates a schematic flow diagram of a sustainable process for iron metal production in accordance with another embodiment.

[0042] FIG. 8 illustrates iron metal production from ore via chloride-based molten salt electrolysis (MSE) process.

[0043] FIG. 9 illustrates the overall process flow of iron production via chloride-MSE, including the upstream non-carbothermic chlorination of ore to FeCl.sub.3 (resulting in separation of ore impurities), and the subsequent electrolytic deposition process.

[0044] FIG. 10 illustrates a cyclic voltammogram for a binary FeCl.sub.3+NaCl mixture at 400 C. at a scan rate of 100 mV/s.

[0045] FIG. 11 illustrates a cyclic voltammogram for a ternary FeCl.sub.3+KCl+LiCl mixture at 500 C. at a scan rate of 100 mV/s.

[0046] FIG. 12 is an image of ruthenium plated on a graphite substrate with (right) and without (left) annealing in air.

[0047] FIG. 13 is a plot comparing anode potential of G-RuO.sub.2 anode and pure graphite anode vs. Ag/AgCl reference electrode [1 wt. % AgCl in KClLiCl (55:45 wt. %)]

[0048] FIG. 14 is a plot showing cell voltage during constant current (250 mA/cm.sup.2) Nd sponge deposition at 475 C. in an electrochemical cell employing a G-RuO.sub.2 anode and a bare graphite anode.

[0049] FIGS. 15(A-B) illustrate images of a Fe.sub.2O.sub.3-coated graphite anode before and after molten salt electrolysis of neodymium metal.

[0050] FIG. 15(C) is a plot showing cell voltage during constant current (200 mA/cm.sup.2) Nd sponge deposition in an electrochemical cell employing a Fe.sub.2O.sub.3-coated graphite anode.

[0051] FIG. 16(A) illustrates images of the anode surface of an Fe.sub.2O.sub.3-coated graphite anode before and after molten salt electrolysis of neodymium metal.

[0052] FIG. 16(B) illustrates profilometry plots of the anode surfaces of an Fe.sub.2O.sub.3-coated graphite anode before and after molten salt electrolysis of neodymium metal.

DETAILED DESCRIPTION

[0053] All scientific and technical terms used in this application have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the application.

[0054] The articles a and an are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, an element means one element or more than one element.

[0055] As used herein, the verb comprise as is used in this description and in the claims and its conjugations are used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. The present invention may suitably comprise, consist of, or consist essentially of, the steps, elements, and/or reagents described in the claims.

[0056] Throughout the description, where compositions are described as having, including, or comprising, specific components, it is contemplated that compositions also consist essentially of, or consist of, the recited components. Similarly, where methods or processes are described as having, including, or comprising specific process steps, the processes also consist essentially of, or consist of, the recited processing steps. Further, it should be understood that the order of steps or order for performing certain actions is immaterial so long as the compositions and methods described herein remains operable. Moreover, two or more steps or actions can be conducted simultaneously.

[0057] The term A and/or B means A or B, or A and B.

[0058] As used herein, the term about or approximately refers to a quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length that varies by as much as 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1% to a reference quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length. In one embodiment, the term about or approximately refers a range of quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% about a reference quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length.

[0059] Throughout this disclosure, various aspects of this invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual and partial numbers within that range, for example, 1, 2, 3, 4, 5, 5.5 and 6. This applies regardless of the breadth of the range.

[0060] Embodiments described herein relate to a non-consumable or dimensionally stable anode, its use in the production, extraction, or recovery of metal(s) from a metal bearing material in non-aqueous molten salts, and particularly its use in a device, system, and process for the production, extraction, or recovery of metal(s) from a metal bearing material using halide molten salt electrolysis. We found that transition metal oxide-coated graphite anodes, and particularly non-ceramic, transition metal oxide-coated graphite anodes, in contrast to ceramic transition metal oxide-coated metallic substrates, are catalytic to and reduce the overpotential for electrolytic halogen gas evolution in a halide-containing molten salt media of an electrochemical cell used for molten salt electrolysis of metal halides. Transition metal oxides, such as RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, or CuO, cannot be readily fabricated into anodes because of mechanical difficulties and therefore must be coated onto a chemically and mechanically stable current collector, such as a graphite/carbon current collector. Graphite substrates can advantageously be adaptable to various geometric configurations, ranging from solids to amorphous cloths, and, unlike metal substrates, are resistant to degradation by halogen gases generated at the anode in moderate or high-temperature non-aqueous halide molten salt media used in molten salt electrolysis. Transition metal oxide coatings can also be readily applied onto graphitic substrates using benign and low-cost techniques, such as electrodeposition. Combining the electrocatalytic effect of transition metal oxides, such as RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr203, Mn.sub.2O.sub.3, CuO, or binary mixtures thereof, and graphite substrates can result in anodes with improved energy efficiency for the co-production of metals, such as Fe, Al, Mg, Ti, Li, Na, Dy, Nd, NdPr, La, and/or Ce, and halogen gas, such as chlorine gas, and that are resistant to degradation by the halogen gas should transition metal oxide coating deteriorate in moderate or high-temperatures non-aqueous halide molten salt media used in molten salt electrolysis. Additionally, as molten salt electrolysis is performed at high temperatures, these transition metal oxides (e.g., Fe.sub.2O.sub.3) are conductive for passing electrical current; hence, their resistive nature is not an issue as it may be in room temperature electrolysis systems.

[0061] FIG. 1 is a schematic illustration of a non-consumable or dimensionally stable anode 10 that is configured to produce, extract, or recover metal(s) from a metal-bearing material and to produce a halogen gas during molten salt electrolysis in a molten salt electrolyte containing halide fused salts. The term halide fused salts refers to any inorganic substance where upon heating, an ionically conductive liquid is produced where one of the atomic components of the substance is a halide atom in any of its valences, wherein it may be a halide ion or an ion containing the halide atom (e.g., Cl.sup. or OCl.sup.).

[0062] The dimensionally stable anode 10 includes a graphite substrate 12 and an electrochemically active coating 14 disposed on at least a portion of the substrate 12 that is non-ceramic, catalytic to halide gas evolution, and resistant to degradation in a halide-containing molten salt media during molten salt electrolysis. While the graphite substrate 12 is illustrated as being plate-shaped, the graphite substrate 12 can include various other shapes, such as a three-dimensional structure that is net-shaped, bar-shaped, sheet-shaped, tubular, linear, porous plate-shaped, porous, or spherical. The graphite substrate 12 can further be in the form of a fibrous graphite mesh, graphite fibers, graphite felt or fabric, and the like.

[0063] In some embodiments, the graphite substrate 12 can be configured to enable the halide-containing molten salt to flow through it. Possible configurations can include a porous graphite substrate, a graphite mesh, a perforated graphite sheet, a planar configuration, and multiplanar geometric configurations.

[0064] The coating 14 disposed on at least a portion of the graphite substrate 12 that is catalytic to halogen gas evolution and resistant to degradation includes at least one electrochemically active transition metal oxide that is not a ceramic or non-ceramic. By non-ceramic it is meant that transition metal oxide coating when deposited or formed on the graphite anode do not form into rigid, polycrystalline ceramic structures and retains its amorphous or non-crystalline structure. Examples of electrochemically active transition metal oxides that can be used to form the non-ceramic, electrochemically active transition metal oxide coating include oxides of ruthenium, iridium, oxides of period 4 transition metals, or mixtures thereof. In some embodiments, the electrochemically active transition metal oxide that is catalytic to halide gas evolution and resistant to degradation in a non-aqueous molten salt electrolyte during molten salt electrolysis can include RuO.sub.2, IrO.sub.2, a period 4 transition metal oxide, such as Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, CuO, or binary mixtures thereof.

[0065] The electrochemically active transition metal oxide of the coating can be substantially amorphous, partially crystalline, or a blend thereof. In some embodiments, where RuO.sub.2 is used as the electrochemically active transition metal oxide, the RuO.sub.2 is substantially amorphous. Amorphous RuO.sub.2 in the electrochemically active coating has higher catalytic activity for halogen gas (e.g., chlorine gas) evolution than crystalline RuO.sub.2, thereby rendering an anode having a low halogen gas evolution potential and capable of promoting halogen gas evolution in a halide-containing molten salt media.

[0066] In some embodiments, the electrochemically active coating 14 can include a 30:70 wt. % to 60:40 wt. % binary mixture of two of RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, or CuO. For example, the binary mixture can include about 30% by weight to about 60% by weight, about 35% by weight to about 60% by weight, about 40% by weight to about 60% by weight, about 45% by weight to about 60% by weight, about 50% by weight to about 60% by weight, about 55% by weight to about 60% by weight, about 30% by weight to about 55% by weight, about 30% by weight to about 50% by weight, about 30% by weight to about 45% by weight, about 30% by weight to about 40% by weight, or about 30% by weight to about 35% by weight of a first transition metal oxide selected from RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, or CuO; and about 40% by weight to about 70% by weight, about 45% by weight to about 70% by weight, about 50% by weight to about 70% by weight, about 55% by weight to about 70% by weight, about 60% by weight to about 70% by weight, about 65% by weight to about 70% by weight, about 40% by weight to about 65% by weight, about 40% by weight to about 60% by weight, about 40% by weight to about 55% by weight, about 40% by weight to about 50% by weight, or about 40% by weight to about 45% by weight of a second transition metal oxide selected from RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, or CuO that differs from the first transition metal oxide, wherein the combination of the first transition metal oxide and second transition forms the balance of the binary mixture.

[0067] In some embodiments, the electrochemically active coating 14 can have a geometric surface coverage ratio of the anode 10 of about 0.000001:1 to about 1:1. For example, the electrochemically active coating can have geometric coverage ratio of about 0.00001:1 to about 1:1, about 0.0001:1 to about 1:1, about 0.001:1 to about 1:1, about 0.01:1 to about 1:1, about 0.1:1 to about 1:1, about 0.2:1 to about 1:1, about 0.3:1 to about 1:1, about 0.4:1 to about 1:1, about 0.5:1 to about 1:1, about 0.6:1 to about 1:1, about 0.7:1 to about 1:1, about 0.8:1 to about 1:1, or about 0.9:1 to about 1:1.

[0068] In other embodiments, the anode 10 can have an a electrochemically active surface area to geometric surface area ratio of about 0.000001:1 to about 10,000:1. For example, the anode can have an a electrochemically active surface area to geometric surface area ratio of about of about 0.00001:1 to about 10,000:1, about 0.0001:1 to about 10,000:1, about 0.001:1 to about 10,000:1, about 0.01:1 to about 10,000:1, about 0.1:1 to about 10,000:1, about 1:1 to about 10,000:1, about 10:1 to about 10,000:1, about 100:1 to about 10,000:1, or about 1000:1 to about 10,000:1.

[0069] In some embodiments, the coating 14 can have a thickness of about 1 m to about 1000 m. For example, the electrochemically active surface coating can have a substantially uniform thickness of about 10 m to about 1000 m, about 100 m to about 1000 m, about 1 m to about 10 m, or about 1 m to about 100 m.

[0070] In other embodiments, the coating 14 can be provided on at least a portion of the surface of the graphite substrate at a surface density of about 10 82 g/cm.sup.2 to about 1000 g/cm.sup.2. For example, the coating can have substantially uniform surface density of about 20 g/cm.sup.2 to about 900 g/cm.sup.2, about 30 g/cm.sup.2 to about 800 g/cm.sup.2, about 40 g/cm.sup.2 to about 800 g/cm.sup.2, about 50 g/cm.sup.2 to about 700 g/cm.sup.2, about 60 g/cm.sup.2 to about 700 g/cm.sup.2, about 70 g/cm.sup.2 to about 600 g/cm.sup.2, or about 80 g/cm.sup.2 to about 700 g/cm.sup.2.

[0071] The coating 14 can be provided as a single layer having the same or uniform composition or as multiple layers having the same or differing compositions. In some embodiments, the coating 14 can include two layers with differing compositions. For example, an intermediate layer (not shown) can be formed between a catalytic layer and the graphite substrate. This arrangement can prevent the halide-containing molten salt media from reaching the graphite substrate even when the halide-containing molten salt media penetrate into the catalytic layer.

[0072] The intermediate layer can be made of, for example, a metal, alloy, a carbon based material, such as boron-doped diamond, a metal compound, such as an oxide and sulfide, or a composite compound, such as a metal composite oxide. For example, the intermediate layer can be formed of a metal, in which case a thin film of tantalum or niobium, etc., may be employed. The intermediate layer can also be formed of an alloy that includes, for example, tantalum, niobium, tungsten, molybdenum, titanium, or platinum. Furthermore, an intermediate layer made of a carbon-based material, such as boron-doped diamond, also has the same effects.

[0073] In other embodiments, the coating 14 can have a substantially uniform thickness across at least the portion of the graphite substrate on which it is disposed or have a non-uniform thickness. The coating 14 can also be porous and/or include non-contiguous portions across portions of the graphite substrate.

[0074] In some embodiments, the non-ceramic, electrochemically active coating 14 can be provided on a portion of the surface of the graphite substrate 12 by electrodepositing at least one transition metal, such as Ru, Ir, Fe, Ni, Cr, Mn, Cu, and binary mixtures thereof, and annealing the electrodeposited transition metal in an atmosphere and at a temperature effective to oxidize the electrodeposited transition metal without forming a ceramic. Advantageously, electrodeposition of transition metals, such as Ru, Ir, Fe, Ni, Cr, Mn, Cu, allows the production of electrochemically active coating on the graphite substrate in a facile manner with small amounts of cost-prohibitive metal plating solution and with greater control of both thickness and distribution of the catalytic coating. Furthermore, the electrolytic method does not require the use of high temperatures, high pressures, or strong oxidizers to produce positive results. By way of example, as illustrated in FIG. 4, ruthenium was deposited on a graphite substrate at a loading of about 250 g/cm.sup.2. The electrodeposited ruthenium metal was then converted to RuO.sub.2 by annealing in air at 400 C. for 18 hours.

[0075] Other methods can also be used to provide an electrochemically active coating that includes a transition metal oxide (e.g., RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, CuO, or binary mixtures thereof) on a portion of the surface of the graphite substrate. Such methods can include physical vapor deposition, chemical vapor deposition methods, sputter coating and sintering, dip coating, electrophoretic deposition, aerosol deposition, or jet spraying a transition metal oxide (e.g., RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, CuO, or binary mixtures thereof) on the graphite substrate, as well as by thermal decomposition of a precursor solution containing a transition metal, such as Ru, Ir, Fe, Ni, Cr, Mn, Cu, deposited by, for example, sputter coating, dip coating, electrophoretic deposition, aerosol deposition, or jet spraying and chemically oxidizing the precursor solution by sintering on the graphite substrate. Sputter coating and sintering can advantageously produce densely packed and adherent layers with a certain degree of crystal structure tunability. The advantage of chemically oxidizing the transition metal offers simplicity and expediency in experimental setup and procedure.

[0076] In some embodiments, the dimensionally stable anode described herein can be used in a system and process for the production, extraction, or recovery of metal(s), such as Fe, Al, Mg, Ti, Li, Na, Dy, Nd, NdPr, La, and/or Ce, by electrowinning and particularly non-aqueous molten salt electrolysis. Molten salt electrolysis can provide high-efficiency production of solid metal or liquid metal while evolving a halogen gas, such as chlorine (Cl.sub.2) gas. Metal produced by the molten salt electrolysis can be recovered, and the halogen gas (e.g., Cl.sub.2 gas) can optionally be recycled in a halogenation process. Advantageously, the dimensionally stable anode, when used in halide molten salt electrolysis, is catalytic to halogen gas (e.g., Cl.sub.2 gas) generation, which prevents large overpotential and suppresses side reactions. This can enable the use of mixed halide electrolytes, such as Cl and F electrolytes, that only produce Cl.sub.2 during molten salt electrolysis.

[0077] For example, a molten salt electrolysis process for neodymium production using chloride-containing salts and fluoride-containing salts can generate perfluorocarbons via reaction with between the graphite anode and fluoride-containing electrolyte. Using the dimensionally stable anode described herein that includes a chlorine-reactive coating, Cl.sub.2 production can be enhanced, and perfluorocarbon or F.sub.2 production can be suppressed at the anode, allowing use of fluoride salts, such as CaF.sub.2, in the electrolyte.

[0078] In some embodiments, a dimensionally stable anode and a cathode can be provided in a chloride-based molten salt electrolyte contained in an electrochemical cell of a molten salt electrolysis reactor for producing metal(s) and chlorine gas from a metal chloride feedstock in moderate or high-temperature chloride molten salt electrolysis. An electrical potential is applied between the cathode and the anode of an electrochemical cell so that the metal chloride dissolved in the chloride-based molten salt is electrolyzed, the metal product(s) is electrodeposited on the cathode of the cell, and Cl.sub.2 gas is generated at the anode of the reactor

[0079] In some embodiments, metal cathode product(s) can include at least one of alkali metal, alkaline earth metal, transition metal, post-transition metal, metalloid/semi-metal, lanthanoid/lanthanide, actinoid/actinide, or combinations thereof. The cathode product(s) can be in solid, liquid, or gas phase. In some embodiments, the metal can be selected from Fe, Al, Mg, Ti, Li, Na, Dy, Nd, NdPr, La, Ce, or combinations thereof.

[0080] In some embodiments, the electrochemical cell or chamber of the molten salt electrolysis reactor can be defined by a container or vessel fabricated from a ceramic, such as alumina, or a high-temperature corrosion-resistant metal, such as Hastelloy or Inconel. Other high-temperature corrosion-resistant materials, such as siliceous refractory material can also be used.

[0081] In some embodiments, the cathode includes an inert metal, such as tungsten or molybdenum.

[0082] In some embodiments, a current source can provide current effective for molten salt electrolysis of the metal chloride(s) to metal and chlorine gas. For example, the anode and cathode can be electrically connected to current source that can provide an operating current density (current applied per unit of electrode surface area) of about 1 mA/cm.sup.2 to about 100 A/cm.sup.2, with an operating range of about 50 mA/cm.sup.2 to about 10 A/cm.sup.2.

[0083] In some embodiments, the anode produces a halogen gas, such as chlorine gas, without the interruption of current from external electrical circuitry for any period of time exceeding 1 second.

[0084] In other embodiments, the cathode product(s) are produced without the interruption of current from external electrical circuitry for any period of time exceeding 1 second.

[0085] In some embodiments, the anode and cathode are separated from one another in the electrochemical cell, such as a batch electrochemical cell. In such a configuration, the batch electrochemical cell can further include a separator or diaphragm positioned between and separating the anode and the cathode. The separator or diaphragm can inhibit redox shuttling and back reaction between metal plated on the cathode and halide gas generated at the anode. The separator or diaphragm can include, for example, a ceramic with a porosity of about 10% to about 60%.

[0086] In some embodiments, for chloride based molten salt electrolysis, a chloride based molten salt electrolyte can include a molten mixture of at least about 50.00 mol % chloride containing fused salts where the balance of the fused salt mixture may be a single electrolyte or mixture of electrolytes where the anion is a carbonate, sulfate, phosphate, fluoride, bromide, iodide, or hydroxide.

[0087] In other embodiments, the chloride-based molten salt electrolyte can include a molten mixture of at least about 50.00 mol % chloride containing fused salts, where the balance of the fused salt mixture may be an inorganic compound of the oxide, nitride, carbide, phosphide, or sulfide variety.

[0088] In some embodiments, the halide containing fused salts provided in the electrochemical cell and in which the metal halide is dissolved can include halides of alkaline metals and alkaline earth metals, such as chlorides of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba either pure or in mixtures, such as eutectic mixtures.

[0089] In some embodiments, the chloride-containing fused salts can include moderate to high temperature chloride-containing fused salts for moderate to high temperature molten salt electrolysis.

[0090] In some embodiments, the moderate temperature chloride-containing fused salts can include a eutectic of at least two of LiCl, KCl, NaCl, CsCl, MgCl.sub.2, BaCl.sub.2, SrCl.sub.2, or CaCl.sub.2. For example, a eutectic of about 55%-60% LiCl and 45%-40% KCl can have a melting point of about 475 C.-575 C., a eutectic of 27%-98% NaCl and 73%-2% SrCl.sub.2 can have a melting point of about 650 C.-800 C., a eutectic of about 66% NaCl and 34% MgCl.sub.2 can have a melting point of about 750 C., a eutectic of about 85%-98% NaCl and about 15%-2% BaCl.sub.2 can have a melting point of about 750 C.-800 C., a eutectic of about 30%-50% NaCl and about 70%-50% CaCl.sub.2 can have a melting point of about 700 C.-750 C., a eutectic of about 50% NaCl and 50% KCl can have a melting point of about 750 C., a eutectic of about 67% KCl and 33% CaCl.sub.2 can have a melting point of about 700 C., a eutectic of about 24% NaCl, 41% KCl, and 35% BaCl.sub.2 can have a melting point of about 650 C., and a eutectic of about 40%-70% LiCl, 0-20% NaCl and about 25%-55% KCl can have a melting point of about 450 C.-600 C.

[0091] In some embodiments, the high temperature chloride-containing fused salt electrolyte can include a eutectic of SrCl.sub.2, BaCl.sub.2, and optionally at least one of LiCl, KCl, NaCl, CsCl, MgCl.sub.2, or CaCl.sub.2. For example, a eutectic of about 54% KCl and 46% BaCl.sub.2 can have a melting point of about 825 C. and a eutectic of about 30% BaCl.sub.2 and about 70% SrCl.sub.2 can have a melting point of about 847 C.

[0092] One example of a molten salt electrolyte that can be used in molten salt electrolysis of the metal chloride is a melt or the binary eutectic mixture of NaCl and KCl (NaClKCl in the 50:50 mole percent ratio) and CaF.sub.2.

[0093] In some embodiments, the electrolysis can be conducted at a current density of about 50 mA/cm.sup.2 to about 10 A/cm.sup.2. For example, typically, at current densities in the 0.2-0.4 A/cm.sup.2 range, Nd electrowon using such melts deposits as dendritic sponge on a tungsten or molybdenum cathode.

[0094] The temperature of the molten salt electrolyte in the molten salt electrolysis can be adjusted in accordance with the type of molten salt electrolyte used. For example, the moderate to high temperature molten salt electrolysis can be conducted at a temperature of about 400 C. to about 1200 C., for example, about 400 C. to about 450 C., about 400 C. to about 500 C., about 400 C. to about 550 C., about 400 C. to about 600 C., about 400 C. to about 650 C., about 400 C. to about 700 C., about 400 C. to about 750 C., about 400 C. to about 800 C., about 400 C. to about 850 C., about 400 C. to about 900 C., about 400 C. to about 950 C., about 400 C. to about 1000 C., about 400 C. to about 1050 C., about 400 C. to about 1100 C., about 400 C. to about 1150 C., about 450 C. to about 1200 C., about 500 C. to about 1200 C., about 550 C. to about 1200 C., about 600 C. to about 1200 C., about 650 C. to about 1200 C., about 700 C. to about 1200 C., about 750 C. to about 1200 C., about 800 C. to about 1200 C., about 850 C. to about 1200 C., about 900 C. to about 1200 C., about 950 C. to about 1200 C., about 1000 C. to about 1200 C., about 1050 C. to about 1200 C., about 1100 C. to about 1200 C., or about 1150 C. to about 1200 C.

[0095] The electrochemical cell of a molten salt electrolysis reactor can include any number of cell configurations, such as a cell with a single electrolysis chamber that includes a single anode and a single cathode, a cell with multiple anodes and cathodes, a cell that includes heterogenous bipolar electrodes, and a cell with multiple chambers each, which includes anodes and cathodes separated by junctions or membranes.

[0096] FIG. 2 illustrates an electrochemical cell 100 suited for moderate temperature batch operation that allows recovery of solid metal electrodeposited on the cathode surface. The electrochemical cell 100 includes an electrolysis chamber 102 that contains a moderate temperature chloride-based molten salt electrolyte 104, such as LiClKCl, NaClKCl or other eutectic mixtures, in which the metal chloride (e.g., NdCl.sub.3 or FeCl.sub.3) is dissolved, as well as a vertically-aligned flat-plate cathode 106 and the dimensionally stable anode 108 described herein to which an electric potential can be applied. The cathode 106 and anode 108 can be provided in other configurations, such as concentric annular electrodes. The cathode 106 and anode 108 are separated from one another in the electrochemical cell 100 by a porous partition wall 110, such as separator or diaphragm 110 positioned between and separating the cathode 106 and anode 108. The separator or diaphragm 110 can inhibit redox shuttling and back reaction between metal plated on the cathode 106 and Cl.sub.2 gas 112 generated at the anode 108. The separator or diaphragm 110 can include, for example, a ceramic with a porosity of about 10% to about 60%.

[0097] FIG. 2 shows that a molten metal chloride, such as NdCl.sub.3, dissolved in the moderate temperature metal molten salt electrolyte 104, such as LiClKCl, NaClKCl or other eutectic mixtures, can be electrodeposited at moderate temperatures (e.g., about 475 C.-500 C.) as a solid dendritic metal sponge 114 on a surface of a tungsten or molybdenum cathode 106 while Cl.sub.2 gas 112 evolution is facilitated on the dimensionally stable anode 108. The deposited Nd can be recovered by scraping the Nd from the surface of the cathode 106. The Cl.sub.2 gas 112 generated at the anode 108 during Nd electrowinning can be recycled.

[0098] FIG. 3 illustrates an example of an electrochemical cell 200 suited for higher temperature continuous molten salt electrolysis operation that allows recovery of molten metal electrodeposited on the cathode surface. The continuous electrolysis can include continuous input of metal-containing feedstock into the cell, continuous production of chlorine gas and metal cathode product(s), and continuous collection of the produced metal cathode product(s) from the cell.

[0099] The electrochemical cell 200 includes an electrolysis chamber 202 that contains a high temperature (e.g., greater than 800 C.) chloride-based molten salt electrolyte 204, for example, BaCl.sub.2SrCl.sub.2 or other eutectic mixtures, in which a metal chloride feedstock (e.g., NdCl.sub.3 or FeCl.sub.3) is continuously input.

[0100] The density of the high-temperature chloride-based molten salt electrolyte 204 can be different (e.g., lower) than the metal 206 electrodeposited from the metal chloride so that molten electrodeposited metal 206 (e.g., Nd or Fe) can separate from the chloride-based molten salt electrolyte 204 in the cell upon electrodeposition. The electrochemical cell 200 can also include concentric annular dimensionally stable anode 208 that surrounds a refractory cathode rod 210. The geometric surface area ratio of anode to cathode can be about 0.5:1 to about 1000:1.

[0101] The concentric annular anode 208 and refractory cathode rod 210 are separated from one another in the electrochemical cell 200 by a porous partition wall 212, such as a separator or diaphragm 212, positioned between and separating the cathode 208 and anode 210. The separator or diaphragm 212 can inhibit redox shuttling and back reaction between metal 206 plated on the cathode 210 and chlorine gas 214 generated at the anode 208. The separator or diaphragm 212 can include a ceramic with a porosity of about 10% to about 60%.

[0102] The refractory cathode rod 210 can be orthogonal or oblique to a bottom 216 of the electrochemical cell 200 so that molten metal 206 electrodeposited on the cathode surface flows through the less dense molten salt electrolyte to an molten metal pool 220 at the bottom of the cell 200 and Cl.sub.2 gas 214 generated by electrolysis at the anode surfaces flows to a Cl.sub.2 removing channel (not shown) at the top of the cell 200.

[0103] In some embodiments, the electrochemical cell includes a means (not shown) for supplying current effective for molten salt electrolysis of the metal chloride(s) to metal and chlorine gas. The current means can supply current at a current density of about 5 mA/cm.sup.2 to about 10 A/cm.sup.2.

[0104] The continuous input of feedstock salts can be achieved through an input device 222, such as a refractory ceramic or metal screw feeder or conveyer or funneling system or slider bearing type assembly whereby the rate of input of the metal containing feedstock can be modulated to increase, decrease or maintain bulk concentration based on optimizing reaction conditions for higher throughput, or conditions. For example, the rate of input of the metal-containing feedstock can be modulated to optimize production of metal cathode product(s) and optionally chlorine gas.

[0105] An example feedstock can include transition metals, transition metal oxides, lanthanide metals, lanthanide metal oxides, post-transition metals, post-transition metal oxides, metalloids, and metalloid oxides whereby the metals to continuously electrowon may be first converted into an inorganic compound of the oxide, nitride, halide, nitrate, sulfate, hydroxide, sulfide, chlorate, carbonate, phosphate, chlorite, or other variety. The metals to be continuously electrowon are then solvated or dissolved or suspended in the chloride based molten salt electrolyte where they may exist in ionic or complex ionic form or as a suspended inorganic molecule and may be reduced at a cathode continuously either by accepting electrons from a polarized cathode directly or by discharging previously attached anions through accepting electrons from a polarized cathode.

[0106] The continuous collection of the metal cathode product(s) can minimize the metal cathode product(s) contact with cations of the same metal while not being held under a deposition potential. The continuous collection metal cathode product(s) can be achieved by drawing, valving, pumping, capillary feed, or slider bearing-like mechanisms utilizing similar aforementioned materials of construction for the reactor lining, collection vessel, and apparatus utilized for tapping or valving, pumping, or slider bearing type assembly. For example, the molten metal pool 220 can be fluidly connected to a collection system 224, such as a refractory valve or spout controlled by a stepper motor 226 or similar control system, which siphons accumulating metal in a collection basin 228 formed during molten salt electrolysis.

[0107] Another method by which continuous drawing of metal cathode product(s) can be achieved is by use of a refractory metal or ceramic which does not combine chemically with the metallic material, which is allowed to fuse in a tube of the refractory material and subsequently drawn off by induction remelting under inert blanket, vacuum, or under air atmospheres.

[0108] In some embodiments, the dimensionally stable anode and molten salt electrolysis reactor described herein can be used in a system and process for the production of iron by molten-salt electrolysis and, particularly, a sustainable system and process for the production, extraction, or recovery of iron from iron oxides and/or iron ore containing iron compounds as well as spent pickle liquor from iron and steel production plants. The process includes non-carbothermic reaction of the iron oxides and/or iron ore containing iron compounds with halogen acid(s) to form an iron halide feedstock and/or dehydrating an aqueous spent pickle liquor containing iron halide to form an iron halide feedstock and subsequently electrolyzing the iron halide feedstock by molten salt electrolysis to iron and halogen(s).

[0109] Advantageously, due to the precipitation of most impurities during the initial non-carbothermic reaction or leaching process, the electrolytic reduction of iron halide using the process described herein is cleaner and more straightforward compared to conventional extraction methods. Furthermore, the molten salt electrolysis process facilitates the recycling of used leaching acid through halogen evolution at the anode, enhancing its economic feasibility.

[0110] Additionally, the process described herein provides not only a standalone technique for iron metal production, but it can also be integrated with current state-of-the-art steel production processes using spent pickle liquor as a raw material from a steel plant. Pickling sludge is the waste product from pickling and includes acidic rinse waters, iron chlorides, metallic salts, and waste acid. Spent pickle liquor is considered a hazardous waste by the EPA. Hence, using this process, we not only offer recycling of chlorine and iron metal but also a way to treat pickling waste.

[0111] As illustrated in the flow diagram of FIG. 5, the process can include reacting iron oxides and/or iron ore containing iron compounds with a halogen acid in a non-carbothermic halogenation reaction to generate an aqueous solution that includes an iron halide. The aqueous solution of iron halide is then dried or dehydrated to form an iron halide feedstock relatively free of water. Alternatively or additionally, a spent pickle liquor containing iron halide from, for example, a low-value waste stream derived from steel processing, such as a pickling bath in the production of steel, can be dehydrated to form the iron halide feedstock. The iron halide feedstock formed by non-carbothermic halogenation and/or dehydrating the spent pickle liquor can be combined with a halide-based molten salt electrolyte and subjected to halide molten salt electrolysis using an electrolysis reactor that includes the DSA described herein. Halide molten salt electrolysis of the iron halide using the DSA described herein can provide high-efficiency electrowinning of solid iron or liquid iron while evolving halogen gas, such as chlorine (Cl.sub.2) gas. The iron produced by molten salt electrolysis can be recovered, and the halogen gas can optionally be recycled in a halogenation process with water separated from the non-carbothermically generated iron halide or pickle liquor to form halogen acid. Molten salt electrolysis using the DSA described herein can potentially lead to reduced energy consumption, stable electrochemical cell operation, and ease of process scalability.

[0112] Referring to FIG. 6, the process of FIG. 5 can generally be performed using a system 300 that includes a non-carbothermic halogenation reactor 312 configured for non-carbothermic halogenation of iron oxides and/or iron ore containing iron compounds to iron halide(s), a dehydration reactor 314 for drying the iron halides and/or dehydrating the spent pickle liquor containing iron halides to form an iron halide feedstock, and a molten salt electrolysis reactor 316 configured for halide molten salt electrolysis of the iron halide(s) to metal and halogen gas. Optionally, the system 300 can include a halogen acid generating reactor 318 for converting halogen gas (e.g., Cl.sub.2 gas) generated in the molten salt electrolysis reactor 316 and water separated from the non-carbothermic generated iron halide or pickle liquor to a halogen acid (e.g., HCl). The halogen acid generated can be optionally transferred to the non-carbothermic halogenation reactor 312 at a molarity effective for non-carbothermic halogenation of iron oxide and/or iron ore.

[0113] The non-carbothermic halogenation reactor 312, dehydration reactor 314, molten salt electrolysis reactor 316, and optional halogen acid generating reactor 318 can be integrated, connected, coupled, or in communication such that products formed in each respective reactors, 312, 314, 316, or 318 including iron halides, water, halogens, and halogen acids can flow or be transferred between respective reactors. For example, an aqueous solution containing iron halides generated in the non-carbothermic halogenation reactor 312 can be transferred or flow to the dehydration reaction 314 and dehydrated or dried, water removed in the dehydration reactor 312 can be transferred or flow to the halogen acid generating reactor 318, halogen gas formed in the molten salt electrolysis reactor 316 can flow to the halogen acid generating reactor 318, and halogen acid generated in the halogen acid generating reactor 318 can be transferred or flow to the non-carbothermic halogenation reactor 312.

[0114] FIGS. 7-9 illustrate, respectively, a schematic flow diagram, a system, and images of a process for the production of iron metal using an iron halide feedstock and halide-based molten salt electrolysis described in FIGS. 5 and 6.

[0115] Referring to FIG. 7, in some embodiments, a process 330 for the production of iron metal using an iron halide feedstock and halide-based molten salt electrolysis starts at step 332 by providing iron oxides (e.g., Fe.sub.2O.sub.3, FeO, and/or Fe.sub.3O.sub.4) and/or iron ore containing iron compounds. The iron oxides and/or iron ore containing iron compounds include iron oxides (e.g., Fe.sub.2O.sub.3, FeO, and/or Fe.sub.3O.sub.4) that can be processed by non-carbothermic halogenation, such as non-carbothermic chlorination, to an iron halide, such as iron chloride, under thermodynamically favorable operating conditions (e.g., negative Gibbs free energy). The iron oxides or iron ore containing iron compounds can be an ore, a concentrate, or any other iron from which an iron oxide may be recovered. For example, the iron ore containing iron compounds can include at least one of taconite, hematite, siderite, ironstone, magnetite ore, limonite, or goethite.

[0116] The iron oxides and/or iron ore containing iron compounds may be processed in any manner that enables the conditions of the iron oxide, e.g., particle size, composition, and component concentration, to be used for the chosen processing method, as such conditions may affect the overall effectiveness and efficiency of processing operations. Desired composition and component concentration parameters can be achieved through a variety of chemical and/or physical processing stages, the choice of which will depend upon the operating parameters of the chosen processing scheme, equipment cost and material specifications. For example, an ore containing iron oxide may undergo comminution, flotation, blending, and/or slurry formation, as well as chemical and/or physical conditioning.

[0117] Conventional production processes for obtaining iron oxides from deposits of iron oxide-bearing ore can include mining and milling the deposit. Alternatively, or in addition, the ore may be subject to physical beneficiation to produce an intermediate ore product. The beneficiation may be performed by a combination of crushing, grinding, screening, sizing, classification, magnetic separation, electrostatic separation, flotation, or gravity separation to concentrate the iron oxide or reject a gangue component, or by other means of benefaction known in the art. Optionally, other various chemical and/or physical processes can be used to transform the iron oxide-bearing ore to a more leachable iron oxide. In one example, the various chemical and/or physical processes can include a pyrometallurgical process (e.g., calcination) applied to a concentrated ore, followed by hydrometallurgical separation steps.

[0118] Referring again to FIG. 7, after the iron oxides and/or iron ore containing iron compounds have been suitably prepared for processing, the iron oxides and/or iron ore containing iron compounds are transferred to the non-carbothermic halogenation reactor and subjected to non-carbothermic halogenation at step 334 to produce an aqueous iron halide solution. The non-carbothermic halogenation step can include reacting the iron oxides and/or iron ore at room temperature (e.g., 25 C.) with a halogen acid solution, such as HCl, HF, or HBr solution, at a molarity or pH effective to halogenate the iron oxides and/or iron ore and form an aqueous solution of the iron halides (e.g., FeX.sub.2 or FeX.sub.3, where X is Cl, F, Br, or I). By way of example, HCl can be provided in an aqueous solution at a concentration of about 1M to about 4M or at a pH less than 1 and combined with the iron oxides to convert the iron oxides to iron chlorides (FeCl.sub.2 or FeCl.sub.3) or hydrated iron chlorides. Advantageously, impurities in the supplied iron oxide and/or iron ore can precipitate during the non-carbothermic reaction and be removed by filtration to provide a cleaner iron halide feedstock for molten salt electrolysis.

[0119] Alternatively and/or additionally, at step 36, a pickle liquor supply can be obtained from, for example, a low-value waste stream derived from steel processing, such as a pickling bath in the production of steel. Pickling sludge is a byproduct from pickling operations in industrial iron and steel production plants, comprising acidic rinse waters, iron chlorides, metallic salts, and waste acid.

[0120] At step 338, after generation of the aqueous iron chloride solution from non-carbothermic reacting of the iron oxides and/or iron ore containing iron compounds with halogen acids and/or obtaining the pickle liquor, water from the halogen acid solution and/or generated by the non-carbothermic halogenation reaction of the halogen acid and the iron oxide and/or from the pickling solution can be separated from the generated iron halide or pickling solution by, for example, evaporation, sublimation, or dehydration, to dry the iron halide and/or dehydrate the pickling solution and form an iron halide feedstock substantially free of water prior to molten salt electrolysis.

[0121] At step 340, the iron halide feedstock formed by drying the iron halide aqueous solution generated by non-carbothermic halogenation and/or dehydrating the aqueous spent pickle liquor containing iron halide can be combined with and dissolved in a halide-based molten salt electrolyte contained in the molten salt electrolysis reactor and electrolyzed by halide-based molten salt electrolysis to produce a pure or substantially pure iron that can be extracted or recovered from the electrolysis reactor. Advantageously, electrolyzing iron via halide-based molten salt electrolysis offers the potential to significantly reduce the electrical energy requirement and operating cost associated with iron production.

[0122] In some embodiments, the electrolysis reactor can include an electrochemical cell or chamber that contains the halide-based molten salt electrolyte in which the iron halide is dissolved and a cathode and an anode to which an electric potential can be applied. An electric potential is applied between the cathode and the anode of an electrochemical cell such that the iron halide dissolved in the halide-based molten salt electrolyte is electrolyzed, iron is electrodeposited on the cathode of the cell, and halogen gas (e.g., Cl.sub.2) is generated at the anode of the reactor.

[0123] In some embodiments, the electrochemical cell or chamber of the molten salt electrolysis reactor can be defined by a container or vessel fabricated from an oxide-based, nitride-based, or silica-based ceramic, such as alumina, or a high-temperature corrosion-resistant metal, such as Hastelloy or Inconel. Other high-temperature corrosion-resistant materials, such as siliceous refractory material or other refractory transition metals, such as molybdenum or tungsten, can also be used.

[0124] The anode can include a dimensionally stable anode (DSA) as described herein. In some embodiments, the DSA includes a graphite substrate coated with a non-ceramic, transition metal oxide coating that is catalytic to halogen (e.g., chlorine) gas evolution. The non-ceramic, transition metal oxide coating can include RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, CuO, or binary mixtures thereof. For example, the non-ceramic, transition metal oxide coating can include a 30:70 wt. % to 60:40 wt. % binary mixture of two of RuO.sub.2, IrO.sub.2, Fe.sub.2O.sub.3, NiO, Cr.sub.2O.sub.3, Mn.sub.2O.sub.3, or CuO. In some embodiments, the non-ceramic, electrochemically active transition metal oxide that is catalytic to halogen (e.g., chlorine) gas evolution can include ruthenium oxide (RuO.sub.2) and optionally iridium oxide (IrO.sub.2). In other embodiments, the electrochemically active transition metal oxide that is catalytic to halogen (e.g., chlorine) gas evolution can include Fe.sub.2O.sub.3.

[0125] In some embodiments, the cathode includes an inert or partially consumable material. Examples of inert or partially consumable materials that can be used as the cathode include a metal, such as tungsten or molybdenum.

[0126] In some embodiments, a current source can provide a current effective for molten salt electrolysis of the iron halide(s) to metal and halogen (e.g., Cl.sub.2) gas. For example, the anode and cathode can be electrically connected to a current source that can provide an operating current density (current applied per unit of electrode surface area) of about 50 mA/cm.sub.2 to about 10 A/cm.sup.2.

[0127] In some embodiments, the anode and cathode are separated from one another in the electrochemical cell. In such a configuration, the electrochemical cell can further include a separator or diaphragm positioned between and separating the anode and the cathode. The separator or diaphragm can inhibit redox shuttling and back reaction between iron plated on the cathode and halogen gas generated at the anode. The separator or diaphragm can include, for example, a refractory material or ceramic with a porosity of about 10% to about 60%.

[0128] The molten salt electrolyte provided in the electrochemical cell includes an eutectic formed by dissolving the iron chloride (FeX.sub.2 and/or FeX.sub.3, where X is a halogen (e.g., Cl, F, Br, I)) in halides of alkaline metals and alkaline earth metals, such as chlorides of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba either pure or in mixtures, such as eutectic mixtures.

[0129] In some embodiments, the molten salt electrolyte can include a moderate or high temperature chloride-based molten salt electrolyte. The moderate or high temperature chloride-based molten salt electrolyte can include a eutectic of iron chloride and at least one or more of LiCl, KCl, NaCl, CsCl, MgCl.sub.2, BaCl.sub.2, SrCl.sub.2, or CaCl.sub.2. The eutectic can have a moderate to high melting temperature of about 400 C.-1200 C. depending on the salts selected for combination with the iron halide. For example, the eutectic can have a melting point of about 450 C.-550 C., about 450 C.-650 C., about 550 C.-750 C., about 650 C.-850 C., about 750 C.-950 C., about 850 C.-1050 C., about 950 C.-1150 C.

[0130] In some embodiments, the electrolysis can be conducted at a current density of about 50 mA/cm.sup.2 to about 10 A/cm.sup.2.

[0131] The temperature of molten salt electrolyte in the molten salt electrolysis step 40 can be adjusted in accordance with the type of molten salt electrolyte used. For example, FIG. 10 illustrates that molten salt electrolysis using an eutectic of NaCl and iron chloride (e.g., FeCl.sub.3) can be performed at a temperature of about 400 C. FIG. 11 illustrates that molten salt electrolysis using an eutectic of LiClKCl and iron chloride (e.g., FeCl.sub.3) can be performed at a temperature of about 500 C.

[0132] The electrochemical cell of a molten salt electrolysis reactor can include any number of cell configurations, such as a cell with a single electrolysis chamber that includes a single anode and a single cathode, a cell with multiple anodes and cathodes, a cell that includes heterogenous bipolar electrodes, and a cell with multiple chambers each, which includes anodes and cathodes separated by junctions or membranes.

[0133] FIG. 8 illustrates an example of an electrochemical cell suited for moderate temperature batch operation that allows recovery of solid iron electrodeposited on the cathode surface. The electrochemical cell includes an electrolysis chamber that contains a moderate temperature chloride based molten salt electrolyte, such as NaCl, LiClKCl, NaClKCl, in which the iron chloride (FeCl.sub.3) is dissolved as well as a vertically-aligned flat-plate cathode and dimensionally stable anode (e.g., RuO.sub.2 coated graphite) to which an electric potential can be applied. The cathode and anode can be provided in other configurations, such as concentrically plated circular electrodes. The cathode and anode are separated from one another in the electrochemical cell by a porous partition wall, such as a separator or diaphragm, positioned between and separating the cathode and anode. The separator or diaphragm can inhibit redox shuttling and back reaction between the metal plated on the cathode and Cl.sub.2 gas generated at the anode. The separator or diaphragm can include, for example, a ceramic with a porosity of about 10% to about 60%.

[0134] FIGS. 8 and 9 show that FeCl.sub.3 formed by non-carbothermic chlorination of iron ore, such as taconite, can be dissolved in a moderate temperature metal molten salt electrolyte, such as NaCl, LiClKCl, NaClKCl or other eutectic mixtures, and electrodeposited at moderate temperatures (e.g., about 475 C.-500 C.) as a solid iron (FIG. 9) on a surface of a tungsten or molybdenum cathode while Cl.sub.2 gas evolution is facilitated on a dimensionally stable anode, such as RuO.sub.2 coated graphite dimensionally stable anode. Referring again to FIG. 5-7, the Cl.sub.2 gas generated at the anode during the molten salt electrolysis can be recycled back into the halogen acid generating reactor for production of HCl used in the non-carbothermic chlorination step.

[0135] Referring again to FIG. 7, following halide-based molten salt electrolysis of the eutectic of iron halide and halide salt, at step 342, the electrolyzed or deposited iron can be collected or recovered from the molten salt electrolysis reactor. In one example for batch molten salt electrolysis performed at moderate temperatures below the melting temperature of the iron, the accumulated iron can be separated periodically from or continuously from the electrochemical cell. For example, the accumulated iron can be recovered by removing the cathode from the molten salt electrolysis reactor and scraping the iron from the cathode.

[0136] Optionally, water, which is generated as a co-product of the non-carbothermic chlorination reaction 334, can be combined with halogen gas (e.g., Cl.sub.2) evolved in the electrolysis reaction in the molten salt electrolysis reactor to regenerate the halogen acid (e.g., HCl). Other, more direct ways of combining water and halogen gas (e.g., Cl.sub.2) to re-generate halogen acid may also be used. Since the process 330 does not involve direct CO.sub.2 generation, and assuming all electrolysis steps utilize clean electricity (no indirect emissions), the process 330 can provide iron from metal oxides while being free of any CO.sub.2 and perfluorocarbon (PFC) emissions.

[0137] Advantageously, the system and process described in FIGS. 7-9 offer possibilities for lowering overpotential losses and enhancing current efficiency, ultimately lowering the specific electrical energy consumption and cost.

Example 1

[0138] This example describes the fabrication and characterization of a dimensionally stable anode that includes a plate-shaped graphite substrate at least partially coated with a transition metal oxide, such as RuO.sub.2.

[0139] Ruthenium metal was deposited onto the graphite substrate at a loading of approximately 250 g/cm.sup.2. The metal was then converted to oxide through annealing in air at 400 C. for 18 hours. As can be seen in FIG. 12, the electrode appears to have a uniform ruthenium coverage prior to annealing (right), and coverage remains uniform but changes to a bluish color, indicating ruthenium oxide after annealing (left).

[0140] These graphite-RuO.sub.2 anodes were used in the electrolysis of Nd solid sponge and showed lower and more stable cell voltage during a 1-hour electrolysis at 250 mA/cm.sup.2 and 475 C. than bare graphite operated under the same conditions. The corresponding electrolysis cell voltage traces can be seen in FIGS. 13 and 14.

[0141] Characterization of DSAs following operation in molten salts was performed to understand how the coatings are modified or degraded during their service life. XRD measurements revealed that the coatings are unchanged. The RuO.sub.2 coating does not significantly degrade, demonstrating that the surface layers are robust under service conditions.

[0142] In addition, the surface morphology of the samples was characterized using SEM and EDS to map chemical changes. As with XRD, these measurements showed plating of NdOCI onto the anodes with many Nd-rich plates covering the surface. There was no evidence of delamination or other degradation of the underlying RuO.sub.2 surface.

Example 2

[0143] This example describes the fabrication and characterization of a dimensionally stable anode that includes a plate-shaped graphite substrate at least partially coated with a transition metal oxide, such as Fe.sub.2O.sub.3.

[0144] Fe.sub.2O.sub.3 powder was deposited onto the graphite substrate and sintered to form a non-ceramic Fe.sub.2O.sub.3 coating. The Fe.sub.2O.sub.3-coated graphite anode was used in the electrolysis of Nd in a molten salt electrolyte.

[0145] FIGS. 15(A-B) illustrate images of an Fe.sub.2O.sub.3-coated graphite anode before and after molten salt electrolysis of neodymium metal.

[0146] FIG. 15(C) is a plot showing cell voltage during constant current (200 mA/cm.sup.2) Nd sponge deposition in an electrochemical cell employing a Fe.sub.2O.sub.3-coated graphite anode.

[0147] FIG. 16(A) illustrates images of the anode surface of an Fe.sub.2O.sub.3-coated graphite anode before and after molten salt electrolysis of neodymium metal.

[0148] FIG. 16(B) illustrates profilometry plots of the anode surfaces of an Fe.sub.2O.sub.3-coated graphite anode before and after molten salt electrolysis of neodymium metal. The profilometry data show that the anode surface is not roughened after molten salt electrolysis in the molten salt electrolyte.

[0149] From the above description, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.