Metal Production from Halide-Based Molten Salt Electrolysis Process

This application is a continuation-in-part of U.S. patent application Ser. No. 18/363,163, filed Aug. 1, 2023 (now U.S. Pat. No. 12,378,684). This application also claims priority from U.S. Provisional Application No. 63/677,001, filed Jul. 30, 2024, the subject matter of which are incorporated herein by reference in their entirety.

This invention was made with government support under DE-EE0010846 awarded by the US Department of Energy. The government has certain rights in the invention.

Graphite is the de facto anode in molten halide systems for either the production of chlorine gas in chloride melts, or as a consumable anode in oxide and oxy-fluoride melts as in the ALCOA process for Al electrowinning or the traditional electrolysis of neodymium oxide to neodymium metal. For chlorine evolution, the large anode overpotential on graphite is a major issue and is often cited as a prohibitive factor in process viability for chloride melt electrolysis due to the increased energy consumption and associated operating costs.

The chlor-alkali industry was revolutionized in the middle of the 20th century with the advent of the Dimensionally Stable Anode (DSA) which was composed of Mixed Metal Oxides (MMO) sintered onto a titanium current collector. The “dimensionally stable” moniker refers to the non-consumable nature of the electrode during electrochemical processing. These chlor-alkali DSAs also brought a significant reduction in anodic overpotential for chlorine evolution and oxygen evolution in electrolytic cells, which utilize aqueous electrolytes. The present invention addresses the challenge of developing a DSA electrode that operates in extreme conditions of non-aqueous molten salt media. Molten salts are significantly aggressive compared to aqueous media, given their higher operating temperatures, their highly corrosive nature, and the higher chlorine evolution rates that they need to support.

At present, industrial metal recovery and purification suffer from the environmental malignity of their byproducts (CO, CO, PFC) and certain critical materials can simply not be produced domestically by those processes. An example is rare-earth metal production using electrowinning with a fluoride-containing electrolyte. Electrowinning of Nd can generate perfluorocarbons (PFCs) via the reaction between the graphite anode and the fluoride-containing electrolyte. Accordingly, the conventional fluoride-based molten salt electrolysis route for neodymium and other rare earth metal production is not attractive from a sustainability point-of-view because of harmful COand perfluorocarbon gas emissions and the energy-intensive nature of this process.

Worldwide steel production is primarily generated by three main processes. The Blast Furnace-Basic Oxygen Furnace (BF-BOF) method, constituting 71% of production, involves the reduction of iron ore to pig iron in a blast furnace, emitting approximately 70% of CO2 in integrated iron-steel production plants. Secondary steel production, mainly utilizing steel scrap in electric arc furnaces (EAF), represents 24% of global production. Direct reduced iron (DRI) production accounts for 5% and is on the rise. Due to this massive environmental burden, efforts to develop cleaner alternatives through the electrolytic production of iron have gained interest. Existing and emerging clean processes ideally aim for emission-free operations by utilizing energy extracted from renewable sources. While processes operating at high temperatures (around 1600° C.) show promise, they face challenges related to high energy consumption, resulting in increased production costs. Conversely, processes operating at low temperatures (60-100° C.) suffer from significantly lower production rates and efficiency. Ideally, we would need a method that combines the advantages of both high and low-temperature processes, offering a clean, cost-effective, and practical solution for sustainable iron metal production.

U.S. Pat. No. 4,956,068 discloses a non-consumable anode that includes an oxide ceramic coating on a metal substrate for molten salt electrolysis of metals such as aluminum. The ceramic oxide coating can include copper oxide in solid solution with at least one further oxide, such as nickel ferrite, copper oxide, and nickel ferrite.

U.S. Pat. No. 6,821,312 discloses a cermet inert anode for the electrolytic production of metals, such as aluminum. The cermet inert anode includes agglomerates of ceramic phase and metal phase particles that are consolidated by pressing and sintering. The ceramic phase may include oxides of Ni, Fe, and at least one additional metal selected from Zn, Co, Al, Li, Cu, Ti, V, Cr, Zr, Nb, Ta, W, Mo, Hf, and rare earths. The metal phase can include Cu, Ag, Pd, Pt, Au, Rh, Ru, Ir, and/or Os. Inert anodes can include a monolithic component of such cermet materials, a substrate with at least one coating of the cermet material, or a core of the cermet material coated with a material of different composition.

WO 00/06802 discloses a cell for electrowinning of aluminum that includes a metal-based anode substrate with a metal core covered with a metal layer, an oxygen barrier layer, one or more intermediate layers, and an iron layer. The anode substrate is covered with an electrochemically active transition metal oxide layer, and in particular an iron oxide layer, which remains dimensionally stable during operation in the cell by maintaining in the electrolyte a sufficient concentration of iron species and dissolved alumina. The iron oxide-based layer is electrochemically active for the oxidation of oxygen ions into molecular oxygen.

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, IrO, FeO, NiO, CrO, MnO, 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, IrO, FeO, NiO, CrO, MnO, 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., FeO) are conductive for passing electrical current; hence, their resistive nature is not an issue as it may be in room temperature electrolysis systems.

In some embodiments, an electrolysis reactor for electrolytically generating one or more metal cathode product(s) during molten salt electrolysis can include a dimensionally stable anode (DSA) and a cathode positioned in a molten salt electrolyte containing fused salts. The dimensionally stable anode can be configured to produce, extract, or recover metal(s) from a metal-bearing material and produce a halogen gas, such as chlorine gas, during electrolysis in the molten salt electrolyte containing fused salts of the electrolytic reactor.

In some embodiments, the DSA can include a graphite substrate and a non-ceramic electrochemically active coating, which is catalytic to halogen gas evolution, disposed on at least a portion of the substrate. The coating on at least a portion of the graphite substrate that is catalytic to halogen gas evolution includes at least one electrochemically active transition metal oxide.

In some embodiments, the non-ceramic, transition metal oxide coating includes RuO, IrO, a period 4 transition metal oxide, such as FeO, NiO, CrO, MnO, CuO, or binary mixtures thereof.

In some embodiments, the non-ceramic, transition metal oxide coating includes a 30:70 wt. % to 60:40 wt. % binary mixture of two of RuO, IrO, FeO, NiO, CrO, MnO, or CuO.

In some embodiments, the non-ceramic, electrochemically active coating has a geometric surface coverage ratio of the substrate surface of about 0.000001:1 to 1:1.

In another embodiment, the dimensionally stable anode has an electrochemically active surface area to geometric surface area ratio of about 0.000001:1 to about 10,000:1

In some embodiments, the non-ceramic, coating has a thickness of about 1 μm to about 1000 μm.

In some embodiments, a transition metal oxide, such as RuO, IrO, FeO, NiO, CrO, MnO, CuO, or a binary mixture thereof, can be sputtered on a surface of the graphite substrate.

In other embodiments, a transition metal oxide, such as RuO, IrO, FeO, NiO, CrO, MnO, CuO, or a binary mixture thereof, can be sintered on a surface of the graphite substrate.

In still other embodiments, the transition metal oxide can include a transition metal that is deposited by, for example, physical vapor deposition, chemical vapor deposition, sputter coating, dip coating, electrophoretic deposition, aerosol deposition, or jet spraying and that is oxidized.

In yet other embodiments, a transition metal oxide, such as RuO, IrO, FeO, NiO, CrO, MnO, CuO, or a binary mixture thereof, can be an electrodeposited transition metal, such as Ru, Ir, Fe, Ni, Cr, Mn, Cu, or binary mixture thereof, that is oxidized by, for example, annealing in an oxygen containing environment.

In some embodiments, the non-ceramic, electrochemically active coating includes at least two layers having differing compositions.

In some embodiments, the molten salt electrolyte provided in the electrolysis reactor includes a molten mixture of at least 50 mol % chloride containing fused salts.

In some embodiments, the balance of the fused salt includes a single electrolyte or mixture of electrolytes where the anion is a carbonate, sulfate, phosphate, fluoride, bromide, iodide, or hydroxide.

In some embodiments, the one or metal cathode product(s) that is generated includes at least one of Fe, Al, Mg, Ti, Li, Na, Dy, Nd, NdPr, La, or Ce, and the molten salt electrolyte includes a metal salt of the one or more metal cathode product(s). For example, the metal salt includes at least one of FeX, FeX, AlX, NdX, MgX, TiX, TiX, LiX, NaX, DyX, DyX, NdPrX, LaX, CeX, or CeX, where X is a halogen.

In some embodiments, the molten salt electrolyte includes a eutectic of the metal salt and at least one of LiCl, KCl, NaCl, CsCl, MgCl, BaCl, SrCl, or CaCl, and the molten salt electrolysis is conducted at a temperature of about 400° C. to about 1200° C. For example, the molten salt electrolyte can include a eutectic of FeXand/or FeX, where X is a halogen, and at least one of LiCl, KCl, NaCl, CsCl, MgCl, BaCl, SrCl, or CaCl, and the molten salt electrolysis is conducted at a temperature of about 400° C. to about 1200° C.

In some embodiments, electrolysis is conducted at a current density of about 50 mA/cmto about 10 A/cm.

Other embodiments described herein relate to a system for the production of iron from iron oxides and/or iron ore containing iron compounds and/or aqueous spent pickle liquor containing iron halide. The system includes an electrolysis reactor for molten salt electrolysis of iron halide feedstock to iron and halogen(s). 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. During electrolysis, iron is produced at the cathode from the iron halide feed stock and halogens are produced at the anode.

In some embodiments, the non-ceramic, transition metal oxide coating includes RuO, IrO, FeO, NiO, CrO, MnO, CuO, or binary mixtures thereof. For example, the transition metal oxide coating can include a 30:70 wt. % to 60:40 wt. % binary mixture of two of RuO, IrO, FeO, NiO, CrO, MnO, or CuO.

In some embodiments, the molten salt electrolyte includes a molten mixture of at least 50 mol % chloride containing fused salts. For example, the molten salt electrolyte includes a eutectic of FeXand/or FeX, where X is a halogen, and at least one of LiCl, KCl, NaCl, CsCl, MgCl, BaCl, SrCl, or CaCl, and the molten salt electrolysis is conducted at a temperature of about 400° C. to about 1200° C.

In some embodiments, electrolysis is conducted at a current density of about 50 mA/cmto about 10 A/cm.

In some embodiments, the system further includes 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.

In some embodiments, the halogenation reactor can include a halogen acid or leaching acid converted from the generated halogen at a molarity effective to convert the iron oxide to the iron halide feedstock.

In some embodiments, the iron ore can include at least one of taconite, hematite, siderite, ironstone, magnetite ore, limonite, or goethite; and/or the aqueous spent pickle liquor can include a product from a pickling bath used in the production of steel.

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.

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.

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.

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.

The term “A and/or B” means “A or B, or A and B”.

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.

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.

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, IrO, FeO, NiO, CrO, MnO, 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, IrO, FeO, NiO, Cr, MnO, 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., FeO) are conductive for passing electrical current; hence, their resistive nature is not an issue as it may be in room temperature electrolysis systems.

is a schematic illustration of a non-consumable or dimensionally stable anodethat 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., Clor OCl).

The dimensionally stable anodeincludes a graphite substrateand an electrochemically active coatingdisposed on at least a portion of the substratethat 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 substrateis illustrated as being plate-shaped, the graphite substratecan 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 substratecan further be in the form of a fibrous graphite mesh, graphite fibers, graphite felt or fabric, and the like.

In some embodiments, the graphite substratecan 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.

The coatingdisposed on at least a portion of the graphite substratethat 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, IrO, a period 4 transition metal oxide, such as FeO, NiO, CrO, MnO, CuO, or binary mixtures thereof.

The electrochemically active transition metal oxide of the coating can be substantially amorphous, partially crystalline, or a blend thereof. In some embodiments, where RuOis used as the electrochemically active transition metal oxide, the RuOis substantially amorphous. Amorphous RuOin the electrochemically active coating has higher catalytic activity for halogen gas (e.g., chlorine gas) evolution than crystalline RuO, 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.

In some embodiments, the electrochemically active coatingcan include a 30:70 wt. % to 60:40 wt. % binary mixture of two of RuO, IrO, FeO, NiO, CrO, MnO, 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, IrO, FeO, NiO, CrO, MnO, 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, IrO, FeO, NiO, CrO, MnO, 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.

In some embodiments, the electrochemically active coatingcan have a geometric surface coverage ratio of the anodeof 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.

In other embodiments, the anodecan 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.