Recovery of rare-earth metals from magnet scrap

Abstract

A process for recovery of rare-earth metals from magnet scrap includes leaching a rare-earth metal containing magnet scrap with halogen acids to form an aqueous leachate solution that includes rare-earth metal halides, at least partially dehydrating the aqueous leachate solution to form a dehydrated or partially dehydrated rare-earth metal halide feedstock, and electrolyzing the dehydrated or partially dehydrated rare-earth metal halide feedstock by molten salt electrolysis to form rare-earth metal and halogen(s).

Description

RELATED APPLICATION

[0001] This application claims priority from U.S. Provisional Application No. 63 / 715,793, filed Nov. 4, 2024, the subject matter of which is incorporated herein by reference in its entirety.BACKGROUND

[0002] Domestic production of rare-earth metals for use in permanent magnets has been hindered by the significant environmental impact of the required purification processing steps to create pure rare-earth oxides from their ores. Additionally, the incumbent oxyfluoride molten salt electrolysis (MSE) process for converting pure oxide to metal produces both dangerous perfluoro-carbons, carbon dioxide and carbon monoxide. The United States mines approximately 15% of the world's supply of neodymium ore, but, due to these dangerous and environmentally unfriendly processing techniques, does not participate in any other portion of the neodymium iron boron magnet supply chain. Due to these difficulties, virtually no recycling of neodymium from used magnets occurs. While hydrogen decrepitation to break up used magnet metals for direct re-sintering into new magnets has been explored to eliminate the need to re-electrolyze any recovered magnets, significant neodymium oxide is formed during this process which weakens the magnet.SUMMARY

[0003] Embodiments described herein relate to a process for recovery of rare-earth metals from magnet scrap. The process includes leaching a rare-earth metal containing magnet scrap with halogen acids to form an aqueous leachate solution that includes rare-earth metal halides and optionally iron halides. The pH of the aqueous leachate solution is increased using an oxide or hydroxide salt or by limiting the acid during leaching to precipitate iron or iron oxide from the aqueous leachate solution. The precipitated iron or iron oxide is removed from the aqueous leachate solution. The aqueous leachate solution is at least partially dehydrated to form a dehydrated or partially hydrated rare-earth metal halide feedstock. The dehydrated or partially hydrated rare-earth metal halide feedstock is electrolyzed by molten salt electrolysis to form rare-earth metal and halogen(s).

[0004] In some embodiments, the rare-earth metal includes at least one of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), or yttrium (Y).

[0005] In some embodiments, the process further includes grinding or crushing the magnet scrap to sufficiently small particles to enhance leaching of the rare-earth metals from the magnet scrap.

[0006] In some embodiments, the rare-earth metal magnet scrap includes neodymium, iron, and oxides thereof. For example, the magnet scrap can include Nd—Fe—B magnet scrap.

[0007] In some embodiments, the magnet scrap includes Nd2O3, and the magnet scrap is leached with an HCl solution at a concentration of about 0.1 M to about 4 M.

[0008] In some embodiments, the pH of the aqueous leachate solution is increased by adding potassium hydroxide at a concentration effective to precipitate iron or iron oxide from the aqueous leachate without affecting neodymium concentration in the aqueous leachate solution.

[0009] In some embodiments, the aqueous leachate is at least partially dehydrated using residual heat from resistive losses associated with the molten salt electrolysis.

[0010] In some embodiments, the process further includes adding at least one rare-earth metal or oxide thereof to the rare-earth metal containing magnet scrap to increase the concentration of rare-earth metal halides in the aqueous leachate solution.

[0011] In some embodiments, the molten salt electrolysis is performed in an electrochemical cell. The electrochemical cell can include an anode and a cathode provided in a molten salt electrolyte. The anode can be inert or non-consumable, partially consumable, and / or dimensionally stable during electrolysis.

[0012] In some embodiments, the anode can include at least one of titanium, graphite, tungsten, molybdenum, or graphite optionally coated with metal oxide or mixed-metal oxide, and the cathode can include an inert or partially consumable material.

[0013] In some embodiments, the rare-earth metal halide feedstock is partially hydrated, and the anode includes graphite coated with a metal oxide or mixed-metal oxide.

[0014] In some embodiments, the inert material can include graphite, tungsten or molybdenum.

[0015] In some embodiments, the molten salt electrolysis can be performed via a batch or continuous process at a temperature effective for electrodeposition of a rare-earth metal on the cathode for recovery at the cathode or into a collection vessel near the cathode.

[0016] In some embodiments, the molten salt includes a eutectic of at least two of LiCl, KCl, NaCl, CsCl, MgCl2, BaCl2, SrCl2, or CaCl2 and the molten salt electrolysis is conducted at a temperature of about 400° C. to about 1400° C.

[0017] In some embodiments, the process further includes supplying current effective for molten salt electrolysis of the rare-earth metal halide to rare-earth metal and halogen gas.

[0018] In some embodiments, electrolysis is conducted at a current density of about 50 mA / cm2 to about 40 A / cm2.

[0019] In some embodiments, the process produces substantially no CO2 or perfluorocarbon emissions during operation.

[0020] Other embodiments described herein relate to a rare-earth metal recovered from magnet scrap by the process described herein.

[0021] Other embodiments described herein relate to a system for recovery of rare-earth metals from magnet scrap. The system can include a halogenation reactor that includes rare-earth metal containing magnet scrap and a halogen acid configured for leaching the rare-earth metal containing magnet scrap to form an aqueous leachate solution that includes rare-earth metal halides, a dehydration reactor that includes the aqueous leachate solution from the halogenation reactor configured to at least partially dehydrate the aqueous leachate solution to form a dehydrated or partially hydrated rare-earth metal halide feedstock, and an electrolysis reactor that includes the dehydrated or partially hydrated rare-earth metal halide feedstock configured for molten salt electrolysis of the dehydrated or partially hydrated rare-earth metal halide feedstock to rare-earth metals and halogen(s). Optionally, the electrolysis reactor can provide residual heat from resistive losses associated with the molten salt electrolysis for dehydration of the aqueous leachate solution.BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 illustrates a schematic flow diagram of a process for recovery of rare-earth metals from magnet scrap.

[0023] FIG. 2 illustrates a schematic diagram of a system for performing the recovery of rare-earth metals from magnet scrap.

[0024] FIG. 3 illustrates a schematic flow diagram of a process for recovery of rare-earth metals from magnet scrap in accordance with another embodiment.

[0025] FIGS. 4(A-B) illustrate UV-VIS spectra of Nd—Fe—B magnet leachate at native pH (˜1) compared to an acid limited leachate (˜pH 5) shows no change in the absorbance of the Nd peak at approximately 575 nm while significantly reducing absorbance of all peaks below 500 nm.

[0026] FIGS. 5(A-B) illustrate images showing Neodymium metal (A) and iron metal (B) deposited from hydrated chloride salts in a chloride based MSE process to create compact metal deposits.DETAILED DESCRIPTION

[0027] For convenience, certain terms employed in the specification, examples, and appended claims are collected here. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0028] 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.

[0029] The terms “comprise,”“comprising,”“include,”“including,”“have,” and “having” are used in the inclusive, open sense, meaning that additional elements may be included, but items not specifically mentioned are not excluded. The terms “such as”, “e.g.,”, as used herein are non-limiting and are for illustrative purposes only. “Including” and “including but not limited to” are used interchangeably.

[0030] It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely”, “only” and the like in connection with the recitation of claim elements, or the use of a “negative” limitation.

[0031] Throughout this disclosure, 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.

[0032] “Optional” or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not.

[0033] The term “or” as used herein should be understood to mean “and / or”, unless the context clearly indicates otherwise.

[0034] 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.

[0035] 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.

[0036] Embodiments described herein relate to a system and process for the recovery of rare-earth metals from magnet scrap and, particularly, relates to a sustainable system and process for the extraction or recovery of rare-earth metals from magnet scrap using molten salt electrolysis. The process includes leaching a rare-earth metal containing magnet scrap to form a rare-earth metal halide feedstock and electrolyzing the rare-earth metal halide feedstock by molten salt electrolysis to form rare-earth metal or rare-earth metal alloys and halogen(s). The rare-earth metal or rare-earth metal alloys can then be reused as raw material for a rare-earth metal magnet.

[0037] As illustrated in the flow diagram of FIG. 1, the process can include leaching magnet scrap that includes a mixture of rare-earth metals (e.g., neodymium) and iron in both the oxide and / or metallic form, with one or more halogen acids to produce an aqueous leachate solution of rare-earth metal (e.g., neodymium) halide and iron halide. The pH of the aqueous leachate solution is increased using an oxide or hydroxide salt or by limiting the acid during leaching to precipitate iron or iron oxide from the aqueous leachate solution. The precipitated iron or iron oxide is removed from the aqueous leachate solution. The aqueous leachate solution can be at least partially dehydrated to form a dehydrated or partially hydrated rare-earth metal halide feedstock that is electrolyzed by halide molten salt electrolysis to form rare-earth metal (e.g., neodymium metal) or iron / rare-earth metal master alloys.

[0038] Halide molten salt electrolysis of the dehydrated or partially hydrated rare-earth metal halide feedstock can provide high-efficiency electrowinning of solid or liquid rare-earth metal (e.g., neodymium metal) or iron / rare-earth metal master alloys while evolving halogen gas, such as chlorine (Cl2) gas. The rare-earth metal (e.g., neodymium metal) or iron / rare-earth metal master alloys produced by molten salt electrolysis can be recovered and formed into fresh rare-earth metal magnets. The halogen gas can optionally be recycled in a halogenation process with water, such as water obtained during at least partially dehydrating the aqueous leachate solution, to form halogen acid.

[0039] Advantageously, the molten salt electrolysis can enable the use of an inert or non-consumable, partially consumable, and / or dimensionally stable anode (DSA), which can potentially lead to reduced energy consumption, stable electrochemical cell operation, and ease of process scalability. The use of a DSA, which includes a graphite substrate coated with metal oxide or mixed-metal oxide as described herein, allows electrolysis of a partially hydrated rare-earth metal halide feedstock, as the metal oxide coating or mixed-metal oxide coating protects the DSA core (e.g., graphite) from reaction with water.

[0040] Referring to FIG. 2, the process of FIG. 1 can generally be performed using a system 10 that includes a non-carbothermic halogenation reactor 12 configured for non-carbothermic halogenation and / or leaching of rare-earth metal and / or iron compounds to rare-earth metal halides and iron halide(s) from rare-earth metal containing magnet scrap, a dehydration reactor 14 for at least partially dehydrating aqueous leachate solution that includes the rare-earth metal halides and iron halide(s) to form a dehydrated or partially dehydrated rare-earth metal halide feedstock, and a molten salt electrolysis reactor 16 configured for halide molten salt electrolysis of the dehydrated or partially dehydrated rare-earth metal halide feedstock to rare-earth metal (e.g., neodymium metal) or iron / rare-earth metal master alloys and halogen gas. Optionally, the system 10 can include a halogen acid generating reactor 18 for converting halogen gas (e.g., Cl2 gas) generated in the molten salt electrolysis reactor 16 and water separated during at least partial dehydration of the aqueous leachate solution to a halogen acid (e.g., HCl). The halogen acid generated can be optionally transferred to the non-carbothermic halogenation reactor 12 at a molarity effective for non-carbothermic halogenation of the rare-earth metal containing magnet scrap.

[0041] The non-carbothermic halogenation reactor 12, dehydration reactor 14, molten salt electrolysis reactor 16, and optional halogen acid generating reactor 18 can be integrated, connected, coupled, or in communication such that products formed in each respective reactors, 12, 14, 16, or 18 including rare-earth metal halides, iron halides, water, halogens, and halogen acids can flow or be transferred between respective reactors. For example, an aqueous solution containing rare-earth metal halides and iron halide(s) generated in the non-carbothermic halogenation reactor 12 can be transferred or flow to the dehydration reaction 14 and at least partially dehydrated, water removed in the dehydration reactor 12 can be transferred or flow to the halogen acid generating reactor 18, halogen gas formed in the molten salt electrolysis reactor 16 can flow to the halogen acid generating reactor 18, and halogen acid generated in the halogen acid generating reactor 18 can be transferred or flow to the non-carbothermic halogenation reactor 12.

[0042] FIG. 3 illustrates a schematic flow diagram of a process 30 for the extraction or recovery of rare-earth metals from magnet scrap using molten salt electrolysis described in FIGS. 1 and 2. The process 30 for the extraction or recovery of rare-earth metals from magnet scrap using molten salt electrolysis starts at step 32 by crushing or grinding used magnets, such as permanent magnets or rare-earth metal containing magnets to have their outer coatings removed. The rare-earth metal containing magnets can include at least one rare-earth metal, such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), or yttrium (Y) or a mixture thereof, iron, and oxides thereof. For example, the rare-earth metal magnet scrap includes neodymium, iron, and oxides thereof. The magnet scrap can be ground or crushed to sufficiently small particles to enhance leaching of the rare-earth metals from the magnet scrap.

[0043] In some embodiments, the magnet scrap can include permanent magnet scrap of the NdFeB type. Permanent magnets of the NdFeB type, when used in the process, may be contained in industrial waste originating for example from the recycling of hard drives of central processing units of PC or laptop computer type, loudspeakers, for example of cell phones or computers, small electric motors, or else be composed of waste from the production of permanent magnets. Such magnets are often surrounded by a layer of nickel. Nevertheless, the coating thereof may be based on other metals, such as cobalt, a copper-cobalt alloy, zinc, etc. The same process can be applied to epoxy-coated magnets.

[0044] The ground or crushed magnet scrap, which includes a mixture of rare-earth metals (e.g., neodymium) and iron in both the oxide and / or metallic form, is then transferred to the non-carbothermic halogenation reactor. Optionally, at least one rare-earth metal, rare-earth metal alloy, or oxide thereof can be added to or mixed with the ground or crushed rare-earth metal containing magnet scrap prior to and / or after transfer to the non-carbothermic halogenation reactor to increase the concentration of rare-earth metal halides to be leached. The at least one rare-earth metal, rare-earth metal alloy, or oxide thereof can include, for example, rare-earth metals selected from Y, La, Ce, Nd, Pr, Sm, Gd, Dy, Tb, and Ho, optionally alloyed with a transition metal, such as Fe and / or Co, or oxides thereof.

[0045] The ground or crushed rare-earth metal containing magnet scrap and optional rare-earth metal, rare-earth metal alloy, or oxide thereof is subjected to non-carbothermic halogenation at step 34 to produce an aqueous leachate solution that includes rare-earth metal halides as well as potentially other metal halides, such as iron halides. The non-carbothermic halogenation step can include reacting the ground or crushed rare-earth metal containing magnet scrap and optional rare-earth metal, rare-earth metal alloy, or oxide thereof at room temperature (e.g., 25° C.) with a halogen acid solution, such as a HCl, HF, or HBr solution, at a molarity or pH effective to halogenate the rare-earth metals and iron oxides and form an aqueous solution of the rare-earth metal halides and iron halides. By way of example, HCl can be provided in an aqueous solution at a concentration of about 0.1M to about 4M or at a pH less than 1 and combined with the ground or crushed rare-earth metal containing magnet scrap and optional rare-earth metal, rare-earth metal alloy, or oxide thereof to convert the rare-earth metals and iron oxides to rare-earth metal halides and iron halides or hydrated iron chlorides.

[0046] By way of example, Nd2O3 can be reacted at room temperature with about 0.1M to 3M HCl in the non-carbothermic halogenation reactor at room temperature to convert the Nd2O3 to NdCl3. Similarly, Fe2O3 can be reacted with undiluted HCl to convert the Fe2O3 to FeCl3.

[0047] At step 36, the aqueous leachate solution that includes the rare-earth metal halides and iron halides can have some or all the iron removed by limiting the initial amount of HCl added or raising the pH of the solution using various oxide or hydroxide salts, such as potassium hydroxide, which will result in a solution of potassium and rare-earth metal halides, such as neodymium chloride, two key components of a halide molten salt electrolyte, or with neodymium oxide produced from ore to create a pure neodymium chloride solution. By way of example, FIGS. 4(A-B) illustrate UV-Vis spectra showing that raising the pH (by limiting the acid used during leaching in this case) can be effective at reducing the iron concentration (series of peaks below 500 nm) through precipitation while not affecting the neodymium concentration (575 nm peak).

[0048] At step 38, after generation of the aqueous leachate solution that includes the rare-earth metal halides and iron halides, the aqueous leachate solution can be at least partially dehydrated by, for example, evaporation or sublimation, to a dehydrated or partially dehydrated (or partially hydrated) rare-earth metal halide feedstock prior to molten salt electrolysis. In some embodiments, the leachate solution can be at least partially dehydrated using residual heat from the resistive losses associated with the molten salt electrolysis process leaving the rare-earth metal-iron mixture as a chloride salt for master alloy production.

[0049] At step 40, the dehydrated or partially hydrated rare-earth metal halide feedstock formed by at least partially dehydrating the aqueous leachate solution generated by non-carbothermic halogenation of the rare-earth metal containing magnet scrap 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 pure or substantially pure rare-earth metals or alloys of metals, such as a neodymium and iron alloy that can be extracted or recovered from the electrolysis reactor. Advantageously, electrolyzing of rare-earth metals via halide-based molten salt electrolysis offers the potential to significantly reduce electrical energy requirement and operating cost associated with rare-earth metal recovery.

[0050] In some embodiments, the electrolysis reactor can include an electrochemical cell or chamber that contains the halide-based molten salt electrolyte in which the rare-earth metal halide and iron halide are dissolved and a cathode and 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 rare-earth metal halide and iron halide dissolved in the halide-based molten salt electrolyte is electrolyzed, rare-earth metal(s) and iron are electrodeposited on the cathode of the cell, and halogen gas (e.g., Cl2) is generated at the anode of the reactor.

[0051] 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.

[0052] The anode can be inert or non-consumable, partially consumable, and / or dimensionally stable during electrolysis. Examples of inert or non-consumable, partially consumable, and / or dimensionally stable anodes include an anode of at least one of titanium, graphite, tungsten, or molybdenum, each of which is optionally coated with a metal oxide or mixed-metal oxide.

[0053] In some embodiments, an anode that includes graphite coated with mixed-metal oxide can form a dimensionally stable anode (DSA) catalytic to halogen (e.g., chlorine) gas evolution. The DSA can include graphite coated with at least one electrochemically active transition metal oxide that is not a ceramic or is non-ceramic. By “non-ceramic” it is meant that the transition metal oxide coating, when deposited or formed on the graphite anode, does 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 RuO2, IrO2, a period 4 transition metal oxide, such as Fe2O3, NiO, Cr2O3, Mn2O3, CuO, or binary mixtures thereof. Advantageously, the use of a DSA, which includes a graphite substrate coated with metal oxide or mixed-metal oxide as described herein, allows electrolysis of a partially hydrated rare-earth metal halide feedstock, as the metal oxide coating or mixed-metal oxide coating protects the DSA core (e.g., graphite) from reaction with water.

[0054] The electrochemically active transition metal oxide of the coating can be substantially amorphous, partially crystalline, or a blend thereof. In some embodiments, where RuO2 is used as the electrochemically active transition metal oxide, the RuO2 is substantially amorphous. Amorphous RuO2 in the electrochemically active coating has higher catalytic activity for halogen gas (e.g., chlorine gas) evolution than crystalline RuO2, 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.

[0055] In some embodiments, the electrochemically active coating can include a 30:70 wt. % to 60:40 wt. % binary mixture of two of RuO2, IrO2, Fe2O3, NiO, Cr2O3, Mn2O3, 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 RuO2, IrO2, Fe2O3, NiO, Cr2O3, Mn2O3, 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 RuO2, IrO2, Fe2O3, NiO, Cr2O3, Mn2O3, 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.

[0056] In other 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.

[0057] In some embodiments, a current source can provide current effective for molten salt electrolysis of the metal halide(s) to metal and halogen (e.g., Cl2) 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 / cm2 to about 40 A / cm2.

[0058] 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 neodymium or 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%.

[0059] The halide based molten salt electrolyte provided in the electrochemical cell and in which the rare-earth metal halide and iron halide are dissolved can include halides of alkaline metals and alkaline earth metals, such as chlorides or fluorides of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba either pure or in mixtures, such as eutectic mixtures.

[0060] In some embodiments, the molten salt electrolyte can include a moderate temperature chloride based molten salt electrolyte. The moderate temperature chloride based molten salt electrolyte can include a eutectic of iron chloride and at least one or more of LiCl, KCl, NaCl, CsCl, MgCl2, BaCl2, SrCl2, or CaCl2. The eutectic can have moderate to high melting temperature of about 400° C.-1400° C. depending on the salts selected for combination with the rare-earth metal halide feedstock. For example, the eutectic can have a melting point of about 400° 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., about 1050° C.-1250° C., about 1150° C.-1350° C., about 1250° C.-1450° C., about 1300° C.-1400° C. or higher.

[0061] The temperature of the 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, 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.

[0062] In some embodiments, the moderate temperature molten salt electrolysis can be conducted at a temperature of about 400° C. to about 1000° C., for example, about 400° C.-550° C., about 450° C.-650° C., about 550° C.-750° C., or about 650° C.-850° C.

[0063] In other embodiments, the high temperature molten salt electrolysis can be conducted at a temperature of about 850° C.-1050° C., about 950° C.-1150° C., about 1050° C.-1250° C., about 1150° C.-1350° C., about 1250° C.-1450° C., or about 1300° C.-1400° C. or higher.

[0064] In some embodiments, the electrolysis can be conducted at a current density of about 50 mA / cm2 to about 40 A / cm2. For example, typically, at current densities in the 0.2-0.4 A / cm2 range, Nd electrowon using such melts deposits as dendritic sponge on a tungsten or molybdenum cathode.

[0065] The electrochemical cell of the 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.

[0066] For example, the electrochemical cell can include an electrolysis chamber that contains a moderate temperature chloride based molten salt electrolyte, such as NaCl, LiCl—KCl, NaCl—KCl, in which the rare-earth metal halide is dissolved as well as a vertically-aligned flat-plate cathode and DSA (e.g., RuO2 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 can be separated from one another in the electrochemical cell by a porous partition wall, such as separator or diaphragm positioned between and separating the cathode and anode. The separator or diaphragm can inhibit redox shuttling and back reaction between metal plated on the cathode and Cl2 gas generated at the anode. The separator or diaphragm can include, for example, a ceramic or transition metal with a porosity of about 10% to about 60%.

[0067] Advantageously, as illustrated in FIGS. 5(A-B), the plating conditions, electrolyte composition, operating temperature and operating current density can be adjusted to efficiently deposit both neodymium metal and iron metal from hydrated salts in a molten salt electrolyte eliminating the process intensive need to fully dehydrate the chloride salts.

[0068] Referring again to FIG. 3, following halide-based molten salt electrolysis of the eutectic of rare-earth metal halide and iron halide salt, at step 42, the electrolyzed or deposited rare-earth metal and 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 rare-earth metal and iron, the accumulated rare-earth metal and 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 rare-earth metal and iron from the cathode.

[0069] Optionally, water from the leachate solution can be combined with halogen gas (e.g., Cl2) 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., Cl2) to re-generate halogen acid may also be used. Since the process 30 does not involve direct CO2 generation, and assuming all electrolysis steps utilize clean electricity (no indirect emissions), the process 30 can provide rare-earth metals and optionally iron from magnet scrap while being free of any CO2 and perfluorocarbon (PFC) emissions.

[0070] Advantageously, the system and process described in FIGS. 1-3 provide easy and sustainable halide-based recycling of rare-earth magnets as well as offset the growing need for rare-earth metals, such as neodymium, to fuel electrification of transportation and increase reliance on consumer electronics while eliminating the need for any further greenhouse gas intensive separation and purification steps. The system and process described herein also allow used magnets of any condition to be returned to pure metal or metal alloy that can be used to make new magnets without any degradation in performance.

[0071] 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.

Claims

1. A process for recovery of rare-earth metals from magnet scrap, the process comprising:leaching a rare-earth metal containing magnet scrap with halogen acids to form an aqueous leachate solution that includes rare-earth metal halides and optionally iron halides;increasing the pH of the aqueous leachate solution using an oxide or hydroxide salt or by limiting the acid during leaching to precipitate iron or iron oxide from the aqueous leachate solution and removing precipitated iron or iron oxide from the aqueous leachate solution;at least partially dehydrating the aqueous leachate solution to form a dehydrated or partially hydrated rare-earth metal halide feedstock; andelectrolyzing the dehydrated or partially hydrated rare-earth metal halide feedstock by molten salt electrolysis to form rare-earth metal and halogen(s).

2. The process of claim 1, wherein the rare-earth metal includes at least one of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), or yttrium (Y).

3. The process of claim 1, further comprising grinding or crushing the magnet scrap to sufficiently small particles to enhance leaching of the rare-earth metals from the magnet scrap.

4. The process of claim 1, wherein the rare-earth metal magnet scrap includes neodymium, iron, and oxides thereof.

5. The process of claim 1, wherein the magnet scrap comprises Nd—Fe—B magnet scrap.

6. The process of claim 1, wherein the magnet scrap includes Nd2O3 and the magnet scrap is leached with an HCl solution at a concentration of about 0.1 M to about 4 M.

7. The process of claim 1, wherein the pH of the aqueous leachate solution is increased by adding potassium hydroxide at a concentration effective to precipitate iron or iron oxide from the aqueous leachate without affecting neodymium concentration in the aqueous leachate solution.

8. The process of claim 1, wherein the aqueous leachate is at least partially dehydrated using residual heat from resistive losses associated with the molten salt electrolysis.

9. The process of claim 1, further comprising adding at least one rare-earth metal or oxide thereof to the rare-earth metal containing magnet scrap to increase the concentration of rare-earth metal halides in the aqueous leachate solution.

10. The process of claim 1, wherein the molten salt electrolysis is performed in an electrochemical cell, the electrochemical cell including an anode and a cathode provided in a molten salt electrolyte, the anode being inert or non-consumable, partially consumable, and / or dimensionally stable during electrolysis.

11. The process of claim 10, wherein the anode comprises at least one of titanium, graphite, tungsten, molybdenum, or graphite optionally coated with metal oxide or mixed-metal oxide and the cathode comprises an inert or partially consumable material.

12. The process of claim 11, wherein the rare-earth metal halide feedstock is partially hydrated and the anode includes graphite coated with metal oxide or mixed-metal oxide.

13. The process of claim 11, wherein the inert material includes graphite, tungsten or molybdenum.

14. The process of claim 10, wherein the molten salt electrolysis is performed via a batch or continuous process at a temperature effective for electrodeposition of a rare-earth metal on the cathode for recovery at the cathode or into a collection vessel near the cathode.

15. The process of claim 10, wherein the molten salt includes a eutectic of at least two of LiCl, KCl, NaCl, CsCl, MgCl2, BaCl2, SrCl2, or CaCl2 and the molten salt electrolysis is conducted at a temperature of about 400° C. to about 1400° C.

16. The process of claim 10, further comprising supplying current effective for molten salt electrolysis of the rare-earth metal halide to rare-earth metal and halogen gas.

17. The process of claim 15, wherein electrolysis is conducted at a current density of about 50 mA / cm2 to about 40 A / cm2.

18. The process of claim 1, producing substantially no CO2 or perfluorocarbon emissions during operation.

19. A rare-earth metal recovered from magnet scrap by the process of claim 1.

20. A system for recovery of rare-earth metals from magnet scrap, the system comprising:a halogenation reactor including rare-earth metal containing magnet scrap and a halogen acid configured for leaching the rare-earth metal containing magnet scrap to form an aqueous leachate solution that includes rare-earth metal halides;a dehydration reactor including the aqueous leachate solution from the halogenation reactor configured to at least partially dehydrate the aqueous leachate solution to form a dehydrated or partially hydrated rare-earth metal halide feedstock; andan electrolysis reactor including the dehydrated or partially hydrated rare-earth metal halide feedstock configured for molten salt electrolysis of the dehydrated or partially hydrated rare-earth metal halide feedstock to rare-earth metals and halogen(s), optionally wherein the electrolysis reactor provides residual heat from resistive losses associated with the molten salt electrolysis for dehydration of the aqueous leachate solution.

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