Process for producing rare earth metals

Abstract

A process for producing rare earth metals (REMs) is provided. This process involves subjecting rare earth oxides (REOs) or rare earth sulfides (RESs) to thermoelectrochemical reduction in a eutectic molten salt to obtain a thermoelectrochemical reduction product containing REMs. The obtained thermoelectrochemical reduction product is further subjected to a purification process. A process for converting REOs to RESs is also provided.

Description

[Technical Field]

[0001] References to related applications This application claims priority to U.S. Provisional Patent Application No. 63 / 508,290, filed on 15 June 2023. The contents of this application are incorporated herein by reference in their entirety.

[0002] Field of Invention The present invention generally relates to a process for producing rare earth metals (REMs). More specifically, the present invention relates to a process for producing REMs from rare earth oxides (REOs). This process involves thermoelectrochemical reduction of REOs or rare earth sulfides (RESs) obtained from REOs in a eutectic molten salt. Thus, the present invention also relates to a process for converting REOs to RESs. [Background technology]

[0003] Background of the Invention Demand for rare earth elements (REEs), also known as rare earth metals (REMs), such as neodymium (Nd) and dysprosium (Dy), is increasing as renewable energy becomes more important globally. [1-5] Strategic rare metals, which are important in clean energy applications such as wind turbines, electric vehicles, and hybrid vehicles, as well as in high-tech industries, are attracting attention. [3;6;7] On the other hand, a large amount of electronic waste (e-waste) consisting of NdFeB magnets is being generated. NdFeB magnets typically consist of 20-30 wt% REE (of which 15-25% is Nd), 50-70 wt% Fe, and 1.0 wt% B [8-11] It is composed of, and other metals such as copper, nickel, and cobalt, at a rate of approximately 5 wt%. The availability of REE is a significant challenge in the manufacture of permanent magnets. To date, less than 1% of REE has been recovered from e-waste. [1;12;13] This is mainly due to a lack of specific and sustainable technologies. [1;7;12-17] .

[0004] REE is primarily recycled from waste magnets in the form of rare earth oxides (REO) through an aqueous metallurgical process. [7;13;18;19] In the wet chemical method, waste magnets are dissolved in a strong inorganic acid and then extracted as various forms of REE, including oxides, sulfates, nitrates, hydroxides, carbonates, and oxalates. The extracted REE is then calcined in an air atmosphere at temperatures exceeding 500°C, resulting in the formation of a substance primarily containing REE in oxide form (REO). It is worth noting that the oxides produced by the aqueous metallurgical route need to be converted into high-purity metals for use in various electronics and high-tech industries. Furthermore, the direct recycling of waste magnets into rare metal alloys such as RE-Fe and RE-Mg (RE = Nd, Dy, or Pr) is carried out using molten fluorides and chlorides without separating Nd and Dy. [7;10;20;21] The product is primarily used for the production of NdFeB alloys. However, the literature lacks crucial information on the conversion of REO to pure rare earth metals using feasible, low-cost, and sustainable methods.

[0005] The inventors also recognize the following literature: US 2024 / 0052456; US 10,309,022; US 2021 / 0277531; US ​​3,748,095; US 2024 / 0158935; Wang et al.

[22] ; and Ben Holcombe et al.

[23] .

[0006] A process is needed to manufacture REM. This process must be efficient, cost-effective, environmentally friendly, and allow for industrialization. [Overview of the project] [Means for solving the problem]

[0007] Summary of the Invention In one aspect of the present invention, the inventors have designed and implemented a process for producing rare earth metals (REM) from rare earth oxides (REO). This process involves thermoelectrochemical reduction of REO or rare earth sulfides (RES) obtained from REO in a eutectic molten salt. This eutectic molten salt has a lower melting point, enabling a safer, more energy-efficient, cost-effective, environmentally friendly, and easy-to-handle process. The thermoelectrochemical reduction is carried out at a temperature below 500°C and at atmospheric pressure. The resulting thermoelectrochemical reduction product is purified using techniques known in the art to produce high-purity REM. These techniques may include water leaching and / or vacuum distillation of the thermoelectrochemical reduction product. Such techniques may also include the formation of a metal alloy based on the thermoelectrochemical reduction product followed by vacuum distillation.

[0008] According to another aspect of the present invention, the inventors have designed and implemented a process for converting REO to RES. This process may include a direct reaction between REO and a sulfur-containing gas that produces RES. The sulfur-containing gas may be S2 gas and / or H2S gas. In one embodiment, this process may include first converting a sulfur-containing gas (e.g., S2) in situ to H2S gas, and then reacting the REO with the H2S gas to produce RES.

[0009] In one embodiment, a reactor adapted to carry out a process according to the present invention is provided. In particular, a thermoelectrochemical reactor for producing REM from REO or RES in a eutectic molten salt is provided. In one embodiment, the reactor cathode design includes an aluminum crucible cathode with a microsieve incorporated at the bottom. In another embodiment, the cathode design includes a perforated aluminum disk adapted to sandwich REO and / or RES pellets. In a further embodiment, the reactor includes a sparger or gas distributor adapted to inject and maintain an inert gas flow into the reactor.

[0010] One embodiment of the present invention provides a thermoelectrochemical system for producing REM from REO or RES in a eutectic molten salt. The thermoelectrochemical system includes a thermoelectrochemical reactor and a molten salt collector operably connected to the reactor via a first line and connected to a vacuum line. In a preferred embodiment, the molten salt collector and the first line are adapted to be heated independently.

[0011] In one embodiment of the present invention, the starting material containing REO is obtained from recycled waste such as waste magnets or materials from end-of-life products. In another embodiment, the starting material containing REO is extracted from natural resources such as ore.

[0012] In one embodiment of the present invention, the resulting REM has high purity, for example, a purity of about 99%.

[0013] Accordingly, the present invention provides the following in accordance with its aspects. (1) A process for producing rare earth metals (REM), comprising subjecting a rare earth oxide (REO) or rare earth sulfide (RES) to thermoelectrochemical reduction in a eutectic molten salt to obtain a thermoelectrochemical reduction product containing REM. (2) The process described in (1), further comprising subjecting the thermoelectrochemical reduction product to a purification process; preferably, the purification process comprising subjecting the thermoelectrochemical reduction product to water leaching, more preferably using cold water; preferably, the purification process comprising subjecting the thermoelectrochemical reduction product to vacuum distillation. (3) The process described in (1), further comprising: (i) dissolving the obtained thermoelectrochemical reduction product in a liquid metal to obtain a REM alloy; and (ii) washing and / or vacuum distilling the REM alloy to produce REM, wherein the liquid metal preferably comprises a metal selected from the group consisting of Ca, K, Zn, Mg, Fe, and Mn. (4) A process according to any one of (1) to (3), wherein the thermoelectrochemical reduction temperature is less than about 500°C, preferably between about 375°C and about 450°C. (5) A process according to any one of (1) to (4), where the pressure during thermoelectrochemical reduction is atmospheric pressure. (6) A process according to any one of (1) to (5), wherein the eutectic molten salt comprises a mixture of at least two salts, where at least one salt is a lithium salt or a calcium salt; preferably, the lithium salt is selected from the group consisting of LiCl, Li2S, Li2O, and LiNO3. Preferably, the calcium salt is CaCl2; preferably, at least one other salt is a non-lithium salt, preferably selected from the group consisting of KCl, CaCl2, and NaNO3. (7) A process according to any one of (1) to (6), wherein the eutectic molten salt contains a mixture of LiCl and KCl. (8) A process according to any one of (1) to (7), wherein the eutectic molten salt comprises a mixture of a first lithium salt and a second salt, and the mass percentage ratio of the first salt to the second salt is about 40:60, about 45:55, or about 48:62; preferably, the mass percentage ratio of the first salt to the second salt is about 45:55. (9) A process according to any one of (1) to (7), wherein the eutectic molten salt comprises a mixture of LiCl and KCl, and the mass percentage ratio is about 40:60, about 45:55, or about 48:62; preferably the mass percentage ratio of LiCl to KCl is about 45:55. (10) A process according to any one of (1) to (7), wherein the eutectic molten salt comprises a mixture of at least two salts selected from the group consisting of CaCl2, NaCl, and MgCl2, and the thermoelectrochemical reduction temperature is greater than approximately 700°C. (11). A process according to any one of (1) to (10), further comprising recovering a eutectic molten salt upon completion of the thermoelectrochemical reduction, and preferably, the recovered eutectic molten salt is subjected to purification and reuse in this process. (12). A process according to any one of (1) to (11), wherein when thermoelectrochemical reduction is performed on RES, a sulfur-containing gas is obtained as a by-product, and the process further comprises recycling the obtained sulfur-containing gas for reuse; preferably, the sulfur-containing gas is S2 gas and / or H2S gas. (13). A process according to any one of (1) to (12), wherein REM is selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), and yttrium (Y); preferably, REM is selected from the group consisting of Nd, Dy, Pr, Ce, Er, and Y; more preferably, REM is Nd, Pr, or Dy. (14). A process according to any one of (1) to (13), wherein the obtained REM has a high purity such as about 99% purity. (15). REM obtained by the process defined by any one of (1) to (14). (16). A process for converting rare earth oxide (REO) to rare earth sulfide (RES), comprising subjecting REO to a reaction with a sulfur-containing gas. (17). A process according to (16), wherein the temperature during the reaction of REO with the sulfur-containing gas is between about 800°C and about 1200°C; preferably, the temperature is between about 600°C and about 700°C. (18). A process according to (16), wherein the sulfur-containing gas is S2 gas and / or H2S gas. (19). A process according to any one of (16) to (18), further comprising a preliminary step of converting a sulfur-containing gas into H2S gas in-situ; preferably, the sulfur-containing gas is S2 gas, and the preliminary step consists of converting S2 gas into H2S gas. (20). RES obtained by the process defined by any one of (16) to (19). (21). A process according to any one of (1) to (20), wherein REO is obtained from recycled waste such as materials from waste magnets or end-of-life products; preferably, REO is obtained from recycled e-waste such as NdFeB magnets. (22). A process according to any one of (1) to (20), wherein REO is extracted from natural resources such as ores. (23). A thermoelectrochemical reactor adapted to perform the process defined by any one of (1) to (14). (24). A thermoelectrochemical reactor for producing REM from REO or RES in a eutectic molten salt, the reactor including a cathode having an aluminum crucible with a micro-sieve incorporated at its bottom. (25). A thermoelectrochemical reactor for producing REM from REO or RES in a eutectic molten salt, the reactor including a cathode having a perforated aluminum disk adapted to sandwich REO and / or RES pellets. (26). A reactor according to any one of (23) to (25), comprising a sparger or gas distributor adapted to inject and maintain a flow of inert gas into the reactor; preferably, the inert gas is argon (Ar). (27). A system for the production of rare earth metals (REM) by thermoelectrochemical reduction in a eutectic molten salt of rare earth oxides (REO) or rare earth sulfides (RES), comprising a thermoelectrochemical reactor and a molten salt collector, wherein the molten salt collector is operatively connected to the reactor via a first line and is operatively connected to a vacuum line. (28) The system according to (27), wherein the molten salt collector and the first line are adapted to be heated independently. (29). A system for producing rare earth metals (REM) by thermoelectrochemical reduction in a eutectic molten salt of a rare earth oxide (REO) or rare earth sulfide (RES), comprising: a cathode in the form of a basket for receiving the REO or RES and the eutectic molten salt; an anode in the form of a high-density graphite rod; and a molten salt collector operably connected to the basket via a first line and operably connected to a vacuum line, wherein the molten salt collector and the first line are adapted to be heated independently; and wherein, upon completion of electrolysis, the molten salt can be recovered from the basket by pressure applied to the molten salt collector. (30) A reactor comprising any one of (23) to (26) or a system comprising any one of (27) to (29), further comprising a programmable controller for controlling heating and cooling. (31) A reactor according to any one of (23) to (26) or a system according to any one of (27) to (29), wherein the cathode and / or molten salt collector includes a Pyrex container. (32). A plant for the production of rare earth metals (REM), wherein the plant embodies a process defined in any one of (1) to (14), and preferably the plant is an industrial plant. (33) A plant for converting REO to RES, wherein the plant embodies a process defined in any one of (16) to (19), and preferably the plant is an industrial plant. (34) A reactor adapted to perform a process defined in any one of (16) to (19). (35) A reactor for use in converting rare earth oxides (REO) to rare earth sulfides (RES) using a sulfur-containing gas, wherein the reactor is a fluidized bed, a rotary kiln, or any suitable multiphase reactor.

[0014] Other objects, advantages, and features of the present invention will become more apparent by reading the following non-limiting description of specific embodiments of the invention, which are shown for illustrative purposes only with reference to the accompanying drawings. [Brief explanation of the drawing]

[0015] Brief explanation of the drawing This patent or application document includes at least one color drawing. A copy of this patent or the published patent application, including the color drawing, will be provided by the Patent Office upon request and payment of the required fees. In the attached drawings: [Figure 1] Figure 1: A process according to the present invention for the clean and sustainable production of rare earth metals (REMs) or rare earth elements (REEs). [Figure 2] Figure 2: a) Gibbs free energy versus temperature for possible sulfidation reactions of Nd-oxides, b) Enlarged view. [Figure 3] Figure 3: A) Nd-oxide in an alumina boat located in the center of a TFR (tubular furnace reactor), B) Residue after treatment. [Figure 4] Figure 4: A) XRD results of NCT7 residue sample; B) XRD results of NCT15 residue sample; C) XRD results of NCT16 residue sample. [Figure 5] Figure 5: EDS mapping of key elements Nd, O, and S for sample NCT16 using two different sampling methods A and B. [Figure 6] Figure 6: Mixture of pelletized Nd oxide and S powder, before treatment (A) and after treatment (B). [Figure 7] Figure 7: XRD results of NCT18 residue samples. [Figure 8]Figure 8: Schematic diagram of the experimental apparatus for neodymium sulfide oxide production using an induction heating reactor. (1) Pure nitrogen gas, (2) MFC, (3) Heating mantle, (4) Glass container, (5) Thermocouple, (6) Pressure gauge, (7) Condenser, (8) Exhaust valve, (9) Quartz tube reactor, (10) Induction heating furnace, (11) Copper coil, (12) Nd2O3 powder bed, (13) Diffuser, (14) Rod, (15) Quartz reactor thermocouple, (16) Induction heating control box, (17) Wash bottle, (18) Exhaust system. [Figure 9] Figure 9: Sulfurization apparatus for sulfurizing Nd2O3 to Nd2S3. [Figure 10] Figure 10: Inconel electrochemical reactor and its dimensions. [Figure 11] Figure 11: Left: Molten CaCl2 / CaCO3 salt at 800°C observed through the flange window. Right: CaCl2 / CaCO3 salt solidified inside the alumina crucible after the reactor has cooled. [Figure 12] Figure 12: Phase diagram of the eutectic LiCl-KCl molten salt electrolyte. [Figure 13] Figure 13. Thermoelectrolysis apparatus. (a) water cooling system, (b) crucible furnace and Inconel reactor, (c) Ar cylinder, (d) potentiostat / galvanostat, (e) electrodes and sparger, and (f) pressure regulator. [Figure 14] Figure 14: Schematic diagram of a thermoelectrochemical apparatus. (AEL: anode electrode, CEL: cathode electrode, REL: reference electrode, spg: sparger, CW: cooling water, HW: hot water, TC: thermocouple, RV: relief valve, HW). [Figure 15] Figure 15: (a) Image of the graphite anode, sparger, and titanium (Ti) basket; (b) Thermoelectrochemical apparatus; (c) Pelleted Nd2O3 powder; (d) Graphite anode, sparger, and Ti basket covered with solidified molten salt after the process; (e) Inside the Ti cathode basket; and (f) Pellet separated from the cathode basket. [Figure 16] Figure 16: (a) Pelleted Nd2O3 powder, (b) Inside the Ti cathode basket after processing, and (c) Reduced Nd2O3 pellets. [Figure 17] Figure 17: XRD pattern of reduced Nd2O3 in a Ti basket. [Figure 18] Figure 18: (a) Donut-shaped Nd2O3 pellet, (b) Nd2O3 pellet attached to a Ti rod, (c) Graphite anode, (d) Ti cathode after reaction, (e) and (f) Graphite anode covered with Nd2O3. [Figure 19] Figure 19: (a) Donut-shaped Nd2O3 pellets, (b) and (c) Nd2O3 pellets attached to a Ti rod and covered with Ti springs and quartz, (d) and (e) Cathode electrode after reaction, (f) Reduced Nd2O3 pellets. [Figure 20] Figure 20: XRD pattern of reduced Nd2O3 attached to a Ti rod. [Figure 21] Figure 21: (a) a handmade aluminum crucible used as a cathode, (b) an aluminum crucible filled with donut-shaped Nd2O3 pellets and a KCl-LiCl electrolyte placed inside an alumina crucible (top view), (c) the aluminum crucible after processing, (d) and (e) top view of the reduced Nd2O3 pellets, and (f) bottom view of the reduced Nd2O3 pellets. [Figure 22] Figure 22: XRD pattern of reduced Nd2O3 in an alumina crucible. [Figure 23] Figure 23: (a) Cyclic voltammetry and (b) Chronoamperometry of an Nd2O3 cathode held in a Ti basket in a LiCl-KCl molten salt under an Ar atmosphere at 400°C. [Figure 24] Figure 24: XRD patterns of Nd2O3 and reduced Nd2O3. [Figure 25] Figure 25: (a-1) SEM image, (a-2) EDX, (a-3) elemental mapping of Nd2O3; and (b-1) SEM image, (b-2) EDX, (b-3) elemental mapping of reduced Nd2O3. [Figure 26]Figure 26: Improved thermoelectrochemical apparatus. Left: Pyrex reactor in a crucible furnace connected to a preheated Pyrex molten salt collector via a heating line. Right: Pyrex reactor. [Figure 27] Figure 27: (a) Thermoelectrochemical cell with two electrode configuration using solid LiCl-KCl electrolyte, (b) Thermoelectrochemical cell using molten electrolyte at 450°C, (c) Thermoelectrochemical cell after processing, (d) and (e) Cathode before processing, (f) Anode before processing, (g) and (h) Cathode after processing, (i) Anode after processing, (j) Solidified electrolyte containing reduced REE, (k) and (m) Separated REM. [Figure 28] Figure 28: XRD patterns of Nd2O3 and Nd2O3 reduced by thermoelectrolysis. [Figure 29] Figure 29: (a) SEM image, (b) EDS spectrum and elemental composition, (c) elemental mapping, and (d) elemental distribution of Nd2O3 reduced by thermoelectrolysis at 450°C and 4.5V DC. [Modes for carrying out the invention]

[0016] Description of the Embodiment Before further describing the present invention, it should be understood that the present invention is not limited to the specific embodiments described below, and that variations of these embodiments may be made and still fall within the scope of the appended claims. It should also be understood that the terms used are for the purpose of describing specific embodiments and are not intended to limit them. Instead, the scope of the present invention is established by the appended claims.

[0017] To provide a clear and consistent understanding of the terms used herein, several definitions are provided below. Furthermore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art relating to this disclosure.

[0018] The words "a" or "an" used in combination with the term "comprising" in the claims and / or specification may mean "one," but are also consistent with meanings such as "one or more," "at least one," and "one or more." Similarly, the word "another" may mean at least two or more.

[0019] The terms “comprising” (and any other form of “comprising,” such as “comprise” or “comprises”), “having” (and any other form of “having,” such as “have” or “has”), “including” (and any other form of “including” or “includes”), or “containing” (and any other form of “containing” or “contains”) as used herein and in the claims are inclusive or open and do not exclude additional, undescribed elements or process steps.

[0020] The terms “rare earth metals” and “rare earth elements” are used interchangeably herein and are denoted as “REM” and “REE,” respectively. These terms refer to any one of the 17 rare earth elements, specifically lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), and yttrium (Y). As used herein, “REM” and “REE” refer to both singular and plural forms; therefore, “REM,” “REMs,” “REE,” and “REEs” are used interchangeably.

[0021] The terms “rare earth oxides” and “rare earth element oxides” are used interchangeably herein and are abbreviated as “REO.” “REO” is used in both singular and plural forms; therefore, “REO” and “REOs” are used interchangeably.

[0022] The terms “rare earth sulfides” and “rare earth element sulfides” are used interchangeably herein and are abbreviated as “RES.” “RES” is used in both singular and plural forms; therefore, “RES” and “RESs” are used interchangeably.

[0023] The terms “electrochemical reduction,” “thermoelectrochemical reduction,” “thermoelectrolysis,” “thermoelectrolytic reduction,” “electrocalcium thermal reduction,” and “electrolithium thermal reduction” refer to the production of REM from REO or RES through the thermoelectrochemical reduction process according to the present invention. These terms are used interchangeably herein.

[0024] The terms "sulfidation," "carbo-sulfidation," "carbothermic sulfidation," "sulfurization," and "carbothermic sulfurization" refer to the conversion of REO to RES through the sulfidation process according to the present invention. These terms are used interchangeably herein.

[0025] The term "eutectic molten salt" refers to the salt used in the thermoelectrochemical reduction of REO or RES according to the present invention. Such a salt comprises at least two salts, including a lithium salt and a non-lithium salt, and melts at a lower temperature than either of the individual salts alone. The lithium salt may be LiCl, Li2S, Li2O, or LiNO3. The non-lithium salt may be KCl, CaCl2, NaCl, MgCl2, or NaNO3.

[0026] The inventors have designed and implemented a process for producing rare earth metals (REM) from rare earth oxides (REO). This process involves thermoelectrochemical reduction of REO or rare earth sulfides (RES) obtained from REO in a eutectic molten salt. The inventors have also designed and implemented a process for converting REO to RES. These processes are described in detail below.

[0027] Regarding the reduction of RES to REM, it is known in this field that pure REM can be produced at extremely high temperatures exceeding 1200°C through the energy-intensive reduction of fluorides. This is not only harmful to the environment but also increases process and plant costs, reducing the overall attractiveness of the process.

[0028] The inventors have developed a novel and sustainable electrolytic lithium thermal reduction of REO and RES using Li generated / dissolved in eutectic molten LiCl-KCl salt at relatively low temperatures (below 500°C). Thus, in some respects, this innovative approach aims to address this problem through the sustainable treatment of RES and REO in LiCl-based molten salts, rather than in molten salts of oxides, nitrates, and fluorides. The sulfur source is also inexpensive, non-toxic, readily available worldwide, and can be applied to the synthesis of clean RES. According to the present invention, the sulfur-concentrated gas released during the thermoelectrolysis of RES can be recovered and reused in the sulfidation process, reducing the amount required. This process is highly practical for the industrial production of high-purity rare earth metals, namely lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), and yttrium (Y). This process consumes less energy without emitting CO2 or producing harmful greenhouse gases such as perfluorocarbon (PFC) gases, particularly CF4 and C2F6.

[0029] In the process according to the present invention, rare earth metals are produced by the lithium thermal reduction of oxides or sulfides in eutectic molten LiC-KCl, and the separation of REM from the cathode can be achieved by liquid Zn or Mg metal. The reducing agent, Li, is produced in situ by the reduction of Li2S or LiO at the anode surface (or oxidation of the anode electrode) in eutectic molten LiCl-KCl salt at temperatures between 500°C. Thus, the reduction of REO(Nd2O3) or RES(Nd2S3) is carried out by lithium dissolved in the molten material at the cathode surface.

[0030] Accordingly, the process according to the present invention may lead to the formation of a REE-Zn(Mg) alloy, and Zn or Mg can be removed by vacuum distillation in a subsequent step. Since the present invention relates to sulfides, energy consumption is reduced by the rapid reduction of sulfides. Furthermore, sulfur is inexpensive, non-toxic, and readily available worldwide, and can be used for the synthesis of clean sulfides used in electrolysis. No CO / CO2 gas is generated in the thermoelectrolysis of RES, and therefore the graphite anode is not consumed. This process prevents carbon contamination of REM by generating S2 gas on the surface of the anode. The exhaust gas (S2) from the cell can be reused and used for the sulfidation of metal oxides and raw materials. Figure 1 shows a proposed general flow chart for producing REM from REO. Its variations and aspects are described herein and will be readily understood by those skilled in the art.

[0031] The process according to the present invention comprises at least the following aspects: conversion of rare metal oxides, carbonates, or chlorides obtained from used or recycled waste streams (such as NdFeB magnets or natural REE-containing ores) into rare metal sulfides by a sulfidation process using S2 gas or other sulfur-containing gases; electrolithium thermal reduction of fresh sulfides or oxides, followed by water leaching; dissolving the resulting product in a liquid metal containing but not limited to Mg and Zn to produce REM alloys such as REM-Zn alloys and REM-Mg alloys; and purification and separation of pure rare earth metals from electrochemically produced alloys by distillation in a vacuum atmosphere.

[0032] According to one aspect of the present invention, clean rare earth metal sulfides are synthesized from oxides by carbon-thermal sulfidation or sulfidation at a temperature of about 600–1200°C in an atmosphere of S2 gas or any other sulfur-containing gas (e.g., in-situ H2S). According to another aspect, the sulfides are electrochemically reduced by Li at 3.0 V DC at a temperature of less than 500°C (e.g., 450°C) with the addition of LiCl in different molar ratios in a eutectic molten LiCl-KCl salt. According to yet another aspect, the electrochemically reduced sample can be dissolved in molten zinc (Zn) or molten magnesium (Mg) to separate the rare metals in the form of a REE-M alloy. Finally, the alloy obtained from the sulfides in a molten LiCl-KCl salt and dissolved in liquid Zn or Mg metal can be treated at 700–900°C under a vacuum atmosphere to extract the rare earth metals (i.e., applicable to all 17 rare earth elements). Therefore, for example, neodymium, which melts at 1021°C, can be separated from Zn and boils at 907°C by vacuum distillation.

[0033] The sulfidation of REO is carried out at temperatures exceeding 600°C using S2 gas or any other sulfur-containing gas. The sulfide is introduced into a basket cathode and reduced to the metal in eutectic molten LiCl-KCl at temperatures below 500°C and an applied DC voltage of 3.0 V. Two cathode designs have been developed. The first design includes an aluminum crucible cathode with a microsieve incorporated at the bottom. The second design includes a perforated aluminum disk with REO or RES pellets sandwiched between it. High-density graphite rods are also used as anodes, and the salt is purified by pre-electrolysis using an auxiliary carbon electrode at 2.0 V in an argon (Ar) atmosphere. The supply charge (Q / C), electrolysis temperature, and pressure can be precisely monitored by a data acquisition unit. The rare earth metal can then be separated from the reduced sample in the form of a REE-M (M=Zn,Mg) alloy with liquid Zn or Mg. Finally, pure REE(Nd,Dy) can be produced by a vacuum distillation process.

[0034] In one aspect of the process according to the present invention, REM can be produced via RES without the use of harmful fluorides, eliminating the generation of CO / CO2 gas. This method makes the production of rare earth metals far more economical and energy-efficient than current methods that use chlorides and fluorides to produce REE alloys.

[0035] The present invention is described in further detail below, including the sulfidation of REO using a sulfur-containing gas to obtain RES, the thermoelectrochemical reduction of REO and RES in a eutectic molten salt, and other aspects of the present invention. Reactors developed by the inventors for carrying out the processes according to the present invention are also described.

[0036] Gas-solid sulfurization process for obtaining RES from REO Materials and equipment: We used 99% pure neodymium(III) oxide (Nd2O3) and 99% sulfur powder, both from Sigma (Germany), as examples of REO. The reaction was carried out in an inert atmosphere under a nitrogen stream (at different flow rates).

[0037] The first stage of the sulfidation process was carried out in a tubular reactor using alumina tubes. For this purpose, two different heating zones were set up based on the boiling point of sulfur and the reaction temperature.

[0038] Thermodynamic analysis and possible reactions: We hypothesized that reactions R.1 to R.6 could arise during the sulfidation of neodymium oxide in the presence and absence of carbon. The changes in Gibbs free energies for these reactions are shown in Figure 2.

[0039] [ka] [ka]

[0040] As discussed above in this specification, neodymium oxide can be reduced only by sulfur, but the likelihood of sulfidation is higher in the presence of carbon (graphite in our tests). Based on these calculations, the overall reaction in the presence (R.7) and absence (R.8) of graphite can be considered as follows:

[0041] [ka]

[0042] On the other hand, when carbon is added to the process, the reaction sequence according to Gibbs free energy is as follows: - Sulfur carbonization and CS2 formation

[0043] [ka]

[0044] -Nd- oxide reaction with CS2 to produce Nd2S3

[0045] [ka]

[0046] FactSage TM Based on thermodynamic studies using software, it is noteworthy that the direct reaction between Nd-oxides and gaseous sulfur can be spontaneous at temperatures below 600°C (at equilibrium).

[0047] Methodology: We tested various weights and fractions of the reagents. The weight fraction of Nd2O3:S was varied from 1:10 to 1:5 under different operating conditions. In experiments using graphite, a stoichiometric ratio of 3:1 was used for C (which could be used in excess). Furthermore, the nitrogen flow rate, i.e., the carrier gas, was varied from 0.5 to 3 standard cubic feet / hour (SCFH), equivalent to 0.25 to 1.5 L / min.

[0048] Following several preliminary tests, we identified two suitable different heating zones where the sulfur crucible and the neodymium crucible were placed within a specific distance of each other. Since the boiling point of sulfur is 444.6°C, we needed to keep the sulfur crucible in a heating zone (defined as the low-temperature zone) at a similar temperature (approximately 500°C) to control the vaporization of sulfur and its passage over the neodymium oxide crucible. During the experiments, the neodymium oxide crucible was placed in a heating zone (defined as the high-temperature zone) at temperatures between 600°C and 1200°C. To minimize sulfur gas waste during furnace heating, an insulator was placed between the high-temperature and low-temperature zones (Nd-oxide boat and sulfur crucible). By maintaining a low carrier gas flow rate, gaseous sulfur continuously passed over the Nd-oxide boat at the operating temperature. For all series of experiments, the heating and cooling rates were less than 7°C / min (4–7°C / min).

[0049] To analyze the phase of each sample after sulfidation, the supply sample and the sulfidated sample were investigated using field emission scanning electron microscopy with X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy mapping (EDS-mapping).

[0050] The selected experiments and their operating conditions are shown in Table 1 below. To verify the results, each process with the specified operating conditions was repeated at least twice.

[0051] [Table 1]

[0052] Example 1 - Analysis of Experimental NCT7 3 g of sulfur powder (S) was placed in a molybdenum (Mo) crucible in the low-temperature zone of the furnace, and the temperature was maintained near the boiling point of S when the high-temperature zone reached 1200°C. Next, 0.5 g of Nd-oxide powder (S:Nd-oxide=6:1) was placed in an alumina boat and introduced into the high-temperature zone (Figure 3). The residence time (i.e., isothermal time) was set to 60 minutes. Furthermore, to remove moisture from the tubes, a nitrogen stream of 1 SCFH was supplied to the reactor after 350°C.

[0053] This nitrogen stream slowly carried the vaporized S2 from the low-temperature zone to the high-temperature zone, resulting in good mass transfer between sulfur gas and Nd-oxide powder in the sulfur atmosphere of the 1200°C tube. After the experiment, the Mo crucible was completely empty, indicating that all the S2 powder had vaporized, while the weight of the Nd-oxide residue had increased by 0.518 g, which may be related to the fact that the molecular weight of S is greater than that of oxygen. Furthermore, the color of the Nd-oxide, particularly on the surface of the powder, changed to a pale pink color (Figure 3B). Visual preliminary analysis suggested that sulfidation had occurred. Therefore, characterization studies were performed by XRD and EDS. The XRD results are shown in Figure 4A.

[0054] XRD results showed that sulfur reacted with neodymium oxide, resulting in the formation of various Nd-S products. The observable pink color may be related to the formation of NdS.

[0055] This result was a promising proof of concept, occurring at a relatively low temperature of 1200°C, despite the fact that the contact between sulfur and neodymium oxide was not yet optimal (i.e., due to the semi-batch nature of the process).

[0056] Example 2 - Analysis of Experimental NCT15 To study the reducing effect of carbon on the sulfidation of neodymium oxide, a series of different experiments were designed. For example, 0.5 g of graphite powder was used as a blanket for 0.5 g of Nd2O3 and placed under a nitrogen flow rate of 1 SCFH. The N2 flow carried the gas from a low-temperature zone of 1200°C over a 60-minute isothermal period. Simultaneously, 5 g of sulfur powder was placed in the low-temperature zone for a possible reaction between C and S gas (reaction R.3). The residual powder had a mass of 0.539, which could correspond to the difference in atomic mass between O and S. XRD results showed that sulfidation occurred, with slight partial sulfidation resulting in the formation of Nd2SO2 and Nd2O2SO4 (Figure 4B).

[0057] Elemental mapping led us to conclude that S and Nd reacted, and that sulfidation was partially successful. However, carbon did not react with oxygen and thus did not reduce the Nd oxide, remaining largely unchanged in the residue in the crucible.

[0058] The motivation for this study was to investigate whether reactions R.3 and R.4 could occur kinetically. The former reaction is assumed to involve carbon first reacting with neodymium oxide, followed by the reaction of the resulting neodymium carbide with sulfur to produce neodymium sulfide. The latter reaction is assumed to involve carbon first reacting with sulfur to produce carbon sulfide, which subsequently reduces neodymium oxide to neodymium sulfide. Since carbon was in direct contact with neodymium oxide in one crucible, we concluded that reaction R.4 did not occur due to the short contact time between carbon and sulfur. Therefore, we hypothesized that it would be more beneficial to produce CS2 in a separate reactor according to reaction R.2 (CS2 boils at 46.3°C) and pass this over the neodymium oxide.

[0059] Example 3 - Analysis of Experimental NCT16 To investigate the effects of S2 powder content and carrier gas flow rate in more detail, this series of experiments was designed with 5 g of sulfur powder in the low-temperature zone and 0.5 g of Nd-oxide in the high-temperature zone (mass S:Nd-oxide ratio = 10:1), under isothermal conditions of 60 minutes at 1200°C. The weight of the residue after the reaction was 0.515 g. XRD of this sample indicates that the Nd-oxide was slightly sulfurized in this experiment. As shown in Figure 4C, a peak for Nd2SO2 was detected.

[0060] EDS and elemental mapping demonstrated reasonable sulfidation of the Nd oxide. The EDS results showed 75.6% Nd, 18.3% S2 (quite significant), and 6.1% O, which may be considered the best result across all experiments at high temperatures (1200°C). Therefore, we decided to perform mapping using two different sampling methods, the results of which are shown in Figure 5.

[0061] In the first series of mapping analyses, O, Nd, and S matched in the map distribution, indicating the formation of a substance containing these three elements. However, in the second analysis, Nd and S matched perfectly on the map, while O was uniformly distributed on the surface. This could explain the formation of the desired product, NdS or Nd2S3 (Figure 5B). In other words, we had a complete sulfidation reaction in some areas of the sample (possibly the surface of the Nd-oxide).

[0062] This series of experiments demonstrates the concept of sulfidation even in the absence of a reducing agent. The promising results and observations of this study suggest that in future scale-up efforts, appropriate reactors (e.g., circular fluidized bed reactors or rotary kilns) should be designed to maintain effective contact between sulfur and neodymium and to utilize sufficient residence time to complete the reaction.

[0063] Example 4 - Analysis of Experimental NCT18 We designed a separate series of experiments at lower temperatures of 600°C and 700°C. To mitigate the limitations of mass transfer, we pelletized a mixture of sulfur and neodymium oxide in a mass ratio of 10:1 using a 10KN pelletizer, where 5 g of sulfur was thoroughly mixed with 0.5 g of Nd2O3 and then pelletized to obtain a donut shape. The pellets were placed in a molybdenum crucible in the high-temperature zone of the reactor (as shown in Figure 6) at 700°C, under an N2 flow rate of 1 SCFH, for an isothermal time of 120 minutes. The residue weight was 0.50g, indicating the melting and complete vaporization of S2 during heating and isothermal time. The color of the sample after treatment was partially blue and light pink on the surface (Figure 6B).

[0064] To retain the vaporized S2 around the crucible before discharging it from the system, we designed a cage box to hold the pellets inside. We then resumed the experiment with a similar operation but at 700°C. Based on the changes in shape and weight loss before and after treatment, we conclude that a gas-solid reaction occurred at 600–700°C, causing the sulfidation of Nd-oxide at different stages.

[0065] The XRD analysis results are shown in Figure 7. They are very similar to the NCT16 residue samples, but the intensity of neodymium sulfide oxide was higher. This indicates that the sulfidation process could proceed even at lower temperatures using controlled operating conditions. However, more careful research is needed regarding process control and characterization. On the other hand, this was another proof of concept for a process designed based on thermodynamic calculations.

[0066] Based on the reported experimental results, we were able to demonstrate the concept of a sulfurization process using sulfur gas for Nd-oxide solids. We were able to conclude that the effect of the reducing agent in the solid phase was not essential. On the other hand, under controlled operating conditions, we were able to complete the experiment at temperatures between 600°C and 700°C, which is certainly a significant advance.

[0067] Example 5 - Sulfurization of REO using continuous sulfur-containing gas The inventors determined that REO can be sulfidized by a continuous flow of sulfur-containing gas through a bed of REO particles / powder. This facilitates mass transfer and heat transfer between the REO powder and the sulfur-containing gas, enabling a high conversion rate from REO to RES. For example, our thermodynamic simulations revealed that the sulfidation of neodymium oxide by reaction with hydrogen sulfide is thermodynamically favorable at temperatures below 1167°C. The following exothermic equation can represent this reaction:

[0068] [ka]

[0069] When one molecule of Nd₂O₃ is exposed to hydrogen sulfide, H₂S dissociates into sulfur species, releasing hydrogen. The sulfur replaces oxygen to produce Nd₂S₃, while the hydrogen produces water. One mole of Nd-oxide requires three molecules of hydrogen sulfide for a complete reaction. Therefore, a rich H₂S stream and carrying out the reaction at a sufficiently high temperature ensure a high sulfidation reaction.

[0070] An apparatus for converting Nd2O3 to Nd2S3 consists of two separate glass containers (Figures 8 and 9). In the first container, H2S is produced, then transported by an inert gas, and introduced into the second container, which contains a vertical quartz tube reactor. The second reactor can also be installed in a horizontal orientation. In the laboratory, there are several methods for producing H2S, including the reaction of iron sulfide with hydrochloric acid or sulfuric acid, and the hydrolysis reaction of thioacetamide (TAA). For this contribution, the hydrolysis reaction of TAA with water is utilized to generate acetamide and H2S.

[0071] [ka]

[0072] However, the TAA hydrolysis reaction is not limited to water; certain mineral acids such as hydrochloric acid and polar organic acids such as acetic acid can also be used. For the current study, 7.5 g of TAA is transferred to a glass round-bottom reactor with multiple inlets. The reactor contains 250 ml of distilled water, and dissolving the TAA forms a 0.4 mole solution. The temperature of the solution is maintained between 60 and 80°C using a heated mantle with a PID temperature controller. The generated H2S accumulates on the distilled water and is then transported to a quartz tube reactor by 500 ml / min of nitrogen. A mass flow controller (MFC) precisely regulates the nitrogen gas flow rate. The nitrogen pipe is inserted into the vessel and extended using special fittings to prevent leakage. Subsequently, an outlet valve regulates the flow outlet and provides a slight positive pressure inside the glass vessel. This outlet is connected to the inlet of the quartz tube reactor. For safety, the pressure in the vessel is measured by a pressure gauge to avoid overpressure.

[0073] The gas enters the quartz tube from the bottom and moves upward. 0.5 g of neodymium oxide powder is placed on porous quartz frit in a 1-inch OD quartz tube reactor. This frit acts as a support for the powder and a diffuser for nitrogen gas, while simultaneously allowing an inert carrier gas containing H2S to pass through. The quartz tube is placed in an induction heating system to quickly and safely heat the powder, raising the powder bed temperature to 800°C. However, other heating systems, including any other form of heat supply method such as microwaves, conventional electric furnaces, and non-electric furnaces (e.g., fuel combustion), can also be utilized.

[0074] More specifically, we can apply electrothermal processes (i.e., induction heating, microwave heating, plasma, etc.) to both RES production processes we have developed: namely, in one aspect, RES production using sulfur vapor in an REO bed is heated by induction heating, microwave heating, etc. In fact, we use sulfur (S) powder and neodymium oxide (Nd2O3) in a weight ratio of 1:8 in a graphite crucible. As an alternative to the graphite crucible, we use an assembly of graphite rods arranged symmetrically in the reactor. The graphite crucible or the assembly of graphite rods acts as an induction heating adsorbent, and considering the difference between the boiling point of sulfur and the reaction temperature, it allows for a high heating rate and minimizes S2 gas waste.

[0075] In the process according to the present invention, sulfur powder is first melted by heating a crucible and reacts with a graphite crucible in the required ratio to form CS2. Subsequently, CS2 reacts with Nd2O3 at a desired temperature in a vertical quartz reactor while purging excess gas by flowing nitrogen from the bottom.

[0076] In another context, the production of RES using a sulfur-containing gas such as H2S or any other form in a REO powder bed is heated by induction heating, microwave heating, etc. When using energized heating methods, for example, with induction heating and microwave heating, we use a graphite crucible inside the bed, as graphite is known to be an excellent receptacle for electromagnetic fields, which can improve the quality of the heat treatment, enhance selective heating characteristics, and improve product selectivity while increasing the conversion of REO to RES. The reactor design for these gas-solid reactions can be a fluidized bed, a rotary kiln, and any other multiphase reactor.

[0077] The induction heating system has a copper coil and operates at a frequency of 70 kHz. The length of the coil is such that it surrounds the powder bed and covers the top and bottom 1 inch of the bed. Since induction heating can only heat conductive materials, a 4-rod assembly is fitted vertically inside the quartz tube reactor and extended into the Nd2O3 powder bed to effectively and rapidly absorb the magnetic field. When the rods absorb the induced magnetic field, they heat up, and this heat is transferred to the powder by convection under an H2S-rich gas stream. The bed temperature, controlled by a PID controller, rises rapidly within minutes to reach a set temperature of 800°C. Once the temperature is regulated, nitrogen gas is introduced into the bed. The sulfurization reaction lasted for 1 hour. Unreacted exhaust H2S is captured by a bottle containing 2 moles of NaOH and then transported to the laboratory exhaust system. After cooling, the sulfurized neodymium is removed from the reactor.

[0078] Thermoelectrochemical reduction of REO and RES in eutectic molten salts Our initial plan was to reduce neodymium sulfide to neodymium metal in a reactor containing a mixture of molten alkaline earth metal salts (e.g., calcium carbonate and calcium chloride) at temperatures between 700°C and 1000°C. We designed and commissioned an Inconel reactor capable of withstanding such high temperatures. The top of the reactor was covered with a water-cooled stainless steel flange / lid. We designed a window on the flange to observe the reaction state inside the reactor. The reactor shape was designed to allow installation inside a crucible furnace. The salt powder was poured into an alumina crucible installed inside the Inconel reactor. This alumina crucible was essential to prevent electrical short circuits between the molten salt and the metal body of the reactor, otherwise the electrochemical reaction would not occur. Therefore, we needed to design a ceramic sleeve / insulator near the reactor flange to prevent any contact between the titanium rods of the anode / cathode electrodes and the sparger tubes. We designed a cruciform sparger with a 45° angled hole to purge air molecules from the reactor. The anode rod was screwed to a graphite tip. Meanwhile, the initial design for the cathode involved attaching a titanium basket with 40-micron holes to the titanium rod to hold the neodymium oxide powder inside without leaking it into the molten salt during the electrochemical reaction. However, the inventors encountered various challenges in carrying out this initial work. During the experimental work, we designed several alternative configurations for the cathode assembly, as described in the next section (e.g., a titanium basket with larger 3 mm holes, titanium wiring surrounding pelletized neodymium oxide powder, an aluminum rod instead of a titanium rod, an aluminum container surrounding an anode rod inserted from the center of the reactor, etc.).

[0079] Figure 10 shows the dimensions and schematic diagram of the designed electrochemical reactor.

[0080] The inventors of the present invention conducted experiments using alkaline earth metal molten salts. After the results of the sulfidation process and the trial operation of the thermoelectric device, we planned to perform reduction experiments to convert neodymium sulfide to neodymium metal using a mixture of alkaline earth metal molten salts. We conducted several troubleshooting tests to verify the feasibility of experiments with a molten mixture of CaCl2 / CaCO3 salts. We needed to fill an alumina crucible with a rather large mass of salt, about 500 g, so that it would reach a sufficient height during melting. We observed that the salt mixture could melt effectively at a sufficiently high temperature (left in Figure 11), but it solidified inside the alumina crucible (right in Figure 11). However, it was important to find a safe solution for recovering and purifying the salt for the next experiment. Therefore, we used another muffler furnace and made some improvements such that the material was melted and poured from the inverted alumina crucible into a metallurgical crucible. However, this technique was judged to be difficult due to the high temperature associated with the molten salt.

[0081] The inventors of the present invention evaluated alternative molten salts by thermodynamic simulations. In fact, after tests using CaCl2 / CaCO3 salts, we decided to search for alternative salts that could be used at much lower temperatures for thermoelectrochemical tests. For this purpose, we conducted a series of thermodynamic simulations using FactSage TM and carried out.

[0082] Regarding the electrothermal reduction of Nd2S3 by LiCl-Li2S molten salt, we hypothesized that alkali salts would be more suitable than alkaline earth salts. Therefore, we initially considered a mixture of LiCl / Li2S salts for the reduction of neodymium sulfide, whereby lithium assists the movement of ions from the cathode to the anode according to the following reaction: Anode reaction:

[0083]

Chemical formula

[0084] Cathode reaction:

[0085] [ka]

[0086] Thermodynamic simulations revealed that these reactions can occur spontaneously even at 100°C. However, evaluation of the LiCl-Li2S phase diagram revealed that Li2S cannot be liquid at temperatures between 100°C and 1000°C. The inventors therefore concluded that these salts may not be suitable for the reduction of neodymium salts and investigated other approaches.

[0087] Regarding the electrothermal reduction of Nd2O3 by LiCl-KCl molten salt, we hypothesized that neodymium oxide might be directly reduced using a mixture of alkali salts of LiCl and KCl. Based on this, we expanded the thermodynamic studies to determine whether this idea is feasible. The entire process was calculated at atmospheric pressure and 400°C.

[0088] Figure 12 shows the phase diagram of LiCl-KCl. It can be observed that LiCl can form a eutectic mixture with KCl. When 59 mol% LiCl is mixed with 41 mol% KCl, a molten salt is formed at approximately 360°C. Therefore, we conclude that using LiCl-KCl may assist us in carrying out thermoelectrochemical reduction reactions at low temperatures compared to other electrolytes such as CaO-CaCl2 and Li2O-LiCl.

[0089] During thermoelectrolytic reduction, LiCl is in the molten salt. + and Cl - It dissociates into Li. After that, the negative charge of the cathode is released by electrostatic force. + It attracts cations. The Li cation attacks Nd2O3 on the cathode surface and then captures its oxygen molecule based on the following redox reaction:

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[0091] The generated Li2O moves from the cathode to the anode through the molten electrolyte in the next step. At the anode surface, the Li2O is reduced, while the graphite anode is oxidized. As a result, Li cations are regenerated (reaction R.19) and moved to the cathode surface for reduction with Nd2O3. CO2 is another product generated from the anode surface (reaction R.20).

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[0093] According to the above reaction, the overall anode reaction and the overall cathode reaction can be described as follows:

[0094] [ka]

[0095] The total potential of the electrochemical cell is equal to the following:

[0096] [ka]

[0097] The relationship between cell potential and Gibbs free energy can be described as follows:

[0098] [ka]

[0099] Here, E cellθ is the cell potential, n is the number of moles of electrons transferred during the process (6 here), F is the Faraday constant (96485 C / mol), and ΔG is the change in Gibbs free energy. Thermodynamic results indicate that this electrochemical reaction has a positive cell potential and negative Gibbs free energy. Therefore, the thermoelectrochemical reduction of Nd2O3 in LiCl-KCl at temperatures below 500°C is a spontaneous reaction. Thus, we conclude that we were able to investigate the direct reduction of neodymium oxide using a LiCl / KCl molten salt.

[0100] Thermoelectrochemical apparatus: We designed different apparatus configurations with respect to salt type and operating temperature. In this specification, we present an apparatus for the reduction of Nd2O3 to pure Nd metal by a thermoelectrometallurgical process in a LiCl-KCl eutectic molten salt. To achieve this objective, we designed and constructed a three-electrode electrochemical cell using a graphite rod as the counter electrode (also called the anode), Ag / AgCl as the reference electrode, and neodymium oxide as the working electrode (also called the cathode). The molten electrolyte contained LiCl and KCl in a mass percentage ratio of 45:55. Furthermore, neodymium oxide powder was first pelletized in a 10-ton hydraulic press and then placed in a titanium (Ti) cathode basket. Heat of the reaction was supplied to the crucible furnace. An external voltage was applied by a potentiostat / galvanostat (VersaSTAT 3-200). All experiments were carried out in an inert atmosphere by injecting Ar gas through a sparger at a flow rate of 50 ml / min. An electrochemical cell was placed in a 500 ml alumina crucible. The electrochemical cell was then transferred to an Inconel reactor. During the experiment, the temperature of the molten salt was recorded using a K-type thermocouple. The electrolysis apparatus is shown in Figure 13. To prevent overheating of the reactor flange and top, the system was cooled with water. A schematic diagram of the apparatus is also shown in Figure 14.

[0101] Thermoelectric metallurgy experimental methodology: For each experiment, a maximum of 300 g of dry LiCl and KCl in a mass percentage ratio of 45:55 was packed into a 500 ml alumina crucible and placed in a thermoelectric reactor, with the upper flange of the reactor equipped for hermetically inserting electrodes. 1.5 g of pelletized neodymium oxide (e.g., Nd2O3 or Nd2S3) was placed in a titanium cathode basket for reduction with molten salt.

[0102] Example 6 - Nd2O3 was reduced to metal Nd at 400°C in a three-electrode cell configuration (Figure 15a) consisting of an Nd2O3 cathode, a graphite anode, and an Ag / AgCl reference electrode. Using different cathode designs, Nd2O3 was immersed in a thermoelectrochemical reactor as a negatively charged electrode. In the first attempt, a Ti basket with 40 μm pores on its surface was used as the cathode. As shown in Figure 15c, the Nd2O3 was pelletized by a hydraulic press operating at 10 tonnes US without the addition of a binder. The resulting pellets were then dried at 100°C for 15 hours before conducting thermoelectrochemical tests. Notably, an Ar gas spagger was applied to the reactor to thoroughly mix the molten salt electrolyte during the experiment. After the reaction, the solidified molten salt covered the surfaces of the Ti basket, Ar gas spagger, and graphite anode (Figure 15d). As can be observed in Figure 15e, the molten salt could not be discharged from the Ti basket, possibly due to the small size of the holes. Furthermore, the pellets retained their blue color after the process, indicating that reduction was not achieved.

[0103] Two reasons may contribute to this failure. First, the small pores in the Ti basket limit the mass diffusion of the Li reducing agent from the electrolyte to the surface of the Nd2O3 pellet. Second, the design of the Ti basket may induce a Faraday cage phenomenon, reducing electron transfer from the anode to the cathode and consequently inhibiting electron diffusion through the Nd2O3 pellet. To overcome these challenges, the inventors designed and constructed a new apparatus.

[0104] Therefore, in the next step, we increased the size of the holes on the Ti cathode basket from 40 μm to 3 mm (Figure 16b). Furthermore, we removed the Ar gas spagger from the electrolyte. This Ar gas spagger was suspended above the electrolyte in the freeboard area to purge the generated gas. By comparing Figures 16a and 16c, it can be observed that the surface of the Nd2O3 pellets discolored and turned gray after the thermoelectric metallurgy process. Based on the XRD analysis shown in Figure 17, the surface of the pellets consists of Nd contaminated with residue.

[0105] To overcome the Faraday cage, the design of the Ti basket was modified, and a donut-shaped pellet attached to a Ti rod was adopted (Figures 18a and b). However, as shown in Figures 16d-f, this design was brittle, and the Nd2O3 broke when immersed in the molten electrolyte. After the reaction, the Nd2O3 pellet was detached from the cathode and attached to the graphite anode.

[0106] To address the above problem, a donut-shaped Nd2O3 pellet was surrounded by a titanium spring, as shown in Figures 19b and 19c. Furthermore, the top and bottom of the titanium spring were covered with quartz disks. As shown in Figures 19d and 19e, this improved design helped to hold the donut-shaped pellet in the cathode electrode. According to Figure 16f, after the thermoelectric metallurgy process, the surface of the pellet became discolored and gray. With regard to the XRD analysis shown in Figure 20, the surface of the pellet consisted of Nd contaminated with residue.

[0107] In particular, the cathode design was significantly modified. As shown in Figures 21a and 21b, an aluminum crucible was used as the cathode electrode. In this regard, a small 3 mm hole was made in the bottom of the aluminum crucible to facilitate electrolyte transfer from the molten salt and cathode discharge at the end of the process. As shown in Figure 21a, a graphite rod was placed in the center of the aluminum crucible at a predetermined distance from the inner aluminum wall. Figures 21c and 21d show the cathode separated after the thermoelectrochemical reaction. According to Figure 21c, the color of the top surface of the pellet did not change significantly. However, as shown in Figure 21f, the bottom of the pellet in contact with the aluminum crucible became a glossy gray, indicating the reduction of Nd2O3 to Nd at 400°C, 3V DC for 2 hours. XRD analysis of the reduced Nd2O3 also confirmed the phase transition (Figure 22). Impurities of KCl and Al originating from the electrolyte and cathode basket were also observed in the XRD pattern. Employing vacuum distillation helps us remove these impurities and achieve high-grade Nd.

[0108] Figures 23a and 23b show cyclic voltammetry and chronoamperometry of the thermoelectrochemical system during the reduction of Nd2O3 in a LiCl-KCl molten salt. Employing cyclic voltammetry helps us define the anode and cathode reactions by their corresponding potentials during the thermoelectrochemical process. Chronoamperometry plots can also help evaluate the kinetics of the electrolytic reduction of Nd2O3 as a function of time. Voltammetry analysis was performed in a LiCl-KCl molten salt using a Ti basket containing Nd2O3 pellets as the working electrode, a graphite rod as the counter electrode, and Ag / AgCl as the reference electrode. For voltammetry measurements, the current change on the working electrode was scanned from 2 V to -2 V and vice versa at a scanning speed of 0.1 V / s. As shown in Figure 23a, three cathode peaks (C1, C2, and C3) were observed for Ag / AgCl at -1.7V, -2.5V, and -3.4V, respectively. Additionally, three anode peaks appeared for Ag / AgCl at -1.9V, -2.6V, and -3.6V, respectively. The cathode peaks at -1.9V and -2.5V for Ag / AgCl are Nd 3+ Nd 2+ and Nd 0 This is due to reduction to . The anodic peaks at -1.9V and -2.6V relative to Ag / AgCl are associated with the reverse reactions R.23 and R.24.

[0109] [ka]

[0110] These results indicate that the thermoelectrochemical reduction of Nd2O3 in LiCl-KCl molten salt occurs in two steps. First, Nd2O3 is converted to soluble NdO by the application of one electron to the cathode surface. Next, NdO is reduced by two electrons on the cathode surface to form pure Nd. Therefore, the formation of NdO is a crucial step for the successful thermoelectrochemical reduction of Nd2O3. Based on the literature, Nd 2+NdO is a stable cation in chloride electrolytes. Three moles of NdO can react with each other in a chloride electrolyte, resulting in the formation of Nd2O3 and pure Nd (reaction R.25). Therefore, Nd 2+ It tends to undergo both oxidation (formation of Nd2O3) and reduction (formation of pure Nd) reactions. To suppress the oxidation reaction, a negative voltage (higher than -2.5V) should be applied using an electrochemical cell.

[0111] [ka]

[0112] According to Figure 23a, the cathode peak at -3.4V for Ag / AgCl and the anode peak at -3.6V for Ag / AgCl are due to the redox reaction of Li as a mediator on the cathode and anode surfaces (reaction R.26).

[0113] [ka]

[0114] Based on this investigation, thermoelectrochemical reduction was performed at a constant cathode voltage of -2.5V relative to Ag / AgCl. Figure 23b shows the current change as a function of time during the thermoelectrochemical reduction of Nd2O3 at a constant cathode voltage of -2.5V relative to Ag / AgCl. At the start of the process, the absolute current decreased sharply from 700mA to 280mA over a 6-minute period. The decrease in absolute current in the initial stage is due to the reactant concentration gradient near the cathode surface (i.e., Li 2+ and Nd 3+ This is due to ) . This result revealed that thermo-electrolytic reduction is controlled by cation diffusion at the start of the process. After 6 minutes, the absolute current increased significantly and reached 615 mA at 100 minutes. From this point onward, the absolute current slowly increased to 700 mA. The increase in absolute current is due to Nd 3+ Nd 2+ and Nd 0This is related to the reduction to anode. When a metal cation is reduced on the cathode surface, more electrons flow from the anode to the cathode through the external circuit, increasing the cathode current.

[0115] XRD analysis was performed to evaluate the phase transition. Figure 24 shows the XRD peaks of Nd2O3 before and after thermoelectrochemical reduction. The main diffraction peaks at 2θ = 26.8°, 29.7°, 30.7°, 40.5°, 45.3°, 47.4°, 49.9°, 53.4°, 55.3°, 57°, 61.8°, 64.1°, 67.6°, 68.6°, 74.2°, 75.8°, 77.7°, 79.8°, 81.4°, 83.5°, 86°, 87.6°, and 88.3° are mapped to the hexagonal structure of Nd2O3 (JCPD card number 00-043-1023). After electrochemical reduction, the XRD peaks changed significantly, and the corresponding Nd2O3 peaks disappeared. According to Figure 24, the appearance of the major peaks at 28° and 40.5° is attributed to neodymium chloride hydrate (NdCl3·H2O) (JCPD card number 00-003-0139). The Cl originates from the electrolyte residue that adsorbs moisture and forms an NdCl3·H2O layer on top of the pellet. These impurities can be removed using vacuum distillation.

[0116] Figure 25 shows SEM-EDX and elemental mapping of Nd2O3 pellets before and after electrolytic reduction. Regarding Figures 25(a-1) and (a-2), the pellets contained only fine powder of Nd and O before processing. However, as shown in Figures 25(b-1) and (b-2), a dense layer of potassium chloride covered the surface of the reduced Nd2O3 after the thermoelectric metallurgy process. Based on Figure 25(a-3), Nd and O atoms show similar distribution patterns, confirming the presence of Nd2O3. On the other hand, for the reduced Nd2O3, the distribution patterns of Nd and O changed in several regions. As shown in Figure 25(b-3), some regions of the reduced Nd2O3 were covered by Nd in the absence of O, suggesting the reduction of Nd2O3 to Nd metal.

[0117] The information shown in Figures 23, 24, and 25 demonstrates the effective conversion of neodymium oxide to neodymium metal using a LiCl / KCl molten salt at 400°C.

[0118] In one aspect, the inventors designed and constructed a reactor that transitions from Inconel to Pyrex. The advantage associated with Pyrex is its reduced susceptibility to salt adhesion to its surface, even after solidification following reactor shutdown.

[0119] Recovery of Molten Salt: The inventors have devised a method for separating and recovering neodymium metal from molten salts before they solidify. We developed a preheated Pyrex container called a molten salt collector, which is connected to the Pyrex reactor via a heating line. This collector is also connected to a vacuum line. After the completion of the thermoelectrochemical process, we apply vacuum pressure to the molten salt collector. This action rapidly moves all the salt from the Pyrex reactor to the collector, where it is recovered, later purified, and subsequently used. This streamlined technique makes our research more efficient and saves a significant amount of time. Figure 26 shows the improved thermoelectrochemical apparatus with a Pyrex reactor and a Pyrex molten salt collector.

[0120] The Pyrex reactor does not require an alumina crucible inside. Instead, we have the option of either introducing the molten salt powder directly into the Pyrex reactor or pouring the molten salt powder into an internal Pyrex beaker. To ensure the integrity of the Pyrex vessel, we equipped both the crucible furnace and the heating mantle of the molten salt collector with programmable controllers. These controllers regulate heating and cooling at a very slow rate, specifically less than 3°C / minute, to prevent any risk of cracking or breakage.

[0121] Example 7 - The experiment was carried out using a two-electrode thermoelectrochemical system. As shown in Figures 27(a), 27(d), and 27(e), Nd2O3 powder was pelletized using a 6-ton hydraulic press, then sandwiched between two perforated aluminum discs and used as the cathode electrode. As shown in Figure 27(f), a graphite rod was used as the anode electrode. The internal temperature of the molten salt was measured using a K-type thermocouple. The electrolyte contained 300g of LiCl salt and 300g of KCl salt in proportions of 45 wt% and 55 wt%, respectively. Figure 28(b) shows that the LiCl-KCl electrolyte formed a complete molten salt at 450°C. After achieving a complete molten salt, the cathode and anode were immersed in the electrolyte and held for 20 minutes to reach equilibrium ion transfer between the electrodes and the electrolyte. Subsequently, a 4.5V DC potential was applied by a power supply for 1.5 hours. At the end of thermoelectrolysis, the electrodes were pushed up and suspended over the electrolyte to discharge the residual salt. The electrolyte was cooled to ambient temperature at a rate of 3°C / min. Figure 27(c) shows the thermoelectrochemical reactor after the process. As shown in Figures 27(g) and (h), the reused Nd2O3 leaked from the cathode and dissolved in the molten salt. According to Figure 27(j), the dissolved REM formed a thin layer at the bottom of the solidified molten salt. The solidified electrolyte containing the REM was treated with cold water to separate this layer. REM is very unreactive in cold water, but LiCl-KCl can dissolve in cold water. Therefore, cold water treatment can help separate the REM from the bottom of the solidified electrolyte. Figures 27(k) and 27(m) show the separated REM after separation of the filter paper from the cold water.

[0122] Figure 31 shows the XRD of Nd2O3 and the obtained REM. The main diffraction peaks at 2θ of 26.8°, 29.7°, 30.7°, 40.5°, 45.3°, 47.4°, 49.9°, 53.4°, 55.3°, 57°, 61.8°, 64.1°, 67.6°, 68.6°, 74.2°, 75.8°, 77.7°, 79.8°, 81.4°, 83.5°, 86°, 87.6°, and 88.3° are mapped to the hexagonal structure of Nd2O3 (JCPD card number 00-043-1023). The XRD peaks of the REM showed a different pattern from the XRD of Nd2O3. According to Figure 28, the diffraction peaks at 13°, 25.6°, 31.3°, 34.6°, 40°, 41.3°, 45.3°, 46.2°, 47.3°, 51.5°, 52.8°, 57.9°, 59.1°, 61.7°, 64.1°, 65.7°, 67.3°, 69.5°, 72°, 74.6°, 76°, 77.5°, 79.87°, 80.6°, 86.9°, 88.8°, and 90.9° indicate neodymium chloride oxide (JCPD card number 00-001-1094). The chloride oxide in the NdClO composition originates from Cl as an electrolyte residue and is converted to ClO after cold water treatment. Furthermore, diffraction peaks at 2θ of 28.4°, 29.4°, 30.5°, 32.5°, 42.1°, 50°, 55.1°, 59°, 77.3°, 79.7°, 81.6°, and 88.4° are attributed to the hexagonal structure of pure Nd (JCPD card number 00-002-0842).

[0123] To further evaluate the obtained REM, SEM-EDX mapping analysis was performed. As shown in Figure 29(a), the obtained REM has a microspherical structure. Based on the EDX analysis shown in Figure 29(b), the REM mainly contains Nd, Cl, and O, with mass concentrations of 60 wt%, 14.3 wt%, and 13.7 wt%, respectively. In addition, 12 wt% of impurities, including C, Ti, Al, and K, were observed in the REM originating from the consumed graphite anode, cathode electrode, and molten salt. These impurities can be easily removed by vacuum distillation. According to the mapping graph, Cl and O show similar elemental distribution patterns, confirming the presence of chloride oxides observed in XRD analysis. Therefore, the Nd-ClO bond may be cleaved during vacuum distillation, resulting in high-purity Nd metal.

[0124] As will be understood by those skilled in the art, the thermoelectrochemical reduction processes described herein with respect to REO and RES can also be carried out with respect to other metal oxides and metal sulfides.

[0125] As will be understood by those skilled in the art, the present invention also relates to combinations of the above embodiments and aspects of the present invention.

[0126] As will be understood by those skilled in the art, other modifications and combinations can be made to the various embodiments of the invention described herein.

[0127] While this disclosure has been described in relation to its particular embodiments, further modifications are possible, and it will be understood that this application is applicable to the essential features described herein, within the scope of known or customary practice in the art, and is intended to cover any modifications, uses, or adaptations, including deviations from this disclosure, in accordance with the appended claims. Features described in the context of individual aspects and embodiments of the invention can be used in combination and / or are interchangeable. Similarly, features described in the context of a single embodiment can also be provided individually or in any suitable subcombination.

[0128] The claims should not be limited by the preferred embodiments described in the examples, but should be given the broadest interpretation consistent with the overall description.

[0129] This specification references numerous documents, the contents of which are incorporated herein by reference in their entirety.

[0130] References: [1] SM Abdelbasir, CT El-Sheltawy, DM Abdo, Journal of Sustainable Metallurgy. 2018, 4. [2] DD Munchen, HM Veit, Waste Management. 2017, 61. [3] Y. Yang, A. Walton, R. Sheridan, K. Guth, R. Gaus, O. Gutfleisch, M. Buchert, B.-M. Steenari, T. Van Gerven, PT Jones, K. Binnemans, Journal of Sustainable Metallurgy. 2017, 3. [4] Z. Hua, Sustainable Inorganic Chemistry. 2016. [5] R. Schulze, M. Buchert, Resources, Conservation and Recycling. 2016, 113. [6] E. Padhan, AK Nayak, K. Sarangi, Hydrometallurgy. 2017, 174. [7] O. Takeda, TH Okabe, Metallurgical and Materials Transactions E. 2014, 1. [8] P. Venkatesan, Z. H. I. Sun, J. Sietsma, Y. Yang, Separation and Purification Technology. 2018, 191. [9] Y. Mochizuki, N. Tsubouchi, K. Sugawara, ACS Sustainable Chemistry & Engineering. 2013, 1.

[10] S. Shirayama, T. H. Okabe, Metallurgical and Materials Transactions B. 2018, 49.

[11] K. K. Yadav, M. Anitha, D. K. Singh, V. Kain, Separation and Purification Technology. 2018, 194.

[12] A. Borthakur, P. Singh, "Recycling of E-Waste," Encyclopedia of Renewable and Sustainable Materials, S. Hashmi, I. A. Choudhury Eds., Elsevier, Oxford 2020, p. 527-534.

[13] K. Binnemans, P. T. Jones, B. Blanpain, T. Van Gerven, Y. Yang, A. Walton, M. Buchert, Journal of Cleaner Production. 2013, 51.

[14] Hoornweg D, B.-T. P, 2012.

[15] S. Hughes, M. Jafs, H. Johto, J. Stal, J. Karonen, "Outotec Solutions for E-Scrap Processing," REWAS 2019, Cham, 2019 / / 2019.

[16] M. Regel-Rosocka, “Electronic wastes, 3(5),” in “Physical Sciences Reviews,” (2018) p. 20180020

[17] Y. Wu, B. Wang, Q. Zhang, R. Li, J. Yu, RSC advances. 2014, v. 4.

[18] MK Jha, A. Kumari, R. Panda, J. Rajesh Kumar, K. Yoo, JY Lee, Hydrometallurgy. 2016, 165.

[19] H.-S. Yoon, J.-J. Kim, K.-W. Chung, S.-D. Kim, J.-Y. Lee, JR Kumar, Hydrometallurgy. 2016, 165.

[20] Z. Hua, J. Wang, L. Wang, Z. Zhao, X. Li, Y. Xiao, Y. Yang, ACS Sustainable Chemistry & Engineering. 2014, 2.

[21] A. Abbasalizadeh, S. Seetharaman, P. Venkatesan, J. Sietsma, Y. Yang, Electrochimica Acta. 2019, 310.

[22] T. Wang, H. Gao, X. Jin, H. Chen, J. Peng, G. Chen, Electrochemistry Communications. 2011, 13(12), p. 1492-1495.

[23] Ben Holcombe et al. Electrochem. Soc. Interface. 2024, 33, p. 49.

Claims

1. A process for producing rare earth metals (REM), comprising subjecting a rare earth oxide (REO) or rare earth sulfide (RES) to thermoelectrochemical reduction in a eutectic molten salt to obtain a thermoelectrochemical reduction product containing REM.

2. The process further includes subjecting the thermoelectrochemical reduction product to a purification process, Preferably, the purification process includes subjecting the thermoelectrochemical reduction product to water leaching, more preferably using cold water. Preferably, the purification process comprises subjecting the thermoelectrochemical reduction product to vacuum distillation, according to claim 1.

3. (i) dissolving the obtained thermoelectrochemical reduction product in a liquid metal to obtain a REM alloy; and (ii) subjecting the REM alloy to washing and / or vacuum distillation to produce REM, Preferably, the process according to claim 1, wherein the liquid metal comprises a metal selected from the group consisting of Ca, K, Zn, Mg, Fe, and Mn.

4. The temperature at which thermoelectrochemical reduction occurs is below approximately 500°C. Preferably, the process according to any one of claims 1 to 3, wherein the thermoelectrochemical reduction temperature is between about 375°C and about 450°C.

5. The process according to any one of claims 1 to 4, wherein the pressure during thermoelectrochemical reduction is atmospheric pressure.

6. The eutectic molten salt contains a mixture of at least two salts, where at least one salt is a lithium salt or a calcium salt. Preferably, the lithium salt is LiCl, Li 2 S, Li 2 O, and LiNO 3 Selected from the group consisting of, Preferably, the calcium salt is CaCl 2 And, Preferably, at least one other salt is a non-lithium salt, preferably KCl, CaCl 2 , and NaNO 3 A process according to any one of claims 1 to 5, selected from the group consisting of the following.

7. The process according to any one of claims 1 to 6, wherein the eutectic molten salt comprises a mixture of LiCl and KCl.

8. The eutectic molten salt comprises a mixture of a first lithium salt and a second salt, and the mass percentage ratio of the first salt to the second salt is approximately 40:60, approximately 45:55, or approximately 48:

62. Preferably, the process according to any one of claims 1 to 7, wherein the mass percentage ratio of the first salt to the second salt is about 45:

55.

9. The eutectic molten salt contains a mixture of LiCl and KCl, with a mass percentage ratio of approximately 40:60, approximately 45:55, or approximately 48:

62. The process according to any one of claims 1 to 7, preferably wherein the mass percentage ratio of LiCl to KCl is about 45:

55.

10. The eutectic molten salt is CaCl 2 , NaCl, and MgCl 2 The process according to any one of claims 1 to 7, comprising a mixture of at least two salts selected from the group consisting of, and wherein the thermoelectrochemical reduction temperature is greater than about 700°C.

11. The process further includes recovering the eutectic molten salt upon completion of the thermoelectrochemical reduction. Preferably, the process according to any one of claims 1 to 10, wherein the recovered eutectic molten salt is subjected to purification and reuse in the process.

12. When thermoelectrochemical reduction is performed on RES, a sulfur-containing gas is obtained as a byproduct, and the obtained sulfur-containing gas is further recycled for reuse. Preferably, the sulfur-containing gas is S 2 gas and / or H 2 The process according to any one of claims 1 to 11, which is a gas.

13. REM is selected from the group consisting of: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), and yttrium (Y). Preferably, REM is selected from the group consisting of Nd, Dy, Pr, Ce, Er, and Y. More preferably, the process according to any one of claims 1 to 12, wherein REM is Nd, Pr, or Dy.

14. The process according to any one of claims 1 to 13, wherein the resulting REM has a high purity, such as about 99% purity.

15. REM obtained by a process defined in any one of claims 1 to 14.

16. A process for converting rare earth oxides (REO) to rare earth sulfides (RES), comprising subjecting the REO to a reaction with a sulfur-containing gas.

17. The temperature during the reaction between REO and sulfur-containing gas is between approximately 800°C and approximately 1200°C. The process according to claim 16, preferably the temperature is between about 600°C and about 700°C.

18. Sulfur-containing gas 2 gas and / or H 2 The process according to claim 16, wherein the gas is S gas.

19. Sulfur-containing gas is H 2 Further including a preliminary step to convert to S gas, Preferably, the sulfur-containing gas is S 2 And the preliminary step is S 2 Gas H 2 The process according to any one of claims 16 to 18, comprising converting to S gas.

20. RES obtained by a process defined in any one of claims 16 to 19.

21. REO is obtained from recycled waste such as materials from discarded magnets and end-of-life products. Preferably, the process according to any one of claims 1 to 20, wherein REO is obtained from recycled e-waste such as NdFeB magnets.

22. The process according to any one of claims 1 to 20, wherein REO is extracted from natural resources such as ore.

23. A thermoelectric reactor adapted to perform a process defined in any one of claims 1 to 14.

24. A thermoelectrochemical reactor for producing REM from REO or RES in a eutectic molten salt, comprising a cathode having an aluminum crucible with a microsieve incorporated at its bottom.

25. A thermoelectrochemical reactor for producing REM from REO or RES in a eutectic molten salt, comprising a cathode having a perforated aluminum disk adapted to sandwich REO and / or RES pellets.

26. A reactor according to any one of claims 23 to 25, comprising a sparger or gas distributor adapted for injecting and maintaining a flow of inert gas into the reactor, Preferably, the reactor is one in which the inert gas is argon (Ar).

27. A system for producing rare earth metals (REM) by thermoelectrochemical reduction in a eutectic molten salt of rare earth oxides (REO) or rare earth sulfides (RES), comprising a thermoelectrochemical reactor and a molten salt collector, Herein, the molten salt collector is operably connected to the reactor via a first line and also operably connected to a vacuum line.

28. The system according to claim 27, wherein the molten salt collector and the first line are adapted to be heated independently.

29. A system for producing rare earth metals (REM) by thermoelectrochemical reduction in a eutectic molten salt of a rare earth oxide (REO) or rare earth sulfide (RES), comprising: A cathode in the form of a basket for receiving REO or RES and eutectic molten salt; Anodes in the form of high-density graphite rods; and A molten salt collector operably connected to a basket via a first line and operably connected to a vacuum line, The system includes, wherein the molten salt collector and the first line are configured to be heated independently; and, upon completion of electrolysis, the pressure applied to the molten salt collector allows for the recovery of the molten salt from the basket.

30. A reactor according to any one of claims 23 to 26 or a system according to any one of claims 27 to 29, further comprising a programmable controller for controlling heating and cooling.

31. The reactor according to any one of claims 23 to 26 or the system according to any one of claims 27 to 29, wherein the cathode and / or molten salt collector comprises a Pyrex vessel.

32. A plant for the production of rare earth metals (REM), which embodies a process defined in any one of claims 1 to 14, Preferably, the plant is an industrial plant.

33. A plant for converting REO to RES, which embodies the process defined in any one of claims 16 to 19, Preferably, the plant is an industrial plant.

34. A reactor adapted to perform a process defined in any one of claims 16 to 19.

35. A reactor for use in converting rare earth oxides (REO) to rare earth sulfides (RES) using sulfur-containing gas, wherein the reactor is a fluidized bed, a rotary kiln, or any suitable multiphase reactor.

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