Process for producing rare earth metals

Abstract

There is provided a process for producing rare earth metals (REM). The process comprises subjecting rare earth oxides (REO) or rare earth sulfides (RES) to a pyro- electrochemical reduction in a eutectic molten salt thereby obtaining a pyro- electrochemical reduction product comprising the REM. The pyro-electrochemical reduction product obtained is further subjected to a purification process. A process for converting REO to RES is also provided.

Description

TITLE OF THE INVENTION PROCESS FOR PRODUCING RARE EARTH METALS CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Provisional Patent Application No. 63 / 508,290 filed on June 15, 2023. The content of this application is incorporated herein in its entirety by reference. FIELD OF THE INVENTION

[0002] The present invention relates generally to processes for producing rare earth metals (REM). More specifically, the invention relates to a process for producing REM from rare earth oxides (REO). The process comprises a pyro-electrochemical reduction, in a eutectic molten salt, of REO or rare earth sulfides (RES) obtained from REO. Accordingly, the invention also relates to a process for the conversion of REO to RES. BACKGROUND OF THE INVENTION

[0003] Demand for the rare earths elements (REE), also called rare earth metals (REM), such as neodymium (Nd) and dysprosium (Dy) is increasing as renewable energy becomes more important across the globe[1-5]. The strategic rare metals, which are important in clean energy applications and high-tech industries such aswind turbines, electric vehicles and hybrid cars, are in the spotlight[3; 6; 7]. On the otherhand, a considerable amount of electronic waste (e-waste) consisting of NdFeB magnets is significantly being generated. The NdFeB magnets are typically composed of 20-30 wt% REE (15-25% of which is Nd), 50-70 wt% Fe, 1.0 wt% B[8-11], and about 5 wt% of other metals such as copper, nickel, and cobalt. The availability of REE is a critical issue in manufacturing the permanent magnets. To date, less than 1% of REE have been recycled from e-waste[1; 12; 13]which is mainly due to the lack of specific and sustainable technologies[1; 7; 12-17].

[0004] REE are mainly recycled from the scrap magnets in the form of rare earth oxides (REO) through the hydrometallurgical processes[7; 13; 18; 19]. In wet-chemical methods, the scrap magnets are dissolved in strong inorganic acids and then extracted as REE in various forms including oxides, sulfates, nitrates, hydroxides, carbonates, and oxalates. The thermal calcination of the extracted REE under air atmosphere at temperatures above 500°C leads to the formation of a material comprising mainly REE in oxide form (REO). Itis worth pointing that the oxides produced by the hydrometallurgical routes require to be converted to high-purity metals in order to be used in various electronic and high- tech industries. In addition, direct recycling of scrapped magnets into rare metal alloys such as RE-Fe and RE-Mg (RE = Nd, Dy, or Pr) has been performed via the molten fluorides and chlorides without separation of Nd and Dy[7; 10; 20; 21]. The products have been mainly employed for manufacturing of NdFeB alloys. Nevertheless, literature lacks essential information on the conversion REO to pure rare earth metals via feasible and low-cost sustainable methods.

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

[0022] ; and Ben Holcombe et al.

[0023] .

[0006] There is a need for processes for producing REM. There is a need for such processes that are efficient, cost effective, environmentally friendly, and that allow for possibility for industrialization. SUMMARY OF THE INVENTION

[0007] According to an aspect of the invention, the inventors have designed and performed a process for producing rare earth metals (REM) from rare earth oxides (REO). The process comprises a pyro-electrochemical reduction, in a eutectic molten salt, of REO or rare earth sulfides (RES) obtained from REO. The eutectic molten salt has a reduced melting point, allowing for a safer, more energy efficient, cost-effective, environmentally friendly, and easier-to-handle process. The pyro-electrochemical reduction is performed at a temperature below 500°C and at atmospheric pressure. The pyro-electrochemical reduction product obtained is purified using techniques known in the art yielding REM of high purity. Such techniques may comprise water leaching and / or vacuum distillation of the pyro-electrochemical reduction product. Such techniques may also comprise formation of a metal alloy based on the pyro-electrochemical reduction product followed by the vacuum distillation.

[0008] According to another aspect of the invention, the inventors have designed and conducted a process for converting REO to RES. The process may comprise a direct reaction between REO and a sulfur-containing gas yielding RES. The sulfur-containing gas may be S2gas and / or H2S gas. In embodiments, the process may comprise first converting the sulfur-containing gas for example the S2to H2S gas in-situ, then reacting REO with H2S gas yielding RES.

[0009] In embodiments of the invention, there is provided a reactor adapted for performing the process according to the invention. In particular, there is provided a pyro- electrochemical reactor for the production of REM from of REO or RES in a eutectic molten salt. In an embodiment, a cathode design of the reactor comprises an aluminum crucible cathode with micro-sieves integrated at the bottom. In another embodiment, a cathode design comprises a perforated aluminum disc adapted for sandwiching the REO and / or RES pellets. In a further embodiment, the reactor comprises a sparger or gas distributor adapted for injecting and maintaining a flow of an inert gas into the reactor.

[0010] In embodiments of the invention, there is provided a pyro-electrochemical system for the production of REM from REO or RES in a eutectic molten salt. The pyro- electrochemical system comprises a pyro-electrochemical reactor and a molten salt collector operably connected to the reactor through a first line and to a vacuum line. In preferred embodiments, the molten salt collector and the first line are each independently adapted to being heated.

[0011] In embodiments of the invention, the starting material comprising the REO is obtained from recycled waste materials such as waste magnets and materials from end- of-life products. In other embodiments, the starting material comprising the REO is extracted from natural sources such as mineral ores.

[0012] In embodiments of the invention the REM obtained has a high purity, for example about 99% purity.

[0013] The invention thus provides the following in accordance with aspects thereof. (1). A process for producing rare earth metals (REM), comprising subjecting rare earth oxides (REO) or rare earth sulfides (RES) to a pyro-electrochemical reduction in a eutectic molten salt thereby obtaining a pyro-electrochemical reduction product comprising the REM. (2). The process according to (1), further comprising subjecting the pyro-electrochemical reduction product to a purification process; preferably the purification process comprises subjecting the pyro-electrochemical reduction product to water leaching, more preferably using cold water; preferably the purification process comprises subjecting the pyro- electrochemical reduction product to vacuum distillation.(3). The process according to (1), further comprising: (i) dissolving the pyro- electrochemical reduction product obtained in a liquid metal to obtain an REM alloy; and (ii) subjecting the REM alloy to washing and / or vacuum distillation to produce the REM, preferably the liquid metal comprises a metal selected from the group consisting of Ca, K, Zn, Mg, Fe, and Mn. (4). The process according to any one of (1) to (3), wherein the temperature of the pyro- electrochemical reduction is below about 500°C, preferably the temperature of the pyro- electrochemical reduction is between about 375°C to about 450°C. (5). The process according to any one of (1) to (4), wherein the pressure during the pyro- electrochemical reduction is atmospheric pressure. (6). The process according to any one of (1) to (5), wherein the eutectic molten salt comprises a mixture of at least two salts, wherein 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). The process according to any one of (1) to (6), wherein the eutectic molten salt comprises a mixture of LiCl and KCl. (8). The 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 a mass percentage ratio of the first and second salts is about 40:60, about 45:55, or about 48:62; preferably the mass percentage ratio of the first and second salts is about 45:55. (9). The process according to any one of (1) to (7), wherein the eutectic molten salt comprises a mixture of LiCl and KCl, and a mass percentage ratio of about 40:60, about 45:55, or about 48:62; preferably the mass percentage ratio of LiCl and KCl is about 45:55. (10). The 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 temperature of the pyro-electrochemical reduction is above about 700°C.(11). The process according to any one of (1) to (10), further comprising recovering the eutectic molten salt upon completion of the pyro-electrochemical reduction, preferably the recovered eutectic molten salt is subjected to purification and re-use in the process. (12). The process according to any one of (1) to (11), wherein, when the pyro- electrochemical reduction is conducted on RES, a sulfur-containing gas is obtained as by- product, and the process further comprises recycling the sulfur-containing gas obtained for re-use; preferably the sulfur-containing gas is S2gas and / or H2S gas. (13). The process according to any one of (1) to (12), wherein the 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 the REM is selected from the group consisting of: Nd, Dy, Pr, Ce, Er, and Y; more preferably the REM is Nd, Pr, or Dy. (14). The process according to any one of (1) to (13), wherein the REM obtained has a high purity such as about 99% purity. (15). An REM obtained by the process as defined in any one of (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 process according to (16), wherein the temperature during the reaction of the REO and 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). The process according to (16), wherein the sulfur-containing gas is S2gas and / or H2S gas. (19). The process according to any one of (16) to (18), further comprising a preliminary step of converting the sulfur-containing gas to H2S gas in-situ; preferably the sulfur- containing gas is S2and the preliminary step consists of converting the S2gas to H2S gas.(20). An RES obtained by the process as defined in any one of (16) to (19). (21). The process according to any one of (1) to (20), wherein the REO is obtained from recycled waste materials such as waste magnets and materials from end-of-life products, preferably REO is obtained from recycled e-waste materials such as NdFeB magnets. (22). The process according to any one of (1) to (20), wherein the REO is extracted from natural sources such as mineral ores. (23). A pyro-electrochemical reactor adapted for performing the process as defined in any one of (1) to (14). (24). A pyro-electrochemical reactor for the production of REM from REO or RES in a eutectic molten salt, the reactor comprising a cathode having an aluminium crucible with micro-sieves integrated at the bottom thereof. (25). A pyro-electrochemical reactor for the production of REM from REO or RES in an eutectic molten salt, the reactor comprising a cathode having a perforated aluminum disc adapted for sandwiching the REO and / or RES pellets. (26). The reactor according to any one of (23) to (25), which is equipped with a sparger or gas distributor adapted for injecting and maintaining a flow of an inert gas into the reactor, preferably the inert gas is argon (Ar). (27). A system for the production of rare earth metals (REM) through pyro-electrochemical reduction in a eutectic molten salt of rare earth oxides (REO) or rare earth sulfides (RES), comprising a pyro-electrochemical reactor and a molten salt collector, wherein the molten salt collector is operably connected to the reactor through a first line and operably connected to a vacuum line. (28). The system according to (27), wherein the molten salt collector and the first line are each independently adapted to being heated. (29). A system for the production of rare earth metals (REM) through pyro-electrochemical reduction in a eutectic molten salt of rare earth oxides (REO) or rare earth sulfides (RES), comprising: a cathode in the form of a basket for receiving the REO or RES and theeutectic molten salt; an anode in the form of a high-density graphite rod; and a molten salt collector operably connected to the basket through a first line and operably connected to a vacuum line, wherein the molten salt collector and the first line are each independently adapted to being heated; and wherein upon completion of the electrolysis, pressure applied to the molten salt collector allows for retrieval of the molten salt from the basket. (30). The reactor according to any one of (23) to (26) or the system according to any one of (27) to (29), further comprising programmable controllers for regulating heating and cooling. (31). The reactor according to any one of (23) to (26) or the system according to any one of (27) to (29), wherein the cathode and / or the molten salt collector comprises a Pyrex vessel. (32). A plant for the production of rare earth metals (REM), which embodies the process as defined in any one of (1) to (14), preferably the plant is an industrial plant. (33). A plant for the conversion of REO to RES, which embodies the process as defined in any one of (16) to (19), preferably the plant is an industrial plant. (34). A reactor adapted for performing the process as defined in any one of (16) to (19). (35). A reactor for use in the conversion of rare earth oxides (REO) to rare earth sulfides (RES) using a sulfur-containing gas, wherein the reactor is a fluidized bed, rotary kiln, or any suitable multiphase reactor.

[0014] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0016] In the appended drawings:

[0017] Figure 1: Process according to the invention for clean and sustainable production of rare earth metals (REM) or rare earth elements (REE).

[0018] Figure 2: a) Gibbs free energy vs Temperature for possible reaction of Nd-oxide sulfurization, b) close-up figure.

[0019] Figure 3: A) Nd-oxide in an alumina boat to be placed in the middle of TFR (tubular furnace reactor), B) residue after treatment.

[0020] Figure 4: A) XRD results of NCT7 residue sample; B) XRD results of NCT15 residue sample; C) XRD results of NCT16 residue sample.

[0021] Figure 5: EDS-mapping of critical elements Nd, O, and S for sample NCT16 with 2 different sampling methods, A and B.

[0022] Figure 6: Mixture of Nd-oxide and S powders, pelletized A) before and B) after treatment.

[0023] Figure 7: XRD results of NCT18 residue sample.

[0024] Figure 8: The scheme of the experimental apparatus for neodymium oxide sulfidation using an induction heating reactor. (1) Pure Nitrogen Gas, (2) MFC, (3) Heating mantle, (4) Glass vessel, (5) Thermocouple, (6) Pressure Guage, (7) Condenser, (8) Outlet valve, (9) Quartz tube reactor, (10) Induction heating furnace, (11) Copper coil, (12) Nd2O3 powder bed, (13) Diffuser, (14) Rods, (15) Quartz reactor thermocouple (16) Induction heating control box, (17) Washing bottle, (18) Exhaust.

[0025] Figure 9: The sulfidation apparatus to sulfide Nd2O3into Nd2S3.

[0026] Figure 10: Inconel electrochemical reactor and its dimensions.

[0027] Figure 11: Left: Molten CaCl2 / CaCO3salt at 800°C observed through the window of flange. Right: Solidified CaCl2 / CaCO3salt inside the alumina crucible after reactor was cooled down.

[0028] Figure 12: Phase diagram of eutectic LiCl-KCl molten salt electrolyte.

[0029] Figure 13 Pyro-electrolysis setup, (a) water chiller, (b) crucible furnace and Inconel reactor, (c) Ar cylinder, (d) potentiostat / galvanostat, (e) electrodes and sparger, and (f) pressure regulator.

[0030] Figure 14: A schematic of pyro-electrochemical setup. (AEL: anode electrode, CEL: cathode electrode, REL: reference electrode, spg: sparger, CW: colling water, HW: hot water, TC: thermocouple, RV: relieve valve, HW).

[0031] Figure 15: (a) Images of the graphite anode, sparger, and titanium (Ti) basket, (b) the pyro-electrochemical setup, (c) pelletized Nd2O3powder, (d) graphite anode, sparger, and Ti basket after process covered by solidified molten salt, (e) inside Ti cathode basket, and (f) separated pellets from the cathode basket.

[0032] Figure 16: (a) pelletized Nd2O3powder, (b) inside Ti cathode basket after process, and (c) reduced Nd2O3pellets.

[0033] Figure 17: The XRD pattern of the reduced Nd2O3in the Ti basket.

[0034] Figure 18: (a) doughnut-shaped Nd2O3pellet, (b) Nd2O3pellet attached to Ti rode, (c) graphite anode, (d) Ti cathode after reaction, (e) and (f) graphite anode covered by Nd2O3.

[0035] Figure 19: (a) Doughnut-shaped Nd2O3pellet, (b) and (c) Nd2O3pellet attached to Ti rode and covered by Ti spring and quartz, (d) and (e) cathode electrode after reaction, (f) reduced Nd2O3pellet.

[0036] Figure 20: The XRD pattern of the reduced Nd2O3 attached to the Ti rod.

[0037] Figure 21: (a) Homemade aluminum crucible used as the cathode, (b) aluminum crucible filled with doughnut-shaped Nd2O3pellet and KCl-LiCl electrolyte placed inside the alumina crucible (top view), (c) aluminum crucible after process, (d) and (e) top surface of reduced Nd2O3pellet, and (f) bottom surface of reduced Nd2O3pellet.

[0038] Figure 22: The XRD pattern of the reduced Nd2O3inside the aluminum crucible.

[0039] Figure 23: (a) cyclic voltammetry and (b) chronoamperometry of Nd2O3cathode held by Ti basket in LiCl-KCl molten salt at 400˚C under Ar atmosphere.

[0040] Figure 24: XRD pattern of Nd2O3and reduced Nd2O3.

[0041] Figure 25: (a-1) SEM images, (a-2) EDX, (a-3) elemental mapping of Nd2O3; and (b-1) SEM images, (b-2) EDX, (b-3) elemental mapping of reduced Nd2O3.

[0042] Figure 26: Modified pyro-electrochemical setup. Left: Pyrex reactor inside the crucible furnace connected to preheated Pyrex molten salt collector via a heated line. Right: Pyrex reactor.

[0043] Figure 27: (a) two-electrode configuration pyro-electrochemical cell with solid LiCl- KCl electrolyte, (b) the pyro-electrochemical cell with molten electrolyte at 450˚C, (c) the pyro-electrochemical cell after process, (d) and (e) cathode before process, (f) anode before the process, (g) and (h) cathode after process, (i) anode after the process, (j) solidified electrolyte contains reduced REE, (k) and (m) separated REM.

[0044] Figure 28: XRD pattens of Nd2O3and reduced Nd2O3by pyro-electrolysis.

[0045] Figure 29: (a) SEM image, (b) EDS spectra and elemental composition, (c) elemental mapping, and (d) elemental distribution of reduced Nd2O3by pyro-electrolysis under 4.5 V DC at 450˚C. DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0046] Before the present invention is further described, it is to be understood that the invention is not limited to the particular embodiments described below, as variations of these embodiments may be made and still fall within the scope of the appended claims. It is also to be understood that the terminology employed is for the purpose of describing particular embodiments; and is not intended to be limiting. Instead, the scope of the present invention will be established by the appended claims.

[0047] In order to provide a clear and consistent understanding of the terms used in the present specification, a number of definitions are provided below. Moreover, unless defined otherwise, all technical and scientific terms as used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure pertains.

[0048] Use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one”, and “one or more than one”. Similarly, the word “another” may mean at least a second or more.

[0049] As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) or “containing” (and any form of containing, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps.

[0050] The terms “rare earth metal” and “rare earth element” are used herein interchangeably and identified respectively as “REM” and “REE”. These terms refer to any one of the seventeen (17) rare earth elements, 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). Everyone of “REM” and “REE” as used herein indicates both singular and plural; accordingly, “REM”, “REMs, “REE”, and “REEs”” are used interchangeably.

[0051] The terms “rare earth oxide” and “rare earth element oxide” are used herein interchangeably and identified as “REO”. “REO” as used indicates both singular and plural; accordingly, “REO” and “REOs” are used interchangeably.

[0052] The terms “rare earth sulfide” and “rare earth element sulfide” are used herein interchangeably and identified as “RES”. “RES” as used indicates both singular and plural; accordingly, “RES” and “RESs” are used interchangeably.

[0053] The term “electrochemical reduction”, “pyro-electrochemical reduction”, “pyro- electrolysis, “pyro-electroreduction”, electro-calciothermic reduction, and “electro- lithiothermic reduction” refer to the production of REM from REO or RES through the pyro- electrochemical reduction process according to the invention. These terms are used herein interchangeably.

[0054] 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 invention. These terms are used herein interchangeably.

[0055] The term “eutectic molten salt” refers to a salt used in the pyro-electrochemical reduction of REO or RES according to the invention. Such salt comprises at least two salts including a lithium salt and a non-lithium salt which melts at a lower temperature thanany of the individual salts alone. The lithium salt may be LiCl, Li2S, Li2O, or LiNO3. And the non-lithium salt may be KCl, CaCl2, NaCl, MgCl2, or NaNO3.

[0056] The inventors have designed and performed a process for producing rare earth metals (REM) from rare earth oxides (REO). The process comprises a pyro- electrochemical reduction, in a eutectic molten salt, of REO or rare earth sulfides (RES) obtained from REO. Also, the inventors have designed and performed a process for converting REO to RES. These processes are described in detail below.

[0057] Regarding the reduction of RES to REM, it is known in the art that pure REM are produced at very high temperatures of more than 1200°C by the energy-intensive reduction of the fluorides, which is not only hazardous to the environment, but also drives up the process and plant costs making the entire process less attractive.

[0058] The inventors have developed a novel and sustainable electro-lithiothermic reduction of REO and RES with in-situ generated / dissolved Li in eutectic molten LiCl-KCl salts at relatively low temperatures, below 500°C. Hence, the present innovative approach according to an aspect, aims to address this problem via sustainable treating of RES and REO in LiCl-based molten salts, instead of the oxides, nitrate and fluorides molten salts. Sulfur resources are also cheap, nontoxic, and readily available globally that can be applied for synthesis of the clean RES. According to the invention, sulfur-enriched gas released during the pyro-electrolysis of RES can be recovered and re-used in the sulfidation step, decreasing the amount required. The process is highly practical for 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). The process consumes less energy without CO2emission or generation of harmful greenhouse gases such as perfluorocarbon (PFC) gases, notably CF4and C2F6.

[0059] In the process according to the invention, the rare earth metals are produced through the lithiothermic reduction of the oxides or the sulfides in the eutectic molten LiC- KCl, and separation of the REM from the cathode can be achieved by liquid Zn or Mg metals. The reductant Li is in-situ generated by reduction of Li2S or LiO at the anode surface (or oxidation of anode electrode) in the eutectic molten LiCl-KCl salt at temperatures between below 500°C. Thus, reduction of REO (Nd2O3) or RES (Nd2S3) is carried out by the dissolved lithium in the melt at the cathode surface.

[0060] Hence, the process according to the invention can lead to the formation of REE- Zn (Mg) alloys, and Zn or Mg can be removed by vacuum distillation in a subsequent step. The invention as it relates to sulfides reduces the energy consumption by rapid reduction of the sulfides. Moreover, sulfur is cheap, nontoxic and readily available globally that could be applied for synthesis of clean sulfides used in the electrolysis. The CO / CO2gases are not generated in the pyro-electrolysis of RES and thus graphite anodes become non-consumable. The process prevents the REM contamination with carbon by the evolution of S2gas on the surface of the anode. The exhaust gas (S2) from the cells may be recycled and used for sulfidation of metal oxides and starting materials. Figure 1 shows the proposed general flow diagram for the production of REM from REO. Variations and aspects thereof are described herein and will be readily understood by a skilled person.

[0061] The process according to the invention comprises at least the following aspects: conversion of rare metal oxides, carbonates, or chlorides obtained from end-of-life or recycled waste streams such as NdFeB magnets or natural REE bearing ores to rare metal sulfides by sulfidation process using S2gas or another sulfur-containing gas; electro- lithiothermic reduction of pristine sulfides or oxides followed by water leaching: dissolution of obtained product in liquid metal including but not limited to Mg and Zn to produce REM alloys such as REM-Zn and REM-Mg alloys; purification and separation of pure rare earth metals from the electrochemically produced alloys by distillation in vacuum atmosphere.

[0062] According to an aspect of the invention, the clean rare earth metal sulfides are synthesized from the oxides by carbothermic-sulfidation or sulfidation in an S2gas or any other sulfur-containing gas (e.g., in-situ H2S) atmosphere at temperatures of about 600- 1200°C. According to another aspect, the sulfides are electrochemically reduced at 3.0 V DC by Li with addition of different molar ratios of LiCl in eutectic molten LiCl-KCl salt at temperatures below 500°C (e.g., 450°C). According to yet another aspect, the electrochemically reduced samples can be dissolved in molten zinc (Zn) or magnesium (Mg) to separate the rare metals in the form of REE-M alloys. Finally, the alloys obtained from the sulfides in molten LiCl-KCl salts and dissolution in liquid Zn or Mg metals, can be treated under vacuum atmosphere at 700-900°C to extract rare earth metals (i.e., applicable to all 17 rare earth elements). Thus, for example, neodymium, which melts at 1021°C, can be separated from Zn, which boils at 907°C by vacuum distillation.

[0063] Sulfidation of REO is carried out at temperatures above 600°C using S2gas or any other sulfur-containing gas. The sulfides are loaded into a basket cathode and reduced to metals in eutectic molten LiCl-KCl at temperatures below 500°C and applied DC voltageof 3.0 V. Two cathode designs are developed. The first design involves an aluminum crucible cathode with micro-sieves integrated at the bottom. The second design comprises a perforated aluminum disc sandwiching the REO or RES pellets. A high-density graphite rod is also used as an anode and the salts are purified by pre-electrolysis using an auxiliary carbon electrode at 2.0 V in an argon (Ar) atmosphere. The supplied charge (Q / C), electrolysis temperature and pressure could be precisely monitored by a data acquisition unit. The rare earth metals can then be separated from the reduced samples by liquid Zn or Mg in the form of REE-M (M=Zn, Mg) alloys. Finally, the pure REE (Nd, Dy) can be produced by vacuum distillation process.

[0064] In an aspect of the process according to the invention, the REM can be produced via RES without using hazardous fluorides which will eliminate the generation of CO / CO2gases. This method makes the production of rare earth metals much more economic and energy efficient than the current practices using the chlorides or fluorides to produce REE alloys.

[0065] The invention is further described in detail below including the sulfidation of REO using a sulfur-containing gas to obtain RES, the pyro-electrochemical reduction of REO and RES in a eutectic molten salt, as well as other aspects of the invention. The reactor developed by the inventors for conducting the process according to the invention, is also described. Gas-solid sulfidation process to obtain RES from REO

[0066] Materials and equipment: We used 99% pure Neodymium (III) oxide (Nd2O3) as an example of REO and 99% sulfur powder both from Sigma (Germany). The reaction was performed in the inert atmosphere under the nitrogen flow (different flowrates).

[0067] The first pathway of sulfidation process was performed in a tubular furnace reactor with an alumina tube. For this purpose, two different heated zones were defined based on the boiling point of sulfur and the reaction temperature.

[0068] Thermodynamics analysis and possible reactions: We hypothesized reactions R.1 to R.6 could occur during neodymium oxide sulfidation with and without presence of carbon. Variation of Gibbs free energy of these reaction is depicted in Figure 2. ^^^^ ^^^^2^^^^3+ 7 ^^^^ → 2 ^^^^ ^^^^ ^^^^2+ 3 ^^^^ ^^^^ R.1 ^^^^2 + ^^^^ → ^^^^ ^^^^2 R.22^^^^ ^^^^ ^^^^2 + 1.5 ^^^^2 → ^^^^ ^^^^2 ^^^^3 + 4 ^^^^ R.3^^^^ ^^^^2^^^^3+ 3 ^^^^ ^^^^2→ ^^^^ ^^^^2^^^^3+ 3 ^^^^ ^^^^ +32 ^^^^2R.4^^^^22 ^^^^ ^^^^2 ^^^^3 + 3 ^^^^2 + 6 ^^^^ → 2 ^^^^ ^^^^2 ^^^^3 + 6 ^^^^ ^^^^ R.6

[0069] As discussed herein above, neodymium oxide can be reduced by sulfur alone, but the potential of sulfidation would be higher in the presence of carbon (graphite in our tests). Based on these calculations, the overall reaction in the presence (R.7) and in the absence (R.8) of graphite can be considered as follows:2 ^^^^ ^^^^2 ^^^^3 + 3 ^^^^2 + 6 ^^^^ → 2 ^^^^ ^^^^2 ^^3^^3 + 6 ^^^^ ^^^^ R.7^^^^ ^^^^2^^^^3+ 2.25 ^^^^2→ ^^^^ ^^^^2^^^^3+2^^^^ ^^^^2(direct reaction) R.8

[0070] Meanwhile, when carbon is added to the operation, the sequence of reactions according to the Gibbs energy is as follows: - Carbonization of sulfur and producing CS2^^^^2+ ^^^^ → ^^^^ ^^^^2R.9 - Nd2S3production via the reaction of Nd-oxide with CS2^^^^

[0071] It is worth mentioning that based on thermodynamic studies with FactSageTMsoftware, the direct reaction of Nd-oxide and gaseous sulfur can be spontaneous at a temperature less than 600°C (in the equilibrium condition).

[0072] Methodology: We tested various weights and fractions of reagents. The weight fractions of Nd2O3:S were varied from 1:10 to 1:5 in different operation conditions. In the experiments that graphite was used, the stoichiometric ratio of 3:1 was used for C (that can be used in excess). Moreover, the nitrogen flowrate, i.e., the carrier gas, varied from 0.5 to 3 standard cubic feet per hour (SCFH), equivalent to 0.25 to 1.5 L / min.

[0073] Following some preliminary tests, we identified two suitable different heating zones to place the crucible of sulfur and the crucible of neodymium within a specific distance. Since boiling point of sulfur is 444.6℃, we had to keep the crucible of sulfur at a heating zone with a similar temperature (around 500℃), defined as the cold zone, to control vaporization of sulfur and its passage over the crucible of neodymium oxide. The crucible of neodymium oxide was placed at a heating zone with a temperature between 600 and1200°C during the experiments, defined as hot zone. An insulator was placed between the hot and cold zones (Nd-oxide boat and sulfur crucible) for minimizing the waste of sulfur gas during the furnace heat up. Keeping a low flowrate of carrier gas, the gaseous sulfur continuously passed over the Nd-oxide boat at the operation temperature. The heating and cooling rates for all rounds of experiments were less than 7 °C / min (4-7 °C / min).

[0074] For the analysis of phases of each sample after the sulfidation, the feed samples and the sulfurized samples were investigated via X-ray diffraction (XRD), and field- emission scanning electron microscopy equipped with an energy dispersive X-ray spectrometry mapping (EDS-mapping).

[0075] The selected experiments and their operation conditions are shown in Table 1 below. Each process with an operation condition was repeated at least twice to verify the results. Table 1. Experimental plan for sulfidation of Nd-oxide E I N e o 2 N 1 N in H N e, er N er N d 1d for the entire tests of this project. Example 1- Analysis of experiment NCT7

[0076] A mass of 3 g of S (sulfur powder) was placed in the molybdenum (Mo) crucible at the cold zone of the furnace to keep the temperature approximately at the boiling point of S when the hot zone was at 1200°C. Then, 0.5 g of Nd-oxide powder (S:Nd-oxide = 6:1)was placed inside an alumina boat to the hot zone (Figure 3). The residence time (i.e., isothermal time) was set at 60 minutes. Moreover, to purge the humidity from the tube, a nitrogen flow of 1 SCFH was applied to the reactor after 350°C.

[0077] The nitrogen flow carried the vaporized S2from the cold zone to the hot zone slowly that led to the better mass transfer between the sulfur gas and the Nd-oxide powders in sulfuric atmosphere of the tube at 1200°C. After the experiment, Mo crucible was completely empty that shows all the S2powder was vaporized whereas the weight of Nd- oxide residue was increased 0.518 g that can be related to the higher molecular weight of S than oxygen. Moreover, the color of Nd-oxide especially on the surface of the powders was changed to light pink (Figure 3B). The visual preliminary analysis indicated that the sulfidation took place. Therefore, XRD and EDS characterization studies were conducted. The XRD result is shown in Figure 4A.

[0078] The XRD results indicate that sulfur reacted with neodymium oxide that resulted in the production of various Nd-S products. The observable pink color can be related to the production of NdS.

[0079] This result was promising proof of concept that happened at a relatively low temperature of 1200°C despite the fact that contact between sulfur and neodymium oxide was not yet optimal (i.e., due to semi batch nature of process). Example 2- Analysis of experiment NCT15

[0080] Different rounds of experiments were designed to study the reducing effect of carbon on sulfidation of neodymium oxide. For example, a mass of 0.5 g of graphite powder was used as the blanket on a mass of 0.5 g Nd2O3that was placed under s nitrogen flowrate of 1 SCFH. N2flow carried the gas from cold zone at 1200°C during 60 minutes isothermal time. Meanwhile, a mass of 5 g sulfur powder was placed in the cold zone for the possible reaction of C and S gas (reaction R.3). The residual powder had a mass of 0.539 that could correspond to the differences between atomic mass of O and S. The XRD results showed that sulfidation occurred so that there were slight partial sulfidation with production of Nd2SO2and Nd2O2SO4(Figure 4B).

[0081] According to mapping of elements, we conclude that S and Nd reacted and sulfidation was partially successful. However, carbon did not react with oxygen to reduce the Nd-oxide so that it remained almost untouched in the residual in crucible.

[0082] A motivation of this research was to investigate whether reaction R.3 and R.4 could occur kinetically. The former reaction assumes carbon reacts initially with neodymium oxide, and subsequently, the produced neodymium carbide would react with sulfur to produce neodymium sulfide. The latter reaction assumes carbon reacts with sulfur initially to produce carbon sulfide, which will subsequently reduce neodymium oxide to neodymium sulfur. Since carbon was in direct contact with neodymium oxide in one crucible, we determined that reaction R.4 did not occur due to short contact time between carbon and sulfur. Therefore, we hypothesized it would be more beneficial to produce CS2in a separate reactor according to reaction R.2 (CS2boils at 46.3°C), and pass it over neodymium oxide. Example 3- Analysis of experiment NCT16

[0083] To better investigate the effectiveness of S2powder content and the carrier gas flowrate, this round of experiments was designed with a mass of 5 g of sulfur powder in the cold zone and a mass of 0.5 g of Nd-oxide (mass S:Nd-oxide ratio = 10:1) at the hot zone under 1200°C for isothermal time of 60 minutes. The residual weight after reaction was 0.515 g. The XRD of this sample shows that Nd-oxide slightly sulfurized in this experiment. The peaks of Nd2SO2are detected as they can be seen in Figure 4C.

[0084] EDS and elemental mapping showed a reasonable sulfidation of Nd-oxide. EDS results showed 75.6% Nd, 18.3% S2(quite significant) and 6.1% %O that can be considered as the best results in all the experiments in high temperatures (1200°C). For this reason, we decided to do the mapping on two different sampling methods and the results are shown in Figure 5.

[0085] In the first series of mapping analysis, O, Nd, and S were matched in the map distribution that showed the production of material containing these 3 elements. However, in the second one, Nd and S were completely matched on the map, while the O was distributed homogenously on the surface. This can prove the production of favorable products of NdS or Nd2S3(Figure 5B). In other words, we had complete sulfidation reactions in some areas of the samples (it might be surface of Nd-oxide).

[0086] This round of experiment proves the concept of sulfurization even in the absence of a reducing agent. The promising results and observations of this research indicate a suitable reactor should be designed (e.g., a circular fluidized bed reactor or a rotary kiln) in future scaleup efforts where an effective contact between sulfur and neodymium could be retained to let the reaction complete over availability of a decent residence time.Example 4- Analysis of experiment NCT18

[0087] We designed another round of experiments at lower temperatures of 600°C and 700°C. To reduce the mass transfer limitations, we pelletized a mixture of sulfur and neodymium oxide with a mass ratio of 10:1 by employing a 10 KN pelletizer, wherein, a mass of 5 g of sulfur was well-mixed with a mass of 0.5 g of Nd2O3and then pelletized to get a doughnut shape. The pellets were placed in the molybdenum crucible (as it is shown in Figure 6) in the hot zone of the reactor at 700°C under 1 SCFH N2flowrate for an isothermal time of 120 minutes. The residual weight was 0.509 that shows the melting and complete vaporization of S2during heat-up and isothermal time. The sample color after treatment was partially blue with the light pink on the surface (Figure 6B).

[0088] In order to retain vaporized S2around the crucible before venting off the system, we designed a cage box inside which pellets were kept. Then, we restarted the experiment with similar operations but at 700°C. Based on the shape changes before and after the treatment and the weight loss, we conclude that there was a gas-solid reaction at 600- 700°C that led to the sulfidation of Nd-oxide in different stages.

[0089] The XRD analysis results are shown in Figure 7. They are very similar to NCT16 residual sample, but the intensity of neodymium sulfide oxide was higher. This showed that even at the lower temperatures, with the controlled operating condition, the sulfidation process could proceed. However, more studied work must be done on the process control and characterization investigation. Meanwhile, it was another proof of concept for the process that was designed based on the thermodynamics calculations.

[0090] According to the results of the reported experiments, we could prove the concept of sulfidation process with sulfur gas on the Nd-oxide solid. We could conclude that the effect of reducing agent in the solid phase was not essential. On the other hand, under controlled operating conditions, the experiments could be completed at temperatures between 600 and 700°C, which is indeed a remarkable breakthrough. Example 5- Sulfidation of REO using a continuous sulfur containing gas

[0091] The inventors have determined that REO can be sulfurized with a continuous flow of a sulfur-containing gas through a bed of REO particles / powders. This allows for enhanced mass transfer and heat transfer between REO powders and sulfur-containing gas to reach a high conversion of REO to RES. For example, our thermodynamic simulation revealed that the sulfidation of neodymium oxide through reacting withhydrogen sulfide is thermodynamically favorable at temperatures less than 1167oC. The following exothermic equation can represent this reaction: Nd2O3+3H2S→Nd2S3+3H2O ΔHo298= -176 kJ / mol R.11

[0092] When one molecule of Nd2O3is exposed to hydrogen sulfide, H2S is dissociated into sulfur species and releases hydrogen. The sulfur replaces the oxygen, generating Nd2S3, while hydrogen produces water. One mole of Nd-oxide needs three hydrogen sulfide molecules for a complete reaction. Therefore, conducting the reaction at a rich H2S stream, as well as a sufficiently high temperature, ensures a high sulfidation reaction.

[0093] The apparatus to convert Nd2O3into Nd2S3consists of two separate glass vessels (Figures 8 and 9). In the first one, H2S is generated, then carried by an inert gas, and introduced into the second vessel, comprising 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 reacting iron sulfide with hydrochloric acid or sulfuric acid and thioacetamide (TAA) hydrolysis reaction. For this contribution, the hydrolysis reaction of TAA and water is utilized to generate acetamide and H2S. CH3CSNH2+H2O→CH3CONH2+H2S R.12

[0094] However, the TAA hydrolysis reaction is not limited to water, and certain mineral acids, such as hydrochloric 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 reactor equipped with several inlets. The reactor contains 250 ml of stilled water, forming a 0.4 molar solution upon the dissolution of TAA. The temperature of the solution is kept between 60-80oC by using a heating mantle equipped with a PID temperature controller. The produced H2S accumulates above the distilled water and then is carried by a 500 ml / min nitrogen to the quartz tube reactor. A mass flow controller (MFC) accurately regulates the nitrogen gas flow rate. The nitrogen pipe is inserted and extended into the vessel with a special fitting to avoid leakage. Then, an outlet valve regulates the flow outlet and provides a slight positive pressure inside the glass vessel. The outlet is connected to the inlet of the quartz tube reactor. For safety, the vessel's pressure is measured by a pressure gauge to avoid over-pressurizing.

[0095] The gas enters the quartz tube from the bottom and moves upward. A 0.5 g neodymium oxide powder is placed inside a 1-inch OD quartz tube reactor over a porous quartz fruit. This frit acts as a support for the powder and a diffuser for the nitrogen gas,and at the same time, it passes the inert carrier gas containing H2S through it. The quartz tube is placed inside an induction heating system to quickly and safely heat up the powder, increasing the powder bed temperature to 800oC. However, other heating systems could also be exploited here, including microwaves, conventional electrical furnaces, and any other form of heat supply method, such as non-electrical furnaces (e.g., burning fuel).

[0096] More specifically, we can employ electrified thermal processes (i.e., induction heating, microwave heating, plasma, etc.) to both RES production processes that we have developed: that is: according to an aspect, RES production by a vapor of sulfur in a bed of REO to be hated by induction heating, microwave heating, etc. In fact, we employ a sulfur (S) powder to neodymium oxide (Nd2O3) weight ratio of 1:8 in a graphite crucible. As an alternative to the graphite crucible, we use an assembly of graphite rods placed inside the reactor with a symmetrical configuration. The graphite crucible or the assembly of graphite rods acts as the induction heating adsorbent, enabling a high heating rate to minimize S2gas waste regards to the differences of sulfur boiling and reaction temperatures.

[0097] In the process according to the invention, by heating the crucible sulfur powder is first melted to react with the graphite crucible in the necessary proportion to form CS2. Subsequently, the CS2reacts with the Nd2O3at the desired temperature within a vertical quartz reactor, with nitrogen flowing from the bottom to purge excess gases.

[0098] According to another aspect, RES production using a sulfur containing gas such as H2S or any other form in a bed of REO powders to be heated by induction heating, microwave heating, etc. When we use electrified heating methods using induction heating and microwave heating, for instance, we can take advantage of using a graphite crucible inside the bed, knowing that graphite is an excellent receptor of electromagnetic field, to enhance the quality of thermal treatment, enhance the selective heating features, and enhance the product selectivity while conversion of REO to RES is increased. The reactor design of these gas-solid reactions can be a fluidized bed, rotary kiln, and any other multiphase reactors.

[0099] The induction heating system has a copper coil, operated with a frequency of 70 kHz. The length of the coil is so that it surrounds the powder bed and covers one inch at the top and bottom of the bed. Since induction heating can only heat the conductive materials, therefore, a four-rod assembly is fitted vertically inside the quartz tube reactor and extended into the Nd2O3powder bed to absorb the magnetic field effectively and quickly. Once the rods absorb the inductive fields, they get heated, and the heat istransferred to the powder through convection under the passing H2S-rich gas stream. The bed temperature, which is controlled by a PID controller, increases rapidly within few minutes to reach 800oC setpoint temperature. Once the temperature was adjusted, the nitrogen gas would be introduced to the bed. The duration of the sulfidation reaction was one hour. The unreacted effluent H2S is captured by a bottle containing two molar NaOH and then transferred to the laboratory exhaust. After cooling, the sulfided neodymium is extracted from the reactor. Pyro-electrochemical reduction of REO and RES in a eutectic molten salt

[0100] Our initial plan was to reduce neodymium sulfide to neodymium metal in a reactor containing a mixture of earth alkali molten salts (e.g., calcium carbonate and calcium chloride) at temperatures between 700 and 1000°C. We designed and commissioned a reactor made of Inconel to withstand such high temperatures. The reactor top was made to be capped by a water-cooled stainless-steel flange / lid. We designed a window on the flange in order to see the reactive condition inside the reactor. The reactor shape was designed so that it could be placed inside a crucible furnace. Powders of salts would be poured inside an alumina crucible placed inside the Inconel reactor. This alumina crucible was essential to prevent electric short circuits between molten salt and metal body of the reactor because otherwise electrochemical reactions would not occur. Accordingly, we had to design ceramic sleeves / insulators to prevent any contact between titanium rods of anode / cathode electrodes and tube of a sparger at their vicinity to the reactor flange. We designed the cross-shape sparger with 45° angle holes for purging out air molecules from the reactor. The anode rod was screwed to a graphite tip. On the other hand, the first design of the cathode was to make a titanium basket with 40-micron holes, attached to a titanium rod, to hold the neodymium oxide powders inside during electrochemical reaction without being leaked into the molten salt. However, the inventors encountered various challenges upon conducting this initial work. During experimental work, we designed several alternative configurations for the cathode assembly as described in the next sections (e.g., titanium basket with larger 3 mm holes, titanium wiring around pelletized neodymium oxide powders, aluminium rod instead of titanium rod, aluminium vessel surrounding the anode rod inserted from the middle of reactor, etc.).

[0101] Figure 10 present dimensions and schematics of the designed electrochemical reactor.

[0102] The inventors performed experiments with earth alkali molten salts. Following the results of sulfidation step and commissioning of the pyro-electro setup, we planned to execute reduction experiments for the conversion of neodymium sulfide to neodymium metal using a mixture of earth alkali molten salts. We carried out several troubleshooting trials to test feasibility of experiments by a molten mixture of CaCl2 / CaCO3salts. We had to fill up the alumina crucible with a quite considerable mass of about 500 g of salts to let it get enough level when melted. Even though we observed the mixture of salts could melt effectively at high enough temperatures (Figure 11 left), it solidified inside the alumina crucible (Figure 11 right). However, it was important to find a safe solution to recover and purify the salt for next experiments. Therefore, we used a separate muffle furnace and made some modifications to let material melt and pour down from the upside-down alumina crucible into a metallurgical crucible. However, this technique was deemed challenging due to high temperatures associated to molten salts.

[0103] The inventors assessed alternative molten salts via thermodynamic simulation. Indeed, following our tests with CaCl2 / CaCO3salts, we decided to look for alternative salts so that a much lower temperature could be used for pyro-electrochemical tests. To do so, we carried out a series of thermodynamic simulations with FactSageTM.

[0104] Regarding electro-thermic reduction of Nd2S3 by LiCl-Li2S molten salts, we hypothesized that alkali salts would be more suitable than earth alkali salts. Therefore, we initially considered a mixture of LiCl / Li2S salts for the reduction of neodymium sulfide so that lithium will help transfer ions from cathode to anode according to the following reactions: Anodic reaction: ^^^^ ^^^^2^^^^( ^^^^)→ 0.5 ^^^^2( ^^^^)+ 2 ^^^^ ^^^^( ^^^^)R.13 ^^^^ ^^^^^^^^( ^^^^)+( ^^^^) ( ^^^^)+( ^^^^)

[0105] Thermodynamic simulation revealed that these reactions can spontaneously occur event at 100°C. However, the evaluation of phase diagram of LiCl-Li2S revealed that Li2S cannot be liquid at temperatures between 100 and 1000°C. The inventors thus concluded that these salts may not be suitable for the reduction of neodymium salts and other approaches were investigated.

[0106] Regarding electro-thermic reduction of Nd2O3by LiCl-KCl molten salts, we hypothesized that we might reduce neodymium oxide directly using a mixture of alkali salts of LiCl and KCl. Accordingly, we extended our thermodynamic investigations to realize whether or not this idea could be feasible. All the processes were calculated at atmospheric pressure and 400˚C.

[0107] Figure 12 indicates the phase diagram of LiCl-KCl. It can be observed that LiCl can create a eutectic mixture with KCl. If 59 mol% of LiCl is mixed with 41 mol% KCl, a molten salt will be formed at around 360˚C. Therefore, we concluded using LiCl-KCl can assist us in conducting the pyro-electrochemical reduction at low temperatures compared to other electrolytes like CaO-CaCl2and Li2O-LiCl.

[0108] During pyro-electroreduction, LiCl will be dissociated to Li+and Cl- in the molten salt. Then, the negative charge of the cathode will attract Li+cations due to the electrostatic force. The Li cations will attack the Nd2O3at the cathode surface and capture its oxygen molecules based on the following redox reactions: ^^^^ ^^^^ E = 3.994 V R.166E = -1.434 V R.17^^^^ ^^^^3++ 3 ^^^^−↔ ^^^^ ^^^^( ^^^^)E = -2.181 V R.18

[0109] The generated Li2O will migrate from cathode to anode through the molten electrolyte in the next step. At the anode surface, Li2O is reduced while graphite anode is oxidized. Consequently, Li cations will be regenerated (reaction R.19) and migrate to the cathode surface for reduction reaction with Nd2O3. CO2is the other product that evolved from the anode surface (reaction R.20). ^^^^ ^^^^2^^^^( ^^^^)↔ 2 ^^^^ ^^^^( ^^^^)+ 0.5 ^^^^2 ( ^^^^)E = -4.999 V R.19 ^^^^2 ( ^^^^)+ ^^^^( ^^^^)↔ ^^^^ ^^^^2 ( ^^^^)E = 4.098 V R.20

[0110] According to the above reaction, the overall anodic and total cathodic reactions can be written as follows:2^^^^ ^^^^2 ^^^^( ^^^^) + ^^^^( ^^^^) ↔ 4 ^^^^ ^^^^( ^^^^ ^^^^) + ^^^^ ^^^^2 ( ^^^^)EAnode= -0.901 V R.216^^^^ ^^^^( ^^^^ ^^^^) + ^^^^ ^^^^2 ^^^^3 ( ^^^^) ↔ 3 ^^^^ ^^^^2 ^^^^( ^^^^) + 2 ^^^^ ^^^^( ^^^^) E Cathode = 0.379 VR.22

[0111] The total potential of the electrochemical cell is equal to:^^^^^^^^ ^^^^ ^^^^ ^^^^= ^^^^( ^^^^ ^^^^ ^^^^ℎ ^^^^ ^^^^ ^^^^)− ^^^^^^^^ ^^^^ ^^^^ ^^^^ ^^^^ECell= 1.280 V (Eq.2)

[0112] The relation of cell potential and Gibbs free energy can be written as follows: ∆ ^^^^ = − ^^^^ ^^^^ ^^^^^^^^ ^^^^ ^^^^ ^^^^ΔG = -741 kJ / mol (Eq.3)

[0113] Where Ecellis the cell potential, n is a mole of electrons transfer during the process (here is 6), F is the Faraday constant (96485 C / mol), and ΔG is the changes of Gibbs free energy. According to the thermodynamic results, the electrochemical reaction has positive cell potential and negative Gibbs free energy. Consequently, the pyro- electrochemical reduction of Nd2O3in LiCl-KCl at temperatures below 500˚C is a spontaneous reaction. In other words, we concluded we could investigate direct reduction of neodymium oxide using LiCl / KCl molten salt.

[0114] Pyro-electrochemical setup: We designed different setup configurations with respect to type of salts and operation temperature. Herein, we present the setup for the reduction of Nd2O3to pure Nd metal by pyro-electrometallurgical process in LiCl-KCl eutectic molten salt. To reach this purpose, a three-electrode configuration electrochemical cell was designed and constructed using graphite rode as a counter electrode (also called the anode), Ag / AgCl as a reference electrode, and neodymium oxides as a working electrode (also called cathode). The molten electrolyte comprises LiCl and KCl with a 45:55 mass percentage ratio. In addition, the neodymium oxide powders were first pelletized with a hydraulic press of 10 tons and then put in the cathode basket made of titanium (Ti). A crucible furnace supplied the heat of the reaction. The external voltage was applied by a Potentiostat / Galvanostat (VersaSTAT 3-200). All the experiments were conducted in an inert atmosphere by injection of Ar gas through a sparge with a flow rate of 50 ml / min. The electrochemical cell was mounted in a 500 ml alumina crucible. The electrochemical cell was then transferred to an Inconel reactor. A type K thermocouple recorded the molten salt temperature during experiments. The electrolysis setup is shown in Figure 13. The system is cooled with water to avoid overheating the flange and upper section of the reactor. A schematic of the setup is also illustrated in Figure 14.

[0115] Pyro-electrometallurgical experimental methodology: For each experiment, a maximum mass of 300 g of dried LiCl and KCl with a mass percentage ratio of 45:55 was filled into a 500 ml alumina crucible and placed inside the pyro-electrochemical reactor, of which the top flange had provisions for gas-tight insertion of electrodes. The 1.5 gpelletized neodymium oxides (e.g., Nd2O3or Nd2S3) were put inside the titanium cathode basket for the reduction by molten salt.

[0116] Example 6- The Nd2O3was reduced to Nd metal in a three-electrode cell configuration consisting of an Nd2O3cathode, graphite anode, and Ag / AgCl reference electrode (Figure 15a) at 400°C. Different cathode designs were utilized to immerse Nd2O3as the negatively charged electrode in the pyro-electrochemical reactor. In the first attempt, a Ti basket with 40 μm holes on its surface was engaged as a cathode. As shown in Figure 15c, Nd2O3was pelletized by a hydraulic press, working at 10 tons US, without adding binder. The obtained pellets were then dried at 100˚C for 15 hours before running the pyro-electrochemical test. Noteworthy is that an Ar gas sparger was applied to the reactor to mix the molten salt electrolyte well during the experiment. After the reaction, the solidified molten salt covered the surface of the Ti basket, Ar gas sparger, and graphite anode (Figure 15d). As can be observed in Figure 15e, the molten salt could not be drained from Ti basket, probably due to the small size of holes. In addition, pellets kept their blue color after the process, indicating no reduction was achieved.

[0117] Two reasons can contribute to this failure. First, the small hole of the Ti Basket limits the mass diffusion of Li reductants from the electrolyte to the surface of the Nd2O3pellet. Second, the design of the Ti basket can cause the Faraday cage phenomenon, decrease the electron migration from anode to cathode, and subsequently block electron diffusion through Nd2O3pellets. The inventors designed and constructed a new setup in order to overcome these challenges.

[0118] Therefore, we increased the size of holes on the Ti cathode basket from 40 μm to 3 mm in the next step (Figure 16b). In addition, the Ar gas sparger was removed from the electrolyte. The Ar gas sparger was hung above the electrolyte in the freeboard region to purge evolved gases. By drawing a comparison between Figures 16a and c, it can be observed that the surface of Nd2O3pellets had a color change and became gray after the pyro-electrometallurgical process. Based on the XRD analysis presented in Figure 17, the pellet’s surface consists of Nd, which is contaminated by residual material.

[0119] To overcome the Faraday cage, the design of the Ti basket was altered, and a doughnut-shaped pellet attached to the Ti rod was employed (Figures 18a and b). However, as shown in Figures 16d to f, this design was brittle, and the Nd2O3was broken when immersed in molten electrolyte. After the reaction, the Nd2O3pellet was detached from the cathode and stuck to the graphite anode.

[0120] To tackle the above-mentioned issue, a titanium spring surrounded the doughnut-shaped Nd2O3pellet, as shown in Figures 19b and c. In addition, the top and bottom of the titanium spring were covered by quartz discs. As demonstrated in Figures 19d and e, the modified design assisted in maintaining the doughnut-shaped pellet in the cathode electrode. According to Figure 16f, the pellet’s surface changed color and became gray after the pyro-electrometallurgical process. Regarding the XRD analysis presented in Figure 20, the pellet’s surface consists of Nd, which is contaminated by residual.

[0121] In particular, the cathode design was significantly changed. As exhibited in Figures 21a and b, an aluminum crucible was used as a cathode electrode. In this regard, small holes of 3 mm size were created at the bottom of the aluminum crucible to facilitate electrolyte transfer and cathode drain from molten salt at the end of the process. As shown in Figure 21a, the graphite rod was placed in the center of the aluminum crucible with determined space from internal aluminum walls. Figures 21c and d demonstrate the cathode separated after the pyro-electrochemical reaction. According to Figure 21c, the color at the top surface of the pellet did not change significantly. However, as illustrated in Figure 21f, the bottom of the pellet in contact with the aluminum crucible became shinygray, indicating the reduction of Nd2O3 to Nd at 3V DC for 2 hours at 400°C. The XRDanalysis of reduced Nd2O3also confirmed the phase transformation (Figure 22). KCl and Al impurities oriented from the electrolyte and cathode basket were also observed in the XRD patterns. Adopting vacuum distillation can aid us in removing these impurities and reaching a high grade of Nd.

[0122] Figures 23a and b indicate the cyclic voltammetry and chronoamperometry of the pyro-electrochemical system during the reduction of Nd2O3in LiCl-KCl molten salt. Adopting cyclic voltammetry aids us in defining the anodic and cathodic reactions with their corresponding potential during the pyro-electrochemical process. The chronoamperometric plot can also assist in evaluating the kinetics of Nd2O3electroreduction as a function of time. The voltammetry analyses were performed using a Ti basket containing Nd2O3pellet as the working electrode, graphite rod as the counter electrode, and Ag / AgCl as the reference electrode in LiCl-KCl molten salt. For the voltammetry measurement, the current alteration on the working electrode was scanned from 2 V to -2 V and vice versa by 0.1 V / s scan rate. According to Figure 23a, three cathodic peaks (C1, C2, and C3) were observed at -1.7V, -2.5 V, and -3.4 V versus Ag / AgCl, respectively. Also, three anodic peaks appeared at -1.9 V, -2.6 V, and -3.6V versusAg / AgCl, respectively. The cathodic peaks at -1.9 V and -2.5 V versus Ag / AgCl are attributed to the reduction of Nd3+to Nd2+and Nd0. The anodic peak at -1.9 V and -2.6 V versus Ag / AgCl are related to the reverse side of reactions R.23 and R.24. ^^^^ ^^^^3++ ^^^^−↔ ^^^^ ^^^^2+ (R.23)^^^^ ^^^^2++ 2 ^^^^−↔ ^^^^ ^^^^0 (R.24)

[0123] According to these results, the pyro-electrochemical reduction of Nd2O3in LiCl- KCl molten salt occurs in two steps. First, Nd2O3is converted to soluble NdO by applying one electron to the cathode surface. Next, NdO is reduced by two electrons at the cathode surface, forming pure Nd. So, the formation of NdO will be a critical step in the successful pyro-electrochemical reduction of Nd2O3. Based on the literature, Nd2+is a stable cation in chloride electrolytes. Three moles of NdO can react with each other inside a chloride electrolyte, leading to the formation of Nd2O3and pure Nd (reaction R.25). Therefore, Nd2+tends to make both oxidation (formation of Nd2O3) and reduction (formation of pure Nd) reactions. To suppress the oxidation reaction, more negative voltage (higher than -2.5)should be applied to the electrochemical cell.3^^^^ ^^^^2+ ↔ 2 ^^^^ ^^^^3+ + ^^^^ ^^^^ (R.25)

[0124] According to Figure 23a, the cathodic peak at - 3.4V versus Ag / AgCl and anodic peaks at -3.6 V versus Ag / AgCl is ascribed to the redox reaction of Li as the mediator agent on the cathode and anode surfaces (reaction R.26). ^^^^ ^^^^++ ^^^^−↔ ^^^^ ^^^^(R.26)

[0125] Based on this investigation, the pyro-electrochemical reduction was performed at a constant cathodic voltage of -2.5 V versus Ag / AgCl. Figure 23b demonstrates the current changes as a function of time during the pyro-electrochemical reduction of Nd2O3at the constant cathodic voltage of -2.5 V versus Ag / AgCl. At the beginning of the process, the absolute current decreased sharply from 700 mA to 280 mA during a period of 6 minutes. The decrease of absolute current at the early stage is attributed to the reactant concentration gradient (i.e., Li2+and Nd3+) near the cathode surface. This result revealed that pyro-electroreduction is controlled by cationic diffusion at the beginning 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 proceeded slowly to 700 mA. The increase in absolute current is related to the Nd3+reduction to Nd2+and Nd0. When metalcations are reduced at the cathode surface, more electrons are passed from the anode to the cathode through the external circuit, increasing the cathodic current.

[0126] To assess the phase transformation, XRD analysis was performed. Figure 24 demonstrates the XRD peaks of Nd2O3before and after pyro-electrochemical reduction. The dominant 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 scribed to hexagonal crystalline structure of Nd2O3(JCPD-Card No. 00-043- 1023). After electrochemical reduction, the XRD peaks changed significantly, and the corresponding peaks of Nd2O3disappeared. According to Figure 24, the appearance of dominant peaks at 28˚ and 40.5˚ is attributed to neodymium chloride hydrate (NdCl3.H2O) (JCPD-Card No.00-003-0139). Cl originates from electrolyte residuals that can adsorb moisture and form the NdCl3.H2O layer at the top of the pellet. Vacuum distillation can be used to eliminate these impurities.

[0127] Figure 25 exhibits the SEM-EDX and elemental mapping of Nd2O3pellets before and after electroreduction. Regarding Figures 25(a-1) and (a-2), pellets contained fine powder of only Nd and O before processing. However, as shown in Figures 25(b-1) and (b-2), a compact layer of potassium chloride covered the surface of reduced Nd2O3after the pyro-electrometallurgical process. Based on Figure 25(a-3), Nd and O atoms showed a similar distribution pattern, confirming the existence of Nd2O3. On the contrary, the distribution pattern of Nd and O changed in some areas for reduced Nd2O3. As indicated in Figure 25(b-3), some area of reduced Nd2O3was covered by Nd in the absence of O, implying the reduction of Nd2O3to Nd metal.

[0128] The information illustrated in Figures 23, 24, and 25 validates the effective conversion of neodymium oxide to neodymium metal utilizing LiCl / KCl molten salt at 400°C.

[0129] According to an aspect, the inventors have designed and constructed a reactor, transitioning from Inconel to Pyrex. An advantage associated with Pyrex is its reduced susceptibility to salt adherence to its surface, even after solidification following reactor shutdowns.

[0130] Recovery of the molten salt: The inventors devised a method to separate and recover neodymium metal from the molten salts before they solidified. We developed a preheated Pyrex vessel, termed the molten salt collector, which is connected to the Pyrex reactor via a heated line. This collector is also linked to a vacuum line. Following thecompletion of a pyro-electrochemical process, we apply vacuum pressure to the molten salt collector. This action swiftly transfers all the salt from the Pyrex reactor into the collector, where it is collected for later purification and subsequent use in subsequent uses. This streamlined technique allows us to conduct our research more efficiently while saving a significant amount of time. Figure 26 depicts the modified pyro-electrochemical setup featuring the Pyrex reactor and Pyrex molten salt collector.

[0131] With the Pyrex reactor, there’s no necessity for an alumina crucible within it. Instead, we have the option to either directly introduce molten salt powders into the Pyrex reactor or pour them into an internal Pyrex beaker. To ensure the integrity of the Pyrex vessels, we’ve 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 gradual rate, specifically less than 3 °C / min, to prevent any risk of cracking or breakage.

[0132] Example 7- The experiment was conducted in a two-electrode configuration pyro-electrochemical system. As shown in Figures 27(a), 27(d), and 27(e), Nd2O3powder was pelletized with a hydraulic press of 6 tons and then sandwiched between two perforated aluminum discs and engaged as a cathode electrode. As demonstrated in Figure 27(f), graphite rode was employed as an anode electrode. The temperature inside the molten salt was measured by a type-k thermocouple. The electrolyte comprised 300 g of LiCl and KCl salts with 45 wt% and 55 wt% portion, 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 inside the electrolyte and kept for 20 minutes to reach an equilibrium ions migration between electrodes and electrolyte. Then, 4.5 V DC potential was applied by a power supply for 1.5 hour. At the end of pyro-electrolysis, the electrodes were pushed up and hung above the electrolyte to drain residual salts. The electrolyte was cool-down at the rate of 3 ˚C / min to ambient temperature. Figure 27 (c) demonstrates the pyro-electrochemical reactor after process. As illustrated in Figures 27(g) and (h), the reused Nd2O3was leaked from the cathode and was dissolved inside the molten salt. According to Figure 27(j), the dissolved REM created a thin layer at the bottom of solidified molten salt. The solidified electrolytes containing REM were treated with cold water to separate this layer. REM reacts very low in cold water, while LiCl-KCl can dissolve in cold water. Therefore, cold water treatment can assist in separating REM from the bottom of the solidified electrolyte. Figures 27(k) and 27(m) illustrate the separated REM after filter paper separation from cold water.

[0133] Figure 31 presents the XRD of Nd2O3and obtained REM. The dominant 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 scribed to hexagonal crystalline structure of Nd2O3(JCPD-Card No.00-043-1023). The XRD peaks of REM indicated a different pattern than the XRD of Nd2O3. According to Figure 28, 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˚, 90.9˚ indicate the neodymium chloride oxide (JCPD-Card No.00-001-1094). The chloride oxide in NdClO composition originates from the Cl as electrolyte residual that, after cold water treatment, is converted to ClO. In addition, the 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 crystal structure of pure Nd (JCPD-Card No.00-002-0842).

[0134] To further assess the obtained REM, the SEM-EDX mapping analysis was performed. According to Figure 29(a), the obtained REM has a microsphere structure. Based on the EDX analysis presented in Figure 29(b), REM mainly comprises Nd, Cl, and O with mass concentrations of 60 wt%, 14.3 wt%, and 13.7 wt%, respectively. In addition, 12 wt% impurities, including C, Ti, Al, and K, were observed in the REM originating from consumed graphite anode, cathode electrode, and molten salt. These impurities can be easily removed by vacuum distillation. According to mapping graphs, Cl and O showed a similar element distribution pattern, confirming the presence of chloride oxide, which was observed in XRD analysis. Therefore, Nd-ClO bonds can be broken during vacuum distillation, resulting in high purity Nd metals.

[0135] As will be understood by a skilled person, the pyro-electrochemical reduction process as described herein in relation to REO and RES can also be performed on the other metal oxides and metal sulfides.

[0136] As will be understood by a skilled person, the invention also relates to combinations of the above embodiments and aspects of the inventions.

[0137] As will be understood by a skilled person, other variations and combinations may be made to the various embodiments of the invention as described herein above.

[0138] While the present disclosure has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations including such departures from the present disclosure as come within known or customary practice withinthe art and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims. Features which are described in the context of separate aspects and embodiments of the invention may be used together and / or be interchangeable. Similarly, features described in the context of a single embodiment may also be provided separately or in any suitable sub-combination.

[0139] The scope of the claims should not be limited by the preferred embodiments set forth in the examples; but should be given the broadest interpretation consistent with the description as a whole.

[0140] The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety. References: [1] S. M. Abdelbasir, C. T. El-Sheltawy, D. M. Abdo, Journal of Sustainable Metallurgy.2018, 4. [2] D. D. München, H. M. Veit, Waste Management.2017, 61. [3] Y. Yang, A. Walton, R. Sheridan, K. Güth, R. Gauß, O. Gutfleisch, M. Buchert, B.-M. Steenari, T. Van Gerven, P. T. 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, A. K. Nayak, K. Sarangi, Hydrometallurgy.2017, 174. [7] O. Takeda, T. H. 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.

[0010] S. Shirayama, T. H. Okabe, Metallurgical and Materials Transactions B.2018, 49.

[0011] K. K. Yadav, M. Anitha, D. K. Singh, V. Kain, Separation and Purification Technology.2018, 194.

[0012] 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.

[0013] K. Binnemans, P. T. Jones, B. Blanpain, T. Van Gerven, Y. Yang, A. Walton, M. Buchert, Journal of Cleaner Production.2013, 51.

[0014] Hoornweg D, B.-T. P, 2012.

[0015] S. Hughes, M. Jåfs, H. Johto, J. Stål, J. Karonen, "Outotec Solutions for E-Scrap Processing," REWAS 2019, Cham, 2019 / / 2019.

[0016] M. Regel-Rosocka, "Electronic wastes, 3(5)," in "Physical Sciences Reviews," (2018) p.20180020

[0017] Y. Wu, B. Wang, Q. Zhang, R. Li, J. Yu, RSC advances.2014, v.4.

[0018] M. K. Jha, A. Kumari, R. Panda, J. Rajesh Kumar, K. Yoo, J. Y. Lee, Hydrometallurgy.2016, 165.

[0019] H.-S. Yoon, C.-J. Kim, K.-W. Chung, S.-D. Kim, J.-Y. Lee, J. R. Kumar, Hydrometallurgy.2016, 165.

[0020] Z. Hua, J. Wang, L. Wang, Z. Zhao, X. Li, Y. Xiao, Y. Yang, ACS Sustainable Chemistry & Engineering.2014, 2.

[0021] A. Abbasalizadeh, S. Seetharaman, P. Venkatesan, J. Sietsma, Y. Yang, Electrochimica Acta.2019, 310.

[0022] T. Wang, H. Gao, X. Jin, H. Chen, J. Peng, G. Chen, Electrochemistry Communications.2011, 13(12), p.1492-1495.

[0023] Ben Holcombe et al. Electrochem. Soc. Interface.2024, 33, p.49.

Claims

CLAIMS:

1. A process for producing rare earth metals (REM), comprising subjecting rare earth oxides (REO) or rare earth sulfides (RES) to a pyro-electrochemical reduction in a eutectic molten salt thereby obtaining a pyro-electrochemical reduction product comprising the REM.

2. The process according to claim 1, further comprising subjecting the pyro- electrochemical reduction product to a purification process, preferably the purification process comprises subjecting the pyro-electrochemical reduction product to water leaching, more preferably using cold water, preferably the purification process comprises subjecting the pyro-electrochemical reduction product to vacuum distillation.

3. The process according to claim 1, further comprising: (i) dissolving the pyro- electrochemical reduction product obtained in a liquid metal to obtain an REM alloy; and (ii) subjecting the REM alloy to washing and / or vacuum distillation to produce the REM, preferably the liquid metal comprises a metal selected from the group consisting of Ca, K, Zn, Mg, Fe, and Mn.

4. The process according to any one of claims 1 to 3, wherein the temperature of the pyro- electrochemical reduction is below about 500°C, preferably the temperature of the pyro-electrochemical reduction is between about 375°C to about 450°C.

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

6. The process according to any one of claims 1 to 5, wherein the eutectic molten salt comprises a mixture of at least two salts, wherein 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. 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 process according to any one of claims 1 to 7, wherein the eutectic molten salt comprises a mixture of a first lithium salt and a second salt, and a mass percentage ratio of the first and second salts is about 40:60, about 45:55, or about 48:62, preferably the mass percentage ratio of the first and second salts is about 45:

55.

9. The process according to any one of claims 1 to 7, wherein the eutectic molten salt comprises a mixture of LiCl and KCl, and a mass percentage ratio of about 40:60, about 45:55, or about 48:62, preferably the mass percentage ratio of LiCl and KCl is about 45:

55.

10. The process according to any one of claims 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 temperature of the pyro-electrochemical reduction is above about 700°C.

11. The process according to any one of claims 1 to 10, further comprising recovering the eutectic molten salt upon completion of the pyro-electrochemical reduction, preferably the recovered eutectic molten salt is subjected to purification and re-use in the process.

12. The process according to any one of claims 1 to 11, wherein, when the pyro- electrochemical reduction is conducted on RES, a sulfur-containing gas is obtained as by- product, and the process further comprises recycling the sulfur-containing gas obtained for re-use, preferably the sulfur-containing gas is S2gas and / or H2S gas.

13. The process according to any one of claims 1 to 12, wherein the 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 the REM is selected from the group consisting of: Nd, Dy, Pr, Ce, Er, and Y,more preferably the REM is Nd, Pr, or Dy.

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

15. An REM obtained by the process as 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 process according to claim 16, wherein the temperature during the reaction of the REO and 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. The process according to claim 16, wherein the sulfur-containing gas is S2gas and / or H2S gas.

19. The process according to any one of claims 16 to 18, further comprising a preliminary step of converting the sulfur-containing gas to H2S gas in-situ, preferably the sulfur-containing gas is S2and the preliminary step consists of converting the S2gas to H2S gas.

20. An RES obtained by the process as defined in any one of claims 16 to 19.

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

22. The process according to any one of claims 1 to 20, wherein the REO is extracted from natural sources such as mineral ores.

23. A pyro-electrochemical reactor adapted for performing the process as defined in any one of claims 1 to 14.

24. A pyro-electrochemical reactor for the production of REM from REO or RES in a eutectic molten salt, the reactor comprising a cathode having an aluminium crucible with micro-sieves integrated at the bottom thereof.

25. A pyro-electrochemical reactor for the production of REM from REO or RES in an eutectic molten salt, the reactor comprising a cathode having a perforated aluminum disc adapted for sandwiching the REO and / or RES pellets.

26. The reactor according to any one of claims 23 to 25, which is equipped with a sparger or gas distributor adapted for injecting and maintaining a flow of an inert gas into the reactor, preferably the inert gas is argon (Ar).

27. A system for the production of rare earth metals (REM) through pyro-electrochemical reduction in a eutectic molten salt of rare earth oxides (REO) or rare earth sulfides (RES), comprising a pyro-electrochemical reactor and a molten salt collector, wherein the molten salt collector is operably connected to the reactor through a first line and operably connected to a vacuum line.

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

29. A system for the production of rare earth metals (REM) through pyro-electrochemical reduction in a eutectic molten salt of rare earth oxides (REO) or rare earth sulfides (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 through a first line and operably connected to a vacuum line, wherein the molten salt collector and the first line are each independently adapted to being heated; and wherein upon completion of the electrolysis, pressure applied to the molten salt collector allows for retrieval of the molten salt from the basket.

30. The reactor according to any one of claims 23 to 26 or the system according to any one of claims 27 to 29, further comprising programmable controllers for regulating 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 the molten salt collector comprises a Pyrex vessel.

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

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

34. A reactor adapted for performing the process as defined in any one of claims 16 to 19.

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

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