FIEUD OF THE INVENTION

[001] This invention is directed to methods for recovery of at least one rare earth metal from ferromagnetic alloy, including a chlorination of the rare earth metal following by separation of the chlorinated product.

BACKGROUND OF THE INVENTION

[002] Rare earth magnets based upon neodymium-iron-boron (NdFeB) are employed in many clean energy and high-tech applications, including hard disk drives (HDDs), motors in electric vehicles and electric generators in wind turbines. In recent years, the supply of rare earth metals has come under considerable strain. This resulted in dramatic price fluctuations for the rare earth metals, in particular, neodymium, praseodymium and dysprosium, the rare earth constituents of NdFeB magnets. According to the EU Critical Materials list (2010, 2014) and the US Department of Energy's energy critical element list (2010), the rare earth metals are classified as at greatest risk of supply shortages compared to those of all other materials used for clean energy technologies.

[003] There are several ways in which these material shortages could be addressed including: (a) opening more rare earth mines, (b) using alternative technologies which do not contain rare earths (c) reducing the amount of rare earth metal used in particular applications such as magnets or (d) recycling the existing stock of magnets containing rare earth metals with various types of equipment. However, with regard to option (a), the mining, beneficiation and separation of rare earth elements is energy intensive, results in toxic by-products from acid leaching processes and the primary ores are nearly always mixed with radioactive elements such as thorium. If alternative technologies are employed, as in option (b) or reduction of rare earth metal quantities as in option (c), compared to permanent magnet machines, this often leads to a drop in efficiency and performance. [004] Recycling of magnet scrap from waste products consists of multiple steps, including preliminary steps; separation of the magnets from the waste product, demagnetization through heat treatment at 300-350°C, decarbonization (for removal of resin) by combustion at 700-1000°C under air or oxygen flow, and deoxidization by hydrogen reduction[l-3]. The main process (separation of rare earth metals and iron) begins after these preliminary stages. Several wet processes: acid dissolution [4], solvent extraction, and the oxalate method [5] are used too for recovery of the neodymium. These wet chemical methods have poor yield from the acid dissolution and effluent treatment steps, which requires a multiple-step process resulting in high cost. It is important that the recovery process for the rare earth metals from magnet scrap has as low cost and as few steps as possible, because recovery of the magnets from the product is itself a multi-step process.

[005] Several works were carried out on the chlorination of magnets with various reagents:

NH4CI [6], FcCh [7], MgCh [8], and chlorine gas with carbon [9]. The use of NH4CI, FeCh, and gCF as chlorinators led to the formation of neodymium chloride and iron and boron alloy remained in the solid metallic form. The resulting mixture of the neodymium chloride and Fe-B metal residue was then separated by vacuum distillation or magnetic separation. The chlorination method is low- cost, simplifies the overall process, and reduces the amount of effluent requiring treatment as a dry process. A method for chlorinating magnets with chlorine and carbon addition at a temperature of

100-1000°C with preliminary oxidation treatment was proposed in [9].

[006] It was shown that preliminary oxidation sintering in an air stream with the conversion of all metals to oxides (Fe2(¾, FeNdCF, NdiCF) dramatically reduces the degree of sublimation of iron and boron during chlorination with pure chlorine. When carbon is added to the chlorination process (carbochlorination process), the degree of sublimation of iron and boron chlorides increases. It is known [10] that the Gibbs energy of the chlorination reaction of metal oxides by chlorine gas is a significant positive value; therefore, successful chlorination of them with pure chlorine is practically impossible. Chlorination of metal oxides showed to be effective with the addition of a reducing agent and the addition of carbon during the chlorination of oxides which dramatically increased the efficiency of the chlorides sublimation process [10].

[007] One of the biggest challenges associated with the recycling of magnets is how to separate efficiently the magnets from the other components.

SUMMARY OF THE INVENTION

[008] This invention provides a method for recovery of at least one rare earth metal from ferromagnetic alloy, the method comprises:

(a) reacting ferromagnetic alloy with at least one chlorine - containing gas to obtain a volatile iron

- containing chloride product and non - volatile at least one rare earth metal chloride;

(b) providing air flow to said volatile iron - containing chloride product, thereby oxidizing the iron

- containing chloride product to iron oxide;

(c) separating said iron oxide product and non - volatile at least one rare earth metal chloride;

(d) cooling said separated non - volatile at least one rare earth metal chloride;

(e) electrolyzing said cooled non - volatile at least one rare earth metal chloride; thereby recovering said at least one rare earth metal.

[009] This invention provides at least one rare earth metal composition prepared by the methods of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[0011] Figure 1 shows the ferromagnetic alloy before atomic hydrogen decrepitation. [0012] Figure 2 shows the ferromagnetic alloy after atomic hydrogen decrepitation.

[0013] Figure 3 is a schematic description of the method of the present invention.

[0014] Figures 4A and 4B show X-ray diffraction (XRD) of the ferromagnetic alloy (initial magnet) before atomic hydrogen decrepitation - Figure 4A: sample 1; Figure 4B: sample 2. (The contents of samples 1 and 2 are provided in Example 3, Table 3 below).

[0015] Figures 5A-5D present characterization of initial magnet characterized by energy dispersive X-ray fluorescence spectroscopy providing SEM image of the initial magnet 1 (Figure 5A); SEM image of the initial magnet 2(Figure 5B); EDS spectrum of the initial magnet -Sample 1 (Figure 5C) ; and EDS spectrum of the initial magnet -Sample 2 (Figure 5D).

[0016] Figure 6 shows the laboratory setup for the atomic hydrogen decrepitation.

[0017] Figure 7 shows powder X-ray diffraction (XRD) pattern of the magnet powder after atomic hydrogen decrepitation.

[0018] Figure 8 shows SEM image of the magnet powder after the atomic hydrogen decrepitation.

[0019] Figure 9 shows the laboratory setup for chlorine treatment for extraction rare earth metals from permanent magnets.

[0020] Figures 10A and 10B show characterization of the composition of the material after chlorine gas treatment by energy dispersive X-ray fluorescence spectroscopy (EDS, LEO Supra) of Sample 1 (Figure 10A) and Sample 2 (Figure 10B).

[0021] Figure 11A shows powder X-ray diffraction (XRD) pattern of the sublimations from neodymium magnet samples following temperature treatment (400°C) with chlorine gas. “1” refers to Fe ₂ 0 ₃ and “2” refers to FeOCl. Figure 11B shows Quantitative phase analysis of the sublimations as obtained from the XRD pattern in Figure 11A.

[0022] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0023] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

[0024] This invention provides a method for recovery of at least one rare earth metal from ferromagnetic alloy, the method comprises:

(a) reacting ferromagnetic alloy with at least one chlorine - containing gas to obtain a volatile iron

- containing chloride product and non - volatile at least one rare earth metal chloride;

(b) providing air flow to said volatile iron - containing chloride product, thereby oxidizing the iron

- containing chloride product to iron oxide;

(c) separating said iron oxide product and non - volatile at least one rare earth metal chloride;

(d) cooling said separated non - volatile at least one rare earth metal chloride;

(e) electrolyzing said cooled non - volatile at least one rare earth metal chloride; thereby recovering said at least one rare earth metal.

[0025] In some embodiments, the method of this invention comprises prior to reacting the ferromagnetic alloy with at least one chlorine - containing gas of step (a), a pre-treatment of the ferromagnetic alloy by decrepitation to form a powder alloy using atomic hydrogen decrepitation treatment. In other embodiments, the decrepitation is performed at room temperature. In other embodiment, the atomic hydrogen decrepitation treatment is performed using electrolysis. In other embodiments, the electrolysis is performed using a first electrode (cathode) of copper, nickel, steel, titanium or combination thereof; and a second electrode (anode) of lead, nickel, steel or combination thereof. In other embodiments, the ferromagnetic alloy is attached to said first electrode (cathode). [0026] This invention thus provides a method for recovery of at least one rare earth metal from ferromagnetic alloy, the method comprising: (i) atomic hydrogen decrepitation said ferromagnetic alloy to form a powder alloy; (ii) magnetic separation of said powder to form a powder alloy having a lower iron content; (iii) reacting said powder alloy having a lower iron content with at least one chlorine-containing gas to obtain volatile iron-containing chloride product and non-volatile at least one rare earth metal chloride; (iv) separating said volatile iron-containing chloride product and non volatile at least one rare earth metal chloride; (v) cooling said separated non-volatile at least one rare earth metal chloride; (vi) electrolyzing said cooled non-volatile at least one rare earth metal chloride; thereby recovering said at least one rare earth metal. In other embodiments, the atomic hydrogen decrepitation is performed at room temperature. In other embodiment, the atomic hydrogen decrepitation is performed using electrolysis. In other embodiments, the electrolysis is performed using a first electrode (cathode) of copper, nickel, steel, titanium, or combination thereof; and a second electrode (anode) of lead, nickel, steel or combination thereof. In other embodiments, the ferromagnetic alloy is attached to said first electrode (cathode).

[0027] This invention also provides a method for recovery of spent neodymium magnets by chlorine treatment that does not require pre-treatment of magnets. These magnets were used without demagnetization, crushing and milling. After treatment at 400°C, a clinker consisting of rare earth metals chlorides and sublimates consisting of iron oxide and iron chlorides were obtained. The resulting rare earth metals chlorides can be easily processed by electrolysis of the molten salts for rare earth metals production [12, 13].

[0028] When referring to a ferromagnetic (can be used interchangeably with ferrimagnetic) alloy it should be understood to encompass any type of source (including spent) of permanent magnet made of a combination of metals that creates its own persistent magnetic field. These metals include, but are not limited to the elements iron, nickel and cobalt, rare-earth metals, naturally occurring minerals (such as lodestone) and any combination thereof. [0029] In some embodiments, said at least one rare earth metal is selected from cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y).

[0030] In some embodiments, the methods pf this invention comprises a reaction with at least one chlorine - containing gas (step (a) or step (iii)). In other embodiments, the reaction is performed at a temperature of between 400°C and 450°C.

[0031] In some embodiments, the at least one chlorine-containing gas which is used in the methods of this invention (step (a) or step (iii)) is present in an amount of 0.5 - 2.0 kg of the chlorine per 1 kg of the ferromagnetic alloy (or powder alloy).

[0032] The method according to any one of the preceding claims, wherein said air flow to the volatile iron - containing chloride product of step (b) is present in an amount of 0.5 - 2.0 kg of the air per 1 kg of the volatile iron - containing chloride product.

[0033] In some embodiments, the methods of this invention comprises a step of electrolyzing the cooled non - volatile at least one rare earth metal chloride (Steps (e), or step (vi)). In other embodiments, the electrolysis is performed using graphite electrodes (cathode, anode). In some further embodiments, said electrolysis is performed at a temperature range of between about 500 to 1500°C. In other embodiments, said electrolysis is performed using potential of between 10 to 15V. [0034] In some embodiments, this invention provides at least one rare earth metal composition prepared by the methods of this invention.

[0035] The following non-limiting examples are presented in order to more fully illustrate certain embodiments of the invention. They should in no way, however, be constmed as limiting the broad scope of the invention. One skilled in the art can readily devise many variations and modifications of the principles disclosed herein without departing from the scope of the invention. EXAMPLES

EXAMPLE 1- Magnets Treatment with Atomic Hydrogen - Decrepitation

[0036] The decrepitation of the ferromagnetic alloy was carried out in aqueous 1M sodium hydroxide solution at room temperature. Electrolysis was carried out with cathode copper electrode and lead anode electrode. Current density was 0.1 A/cm ² . Uncrushed ferromagnetic alloy was attached to the cathode electrode. The atomic hydrogen that is released at the cathode passes through a layer of pieces of a ferromagnetic alloy and reacted with him. The pieces of a ferromagnetic alloy are scattered by atomic hydrogen reaction with ferromagnetic alloy powder production. Figures 1, 2 and 8 show the ferromagnetic alloy before and after atomic hydrogen decrepitation. Characterization of the initial magnets.

[0037] Used magnet pieces were used as input material.

[0038] Content of components presented in the Table 1.

Table 1. Content of components in the used magnet pieces.

[0039] Photo of some magnet pieces is presented in the Figure 1.

[0040] Material X-ray diffraction (XRD) was performed on an Ultima III diffractometer (Rigaku Corporation, Japan) with quantitative phase analysis accomplished using Jade_10 (MDI, Cal.) software and the ICSD database (Figure 4A).

[0041] The composition of the material was characterized by energy dispersive X-ray fluorescence spectroscopy (EDS, FEO Supra) (Figures 5A-5D).

Thermodynamic Calculations.

[0042] Calculations of Gibbs energy were performed using a computer program and based on standard values for the pure substances [11] The Gibbs energy (AG) in the temperature range 273- 473 K is shown in Table 2 for reactions with hydrogen. Group 1- reactions with atomic hydrogen; Group 2 - reactions with molecular hydrogen; Group 3 - hydrolysis reactions of metal hydrides in the water.

Table 2. Gibbs energy (AG) calculated for magnet treatment with hydrogen. s - solid, 1 - liquid, g - gas. [0043] Under the above conditions, the Gibbs energy of the reactions (1, 2) in Group 1 for rare metals were strongly negative (- 520-570 kJ/mole).

[0044] Thermodynamic calculations predict that the reactions of Nd and Pr from magnets with atomic hydrogen gas can result in the formation of Nd and Pr hydrides within a wide temperature range, including the range of interest 273-373 K. Dysprosium is present in magnets as an additive in the form of oxide Dy ₂ 0 ₃ and can react with atomic hydrogen with metallic dysprosium or Dy¾ production (reactions 4, 5). Group 2 includes hydrogen treatment reactions between magnet components and molecular hydrogen. The likelihood of reactions (6, 7) is ensured over the entire temperature range of interest too, with the most negative value being AG = -163 kJ/mole for reaction (6). However, the value of Gibbs energy for reactions (6, 7) is much lower than for reactions (1, 2). Dy ₂ 0 ₃ does not react with molecular hydrogen (reactions 8, 9). Iron from a magnet practically does not participate in reactions with hydrogen under our conditions (reactions 3, 8). Group 3 includes hydrolysis reactions of the neodymium, praseodymium, and dysprosium hydrides in the water. Under our conditions, the Gibbs energy of the hydrolysis reactions (11-16) in Group 3 for rare metals is strongly negative (- 350-530 kJ/mole). Thermodynamic calculations predict that the hydrolysis reactions of the neodymium, praseodymium, and dysprosium hydrides can result in the formation of Nd, Pr, and Dy hydroxides or oxides within a wide temperature range, including the range of interest 273-373 K.

[0045] The chemical decrepitation of magnet described by reactions (1, 2) showing Gibbs energy of - 520-570 kJ/mole, thereby predicting rapid chemical decrepitation of magnet upon atomic hydrogen treatment. Dy ₂ 0 ₃ can react with atomic hydrogen with metallic dysprosium or Dy¾ production (reactions 4, 5). These reactions (1, 2, 4, 5) lead to the magnet decrepitation to obtain a magnet powder with a particle size of less than 200 mesh. Experimental Procedure

[0046] The laboratory setup is described in Figure 6. Test duration was 2-4 hours. Temperature was varied from room temperature to boiling temperature. Potential was 4.7 V, current - 13-15A. Cathode current density was 0.8-0.9 A/cm ² .

[0047] Glass with one mole/liter KOH solution was used as electrolytic bath. Titanium was used as cathode, nickel plate - as anode. Pieces (30-40 mm) of the neodymium magnet (as they are, without demagnetization, crushing and milling) were placed on the titanium grid, connected with cathode. Atomic hydrogen, which was emitted during electrolysis, released on the surface of the magnet pieces, and decrepitated them with powder production. Magnet powder passed through the grid and collected at the bottom of the electrolytic bath. Figure 7 shows the Powder X-ray diffraction (XRD) pattern of the magnet powder after decrepitation; and Figure 8 shows in a photo and SEM image of the magnet powder after decrepitation.

EXAMPLE 2-Rare-Earth Metal Extraction Including Atomic Hydrogen - Decrepitation Step

[0048] Treatment of the powder of the ferromagnetic alloy with chlorine gas at 400-450°C. The material was loaded into the reactor. Chlorine was fed into the reactor, heated to a temperature 400- 450°C. After the reaction, the chlorides of iron and boron were sublimated and removed from the reactor. Iron chloride was captured in a scrubber with water, and boron chloride was removed with gases. Chlorides of rare earth metals remained in the reactor. Iron-containing chloride vapor product (FcCh) were received in the scrubber and non-volatile neodymium and praseodymium chlorides (NdCh _, PrCh) in the reactor.

EXAMPLE 3 - Rare-Earth Metal Extraction Without Pre-Treatment of Atomic Hydrogen - Decrepitation

[0049] In this Example, a process for rare-earth extraction did not require pre-treatment of magnets. The magnets that were used did not include demagnetization, crushing and milling pre- treatments. After treatment at 400°C, a clinker consisting of rare earth metals chlorides and sublimates consisting of iron oxide and iron chlorides were obtained.

Characterization of the initial magnets.

[0050] Used magnet pieces were used as input material. Content of components presented in the Table 3.

Table 3. Content of components in the used magnet pieces.

[0051] Material X-ray diffraction (XRD) was performed on an Ultima III diffractometer (Rigaku Corporation, Japan) with quantitative phase analysis accomplished using Jade_10 (MDI, Cal.) software and the ICSD database (Figure 4A and 4B).

[0052] The composition of the material was characterized by energy dispersive X-ray fluorescence spectroscopy (EDS, LEO Supra) (Table 3 and Figures 4A and 4B).

[0053] Table 3 shows that both magnets are made up of the same elements, but the relationships between the elements are rather different. According to X-ray diffraction patterns, the first sample (Fig. 4A) is a well-crystalline material with an average crystal size of about 70 nm, while the second (Fig. 4B) consists of nanocrystals with a size of about 5 nm.

[0054] All the main peaks in Figure 4A correspond well to NdiFewB and NdPrFe^B (their peaks have almost identical positions), and the remaining peaks correspond to Dy2(¾, which were only a few percent. According to the EDS results (Table 3), the two main phases in sample 1 had the same amount. In Figure 4B, peaks of NdiFe^B (or NdPrFewB), were observed, but they were relatively small. Compounds shown above the main peaks in Figure 5B were found, given also in Table 3. Thermodynamic Calculations.

[0055] Calculations of Gibbs energy were performed using a computer program and based on standard values for the pure substances [11] The Gibbs energy (AG) in the temperature range 373- 773 K is shown in Table 4 for chlorination reactions with chlorine gas.

Table 4. Gibbs energy (AG) calculated for high temperature treatment of used magnet. s - solid, g - gas.

[0056] Under sintering conditions, the Gibbs energy of the reactions (1 - ,6, 8) was strongly negative within a wide temperature range, including the range of interest 573-673 K, with the most negative value being AG = - (800-900) kJ/mole for reactions (3 and 5). Thus, the highest probability of reactions (1) - (6, 8) can be expected immediately after injection of the chlorine gas. Dysprosium was present in magnets as an additive in the form of oxide Dy203 and did not react with chlorine (reaction 7 from Table 4).

Experimental Procedure.

[0057] Sintering of neodymium magnet with chlorine gas was carried out in a temperature- controlled laboratory furnace at 400°C: sintering time was 2 hour. The laboratory setup is described in Figure 9.

[0058] Pieces (30-40 mm) of the neodymium magnet (as they were, without demagnetization, crushing and milling) were placed in the furnace in a Pyrex glass crucible. Prior to heating, the quartz reactor was cleaned under 100 ml/min nitrogen flow, following which the furnace was heated to a given temperature, again under 100 ml/min nitrogen flow. Chlorine gas was fed into the reactor after the latter had reached the designated temperature. All elements (iron, neodymium, praseodymium, and boron) were chlorinated in accordance with reactions (1-6, 8) from Table 4. Dysprosium oxide Dy ₂ 0 ₃ did not react with chlorine (reaction 7 from Table 4).

[0059] Chlorides of iron and boron were sublimated (Boiling point of the FcCh is 316°C, boiling point of the BCh is -107°C) and rare earth metals chlorides remain in the residual clinker (Boiling point of the NdCh is 1600°C, boiling point of the PrCb is 1710°C). Rare earth metals chlorides and

Dy ₂₍ ¾ were formed of the solid powder clinker (Melting point of the NdCh is 758°C, melting point of the PrCh is 786°C, melting point of the Dy ₂₍ ¾ is 2408°C). Air was added to the top part of the reactor for iron chloride oxidation in accordance with reaction (7):

2 FeCk + 1.5 0 ₂ = Fe ₂ 0 ₃ +3 Cl ₂ (7)

[0060] Chlorine was obtained by reaction (7) and could have returned to the Pilot or industrial unit to the chlorination stage, therefore a circulation of chlorine gas can be achieved.

[0061 ] After cooling under nitrogen flow, the crucible was removed from the furnace and broken.

The final product (solid NdCh - PrCh clinker) was weighed and analyzed with XRD and EDS.

Mixture of the iron chloride and iron oxide was collected from the top part of the reactor and analyzed with XRD and EDS.

[0062] The composition of the material was characterized by energy dispersive X-ray fluorescence spectroscopy (EDS, LEO Supra) (Figures 10A-10B and Table 5).

Table 5. The composition of the neodymium clinker (mass %).

[0063] The resulting rare earth metals chlorides can be easily processed by electrolysis of the molten salts for metallic rare earth metals production [12-13].

[0064] Quantitative phase analysis of X-ray diffraction patterns of sublimations (Figure 11 A) showed that two crystalline iron-content phases (hematite FC ₂ O ₃ and iron (PI) oxide chloride FeOCl) were obtained with hematite being dominant (Figure 1 IB). List of references cited:

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[0065] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the tme spirit of the invention.