Rare earth extraction by molten borate electrolysis

Abstract

Method of extracting rare earth elements from a rare earth feedstock. The rare earth feedstock may be a rare earth ore, concentrate, or mixed alloy. The rare earth feedstock is reacted in an electrolysis cell containing a molten borate electrolyte and a host metal to produce a rare earth- containing host alloy. The rare earth-containing host alloy may then be reacted in a second refining cell to produce rare earth metal products.

Description

RARE EARTH EXTRACTION BY MOLTEN BORATE ELECTROLYSISCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of and priority to United States Provisional Application No. 63 / 528,236, filed on July 21, 2023, the entire disclosure of which is hereby incorporated by reference as if set forth in its entirety herein.TECHNICAL FIELD

[0002] Embodiments herein generally relate to methods of extracting rare earth elements via molten salt electrolysis and, more specifically but not exclusively, to the extraction of rare earth elements using molten borate salts.BACKGROUND

[0003] The mining of low concentration rare earth ores yields a mixture of rare earth compounds and gangue (undesirable compounds), including phosphates, sulfides, and oxides such as aluminum oxide, iron oxide, and silica. Current extraction methods include hydrometallurgy and solvent extraction which suffer from low space-time yields and make use of toxic chemicals, which complicate disposal of waste byproducts. Incumbent electrolysis processes typically require additional pre-processing steps to dissolve the metal compounds prior to electrolysis, such as converting rare earth ores to rare earth halides. Such steps incur a chemical cost and may suffer from low yields. Electrolysis with halide salts may result in a large quantity of environmentally deleterious byproducts like perfluorocarbons. Energy-intensive refining processes may also carry a significant carbon emissions cost which makes the technologies unattractive from an environmental perspective.SUMMARY

[0004] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description section. This summary is not intended to identify or exclude key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0005] Current methods for aluminum extraction are limited by economic constraints. The spot price for refined commercial-grade aluminum is too low to make a multistage aluminum extraction process economically viable. Accordingly, most commercial smelters refine aluminum ore in a single-stage process.

[0006] Embodiments of the current invention shift the focus from aluminum refinement to rare earth extraction, yielding high-grade aluminum as a byproduct of that process, which in some embodiments is a multi-stage process. The higher prices for the refined rare earth elements plus the high-grade aluminum byproduct make the refinement process economically viable, even in multiple stages.

[0007] In one aspect, embodiments relate to a method for rare earth extraction. The method may comprise providing a first electrolytic cell containing a first molten electrolyte comprising at least one of boron oxide or a borate salt; running a current through the electrolyte via at least two electrodes; receiving, at the first electrolytic cell, a host metal; dissolving, in the first electrolyte, a feedstock comprising at least one rare earth material; and producing an intermediate alloy of the at least one rare earth element and the host metal.

[0008] In some embodiments, the electrolyte additionally comprises at least one of a salt or metal, provided that the feedstock remains soluble in the electrolyte and the solution is a liquid over the process temperature range for the first electrolytic cell.

[0009] In some embodiments, the rare earth feedstock is physically processed prior to dissolution in the electrolyte.

[0010] In some embodiments, the current through the electrolytic cell is constant.

[0011] In some embodiments, the potential applied to the electrolytic cell is constant.

[0012] In some embodiments, the host metal is at least one of lead, antimony, tin, zinc, bismuth, gallium, or indium.

[0013] In some embodiments, the intermediate alloy is subsequently transferred to a second electrolytic cell for refinement.

[0014] In some embodiments, the second electrolytic cell contains a second molten electrolyte comprising at least one of borate salts or halide salts, and the intermediate metal alloy is largely insoluble in the second molten electrolyte.

[0015] In some embodiments, the second electrolytic cell comprises an electrode and current is applied to the second molten electrolyte and the intermediate alloy.

[0016] In some embodiments, the operating potential of the first or second electrolytic cell is controlled by the position of an electrode in the cell.

[0017] In some embodiments, at least one of the electrolytic cells comprises a means for temperature control.

[0018] In one aspect, embodiments relate to a system for rare earth extraction. The system may comprise a first electrolytic cell configured to receive a first molten electrolyte comprising at least one of boron oxide or a borate salt; apply a current to the electrolyte via at least two electrodes; receiving a host metal; dissolve, in the first electrolyte, a feedstock comprising at least one rare earth material; produce an intermediate alloy of the at least one rare earth element and the host metal.

[0019] In some embodiments, the electrolyte additionally comprises at least one of a salt or metal, provided that the feedstock remains soluble in the electrolyte and the solution is a liquid over the process temperature range for the first electrolytic cell.

[0020] In some embodiments, the system further comprises means for physically processing the feedstock prior to dissolution in the electrolyte.

[0021] In some embodiments, the system applies a constant current through the electrolytic cell.

[0022] In some embodiments, the system applies a constant potential to the electrolytic cell.

[0023] In some embodiments, the host metal is at least one of lead, antimony, tin, zinc, bismuth, gallium, or indium.

[0024] In some embodiments, there are means for transferring the intermediate alloy to a second electrolytic cell for refinement.

[0025] In some embodiments, the second electrolytic cell is configured to receive a second molten electrolyte comprising at least one of borate salts or halide salts, and the intermediate metal alloy is largely insoluble in the second molten electrolyte.

[0026] In some embodiments, the second electrolytic cell further comprises an electrode for applying current to the second molten electrolyte and the intermediate alloy.

[0027] In some embodiments, the system further comprises means for controlling the operating potential of the first or second electrolytic cell by varying the position of an electrode of the cell.

[0028] In some embodiments, at least one of the electrolytic cells comprises a means for temperature control.BRIEF DESCRIPTION OF DRAWINGS

[0029] Non-limiting and non-exhaustive embodiments of this disclosure are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified:

[0030] Figure 1 depicts a high-level outline describing one embodiment of a method of rare earth extraction;

[0031] Figure 2 depicts the process flow of reactants and products in embodiments where a single-stage extraction cell is used; and

[0032] Figure 3 depicts the process flow of reactants and products in embodiments where an extraction cell and a refining cell are operating in series.DETAILED DESCRIPTION

[0033] Various embodiments are described more fully below with reference to the accompanying drawings, which form a part hereof, and which show specific exemplary embodiments. However, the concepts of the present disclosure may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided as part of a thorough and complete disclosure, to fully convey the scope of the concepts, techniques and implementations of the present disclosure to those skilled in the art. Embodiments may be practiced as methods, systems or devices. The following detailed description is, therefore, not to be taken in a limiting sense.

[0034] Reference in the specification to “one embodiment” or to “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one example implementation or technique in accordance with the present disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

[0035] In addition, the language used in the specification has been principally selected for readability and instructional purposes and may not have been selected to delineate or circumscribe the disclosed subject matter. Accordingly, the present disclosure is intended to be illustrative, and not limiting, of the scope of the concepts discussed herein.Definitions

[0036] Unless otherwise specified, the following terms as used herein shall have the meanings as provided below:

[0037] The term “rare earth ore” refers to any ore which contains at least one rare earth element, and which may contain aluminum, silicon, iron or other metal compounds as additional constituents.

[0038] The term “rare earth concentrate” refers to any concentrate which contains at least one rare earth element, why may be a rare earth ore benefacted or concentrated to remove gangue.

[0039] The term “rare earth feedstock” refers to a rare earth ore, a rare earth concentrate, a rare earth compound, or any combination of the above.

[0040] The term “extraction cell” refers to the first electrolysis cell in the method, where a rare earth feedstock is converted into an intermediate rare earth alloy.

[0041] The term “refining cell” refers to an optional second electrolysis cell in the method, where the intermediate rare earth alloy from the first extraction cell is refined into rare earth metal.

[0042] The term “host metal” refers to an additional metal added to the extraction cell for the purpose of forming a liquid-metal alloy containing the intermediate alloy product from the extraction cell. Any metal that melts below the cell operating temperature and is less reactive than rare earth elements may be used as a host metal, including metals such as lead, tin, antimony, zinc, bismuth, gallium, and indium.

[0043] The term “intermediate alloy” refers to an intermediate metallic product of the first extraction cell, which consists of at least one rare earth element. The intermediate metal alloy may contain additional host metals such as lead, tin, antimony, zinc, bismuth, gallium, and indium.

[0044] The term “borate salt” refers to a class of salts containing at least one cationic species and at least one oxyborate anion.

[0045] The term “oxyborate anion” refers to a class of anions described with the general formula BxOy~, where the integers x, y, and n are positive and non-zero. Example oxyborate anions include but are not limited to BO|_, B2^4 A and B40 ~.

[0046] The term “halide salt” refers to a class of salts containing at least one cationic species and at least one halide anionic species. Examples of halide anionic species include but are not limited to fluoride, chloride, bromide, and iodide.Embodiments

[0047] Embodiments consist of configurations of electrolysis cells and methods to extract rare earth elements using the same. In one embodiment, the method consists of taking a feedstock comprising some fraction of rare earth elements, and first dissolving the feedstock in an electrolyte in a first electrolysis cell, termed an extraction cell. Current is passed through the extraction cellto produce an intermediate alloy of rare earth elements and optionally a host metal at the cathode, and an anodic byproduct is produced at the anode. The intermediate rare earth-containing alloy may be optionally transferred to a second electrolysis cell, termed a refining cell, where isolated rare earth elements may be produced from the intermediate alloy.

[0048] Figure 1 depicts an outline of the process 100 including the optional refining step. An electrolytic cell is provided (Step 104). A borate electrolyte is added to the cell by, e.g., melting boron oxide or a borate salt (Step 108). A current is applied to the borate electrolyte via two or more electrodes (Step 112); the current may be varied to control the temperature of the electrolyte as the cell operates. The electrolysis cell may be additionally charged with a molten borate salt and a host metal (Step 116). A rare earth feedstock is charged into the electrolysis cell (Step 120), resulting in an intermediate product of the host metal and rare earth elements in metallic form. The intermediate product may be optionally charged to a second electrolysis cell, termed a refining cell (Step 124). The refining cell separates the rare earth elements from the host metal producing a rare earth metal product.Feedstock

[0049] In some embodiments, rare earth feedstock may consist of at least one rare earth ore, defined as an ore containing at least one rare earth element. Rare earth ores may contain multiple rare earth elements, which may be in the form of rare earth metal oxides or other rare earthcontaining compounds. The rare earth feedstock may consist of a concentrate beneficiated from at least one rare earth ore, with the amount of gangue compounds reduced. The rare earth feedstock may consist of a single rare earth oxide or a combination of rare earth oxides.

[0050] In some embodiments, the rare earth feedstock may consist of at least one of a rare earth ore, a rare earth concentrate, and rare earth oxides.

[0051] In embodiments of this invention, any of the rare earth elements of the lanthanide or actinide series may be extracted. The rare earth elements may be isolated or produced in combination. Embodiments of this invention may be used to extract and purify rare earth elements such as neodymium, dysprosium, and samarium.

[0052] In some embodiments, the rare earth feedstock may be directly added to the extraction cell. In other embodiments, the rare earth feedstock may be crushed, pulverized, or otherwise processed physically prior to adding to the extraction cell.

[0053] In some embodiments of this invention, the rare earth ores processed may include monazite, bastnasite, kozoite, xenotime, fergusonite, gadolinite, euxenite, polycrase, blomstrandine, samarskite, cerite, and gadolite.Extraction Cell

[0054] In embodiments of this invention, rare earth feedstocks are processed in a first electrolysis cell, termed the extraction cell. Figure 2 depicts the process flow of reactants and products of an extraction cell. The rare earth feedstock 200 is dissolved in an electrolyte 204 contained in the first electrolysis cell pot 208, forming metal ions and anionic species 216 that may be oxygen-containing. In some embodiments, additional charged complexes may form between at least one of elements present in the rare earth feedstock 200 and the compounds present in the electrolyte. The extraction cell electrolyte 204 includes at least one of boron oxide and borate salt. Additional salts and metals may be present in the electrolyte 204, under the constraint that the rare earth feedstock 200 is at least partially soluble in the electrolyte 204 and the solution is a liquid over the process temperature range for the first electrolysis cell. In some embodiments, the process temperature is selected so that the free energy of reducing the rare earth oxides is less than the free energy of the oxidation of carbon.

[0055] In embodiments of this invention, at least two electrodes may be in contact with the electrolyte in each electrolysis cell, with at least one serving as a cathode and at least one serving as the anode. In some embodiments, the electrodes may be carbonaceous. In some embodiments, the electrodes may be comprised of an inert material such as platinum or a mixed metal ceramic. In some embodiments, a metal alloy may serve as a cathode, and in such cases, a current collector connects the metal alloy cathode to the electrical buswork. The current collector may be comprised of a conductive material such as carbon.

[0056] In embodiments of this invention, current 220 is passed through the electrolysis cell, from the anode through the electrolyte to a metal alloy serving as the cathode. At the positive electrode which serves as the anode, an anodic product is produced. In embodiments where a rare earth oxide is the feedstock, an oxygen byproduct may be produced. Oxygen gas may be produced if the electrode is inert; otherwise, if the electrode is carbonaceous, the gas may be an oxide of carbon. In embodiments where a rare earth sulfide is the feedstock, a sulfur byproduct may be produced. At the negative electrode which serves as the cathode, metal ions are reduced to form an alloy. The metal alloy may be liquid at the process temperature and is electrically conductive, forming a circuit between the anode, electrolyte 204, and the metal alloy serving as a cathode. At least one of the rare earth metals, metal impurities from the gangue, and host metals may be reduced and join the metal alloy, forming an alloy of rare earth and other metals termed an intermediate alloy 212.

[0057] In some embodiments, the current 220 applied across the electrolysis cell is constant, operating the cell in a galvanostatic fashion. Multiple electrolysis cells may be run in series withthe current passing from one cell to subsequent cells in the series. Under galvanostatic operation, the voltage of each electrolysis cell floats and corresponds to the sum of the electrochemical potential of the rare earth intermediate alloy being produced at the cathode, the ohmic loss through the electrolyte, and the activation overvoltages on the electrodes, buswork, and other sources of system resistances.

[0058] In some embodiments, current 220 is applied across the electrolysis cell at constant voltage, in a potentiostatic manner. Under potentiostatic operation, the power supply will adjust the applied potential to maintain the constant voltage setpoint.

[0059] In some embodiments, an optional host or carrier metal species 224 may be introduced to assist in formation and handling of the intermediate alloy 212. A metal that melts below 1000 °C and is less reactive than rare earth elements may be used as a host metal 224. This host metal 224 may consist of at least one of lead, antimony, tin, zinc, bismuth, gallium, indium, or another suitable metal.

[0060] In some embodiments, the products of the extraction cell are the used electrolyte, anodic product 216, and a rare earth-containing intermediate metal alloy 212.Transfer to Refining Cell

[0061] In embodiments of this invention, the intermediate alloy product of at least one extraction cell is collected.

[0062] In some embodiments, the intermediate alloy may be optionally fed into at least one refining electrolysis cell. In some embodiments, the intermediate alloy product of the extraction cells may be transferred continuously to the refining electrolysis cells. In other embodiments, the intermediate alloy product of the extraction cells may be collected and transferred batchwise into the refining electrolysis cells.

[0063] In some embodiments, an electrolysis cell may be operated in both an extraction cell configuration and a refining cell configuration. The electrolysis cell may then be periodically reconfigured to run in extraction and refining modes. Reconfiguration may be accomplished while the electrolysis cell is at temperature and contains molten electrolyte. Reconfiguration may entail the replacement of at least one electrode, the addition of new metals or salts to the electrolyte, and rewiring the electrical connections of the electrolysis cell.Refining Cell

[0064] In some embodiments of this invention, the intermediate alloy is processed in an optional second electrolysis cell, termed a refining cell. Figure 3 depicts the process flow of reactants and products of an extraction and refining cell in series. The intermediate metal alloy212 is charged into a second electrolyte 300 in the second electrolysis cell pot 304. The second electrolyte 300 may comprise at least one of borate salts and halide salts, which are liquid at the operating temperature of the electrolysis cell 304. Additional salts may be present, under the constraint that the intermediate metal alloy 212 is largely insoluble in the solution, and the salts cannot be electrolyzed. In some embodiments, the process temperature is selected such that the most favorable electrochemical reactions to occur are those where rare earth oxides are reduced to rare earth metals.

[0065] In embodiments of the second electrolysis cell, at least two electrodes may be in contact with the electrolyte of the second electrolysis cell, with at least one serving as a cathode and at least one serving as an anode. In some embodiments, the cathode electrodes may be carbonaceous. In some embodiments, the cathode electrodes may be comprised of an inert material such as platinum or a ceramic. The intermediate alloy from the first extraction cell serves as the anode in the refining cell.

[0066] In embodiments of the refining cell, current 308 is passed through the cell 304, producing a purified rare earth metal 312 at the cathode, and leaving the remainder of the intermediate metal alloy at the anode. Under current, metal ions are dissolved into the electrolyte 300 at the intermediate alloy anode and traverse the anode-cathode gap to deposit at the cathode. The rare earth metal product 312 may be solid or liquid at the process temperature of the second electrolysis cell 304. The product 312 may be conductive under the process conditions, forming part of the circuit between the cathode, electrolyte, and anode.

[0067] In some embodiments, current is applied to the electrolysis cell 304 galvanostatically or potentiostatically. Multiple electrolysis cells of this design may be run in series or parallel, with the electrolysis cells being connected electrically in series or parallel.

[0068] In some embodiments, the refined rare earth metal 312 is periodically collected. In some embodiments, the refined products 312 are collected continuously.

[0069] In some embodiments, the products of the refining cell are the used electrolyte, miscellaneous waste products including the host metal 316, and a rare earth metal alloy 312.Controls

[0070] In some embodiments, the electrolysis cells are self-heated and the temperature of the electrolyte is determined by the balance between the operating current and ohmic losses which govern heat generation and the heat loss to the environment.

[0071] In some embodiments, the potential of individual electrolysis cells is controlled via adjusting the position of at least one of the electrodes. The electrode may be kept in contact withthe electrolyte and moved to a particular distance from the metal alloy in the electrolysis cell to maintain an operating potential setpoint.

[0072] In some embodiments, insulation may be added or removed to the electrolysis cell to control the rate of heat loss to the environment.

[0073] In some embodiments, heat may be added to the electrolysis cells via at least one of an immersion heating system, radiative heating system, an inductive heating system, a resistive heating system, and a combustion heating system. In some embodiments, heat may be removed from the electrolysis cells via the integration of a heat exchanger to the electrolysis cell pot, which can be plumbed to a chiller or some other method of cooling.Equivalents

[0074] The methods, systems, and devices discussed above are examples. Various configurations may omit, substitute, or add various procedures or components as appropriate. For instance, in alternative configurations, the methods may be performed in an order different from that described, and that various steps may be added, omitted, or combined. Also, features described with respect to certain configurations may be combined in various other configurations. Different aspects and elements of the configurations may be combined in a similar manner. Also, technology evolves and, thus, many of the elements are examples and do not limit the scope of the disclosure or claims.

[0075] Embodiments of the present disclosure, for example, are described above with reference to block diagrams and / or operational illustrations of methods, systems, and computer program products according to embodiments of the present disclosure. The functions / acts noted in the blocks may occur out of the order as shown in any flowchart. For example, two blocks shown in succession may in fact be executed substantially concurrent or the blocks may sometimes be executed in the reverse order, depending upon the functionality / acts involved. Additionally, or alternatively, not all of the blocks shown in any flowchart need to be performed and / or executed. For example, if a given flowchart has five blocks containing functions / acts, it may be the case that only three of the five blocks are performed and / or executed. In this example, any of the three of the five blocks may be performed and / or executed.

[0076] A statement that a value exceeds (or is more than) a first threshold value is equivalent to a statement that the value meets or exceeds a second threshold value that is slightly greater than the first threshold value, e.g., the second threshold value being one value higher than the first threshold value in the resolution of a relevant system. A statement that a value is less than (or is within) a first threshold value is equivalent to a statement that the value is less than or equal to asecond threshold value that is slightly lower than the first threshold value, e.g., the second threshold value being one value lower than the first threshold value in the resolution of the relevant system.

[0077] Specific details are given in the description to provide a thorough understanding of example configurations (including implementations). However, configurations may be practiced without these specific details. For example, well-known circuits, processes, algorithms, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the configurations. This description provides example configurations only, and does not limit the scope, applicability, or configurations of the claims. Rather, the preceding description of the configurations will provide those skilled in the art with an enabling description for implementing described techniques. Various changes may be made in the function and arrangement of elements without departing from the spirit or scope of the disclosure.

[0078] Having described several example configurations, various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosure. For example, the above elements may be components of a larger system, wherein other rules may take precedence over or otherwise modify the application of various implementations or techniques of the present disclosure. Also, a number of steps may be undertaken before, during, or after the above elements are considered.

Claims

CLAIMSWhat is claimed is:

1. A method for rare earth extraction, the method comprising: providing a first electrolytic cell containing a first molten electrolyte comprising at least one of boron oxide or a borate salt; running a current through the electrolyte via at least two electrodes; receiving, at the first electrolytic cell, a host metal; dissolving, in the first electrolyte, a feedstock comprising at least one rare earth material; producing an intermediate alloy of the at least one rare earth element and the host metal.

2. The method of claim 1, wherein the electrolyte additionally comprises at least one of a salt or metal, provided that the feedstock remains soluble in the electrolyte and the solution is a liquid over the process temperature range for the first electrolytic cell.

3. The method of claim 1, further comprising physically processing the feedstock prior to dissolution in the electrolyte.

4. The method of claim 1, wherein the applied current is constant.

5. The method of claim 1, wherein the applied potential is constant.

6. The method of claim 1, wherein the host metal is at least one of lead, antimony, tin, zinc, bismuth, gallium, or indium.

7. The method of claim 1, further comprising transferring the intermediate alloy to a second electrolytic cell for refinement.

8. The method of claim 7, wherein the second electrolytic cell contains a second molten electrolyte comprising at least one of borate salts or halide salts, and the intermediate metal alloy is largely insoluble in the second molten electrolyte.

9. The method of claim 8, wherein the second electrolytic cell comprises an electrode and current is applied to the second molten electrolyte and the intermediate alloy.

10. The method of claim 1, wherein the operating potential of the first or second electrolytic cell is controlled by the position of an electrode of the cell.

11. The method of claim 1, wherein at least one of the electrolytic cells comprises a means for temperature control.

12. A system for rare earth extraction, the system comprising: a first electrolytic cell configured to: receive a first molten electrolyte comprising at least one of boron oxide or a borate salt; apply a current to the electrolyte via at least two electrodes; receive a host metal; dissolve, in the first electrolyte, a feedstock comprising at least one rare earth material; and produce an intermediate alloy of the at least one rare earth element and the host metal.

13. The system of claim 12, wherein the electrolyte additionally comprises at least one of a salt or metal, provided that the feedstock remains soluble in the electrolyte and the solution is a liquid over the process temperature range for the first electrolytic cell.

14. The system of claim 12, wherein the system further comprises means for physically processing the feedstock prior to dissolution in the electrolyte.

15. The system of claim 12, wherein the applied current is constant.

16. The system of claim 12, wherein the applied potential is constant.

17. The system of claim 12, wherein the host metal is at least one of lead, antimony, tin, zinc, bismuth, gallium, or indium.

18. The system of claim 12, further comprising means for transferring the intermediate alloy to a second electrolytic cell for refinement.

19. The system of claim 18, wherein the second electrolytic cell is configured to receive a second molten electrolyte comprising at least one of borate salts or halide salts, and the intermediate metal alloy is largely insoluble in the second molten electrolyte.

20. The system of claim 19, wherein the second electrolytic cell further comprises an electrode for applying current to the second molten electrolyte and the intermediate alloy.

21. The system of claim 12, wherein the system further comprises means for controlling the operating potential of the first or second electrolytic cell by varying the position of an electrode of the cell.

22. The system of claim 12, wherein at least one of the electrolytic cells comprises a means for temperature control.

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