METHODS FOR ELECTROMETALLIZATING RARE EARTH ELEMENTS USING ANHYDROUS ELECTROLYTES COMPRISING ONE OR MORE SILYLAMIDE COMPOUNDS
20260043162 ยท 2026-02-12
Inventors
Cpc classification
C25C1/22
CHEMISTRY; METALLURGY
C25C7/08
CHEMISTRY; METALLURGY
International classification
Abstract
A method for electrometallizing one or more rare earth elements includes combining a rare earth element-containing compound comprising one or more rare earth elements with a silylamide-containing anhydrous electrolyte comprising one or more silylamide compounds to form a complex-containing anhydrous electrolyte comprising one or more silylamide-rare earth element complexes. The method also includes applying an electrical potential across electrodes of an electrochemical cell containing the complex-containing anhydrous electrolyte. The electrodes are disposed in the complex-containing anhydrous electrolyte. The method further includes collecting a deposit of at least one rare earth element on at least one electrode. Also disclosed is a system for electrometallizing one or more rare earth elements.
Claims
1. A method for electrometallizing one or more rare earth elements, comprising: combining a rare earth element-containing compound comprising one or more rare earth elements with a silylamide-containing anhydrous electrolyte comprising one or more silylamide compounds to form a complex-containing anhydrous electrolyte comprising one or more silylamide-rare earth element complexes; applying an electrical potential across electrodes of an electrochemical cell containing the complex-containing anhydrous electrolyte, the electrodes disposed in the complex-containing anhydrous electrolyte; and collecting a deposit of at least one rare earth element on at least one electrode.
2. The method of claim 1, wherein the one or more silylamide compounds has the following chemical formula: ##STR00004## wherein: A comprises at least one of lithium, sodium, potassium, or calcium; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 each independently comprises hydrogen, an alkyl group, or a combination thereof; and X is 1 or 2.
3. The method of claim 2, wherein A comprises lithium, calcium, or a combination thereof.
4. The method of claim 2, wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are a methyl group.
5. The method of claim 2, wherein at least one of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 is an alkyl group comprising from one carbon atom to six carbon atoms.
6. The method of claim 1, wherein the one or more silylamide compounds comprise lithium bis(trimethylsilyl)amide, sodium bis(trimethylsilyl)amide, potassium bis(trimethylsilyl)amide, calcium bis(trimethylsilyl)amide, or a combination thereof.
7. The method of claim 1, wherein the rare earth element comprises lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, yttrium, or a combination thereof.
8. The method of claim 1, wherein applying the electrical potential across the electrodes of the electrochemical cell comprises applying the electrical potential at a temperature of from about 20 C. to about 25 C.
9. The method of claim 1, wherein applying the electrical potential across the electrodes of the electrochemical cell comprises applying the electrical potential across at least two electrodes maintained under an inert atmosphere.
10. The method of claim 1, wherein applying an electrical potential across electrodes of an electrochemical cell comprises reducing the one or more silylamide-rare earth element complexes to deposit the one or more rare earth elements on the at least one electrode.
11. A method for electrometallizing at least one rare earth element, comprising: combining a rare earth element-containing compound comprising at least one rare earth element with a silylamide-containing anhydrous electrolyte comprising at least one silylamide compound to form a complex-containing anhydrous electrolyte comprising at least one silylamide-rare earth element complex; providing an electrochemical cell comprising the complex-containing anhydrous electrolyte, at least one cathode disposed in the complex-containing anhydrous electrolyte, and at least one anode disposed in the complex-containing anhydrous electrolyte; applying an electrical potential across the at least one cathode and the at least one anode of the electrochemical cell; collecting a deposit comprising the at least one rare earth element on the at least one cathode of the electrochemical cell; and recovering the at least one rare earth element from the collected deposit, wherein the at least one silylamide compound has the following chemical formula: ##STR00005## wherein: A comprises at least one of lithium, sodium, potassium, or calcium; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 each independently comprises hydrogen, a C1-C6 alkyl group, or a combination thereof; and X is 1 or 2.
12. The method of claim 11, wherein the rare earth element-containing compound comprises a rare earth salt, a rare earth oxide, a rare earth nitrate, a rare earth chloride, a rare earth trifluoromethanesulfanone, a rare earth carbonate, a rare earth bistriflimide, or a combination thereof.
13. The method of claim 11, wherein the rare earth element comprises neodymium, dysprosium, or a combination thereof.
14. The method of claim 11, wherein the at least one silylamide compound comprises lithium bis(trimethylsilyl)amide, calcium bis(trimethylsilyl)amide, or a combination thereof.
15. The method of claim 11, wherein the at least one silylamide compound is substantially free of one or more of fluorine, oxygen, sulfur, or boron atoms.
16. A system for electrometallizing one or more rare earth elements, the system comprising: a container configured to contain a complex-containing anhydrous electrolyte therein, the complex-containing anhydrous electrolyte comprising at least one silylamide-rare earth element complex; an electrodeposition reservoir configured to receive an amount of the complex-containing anhydrous electrolyte from the container, the electrodeposition reservoir including: a reservoir inlet configured to facilitate an addition of the complex-containing anhydrous electrolyte into the electrodeposition reservoir; and a reservoir outlet configured to facilitate a removal of a spent complex-containing anhydrous electrolyte from the electrodeposition reservoir, the spent complex-containing anhydrous electrolyte exhibiting a lower amount of the at least one silylamide-rare earth element complex compared to the complex-containing anhydrous electrolyte; at least one counter-electrode and at least one working electrode disposed below a surface of the complex-containing anhydrous electrolyte in the electrodeposition reservoir, the at least one counter-electrode configured to release electrons to the complex-containing anhydrous electrolyte upon an application of an electrical potential across the at least one counter-electrode and at least one working electrode, and the at least one working electrode configured to receive a deposit of the at least one rare earth element from a reduction of the complex-containing anhydrous electrolyte upon the application of the electrical potential across the at least one counter-electrode and the at least one working electrode; and a potential source configurated to apply the electrical potential across the at least one counter-electrode and the at least one working electrode.
17. The system of claim 16, wherein the system is configured to operate in a batch mode, a semi-batch mode, or a continuous mode.
18. The system of claim 16, wherein the potential source is configured to apply the electrical potential of from about +1.0V to about 4.0V across the at least one counter-electrode and at least one working electrode.
19. The system of claim 16, wherein the potential source is configured to generate a current density of from about 0.5 mA/cm.sup.2 to about 5 mA/cm.sup.2 between the at least one counter-electrode and the at least one working electrode, and through the complex-containing anhydrous electrolyte.
20. The system of claim 16, further comprising a controlled environment enclosure dimensioned and configured to contain the electrodeposition reservoir, the at least one counter-electrode, the at least one working electrode, and the potential source therein, the controlled environment enclosure including at least one evacuation outlet configured to facilitate a removal of an ambient atmosphere within the controlled environment enclosure, and at least one inert gas inlet configured to receive the inert gas into the controlled environment enclosure.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DETAILED DESCRIPTION
[0021] The disclosure relates to methods and systems for electrometallizing rare earth elements (REEs) from rare earth element-containing compounds in an anhydrous electrolyte comprising a silylamide compound. The disclosed methods and systems allow for an increased efficiency of rare earth metal electrodeposition and an enhanced metal purity of the electrodeposit, compared to conventional methods for electrometallizing rare earth elements from rare earth containing compounds.
[0022] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown, by way of illustration, specific example embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable a person of ordinary skill in the art to practice the disclosure. However, other embodiments may be utilized, and structural, material, and process changes may be made without departing from the scope of the disclosure.
[0023] The illustrations presented herein are not meant to be actual views of any particular method, system, device, or structure, but are merely idealized representations that are employed to describe the embodiments of the disclosure. The drawings presented herein are not necessarily drawn to scale. Similar structures or components in the various drawings may retain the same or similar numbering for the convenience of the reader; however, the similarity in numbering does not mean that the structures or components are necessarily identical in size, composition, configuration, or any other property.
[0024] It will be readily understood that the components of the embodiments as described herein and illustrated in the drawings may be arranged and designed in a wide variety of different configurations. Thus, the following description of various embodiments is not intended to limit the scope of the disclosure, but is merely representative of various embodiments. While the various aspects of the embodiments may be presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
[0025] The following description may include examples to help enable one of ordinary skill in the art to practice the disclosed embodiments. The use of the terms exemplary, by example, and for example, means that the related description is explanatory, and though the scope of the disclosure is intended to encompass the examples and legal equivalents, the use of such terms is not intended to limit the scope of any embodiments or this disclosure to the specified components, acts, features, functions, or the like.
[0026] Thus, specific implementations shown and described are only examples and should not be construed as the only way to implement the disclosure unless specified otherwise herein. Elements, apparatuses, and methods may be shown in block diagram form in order not to obscure the disclosure in unnecessary detail. Conversely, specific implementations shown and described are exemplary only and should not be construed as the only way to implement the disclosure unless specified otherwise herein. It will be readily apparent to one of ordinary skill in the art that the disclosure may be practiced by numerous other recovery solutions. For the most part, details concerning flow rates and the like have been omitted where such details are not necessary to obtain a complete understanding of the disclosure and are within the abilities of persons of ordinary skill in the relevant art.
[0027] As used herein, the singular forms following a, an, and the are intended to include the plural forms as well, unless the context clearly indicates otherwise.
[0028] As used herein, the term may with respect to a material, structure, feature, or method act indicates that such is contemplated for use in implementation of an embodiment of the disclosure, and such term is used in preference to the more restrictive term is so as to avoid any implication that other compatible materials, structures, features, and methods usable in combination therewith should or must be excluded.
[0029] As used herein, the term about used in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the given parameter, as well as variations resulting from manufacturing tolerances, etc.). In some embodiments, the term about refer to plus or minus 10% of the indicated number. For example, about 10% may indicate a range of 9% to 11%, and about 1 may mean from 0.9 to 1.1. Other meanings of about may be apparent from the context, such as rounding off, so, for example about 1 may also mean from 0.5 to 1.4.
[0030] As used herein, the term substantially in reference to a given parameter, property, or condition means and includes to a degree that one skilled in the art would understand that the given parameter, property, or condition is met with a small degree of variance, such as within acceptable manufacturing tolerances. By way of example, depending on the particular parameter, property, or condition that is substantially met, the parameter, property, or condition may be at least 90.0% met, at least 95.0% met, at least 99.0% met, or even at least 99.9% met.
[0031] In general, the amount of a compound in a composition as disclosed herein is expressed by weight which refers to a percentage of the compound's weight in a total weight of the composition. Unless indicated otherwise, all concentrations are expressed as weight percentage concentrations.
[0032] As used herein, the term comprise(s), comprising, include(s), including, having, has, contain(s), containing, and variants thereof, are open-ended transitional phrases, terms, or words that are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Where the term comprising is used, the disclosure also contemplates other embodiments comprising. consisting of. or consisting essentially of elements presented herein, whether explicitly set forth or not.
[0033] A method for electrometallizing one or more rare earth elements, in accordance with embodiments of the disclosure, comprises combining a rare earth element-containing compound comprising one or more rare earth elements with an anhydrous electrolyte comprising one or more silylamide compounds to form an anhydrous electrolyte comprising one or more silylamide-rare earth element complexes (silylamide-REE complex). The electrodes of an electrochemical cell are disposed in the anhydrous electrolyte comprising one or more silylamide-REE complexes, and an electrical potential is applied across the electrodes. The silylamide-REE complex in the anhydrous electrolyte is electrochemically reduced to form one or more rare earth elements (REEs), which deposit on at least one of the electrodes. The method comprises recovering (e.g., collecting) a deposit of at least one of the REEs on at least one of the electrodes.
[0034] As used herein, the term rare earth element (REE) includes one or more 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). The term also includes any molecule or ion that includes one or more of the foregoing elements.
[0035] As used herein, the term rare earth element-containing compound includes but is not limited to a rare earth salt, a rare earth oxide, a rare earth nitrate, a rare earth chloride, a rare earth triflate (e.g., trifluoromethanesulfanone), a rare earth carbonate, a rare earth bistriflimide, or a combination thereof. The rare earth-containing compound may be obtained from a naturally occurring ore comprising one or more rare earth-containing compounds as well as industrial and consumer products that include one or more rare earth-containing compounds. The REEs may be recycled from, by way of example only, advanced electric vehicle batteries, traction motors, advanced light-weight alloys, telecommunication devices, energy-efficient refrigeration magnets, micro-electronics, satellites, and defense weapons systems.
[0036] With reference to
[0037] In some embodiments, the silylamide compound may be a salt of an N-coordinated compound having the following chemical formula:
##STR00002## [0038] wherein: [0039] A comprises at least one of lithium, sodium, potassium, or calcium; [0040] R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 each independently comprises hydrogen, an alkyl group, or a combination thereof; and [0041] X is 1 or 2.
[0042] The silylamide compound may be produced by conventional techniques, such as from commercially available salts. Therefore, the silylamide compound may be easily prepared.
[0043] In some embodiments, A comprises at least one of lithium or calcium.
[0044] As used herein, the term alkyl means and includes a cyclic or non-cyclic, branched or unbranched, saturated or unsaturated hydrocarbon group that is unsubstituted (i.e., containing only hydrogen and carbons atoms) or substituted.
[0045] In some embodiments, the alkyl group includes from one carbon atom to 12 carbon atoms (C1-C12 alkyl). In some embodiments, the alkyl group includes from one carbon atom to 8 carbon atoms (C1-C8 alkyl). In some other embodiments, the alkyl group includes from about one carbon atom to 6 carbon atoms (C1-C6 alkyl). In some further embodiments, the alkyl group includes from one carbon atom to 4 carbon atoms (C1-C4 alkyl).
[0046] Non-limiting examples of unsubstituted alkyl groups are methyl, ethyl, propyl, isopropyl, butyl, and tert-butyl. Non-limiting examples of substituents for the alkyl group are alkenyl, alkenyloxy, alkoxy, alkynyl, alkynyloxy, halogen, haloalkoxy, aryl, heterocyclyl, or any combination thereof.
[0047] As used herein, the term alkenyl means and includes branched or unbranched substituent consisting of carbon and hydrogen and comprising at least one carbon-carbon double bond, such as (without limitation) vinyl, allyl, butenyl, pentenyl, and hexenyl.
[0048] As used herein, the term alkenyloxy means and includes an alkenyl further consisting of a carbon-oxygen single bond, such as (without limitation) allyloxy, butenyloxy, pentenyloxy, and hexenyloxy.
[0049] As used herein, the term alkoxy means and includes an alkyl further consisting of a carbon-oxygen single bond, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, and tert-butoxy.
[0050] As used herein, the term alkynyl means and includes branched or unbranched substituent consisting of carbon and hydrogen and comprising at least one carbon-carbon triple bond, such as (without limitation) ethynyl, propargyl, butynyl, and pentynyl.
[0051] As used herein, the term alkynyloxy means and includes an alkynyl further consisting of a carbon-oxygen single bond, such as (without limitation) pentynyloxy, hexynyloxy, heptynyloxy, and octynyloxy.
[0052] As used herein, the term halogen means and includes fluorine, chlorine, bromine, and/or iodine.
[0053] As used herein, the term haloalkoxy means and includes an alkoxy further comprising at least one halogens, such as (without limitation) chloromethoxy, trifluoromethoxy, 2,2-difluoropropoxy, chloromethoxy, trichloromethoxy, 1,1,2,2-tetrafluoroethoxy, and pentafluoroethoxy.
[0054] As used herein, the term aryl means and includes a cyclic, aromatic substituent consisting of hydrogen and carbon, such as (without limitation) phenyl, naphthyl, and biphenyl.
[0055] As used herein, the term heterocyclyl means and includes a cyclic substituent that is fully saturated, partially unsaturated, or fully unsaturated, where the cyclic structure contains at least one carbon and at least one heteroatom, where said heteroatom is nitrogen, sulfur, or oxygen. Examples of aromatic heterocyclyls include, but are not limited to, benzofuranyl, benzoisothiazolyl, benzoisoxazolyl, benzoxazolyl, benzothienyl, benzothiazolyl cinnolinyl, furanyl, indazolyl, indolyl, imidazolyl, isoindolyl, isoquinolinyl, isothiazolyl, isoxazolyl, oxadiazolyl, oxazolinyl, oxazolyl, phthalazinyl, pyrazinyl, pyrazolinyl, pyrazolyl, pyridazinyl, pyridyl, pyrimidinyl, pyrrolyl, quinazolinyl, quinolinyl, quinoxalinyl, tetrazolyl, thiazolinyl, thiazolyl, thienyl, triazinyl, and triazolyl. Examples of fully saturated heterocyclyls include, but are not limited to, piperazinyl, piperidinyl, morpholinyl, pyrrolidinyl, tetrahydrofuranyl, and tetrahydropyranyl. Examples of partially unsaturated heterocyclyls include, but are not limited to, 1,2,3,4-tetrahydro-quinolinyl, 4,5-dihydro-oxazolyl, 4,5-dihydro-1H-pyrazolyl, 4,5-dihydro-isoxazolyl, and 2,3-dihydro-[1,3,4]-oxadiazolyl.
[0056] In some embodiments, each of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 is the same.
[0057] In some embodiments, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are a methyl group (i.e., an alkyl group containing one carbon atom).
[0058] In some embodiments, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 each independently comprises from one carbon atom to 6 carbon atoms.
[0059] In some embodiments, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 each independently comprises from one carbon atom to 4 carbon atoms.
[0060] In some embodiments, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 each independently comprises from one carbon atom to 2 carbon atoms.
[0061] In some embodiments, at least one of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 is an alkyl group comprising from one carbon atom to six carbon atoms.
[0062] In some embodiments, the silylamide compound comprises lithium bis(trimethylsilyl)amide, sodium bis(trimethylsilyl)amide, potassium bis(trimethylsilyl)amide, calcium bis(trimethylsilyl)amide, barium bis(trimethylsilyl)amide, manganese bis(trimethylsilyl)amide, or a combination thereof.
[0063] In some embodiments, the silylamide compound comprise lithium bis(trimethylsilyl)amide, calcium bis(trimethylsilyl)amide, or a combination thereof.
[0064] In some embodiments, the silylamide compound is substantially free of one or more of fluorine, oxygen, sulfur, or boron atoms.
[0065] In some embodiments, the anhydrous electrolyte comprising silylamide compound is substantially free of ionic liquid.
[0066] The rare earth element-containing compound may comprise one or more REEs. In some embodiments, the rare earth element-containing compound comprises neodymium, dysprosium, or a combination thereof.
[0067] The anhydrous electrolyte comprising one or more silylamide compounds may be combined with the rare earth element-containing compound at a predetermined amount of the one or more silylamide compounds (silylamide compound) to the amount of REEs present in the rare earth element-containing compound. In some embodiments, the predetermined amount of the anhydrous electrolyte comprising silylamide compound may be such that the amount of silylamide compound relative to the amount of REEs present in the rare earth element-containing compound is in a ratio of from about 1:1 to about 1:5 silylamide compound to REEs, or in a ratio of from about 1:1.5 to about 1:3 silylamide compound to REEs, or in a ratio of about 1:2 silylamide compound to REEs.
[0068] In some embodiments, the anhydrous electrolyte comprises one or more silylamide compounds in an amount from about 3,500 parts per million (ppm) to about 10 ppm, from about 1,000 ppm to about 10 ppm, from about 500 ppm to about 10 ppm, from about 200 ppm to about 10 ppm, or from about 35 ppm to about 10 ppm.
[0069] Upon combining the anhydrous electrolyte comprising silylamide compound with the rare earth element-containing compound (110 of
##STR00003##
[0070] With reference again to
[0071] In some embodiments, the electrodes include at least a working electrode and a counter-electrode, and applying the electrical potential across the at least two electrodes positioned in the amount of the anhydrous electrolyte comprising one or more silylamide-REE complexes in an electrochemical cell 120 includes applying an electrical potential across the working electrode and the counter-electrode. The applied electrical potential in accordance with embodiments of the disclosure may range from about +1.0V to about 4.0V. At such applied electrical potentials, the current densities created at the electrodes may range from about 0.5 mA/cm.sup.2 to about 5 mA/cm.sup.2.
[0072] Applying the electrical potential enables the reduction of the silylamide-REE complex to be conducted in the electrochemical cell at a low temperature. For example, the reduction of the silylamide-REE complex may be conducted at a temperature ranging from about 15 C. to about 150 C., such as from about 20 C. to about 125 C., or from about 25 C. to about 100 C. In some embodiments, the electrical potential is applied under ambient conditions (e.g., approximately atmospheric pressure at a temperature of from about 20 C. to about 25 C.).
[0073] In some embodiments, an electrical potential is applied across at least two electrodes in the electrochemical cell 120 in an inert environment. For example, the electrochemical cell may contain an inert environment during the reduction of the silylamide-REE complex. The electrochemical cell may contain, for example, less than about 10 ppm of water and less than about 1 ppm of oxygen. In some embodiments, an inert gas (e.g., argon) may be disposed over the anhydrous electrolyte comprising one or more silylamide-REE complexes, to create the inert environment in the electrochemical cell.
[0074] Referring again to
[0075]
[0076] The system 200 also includes an electrodeposition reservoir 210 dimensioned and configured to receive an amount of the anhydrous electrolyte comprising at least one silylamide-REE complex 216 from the container 205. The electrodeposition reservoir 210 in some embodiments comprises a chemically and/or electrically inert material of construction, so as to minimize (e.g., prevent) interference with the electrochemical reactions of the rare earth elements occurring therein. Alternatively, at least the liquid contacting surfaces of the electrodeposition reservoir 210 may be lined (e.g., coated) with a chemically and/or electrically inert material to minimize (e.g., prevent) interference with the electrochemical reactions of rare earth elements.
[0077] As shown in
[0078] The reservoir inlet 212 and the reservoir outlet 214, and the corresponding inlet and outlet valves 213, 215, allow the system 200 to be operable in any of a batch, semi-batch, or continuous mode of operation. For example, in a batch mode of operation, the electrodeposition reservoir 210 may contain a fixed amount of fresh anhydrous electrolyte comprising silylamide-REE complex 216, as shown, for example, in
[0079] A semi-batch mode of operating the system 200 begins as described above for the batch mode. However, after intermittent intervals of applying the electrical potential to the fresh anhydrous electrolyte comprising silylamide-REE complex 216, an amount of spent anhydrous electrolyte comprising silylamide-REE complex 216 is discharged through the reservoir outlet 214, and an approximately equal amount of fresh anhydrous electrolyte comprising silylamide-REE complex 216 is added to the electrodeposition reservoir 210 through the reservoir inlet 212. In a continuous mode of operation of the system 200, an amount of spent anhydrous electrolyte comprising silylamide-REE complex 216 is continuously discharged from the electrodeposition reservoir 210 at a predetermined discharge flowrate, while fresh anhydrous electrolyte comprising silylamide-REE complex 216 is continuously added to the electrodeposition reservoir 210 at a substantially similar flowrate.
[0080] The electrodeposition assembly 220 of the system 200 includes at least two electrodes 222, 224, which are disposed below a surface 216 of the anhydrous electrolyte comprising silylamide-REE complex 216 in the electrodeposition reservoir 210, such as is shown, by way of example, in
[0081] In some embodiments, the system 200 for electrometallizing one or more rare earth elements includes at least three electrodes: an anode 222, a cathode 224, and a reference electrode (e.g., Saturated Calomel Electrode (SCE) (not shown), which is a reference electrode based on the reaction between elemental mercury and mercury (I) chloride) used as an internal reference system in order to correct for potential shift of an employed platinum pseudo-reference. The reference electrode may be separated from electrodes 222, 224 in the anhydrous electrolyte comprising silylamide-REE complex 216 in the electrodeposition reservoir 210, such as, for example, by a glass frit.
[0082] Although the system 200 of
[0083] The electrodes 222, 224 may be formed of and include an electrically conductive material such as, by way of example, noble or transition metals, Group 10 or Group 11 metals, glassy carbon, etc. In some embodiments, the electrically conductive material includes nickel, palladium, platinum, copper, silver, gold, glassy carbon (GC), or combinations thereof. With the exception of glassy carbon, each of these electrically conductive materials exhibits similar characteristics with regard to the aforementioned reduction potentials, such that they may be used essentially interchangeably in the electrodeposition assembly 220. The selection of the electrically conductive material for electrodes 222, 224 may be determined, at least in part, by such factors as the cost of the electrode materials, the type of rare earth elements to be deposited thereon, the efficiency of the electrode materials, the volume of rare earth containing ionic solution to be processed, etc. In at least some embodiments, one or more of the cathodes 224 may be formed of an intermediate material to be incorporated into a final product, such that once the rare earth element deposits 300 are formed on the intermediate material of the cathode 224, the cathode 224 comprises a final or near final product material.
[0084] Furthermore, the electrodes 222, 224 of the system 200 may be formed in any suitable shapes. Non-limiting examples of the electrode shape include a wire, a cylinder, a disc, a gauze-like material, etc. In some embodiments, the electrodes 222, 224 are from about 1.0 mm to about 5.0 mm in diameter. In some other embodiments, the sizes and shapes of the electrodes 222, 224 may be altered (e.g., scaled up) for larger-scale industrial applications.
[0085] With continued reference to
[0086] The system 200 for electrometallizing one or more rare earth elements in at least some embodiments includes a controlled environment 230 within which the system 200 is operated. The controlled environment 230 includes an enclosure 232 that is dimensioned and configured to contain (e.g., surround) the electrodeposition reservoir 210, including the anhydrous electrolyte comprising silylamide-REE complex 216 and the electrodes 222, 224. The enclosure 232, in accordance with some embodiments, is dimensioned and configured to completely surround and contain the electrodeposition reservoir 210 and its contents therein, as shown by way of example in
[0087] As with the electrodeposition reservoir 210, the enclosure 232 defining the controlled environment 230 may be constructed of a chemically and/or electrically inert material of construction, so as to minimize (e.g., prevent) interference with the electrochemical reactions occurring therein. Alternatively, at least the internal surfaces of the enclosure 232 may be lined (e.g., coated) with a chemically and/or electrically inert material to minimize (e.g., prevent) interference with the electrochemical reactions.
[0088] The enclosure 232 includes an evacuation outlet 234 and an inert gas inlet 236. The evacuation outlet 234 allows for the ambient atmosphere within the enclosure 232 to be removed such as via a vacuum pump, vacuum line, etc. The ambient atmosphere (e.g., ambient air) may include compounds (e.g., oxygen, water vapor, trace contaminants, etc.) that interfere and/or have detrimental effects on the intended electrochemical deposition processes conducted within the system 200 for recovering rare earth elements. In some embodiments, an evacuation valve 235 is disposed in communication with the evacuation outlet 234 to further facilitate the removal of the ambient atmosphere from the enclosure 232.
[0089] The inert gas inlet 236 is provided to facilitate the introduction of one or more inert gasses under which the system 200 for recovering rare earth elements may operate without interference with the electrochemical deposition processes. An inert gas valve 237 may be disposed in communication with the inert gas inlet 236 to facilitate the addition of one or more inert gasses (e.g., argon, nitrogen, helium, etc.) into the enclosure 232.
[0090] In accordance with at least some embodiments, the inert atmosphere within the enclosure 232 of the controlled environment 230 has a water content of less than about 25 ppm, less than about 15 ppm, or less than about 10 ppm. In accordance with further embodiments, the inert atmosphere within the enclosure 232 of the controlled environment 230 has an oxygen content of less than about 5 ppm, less than about 3 ppm, or less than about 1 ppm.
[0091] The disclosed method for electrometallizing one or more rare earth elements from the rare earth element-containing compound(s) provides an increased efficiency of rare earth metal electrodeposition compared to conventional methods for electrometallizing rare earth elements. The silylamide compound in the anhydrous electrolyte functions as a ligand for the positively charged REE of the rare earth element-containing compound, resulting in a silylamide-REE complex. The complexation of the positively charged REE with the silylamide compound facilitates the electrochemical reduction of the positively charged REE, thereby allowing the electrometallization of REEs to take place efficiently, even at room temperature. The disclosed methods for electrometallizing one or more rare earth elements may also be conducted at a lower temperature, compared to the conventional methods for electrometallizing one or more rare earth elements. Conventional methods include Fuse Salt Electrolysis processes, which uses a molten-salt eutectic and is conducted at a temperature between about 600 C. and about 1200 C. The disclosed methods for electrometallizing one or more rare earth elements may be performed in anhydrous conditions, thus minimizing eliminating (if not eliminating) the drawbacks known for using water as an electrolyte.
[0092] By using an anhydrous electrolyte comprising the silylamide compound as the electrolyte in the disclosed method, the nucleophilicity of the electrolyte may be adjusted, the Lewis acid-base chemistry between the positively charged REEs in the rare earth element-containing compound and the nitrogen of the silylamide compound may enhance the ligand environment of the positively charged REEs, and the electrochemical interface may be modified. These may enable tuning the coordination sphere, improving reduction kinetics and product stability during the electrodeposition of REEs.
[0093] The silylamide compound present in the disclosed anhydrous electrolyte is non-toxic and substantially free of fluorine, oxygen, sulfur and/or boron atoms. The silylamide compound is also robust as a ligand for the complexation of the positively charged REEs in both cathodic and anodic reactions, and provides a stable anode system. Sec EXAMPLES 3 and 4. Furthermore, the silylamide compound may not be susceptible to oxidation.
[0094] The method for electrometallizing one or more rare earth elements utilizing an anhydrous electrolyte comprising silylamide compound demonstrates a highly reversible stripping behavior and a stable cathodic performance. See EXAMPLE 2.
[0095] The purity of rare earth elements (e.g., Nd, Dy) achieved by the method for electrometallizing one or more rare earth elements utilizing an anhydrous electrolyte comprising silylamide compound is higher than the purity of rare earth elements (e.g., Nd, Dy) reported for the conventional methods using the fluorinated ionic liquid electrolyte or the borohydride-based electrolytes. See EXAMPLES 3-5.
[0096] The scale-up of the electrometallization of one or more rare earth elements utilizing an anhydrous electrolyte comprising silylamide compound confirms the selective and efficient electrodeposition of high-purity rare earth elements (e.g., Nd) with consistent performance across multiple batches. See EXAMPLE 4. The method may be used to generate over one gram of rare earth elements (e.g., Nd) with near-theoretical mass efficiency and minimal contamination. Structural and compositional analyses suggest a predominantly metallic character of the isolated electrodeposit (e.g., metallic Nd) with a surface oxidation likely occurring upon air exposure.
[0097] The method for electrometallizing one or more rare earth elements utilizing an anhydrous electrolyte comprising silylamide compound exhibits an electrorefining behavior. For example, as discussed in EXAMPLE 3, dysprosium (Dy) may be co-deposited with Nd during the electrodeposition of Nd from the anhydrous electrolyte comprising silylamide-Nd complex using a Dy sacrificial anode. Furthermore, the concentration of Nd in the anhydrous electrolyte comprising silylamide-Nd complex remains substantially unchanged throughout a prolonged electrodeposition operation (e.g., more than 200 hours). This dual capability (simultaneous anodic dissolution and cathodic recovery of rare earth metals) may enable a stable, long-duration electrodeposition without loss of active species. As a result, the anhydrous electrolyte comprising silylamide compound may allow for a sustainable and scalable REE electrodeposition, while preserving a solution homogeneity and REE (e.g., Nd) feedstock loading.
[0098] Furthermore, the method for electrometallizing one or more rare earth elements provides the electrodeposited REEs with an enhanced metal purity. Sec EXAMPLES 3-5. For example, the method may produce the electrodeposited REE at a purity of greater than about 90%, greater than about 95%, or greater than about 99%.
[0099] The transition to a clean energy economy depends on the development of sustainable, scalable, and environmentally responsible methods for rare earth element (REE) production. The conventional processes (e.g., a molten fluoride salt electrolysis) for electrometallizing rare earth elements are energy-intensive and chemically aggressive. They are commonly based on the use of fluorinated ionic liquids and/or borohydride complexes, and suffer from numerous limitations including corrosivity, ligand instability, narrow electrochemical windows, and complex or hazardous synthesis protocols. In contrast, the disclosed methods for electrometallizing rare earth elements utilize an anhydrous electrolyte comprising silylamide compound that is substantially free of oxygen- and fluorine-containing ligands. The silylamide compound used in the methods is non-toxic and lower in cost compared to the ionic liquid electrolyte used in the conventional methods. Furthermore, compared to the triflate-based ionic liquids and borohydride salts used in the conventional methods for electrometallizing rare earth elements, the silylamide-based electrolyte of the disclosure provides a more stable and tunable coordination environment that is well-suited for the REE electrochemistry under ambient and anhydrous conditions.
[0100] In addition, the disclosed methods enable a reduction of the production cost and the amount of generated hazardous waste, as compared to the conventional methods for electrometallizing rare earth elements. The disclosed methods also do not produce HF or rare earth fluoride salts, which are hazardous and expensive to dispose of. The disclosed methods may also use significantly less energy than the conventional methods.
[0101] The following examples serve to explain embodiments of the disclosure in more detail. These examples are not to be construed as being exhaustive, exclusive, or otherwise limiting as to the scope of the disclosure.
EXAMPLES
Example 1. Analysis of a Complex-Containing Anhydrous Electrolyte Comprising Silylamide-Nd Complex Using Visible and Near-Infrared (Vis-NIR) Spectrophotometer
[0102] The complex-containing anhydrous electrolytes comprising different concentrations of the silylamide-Nd complex were prepared as follows: lithium bis(trimethylsilyl)amide (Li-silylamide) was dissolved in an anhydrous tetrahydrofuran (THF) under extended stirring to provide an anhydrous solution, which was then filtered to provide an anhydrous electrolyte comprising lithium silylamide (Li-silylamide electrolyte) at a concentration of 0.4 molarity (M) in THF. The term molarity is defined as the number of moles of solute per liter of solution. A selected amount of an anhydrous powder of neodymium chloride (NdCl.sub.3) was added to the Li-silylamide electrolyte under stirring. The reaction between the neodymium chloride and the Li-silylamide electrolyte was allowed to take place for a few hours, resulting in a complex-containing anhydrous electrolyte comprising silylamide-Nd complex with negligible precipitation.
[0103] The Vis-NIR spectrum of the complex-containing anhydrous electrolyte was taken under an inert atmosphere, while being contained in a quartz cuvette that had been dried under argon flow. The Vis-NIR spectra were collected at a 0.5 nm resolution using a Shimadzu UV-3600 Plus spectrophotometer available from Shimadzu Corporation. First, the Vis-NIR spectrum of the anhydrous Li-silylamide electrolyte was taken and employed as a baseline (i.e., substantially free of the silylamide-Nd complex). Then, the Vis-NIR spectra of the complex-containing anhydrous electrolytes comprising different concentrations of the silylamide-Nd complex were taken.
[0104]
[0105] As shown in
Example 2. Voltametric Analysis of the Complex-Containing Anhydrous Electrolytes Comprising Silylamide-Nd Complex
[0106] A voltammetry study was carried out using a standard three-electrode configuration. A platinum disc having a 1.5 mm-diameter was used as a working electrode; a Nd/Dy rod was used as a counter electrode; and a platinum wire was used as a pseudo-reference electrode. The electrochemical analysis was performed using a potentiostat (a Bio-logic SP 150 electrochemical workstation commercially available from Bio-Logic USA, LLC.). The voltammetry experiments were conducted in a glovebox under argon atmosphere and ambient conditions (a temperature of 25 C. and 1 atm).
[0107] The cyclic voltammetry was initially performed using Li-silylamide in THF under Nd-free conditions at two concentrations of lithium ions (0.4 M and 1.0 M). Both electrolytes displayed chemically reversible Li plating and stripping processes, with a half-potential of approximately 3.3V vs. Fc.sup.+/Fc. Increasing the Li salt concentration did not have any substantial increase on the electron transfer kinetics nor on the magnitude of the voltametric currents. Quantitative analysis of the stripping peak revealed that nearly 90% of the plated Li was stripped upon reoxidation at a scan rate of 20 mV/s, indicating relatively high coulombic efficiency. The stripping charge increased with repeated cycling. This behavior was consistent with the Li deposition in solvated ionic liquids, where improved cycling stability was attributed to interfacial conditioning. Notably, the broader oxidation envelope observed in the reverse scan suggested partial reversibility. Additionally, the presence of three distinct anodic peaks about 2.6V, 2.1V, and 1.5V vs. Fc.sup.+/Fc) during stripping was likely indicative of LiPt alloy formation or co-deposition phenomena, reinforcing the importance of evaluating background contributions prior to Nd introduction.
[0108]
[0109] Initial introduction of small (10 mM) concentrations of NdCl.sub.3 into the Li-silylamide electrolyte led to significant alterations in voltametric traces. Upon Nd addition, the cathodic onset shifted positively by approximately 0.3V, significantly greater than the shift (about 0.2V) previously reported in Ca(BH.sub.4).sub.2 systems. More notably, the introduction of such small concentrations of Nd.sup.3+ resulted in faster electron transfer kinetics, featuring a sharp increase in voltametric currents. The magnitude of this current enhancement could not be attributed solely to changes in ionic strength (I=C.sub.iZ.sub.i.sup.2) of the electrolyte, which would drop the electrolyte Ohmic resistance. For instance, while the addition of 10 mM of NdCl.sub.3 increased the ionic strength from 0.4 to 0.49, this modest change produced a far greater kinetic impact than increasing the ionic strength from 0.4 to 1.0 in the Nd-free background electrolyte. This disproportionate response strongly suggested a dominant electrochemical contribution from Nd.sup.3+ species, beyond mere ionic strength effects.
[0110] As shown in
[0111]
[0112]
[0113] Analysis of stripping efficiency (SE %) as a function of cycle number, as shown in
[0114] While a modest decline in the striping efficiency was observed at higher Nd concentrations, this was attributed to stoichiometry-dependent speciation heterogeneity rather than intrinsic electrolyte degradation. These findings underscored the importance of ligand-to-metal ratios in controlling coordination dynamics and redox behavior in nitrogen-based systems.
Example 3. Electrodeposition of Nd from a Complex-Containing Anhydrous Electrolyte Comprising Silylamide-Nd Complex
[0115] To assess the viability of the silylamide electrolyte for rare earth metal electrodeposition, the electrodeposition experiments were performed under various controlled conditions.
[0116] The chronopotentiometric electrodeposition experiments were carried out using a standard three-electrode configuration. A platinum or copper plate with defined geometric surface area was used as the working electrode; a dysprosium (Dy) rod was used as a counter electrode; and a platinum wire was used as a pseudo-reference electrode. The electrochemical analysis was performed using a potentiostat (a Bio-logic SP 150 electrochemical workstation commercially available from Bio-Logic USA, LLC.). The chronopotentiometric experiments were conducted under inert atmosphere (e.g., argon atmosphere) and ambient conditions (a temperature of 25 C. and 1 atm).
[0117] Prior to starting the electrochemical experiments, the working electrode was cleaned by removing any electrolytes left on the surface of the working electrode with a low-lint, absorbent wipes (KIMWIPES delicate task wipes available from Kimberly-Clark Corporation). The wiped working electrode was placed in a 10% HNO.sub.3 solution (diluted from 70% HNO.sub.3 using 18 M H.sub.2O), where any deposited materials were allowed to dissolve completely. Thereafter, the working electrode was rinsed with 18 M H.sub.2O, rinsed with acetone, and dried under argon flow before being transferred into the glovebox. The counter electrode and the pseudo-reference electrode were cleaned by rinsing with acetone before drying under argon flow.
[0118] The chronopotentiometric experiments were conducted for both the Nd-free Li-silylamide electrolyte (Nd-free electrolyte) and the Nd-loaded electrolytes (the electrolytes comprising silylamide-Nd complex) to evaluate electrodeposition behavior and system stability. Key electrodeposition performance metrics, including Faradaic or mass efficiency (FE %), deposition rate (mA/cm.sup.2), and product purity (Nd %), were systematically determined to benchmark the effectiveness and selectivity of the silylamide-based system. Initial baseline experiments were conducted in Nd-free Li-silylamide electrolytes to establish the electrochemical robustness of the silylamide ligand. Dysprosium (Dy) metal was initially employed as a sacrificial anode to examine anodic dissolution under oxidative conditions, while distinguishing it from the main catholyte (Nd) feedstock.
[0119] A constant cathodic current density of 1 mA/cm.sup.2 was applied to the electrochemical cell comprising the Nd-free electrolyte. In the absence of Nd, the working electrode potential exhibited an initial cathodic value around 3.3V, which gradually stabilized around 3V over the course of deposition. This baseline experiment using the Nd-free system demonstrated that the silylamide ligand remained chemically stable even under strongly reducing cathodic conditions. The observed metallic, silvery deposit on the working electrode surface oxidized rapidly upon air exposure to forming a white film, strongly indicative of effective electrodeposition of the elemental lithium metal. Inductively coupled plasma mass spectrometry (ICP-MS) confirmed the high purity of Li in the deposit. These results affirmed the ability of the silylamide system to support Li metal plating without undergoing ligand degradation, thus confirming the electrolyte's high electrochemical and chemical stability.
[0120] The anhydrous electrolyte comprising silylamide-Nd complex used in the chronopotentiometric experiments was obtained by loading the 0.4 M Li-silylamide/THF electrolyte with 0.25 M Nd.sup.3+ using the similar synthesis as described in EXAMPLE 1. The anhydrous electrolyte had a water content of less than 8-12 ppm.
[0121] The anhydrous electrolyte comprising the silylamide-Nd complex was placed in an electrochemical cell similar to the electrochemical system 200 shown in
[0122]
[0123] As shown in
[0124] Upon passing a total charge of about 200 C during the 20-hour chronopotentiometric deposition of Nd from the Nd-free electrolyte, a thick black dendritic deposit formed on the platinum cathode that was clearly distinct from the silvery appearance of metallic lithium deposits obtained from the Nd-free electrolyte. As an initial qualitative and visual assessment of the chemical stability, the electrodeposited material was thoroughly rinsed to remove the residual electrolyte and then transferred from inert atmosphere to ambient air. The deposit rapidly changed color from dark black to white within seconds of air exposure, indicating high susceptibility to oxidation. This reactivity with atmospheric oxygen was characteristics of zero-valent rare earth metals, supporting the presence of metallic Nd in the deposit.
[0125] At the end of the chronopotentiometric deposition experiments, the electrodeposit formed on the working electrode was removed from the working electrode, and rinsed three times with anhydrous acetone. The rinsed deposit was dissolved in an anhydrous THF to provide an anhydrous THE solution, which was then centrifuged at a speed of about 10,000 rpm for about 5-10 minutes under an inert atmosphere to provide an isolated deposit.
[0126] TABLE 1 shows the energy-dispersive X-ray spectroscopy (EDS) analysis results showing the percentage by weight of the elements in the electrodeposit before and after rinsing the electrodeposit with anhydrous acetone. More than 93% by weight of the electrodeposit was Nd metal obtained by the electrometallization of Nd as described above.
TABLE-US-00001 TABLE 1 Weight, % Before Rinsing the After Rinsing the Element Electrodeposit Electrodeposit Carbon 5.19 1.56 Nitrogen 0.58 0.17 Oxygen 19.66 2.78 Fluorine 0.00 0.01 Silicon 0.73 0.07 Chlorine 6.96 1.90 Neodynium 65.13 93.38 Dysprosium 1.74 0.12
[0127] TABLE 2 shows the electrometallization of Nd described above at different electrical current levels and processing times.
TABLE-US-00002 TABLE 2 Amount of Anhydrous Concentration Electrolyte of Nd.sup.3+ in the comprising Amount of Nd-containing Li-silylamide Time Nd obtained compound compound Current Period per charge 250 mM 15 mL 1 mA 22 hours 36 mg/80 C (about 0.45 mg/C) 250 mM 15 mL 3.5 mA 20 hours 53 mg/265 C (about 0.2 mg/C) 250 mM 15 mL 3.5 mA 43 hours 125 mg/460 C (about 0.3 mg/C)
[0128] TABLE 3 shows the mass efficiency of the electrometallization of Nd at the electrical current of about 5 mA.
TABLE-US-00003 TABLE 3 Amount of Nd obtained Charge Mass Efficiency Batch (mg) (C) (mg/C) #1 300 850 0.35 #2 400 1030 0.38 #3 381 805 0.47 Total 1064 2690 0.40
[0129]
[0130]
[0131] The EDS mapping confirmed that the isolated deposit contained a high Nd content (more than about 90%), alongside minor oxygen (about 3%) that was likely introduced during air exposure, and trace levels of organic contamination from residual electrolyte. The subsurface analysis via FIB cross-sectioning revealed a marked reduction in oxygen content to approximately 0.65% within the bulk of the isolated deposit, confirming that oxidation (likely from oxygen in the FIB chamber) was predominantly limited to the surface. Complementary inductively coupled plasma (ICP) analysis of the bulk elemental composition, combined with the total charge passed, indicated a Faradaic efficiency exceeding 90%. These results confirmed the efficient electrodeposition of high-purity Nd and underscored the critical role of inert handling in preserving the metallic integrity of rare earth deposits.
[0132] Remarkably, the FIB-EDS analysis revealed a significant presence of Dy (more than 8.5%) within the isolated deposit, confirming successful electrorefining from the Dy sacrificial anode. This demonstrated not only the feasibility of Dy oxidative stripping into the electrolyte comprising silylamide compound, but also its subsequent co-deposition with Nd at the cathode. Such efficient anodic dissolution and cathodic incorporation underscored the broad electrochemical window and exceptional redox stability of the electrolyte comprising silylamide compound. Unlike the conventional borohydride system with a short anodic window, the electrolyte comprising silylamide compound simultaneously supported anodic oxidation of a Dy metal source and cathodic deposition of Nd.sup.3+ with high selectivity and appreciable deposition rates.
Example 4. Scalability of the Electrometallization of Nd from an Anhydrous Electrolyte Comprising Silylamide-Nd Complex
[0133] The scalability of the electrometallization of Nd from an anhydrous electrolyte comprising silylamide-Nd complex was tested under gram-scale electrodeposition conditions to assess its performance at preparative scale.
[0134] The chronopotentiometric electrodeposition experiments were carried out using the same protocol as described in EXAMPLE 3, except that a neodymium (Nd) rod was used as a sacrificial anode for a homogenous REE electrorefining and an increased Nd purity in the obtained deposits. Furthermore, this experimental design ensured accurate evaluation of mass efficiency, deposit purity, and electrochemical stability of the anhydrous electrolyte comprising silylamide-Nd complex.
[0135] To evaluate the preparative-scale applicability of the electrolyte comprising silylamide compound, gram-scale electrodeposition experiments were conducted in three consecutive batches, allowing for a systematic assessment of deposition performance under sustained galvanostatic conditions. Achieving gram-scale production necessitated a tenfold increase in deposition duration (from an initial 20-hour electrodeposition operation to more than 200-hour electrodeposition operation), highlighting the importance of long-term electrolyte stability. Based on theoretical calculations and assuming near 100% Faradaic efficiency, producing one (1) gram of Nd required a cumulative charge input of over 2000 C. Accordingly, scaled experiments employed an average current density of 1.5 mA/cm.sup.2 and were conducted in an inert, hermetically sealed electrochemical cell to reduce solvent evaporation and product contamination over the extended electrodeposition operation.
[0136]
[0137] In Batch 1, a current density of 2 mA/cm.sup.2 was applied for over 40-hours. The Nd sacrificial anode maintained a stable potential near 0V, while the cathode potential exhibited a slight decay over time, averaging around 3.5V. This yielded a relatively stable overall cell potential (E.sub.cell) of approximately 3.5V. The consistent anode behavior and modest cathodic drift reflected efficient anodic dissolution of Nd and the initial robustness of the electrolyte system under applied electrochemical conditions.
[0138] For Batch 2, the applied current density was reduced to 1 mA/cm.sup.2 and the deposition extended to about 90-hours. Under these conditions, the E.sub.cell decreased to about 2.5V, with the sacrificial Nd anode potential stabilizing at approximately 0.5V and the cathode potential averaging 3.0V. Again, the cathode potential displayed a gradual decay over time, although less pronounced than in the following batch. The lower operating voltage at reduced current density suggested an enhanced energy efficiency and an improved electrochemical balance under less aggressive rate conditions.
[0139] In Batch 3, the current density was maintained at 1 mA/cm.sup.2. While the Nd anode continued to exhibit stable behavior around 0.5V, the cathode potential underwent a more substantial decline toward the end of the electrolysis. This growing cathodic polarization likely reflected a progressive increase in electrolyte resistance during prolonged deposition. A plausible contributing factor was the gradual depletion or partial co-deposition of lithium ions alongside Nd, which could reduce ionic conductivity and contribute to voltage drift.
[0140] The key performance metrics from the scale-up electrometallization of Nd from the anhydrous electrolyte comprising silylamide-Nd complex are summarized in TABLE 4.
TABLE-US-00004 TABLE 4 Current Mass Nd Metal % Nd Bulk Purity Batch Density Time Charge Deposit Efficiency Purity % (vs. C, N, O, [Nd.sup.3+] = 0.25M (mA/cm.sup.2) (Hrs.) (C) Mass (mg) (mg/C) (vs. Li) Si, B, F, Cl) Batch 1 2 46 838 291 0.35 95 91.4 Batch 2 1 95 1035 392 0.38 93.6 93.8 Batch 3 1 74 805 381 0.47 92.6 91.8 Total/Average 1.5 215 2678 1064 0.4 0.94 92.3
[0141] A consistent performance across all three batches emphasized the reproducibility and robustness of the silylamide-based electrolyte system. Using the applied current densities (from about 1 mA/cm.sup.2 to about 2 mA/cm.sup.2), a total charge of 2678 C was transferred and a cumulative deposited mass of 1064 mg was obtained. The average mass efficiency was 0.40 mg/C, approaching the theoretical value of about 0.45 mg/C for Nd deposition, with Batch 3 achieving the highest experimental efficiency of 0.47 mg/C.
[0142] Elemental analysis of the deposits reinforced the selectivity and effectiveness of the system. The average Nd metal purity (Nd/(Nd+Li)) reached 93.4%, with Batch 1 exhibiting the highest value at 95%, reflecting favorable deposition conditions and minimal co-deposition. The total bulk purity, excluding minor contributions from electrolyte elements (C, N, O, Si, B, F, and Cl), remained high, averaging 92.3%, with Batch 2 yielding the highest at 93.8%. These values confirmed minimal contamination from electrolyte-derived species and demonstrated the chemical compatibility of the silylamide-based electrolyte system under the scale-up deposition conditions.
[0143] Interestingly, ICP analysis of the post-electrolysis electrolyte revealed that the Nd concentration remained nearly unchanged from its initial value (about 0.25 M), despite extended electrodeposition over multiple batches. This observation provided strong evidence for the system's capability to support electrorefining, wherein anodic dissolution and cathodic deposition of Nd occurred in a balanced and sustained manner, maintaining a consistent Nd.sup.3+ concentration throughout the process. This behavior reflected not only the electrochemical reversibility of the system but also its chemical stability during prolonged operation.
[0144]
[0145]
[0146] The X-ray diffraction (XRD) analysis was employed to gain structural insight into the electrodeposited material. As shown in
[0147] The analysis results shown in
[0148] Taken together, these findings demonstrate that the anhydrous electrolyte comprising silylamide compound supported sustained, selective, and high-yield electrodeposition of rare earth metals (e.g., metallic Nd) at preparative scales. The system exhibited remarkable electrochemical stability, high product purity, and near-theoretical mass efficiency, therefore supporting its potential use for rare earth recovery and refining.
Example 5. Electrometallization of Dysprosium (Dy) from an Anhydrous Electrolyte Comprising a Silylamide-Dy Complex
[0149] A dysprosium (Dy)-containing compound and an anhydrous electrolyte comprising a silylamide compound were combined to provide an anhydrous electrolyte comprising silylamide-Dy complex. The obtained anhydrous electrolyte had a water content of less than 8-12 ppm. The anhydrous electrolyte comprising silylamide-Dy complex was placed in an electrochemical cell similar to the electrochemical system 200 shown in
[0150] After the chronopotentiometric electrodeposition experiments using the protocol as described in EXAMPLE 3, the isolated electrodeposits were subjected to the SEM-FIB analysis to evaluate their morphology characteristics. The isolated electrodeposits were also analyzed by the energy-dispersive X-ray spectroscopy (EDS) to determine the contents therein. TABLE 5 shows the EDS analysis results of the isolated electrodeposits.
TABLE-US-00005 TABLE 5 Weight, % Element Experiment #1 Experiment #2 Carbon 1.07 1.07 Nitrogen 0.24 0.24 Oxygen 2.33 2.30 Fluorine 0.27 0.25 Silicon 0.51 0.50 Chlorine 1.48 1.27 Neodynium 0.94 0.24 Dysprosium 93.16 94.11
[0151] As shown in TABLE 5, the electrometallization of dysprosium (Dy) from the anhydrous electrolyte comprising a silylamide-Dy compound provided the isolated electrodeposits comprising the metallic Dy of greater than 93% purity.
[0152] The embodiments of the disclosure described above and illustrated in the accompanying drawings do not limit the scope of the disclosure, which is encompassed by the scope of the appended claims and their legal equivalents. Any equivalent embodiments are within the scope of this disclosure. Indeed, various modifications of the disclosure, in addition to those shown and described herein, such as alternate useful combinations of the elements described, will become apparent to those skilled in the art from the description. Such modifications and embodiments also fall within the scope of the appended claims and equivalents.