CHEMICALLY FACILITATED ELECTROCHEMICAL METHODS FOR RECOVERY OF RARE EARTH ELEMENTS

Abstract

A method for recovery of rare earth elements includes forming a rare earth containing ionic solution comprising an ionic liquid and a solvent having one or more rare earth elements dissolved therein. The method also includes adding a polar protic solvent to the rare earth containing ionic solution, and applying an electrical potential across the rare earth containing ionic solution. The method further includes collecting a deposit of at least one rare earth element on at least one electrode disposed in the rare earth containing ionic solution, and recovering the deposit of at least one rare earth element from the at least one electrode. Additional methods for recovery of rare earth elements are disclosed.

Claims

1. A method for recovery of rare earth elements comprising: forming a rare earth containing ionic solution comprising an ionic liquid and a solvent having one or more rare earth elements dissolved therein; adding a polar protic solvent to the rare earth containing ionic solution; applying an electrical potential across the rare earth containing ionic solution; collecting a deposit of at least one rare earth element on at least one electrode disposed in the rare earth containing ionic solution; and recovering the deposit of the at least one rare earth element from the at least one electrode.

2. The method of claim 1, wherein adding the polar protic solvent to the rare earth containing ionic solution comprises creating a metal species coordination environment therein.

3. The method of claim 2, wherein adding the polar protic solvent to the rare earth containing ionic solution comprises creating a metal species coordination environment therein which facilitates reduction of the one or more of rare earth metal complexes via a single step reduction pathway.

4. The method of claim 2, wherein creating the metal species coordination environment in the rare earth containing ionic solution comprises facilitating partitioning of rare earth metal complexes in the rare earth containing ionic solution.

5. The method of claim 4, wherein creating the metal species coordination environment comprises facilitating reduction of the rare earth metal complexes via a single step reduction pathway.

6. The method of claim 1, wherein adding the polar protic solvent to the rare earth containing ionic solution comprises adding the polar protic solvent to the rare earth containing ionic solution at a concentration ratio of about 1:2 polar protic solvent:rare earth elements.

7. The method of claim 1, wherein adding the polar protic solvent to the rare earth containing ionic solution comprises adding water to the rare earth containing ionic solution.

8. The method of claim 6, wherein adding the polar protic solvent to the rare earth containing ionic solution comprises adding water to the rare earth containing ionic solution.

9. The method of claim 1, wherein forming the rare earth containing ionic solution comprising the ionic liquid and the solvent having one or more rare earth elements dissolved therein comprises forming the rare earth containing ionic solution having from about 10 mM to about 500 mM of the rare earth elements.

10. The method of claim 1, wherein forming the rare earth containing ionic solution comprising the ionic liquid and the solvent having one or more rare earth elements dissolved therein comprises forming the rare earth containing ionic solution comprising the ionic liquid having the following chemical formula: ##STR00003## wherein, R1 is selected from the group of a pyrrolidinium ion (C.sub.4H.sub.10N.sup.+), an N-pyrrolidinium ion, an N-phenyl ion, and an N-N phenyl ion; R2 is selected from the group of cyanide, carboxyl, hydrogen, a hydrocarbon group containing at least 1 carbon atom and up to 12 carbon atoms, a difluoromethanesulfonamide ion, a perfluorobutanesulfonic acid ion, and, an n-methylsulfonyl ion; and, R3 is selected from the group of cyanide, carboxyl, hydrogen, and a hydrocarbon group containing at least 1 carbon atom and up to 12 carbon atoms, and an n-methylsulfonyl ion.

11. The method of claim 1, wherein forming the rare earth containing ionic solution comprising the ionic liquid and the solvent having one or more rare earth elements dissolved therein comprises forming the rare earth containing ionic solution comprising the ionic liquid including one or more of 1-butyl-1-methylpyrrolidinium triflate (BMPyOTf), 1-butyl-1-methylpyrrolidinium bistriflimide (BMPyNTf.sub.2), bistriflimide pyrrolidinium, imidazolium, piperidinium, 6, 6, 7, 7, 8, 8, 8-heptafluoro-2, 2-dimethyl-3, 5-octanedione, hexafluoroacetylacetone, 1, 1, 5, 5, 6, 6, 6-octafluoro-2, 4-hexanedione, 1, 1, 1-trifluoro-2, 4-pentanedione, 1, 1, 1-trifluoro-5, 5-dimethyl-2, 4-hexanedione, 4, 4, 4-trifluoro-1-phenyl-1, 3-butanedione, or a phosphonium-based ionic liquid.

12. The method of claim 1, wherein forming the rare earth containing ionic solution comprising the ionic liquid and the solvent having one or more rare earth elements dissolved therein comprises forming the rare earth containing ionic solution comprising one or more of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium.

13. The method of claim 1, wherein applying the electrical potential across the rare earth containing ionic solution comprises applying the electrical potential of from about +1.0V to about 4.0V across the rare earth containing ionic solution.

14. The method of claim 1, wherein applying the electrical potential across the rare earth containing ionic solution comprises applying the electrical potential across the rare earth containing ionic solution containing at a temperature of from about 20 Celsius to about 25 Celsius.

15. The method of claim 1, wherein applying the electrical potential across the rare earth containing ionic solution comprises applying the electrical potential across the rare earth containing ionic solution in an inert atmosphere.

16. A method for recovery of rare earth elements comprising: dissolving one or more rare earth elements from one or more rare earth containing components into a solvent; combining an ionic liquid with the solvent containing the one or more rare earth elements to form a rare earth containing ionic solution; adding a polar protic solvent to the rare earth containing ionic solution; applying an electrical potential across at least two electrodes operatively positioned in the rare earth containing ionic solution; collecting a deposit of at least one rare earth element on at least one of the at least two electrodes; and recovering the deposit of the at least one rare earth element from the at least one of the least two electrodes.

17. The method of claim 16, wherein adding a polar protic solvent to the rare earth containing ionic solution comprises combining from about 0.5 percent to about 30 percent by volume of the solvent containing the one or more of rare earth relative to the volume of the ionic liquid.

18. The method of claim 16, wherein dissolving one or more rare earth elements from one or more rare earth containing components into a solvent comprises dissolving the one or more rare earth elements into the solvent comprising propylene carbonate, dimethyl formamide, dimethyl sulfoxide (DMSO), trimethyl phosphate, a sulfonate, acetonitrile, acetic acid, ammonia, bistriflimide acid, or combinations thereof.

19. The method of claim 16, wherein applying the electrical potential across the at least two electrodes operatively positioned in the rare earth containing ionic solution comprises forming a current density of from about 0.5 mA/cm.sup.2 to about 5 mA/cm.sup.2 at the at least two electrodes.

20. A method for recovery of rare earth elements from rare earth containing materials comprising: separating rare earth containing components from a rare earth containing material; drying the rare earth containing components to reduce a water content therein to below about 5 percent by weight; dissolving the dried rare earth containing components in a solvent to a rare earth element concentration of from about 10 mM to about 500 mM in the solvent; combining an ionic liquid with the solvent containing the rare earth elements to form a rare earth containing ionic solution, the solvent comprising from about 0.5 percent to about 30percent of a total amount of the ionic liquid by volume; adding a polar protic solvent to the rare earth containing ionic solution, wherein the polar protic solvent is added to a concentration of about 50 percent of the concentration of the rare earth elements in the rare earth containing ionic solution; applying an electrical potential of from about +1.0V to about 4.0V across at least one anode and at least one cathode operatively positioned in the rare earth containing ionic solution in an electrochemical cell; collecting a deposit of at least one rare earth element on the at least the one cathode; and recovering the deposit of the at least one rare earth element from the at least one cathode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The applications and advantages of one or more embodiments of the disclosure will be apparent to one of ordinary skill in the art from the summary and detailed description in conjunction with the appended drawings.

[0010] FIG. 1 is a flow diagram of a method to recover one or more rare earth elements, in accordance with embodiments of the disclosure.

[0011] FIG. 2 is a simplified schematic illustration of a system for recovering one or more rare earth elements, in accordance with embodiments of the disclosure.

[0012] FIG. 3 presents cyclic voltammetry traces of a 100 mM dysprosium triflate (Dy(OTf).sub.3) complex in a pyrrolidinium triflate (BMPyOTf) ionic liquid at water concentrations of 35 ppm and 200 pmm, in accordance with embodiments of the disclosure.

[0013] FIG. 4 presents cyclic voltammetry traces of a 100 mM dysprosium triflate (Dy(OTf).sub.3) complex in a pyrrolidinium triflate (BMPyOTf) ionic liquid at water concentrations ranging from 35 ppm to 3,500 ppm, in accordance with embodiments of the disclosure.

[0014] FIG. 5 presents linear sweep voltammetry traces of 20 mM, 50 mM, and 100 mM dysprosium triflate (Dy(OTf).sub.3) complex in a pyrrolidinium triflate (BMPyOTf) at a water concentration of 500 ppm, in accordance with embodiments of the disclosure.

[0015] FIG. 6 is a graph showing faradaic efficiency and chronoamperometric current densities of 100 mM dysprosium triflate (Dy(OTf).sub.3) complex in a pyrrolidinium triflate (BMPyOTf) at different water concentrations, in accordance with embodiments of the disclosure.

[0016] FIG. 7 is a scanning electron microscope (SEM) image of electrodeposited dysprosium on a copper electrode obtained from a solution comprising Dy(OTf).sub.3 in BMPyOTf at a water concentration of 500 ppm, in accordance with embodiments of the disclosure.

[0017] FIG. 8 is a scanning electron microscope (SEM) image of electrodeposited dysprosium on a copper electrode obtained from a solution comprising Dy(OTf).sub.3 in BMPyOTf at a water concentration of 3,500 ppm, in accordance with embodiments of the disclosure.

DETAILED DESCRIPTION

[0018] 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.

[0019] 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.

[0020] It will be readily understood that the components of the embodiments as generally 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.

[0021] 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.

[0022] 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.

[0023] As used herein, rare earth elements (REEs) include 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). As used herein, rare earth elements or REEs also includes any molecule, ion, complex, compound, or salt that includes one or more of the foregoing elements.

[0024] As used herein, rare earth containing components (RECCs) include but are not limited to rare earth salts, rare earth oxides, rare earth nitrates, rare earth chlorides, rare earth triflates (e.g., trifluoromethanesulfanone), rare earth carbonates, rare earth bistriflimides, rare earth metal complexes (e.g., a rare earth element complexed with a ligand), or combinations thereof.

[0025] As used herein rare earth containing materials include but are not limited to naturally occurring ores comprising rare earth containing components as well as industrial and consumer products that include rare earth containing components which may be recycled to recover REEs, such as, by way of example only, rare earth containing magnets, light emitting diodes, end-of-life consumer electronics and microelectronics (e.g., shredded circuit boards, capacitors, sensors, etc.), windmills and hydroelectric turbines, electric vehicle traction motors, batteries, rare earth containing ceramic materials, optical devices, solid oxide fuel cells, and phosphors such as are commonly found in fluorescent lamps.

[0026] Recovery of rare earth elements from rare earth containing materials has been proposed as an alternative to current high-cost and hazardous rare earth element production processes. To enable recovery, the rare earth containing components are separated from the rare earth containing materials and the REEs are recovered for use in future products and/or manufacturing processes.

[0027] A chemically facilitated electrochemical method for recovery of REEs from RECCs in low temperature ionic liquids is disclosed. The facilitated electrochemical method enables the recovery of REEs through the use of an electrochemical cell including at least a working electrode and a counter-electrode in a rare earth containing ionic solution, and an electrical potential applied across the electrodes of the electrochemical cell. One or more polar protic solvents (e.g., water) may be added to the rare earth containing ionic solution to form a metal species coordination environment therein. Coordinating ligands may act as electron donors or electron withdrawers (e.g., Lewis acids or bases), which impact the kinetics and thermodynamics of electron transfer for metal conversion.

[0028] Although the metal species coordination environment provides easier thermodynamics, faster kinetics, higher efficiency, and a suitable interface for recovery of REEs, these advantages are balanced against limiting factors caused by the polar protic solvent, such as metal instability, limited purity, hydrogen evolution, and a limited robustness of the production process. The embodiments disclosed herein encompass advantageous methods, systems and parameters for recovery of REEs.

[0029] Referring to FIG. 1, a method for recovery of rare earth elements 100 in accordance with some embodiments of the disclosure includes separating RECCs from rare earth containing materials 110. Non-limiting examples of rare earth containing materials, as described above, include naturally occurring ores comprising rare earth containing components as well as industrial and consumer products containing REEs which may be recycled to recover REEs, such as, rare earth containing magnets, light emitting diodes, end-of-life consumer electronics and microelectronics (e.g., shredded circuit boards, capacitors, sensors, etc.), windmills and hydroelectric turbines, electric vehicle traction motors, batteries, rare earth containing ceramic materials, optical devices, solid oxide fuel cells, and phosphors present in fluorescent lamps.

[0030] The method recovering rare earth elements 100 includes drying the rare earth containing components 120. For example, a dryer (e.g., furnace, evaporator, vacuum dryer, etc.) may be used to dry the RECCs. By way of example, in a vacuum dryer, the RECCs may be heated for from about 4 to about 10 hours at from about 80 C. to about 100 C. In other embodiments, the RECCs may be dried to a predetermined water concentration. The RECCs may be dried to a predetermined water concentration of less than about 5 percent by volume, such as less than about 1 percent by volume, less than about 0.5 percent by volume, or less than about 0.1 percent by volume, such as may be measured directly or indirectly (e.g., via chromatography, thermogravimetric analysis, Karl-Fisher analysis, etc.). This allows for the subsequent determination of relative amounts of ionic liquids, solvents and polar protic solvents to be added to the dried RECCs to form a rare earth containing ionic solution, as described in further detail below.

[0031] The method for recovery of rare earth elements 100 in accordance with embodiments of the present disclosure also includes dissolving the dried RECCs in a solvent 130, as shown in FIG. 1. For example, the RECCs may be dissolved in a solvent including, but not limited to, propylene carbonate, dimethyl formamide, dimethyl sulfoxide (DMSO), trimethyl phosphate, sulfonates, acetonitrile, acetic acid, ammonia, bistriflimide acid, or combinations thereof. The amount of solvent used to dissolve the RECCs depends on several factors including the mass of RECCs to be dissolved and the presence, or lack thereof, of non-rare earth containing materials present in the RECCs. In at least some embodiments, the solvent acts as an oxidizing agent to begin the oxidation of the REEs present in the RECCs.

[0032] With reference again to FIG. 1, the method for recovery of rare earth elements 100 further includes forming a rare earth containing ionic solution 140. In some embodiments, forming the rare earth containing ionic solution 140 includes combining one or more ionic liquids with the solvent having the rare earth components dissolved therein. At least one ionic liquid may comprise a non-aqueous ionic liquid. In other embodiments, forming the rare earth containing ionic solution 140 includes combining a predetermined amount of ionic liquid with a predetermined amount of the solvent containing the rare earth components dissolved therein. For example, the predetermined amount of the ionic liquids may comprise about 99.5% by volume of the total volume of the rare earth containing ionic solution, or about 95% by volume of the total volume of the rare earth containing ionic solution, or about 90% by volume of the total volume of the rare earth containing ionic solution, or about 80% by volume of the total volume of the rare earth containing ionic solution, or about 70% by volume of the total volume of the rare earth containing ionic solution. Stated otherwise, the rare earth containing ionic solution comprises from about 0.5% by volume to about 30% by volume of the solvent containing the rare earth components and about 70% to about 99.5% by volume of the one or more ionic liquids.

[0033] The ionic liquids utilized in accordance with embodiments of the method for recovery of rare earth elements 100 may exhibit high diffusivity and metal loading capacity, with a wide electrochemical window (EW) and a low vapor pressure. The ionic liquids may include, but are not limited to, non-aqueous ionic liquids, neutral ligand ionic liquids, REE beta-diketones, phosphonated derivatized ligand complexes, or combinations thereof. In some embodiments, the ionic liquid has the following chemical formula:

##STR00001##

where R.sub.1 is selected from the group of a pyrrolidinium ion (C.sub.4H.sub.10N.sup.+), an N-pyrrolidinium ion, an N-phenyl ion, and an N-N phenyl ion; R.sub.2 is selected from the group of cyanide, carboxyl, hydrogen, hydrocarbon groups containing at least 1 and up to 12 carbon atoms, a triflate anion (OTf).sup..sub.3, a difluoromethanesulfonamide ion, a perfluorobutanesulfonic acid ion, and an n-methylsulfonyl ion; and, R.sub.3 is selected from the group of cyanide, carboxyl, hydrogen, and hydrocarbon groups containing at least 1 and up to 12 carbon atoms, a triflate anion, and an n-methylsulfonyl ion.

[0034] In some embodiments, the ionic liquid has the following chemical formula:

##STR00002##

where, R.sub.2 is selected from the group of cyanide, carboxyl, hydrogen, hydrocarbon groups containing at least 1 and up to 12 carbon atoms, a triflate anion (OTf).sup..sub.3, and a triflimide anion; and, R.sub.3 is selected from the group of cyanide, carboxyl, hydrogen, and hydrocarbon groups containing at least 1 and up to 12 carbon atoms, a triflate anion, dicyanamide anion, and a triflimide anion.

[0035] In other embodiments, the ionic liquid includes one or more of 1-butyl-1-methylpyrrolidinium triflate (BMPyOTf), 1-butyl-1-methylpyrrolidinium bistriflimide (BMPyNTf.sub.2), bistriflimide pyrrolidinium, imidazolium, piperidinium, 6, 6, 7, 7, 8, 8, 8-heptafluoro-2, 2-dimethyl-3, 5-octanedione, hexafluoroacetylacetone, 1, 1, 5, 5, 6, 6, 6-octafluoro-2, 4-hexanedione, 1, 1, 1-trifluoro-2, 4-pentanedione, 1, 1, 1-trifluoro-5, 5-dimethyl-2, 4-hexanedione, 4, 4, 4-trifluoro-1-phenyl-1, 3-butanedione, or a phosphonium-based (e.g., phosphonium NTf.sub.2-based) ionic liquid.

[0036] The viscosity of the rare earth containing ionic solution may range from about 90 cP to about 150 cP at ambient operating conditions (e.g., approximately atmospheric pressure at a temperature of from about 20 Celsius to about 25 Celsius). The concentration of rare earth elements (e.g., in the form of Dy(OTf).sub.3) in the rare earth containing ionic solution (e.g., BMPyOTf in solvent) may range from about 10 mM to about 500 mM. In some embodiments, the concentration of the rare earth elements within the rare earth containing ionic solution may range from about 20 mM to about 300 mM. In other embodiments, the concentration of the rare earth elements within the rare earth containing ionic solution may range from about 50 mM to about 100 mM.

[0037] The method for recovery of rare earth elements 100 in accordance with embodiments of the disclosure also includes adding an amount of a polar protic solvent to the rare earth containing ionic solution 150, as shown in FIG. 1. In some embodiments, adding an amount of a polar protic solvent to the rare earth containing ionic solution 150 includes adding multiple polar protic solvents to the rare earth containing ionic solution, and in yet further embodiments, adding an amount of a polar protic solvent to the rare earth containing ionic solution 150 includes adding a predetermined amount of one or more polar protic solvents to the rare earth containing ionic solution. The predetermined amount of the polar protic solvent may be such that the amount of polar protic solvent relative to the amount of rare earth elements present in the rare earth containing components in the rare earth containing ionic solution is in a ratio of from about 1:1 to about 1:5, or in ratio of from about 1:1.5 to about 1:3, or in a ratio of about 1:2 polar protic solvent to rare earth elements. By way of example, the predetermined amount of the one or more polar protic solvents may include an amount which results in a concentration of the polar protic solvent in the rare earth containing ionic solution of about 3,500 ppm, or about 1,000 ppm, or about 500 ppm, or about 200 ppm, or about 35 ppm. The polar protic solvent may include, but is not limited to, water, an alcohol (e.g., methanol, ethanol, etc.), ammonia, acetic acid, or combinations thereof. In some embodiments, the polar protic solvent is water.

[0038] The addition of the polar protic solvent to the rare earth containing ionic solution facilitates the formation of a metal species coordination environment therein, where the rare earth elements are partitioned between water-coordinated and ionic liquid (IL)-coordinated speciation (i.e., the metal species coordination environment facilitates partitioning of the rare earth metal complexes in the rare earth containing ionic solution). The metal species coordination environment affects the solubility and diffusion of the metal species, as well as a charge or electron delocalization. The diffusion coefficients governing the metal species coordination environment are discussed in the Examples presented below. Specifically, the formation of the metal species coordination environment results in a shift in the reduction mechanism of rare earth metal complexes from a consecutive (1+2e) pathway to a single step (3e) pathway. Further, this shift allows for the reduction of the rare earth metal complexes to be conducted at more positive electrical potentials and reduced current densities.

[0039] In some embodiments, the metal species coordination environment in the rare earth containing ionic solution is formed by [Dy(III)(NTf.sub.2).sub.5].sup.2 complexes in an NTf.sub.2-based ionic liquid. In other embodiments, the metal species coordination environment in the rare earth containing ionic solution is formed by dysprosium triflate (Dy(OTf).sub.3) complexes in a pyrrolidinium triflate (BMPyOTf) ionic liquid.

[0040] With reference once again to FIG. 1, the method for recovery of rare earth elements 100 also includes applying an electrical potential across at least two electrodes operatively positioned in an amount of the rare earth containing ionic solution in an electrochemical cell 160. The electrical current flowing between the electrodes and through the rare earth containing ionic solution provides a supply of electrons from at least one of the electrodes to the anions in the rare earth containing ionic solution, facilitating the reduction of the rare earth metal complexes present therein, as discussed below. In some embodiments, the electrodes include at least a working electrode (e.g., an anode) and a counter-electrode (e.g., a cathode), and applying the electrical potential across the at least two electrodes operatively positioned in the amount of the rare earth containing ionic solution in an electrochemical cell 160 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.

[0041] In some embodiments, applying an electrical potential across at least two electrodes operatively positioned in an amount of the rare earth containing ionic solution in an electrochemical cell 160 is performed at a low temperature. For example, applying an electrical potential across at least two electrodes operatively positioned in an amount of the rare earth containing ionic solution in an electrochemical cell 160 may be performed at a rare earth ionic solution temperature ranging from about 15 Celsius to about 150 Celsius, such as from about 20 Celsius to about 125 Celsius or from about 25 Celsius to about 100 Celsius. In accordance with some embodiments, applying an electrical potential across at least two electrodes operatively positioned in an amount of the rare earth containing ionic solution in an electrochemical cell 160 is performed under ambient conditions (e.g., approximately atmospheric pressure at a temperature of from about 20 Celsius to about 25 Celsius).

[0042] Further, applying an electrical potential across at least two electrodes operatively positioned in an amount of the rare earth containing ionic solution in an electrochemical cell 160 in some embodiments is performed in an inert environment that includes less than about 10 ppm H.sub.2O and less than about 1 ppm O.sub.2. In some embodiments, an inert gas (e.g., argon) may be disposed over the rare earth containing ionic solution, to create the inert environment.

[0043] With continued reference to FIG. 1, the method for recovery of rare earth elements 100 further comprises reducing the rare earth metal complexes in the rare earth containing ionic solution 170. The reduction reactions of the rare earth metal complexes in the rare earth containing ionic solution are facilitated by the electrical potential applied across the electrodes in the rare earth containing ionic solution, as described above. More particularly, the current between the electrodes provides a supply of electrons to the anions in the rare earth containing ionic solution which facilitates reduction of the rare earth metal complexes present therein into the REEs. Due to the increasing number of electrons, the positively charged REEs in the metal species coordination environment of the rare earth containing ionic solution are driven towards the negatively charged working electrode, and are ultimately deposited on the working electrode through an electrodeposition process. In at least some embodiments, the reduction reaction may be reversed by reversing the potential to arrive at the products of the oxidation reaction.

[0044] The method for recovery of rare earth elements 100 further comprises collecting a deposit of at least one rare earth element on at least one of the electrodes 180 which are operatively positioned in the rare earth containing ionic solution. Specifically, and as described above, the applied potential across the electrodes provides a supply of free electrons in the rare earth containing ionic solution. As a result, the positively charged REEs formed therein are driven towards the negatively charged working electrode, and the REEs are deposited on the working electrode via an electrodeposition process.

[0045] The reduction potential of a reduction reaction is an indication of the tendency for a species to acquire or lose electrons. The reduction potential indicates the tendency for metal complexes (e.g., dysprosium triflate (Dy(OTf).sub.3)) to acquire electrons, dissociating the metal (e.g., dysprosium metal) from the anions, and allowing the metal to be deposited on the working electrode. In embodiments disclosed herein, the reduction potential may be adjusted to increase the electrodeposition of the REE (e.g., dysprosium metal), through the addition of small predetermined amounts of at least one polar protic solvent to the rare earth containing ionic solution, as described above.

[0046] Looking again to FIG. 1, the method for recovery of rare earth elements 100 includes recovering the deposit of the at least one rare earth element from the at least one electrode 190. In some embodiments, recovering the deposit of the at least one rare earth element from the at least one electrode 190 includes removing the rare earth elements deposited on the electrode which may include physical separation of the rare earth element from the electrode, chemically facilitated removal of the rare earth element from the electrode, or combinations thereof. In some embodiments, the method for recovery of rare earth elements 100 further includes drying the deposits of rare earth elements recovered from the at least one electrode and preparing the recovered rare earth elements for final use.

[0047] With reference next to FIG. 2, presented therein is a simplified schematic illustration of a system 200 for recovering rare earth elements, in accordance with embodiments of the disclosure. The system 200 includes an electrodeposition reservoir 210 dimensioned and configured to receive an amount of a rare earth containing ionic solution 216, prepared in accordance with the method for recovery of a rare earth element 100 described hereinabove, therein. The rare earth containing ionic solution 216 may include a predetermined amount of a polar protic solvent to form a metal species coordination environment therein, also as described above. In accordance with some embodiments, the system 200 may include a drying device (e.g., a furnace) (not shown) to reduce an initial water content of the rare earth containing component.

[0048] 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.

[0049] As shown in FIG. 2, the electrodeposition reservoir 210 in some embodiments includes a reservoir inlet 212 and a reservoir outlet 214. The reservoir inlet 212 is provided to facilitate the addition of an amount of a so-called fresh rare earth containing ionic solution 216, i.e., an amount of rare earth containing ionic solution that has not yet been exposed to an electrical potential in an electrodeposition cell, into the electrodeposition reservoir 210. In some embodiments, an inlet valve 213 is disposed in communication with the reservoir inlet 212 to further facilitate the addition of the fresh rare earth containing ionic solution 216, as needed.

[0050] Conversely, the reservoir outlet 214 facilitates the removal of so-called spent rare earth containing ionic solution, i.e., rare earth containing ionic solution that has been exposed to an electrical potential for a sufficient time so as to deplete (e.g., substantially deplete) the amount of the rare earth elements contained therein, from the electrodeposition reservoir 210. An outlet valve 215 may be disposed in communication with the reservoir outlet 214 to further facilitate the removal of spent earth containing ionic solution from the electrodeposition reservoir 210.

[0051] 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 rare earth containing ionic solution 216, as shown, for example, in FIG. 2, through the reservoir inlet 212, after which, the inlet valve 213 and the outlet valve 215 are closed. A potential is applied to the fresh rare earth containing ionic solution 216 by an electrodeposition assembly 220, described in more detail below, for a period of time sufficient to deplete (e.g., substantially deplete) the rare earth containing ionic solution of the rare earth metal, after which, the outlet valve 215 is opened, and the spent solution is removed from the electrodeposition reservoir 210, which is then ready to receive additional fresh rare earth containing ionic solution 216.

[0052] 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 rare earth containing ionic solution 216, an amount of spent rare earth containing ionic solution is discharged through the reservoir outlet 214, and an approximately equal amount of fresh rare earth containing ionic solution 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 rare earth containing ionic solution is continuously discharged from the electrodeposition reservoir 210 at a predetermined discharge flowrate while fresh rare earth containing ionic solution 216 is added to the electrodeposition reservoir 210 at a substantially similar flowrate.

[0053] In some embodiments, the electrodeposition reservoir 210 is disposed in communication with a heat source (not shown) such that the rare earth containing ionic solution 216 contained therein may be heated to a preselected temperature. For example, the rare earth containing ionic solution 216 may be heated to a temperature of about 150 Celsius, or about 125 Celsius, or about 100 Celsius, or about 50 Celsius. In accordance with some embodiments, the rare earth containing ionic solution 216 is processed under ambient conditions (e.g., atmospheric pressure at a temperature of from about 20 Celsius to about 25 Celsius).

[0054] The electrodeposition assembly 220 of the system 200 includes at least two electrodes 222, 224 which are operatively disposed below a surface 216 of the rare earth containing ionic solution 216 in the electrodeposition reservoir 210, such as is shown, by way of example, in FIG. 2. Specifically, the electrodeposition assembly 220 includes at least one positively charged anode 222, which releases electrons into the rare earth containing ionic solution 216, and one negatively charged cathode 224, onto which the rare earth elements from the rare earth containing ionic solution 216 are deposited. The anode 222 and cathode 224 are sometimes referred to as a counter-electrode and a working electrode, respectively. FIG. 2 presents by way of example the system 200 during use and operation and having a deposit of the rare earth element 300 on the cathode 224.

[0055] In some embodiments, the system 200 for recovering rare earth elements includes at least three electrodes, an anode 222, a cathode 224, and a reference electrode couple (e.g., Ferrocene (Fc+/Fc)) (not shown) 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 rare earth containing ionic solution 216 in the electrodeposition reservoir 210, such as, for example, by a glass frit.

[0056] While not illustrated in FIG. 2, the system 200 for recovering of rare earth elements may employ tens, hundreds, or even thousands of electrodes 222, 224, wherein some of the electrodes are positively charged anodes 222 which emit electrons to facilitate reduction of the rare earth metal complexes in the rare earth containing ionic solution, while others of the electrodes are negatively charged cathodes 224 which receive a deposit of the rare earth element 300 thereon. The electrodes 222, 224 used for reduction and recovery of the rare earth metal complexes in the rare earth containing ionic solution 216, respectively, may be alternated, facilitating the operation of a continuous reduction and chemical electrodeposition process.

[0057] The electrodes 222, 224 comprise 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 exhibit 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.

[0058] The electrodes 222, 224 may be formed in the shape of 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 other embodiments, the sizes and shapes of the electrodes 222, 224 may be altered (e.g., scaled up) for larger-scale industrial applications.

[0059] The electrodeposition assembly 220 further comprises a potential source 226 configured to apply an electrical potential across the electrodes 222, 224. Conductors 228 provide an electrical connection between the potential source 226 and the electrodes 222, 224. When the electrical potential is applied across electrodes 222, 224, a current is generated between the anode 222 and the cathode 224, and through the rare earth containing ionic solution 216 in the electrodeposition reservoir 210. The potential source 226 is dimensioned and configured to apply an electrical potential of from about 1.0V to about 4.0V across the electrodes 222, 224. At these applied potentials, the resultant current densities generated will be from about 0.5 mA/cm.sub.2 to about 5 mA/cm.sub.2 relative to the applied current and the surface area of the electrode. In other embodiments, the current densities may range from about 0.5 mA/cm.sup.2 to about 2 mA/cm.sup.2.

[0060] The system 200 for recovering 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 which is dimensioned and configured to contain (e.g., surround) the electrodeposition reservoir 210 including the rare earth containing ionic solution 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 FIG. 2.

[0061] 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.

[0062] 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) includes components (e.g., oxygen, water vapor, trace contaminants, etc.) which may 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.

[0063] The inert gas inlet 236 is provided to facilitate the addition 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.

[0064] 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 that 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.

[0065] 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

Recovery of Dysprosium by Electrodeposition in an Ionic Liquid

[0066] A dysprosium triflate (Dy(OTf).sub.3, 99.5%) stock solution was obtained from Strem Chemicals; 1-butyl-1-methylpyrrolidinium triflate (BMPyOTf, 99.5%) ionic liquid was obtained from IoLiTec; anhydrous acetone (99.8%) used to rinse the electrodeposited materials was obtained from Acros Organics; and, trace metal grade nitric acid (HNO.sub.3, 65-75%) used in the dissolution of electrodeposited materials was obtained from Fisher Chemical. Preparation of Dy(OTf).sub.3 in BMPyOTf solution was conducted in a glovebox under an inert argon atmosphere (H.sub.2O<8-12 ppm, O.sub.2<0.5-1.5 ppm). Specific water concentrations in solutions of Dy(OTf).sub.3 in the ionic liquid were achieved by dissolving either dried Dy(OTf).sub.3 (e.g., under vacuum for over 4 hours at 80 to 100 Celsius) or stock Dy(OTf).sub.3 in dried BMPyOTf (e.g., under vacuum for over 7 to 9 hours at 80 to 100 Celsius). The dried Dy(OTf).sub.3 produced solutions with low water concentrations, while the stock Dy(OTf).sub.3 produced solutions with higher water concentrations. The solutions were combined to obtain solutions with water concentrations ranging from about 35 ppm to about 3,500 ppm, which were confirmed using Karl-Fisher analysis.

[0067] Electrochemical analysis was performed using a Bio-Logic SP-150 Potentiostat, with voltammetric measurements carried out using a standard three-electrode configuration. Platinum discs, ranging from about 1.0 to 2.0 mm diameter and about 2.5 to 3.5 mm diameter, were used as working electrodes, while platinum wires were used as pseudo-reference and counter electrodes. In the case of chronoamperometric electrodeposition measurements, 2.5 to 3.5 mm platinum discs or copper plates were used as the working electrodes, where the cathodic and anodic compartments were separated by a glass frit. A ferrocenium/ferrocene (Fc+/Fc) couple was used as an internal reference system in order to correct shifts of the employed platinum pseudo-reference. The ionic liquids exhibited significant viscosity and solution resistance, therefore, voltammograms were recorded with iR drop compensation. All electrochemical measurements were conducted in the glovebox under the inert argon atmosphere, as described above.

[0068] Deposits containing dysprosium were obtained from electrodeposition and were rinsed with anhydrous acetone, and allowed to dry under the inert argon atmosphere. After cleaning, the dysprosium deposits were dissolved in 8-12% HNO.sub.3. Samples for energy-dispersive X-ray coupled to scanning electron microscopy (EDS-SEM) and X-ray photoelectron spectroscopy (XPS), were prepared from the dysprosium electrodeposited on copper plates. The dysprosium deposits were washed with anhydrous acetone to remove any traces of the ionic liquid, and then dried and sealed inside the glove box. Morphological and elemental characterization of the dysprosium deposits were performed with energy-dispersive X-ray spectroscopy coupled to scanning electron microscopy (i.e., EDS-SEM, JEOL JSM 6610LV).

[0069] Dysprosium reduction in ionic liquids has been reported to follow both consecutive two step (1+2e) and single step (3e) pathways, wherein the voltammetry of Dy(OTf).sub.3 reduction in BMPyOTf has been shown to exhibit two reduction waves and one main oxidation peak at about 2.3V, 2.8V and OV, respectively, as shown in FIG. 4. The forward features were assigned to reduction processes, which led to the deposition of dysprosium metal on the electrode surface, while the sharp oxidation peak during the backward scan was attributed to oxidative stripping of the dysprosium metal from the electrode surface. Evolution of the voltammetric response from one main reduction peak at low metal concentrations to two reduction peaks (Red1 and Red2) at higher concentrations suggested the reduction of two co-existent speciations in solution. The first more positive wave (Red1) was attributed to a 3e-reduction of weakly IL-coordinated metal complexes to form dysprosium metal. This was supported by the observed reversible features of the Dy(II)/Dy(III) wave at more positive potentials (e.g., 1V vs Fc+/Fc) and the oxidative stripping peak (e.g., at 0V vs Fc+/Fc) when scanning the potentials at the first reduction wave.

[0070] Voltammetric analysis of 100 mM Dy(OTf).sub.3 in BMPyOTf on a platinum electrode was initially performed under dry conditions (i.e., about 35 ppm water content), and as shown in the voltammetry scans of FIG. 3, two reduction waves were observed at about 1.1V to 1.5V and 3.2V to 3.5V. The first wave exhibited significant chemical reversibility during the backward scan, with a half potential about 1.1V to about 1.3V, also shown in FIG. 3. The positive potential and chemical reversibility of this wave was consistent with 1e reduction to form a Dy(II) intermediate. The second more negative wave, shouldering the cathodic decomposition of the pyrrolidinium ionic liquid, exhibited no corresponding oxidation peak during the backward scan to about +1.5V vs Fc+/Fc. Additionally, the peak current appeared to be much higher than a 2e transfer, relative to the 1e Dy(II) wave.

[0071] Introduction of small amounts of water (i.e., about 200 ppm) to the 100 mM Dy(OTf).sub.3 in BMPyOTf solution resulted in substantial changes in the voltammetric response. The main variations observed are shown in FIG. 3 and included the emergence of a new reduction wave at more positive potentials at about 2.1V to 2.5V, with a corresponding oxidation peak at about +0.3V to 0.2V. Additionally, a significant decrease in the current density of the more negative wave was observed. The positive potential, significant chemical reversibility and sharpness of the oxidation peak were all consistent with the emerging Red1wave attributed to a 3e reduction of Dy(III) to Dy (metal). In fact, the introduction of small amounts of water appeared to switch the reduction from a consecutive (1+2e) pathway to a single step (3e) pathway.

[0072] To further investigate the nature of the emerging wave (Red1) and the more negative wave (Red2), voltammetric traces were recorded for 100 mM Dy(OTf).sub.3 in BMPyOTf solution at various water concentrations. Increased water concentrations from about 35 ppm to about 3,500 ppm resulted in a continuous growth of the Red1 wave and the oxidation peak, and the peak potentials of both reduction waves were shifted, as shown, once again, in FIG. 4. The potential shifts of both reduction waves as a function of water concentration are shown in the inset of FIG. 4. Small amounts of water (e.g., from about 35 ppm to about 500 ppm) mainly led to the emergence and growth of the Red1 wave, with no significant shift in peak potentials. At concentrations of water above 500 ppm, both the Red1 and Red2 waves gradually shifted to more positive potentials, with increased current densities. As a result, the difference in the peak potentials between the two waves collapsed by about 0.5V (e.g., from about 1.0V to about 0.5V). The voltammograms in FIG. 4 clearly demonstrate the evolution of the single negative wave (3.3V) at 35 ppm into the Red2 wave (2.9V) at 3,500 ppm.

[0073] The correlation between water introduction and heterogeneous speciation was further evaluated via voltammetric inspection carried out at different metal loadings at a constant water concentration. FIG. 5 presents linear sweep voltammetry traces of 20 mM, 50 mM, and 100 mM dysprosium triflate (Dy(OTf).sub.3) complex in a pyrrolidinium triflate (BMPyOTf), as well as of the metal-free ionic liquid, at a water concentration of about 500 ppm. As shown in FIG. 5, at 20 mM Dy(OTf).sub.3, dysprosium reduction exhibited two waves at 2.1 and 2.8V with much higher peak currents for the Red2 wave as compared to the Red1 wave. The background voltammogram of the metal-free ionic solution exhibited water reduction at much more negative potentials than the Red1 wave, but comparable to the Red2 wave. Increasing the Dy(OTf).sub.3 concentration from about 20 mM to about 50 mM, and to about 100 mM led to a substantial rise in the Red1 wave current and a significant shift of the Red2 wave to more negative potentials.

[0074] The results observed were consistent with dysprosium partitioning between water-coordinated and IL-coordinated speciation. At equimolar fractions, the water molecules were partially coordinated to the dysprosium complex (e.g., Red1), while other fractions thereof remained as free or weakly-coordinated molecules. As metal loading increased, which effectively decreased the water concentration, the fraction of metal-coordinated water (Dy-H.sub.2O) increased at the expense of free or weakly-coordinated water (IL-coordinated complex), which resulted in a rise of Red1 at the expense of Red2, as shown in FIG. 5. The current decrease and negative potential shift in Red2 suggested high coupling between the reduction of the IL-coordinated dysprosium complex and water electrolysis.

[0075] The observed voltammetric measurements were in agreement with a double featured reduction process, wherein the result of triflate anion (OTf).sup..sub.3 displacement by water molecules was that the metal dysprosium complex was partitioned between water-coordinated and IL-coordinated speciation.

[0076] Thus, the mechanism for the Dy(OTf).sub.3 reduction in BMPyOTf was expected to follow one of three pathways. In highly dry environments, where water molar fraction x.sub.H20 (i.e., water/Dy(OTf).sub.3%) is very small (e.g., x.sub.H20 of approximately 5%), dysprosium is fully (e.g., strongly) coordinated to IL-anions and reduced in a consecutive 1+2e process. In this mechanism, the very negative potentials (e.g., 3.3V) of the 2e reduction to dysprosium metal was coupled to a chemical reaction (EC/EC'), which led to negligible and/or unstable (e.g., no stripping peak) metal electrodeposition at the electrode surface. Introduction of water at low concentrations (5%<x.sub.H20<30%) led to displacement of the IL-ligand to the metal center and significant partitioning into water-coordinated complex, which resulted in the emergence of a new reduction wave (Red1) at more positive potentials (e.g., 2.4V). Within this heterogeneity, the fraction of the IL-coordinated speciation which remained was reduced at more negative potentials in a consecutive process. Under wet conditions (e.g., x.sub.H20>30%), the water impact went beyond metal coordination and ligands displacement, and triggered the catalytic hydrogen evolution reaction (HER). This was likely due to the increased concentration of free or weakly-coordinated water molecules. A consequence of coupling the electrodeposition to the fast-catalytic HER, both reduction waves (Red1 and Red2) were substantially shifted to more positive potentials, once again, as shown in FIG. 4.

[0077] The correlation between the bulk distribution of the heterogeneous speciation and reduction currents appeared to be restricted to voltammetric timescales. According to Equation 1 below, the triflate anion (OTf.sup..sub.3 concentration at the interface was expected to increase during continuous metal electrodeposition, shifting the equilibrium towards IL-coordinated dysprosium speciation. As a result, dysprosium reduction would ultimately be driven under the thermodynamics of the Red2 process. This was consistent with previously reported decrease in voltammetric current of Red1 relative to Red2, at multiple potential scans.

[00001]$\begin{array}{cc}D{y\left(\mathrm{OTf}\right)}_3+3e^{-}.Math.\mathrm{Dy}\left(0\right)+3O{\mathrm{Tf}}^{-}& \left(\mathrm{Eq}.1\right)\end{array}$

[0078] Using the IR determined speciation concentrations, diffusion coefficients (D) of the water-coordinated complex were evaluated from voltammetric traces. In this analysis, both semi-integral (SI) and semi-derivative (SD) voltammograms were employed to extract the D values from SI and SD traces of 50 and 100 mM Dy(OTf).sub.3 solutions. The D values obtained for both speciations are summarized in Table 1. Note that the extracted D values should be considered upper limits, due to potential contributions from catalytic component in the total faradaic currents.

TABLE-US-00001 TABLE 1 Electrochemical and Spectroscopic Properties of the Observed Dysprosium Speciation E.sub.red (V vs NIR (1850- Dy Speciation Fc.sup.+/Fc) D (m.sup.2/s) 2000, nm) IR (cm.sup.1) Dy-IL 3.3 7.6 10.sup.12 Blank 1334; 1054 DyH.sub.2O 2.4 3.3 10.sup.11 1970 1322; 1050

[0079] As observed from the voltammetric analysis, the introduction of small amounts of water (e.g., about 500 ppm) shifted the reduction process to more positive potentials and led to substantially increased current densities. Thus, electrodeposition metrics were examined and included the faradaic efficiency (FE), electrodeposition rates, metal stability and purity in systems in which water was added.

[0080] The impact of water concentration on the electrodeposition metrics; i.e., the faradaic efficiency and deposition rates, of dysprosium metal were initially determined at different applied potentials at different water concentrations. FIG. 6 is a graph of faradaic efficiency and chronoamperometric current densities of 100 mM Dy(OTf).sub.3 in BMPyOTf at different water concentrations. The passing charge was maintained at about 0.5 C/cm.sup.2 to about 1.5 C/cm.sup.2 for all of the samples evaluated to prevent possible variations due to the deposited amount of the film thickness. As was expected from the results of the voltammetric analysis, the increased overpotentials led to significantly increased metal deposition rates. Remarkably, the FE values seemed to increase at more negative applied potentials.

[0081] To further examine the changes in system efficiency, electrodeposition experiments were carried out at different water concentration. Given the highly negative reduction potential of Red2 in highly dried conditions (e.g., 35 ppm water), the deposition was run at applied potentials of about 3.1V to about 3.5V. It was noted that even at these very negative potentials, the deposition currents were still low (e.g., about <0.15 to about 0.25 mA/cm.sup.2). Under the highly dried conditions, negligible deposit amounts were obtained at a deposition current of about 0.8 C/cm.sup.2, leading to very low FE values (e.g., <2%). Consistent with the emergence of the positive voltammetric wave (Red1) at more positive potentials (e.g., about 2.4V), the addition of water boosted the deposition rate by about one order of magnitude. Moreover, the FE values increased by almost two orders of magnitude between a highly dried condition (e.g., 35 ppm water) and a wet condition (e.g., 3,500 ppm water). The observed FE increase was attributed to rate improvement in crystal growth, under a progressive nucleation process.

[0082] Given the observed impact of water addition on the nucleation process, morphology analysis of the dysprosium deposits obtained at different water concentrations was performed using SEM techniques. FIGS. 7 and 8 present scanning electron microscope (SEM) images of electrodeposited dysprosium on a copper electrode obtained from solutions comprising Dy(OTf).sub.3 in BMPyOTf at water concentrations of 500 ppm and 3,500 ppm, respectively.

[0083] As shown in FIGS. 7 and 8, the electrodeposited dysprosium films generally exhibited a powdery form with dendritic particles of sub-micrometer diameters. While the same charge density (e.g., 1 C/cm.sup.2) was passed for the dysprosium deposits obtained, the increased water concentration had a significant impact on the particle morphology. At the higher water concentration (e.g., about 3,500 ppm), the particles were denser and more aggregated, with heterogeneous surfaces between rough and smooth regions, as shown in FIG. 8. These morphologic differences are consistent with observed changes in the nucleation process from spontaneous and progressive regimes with increased water concentration. This also correlated well with the observed deposition rates between low and high-water concentrations, as observed under chronoamperometric analysis.

[0084] Irrespective of the dysprosium oxidation state and morphologic structure, quantification of dysprosium concentration in the electrodeposited material, obtained in two different water concentrations, was performed. In this analysis, the dysprosium surface composition was determined using EDS characterization. Reported dysprosium compositions in electrodeposits obtained from ionic liquids ranged from 10 to 75%, based on surface analysis by EDS. Elemental compositions from EDS analysis in the electrodeposited dysprosium films are displayed in FIGS. 7 and 8. Surface compositions of both samples included significant amounts of O, F, C and S elements, which likely originated from the electrolyte components. In agreement with the observed faradaic efficiencies, a very low (e.g., approximately 5%) dysprosium concentration was observed in the dysprosium films deposited under low water conditions (e.g., about 500 ppm), while it increased by about one order of magnitude in the dysprosium films deposited at higher water concentrations (e.g., about 3,500 ppm).

[0085] The impacts of water concentration on the electrodeposition of dysprosium in a pyrrolidinium triflate system demonstrated that the water concentration appeared to exhibit both promoting and mitigating effects on the dysprosium electrodeposition process. Under dry conditions (e.g., about 35 ppm water), the reduction proceeded via consecutive 1+2e mechanism, where solvation of the dysprosium complex was predominantly characterized by full IL-coordination. As a result of full IL-coordination, dysprosium reduction to its zero valent metal occurred at very negative potentials (e.g., Red2). However, electrodeposition under those conditions seemed to be unstable and inefficient. Introduction of small amounts of water (e.g., about 500 ppm) appeared to overcome these limitations via a partial partitioning of the dysprosium complex into highly water-coordinated speciation. This resulted in the emergence of a new 3e wave at more positive potentials (e.g., Red1). In addition to the displacement of IL-coordination, water introduction led to faster electrocrystallization processes. Thus, the presence of water was essential to sustain the structured ionic liquid interface by neutralizing the electrostatic interactions between IL components and the released triflate anions upon metal reduction. Higher water concentrations resulted in the solvation of the remaining dysprosium fraction, leading to a significant shift of the Red2 process. This shift was correlated to the coupling of the Red2 process with HER under higher water concentrations (e.g., 3,500 ppm). Parallel to these coordination effects on speciation and reduction mechanisms, higher concentrations of water were demonstrated to alter the chemical stability of the zero valent dysprosium metal under long electrodeposition conditions. This was predicted from stripping voltammetry and consolidated by XPS analysis. Furthermore, evaluation of the dysprosium content at the surface and bulk of the obtained electrodeposited material showed a limited purity (e.g., approximately 60%), with substantial contamination by electrolyte components. These results were consistent with severe decay in system efficiency, under extended deposition scale.

[0086] In summary, a complex interplay of water effects on the electrodeposition process of dysprosium were observed in the studied ionic liquid. On the one hand, increased water concentration appeared to promote coordination interactions and structural sustainability of the IL interface, as exhibited by the lowered thermodynamics of the reduction and the increased crystal growth and deposition rates. On the other hand, the increased water concentration presented an oxidative environment that mitigated the chemical stability of the zero valent dysprosium metal and the robustness of the system efficiency. It appeared that under a voltammetric timescale, the hydrophobic ionic liquid interface provided a protective environment for the reduced materials. Under longer electrolytic conditions, water may destroy the ionic liquid layer and oxidize the reduced material. At higher water concentrations (e.g., 3,500 ppm), HER become prominent and led to severe decay of faradaic efficiency which resulted from direct or indirect water electrolysis.

[0087] 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.