CROSS-REFERENCE TO RELATED APPLICATIONS

[0001 ] This application claims priority to U.S. Provisional Application No.

62/532,586, titled "Closed-Loop Reduction of Pure Scandium Metal or Rare Earths," filed on July 14, 2017, which is hereby incorporated by reference in its entirety for all purposes.

[0002] All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The patent and scientific literature referred to herein establishes knowledge that is available to those skilled in the art. The issued patents, applications, and other publications that are cited herein are hereby incorporated by reference to the same extent as if each was specifically and individually indicated to be incorporated by reference. In the case of inconsistencies, the present disclosure will prevail.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0003] This invention was made with government support under grant number

1,648,081 awarded by the National Science Foundation. The government has certain rights in the invention.

FIELD OF THE INVENTION

[0004] Embodiments of the invention relate to produc tion of rare earth metals from oxides.

BACKGROUND

[0005] Scandium, yttrium and other rare earth metals have important potential applications, from strengtheners for aluminum and magnesium alloys, to magnets, and nuclear applications. In particular, scandium increases room-temperature strength of aluminum more than any other element per mole of addition. Scandium aluminide nano-particles, sometimes called strengthening precipitates, deposited throughout an aluminum alloy can maintain their fine size and dispersion at elevated temperature. The scandium-aluminum alloy thus retains its strength even through welding or sintering operations, including 3-D printing by selective laser sintering or wire melting. For example, a motorcycle was 3-D printed using aluminum alloy that contains about 1 wt. % scandium (see Airbus AP Works's "Light Rider," claimed as the world's first 3-D printed motorcycle). Alcoa/Arconic, sporting goods makers, and metal 3-D printers are current or future Al-Sc alloy users. Gadolinium is similarly one of the preferred strengtheners for magnesium alloys, improving its high-temperature strength considerably. Thus, there is a need for an improved technology to produce rare earth metals. Furthennore, it is desirable for scandium or rare earth metal production technology to be compatible with western labor markets and workplace safety and environmental standards.

[0006] Due to the slow dissolution kinetics of scandium metal in liquid aluminum, Al-Sc alloy is typically introduced in the form of Al-2 wt. % Sc "master alloy." The liquidus temperature of 800 °C for this 2% by weight scandium composition makes it easier to produce than higher-scandium master alloy, and it dissolves very quickly in liquid aluminum. Thus, 2% by weight Sc master alloy is the preferred precursor for most of the scandium metal used in aluminum alloys. But there are two recent developments in higher scandium fraction materials.

[0007] First recent development is a high-entropy alloy with composition

Al2oLi2oMgioSc2oTi3o that has about 5.9 GPa hardness with a density of about 2.67 g/cm ³ and potential strength/density of about 2 GPa strength (Mater. Res. Lett 3(2):95, 2015): herein incorporated by reference in its entirety)-

[0008] Second recent development is an aluminum with up to 40% by weight scandium that is a sputtering target for reactive sputtering of high-performance AlScN piezoelectric (IEEE Trans. Ferroelectr. Freq. Control 61(8): 1329, 2014; herein incorporated by reference in its entirety).

[0009] The above two applications contain higher fraction of scandium and use of pure scandium metal is preferred for production. Thus, there is a need for an improved technology to produce pure scandium metal.

SUMMARY

[0010] Methods for producing rare earth metals from rare earth metal oxides are provided. In some embodiments, a method for producing a rare earth metal from a rare earth metal oxide can include a) dissolving a first portion of rare earth metal oxide in an acid to prepare a first rare earth metal-acid solution; b) reacting a first portion of alkali metal fluoride with the first rare earth metal-acid solution, thereby precipitating a first portion of rare earth metal fluoride and, optionally, adding a first base to a remaining second rare earth metal-acid solution; c) reacting a first portion of alkali metal with the first portion of rare earth metal fluoride to produce a first part of first portion of rare earth metal and a second portion of alkali metal fluoride; d) collecting the first portion of rare earth metal; e) recycling at least a part of a remaining first portion of rare earth metal fluoride and the second portion of alkali metal fluoride from step c) for a reaction in a second rare earth metal-acid solution comprising a dissolved second portion of rare earth metal oxide, thereby precipi tating a second portion of rare earth metal fluoride and, optionally, adding a second base to a remaining second rare earth metal-acid solution; f) reacting a second portion of alkali metal with the second portion of rare earth metal fluoride to produce a second portion of rare earth metal and a third portion of alkali metal fluoride; and g) collecting the second portion of rare earth metal.

[0011 ] In some embodiments, a method of producing scandium from scandium oxide can include a) dissolving a first portion of SC2O3 in an acid to prepare a first Sc-acid solution, wherein the acid can include HC1 and HNO3 with a ratio of about 1 :3 and with a temperature between about 160 °C to about 200 °C; b) reacting a first portion of LiF with the first Sc-acid solution, thereby precipitating a first portion of ScF3 and, optionally, after step b), adding a first base to a remaining first Sc-acid solution, thereby precipitating a first mixture comprising hydroxides, carbonates, or fluorides of Li and Sc, wherein the first base including NaOH, NaaCCb, NH4OH or (NHU^CCh, collecting and heating the first mixture comprising hydroxides, carbonates, or fluorides of Li and Sc to drive off at least a portion of water or carbon dioxide, thereby producing a second mixture comprising oxides of Li and Sc, and causing an electrolysis of the second mixture to produce a first portion of Li and a third portion of Sc; c) include reacting the first portion of Li with the first portion of ScF3 to produce a first portion of Sc and a second portion of LiF; d) collecting the first portion of Sc; e) recycling at least a part of a remaining first portion of ScF3 and the second portion of LiF from step c) for a reaction in a second Sc-acid solution comprising a dissolved second portion of SC2O3, thereby precipitating a second portion of ScF3 and, optionally, after step e), adding a second base to a remaining second Sc-acid solution, thereby precipitating a third mixture including hydroxides, carbonates, or fluorides of Li and Sc, wherein the second base is selected from the group consisting of NaOH, NaiCCb, NH4OH or (NFLOiCCb, collecting and heating the third mixture comprising hydroxides, carbonates, or fluorides of Li and Sc to drive off at least a portion of water or carbon dioxide, thereby producing a fourth mixture comprising oxides of Li and Sc, and causing an electrolysis of the fourth mixture to produce a second portion of Li and a fourth portion of Sc; f) reacting the second portion of Li wi th the second portion of ScF3 to produce a second portion of Sc and a third portion of LiF; and g) collecting the second portion of Sc. [0012] In some embodiments, a method of producing scandium from scandium oxide can include a) dissolving a first portion of SC2O3 in an acid to prepare a first Sc-acid solution, wherein the acid comprises HC1 and H O3 with a ratio of about 1:3 and with a temperature between about 160 °C to about 200 °C, b) reacting a first portion of NaF with the first Sc-acid solution, thereby precipitating a first portion of ScF3 and, optionally, after step b), adding a first base to a remaining first Sc-acid solution, thereby precipitating a first mixture comprising oxides or fluorides of Sc, wherein the first base including NaOH, Na2C03, NH4OH or (NH 2CO3, and adding at least a portion of the first mixture comprising oxides or fluorides of Sc to a second Sc-acid solution in step e); c) reacting a first portion of Na with the first portion of ScF3 to produce a first portion of Sc and a second portion of NaF; d) collecting the first portion of Sc; e) recycling at least a part of a remaining first portion of ScF3 and the second portion of NaF from step c) for a reaction in the second Sc-acid solution including a dissolved second portion of SC2O3, thereby precipitating a second portion of ScF3 and, optionally, after step e), adding a second base to a remaining second Sc-acid solution, thereby precipitating a second mixture comprising oxides or fluorides of Sc, wherein the second base including NaOH, Na2C03, NH4OH or (NH ₄ )2C03, and adding at least a portion of the second mixture comprising oxides or fluorides of Sc to a third Sc-acid soluti on in step h); f) reacting a second portion of Na wi th the second portion of ScF3 to produce a second portion of Sc and a third portion of NaF; g) collecting the second portion of Sc; h) recycling at least a part of a remaining second portion of ScF3 and the third portion of NaF from step f) for a reaction in a third Sc-acid solution comprising a dissolved third portion of SC2O3, thereby precipitating a third portion of ScFs; i) reacting a third portion of Na with the third portion of ScF3 to produce a third portion of Sc and a fourth portion of NaF; and j) collecting the third portion of Sc.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The following figures are illustrative only and are not intended to be limiting.

[0014] Figure 1 shows a flow chart of an overall process for producing scandium from its oxide with an optional lithium electrolysis process.

[0015] Figure 2 shows a flow chart of a process for producing scandium from its oxide with an optional lithium electrolysis process. [0016] Figure 3 shows a flow chart of an overall process for producing scandium from its oxide with an optional scandium precipitation process.

[0017] Figure 4 shows a flow chart of a process for producing scandium from its oxide with an optional scandium precipitation process.

[0018] Figure 5 shows an illustrative embodiment of a schematic of a L12O reduction cell using a porous MgO membrane.

[0019] Figure 6 shows a schematic of LiF-Li20-Sc203 electrolysis in a cell.

[0020] Figure 7 shows a graph result of an energy-dispersive x-ray spectroscopy

(EDS) analysis of scandium.

DETAILED DESCRIPTION

[0021] Described herein are methods of producing rare earth metals from rare earth metal oxides. Although oxide electrolysis in a molten fluoride bath can produce light rare earth metals such as lanthanum, cerium, praseodymium and neodymium, and intermediates samarium and europium, this practice is less desirable for heavy rare earth metals with high melting points. Instead, heavy rare earth metals, including yttrium and scandium, can be produced by metallothermic reduction of their fluorides using calcium or lanthanum. Because these are among the most stable oxides in the periodic table, there are only limited methods to convert these stable oxides into fluorides. One such method is high-temperature

hydrofluorination. Scandium oxide for example is reacted with FIF gas or NH4HF2 at a temperature of 700 °C or above to convert it to scandium fluoride, resulting in a highly dangerous operation with a high energy cost. Even after the metallothermic reduction of scandium fluoride into scandium, calcium or lanthanum remains as a contaminant within the produced scandium metal, and the contaminant may be removed by a further distillation to purify the scandium metal. This purification process further adds to the cost of producing rare earth metals such as scandium from the oxides.

[0022] Methods for producing rare earth metals from rare earth metal oxides are provided. In some embodiments, a method for producing a rare earth metal from a rare earth metal oxide can include a) dissolving a first portion of rare earth metal oxide in an acid to prepare a first rare earth metal-acid solution; b) reacting a first portion of alkali metal fluoride with the first rare earth metal-acid solution, thereby precipitating a first portion of rare earth metal fluoride and, optionally, adding a first base to a remaining second rare earth metal-acid solution; c) reacting a first portion of alkali metal with the first portion of rare earth metal fluoride to produce a first part of first portion of rare earth metal and a second portion of alkali metal fluoride; d) collecting the first portion of rare earth metal; e) recycling at least a part of a remaining first portion of rare earth metal fluoride and the second portion of alkali metal fluoride from step c) for a reaction in a second rare earth metal-acid solution comprising a dissolved second portion of rare earth metal oxide, thereby precipitating a second portion of rare earth metal fluoride and, optionally, adding a second base to a remaining second rare earth metal-acid solution; f) reacting a second portion of alkali metal with the second portion of rare earth metal fluoride to produce a second portion of rare earth metal and a third portion of alkali metal fluoride; and g) collecting the second portion of rare earth metal.

[0023] In some embodiments, the method comprises h) recycling at least a part of a remaining second portion of rare earth metal fluoride and the third portion of alkal i metal fluoride from step f for a reaction in a third rare earth metal-acid solution comprising a dissolved third portion of rare earth metal oxide, thereby precipitating a third portion of rare earth metal fluoride; i) reacting a third portion of alkali metal with the third portion of rare earth metal fluoride to produce a third portion of rare earth metal and a fourth portion of alkali metal fluoride; and j) collecting the third portion of rare earth metal.

[0024] In some embodiments, the method comprises, after step b), adding the first base to the remaining first rare earth metal-acid solution, thereby precipitating a first mixture comprising hydroxides, carbonates, or fluorides of alkali metal and rare earth metal; collecting and heating the first mixture comprising hydroxides, carbonates, or fluorides of the alkali metal and the rare earth metal to dri ve off at least a porti on of water or carbon dioxide, thereby producing a second mixture comprising oxides of the alkali metal and the rare earth metal; and causing an electrolysis of the second mixture to produce at least a part of the first portion of alkali metal and a fourth portion of rare earth metal.

[0025] In some embodiments, the electrolysis of the second mixture can produce the at least the part of the first portion of alkali metal and the fourth portion of rare earth metal together in an alloy.

[0026] In some embodiments, the method comprises adding the at least the part of the first portion of alkali metal and the fourth portion of rare earth metal produced from the electrolysis of the second mixture to the reaction in step c). [0027] In some embodiments, the method comprises, after step e) adding the second base to the remaining second rare earth metal-acid solution, thereby precipitating a first mixture comprising hydroxides, carbonates, or fluorides of alkali metal and rare earth metal; collecting and heating the first mixture comprising hydroxides, carbonates, or fluorides of the alkali metal and the rare earth metal to drive off at least a portion of water or carbon dioxide, thereby producing a second mixture comprising oxides of the alkali metal and the rare earth metal; and causing an electrolysis of the second mixture to produce at least a part of the second portion of alkali metal and a fifth portion of rare earth metal.

[0028] In some embodiments, the electrolysis of the second mixture can produce the at least the part of the second portion of alkali metal and the fifth portion of rare earth metal together in an alloy.

[0029] In some embodiments, the method comprises adding the at least the part of the second portion of alkali metal and the fifth portion of rare earth metal produced from the electrolysis of the second mixture to the reaction in step f).

[0030] In some embodiments, the method comprises, after step b) adding the first base to the remaining first rare earth metal-acid solution, thereby precipitating a mixture comprising oxides or fluorides of rare earth metal; and adding at least a portion of the mixture comprising oxides or fluorides of the rare earth metal to the second rare earth metal-acid solution in step e).

[0031 ] In some embodiments, the method comprises, after step e) adding the second base to the remaining second rare earth metal-acid solution, thereby precipitating a mixture comprising oxides or fluorides of the rare earth metal; and adding at least a portion of the mixture comprising oxides or fluorides of the rare earth metal to the third rare earth metal- acid solution in step h).

[0032] In some embodiments, the rare earth metal can be scandium, yttrium, or a lanthanide.

[0033] In some embodiments, the rare earth metal can be scandium.

[0034] In some embodiments, the first or the second base can include a hydroxide or carbonate base.

[0035] In some embodiments, the first or the second base can include LiOH,

NaOH, KOH, CsOH, Mg(OH) ₂ , Ca(OH) ₂ . Sr(OH)2, Ba(OH) ₂ , NH ₄ OH, L12CO3, NaiCOs,

K2CO3, CS2CO3, MgC0 ₃ , CaC0 ₃ , SrCOa, BaCOa, or (NH 2CO3, or a mixture thereof. [0036] In some embodiments, the first and the second base can include NaOH,

Na2C0 ₃ , NH4OH or (NH ₄ )2C0 ₃ .

[0037] In some embodiments, the acid can include HQ, HNO3, H2SO4, HI, HBr,

HCIO4, or HQO3, HF, H3PO4, or a mixture thereof.

[0038] In some embodiments, the acid can include HQ and HN03.

[0039] In some embodiments, a ratio of HQ to HNO3 can be between about 1 : 1 and 1: 10.

[0040] In some embodiments, a ratio of HQ to HNO3 is about 1:3.

[0041] In some embodiments, step a) can be performed at a temperature of at least about 80 °C.

[0042] In some embodiments, step a) can be performed at a temperature of at least about 150 °C.

[0043] In some embodiments, step a) can be performed between about 160 °C to about 200 °C.

[0044] In some embodiments, the alkali metal fluoride can be LiF, NaF, or KF.

[0045] In some embodiments, the alkali metal fluoride can be LiF.

[0046] In some embodiments, the alkali metal fluoride can be NaF.

[0047] In some embodiments, a method of producing scandium from scandium oxide can include a) dissolving a first portion of SC2O3 in an acid to prepare a first Sc-acid solution, wherein the acid can include HQ and H O3 with a ratio of about 1:3 and with a temperature between about 160 °C to about 200 °C; b) reacting a first portion of LiF with the first Sc-acid solution, thereby precipitating a first portion of ScF3 and, optionally, after step b), adding a first base to a remaining first Sc-acid solution, thereby precipitating a first mixture comprising hydroxides, carbonates, or fluorides of Li and Sc, wherein the first base including

NaOH, NazCOs, NH4OH or (NH^CC , collecting and heating the first mixture comprising hydroxides, carbonates, or fluorides of Li and Sc to drive off at least a portion of water or carbon dioxide, thereby producing a second mixture comprising oxides of Li and Sc, and causing an electrolysis of the second mixture to produce a first portion of Li and a third portion of Sc; c) include reacting the first portion of Li with the first portion of ScF3 to produce a first portion of

Sc and a second portion of LiF; d) collecting the first portion of Sc; e) recycling at least a part of a remaining first portion of ScFs and the second portion of LiF from step c) for a reaction in a second Sc-acid solution comprising a dissolved second portion of SC2O3, thereby precipitating a second portion of ScFs and, optionally, after step e), adding a second base to a remaining second Sc-acid solution, thereby precipitating a third mixture including hydroxides, carbonates, or fluorides of Li and Sc, wherein the second base is selected from the group consisting of NaOH, Na_C03, NH4OH or (NH ₄ )2C03, collecting and heating the third mixture comprising hydroxides, carbonates, or fluorides of Li and Sc to drive off at least a portion of water or carbon dioxide, thereby producing a fourth mixture comprising oxides of Li and Sc, and causing an electrolysis of the fourth mixture to produce a second portion of Li and a fourth portion of Sc: f) reacting the second portion of Li with the second portion of ScFs to produce a second portion of Sc and a third portion of LiF; and g) collecting the second portion of Sc.

[0048] In some embodiments, a method of producing scandium from scandium oxide can include a) dissolving a first portion of SC2O3 in an acid to prepare a first Sc-acid solution, wherein the acid comprises HQ and HNO3 with a ratio of about 1 :3 and with a temperature between about 160 °C to about 200 °C, b) reacting a first portion of NaF with the first Sc-acid solution, thereby precipitating a first portion of ScFs and, optionally, after step b), adding a first base to a remaining first Sc-acid solution, thereby precipitating a first mixture comprising oxides or fluorides of Sc, wherein the first base including NaOH, NaiCC , NH ₄ OH or (NH 2CO3, and adding at least a portion of the first mixture comprising oxides or fluorides of Sc to a second Sc-acid solution in step e); c) reacting a first portion of Na with the first portion of ScF3 to produce a first portion of Sc and a second portion of NaF; d) collecting the first portion of Sc; e) recycling at least a part of a remaining first portion of ScF3 and the second portion of NaF from step c) for a reaction in the second Sc-acid solution including a dissolved second portion of SC2O3, thereby precipitating a second portion of ScF3 and, optionally, after step e), adding a second base to a remaining second Sc-acid solution, thereby precipitating a second mixture comprising oxides or fluorides of Sc, wherein the second base including NaOH, Na2C03, NH4OH or (NH ₄ )2C03, and adding at least a portion of the second mixture comprising oxides or fluorides of Sc to a third Sc-acid solution in step h); f) reacting a second portion of Na with the second portion of ScFs to produce a second portion of Sc and a third portion of NaF; g) collecting the second portion of Sc; h) recycling at least a part of a remaining second portion of ScF3 and the third portion of NaF from step f) for a reaction in a third Sc-acid solution comprising a dissolved third portion of SC2O3, thereby precipitating a third portion of SCF3; i) reacting a third portion of Na with the third portion of ScF3 to produce a third portion of Sc and a fourth portion of NaF; and j) collecting the third portion of Sc. [0049] In one aspect, rare earth metal oxides can be dissolved in an acidic solution such as HC1 and/or HNOs to fonn a rare earth metal-acid solution. Aqueous alkali metal fluorides such as LiF can react with the excess rare earth metal in the solution, such as Sc(NOs)3 to produce ScF3 precipitates and L1NO3. Some unreacted Sc(NC )3 can remain in the solution. The liquid and nitrate in the solution can be driven off as a vapor to leave behind Li OH with some Sc(OH)3. Alternatively, a reagent can be used to precipitate a Li and Sc compound or mixture of compounds e.g. carbonates/hydroxides/oxalates. Afterwards, the Li and Sc compound(s) can be calcined into oxides, and electrolytically reduced. The resulting Li with some Sc can be then used to reduce ScFs in a welded retort comprising Ta, Nb, Mo, V, W, or Cr. In some embodiments, this process can avoid the costly hydrofluorination step, minimize rare earth metal losses, potentially replace welded refractory metal retorts with much less expensive metals, and/or reduce energy consumption.

[0050] In some embodiments, the acidic solution can comprise any mineral acid or inorganic acid such as HQ, HNO3, H2SO4, HI, HBr, HCIO4, HCIO3, HF, or R3PO4, or a mixture thereof. In some embodiments, the acidic solution can comprise any strong acid such as HQ, HNO3, H2SO4, HI, HBr, HQO4, or HQO3, or a mixture thereof. In some embodiments, the acidic solution can comprise HCL or HNO3, or a mixture thereof. In some embodiments, the acidic solution can comprise HCL and HNO3 with a ratio of about 1 : 1 to about 1: 10. In some embodiments, the alkali metal fluoride is LiF, NaF, KF, RbF, or CsF, or a combination thereof. In some embodiments, the alkali metal fluoride is LiF or NaF.

[0051] Figure 1 shows a flow chart of an overall process for producing scandium from its oxide with an optional lithium electrolysis process. This process can have many advantages. For example, a high-temperature hydrofluorination step or ammonium bifluoride reaction associated with high energy cost and safety risks can be avoided. A recovery of excess rare earth metal nitrate or other solution which does not precipitate as fluoride can result in a very high yield in scandium production. A recovery of excess rare earth fluoride from a metallothermic reduction can also help with a high yield in scandium production. Most reagents are recycled in closed loop, thereby increasing efficiency and yield. There is also a potential independence from the use of tantalum or tungsten. This overall process as illustrated in Figure 1 can also help produce scandium metal with improved purity.

[0052] In some embodiments, the processes described herein can be used for production of any rare earth metals in the periodic table such as Sc, Y, or any lanthanoids such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. In some embodiments, the processes described herein can be used for production of Sc, Y, or any heavy rare earth metals such as Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. hi some embodiments, processes described herein can be used for production of Sc or Y.

[0053] In some embodiments, at least some of the steps can be performed in the closed-loop condition. In some embodiments, Li reagent can be recycled using an electrolysis process, thereby preferably increasing the scandium production yield. For example, LiF precipitation of ScF3 can have a yield of about 80-90%, with excess Sc ^3÷ remaining in solution to prevent HF formation. In this process, the remaining Sc ³⁺ is not lost because it is

electrolytically reduced together with Li and fed into the metallothermic reduction step.

Likewise, metallothermic reduction can use excess ScF.3 to lower the lithium content and activity in Sc metal product, avoiding an Sc distillation step, and to potentially line the retort and allow the use of lower-cost retort materials than tantalum such as niobium, molybdenum, vanadium, or even chromium. In some embodiments, this preferably provides safe low-cost aqueous ScF3 synthesis, and metallothermic reduction with excess ScF3 for higher purity. Again, ScF3 is not lost here, because it is recirculated back with LiF to the digestion/metathesis/precipitation step.

[0054] The flow chart in Figure 1, among other things, can invol ve the following five-unit operations: digestion-metathesis-precipitation; precipitation and calcination/drying; wet scrubbing (not shown in Figure 1); molten salt electrolysis reduction; and metallothermic reduction. The overall reaction for producing scandium from its oxide is: SC2O3 + FINO3 + (NH4)2C03→ Sc + O2 + H2O + CO2 + NH4NO3. In some embodiments, with nitrate recover}' from wet scrubbing, the overall reaction can be: SC2O3 + H2O2→ Sc + O2 + H2O.

[0055] In some embodiments, the process can start with a dissolution of a rare earth metal oxide such as SC2O3 in an acid. The oxide can dissolve to form a rare earth metal oxide solution, for example, SC2CI3 or Sc2(N03)3, and undergo fluoride digestion-metathesis- precipitation. This reaction can be performed by a fluoride such as LiF, and the reaction formula is: 3 LiF(aq) + Sc ^3÷ (aq)→ ScF3(s) + Li ⁺ (aq). This reaction can be based on different solubility products between LiF at 1.84x 10 ^"3 (slightly soluble) (see CRC Handbook of Chemistry and Physics, 84th Edition (2004); herein incorporated by reference in its entirety) and rare earth metal fluorides, the highest of which is ScF ₃ at 3.0* 10 ^"12 (see Bull. Chem. Soc. Jpn. 57: 1689- 1690, 1984; herein incorporated by reference in its entirely). Using these two gives [Li] = [F] = 0.043; that fluoride concentration can lead to [Sc] = 3.8* 10 ^"8 .

[0056] As illustrated in Figure 1, in some embodiments, LiF as well as ScF3 from the metallothermic reduction can be recirculated to perform the digestion-metathesis- precipitation step. This way, LiF and ScF3, left over from the metallothermic reduction is not wasted, and this can improve the overall scandium production yield.

[0057] In some embodiments, fluoride solubility products of rare earths including yttrium are orders of magnitude lower than that of scandium. (Bull. Chem. Soc. Jpn. 57: 1689- 1690, 1984; herein incorporated by reference in its entirety.) Therefore, LiF as described in the process can also be used to precipitate YF3, GdF3, DyF3, TbF3, or any other rare earth metal fluorides. Therefore, in some embodiments, the process can be used to replace

hydrofluorination.

[0058] In some embodiments, excess Sc ion can remain in the solution with

L1NO3 and L12O, and is co-reduced with Li as described below in the precipitation,

drying/calcining, and electrolysis steps. This can result in yet another recirculation that can improve yield.

[0059] The flow chart in Figure 1 shows precipitation and drying/calcining that can be done, for example, using two different methods. As illustrated in Figure 1, L1NO3 and Sc(N03)3 can remain after the digestion-metathesis-precipitation reaction, which can undergo the drying/calcining process step and convert to lithium oxides, lithium carbonates, scandium oxides, and scandium carbonates.

[0060] For the first method, in some embodiments, the whole nitrate solution can be dried to reduce the volume of liquid, e.g. by membrane filtration or distillation, followed by calcination of the resulting hydrate/hydroxide to form the oxides.

[0061] For the second method, in some embodiments, a precipitating agent, such as sodium or ammonium hydroxide or carbonate, can be used to precipitate lithium and any remaining scandium. Lithium and scandium precipitates can be filtered, dried, and calcined. This method preferably uses less energy than filtration/distillation and calcination. In some embodiments, complete calcination may be skipped for carbonates, which could be used directly as reduction cell feedstock with in situ calcination, as CO2 solubility in LiCl-LiiO is relatively low (Fl. Phase Equilibr. 385:48, 2014; herein incorporated by reference in its entirety) - unless this leads to passivation at the cathode as described below. In some embodiments, input of nitric acid and ammonium carbonate rather than H2O2, and managing the resulting aqueous waste optionally including NH3NO3 (which might be salable) may be preferred. In some

embodiments, this method may reduce rare earth metal yield due to losses in the solution phase, as rare earth hydroxides precipitate at lower pH than LiOH. [0062] In some embodiments, when HNO3 is used as an acid to dissolve rare earth metals, remaining NO, NO2, or NOx in the rare earth metal-acid solution from the metathesis/precipitation step can be recycled using wet scrubbing. In some embodiments, wet scrubbing can be H2O2 reacting with NO and NO2 gases (produced from the drying/calcining step) to form nitric acid at high conversion rate (J. Air Waste Mgt. Assoc. 46(2): 127-133, 1996; herein incorporated by reference in its entirety)- In alternate embodiments, catalytic reduction could be used to reduce NOx to N2 and O2 or react NOx with a fuel such as natural gas. In some embodiments, the nitric acid formed under this web scrubbing step can be recirculated back to the digestion step to dissolve scandium oxide or any rare earth metal oxides.

[0063] The electrolytic reduction step can convert lithium and scandium compounds (e.g., lithium and scandium oxides, and lithium and scandium carbonates) into lithium and scandium metals. In some embodiments, the produced lithium and scandium metals can be used for the metallothermic reduction shown in Figure 1.

[0064] In some embodiments, electrolytic reduction can use a low-solubility membrane such as a solid oxygen ion-conducting membrane (SOM) or porous ceramic. In some embodiments, a zirconia SOM can be preferably suited to lithium (see US Patent 4,804,448; herein incorporated by reference in its entirety) as zirconia has negligible solubility in LiF-Li20, whose eutectic temperature is 820 °C (LiF melts at 849 °), with 10 wt. % oxide solubility (see Metall. Trans. 24(6): 1031 (1993); herein incorporated by reference in its entirety), and in LiCl- L12O with 8 wt. % oxide solubility at 650°C (J. Nucl. Mater. 300(1): 15 (2002); herein incorporated by reference in its entirety), hi some embodiments, lithium can float at the cathode, and may be kept away from the SOM, e.g. using a steel or similarly immiscible solid metal sponge for the cathode, or an inverted conduit directing the floating lithium away from the anode. The Li-Sc phase diagram (see JPEDAV 30: 117; herein incorporated by reference in its entirety) shows considerable scandium metal solubility even at a relatively low electrolysis temperature of 850°C. Thus, any scandium left in solution can be present as SC2O3, and can dissolve in the bath and eventually be reduced with the lithium.

[0065] The Li-Sc phase diagram by H. Okamoto, as referenced above, shows that

LiCl-Li20 can have a very low solubility for MgO since AG° for the reaction Li20 + MgC12→ 2 LiCl + MgO is about -201 kJ/mol at about 650 °C. In some embodiments, MgO crucibles are used to contain LiCl melts (Y. Sakamura, M. Kurata, and T. Inoue, J. Electrochem. Soc, 153, D31 2006). This could suggest an electrolytic cell using a porous MgO membrane similar to that used by Alcoa (D. De Young, US Patent 4,988,417; herein incorporated by reference in its entirety). In some embodiments, unlike the method described by Alcoa, a schematic of a L12O reduction cell 500 using a porous MgO membrane 502, as shown in Figure 5, can use a porous membrane only to segregate the anode product from the lithium metal. The Alcoa patent used the membrane to separate a carbonate-containing anolyte from the LiCl catholyte.

[0066] In some embodiments, a cathode 510 as shown in Figure 5 can comprise

Li. An anode 508 shown in Figure 5 can comprise a solid Ag. In some embodiments, L12O 504 can be added and O2 506 can be produced as illustrated in Figure 5.

[0067] In some embodiments, the system, as shown in Figure 5 could avoid carbon in the feedstock. Thus, a reaction between lithium metal and small amounts of carbonate in the cathode compartment forming carbon and L12O and passivating the cathode may be avoided.

[0068] The porous MgO membrane 502 as illustrated in Figure 5 could be economically fabricated by calcining natural magnesite.

[0069] In some embodiments, e.g., as illustrated in Figure 5, segregation of the reaction products could rely on the LiCl-Li20 wetting the porous MgO 502 and preventing O2 bubbles 506 from passing through the membrane.

[0070] The metallothermic reduction step can react ScF. precipitates with lithium metal to produce scandium metal. In some embodiments, the ScF3 precipitates can come from the digestion-metathesis-precipitation step as illustrated in Figure 1. The lithium metal, likewise, can come from the electrolytic reduction step as illustrated in Figure 1. In some embodiments, any unreacted ScF.3 as well as LiF produced from the metallothermic reduction step can be recycled for the digestion-metatliesis-precipitation step as illustrated in Figure 1. This recycling, as stated above, can help increase the yield rate of scandium .

[0071] The metallothermic reduction step shown in Figure 1, in some embodiments, can be done in a welded vacuum retort. An excess rare earth fluoride can minimize lithium contamination of the scandium product, though the low solubility of Li in solid rare earths - much lower than those of Ca and La - can mean that large excess is preferably not required. Lithium and scandium can boil at about 1,342 °C and 2,836 °C respectively, and LiF and ScF3 at about 1,673 °C and 1,607 °C respectively. Thus, lithium can preferentially evaporate, react with ScF3 present, and form lithium fluoride. In some embodiments, with slight excess ScFs, all or almost all of the lithium can be consumed, preventing vapor buildup and pressure accumulation. [0072] In some embodiments, rare earth metal fluoride can also line the crucible, enabling lower-cost materials. One possible crucible material for metallothermic rare earth reduction can be tantalum, which has a very low solubility in both rare earth metal solids and lithium liquid (see J. Alloy Phase Diagrams, 6(1), Jan 1990; herein incorporated by reference in its entirety, but considerably higher in scandium liquid, as shown in the phase diagram illustrated in J. Less-Comm. Met., 10(2), 108-115 (1966); herein incorporated by reference in its entirety). Using tantalum, the reduction temperature is preferred to be kept below the Sc-Ta eutectic temperature of about 1,520 °C. In alternate embodiments, the following materials can be considered: Nb where the reduction temperature is preferred to be kept below the Sc-Nb eutectic temperature of about 1 ,500 °C (see Smithells Metals Handbook Eighth Edition p. 11- 422 herein incorporated by reference in its entirety), V where the reduction temperature is preferred to be kept below the Sc-V eutectic temperature of about 1,420 °C (see phase Diagrams of Binary Vanadium Alloys, 1989; herein incorporated by reference in its entirety), W where the reduction temperature is preferred to be kept below the Sc-W eutectic temperature of about 1510 °C (see J . Phase Equilibria, 21, 574 (2000); herein incorporated by reference in its entirety), Mo where the reduction temperature is preferred to be kept below the Sc-Mo eutectic temperature of about 1,370 °C (the Sc-Mo phase diagram was calculated based on thermod iamic functions), and Cr where the reduction temperature is preferred to be kept below the Sc-Cr eutectic temperature of about 1,090°C (Smithells Metals Handbook Eighth Edition p. 11-240; herein incorporated by reference in its entirety). At the preferred reduction temperatures, the process would produce scandium sponge. Therefore, in some embodiments, crucible materials can comprise Ta, Nb, V, W, Mo, or Cr.

[0073] In some embodiments, like scandium, lithium liquid dissolves very little

W (see J. Phase Equilibria, 21, 574 (2000); herein incorporated by reference in its entirety), Nb (see Bull. Alloy Phase Diagrams, 9(4), Aug 1988; herein incorporated by reference in its entirety). Mo (see At. Energ. (USSR), 7, 531-536 (1959) in Russian; At. Energy, 7, 987-992 (1961); Acta Metall., 9, 519-520 (1961); USAEC Rep. No. ΉΜ-850 (1965); each of which hereby incorporated by reference in its entirety), V (see Phase Diagrams of Binary Vanadium Alloys, 1989, and Bull. Alloy Phase Diagrams, 9(4), Aug 1988; each of which hereby incorporated by reference in its entirety') or Cr (see Bull. Alloy Phase Diagrams, 5(4), Aug 1984; herein incorporated by reference in its entirety). Therefore, Nb, Mo, V, or Cr are possible crucible materials with lower cost that are easier to weld compared to tantalum. In some embodiments, a crucible material comprising tungsten can be more durable and contaminate the product less. [0074] In some embodiments, the process can achieve profitable operation at an industrial scale. For example, costs of digestion and metatliesis/precipitation can decline rapidly with an increasing scale. In some embodiments, this process can achieve 1) successful precipitation of ScF3 solid from aqueous solution using LiF with greater than 80% yield; 2) successful reduction of lithium metal from its oxide in molten LiF-LkO solution; and/or 3) successful reduction of scandium metal from ScF3 by reaction with lithium metal.

[0075] In some embodiments, ScF3 precipitation is preferably reacted at higher scandium concentration and higher pH than achievable by acid digestion at 1 arm due to poor SC2O3 dissolution kinetics below 100 °C and weak acidity. In some embodiments, dissolution of SC2O.3 or any rare earth metals can be performed at about 80 °C or higher. In some

embodiments, dissolution of SC2O3 or any rare earth metals can be performed at about 150 °C or higher. In some embodiments, microwave dissolution of SC2O3 or any rare earth metals can be performed at about 150 °C or higher in a sealed chamber. In some embodiments, dissolution of SC2O3 or any rare earth metals can be performed between about 160 °C to about 200 °C in a sealed chamber. In some embodiments, microwave dissolution in a sealed vessel at about 180°C can be used, and a base is preferably added to increase the pH prior to addition of LiF or any other alkali metal fluorides.

[0076] In some embodiments, the base can comprise LiOH, NaOH, KOH, CsOH,

Mg(OH)2, Ca(OH) ₂ , Sr(OH) ₂ , Ba(OH) ₂ , NH4OH, L12CO3, Na ₂ C03, K2CO3, CS2CO3, MgCCb, CaCO.3, SrCO.3, BaCO.3, or (NH 2CO3, or a mixture thereof.

[0077] In some embodiments, having demonstrated the process for scandium production, yttrium and other rare earth metals from lanthanum to lutetium can work better than scandium, due to much lower fluoride solubility products in water (e.g., by 5-15 orders of magnitude) and lower metal melting points.

[0078] The detailed flow chart in Figure 1 shows nine process Inputs labeled

Stream 1-9 and eight process Outputs labeled Stream 10-17 as explained below:

[0079] Nine Inputs labeled Stream 1-9

[0080] Stream 1 can comprise SC2O3 raw material for digestion. In some embodiments, Stream 1 can comprise oxides comprising any rare earth metals in the periodic table such as Sc, Y, or any lanthanoids such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. [0081] Stream 2 can comprise HNO3/HCI to dissolve SC2O3. In some other embodiments. Stream 2 can comprise any mineral acid or inorganic acid such as HQ, HNO3, H2SO4, HI, HBr, HCIO4, HCIO3, HF, or H3PO4, or a mixture thereof that can dissolve oxides comprising any rare earth metals as described above. In some embodiments, Stream 2 can comprise any strong acid such as HCL HNO3, H2SO4, HI, HBr, HCIO4, or HCIO3, or a mixture thereof. In some embodiments, Stream 2 can comprise HCL or HNO3, or a mixture thereof.

[0082] Stream 3 can comprise LiF/NaF make-up material for metathesis, to account for lithium/sodium losses. In some embodiments, Stream 3 can comprise any alkali metal fluorides such as LiF, NaF, KF, RbF, or CsF, or a combination thereof. In some embodiments, Stream 3 can comprise alkali metal fluorides such as LiF or NaF. In some embodiments, Stream 3 can comprise LiF.

[0083] Stream 4 can comprise NaOH, NH4OH, Na ₂ C0 ₃ or (NH ₄ )2C0 ₃ to precipitate LiOH-Sc(OH)3 or Li2C03-Sc2(C03)3. In some embodiments. Stream 4 can be precipitating agent comprising hydroxides or carbonates. In some embodiments, Stream 4 can be precipitating agent comprising sodium or ammonium hydroxide or carbonate. In some embodiments, Stream 4 can be precipitating agent comprising hydroxides, carbonates. In some embodiments, Stream 4 can be precipitating agent comprising sodium hydroxide, sodium carbonate, ammonium hydroxide, or ammonium carbonate.

[0084] Stream 5 can comprise NaOH or HC1 to neutralize solution from lithium precipitation. In some embodiments. Stream 5 can comprise any base or acid that can neutralize solution from any alkali metal precipitation.

[0085] Stream 6 can comprise H2 and/or Ar gas to help convert LiOH or L12CO3 as well as Sc(OH)3 or Sc2(C03)3 to L12O and SC2O3. In some embodiments, this step may not be needed for carbonate drying.

[0086] Stream 7 can comprise carbon for the lithium and/or Sc molten salt electrolysis anode.

[0087] Stream 8 can comprise tantalum or other refractory metal crucibles comprising Nb, V, W, Mo, or Cr.

[0088] Stream 9 can comprise make-up lithium or sodium metal. In some embodiments. Stream 9 can comprise alkali metals such as Na, K, Rb, or Cs

[0089] Eight Outputs labeled Stream 10-17. [0090] Stream 10 can comprise NaN03/NH*N03 or Na2C0 ₃ /(NH4)2CC>3 solution remaining from LiOH-Sc(OH)3 precipitation and neutralization, likely to discharge, possibly for off-take/resale.

[0091] Stream 11 can comprise water and/or CO2 from LiOH-Sc(OH)3 (or

Li2C03-Sc2(COj)3) calcination, plus sparging gas, much of which may be recoverable.

[0092] Stream 12 can comprise unused carbon anode stubs.

[0093] Stream 13 can comprise CO2 and/or O2 anode gas from molten salt electrolysis.

[0094] Stream 14 can comprise LiF bath losses in Li electrolysis with small amounts of SC2O3.

[0095] Stream 15 can comprise spent or consumed tantalum metal crucibles during the reactions. In some embodiments, Stream 15 can comprise any materials that crucibles used in this process are made of. For example, Stream 15 can comprise spent or consumed Nb, V, W, Mo, or Cr.

[0096] Stream 16 can comprise scandium metal product. In some embodiments,

Stream 16 can be any rare earth metal product including Sc, Y, or any lanthanoids such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu.

[0097] Stream 17 can comprise nitric/hydrochloric acid solution vapor from

SC2O3 dissolution and/or ScF3 drying. In some embodiments, Stream 17 can be any acid vapor from dissolving any rare earth metal oxides and/or any rare earth metal fluorides drying.

[0098] In Figure 1, the Streams and Compositions tabs track input and output of each compound in the flow chart, which can ensure that every element is conserved. They can also be used to calculate the cost of each input stream, and value of each output stream, as the basis for raw material costs and income of the plant.

[0099] In some embodiments, process steps and governing equations for Figure 1 are as follows.

[00100] SC2O3 Dissolution Reaction.

SC2O3 (s) + vi ScF ₃ (s) + (6+3vi+wi) HNO3 (aq) + xi H2O→ (2+vi) Sc(N0 ₃ )3 (aq) + (wi-zi) HNO3 (aq) + 3vi HF (aq) + (3+xi-ji) H2O (1) +yi H2O (g) + zi HNO3 (g) (Eq. 1)

[00101] In some embodiments, dissolution reaction can involve dissolving any rare earth metal oxides using any types of acid. The flow chart in Figure 1 shows dissolving SC2O3 using nitric acid and/or hydrochloric acid. In some embodiments, any unreacted ScF3 from the metallothermic reduction step can be recycled under this dissolution reaction. This dissolution reaction can produce scandium-acid solution as well as some acid vapor (Stream 17).

[00102] Parameters of the SC2O3 dissolution reaction can be ScF3 ratio vi, excess acid wi, excess water xi, evaporative water loss yi, and evaporative nitric acid loss zi. In some embodiments, the model assumes complete or near complete scandium oxide/fluoride dissolution. In some embodiments, all resulting solution goes to the metathesis/precipitation step.

[00103] In some embodiments, SC2O3 digestion can be optimized by

experimenting with temperature, pressure, pH, and reagents.

[00104] Metathesis/Precipitation Reaction.

[00105] All following chemical formulas are in aqueous (aq) state unless indicated otherwise):

[00106] In some embodiments, metathesis/precipitation reaction can be performed by reacting any rare earth metal-acid solution produced with any alkali metal fluorides and optionally with any bases such as LiOH, NaOH, KOH, CsOH, Mg(OH) ₂ , Ca(OH) ₂ , Sr(OH) ₂ , Ba(OH) ₂ , NH ₄ OH, Li ₂ C03, Na ₂ C03, K2CO3, CS2CO3, MgC0 ₃ , CaCCfc, SrCOs, BaC0 ₃ , or (NH 2CO3, or a mixture thereof. The flow chart in Figure 1 shows reacting scandium-acid solution with LiF to produced ScF3 precipitates. In some embodiments, LiF can be recycled from the metallothermic reduction step, and additional make-up LiF can be also added as represented by Stream 3. In some embodiments, the reacted lithium can be recycled through lithium precipitation, calcination/drying, and molten salt electrolysis steps as illustrated in the flow chart.

[00107] Parameters of this metathesis/precipi tation reac tion as shown in Figure 1 can be base addition V2 (raises pH, reduces HF concentration), SC2O3 reversion W2, excess Sc(N03)3 X2 (can be negative), scandium fluoride metathesis reaction extent V2, and retained solution salts in the ScF3 product Z2. In some embodiments, excess Sc(N03)s can remain in solution with L1NO3. In some embodiments, some fluoride can be retained in solution mainly as HF (shown above as LiF, it's more likely Li ^÷ + OH + HF), as it is a relatively weak acid. [00108] In some embodiments, Metathesis/Precipitation Reaction's ScF3 precipitation yield can be optimized by experimenting with pH, temperature, other reagents, and LiF concentration.

[00109] Sc/Li Precipitation.

[00110] Two possible precipitating reagents in this step are OH ^" and CO3 ^2" , with sodium or ammonium cations or other bases. Reactions are shown here for ammonium cations.

[00111] Parameters of the Sc/Li Precipitation can be excess precipitating agent x ₃ and lithium reaction extent ys. hi some embodiments, there can also be Sc ^3H~ in the solution, that should precipitate preferentially over lithium in the hydroxide or carbonate case:

[00112] Parameters can be scandium reaction extent Z3. In some embodiments, both reagents can increase pH, reducing HF concentration and precipitating more ScF3 and LiF. Another parameter W3 is fraction of "LiF" from the prior step which precipitates out in this step due to the change in pH.

[00113] In some embodiments, any precipitating agents, such as sodium or ammonium hydroxide or carbonate can be used for this step. In some embodiments, as illustrated in Figure 1, waste solution from this step can be neutralized using any neutralizing agent (Stream 5), such as NaOH or HQ, or any base or acid. The neutralized waste solution (Stream 10) can be NaN03/NH4N03 or Na2C03/(NH4)2C03, and this can be discharged or possibly recycled or resold.

[00114] In some embodiments, lithium precipitation yield can be optimized by experimenting/researching with conditions for precipitation of LiOH and Sc(OH)3, or Li2C03 and Sc2(C0 ₃ )3.

[00115] Calcination/Drying. [00116] Calcmation/Drying lithium/scandium precipitation for hydroxides or carbonates; for the hydroxide:

[00117] In some embodiments, as illustrated in Figure 1, sparging gas (Stream 6) such as H2 and/or Ar gas can be used to help convert LiOH or L12CO3 as well as Sc(OH)3 or Sc2(C03)3 to L12O and SC2O3. In some embodiments, this step may not be needed for carbonate drying. Any leftover water (or CO2) and sparging gas from this reaction can be recovered and reused (Stream 11).

[00118] Parameters can be lithium and scandium reaction extents xn and j¼, and sparging gas ratio z ₄ which can be the molar ratio of H2 or Ar to total Li+Sc ions (not shown in reactions).

[00119] In some embodiments, water can be removed from hydroxide or carbonate precipitate, and CC can be removed from L12CO3 and Sc2(C03)3.

[00120] Molten Salt Electrolysis.

[00121] Molten Salt Electrolysis reaction depends on whether lithium oxide or carbonate is fed:

[00122] Parameters can be CO fraction of exhaust gas:

Scandium oxide or carbonate can also be reduced at the cathode, preferentially to Li. In some embodiments, using a carbon anode (Stream 7) can produce some carbonate in the electrolysis cell, resulting in some amount of carbon formation at the cathode by the reaction:

[00123] In some embodiments, a porous or ion-conducting membrane or similar means can be used to separate the anode region with CO/CO2 or oxygen gas from cathode region with Li metal to increase yield and scale. In some embodiments, Li and Sc produced from this reaction can be used for metallothermic reduction, thereby increasing the overall efficiency and the scandium yield performance.

[00124] Metallothermic Reduction. [00125] The reaction is:

[00126] Parameters can be xe excess ScF3 (leaves the reactor and recirculates with LiF), ye final extent of reaction, and Z6 consumption of tantalum from the crucible. In some embodiments, Ta— or other crucible material (Nb, W, V, Mo, Cr)— and Li metals can enter the Sc metal product as impurities.

[00127] In some embodiments, Nb, W, V, Cr, or Mo can be used to replace Ta as retort material. Effect of ScF3:Li mole ratio on Sc product purity and ScF3 crucible liner can be tested to further improve scandium purity and/or yield.

[00128] In some embodiments, the metallothermic reduction step can be performed with any other alkali earth metals such as (Li, Na, K, Rb, Cs, and Fr), but Li or Na is preferred. In some embodiments, metallothermic reduction can use recycled Li produced from the molten salt electrolysis step. In some embodiments, LiF produced from this metallothermic reaction as well as any unreacted ScFs can be recirculated back to either the dissolution step or the metathesis/precipitation step shown in Figure 1, thereby recycling Li and F in a closed-loop. Unreacted ScF3 can also be recycled in Figure 1, thereby increasing the scandium production yield.

[00129] Figure 2 shows a flow chart of a process for producing scandium from its oxide with an optional lithium electrolysis process according to aspects of the disclosed subject matter. The flow chart in Figure 2 is similar to the flow chart in Figure 1.

[00130] While Figure 1 illustrates the overall process for producing scandium including various inputs (Stream 1-9) and various outputs (Stream 10-17), Figure 2 illustrates a part of the overall the process for producing scandium with two inputs of scandium oxide (Stream 1) and acid (Stream 2) and an output of scandium metal (Stream 16). Although Figure 2 illustrates the process of producing scandium, in some embodiments, the process illustrated in Figure 2 can be used to produce any rare earth metals from their oxides.

[00131] In some embodiments, as illustrated in Figure 1 and/or Figure 2, scandium production process can start by dissolution of scandium metal with nitric acid and/or hydrochloric acid. In some embodiments, any types of acid, such as HC1, HN0 ₃ , H2SO4, HI, HBr, HCIO4, HCIO3, HF, or H3PO4, or a mixture thereof can be used to dissolve scandium oxides or any other rare earth metal oxides. [00132] In some embodiments, scandium-acid solution produced from the dissolution step can go through the metathesis/precipitation step as illustrated in Figure 1 and/or Figure 2. The metathesis/precipitation step can involve reacting scandium ions in the scandium- acid solution with LiF to precipitate the scandium ions, thereby producing ScF3. In some embodiments, the precipitation agent, LiF, can be recycled from the metallothermic reduction step as illustrated in Figure 1 and/or Figure 2. In some embodiments, any other alkali earth fluorides such as NaF, KF, RbF, or CsF, that can be used to precipitate scandium ions (or any other rare earth metal ions in rare earth metal-acid solution).

[00133] In some embodiments, the remaining solution from the

metathesis/precipitation step can be recycled through the lithium/scandium precipitation, the calcination/drying, and the molten salt electrolysis steps as illustrated in Figure 1 and/or Figure 2. This recycling steps using electrolysis can produce Li and Sc, that can be recirculated to the metallothermic reduction step.

[00134] In some embodiments, the metallothermic reduction step as illustrated in Figure 1 and/or Figure 2 can react ScF3 produced from the metathesis/precipitation step with Li metal produced from the molten salt electrolysis step, thereby producing scandium metal. In some embodiments, make up lithium metal (or other alkali metals such as Na, K, Rb, or Cs) can be used to reduce scandium fluoride to produce scandium metal (or other rare earth metals such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).

[00135] In some embodiment, LiF can be produced under the metallothermic reduction step as illustrated in Figure 1 and/or Figure 2. This LiF as well as any unreacted ScF3 can be recirculated back into the process by adding them to the dissolution step and/or the metathesis/precipitation step as illustrated in Figure 1 and/or Figure 2.

[00136] In some embodiments, lithium oxide can be expensive, and electrolytic reduction to lithium metal with a carbon anode may be unfavorable due to the stability of lithium carbonate and CO reactivity with lithium metal. Therefore, scandium recovery by precipitation can also be performed without the molten salt electrolysis step as illustrated in Figure 1 and/or Figure 2. A process for producing scandium without the optional molten salt electrolysis recycling step is illustrated in Figure 3 and/or Figure 4.

[00137] In some embodiments, in addition to avoiding the electrolysis step, Figures 3 and/or 4 can provide for the use of other Group I reductants such as Na, K, Rb, and Cs, as well as Group II reductants. Group II fluoride solubilities in water tend to be orders of magnitude lower than those of Group I fluorides, therefore Group I fluorides are preferable for metathesis/precipitation, and Group I reductants are preferable for metallothermic reduction.

[00138] Figure 3 shows a flow chart of an overall process for producing scandium from its oxide with an optional scandium precipitation process according to aspects of the disclosed subject matter. The overall process of producing scandium illustrated in Figure 3 is similar to the process shown in Figure 1. But the process illustrated in Figure 3 instead rinses and calcines the scandium precipitates (e.g., Sc(OH)3, Sc2(C03)3, SC2O3) and recycles them by adding them to the dissolution step.

[00139] In some embodiments, as illustrated in Figure 3, scandium production process can start by dissolution of scandium metal with nitric acid and/or hydrochloric acid. In some embodiments, any types of acid, such as HC1, HNO3, H2SO4, HI, HBr, HCIO4, HCIO3, HF, or FI3PO4, or a mixture thereof can be used to dissolve scandium oxides or any other rare earth metal oxides.

[00140] In some embodiments, scandium-acid solution produced from the dissolution step can go through the metathesis/precipitation step as illustrated in Figure 3. The metathesis/precipitation step can involve reacting scandium ions in the scandium-acid solution with LiF or NaF to precipitate the scandium ions, thereby producing ScF3. In some

embodiments, a portion of the precipitation agent, LiF or NaF, can be recycled from the metallothermic reduction step as illustrated in Figure 3. In some embodiments, any other alkali earth fluorides such as NaF, KF, RbF, or CsF, that can be used to precipitate scandium ions (or any other rare earth metal ions in rare earth metal-acid solution). In some embodiments, NaF can be preferred due to its higher solubility than LiF's solubility. Fligher NaF solubility makes NaF less likely to precipitate, therefore the ScF3 precipitate can be purer. NaF with higher solubility can allow the metathesis/precipitation step to have higher yield and lower alkali fluoride in the precipitate.

[00141] In some embodiments, the remaining solution from the

metathesis/precipitation step can be recycled through the scandium precipitation step, as illustrated in Figure 3. In some embodiments, a precipitating agent comprising hydroxide or carbonate can be added to the remaining scandium-acid solution from the

metatliesis/precipitation step to precipitate any remaining scandium ions. In some embodiments, scandium ions can be precipitated with a precipitating agent comprising hydroxide or carbonate or other bases as described above with respect to equation 5 and/or equation 6. In some embodiments, Sc ions in the solution can precipitate preferentially over lithium in the hydroxide or carbonate, therefore the precipitation can be stopped before Li ions or Na ions (or any alkali metal ions) begin precipitating.

[00142] In some embodiments, the scandium precipitates (e.g., Sc(OH)3, Sc2(C03)3, and/or SC2O3) can be collected, rinsed, and calcined and recycled back to the dissolution step as illustrated in Figure 3.

[00143] In some embodiments, after some of the scandium ions precipitate, a precipitating agent comprising hydroxide, or carbonate, or other bases can be further added to the remaining solution to further precipitate Li, Na, or any other alkali metal ions as well as any remaining scandium ions. In some embodiments, Li, Na, or any other alkali metal ions can be precipitated according to equation 3 and/or equation 4 as stated above. In some embodiments, the precipitated Li, Na, or any other alkali metal ions (and possibly any remaining Sc ions) can be recycled using the optional Li/Na/Sc metal recovery process similar to those discussed with respect to Figure 1 and/or Figure 2. In some embodiments, the precipitated Li, Na, or any other alkali metal ions (and possibly any remaining Sc ions) can optionally go through the steps of calcination, drying, and molten salt electrolysis to produce Li, Na or any other alkali metal as well as any scandium metal, which can be then added to the metallothermic reduction step.

[00144] In some embodiments, the metallothermic reduction step as illustrated in Figure 3 can react ScF3 produced from the metathesis/precipitation step with Li, Na, or any other alkali metal, thereby producing scandium metal. In some embodiments, Li, Na, or any other alkali metal metals can be optionally recovered from the solution remaining from the metathesis/precipitation step using the process as described above. In some embodiments, Li may be preferred due to its higher melting and boiling points.

[00145] In some embodiments, LiF, NaF, or any other alkali metal fluorides can be produced under the metallothermic reduction step as illustrated in Figure 3. This LiF or NaF as well as any unreacted ScF3 can be recirculated back into the process by adding them to the dissolution step and/or the metathesis/precipitation step as illustrated in Figure 3.

[00146] Figure 4 shows a flow chart of a process for producing scandium from its oxide with an optional scandium precipitation process. The process of producing scandium as illustrated in Figure 4 is similar to the process shown in Figure 3, but Figure 4 illustrates a part of the overall th e process for producing scandium with an optional scandium precipitation process.

EXAMPLES [00147] Example 1: Digestion-Metathesis-Precipitation (DMP)

[00148] SC2O3 digestion with lithium fluoride metathesis and precipitation can take advantage of the higher aqueous solubility of LiF than ScF (and other rare earth fluorides). The overall reaction of that step (equations 1-2) is, for 10% excess SC2O3:

[00149] LiF Solubility Experiment in Water

[00150] Literature showed 0.132 wt. % solubility of LiF in water at room temperature, and 0.15 wt. % solubility at 81°C (R.O. Bach. 1972, J. Chem. Eng. Data 17, 491 (1972); herein incorporated by reference in its entirety). Due to the low increase in solubility with temperature, the first experiment attempted to replicate the conditions at room temperature.

[00151] 100 mL of total solution with lOx excess LiF was used. After sufficient time to dissolve at the specified temperature, a filtration apparatus removed any remaining LiF solids from the vessel. Solubility experiment results were consistent with literature values. No HF was detected.

[00152] SC2O3 Dissolution Experiment

[00153] Literature showed little data on this reaction, general oxide dissolution procedures were employed to complete this step using HN0 ₃ , HQ and mixtures of the two.

[00154] Acid mixtures were added to teflon eVHP vessels containing known amounts of SC2O3. Vessels were loaded into a Questran Microwave able to reach 230 °C and 1000 PSI to perform dissolution with varying dwell time and maximum temperature. Following the dissolution, vessels were removed and visually inspected to determine if Sc20 ₃ had been fully dissolved. If no powder was observed, new vessels were loaded with more Sc20 ₃ . This procedure continued until some Sc20 ₃ did not dissolve, indicating maximum solubility at that acid composition.

[00155] Total volume in the vessel relative to the head space did not play a major role in the dissolution results. Temperature and time, however, had significant impacts. The most promising experiments took place at or above 200 °C with a dwell time of at least two hours. Results did not significantly improve when the dwell time was above two hours. [00156] Using the same operating point for each test moving forward, 30 mL of acid mixtures were loaded in the microwave vessels. Each experiment was conducted in triplicate. The results from dissolution are summarized below:

[00157] Table 1: Dissolution of SC2O3 in various acid/acid mixture

[00158] According to Table 1 , the top performing acid was a 3: 1 by weight mixture of 70% HNO3 - 37% HQ, capable of dissolving 225g/L of SC2O3. This mixture also performed well slightly diluted by 16%, reaching 214 g/L.

[00159] In some embodiments, the acid mixture can be further optimized by experimenting with the ratio of HNO3 and HC1 from about 1:1 to about 1:10. In some embodiments, the ratio of HNO3 and HQ acid mixture can be between about 1 : 1 and 1:10.

[00160] Sc(N03)3 Solution pH Adjustment Experiment

[00161] Calculations showed formation of ScF3 is more favorable at pH above 3.

[00162] Concentrated Ammonium hydroxide was selected to raise pH. It was added in small doses to the Sc(N03)3 solution with mixing until the highest pH was achieved without a precipitate forming.

[00163] Solution pH after adjustment averaged 3.8. Above this pH, milky white precipitate formed. Precipitate analyzed via XRD contained ammonium nitrate and scandium hydroxide.

[00164] Metathesis Experiment

[00165] Acid mixtures and SC2O3 concentrations shown below in Table 2 were made by microwave. LiF and a base (for example, NaOH, Na.C03, NH4OH or (ΝΗ4)2CO3) were added to scandium-acid solution until a precipitate formed. The final product was analyzed via XRD.

[00166] Table 2: Dissolution of SC2O in various acid/acid mixture

[00167] Following digestion, solutions were divided into 30 mL vessels. Multiple experiments tested the effect of adding the base first versus LiF first. Results showed that the conversion to ScF3 in each solution increased by about 3-5 times when adding LiF first. LiF was added at 10% excess fluoride for the conversion reaction and then the pH was increased to the range of about 4.5-5.5 using NaOH, then the precipitate was filtered. Ammonium bases were removed from consideration at this point due to formation of ammonium nitrate, which has an auto-ignition temperature of 300 °C.

[00168] Two parameters in the metathesis step were mixing and reaction times. First, reaction time was tested by running 100 g/L SC2O3 in the 3: 1 HN03-HC1-16% dilution in eight separate vessels (4 times tested in replicate). Then 10% excess LiF was added to each vessel, but allowed to sit for 15 min, 30 min, two hours and four hours respectively. A base increased pH to about 5, and precipitate was filtered and analyzed via XRD. 15 min was not sufficient to generate a consistent response, but there was no significant change in conversion between 2 and 4-hour data points and only a small improvement over the 30 min points which replicated well. Therefore, 30 min is likely sufficient time to generate a consistent response.

[00169] Next, LiF addition timing and mixing were tested to see any effect on the reaction. LiF was added to the same acid mixture in the time study, but in one set of samples in 25% intervals over the 30 min, and in the other all upfront. It was found that there was no difference between the two methods, therefore adding LiF all upfront was chosen due to its simplicity.

[00170] Mixing versus not mixing was tested in the same acid/oxide solution with LiF reaction time of 30 min, with one vessel agitated the full 30 min, and the other mixed for 30 seconds initially and allowed to sit statically for the remaining time. Then as with previous tests, samples were increased to pH of about 5 and filtered prior to XRD analysis. XRD showed that mixing did not have an effect on the conversion and therefore mixing was eliminated for future experiments.

[00171] Experimental Matrix

[00172] An experimental matrix was designed around the results gathered above. Each acid composition was at various Sc ₂ O ₃ concentrations, and ScF3 conversion and total Sc recovery were calculated at each point. Results are as follows:

[00173] Table 3: Experimental Matrix and Result

[00174] Conclusions and Next Steps

[00175] In Table 3 above, preferred operating points are shown in bold. 100 g/L SC2O3 solutions generally performed well, independent of acid composition. Na2C03 performed much better than NaOH at both SCFJ yield and total Sc recovery. High ScF3 yield reduced the amount of SC2O3 recirculating back to the dissolution and metathesis/precipitation steps, reducing equipment sizes and acid/base costs. This process can generate 20-30 tonnes of aqueous waste per tonne Sc metal product, and avoiding nitrates reduces permitting and other disposal costs.

[00176] In some embodiments, LiF concentration can be varied. pH can be increased further to precipitate LiOH and likely Sc(OH>3 to increase scandium yield. Fluorides can be added during dissolution, for example, ScF3 and LiF, recirculated from metallothermic reduction on these aqueous operations can increase the overall yield. Lastly, NaF or other alkali metal fluorides can be used instead of LiF as the ScF3 precipitating agent.

[00177] Example 2: Electrolysis

[00178] The by-product of metathesis-precipitation contains lithium and scandium nitrate in solution which can potentially be co-precipitated as either hydroxides or carbonates. These can be calcined to oxide.

[00179] Batch electrolysis in a cell design 600 shown in Figure 6 was run. The electrolyte was mainly LiF with small amounts of L12O and SC2O3. Mixed oxide feed can simulate a feedstock that would result from earlier steps as discussed above. The goal of electrolysis was the co-reduction of the mixed oxide to form a Li-Sc alloy. The overall lithium oxide reduction reaction followed equation 9 above.

[00180] At 1,000 °C, liquid Li metal density is about 0.43g/cm ³ and liquid LiF density is about 1.8g/cm ³ . Electrolysis thus produces a floating metal as a product unless the weight fraction of scandium exceeds 90 percent. To contain the Li and Li vapors, lithium metal 606 in Figure 6 is produced inside a dam located around a tungsten cathode that is separate from the atmosphere of the cell as shown in Figure 6.

[00181] Experiment 1: Assembly and Procedure [00182] The cell was assembled inside of an IN FIN I UM QuadCell unit, which is designed for controlled atmosphere electrolysis up to 1,200°C. First the graphite crucible 602 was filled with electrolyte comprised of 2.5kg LiF, 50g LiaO, and 7g SC2O3. The lid was then placed on the cell and Ar purged the cell. Next, two 1" graphite anodes 612 and a 0.25" tungsten cathode 614 were loaded into the cell, then the dam assembly was loaded.

[00183] The dam consisted of a zirconia tube 608 encased in steel 610 as shown in Figure 6, such that Li-Sc product metal would remain in a separate atmosphere if the zirconia tube failed. The zirconia dam 608 had 1" in diameter and 4" length and was suspended using 3 small metal tabs. This limited the conduction path by which liquid metal might short from the cathode to the steel. Internal volume was about 51 cm ³ which can contain up to about 25g of liquid Li metal.

[00184] The salt bath was heated slowly to 1,000°C to ensure complete salt drying prior to electrolysis. Once melted, electrodes were lowered into the 4.5" deep bath. Anodes were immersed about 4" into the bath, and the dam and cathode were immersed 1.75" and 2" into the bath respectively.

[00185] Electrolysis ran at 4.0V, producing about 80A current, and was discontinued after about lOOAmp-hours when voltage between the dam and cathode fell below 0. IV indicating short circuiting. During electrolysis a mass spectrometer monitored the CO and CO2 concentrations outside the dam. At the end, electrodes were lifted out of the bath and the power supply was shut off.

[00186] During the electrolysis, no gas evolution was observed at the anodes, but a layer of carbon dust floated on the bath surface.

[00187] After the cell was cooled but before disassembly, the inside of the dam was exposed to a small amount of air for about 30 minutes to passivate any reactive metal that may have evaporated and condensed. Both the surface of the salt in the dam and the cathode contained a red deposit and no metallic deposit. The red powder was analyzed via EDS and XRD, identifying the red compound as L13N.

[00188] Electrolysis anode gases can react with L12O feedstock at 950°C to form lithium carbonate by the following reactions:

2 CO (g) + L12O→ L12CO3 + C; CO2 (g) + L12O→ L12CO3 (Eq. 13)

[00189] These reactions could also explain why no gas evolution was observed.

To test this hypothesis, a small amount of bath was analyzed via XRD. Results showed 97.9% griceite (LiF) and 2.12% zabuyelite (L12CO3) indicating that most of the oxide added to the bath converted to carbonate.

[00190] Dissolved carbonate ions can cause several problems in a lithium cell. The main concern is the reaction between the CO3 ions and Li metal product at the cathode to form lithium oxide, which dissolves back in solution, and carbon dust. This may explai why no metal was recovered.

[00191] Experiment 2: Assembly and Procedure

[00192] To test the reduction of a now carbonate feed stock, the cell was assembled following the sample procedure as the first experiment with three deviations. The deviations from the original procedures were employed to reduce the back reaction observed in experiment one.

[00193] The first deviation was that fresh salt was not used. Instead the previous bath which contained carbonate was used. The second deviation was to simulate a tortuous path to the cathode to limit diffusion of the carbonate ion to the cathode by lowering the dam 0.5" from the bottom of the crucible. The cathode was also recessed into the dam 0.5", unlike the previous experiment where the cathode had been exposed 0.25". This should result in mass transport limitation at the cathode, creating an area low in carbonate ion concentration. The last deviation was that operating temperature was increased from 950 °C to 1,000 °C, which was set to help reduce the conversion of dissolved oxide. At temperatures over 980 °C, CO is less likely to react with dissolved lithium oxide, which can help reduce the overall conversion to carbonate.

[00194] After the cell was cooled but before disassembly, the dam was exposed to a small amount of air for about 30 minutes to passivate any reactive metal fines formed by evaporation and condensation. The cathode was then removed from the cell. Li metal deposit is visible on the cathode and was found on the inside of the dam as well. A small amount of carbon was also present on the metal at the cathode, possibly due to carbonate ion reaction with product lithium metal. The total mass of metal product was about 2.9 g.

[00195] Using graphite anodes complicated electrolysis because some of the current converted dissolved oxide into carbonate which reacts with product metal. However, carbonate electrolysis has shown some promise if carbonate ions could be kept away from the cathode. Making carbonates in the Li precipitation step turns the calcination unit operation into a lower-temperature drying operation, and would reduce the danger of hydroxide reaction with fluoride bath to form HF. [00196] In alternate embodiments, it may be possible to use zirconia solid electrolyte membranes at the anodes to prevent carbonate formation, as zirconia should be very stable in this molten salt system .

[00197] Example 3: Metallothermic Reduction of ScF ₃

[00198] An aspect of this process is the deliberate use of excess ScFi vs. Li in the metallothermic reduction step. The LiF and ScF3 remaining after this step can return to the dissolution or metathesis-precipitation operation, so excess ScF3 is not lost. This excess ScF3 can lead to low lithium activity in the system, and high Sc metal purity. Solubility of Li in Sc is also lower than that of Ca resulting in higher Sc metal purity than today's metallurgical grade material.

[00199] A HSC Chemistry thermodynamics calculation examined the effect of a small amount of excess ScF3 on Sc product purity. Species present were Sc, Li and F, in the following ratios: 1 ScF ₃ + 2.7 Li + 0.1 Sc. At equilibrium at 900 °C this produced 1 Sc + 2.7 LiF + 0.1 ScF3. Equilibrium scandium purity was higher than 99.5 wt. %, which is better than today's 98% pure Sc which sells for $3300/kg.

[00200] Using an induction melter in a glovebox, 4.02 grams of Li and 0.99 grams of Sc metals were melted in a tantalum crucible. After the Li-Sc alloy solidified, it was covered with 22.44 grams of scandium fluoride to minimize oxidation. A tantalum lid was placed on the crucible, and it was removed from the glove box and placed into a 1018 steel vessel, and a lid with an exit tube was welded on. The steel vessel was placed in a kiln and a vacuum was pulled on the steel vessel while it was held at 150 °C for 24 hours to drive off any moisture. Argon was then added to the vessel to a pressure of about 0.25 aim to suppress lithium evaporation at high temperature.

[00201] The vessel was sealed by heating a section of the vacuum tube with an oxy-acetylene torch and crimping the heated area with bolt cutters. The container was placed in an inert atmosphere inside a furnace to prevent the 1018 steel from oxidizing and heated to 900 °C for six hours to allow the metallothermic reduction to run to completion.

[00202] After cooling, the vessel was removed from the furnace, placed into a glove box, and the vacuum tube cut to return pressure to 1 atm. The container was removed from the glove box and placed in a fume hood for 24 hours, so air could diffuse in and passivate lithium, if present. [00203] A metal-salt sponge was found in the crucible as indicated in the left picture show in Figure 7. A SEM backscatter image showed two distinct areas. Figure 7 in the middle also shows a graph result of an EDS analysis of the brighter area, which indicates that it contained scandium and no fluorine (Lithium cannot be detected via EDS). Several pieces of sponge were added to water and no reaction was observed. As lithium reacts with water, this indicates that metal is only scandium and metallothermic reduction succeeded.

[00204] While conducting experiments for three examples above, the following preferred methods were identified. In some embodiments, dissolving SC2O3 at atmospheric pressure can be improved by dissolving SC2O3 at 180 °C in a pressure vessel, which can increase Sc ³⁺ by more than fifteen times. In some embodiments, weak acidity of HF can decrease ScF3 precipitation rate. Using solid LiF instead of solution can increase F ^" , resulting in improved ScFs precipitation. Adding a base after LiF can raise pH, releasing F ^" from HF, thereby ScFs precipitation yield can be improved.

[00205] In some embodiments, creating a longer anode-cathode path can lead to mass transfer limitation at the cathode, improving L12CO3 electrolysis and some deposition of Li metal. In alternate embodiments, as illustrated in the flow charts in Figure 3 and Figure 4, Sc losses can also be recovered without electrolysis.

[00206] The three examples above analyzed a scandium metal production flow chart. This model estimates about 90-92 % final scandium yield. The scandium metal production flow chart can also scale well, e.g. costs of digestion, cost of

metathesis/precipitation, etc. can decline rapidly with increasing scale. With HF and good yield, this process could quickly take a large share of this growing market.

[00207] As will be apparent to one of ordinary skill in the art from a reading of this disclosure, further embodiments of the present invention can be presented in forms other than those specifically disclosed above. The particular embodiments described above are, therefore, to be considered as illustrative and not restrictive. Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific embodiments described herein. Although the invention has been described and illustrated in the foregoing illustrative embodiments, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the details of implementation of the invention can be made without departing from the spirit and scope of the invention, which is limited only by the claims that follow. Features of the disclosed embodiments can be combined and rearranged in various ways within the scope and spirit of the invention. The scope of the invention is as set forth in the appended claims and equivalents thereof, rather than being limited to the examples contained in the foregoing description.