Method for producing rare earth metals and use thereof

Abstract

The application discloses a preparation method and application of a rare earth metal, and relates to the technical field of rare earth metal preparation, and particularly relates to a preparation method of a rare earth metal, which comprises the following steps: 1) providing an electrolyte, wherein the electrolyte is a mixture of a polar aprotic solvent and a lithium salt; wherein the polar aprotic solvent is at least one selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether and N-methyl pyrrolidone; 2) mixing a rare earth compound with the electrolyte in step 1) to obtain an electrolyte containing the rare earth compound; 3) electrolyzing the electrolyte containing the rare earth compound under a constant potential; and 4) after electrolysis, taking out a cathode sheet, removing residual electrolyte on the surface of the cathode sheet, and collecting the rare earth metal on the surface of the cathode sheet. The preparation method can obtain the rare earth metal, and does not need to add any other additive in the electrolysis process.

Description

Technical Field

[0001] This invention relates to a method for preparing rare earth metals and their applications. It belongs to the field of metallurgy. Background Technology

[0002] Rare earth elements are indispensable strategic resources in modern industry, possessing excellent magnetic, optical, and electrical properties, and are widely used in metallurgy, military, petrochemical, glass and ceramics, and new materials. Rare earth elements can also improve the morphology of inclusions and purify grain boundaries. Adding small amounts of rare earth elements to aluminum or magnesium alloys can improve the alloy's airtightness, high-temperature performance, and corrosion resistance, and is widely used in aerospace materials. With continuous advancements in science and technology, rare earth elements have been widely applied in many high-tech industries and cutting-edge defense technologies.

[0003] Currently, rare earth metals are mainly produced industrially using molten salt electrolysis and metallothermic processes. The chloride molten salt electrolysis method was the earliest method used in my country for rare earth metal preparation, but it suffers from drawbacks such as high energy consumption, low current efficiency, and the generation of large amounts of chlorine gas, posing significant harm to the environment and human health. Due to the shortcomings of the chloride molten salt system, the fluoride-oxide molten salt system has gradually replaced it, becoming the most widely used method for rare earth metal preparation. The metallothermic reduction method uses highly reactive metals at high temperatures to reduce rare earth compounds to rare earth metals, but it suffers from drawbacks such as excessively high temperatures, inability to produce continuously, and low yield.

[0004] Due to the high reactivity of rare earth metals, direct electrodeposition of rare earth metals and their alloys in aqueous solutions is challenging, requiring the addition of leveling agents and complexing agents to shift the deposition potential of the rare earth metals positively, making the process cumbersome. Both organic solvents and ionic liquids can be used for room temperature electrodeposition. However, organic solvent systems are flammable, toxic, and have low conductivity; the reactive metal raw materials they can dissolve are generally organometallic, and their solubility for inorganic salts is poor. Ionic liquids, as a novel green solvent, possess advantages such as low melting point, low vapor pressure, good stability, and a wide electrochemical window, providing a new research approach for the green and low-carbon preparation of rare earth metals.

[0005] CN117265599A discloses a method for preparing rare earth metal neodymium by low-temperature molten salt electrolysis. The method mainly uses a mixture of neodymium fluoride, lithium fluoride, and calcium fluoride as the electrolyte, employs graphite as the anode, and a tungsten rod as the inert cathode. Neodymium oxide, an electrolytic raw material, is added to the electrolyte with a mass ratio of NdF3:LiF:CaF2 = (30-60%):(5%-20%):(20-50%). The content of added neodymium oxide is 2%-10% of the total mass of the molten salt electrolyte. A voltage of 3-6V is applied between the two electrodes, and the electrolysis temperature is 900-1020℃, yielding a rare earth metal neodymium alloy.

[0006] CN105803484A discloses a method for preparing rare earth metals, comprising the following steps: mixing rare earth salts, ionic liquids, and hydroxyl ether solvents to form an electrolyte, and placing the electrolyte in an electrolytic cell; electrolyzing the electrolyte to form rare earth metals. This preparation method uses hydroxyl ether solvents as additives, utilizing the hydroxyl groups to co-dissolve the rare earth salts. The anion of the ionic liquid is BF4 or PF6, and the cation is an alkylimidazolium or alkylpyridine.

[0007] CN117089892A discloses a method for preparing rare earth neodymium metal using ionic liquid electrolysis of neodymium oxide, belonging to the field of rare earth neodymium metal electrolytic smelting technology. The method includes: mixing an ionic liquid, a molecular solvent / additive, and a rare earth metal salt to form an electrolyte; placing the electrolyte in an electrolytic cell; the rare earth metal salt being neodymium trifluoromethanesulfonate salt; electrolyzing the electrolyte to obtain rare earth neodymium metal; as electrolysis proceeds, the rare earth neodymium metal is reduced and deposited at the cathode, while simultaneously, a metal ligand salt is generated at the anolyte. During electrolysis, a non-reactive electrode is used as the cathode, and an iron plate as the anode; the non-reactive electrode is glassy carbon. The ionic liquid is one of 1-octyl-1-methylpyrrolidineonium bis(trifluoromethanesulfonyl)imide salt, n-butyltrimethylammonium bis(trifluoromethanesulfonyl)imide salt, or trimethylpentylphosphine bis(trifluoromethanesulfonyl)imide salt.

[0008] To date, there have been no reports on methods for obtaining rare earth metals by electrolyzing mixtures of polar aprotic solvents and lithium salts as electrolytes. Summary of the Invention

[0009] In view of this, one object of the present invention is to provide a method for preparing rare earth metals, which can obtain rare earth metals without adding any other additives or co-solvents, and at a low electrolysis temperature. Another object of the present invention is to provide the application of a mixture as an electrolyte in the electrolysis of rare earth compounds to obtain rare earth metals.

[0010] The present invention achieves the above objectives using the following technical solutions.

[0011] On one hand, the present invention provides a method for preparing rare earth metals, comprising the following steps:

[0012] 1) Provide an electrolyte, wherein the electrolyte is a mixture of a polar aprotic solvent and a lithium salt; wherein the polar aprotic solvent is selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether and N-methylpyrrolidone;

[0013] 2) Mix the rare earth compound with the electrolyte from step 1) to obtain an electrolyte containing the rare earth compound;

[0014] 3) Electrolysis of electrolytes containing rare earth compounds under constant potential;

[0015] 4) After electrolysis, remove the cathode plate, remove the residual electrolyte on the surface of the cathode plate, and collect the rare earth metals on the surface of the cathode plate.

[0016] According to the preparation method of the present invention, preferably, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium dioxalate borate.

[0017] According to the preparation method of the present invention, preferably, the amount of lithium salt added is 0.1 to 0.5 mol / L based on the volume of the polar aprotic solvent; no other additives are added to the electrolyte.

[0018] According to the preparation method of the present invention, preferably, the rare earth compound is a rare earth trifluoromethanesulfonate compound.

[0019] According to the preparation method of the present invention, preferably, the rare earth compound is selected from one of neodymium trifluoromethanesulfonate, dysprosium trifluoromethanesulfonate, samarium trifluoromethanesulfonate, scandium trifluoromethanesulfonate, lanthanum trifluoromethanesulfonate, and ytterbium trifluoromethanesulfonate.

[0020] According to the preparation method of the present invention, preferably, based on the volume of the electrolyte obtained in step 1), the amount of rare earth compound added is 0.05 to 0.2 mol / L.

[0021] According to the preparation method of the present invention, preferably, in step 3), the anode is a platinum electrode, and the cathode is selected from one of copper sheet, aluminum sheet, low carbon steel sheet and tungsten sheet; a silver wire is used as a reference electrode, and the electrolysis voltage is -2.6 to -3.6V.

[0022] According to the preparation method of the present invention, preferably, in step 3), the electrolysis temperature is 30-70°C and the electrolysis time is 0.5-2h.

[0023] According to the preparation method of the present invention, preferably, in step 4), after the cathode sheet is removed, it is cleaned with an organic solvent to remove the residual electrolyte on the surface of the cathode sheet, wherein the organic solvent is selected from acetonitrile or acetone.

[0024] On the other hand, the present invention also provides the application of a mixture as an electrolyte in the electrolysis of rare earth compounds to obtain rare earth metals, said mixture being obtained by mixing a polar aprotic solvent and a lithium salt; wherein the polar aprotic solvent is selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether and N-methylpyrrolidone;

[0025] The steps include the following:

[0026] 1) Provide the mixture as an electrolyte;

[0027] 2) Mix the rare earth compound with the electrolyte from step 1) to obtain an electrolyte containing the rare earth compound;

[0028] 3) Electrolysis of electrolytes containing rare earth compounds under constant potential;

[0029] 4) After electrolysis, remove the cathode plate, remove the residual electrolyte on the surface of the cathode plate, and collect the rare earth metals on the surface of the cathode plate.

[0030] The rare earth metal preparation method of this invention can obtain rare earth metals by electrolytic deposition on the surface of a cathode plate without adding any other additives or co-solvents, and without using carbonate organic solvents. The electrolysis temperature is relatively low, which is beneficial for widespread application. Attached Figure Description

[0031] Figure 1 This is a SEM image of the coating on the surface of the cathode aluminum sheet after electrolysis in Example 4.

[0032] Figure 2 This is an EDS result image of the coating on the surface of the cathode aluminum sheet after electrolysis in Example 4. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] <Preparation Method>

[0035] The method for preparing rare earth metals according to the present invention includes the following steps: (1) electrolyte preparation step; (2) electrolyte formation step containing rare earth compounds step; (3) electrolysis step; (4) post-treatment step. These are described in detail below.

[0036] Electrolyte preparation steps

[0037] An electrolyte is provided, which is a mixture of a polar aprotic solvent and a lithium salt; wherein the polar aprotic solvent is selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and N-methylpyrrolidone. This allows rare earth metals to be electrodeposited on the cathode surface via electrolysis without the addition of any other additives.

[0038] In this invention, the polar aprotic solvent may be selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and N-methylpyrrolidone, preferably selected from one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and N-methylpyrrolidone.

[0039] Existing technologies have reported the use of imidazolinone solvents to prepare electrolytes. However, the viscosity of imidazolinone solvents changes significantly with temperature, and the ion migration rate decreases at low temperatures, resulting in low deposition efficiency for rare earth metals with high reduction potentials. The polar aprotic solvents used in this invention, especially ether-based polar aprotic solvents, have lower viscosity and lower temperature sensitivity. They can form stable solvation structures with lithium salts at near-room temperature, significantly improving the solubility of rare earth compounds. Furthermore, they have a wide electrochemical window, which can suppress hydrogen evolution reaction during electrodeposition, improve the purity of the obtained rare earth metals, and are suitable for the deposition of various rare earth metals. In addition, the electrolyte of this invention can be recycled by adding lithium salt.

[0040] In this invention, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium dioxalate borate, preferably lithium bis(trifluoromethanesulfonyl)imide. The combined use of such a lithium salt with the polar aprotic solvent of this invention is more conducive to forming a stable solvation structure, improving the solubility of rare earth compounds, and increasing the yield of the obtained rare earth metals.

[0041] In this invention, the polar aprotic solvent and lithium salt have a purity of ≥98%. Preferably, the lithium salt has a purity of ≥99%. N-methylpyrrolidone has a purity of ≥98%. Ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and triethylene glycol dimethyl ether have a purity of ≥99%.

[0042] In this invention, based on the volume of the polar aprotic solvent, the amount of lithium salt added is 0.1–0.5 mol / L, preferably 0.3–0.5 mol / L, and more preferably 0.4–0.5 mol / L. No other additives are added to the electrolyte.

[0043] According to one embodiment of the present invention, at room temperature, a polar aprotic solvent and a lithium salt are separately added to an electrolytic cell and stirred and mixed at a speed of 200–400 r / min until uniform mixing is achieved and a fluid electrolyte with good flowability is formed. The polar aprotic solvent and the lithium salt can be stirred and mixed for 1–4 hours.

[0044] Steps for forming electrolytes containing rare earth compounds

[0045] By mixing rare earth compounds with the electrolyte described above, an electrolyte containing rare earth compounds is obtained. This is advantageous for obtaining rare earth metals through electrolysis.

[0046] In this invention, the rare earth compound is a trifluoromethanesulfonate rare earth compound. The rare earth compound is selected from one of neodymium trifluoromethanesulfonate, dysprosium trifluoromethanesulfonate, samarium trifluoromethanesulfonate, scandium trifluoromethanesulfonate, lanthanum trifluoromethanesulfonate, and ytterbium trifluoromethanesulfonate. Based on the volume of the electrolyte, the amount of rare earth compound added is 0.05–0.2 mol / L, preferably 0.08–0.2 mol / L, and more preferably 0.1–0.2 mol / L. This is beneficial for improving electrolysis efficiency and increasing the yield of the obtained rare earth metals without reducing the purity of the rare earth metals.

[0047] Electrolysis steps

[0048] In this invention, an electrolyte containing rare earth compounds is electrolyzed under constant potential. This allows rare earth metals to be electrodeposited on the surface of the cathode.

[0049] Using a silver wire as the reference electrode, the electrolysis voltage can be -2.6 to -3.6V, preferably -2.8 to -3.6V, more preferably -3.0 to -3.6V, and even more preferably -3.2 to -3.6V. The electrolysis temperature can be 30 to 70℃, preferably 40 to 70℃. The electrolysis time can be 0.5 to 2 hours, for example, 0.5 hours, 1 hour, 1.5 hours, or 2 hours. This is beneficial for improving the yield of rare earth metals, i.e., increasing the weight percentage of rare earth metals.

[0050] In this invention, the anode is an inert metal platinum sheet electrode. The cathode can be one of copper, aluminum, low-carbon steel, or tungsten sheets, or other substrates that require coating with rare earth metals (e.g., neodymium iron boron substrate coated with heavy metals). According to a specific embodiment of the invention, the cathode is formed of an aluminum sheet.

[0051] Post-processing steps

[0052] After electrolysis, the cathode plate is removed, the residual electrolyte on its surface is cleaned, and the rare earth metals on the cathode plate are collected. This helps to improve the purity of the obtained rare earth metals.

[0053] According to one embodiment of the present invention, after the cathode plate is removed, it is cleaned with an organic solvent to remove residual electrolyte on the surface of the cathode plate. The organic solvent is selected from acetonitrile or acetone, preferably acetonitrile. The weight percentage of rare earth metals in the deposited layer (or plating) on ​​the cathode plate is greater than 15 wt%, preferably greater than 21 wt%, more preferably greater than or equal to 25 wt%, even more preferably greater than or equal to 29 wt%, and can be greater than 39 wt%. In addition to rare earth metals, the deposited layer also contains some lithium salts and lithium metal.

[0054] According to a specific embodiment of the present invention, a method for preparing a rare earth metal includes the following steps:

[0055] 1) An electrolyte is provided, wherein the electrolyte is a mixture of a polar aprotic solvent and a lithium salt; wherein the polar aprotic solvent is selected from one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and N-methylpyrrolidone; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide; the amount of lithium salt added is 0.1–0.5 mol / L based on the volume of the polar aprotic solvent;

[0056] 2) Mix the rare earth compound with the electrolyte from step 1) to obtain an electrolyte containing the rare earth compound; wherein the rare earth compound is a rare earth trifluoromethanesulfonic acid compound; based on the volume of the electrolyte from step 1), the amount of rare earth compound added is 0.05 to 0.2 mol / L.

[0057] 3) Using an aluminum sheet as the cathode and a platinum electrode as the anode, an electrolyte containing rare earth compounds is electrolyzed under constant potential; a silver wire is used as the reference electrode, the electrolysis voltage is -2.6 to -3.6V, the electrolysis temperature is 30 to 70℃, and the electrolysis time is 0.5 to 2h.

[0058] 4) After electrolysis, remove the cathode aluminum sheet, remove the residual electrolyte on the surface of the cathode aluminum sheet, and collect the rare earth metals on the surface of the cathode aluminum sheet.

[0059] <Application>

[0060] This invention also provides the application of a mixture as an electrolyte in the electrolysis of rare earth compounds to obtain rare earth metals, said mixture being obtained by mixing a polar aprotic solvent and a lithium salt; wherein the polar aprotic solvent is selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and N-methylpyrrolidone; comprising the following steps:

[0061] 1) Provide the mixture as an electrolyte;

[0062] 2) Mix the rare earth compound with the electrolyte from step 1) to obtain an electrolyte containing the rare earth compound;

[0063] 3) Electrolysis of electrolytes containing rare earth compounds under constant potential;

[0064] 4) After electrolysis, remove the cathode plate, remove any residual electrolyte from its surface, and collect the rare earth metals from the cathode plate surface. Detailed steps and parameters are described above and will not be repeated here.

[0065] <Test Methods and Raw Material Specifications>

[0066] The testing methods in the following examples are described below: SEM and EDS: both were performed using a ZEISS EV018 microscope (Germany). In the following examples, the Shanghai Chenhua electrochemical workstation was used as the electrolysis power source.

[0067] In the following examples, the purity of diethylene glycol dimethyl ether is >99%, the purity of ethylene glycol dimethyl ether is >99%, the purity of N-methylpyrrolidone is >98%, the purity of lithium bis(trifluoromethanesulfonylimide) is >99%, the purity of neodymium trifluoromethanesulfonate is ≥98%, the purity of dysprosium trifluoromethanesulfonate is ≥98%, and the purity of samarium trifluoromethanesulfonate is ≥98%.

[0068] In the following embodiments, the weight percentage of rare earth metals is obtained directly from EDS analysis using a scanning electron microscope. It represents the percentage of the weight of rare earth metals in the electrodeposited coating (or deposited layer) relative to the total weight of the coating. The coating refers to the material deposited on the cathode sheet and does not include the cathode sheet substrate itself.

[0069] Example 1

[0070] 1) Provide the electrolyte. At room temperature, diethylene glycol dimethyl ether and lithium bis(trifluoromethanesulfonyl)imide (based on the volume of diethylene glycol dimethyl ether, the amount of lithium bis(trifluoromethanesulfonyl)imide added is 0.5 mol / L) are added separately to the electrolytic cell and stirred at a stirring speed of 200 r / min until they are uniformly mixed to form a fluid electrolyte.

[0071] 2) Add neodymium trifluoromethanesulfonate, a rare earth compound, to the electrolyte (the amount of neodymium trifluoromethanesulfonate added is 0.1 mol / L based on the volume of the electrolyte), and continue stirring until the mixture is homogeneous and has good fluidity, thus obtaining an electrolyte containing rare earth compounds.

[0072] 3) Using aluminum sheet as cathode and high-purity platinum sheet as anode, the system temperature is controlled at 50℃ and the electrolysis voltage is -2.6V (using silver wire as reference electrode) to electrolyze the electrolyte containing rare earth compounds for 2 hours.

[0073] 4) After electrolysis, remove the cathode aluminum sheet and clean it with acetonitrile to obtain the rare earth metal neodymium deposited on the surface of the cathode aluminum sheet.

[0074] The deposited material (which can be called a coating or deposit) on the aluminum sheet was analyzed by EDS, and the results showed that the weight percentage of the rare earth metal neodymium on the aluminum sheet substrate was 15.87 wt%.

[0075] Examples 2-6

[0076] The only difference from Example 1 is the electrolysis voltage. Some process parameters and results are shown in Table 1.

[0077] Table 1

[0078]

[0079] As can be seen from the results of Examples 1 to 6 above, under the same temperature and time conditions, the amount of rare earth metal neodymium deposited on the cathode aluminum sheet increased significantly when the electrolysis voltage was gradually adjusted from -2.6V to -3.2V. However, when the electrolysis voltage was further adjusted to -3.6V, the amount of rare earth metal neodymium obtained tended to decrease.

[0080] The SEM results of the rare earth metal neodymium obtained on the cathode aluminum sheet in Example 4 are as follows: Figure 1 As shown, the EDS results are as follows: Figure 2 As shown. From Figure 1 As can be seen, the rare earth metal neodymium is distributed in a granular manner, and the coating is dendrite-free and densely packed on the cathode aluminum sheet. From... Figure 2 As can be seen, the coating contains neodymium (Nd). It should be noted that... Figure 2 The Al in the figure represents aluminum on the cathode aluminum sheet, and the O should be caused by the oxidation of rare earth metals.

[0081] Examples 7-10

[0082] The only difference from Example 4 is the electrolysis temperature. Some process parameters and results are shown in Table 2.

[0083] Table 2

[0084]

[0085] As shown in the results of Examples 4, 7 to 10 above, under the same electrolysis voltage and time conditions, the neodymium content of rare earth metals increases significantly when the electrolysis temperature increases from 30°C to 50°C. However, the content begins to decrease when the temperature continues to rise to 60°C, and dendritic structures appear on the coating surface as the temperature continues to rise. Higher deposition potentials or higher temperatures can lead to the formation of dendritic structures. Dendritic structures mainly exhibit a tree-like morphology. The presence of dendritic structures results in weak bonding between the coating (i.e., the material deposited on the cathode during electrolysis) and the substrate (referring to the cathode), making it prone to detachment. If the rare earth metals obtained from electrolysis are used as neodymium iron boron magnets, the dendritic structure will disrupt the crystal lattice arrangement and reduce its performance. Therefore, it is generally necessary to avoid the formation of dendritic structures during the electrodeposition process.

[0086] Examples 11-12

[0087] The only difference from Example 4 is the electrolysis time. Some process parameters and results are shown in Table 3.

[0088] Table 3

[0089]

[0090] As can be seen from the results of Examples 4, 11, and 12 above, under the same conditions of electrolysis voltage and electrolysis temperature, extending the electrolysis time from 0.5h to 2h significantly increases the content of neodymium rare earth metal in the product. Appropriately extending the time is beneficial to the growth of the deposited layer (or coating), that is, it is beneficial to improve the yield of neodymium rare earth metal.

[0091] Example 13

[0092] 1) Provide the electrolyte. At room temperature, ethylene glycol dimethyl ether and lithium bis(trifluoromethanesulfonyl)imide (based on the volume of ethylene glycol dimethyl ether, the amount of lithium bis(trifluoromethanesulfonyl)imide added is 0.5 mol / L) are added separately to the electrolytic cell and stirred at a stirring speed of 200 r / min to form a homogeneous electrolyte with good flowability.

[0093] 2) Add the rare earth compound samarium trifluoromethanesulfonate to the electrolyte (the amount of samarium trifluoromethanesulfonate added is 0.2 mol / L based on the volume of the electrolyte), and continue stirring until the mixture is uniform and has good fluidity to obtain an electrolyte containing rare earth compounds.

[0094] 3) Using aluminum sheet as cathode and high-purity platinum sheet as anode, the system temperature is controlled at 50℃ and the electrolysis voltage is -3.2V (using silver wire as reference electrode) to electrolyze the electrolyte containing rare earth compounds for 2 hours;

[0095] 4) After electrolysis, the cathode aluminum sheet is removed and cleaned with acetonitrile to obtain the rare earth metal samarium deposited on the surface of the cathode aluminum sheet.

[0096] EDS analysis results indicate that the weight percentage of samarium, a rare earth metal, prepared on an aluminum substrate is 39.38 wt%.

[0097] Example 14

[0098] 1) Provide the electrolyte. At room temperature, N-methylpyrrolidone and lithium bis(trifluoromethanesulfonylimide) (based on the volume of N-methylpyrrolidone, the amount of lithium bis(trifluoromethanesulfonylimide) added is added to the electrolytic cell and stirred at a stirring speed of 200 r / min to form a homogeneous electrolyte with good flowability.

[0099] 2) Add the rare earth compound dysprosium trifluoromethanesulfonate to the electrolyte (the amount of dysprosium trifluoromethanesulfonate added is 0.2 mol / L based on the volume of the electrolyte), and continue stirring to mix evenly. The electrolyte has good fluidity and contains rare earth compounds.

[0100] 3) Using aluminum sheet as cathode and high-purity platinum sheet as anode, the system temperature is controlled at 50℃ and the electrolysis voltage is -3.2V (using silver wire as reference electrode) to electrolyze the electrolyte containing rare earth compounds for 2 hours.

[0101] 4) After electrolysis, the cathode aluminum sheet is removed and cleaned with acetonitrile to obtain rare earth metal dysprosium deposited on the surface of the cathode aluminum sheet.

[0102] EDS analysis results show that the weight percentage of rare earth metal dysprosium obtained on the aluminum substrate is 25.13 wt%.

[0103] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for preparing rare earth metals, characterized in that, Includes the following steps: 1) An electrolyte is provided, wherein the electrolyte is a mixture of a polar aprotic solvent and a lithium salt; wherein the polar aprotic solvent is selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and N-methylpyrrolidone; and the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium dioxalate borate. 2) Mix the rare earth compound with the electrolyte from step 1) to obtain an electrolyte containing the rare earth compound; wherein the rare earth compound is a rare earth trifluoromethanesulfonic acid compound. 3) Electrolysis of electrolytes containing rare earth compounds under constant potential; 4) After electrolysis, remove the cathode plate, remove the residual electrolyte on the surface of the cathode plate, and collect the rare earth metals on the surface of the cathode plate.

2. The preparation method according to claim 1, characterized in that, Based on the volume of the polar aprotic solvent, the amount of lithium salt added is 0.1–0.5 mol / L; no other additives are added to the electrolyte.

3. The preparation method according to claim 1, characterized in that, The rare earth compound is selected from one of neodymium trifluoromethanesulfonate, dysprosium trifluoromethanesulfonate, samarium trifluoromethanesulfonate, scandium trifluoromethanesulfonate, lanthanum trifluoromethanesulfonate, and ytterbium trifluoromethanesulfonate.

4. The preparation method according to claim 1, characterized in that, Based on the volume of the electrolyte obtained in step 1), the amount of rare earth compound added is 0.05–0.2 mol / L.

5. The preparation method according to claim 1, characterized in that, In step 3), the anode is a platinum electrode, and the cathode is selected from copper, aluminum, low carbon steel and tungsten sheets; silver wire is used as the reference electrode, and the electrolysis voltage is -2.6 to -3.6V.

6. The preparation method according to claim 1, characterized in that, In step 3), the electrolysis temperature is 30–70°C and the electrolysis time is 0.5–2 hours.

7. The preparation method according to claim 1, characterized in that, In step 4), after the cathode plate is removed, it is cleaned with an organic solvent to remove the residual electrolyte on the surface of the cathode plate. The organic solvent is selected from acetonitrile or acetone.

8. The use of a mixture as an electrolyte in the electrolysis of rare earth compounds to obtain rare earth metals, characterized in that, The mixture is obtained by mixing a polar aprotic solvent and a lithium salt; wherein the polar aprotic solvent is selected from at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and N-methylpyrrolidone; and the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium dioxalate borate. Includes the following steps: 1) Provide the mixture as an electrolyte; 2) Mix the rare earth compound with the electrolyte from step 1) to obtain an electrolyte containing the rare earth compound; wherein the rare earth compound is a rare earth trifluoromethanesulfonic acid compound. 3) Electrolysis of electrolytes containing rare earth compounds under constant potential; 4) After electrolysis, remove the cathode plate, remove the residual electrolyte on the surface of the cathode plate, and collect the rare earth metals on the surface of the cathode plate.

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