Preparation method and application of rare earth metal

Abstract

The invention discloses a preparation method and application of rare earth metal, and the preparation method comprises the following steps: 1) providing an electrolyte 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-methyl pyrrolidone; 2) mixing a rare earth compound with the electrolyte in the step 1) to obtain an electrolyte containing the rare earth compound; (3) electrolyzing the electrolyte containing the rare earth compound under constant potential; and (4) after electrolysis is finished, the cathode piece is taken out, residual electrolyte on the surface of the cathode piece is removed, and rare earth metal on the surface of the cathode piece is collected. According to the preparation method, rare earth metal can be obtained, and no other additives are added in the electrolysis process.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of rare earth metals, belonging to the field of metallurgy. Background Art

[0002] Rare earth elements are an indispensable strategic resource in modern industry. Their excellent magnetic, optical, and electrical properties have led to their widespread application in metallurgy, military affairs, petrochemicals, 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 improves their airtightness, high-temperature performance, and corrosion resistance, leading to their widespread use in aerospace materials. With the continuous advancement of science and technology, rare earth elements are finding widespread application in many high-tech industries and cutting-edge defense technologies.

[0003] At present, the main industrial methods for producing rare earth metals are molten salt electrolysis and metallothermic methods. The chloride molten salt system electrolysis method is the earliest method used in my country to prepare rare earth metals, but the production process has disadvantages such as high energy consumption, low current efficiency, and the production of large amounts of chlorine gas, which poses great harm to the environment and human health. Based on the defects of the chloride molten salt system, after continuous development, the fluoride-oxide molten salt system has gradually replaced the chloride molten salt system and become a very widely used rare earth preparation method. The metallothermic reduction method uses highly active metals under high temperature conditions to reduce rare earth compounds to rare earth metals. It has the disadvantages of excessively high temperatures, inability to produce continuously, and low output.

[0004] Due to the reactivity of rare earth metals, direct electrodeposition of rare earth metals and their alloys in aqueous solution is difficult. Leveling agents and complexing agents must be added to the aqueous solution 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 electrical conductivity. The active metal raw materials they can dissolve are generally organometallics, which have poor solubility for inorganic salts. As a new type of green solvent, ionic liquids offer advantages such as low melting point, low vapor pressure, good stability, and a wide electrochemical window, providing new research ideas 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, adopts graphite as the anode, and a tungsten rod as the inert cathode. Neodymium oxide, an electrolysis raw material, is added to the electrolyte composed of a mass ratio of NdF3:LiF:CaF2 = (30-60%): (5%-20%): (20-50%). The content of the 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. The electrolysis temperature is 900-1020°C to obtain a rare earth metal neodymium alloy.

[0006] CN105803484A discloses a method for preparing rare earth metals, comprising the following steps: mixing a rare earth salt, an ionic liquid, and a hydroxy ether solvent to form an electrolyte, placing the electrolyte in an electrolytic cell, and electrolyzing the electrolyte to form the rare earth metal. This preparation method uses a hydroxy ether solvent as an additive, utilizing the hydroxyl groups therein to dissolve the rare earth salt. The anion of the ionic liquid is BF4 or PF6, and the cation of the ionic liquid is an alkyl imidazole or alkyl pyridine.

[0007] CN117089892A discloses a method for preparing rare earth metal neodymium using ionic liquid electrolysis of neodymium oxide, belonging to the field of rare earth metal neodymium electrolytic smelting technology. The method comprises: 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 is neodymium trifluoromethanesulfonate; electrolyzing the electrolyte to produce rare earth metal neodymium; as the electrolysis proceeds, the rare earth metal neodymium is reduced and deposited at the cathode, while the anode reaction produces a metal ligand salt. During the electrolysis process, a non-reactive electrode serves as the cathode and an iron plate serves as the anode. The non-reactive electrode is glassy carbon. The ionic liquid is one of 1-octyl-1-methylpyrrolidinium bis(trifluoromethanesulfonylimide), n-butyltrimethylammonium bis(trifluoromethanesulfonylimide), and trimethylpentylphosphine bis(trifluoromethanesulfonylimide).

[0008] So far, there has been no report on a method for obtaining rare earth metals by electrolysis using a mixture of a polar aprotic solvent and a lithium salt as an electrolyte. 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 a mixture for use as an electrolyte in the electrolysis of rare earth compounds to obtain rare earth metals.

[0010] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0011] In one aspect, the present invention provides a method for preparing a rare earth metal, comprising the following steps:

[0012] 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-methylpyrrolidone;

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

[0014] 3) electrolyzing the electrolyte containing the rare earth compound at a constant potential;

[0015] 4) After the electrolysis is completed, the cathode sheet is removed, the residual electrolyte on the surface of the cathode sheet is removed, and the rare earth metal on the surface of the cathode sheet is collected.

[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 bis(oxalatoborate).

[0017] According to the preparation method of the present invention, preferably, based on the volume of the polar aprotic solvent, the amount of lithium salt added is 0.1 to 0.5 mol / L; and 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 trifluoromethanesulfonic acid rare earth 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 a copper sheet, an aluminum sheet, a low-carbon steel sheet and a 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 0.5-2 h.

[0023] According to the preparation method of the present invention, preferably, in step 4), the cathode sheet is taken out and then 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 a use of a mixture as an electrolyte for electrolyzing rare earth compounds to obtain rare earth metals, wherein 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;

[0025] The steps include:

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

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

[0028] 3) electrolyzing the electrolyte containing the rare earth compound at a constant potential;

[0029] 4) After the electrolysis is completed, the cathode sheet is removed, the residual electrolyte on the surface of the cathode sheet is removed, and the rare earth metal on the surface of the cathode sheet is collected.

[0030] The method for preparing rare earth metals of the present invention can deposit rare earth metals on the surface of a cathode sheet through electrolysis without adding any other additives or cosolvents, and without using carbonate organic solvents. The electrolysis temperature is relatively low, which is conducive to promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0032] Figure 2 This is the EDS result of the coating on the surface of the cathode aluminum sheet after electrolysis in Example 4. DETAILED DESCRIPTION

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

[0034] <Preparation method>

[0035] The method for preparing rare earth metals of the present invention comprises the following steps: (1) preparing an electrolyte; (2) forming an electrolyte containing a rare earth compound; (3) electrolysis; and (4) post-treatment. Detailed descriptions are given below.

[0036] Electrolyte preparation steps

[0037] 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 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-methylpyrrolidone. This allows rare earth metals to be electrodeposited on the cathode surface through electrolysis without the addition of any other additives.

[0038] In the present invention, the polar aprotic solvent can 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-methyl pyrrolidone, and is 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-methyl pyrrolidone.

[0039] Prior art reports have reported the use of imidazolinone solvents to prepare electrolytes. However, the viscosity of imidazolinone solvents varies significantly with temperature, the ion migration rate decreases at low temperatures, and the deposition efficiency of rare earth metals with high reduction potentials is low. The polar aprotic solvents used in the present invention, especially ether polar aprotic solvents, have lower viscosity and weaker temperature sensitivity. They can form stable solvation structures with lithium salts at near room temperature, significantly improving the solubility of rare earth compounds. In addition, the electrochemical window is wide, which can inhibit the hydrogen evolution reaction during the electrodeposition process, improve the purity of the resulting rare earth metals, and is suitable for the deposition of a variety of rare earth metals. In addition, the electrolyte of the present invention can be recycled by supplementing with lithium salts.

[0040] In the present invention, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl imide), lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(oxalatoborate), preferably lithium bis(trifluoromethanesulfonyl imide). The use of such a lithium salt in combination with the polar aprotic solvent of the present invention facilitates the formation of a stable solvation structure, enhances the solubility of the rare earth compound, and increases the yield of the resulting rare earth metal.

[0041] In the present invention, the polar aprotic solvent and the lithium salt have a purity of greater than or equal to 98%. Preferably, the purity of the lithium salt is greater than or equal to 99%. The purity of N-methylpyrrolidone is greater than 98%. The purity of 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 is greater than or equal to 99%.

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

[0043] According to one embodiment of the present invention, a polar aprotic solvent and a lithium salt are added to an electrolytic cell at room temperature and stirred at a speed of 200 to 400 rpm to form a fluid electrolyte. The polar aprotic solvent and the lithium salt are stirred for 1 to 4 hours.

[0044] Steps for forming an electrolyte containing a rare earth compound

[0045] Mixing the rare earth compound with the electrolyte described above to obtain an electrolyte containing the rare earth compound is beneficial for obtaining rare earth metals by electrolysis.

[0046] In the present 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 rare earth compound is added in an amount of 0.05 to 0.2 mol / L, preferably 0.08 to 0.2 mol / L, and more preferably 0.1 to 0.2 mol / L. This helps improve electrolysis efficiency and the yield of the resulting rare earth metal without reducing the purity of the rare earth metal.

[0047] Electrolysis steps

[0048] In the present invention, the electrolyte containing the rare earth compound is electrolyzed at a constant potential, so that the rare earth metal can be electrodeposited on the surface of the cathode.

[0049] Using a silver wire as a reference electrode, the electrolysis voltage can be -2.6 to -3.6 V, preferably -2.8 to -3.6 V, more preferably -3.0 to -3.6 V, and even more preferably -3.2 to -3.6 V. The electrolysis temperature can be 30 to 70°C, preferably 40 to 70°C. The electrolysis time can be 0.5 to 2 hours, for example, 0.5 hours, 1 hour, 1.5 hours, or 2 hours. This helps increase the yield of the rare earth metal obtained, that is, increase the weight percentage of the rare earth metal.

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

[0051] Post-processing steps

[0052] After the electrolysis is completed, the cathode is removed, the residual electrolyte on the surface of the cathode is removed, and the rare earth metal on the surface of the cathode is collected. This helps to improve the purity of the obtained rare earth metal.

[0053] According to one embodiment of the present invention, after the cathode sheet is removed, it is cleaned with an organic solvent to remove residual electrolyte from the surface of the cathode sheet. The organic solvent is selected from acetonitrile or acetone, preferably acetonitrile. The weight percentage of the rare earth metal in the deposited layer (or coating) on ​​the cathode sheet is greater than 15wt%, preferably greater than 21wt%, more preferably greater than or equal to 25wt%, even more preferably greater than or equal to 29wt%, and may be greater than 39wt%. In addition to the rare earth metal, 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 of the present invention comprises the following steps:

[0055] 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 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; and the lithium salt is lithium bis(trifluoromethanesulfonyl imide); and the amount of the lithium salt added is 0.1 to 0.5 mol / L based on the volume of the polar aprotic solvent;

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

[0057] 3) electrolyzing the electrolyte containing the rare earth compound at a constant potential using an aluminum sheet as a cathode and a platinum electrode as an anode; wherein a silver wire is used as a reference electrode, the electrolysis voltage is -2.6 to -3.6 V, the electrolysis temperature is 30 to 70° C., and the electrolysis time is 0.5 to 2 hours;

[0058] 4) After the electrolysis is completed, the cathode aluminum sheet is taken out, the residual electrolyte on the surface of the cathode aluminum sheet is removed, and the rare earth metal on the surface of the cathode aluminum sheet is collected.

[0059] <Application>

[0060] The present invention also provides a method for using a mixture as an electrolyte for electrolyzing rare earth compounds to obtain rare earth metals, wherein 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 method comprises the following steps:

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

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

[0063] 3) electrolyzing the electrolyte containing the rare earth compound at a constant potential;

[0064] 4) After the electrolysis is completed, the cathode is removed, the residual electrolyte on the surface of the cathode is removed, and the rare earth metal on the surface of the cathode is collected. The detailed steps and parameters are as described above and are not repeated here.

[0065] <Test method and raw material description>

[0066] The test methods in the following examples are described as follows: SEM and EDS: both were tested using a German ZEISS EV018 microscope. In the following examples, a Shanghai Chenhua electrochemical workstation was used as the electrolysis power source.

[0067] In the following examples, the purity of the diethylene glycol dimethyl ether used is >99%, the purity of ethylene glycol dimethyl ether is >99%, the purity of N-methylpyrrolidone is >98%, the purity of lithium bis(trifluoromethanesulfonyl)imide 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 examples, the weight percentage of rare earth metals is obtained directly from EDS analysis using a scanning electron microscope (SEM). It represents the percentage of the weight of the rare earth metal in the electrodeposited coating (or deposited layer) relative to the weight of the entire coating. The coating refers to the material deposited on the cathode sheet and does not include the cathode substrate itself.

[0069] Example 1

[0070] 1) Providing an electrolyte. At room temperature, diglyme and lithium bis(trifluoromethanesulfonylimide) (the amount of lithium bis(trifluoromethanesulfonylimide) added is 0.5 mol / L based on the volume of diglyme) into an electrolytic cell and stirred at a stirring speed of 200 r / min. The mixture is stirred and mixed uniformly in the electrolytic cell to form an electrolyte with good fluidity.

[0071] 2) adding a rare earth compound, neodymium trifluoromethanesulfonate, to the electrolyte (based on the volume of the electrolyte, the amount of neodymium trifluoromethanesulfonate added is 0.1 mol / L), and continuing to stir until the mixture is evenly mixed and has good fluidity, thereby obtaining an electrolyte containing a rare earth compound.

[0072] 3) Using an aluminum sheet as the cathode and a high-purity platinum sheet as the anode, the system temperature was controlled at 50°C, the electrolysis voltage was -2.6V (using a silver wire as the reference electrode), and the electrolyte containing the rare earth compound was electrolyzed for 2 hours.

[0073] 4) After the electrolysis is completed, the cathode aluminum sheet is taken out and cleaned 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 a deposition layer) on the aluminum sheet was detected 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 to 6

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

[0077] Table 1

[0078]

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

[0080] Among them, 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. Figure 1 It can be seen that the rare earth metal neodymium is distributed in granular form, the coating has no dendrites and is densely packed on the cathode aluminum sheet. Figure 2 It can be seen that the coating contains neodymium (Nd). Figure 2 The Al in the figure is the aluminum on the cathode aluminum sheet, and the O should be caused by the oxidation of rare earth metals.

[0081] Examples 7 to 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] From the results of Examples 4, 7 to 10 above, it can be seen that, under the same electrolysis voltage and time conditions, the rare earth metal neodymium content obtained when the electrolysis temperature is increased from 30°C to 50°C increases significantly, but continues to rise to 60°C and begins to show a downward trend, and when the temperature continues to rise, a dendritic structure will appear on the surface of the coating. Dendritic structures may appear when the deposition potential is high or the temperature is high. The dendritic structure mainly presents a tree-like morphology. If a dendritic structure appears, it will cause the coating (i.e., the substance deposited on the cathode sheet during electrolysis) and the substrate (referring to the cathode sheet) to be weakly bonded and easy to fall off. If the rare earth metal obtained by electrolysis is used as a rare earth functional material neodymium iron boron magnet, the dendritic structure will destroy the lattice arrangement and reduce its performance. Therefore, it is generally necessary to avoid the appearance of dendritic structures during the electroplating process.

[0086] Examples 11-12

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

[0088] Table 3

[0089]

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

[0091] Example 13

[0092] 1) Providing an electrolyte. Ethylene glycol dimethyl ether and lithium bis(trifluoromethanesulfonyl imide) (the amount of lithium bis(trifluoromethanesulfonyl imide added is 0.5 mol / L based on the volume of ethylene glycol dimethyl ether) are added to an electrolytic cell at room temperature and stirred at a stirring speed of 200 r / min until uniformly mixed in the electrolytic cell to form an electrolyte with good fluidity.

[0093] 2) adding a rare earth compound samarium trifluoromethanesulfonate (the amount of samarium trifluoromethanesulfonate added is 0.2 mol / L based on the volume of the electrolyte) to the electrolyte, and continuing to stir until the mixture is evenly mixed and has good fluidity, thereby obtaining an electrolyte containing a rare earth compound.

[0094] 3) Using an aluminum sheet as the cathode and a high-purity platinum sheet as the anode, the system temperature was controlled at 50°C, the electrolysis voltage was -3.2V (using a silver wire as the reference electrode), and the electrolyte containing the rare earth compound was electrolyzed for 2 hours;

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

[0096] EDS detection results show that the weight percentage of rare earth metal samarium prepared on the aluminum substrate is 39.38wt%.

[0097] Example 14

[0098] 1) Providing an electrolyte. At room temperature, add N-methylpyrrolidone and lithium bis(trifluoromethanesulfonylimide) (the amount of lithium bis(trifluoromethanesulfonylimide) added is 0.5 mol / L based on the volume of N-methylpyrrolidone) to an electrolytic cell and stir at a stirring speed of 200 r / min until the mixture is uniformly stirred in the electrolytic cell to form an electrolyte with good fluidity.

[0099] 2) adding a rare earth compound dysprosium trifluoromethanesulfonate to the electrolyte (based on the volume of the electrolyte, the amount of dysprosium trifluoromethanesulfonate added is 0.2 mol / L), continuing to stir and mix evenly, and obtaining an electrolyte containing a rare earth compound with good fluidity.

[0100] 3) Using an aluminum sheet as the cathode and a high-purity platinum sheet as the anode, the system temperature was controlled at 50° C., the electrolysis voltage was -3.2 V (using a silver wire as the reference electrode), and the electrolyte containing the rare earth compound was electrolyzed for 2 h.

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

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

[0103] The present invention is not limited to the above-mentioned embodiments. Any modification, improvement, or substitution that can be conceived by those skilled in the art without departing from the essential content of the present invention shall fall within the scope of the present invention.

Claims

1. A method for preparing rare earth metals, characterized in that: The following steps are involved: 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-methylpyrrolidone; 2) mixing the rare earth compound with the electrolyte of step 1) to obtain an electrolyte containing the rare earth compound; 3) electrolyzing the electrolyte containing the rare earth compound at a constant potential; 4) After the electrolysis is completed, the cathode sheet is removed, the residual electrolyte on the surface of the cathode sheet is removed, and the rare earth metal on the surface of the cathode sheet is collected.

2. The preparation method according to claim 1, characterized in that The lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate and lithium bis(oxalatoborate).

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

4. The preparation method according to claim 1, characterized in that The rare earth compound is a trifluoromethanesulfonic acid rare earth compound.

5. The preparation method according to claim 4, 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.

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

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

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

9. The preparation method according to claim 1, characterized in that In step 4), the cathode sheet is taken out and then 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.

10. Use of a mixture as an electrolyte for electrolyzing 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; The steps include: 1) providing the mixture as an electrolyte; 2) mixing the rare earth compound with the electrolyte of step 1) to obtain an electrolyte containing the rare earth compound; 3) electrolyzing the electrolyte containing the rare earth compound at a constant potential; 4) After the electrolysis is completed, the cathode sheet is removed, the residual electrolyte on the surface of the cathode sheet is removed, and the rare earth metal on the surface of the cathode sheet is collected.

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