Method for preparing rare earth metal or rare earth alloy

Abstract

The invention discloses a method for preparing rare earth metal or rare earth alloy, and belongs to the technical field of inorganic chemistry. According to the method, a eutecticevaporate electrolyte is used for conducting constant-potential electrodeposition at the temperature of 50-80 DEG C, the eutecticevaporate electrolyte comprises ethylene glycol, choline chloride, urea, induction salt and a rare earth compound, the induction salt is Zn salt or Li salt, the electrodeposition cathode potential is controlled to be-1.2 V to-2.0 V (vs.Ag / Ag +), constant-potential electrodeposition is conducted, and the rare earth metal or the rare earth zinc alloy is obtained. The induction salt is added into the eutectic electrolyte, deposition of rare earth is effectively induced, separated components are controlled to be rare earth elements or rare earth zinc alloy by controlling the variety and the adding amount of the induction salt, and the efficient electroreduction deposition capacity on main salt rare earth ions is still kept under the condition of low-concentration rare earth.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic chemistry, and more specifically, relates to a method for preparing rare earth metal or rare earth alloy. Background Art

[0002] The traditional method of preparing rare earth metals and their alloys is mainly to use pyrometallurgical processes under high temperature conditions, such as molten salt electrolysis and metal thermal reduction. Among them, the molten salt electrolysis process is widely used in the preparation of rare earth metals and their alloys. 90% of rare earth metals are prepared by molten salt electrolysis, which has the advantages of continuous production, large scale and high production efficiency. However, the molten salt electrolysis method has the problems of high energy consumption and high carbon emissions, and high-temperature molten salt is highly corrosive to equipment. Therefore, the development of green electrolysis technology for rare earth metals and their alloys near room temperature is of great value to low-carbon clean production.

[0003] The green electrolyte system is the basis for realizing the preparation of rare earth metals by near-room temperature electrodeposition. Rare earth metals and alloys that can only be obtained in high-temperature molten salts can be obtained at near-room temperature, and the electrolysis process does not need to be carried out under high temperature conditions, so there will be no corrosion of the equipment by high-temperature molten salts. The existing green electrolytes used for near-room temperature electrodeposition to prepare rare earth metals include ionic liquids and low eutectic solvents. Among them, ionic liquids as a low-temperature molten salt are ideal carriers for electrodeposition to prepare metals. Compared with aqueous solution systems and organic solvents, ionic liquid electrodeposition processes have the advantages of being non-toxic, free of hydrogen evolution reaction, wide electrochemical window, and high conductivity. For example, patent publications CN 105839152 A, CN 111005037 A, and CN 105803484 A all disclose the use of ionic liquids as a green electrolyte, adding rare earth compounds and other components to prepare electrolytes, but the preparation cost of ionic liquids is high, the solubility of commonly used and readily available rare earth compounds is limited, and the organic solvents of some systems are harmful to the human body, thereby limiting the further application of ionic liquids.

[0004] Compared with ionic liquids, deep eutectic solvents (DESs) generally have lower melting points and similar physical and chemical properties to ionic liquids. However, the synthesis method of DESs is extremely simple and efficient, with 100% atomic conversion rate. It can be obtained by simply heating and mixing cheap, non-toxic, and biodegradable raw materials. Compared with ionic liquids with higher synthesis costs and greater toxicity, deep eutectic solvents are a new generation of green solvent systems.

[0005] At present, a variety of DESs (such as ChCl / Urea, ChCl / EG, etc.) have been used as electrolyte systems to achieve the electrodeposition of some rare earth metal alloy materials (Ni-La, Sm-Co, La-Co and Ce-Ni). For example, Patent Publication No. CN108767267A discloses a method for preparing concave cubic platinum-rare earth alloy nanocrystals based on a low eutectic solvent. The invention uses a green new type of non-aqueous low eutectic solvent as a medium and uses electrochemical cyclic voltammetry to prepare a concave cubic platinum-rare earth alloy nanocrystal with a surface {hk0} high-index crystal face structure.

[0006] For example, Gomez et al. studied the suitability of the ChCl / 2Urea system for the electrodeposition of Co, Sm and Co-Sm in "Electrodeposition of Co, Sm and SmCo from a deepeutectic solvent", and the deposition was carried out at 70°C. However, it can only be used to deposit rare earth alloys because the iron group inorganic salts added to the above electrolysis system generate intermediate species during the electrolysis process to induce rare earth to co-deposit with it, and the complex deposition mechanism makes it difficult to control its composition. For more active rare earth elements, the rare earth ions dissolved in the low eutectic solvent are wrapped in a stable solvation shell by the solvent molecules, resulting in a high driving force for the deposition of rare earths, making it difficult to generate a single rare earth metal.

[0007] Therefore, in view of the difficulty in preparing a single rare earth metal in a low-eutectic solvent system, it is urgent to develop a low-cost, green and low-carbon electrolyte system to prepare rare earths or rare earth alloys. Summary of the invention

[0008] 1. Problem to be solved

[0009] In view of the low efficiency of rare earth metal precipitation using existing low eutectic solvents, the present invention provides a low eutectic electrolyte and a method for preparing rare earth metals or rare earth alloys. Rare earth metals or rare earth alloys can be prepared under near room temperature conditions using the low eutectic electrolyte.

[0010] 2. Technical solution

[0011] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0012] The first object of the present invention is to provide a eutectic electrolyte, which comprises choline chloride, ethylene glycol, urea, an induction salt and a rare earth compound.

[0013] The eutectic electrolyte is a eutectic system composed of choline chloride-ethylene glycol-urea-inducing salt-rare earth compound, wherein the molar fraction of choline chloride in the eutectic system is 10%-30%, preferably 15%-25%; the molar fraction of ethylene glycol is 30%-50%, preferably 35%-45%; the molar fraction of urea is 30%-50%, preferably 35%-45%, and the sum of the molar fractions of choline chloride, ethylene glycol and urea is 1.

[0014] The content of the inducing salt is 0-0.1 mol / L, preferably 0.01-0.05 mol / L; the content of the rare earth compound is 0.01-1.5 mol / L, preferably 0.1-0.2 mol / L.

[0015] The rare earth elements include all lanthanide elements (lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu)) and at least one of scandium (Sc) and yttrium (Y).

[0016] The rare earth compound is a rare earth chloride compound, a rare earth nitrate compound, a rare earth sulfate compound, a rare earth carbonate compound, or a rare earth fluoride compound, preferably a rare earth chloride compound or a rare earth nitrate compound.

[0017] The inducing salt is a Zn salt or a Li salt. The Zn salt is a chloride, nitrate, carbonate, or fluoride of Zn, namely, ZnCl2, Zn(NO3)2, ZnCO3, or ZnF2. The Li salt is a chloride, nitrate, carbonate, or fluoride of Li, namely, LiCl, LiNO3, Li2CO3, or LiF.

[0018] The preparation steps of the electrolyte are as follows: ethylene glycol and a rare earth compound are fully mixed, heated to form a clear, uniform and transparent ethylene glycol-rare earth compound solution, and then choline chloride, urea and an induction salt are added to the solution, and after fully heating and stirring, a clear, uniform and transparent low-melting electrolyte is obtained.

[0019] Furthermore, the raw materials of the low-melting eutectic electrolyte in step S1 are all vacuum dried to ensure that the formed low-melting eutectic electrolyte is an anhydrous system to avoid water electrolysis reaction during the reaction process. The specific steps of the drying treatment are: placing the sample in a vacuum drying oven for drying treatment, controlling the temperature of the vacuum drying oven to 60-90°C, and preferably the drying and dehydration temperature is 70-80°C.

[0020] Furthermore, the heating temperature of preparing the ethylene glycol-rare earth compound solution is 70-140° C., preferably, the heating temperature is 110-130° C. The heating temperature of adding choline chloride, urea, and induction salt is 20-100° C., preferably, the heating temperature is 70-80° C.

[0021] Another object of the present invention is to provide a method for preparing rare earth metals or rare earth alloys, using the above-mentioned eutectic electrolyte, which comprises the steps of performing constant potential electrodeposition:

[0022] In an inert gas atmosphere, the electrolyte temperature was controlled to be 50-80°C and the cathode potential was -1.2-2.0V (vs.Ag / Ag + ) to perform constant potential electrodeposition, and obtain an electrodeposition product at the cathode. After the product is soaked and washed with anhydrous ethanol, the electrode is stored in a vacuum tank and dried to obtain a rare earth metal single substance or a rare earth alloy on the cathode. The rare earth alloy is a rare earth alloy based on an induction salt metal. Specifically, when zinc salt is used as the induction salt, the rare earth alloy is a rare earth zinc alloy, and when lithium salt is used as the induction salt, a rare earth metal single substance is obtained.

[0023] The electrodeposition process adopts a three-electrode system, wherein the cathode is selected from one or more of copper sheet, tungsten sheet, molybdenum sheet or stainless steel, the anode is selected from one or more of platinum sheet or graphite, and the Ag / AgCl electrode is a reference electrode, which is inserted into an electrolytic cell filled with a low eutectic electrolyte to form a three-electrode system.

[0024] The electrode surface is also pretreated, and the pretreatment steps are: the cathode and the anode are repeatedly ultrasonically cleaned with anhydrous ethanol and deionized water after grinding and polishing, and finally rinsed with deionized water and dried for use. The electrode polishing operation is to polish the anode on the deerskin surface with 500nm, 300nm, and 50nm polishing powders in turn, and the cathode is polished with 60 mesh, 400 mesh, 1000 mesh, 2000 mesh sandpaper and 50nm polishing powder in turn. The polishing powder is preferably aluminum oxide. The Ag / AgCl reference electrode is immersed in a porous ceramic quartz glass tube containing a saturated potassium chloride solution.

[0025] Furthermore, the inert gas in step S3 is nitrogen or argon. The time for passing the inert gas before electrolysis is at least 30 minutes, and the longer the time, the better. Inert gas is passed during the electrolysis process. First, because the components of the electrolysis system, choline chloride and ethylene glycol, have certain hygroscopicity, especially choline chloride. If there is water in the system, hydrogen evolution reaction will occur during the electrolysis process, resulting in the formation of a passivation film, which affects the deposition of rare earths; second, the deposited rare earths are highly active and have strong aerobicity. If there is interference from oxygen, the deposited rare earth elements will be oxidized. Therefore, the inert gas is passed to keep the electrolysis system in an anhydrous and oxygen-free environment.

[0026] During the electrolysis process, the precipitated components are controlled to be rare earth elements or rare earth alloys by controlling the type and addition amount of the inducing salt: when the inducing salt is a zinc salt, although the rare earth ion has a more negative reduction potential than the zinc ion, the reduction potentials of the two are close, and the co-precipitation of the two is achieved by controlling the potential. When the molar ratio of the rare earth compound to the inducing salt is ≥10, the cathode electrolysis product is a rare earth metal powder with a rare earth mass fraction of >98%; when the molar ratio of the rare earth compound to the inducing salt is <10, the cathode electrolysis product is a rare earth alloy; when the inducing salt is a lithium salt, since the lithium ion has a more negative reduction potential than the rare earth ion, the reduction potentials of the two are greatly different and co-precipitation cannot occur, and the cathode electrolysis products are all rare earth metals.

[0027] The main features of the present invention are:

[0028] (1) The electrolytic system takes into account both the solubility of rare earths and the sensitivity of rare earth electrodeposition.

[0029] Conventional low eutectic solvent electrolysis systems have low yields for rare earth reduction. This is because conventional low eutectic solvents have good solubility for rare earths, and rare earth ions interact with hydrogen bond donor molecules or hydrogen bond acceptor anions of the low eutectic solvent to form stable coordination units, which is very unfavorable in the electrolysis process. The cyclic voltammetry curve shows that the reduction signal of rare earths will only appear when the rare earth concentration in the electrolyte is very high. If a single rare earth metal is to be prepared, it is necessary to find suitable additives to improve the coordination environment of rare earth ions at the molecular level, weaken the complexing ability of the low eutectic solvent, reduce the desolvation energy of rare earth ions during the deposition process, and reduce the reaction energy barrier for the generation of electroactive substances. Therefore, the present invention adds inducing salts in the system to effectively induce the deposition of rare earths. After the inducing salts are introduced into the electrolytic system, on the one hand, the inducing salts will be rapidly deposited on the cathode surface at the beginning of electrolytic deposition, increasing the superpotential of hydrogen and reducing the occurrence of hydrogen evolution side reactions. On the other hand, the addition of inducing salts will attract solvent molecules, anions, etc. around rare earth ions, weaken the complexing ability of rare earth metals in the diffusion layer, improve the coordination environment around rare earth metals, and reduce the precipitation potential of rare earth metals, thereby being more conducive to the deposition of rare earth metals. The low eutectic solvent electrolysis system in the present invention not only has a significant improvement in the solubility of rare earth compounds compared to traditional ionic liquid systems, up to 1.53 mol / L, meeting the actual electrolysis needs; and in the cyclic voltammetry curve test under low rare earth concentration conditions (minimum 0.01 mol / L), reduction signals can still be observed. This shows that the electrolysis system still maintains the efficient deposition ability of the main salt rare earth ions under low rare earth concentration conditions.

[0030] (2) The product composition is controllable.

[0031] The method of the present invention can not only prepare a single rare earth metal, but also produce rare earth zinc alloy products of different components as needed to meet different application requirements. The present application achieves the deposition of a single rare earth metal or alloy by regulating the ratio of different components in the electrolyte system. When a Zn salt is used as an inducer, the ratio of the rare earth compound to the Zn salt is used to deposit a single rare earth metal or alloy. In this electrolytic system, the deposition of rare earth metal ions and inducing salt ions is controlled by diffusion. During electrodeposition, the reduction potential of the inducing salt is relatively positive. The inducing salt of the diffusion layer is preferentially reduced and deposited on the working electrode substrate, providing a large number of active sites for electrodeposition. If the ratio of the rare earth compound to the inducing salt is ≤10, the rare earth compound and the inducing salt enter the diffusion layer together, then remove the solvation shell and adsorb to the electrode surface, and jointly deposit as an alloy layer; if the ratio of the rare earth compound to the inducing salt is greater than 10, the concentration of the rare earth compound in the diffusion layer is relatively high, and the desolvation is preferentially adsorbed to the electrode surface to occupy a large number of active sites, and then the electrons of the single rare earth ion nucleate and grow on the surface.

[0032] (3) Compared with the current rare earth metal smelting process: energy consumption is significantly reduced.

[0033] Among the existing industrial rare earth metal preparation processes, oxide molten salt electrolysis is the most important and widely used rare earth metal production process today. However, oxide molten salt electrolysis requires high energy consumption and can only form molten salt at high temperatures. The electrolysis temperature of rare earth metals reaches 900°C. The electrolyte used in the present invention is in a molten state at room temperature and is a near-room temperature electrolyte system. The temperature of the electrolysis process is 25-90°C, which effectively reduces the energy consumption of oxide molten salt electrolysis. In addition, high-temperature operation has high requirements for equipment materials and design, while the present invention performs electrolysis under near-room temperature conditions, and the high-temperature resistance requirements of equipment materials are reduced, the equipment design is simpler, and the equipment cost and maintenance difficulty are effectively reduced.

[0034] (4) The electrolyte system has a low melting point, is cheap, readily available, green and non-toxic.

[0035] The present invention adopts a choline chloride-urea-ethylene glycol-rare earth compound-inducing salt composite eutectic electrolyte, wherein choline chloride is a hydrogen bond acceptor, ethylene glycol and urea are hydrogen bond donors, and no organic additive harmful to the human body needs to be added. The above components are stirred and heated in a certain proportion to obtain an electrolyte. The eutectic electrolyte is biodegradable, and the raw materials involved in the system, such as choline chloride and urea, can be used as feed additives, and urea can also be used as an organic nitrogen fertilizer as a nitrogen source for plants. Choline chloride, ethylene glycol, urea and other raw materials are low in price and are all commercially available.

[0036] 3. Beneficial effects

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) Inducing salt is added to the eutectic electrolyte of the present invention to effectively induce the deposition of rare earth. On the one hand, the inducing salt is rapidly deposited on the cathode surface at the beginning of electrolytic deposition, thereby increasing the hydrogen overpotential and reducing the occurrence of hydrogen evolution side reaction. On the other hand, the inducing salt weakens the complexing ability of rare earth metals in the diffusion layer, improves the coordination environment around the rare earth metals, and reduces the precipitation potential of the rare earth metals, thereby being more conducive to the deposition of rare earth metals. Under the condition of low rare earth concentration, the efficient deposition ability of the main salt rare earth ions is still maintained;

[0039] (2) The low-melting electrolyte of the present invention is in a molten state at room temperature and is a near-room temperature electrolyte system with an electrolysis temperature of 25-90°C, which effectively solves the high temperature problem generated by the traditional oxide molten salt electrolysis method. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but it should be understood that these drawings are designed only for explanation purposes and are not intended to limit the scope of the present invention. In addition, unless otherwise specified, these drawings are intended only to conceptually illustrate the structural configurations described herein and are not necessarily drawn to scale.

[0041] Figure 1 1 is the cyclic voltammetry curve of the eutectic electrolyte in Example 1 of the present invention;

[0042] Figure 2 cyclic voltammetry curve of the eutectic electrolyte in Example 2 of the present invention;

[0043] Figure 3 cyclic voltammetry curve of the eutectic electrolyte in Example 3 of the present invention;

[0044] Figure 4 This is a SEM scanning electron microscope image of the rare earth zinc alloy product in Example 1 of the present invention;

[0045] Figure 5 This is a SEM scanning electron microscope image of the rare earth zinc alloy product in Example 2 of the present invention;

[0046] Figure 6 This is a SEM scanning electron microscope image of the rare earth metal product in Example 3 of the present invention;

[0047] Figure 7 This is an EDS spectrum analysis diagram of the rare earth zinc alloy product in Example 1 of the present invention;

[0048] Figure 8 This is an EDS spectrum analysis diagram of the rare earth zinc alloy product in Example 2 of the present invention;

[0049] Fig. 9 This is an EDS spectrum analysis diagram of the rare earth metal product in Example 3 of the present invention;

[0050] Fig.10 This is a physical picture of the white flocculent product produced at the cathode after electrolysis in the comparative example of the present invention. DETAILED DESCRIPTION

[0051] The following detailed description of exemplary embodiments of the present invention refers to the accompanying drawings, which form a part of the description, and in which exemplary embodiments of the present invention that can be implemented are shown as examples. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention, it should be understood that other embodiments can be implemented and various changes can be made to the present invention without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but is only for the purpose of illustrating and not limiting the description of the characteristics and features of the present invention, so as to propose the best mode for performing the present invention and to enable those skilled in the art to implement the present invention. Therefore, the scope of the present invention is limited only by the appended claims.

[0052] It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention. As used herein, the terms "parallel" and "perpendicular" are not limited to their strict geometric definitions, but include tolerances for reasonable and inconsistent machining or human errors.

[0053] Unless otherwise specified, the materials in the present invention are all commercially available.

[0054] Deep eutectic solvents, also known as deep eutectic solvents (DESs), refer to low eutectic mixtures formed by Lewis (or Brφnsted) acids (hydrogen bond donors) and bases (hydrogen bond acceptors) through hydrogen bonds. The essential difference between low eutectic solvents and ionic liquid solvents is that ionic liquids mainly exist in the form of free anion and cation pairs, while low eutectic solvents are formed by the weak hydrogen bonding between the components. Affected by the charge delocalization effect, DESs generally have a low melting point and have physical and chemical properties similar to ILs. The synthesis method of DESs is extremely simple and efficient, with a 100% atomic conversion rate. It can be obtained by simply heating and mixing cheap, non-toxic, and biodegradable raw materials. Compared with ionic liquids with higher synthesis costs and greater toxicity, low eutectic solvents are a new generation of green solvent systems.

[0055] Example 1

[0056] In a low-melting electrolyte of Example 1, the inducing salt is anhydrous zinc chloride (ZnCl2), and the rare earth raw material is anhydrous yttrium chloride (YCl3), which includes: ethylene glycol, choline chloride, urea, an inducing salt and a rare earth compound, the molar fraction of choline chloride is 20%, the molar fraction of urea is 40%, and the molar fraction of ethylene glycol is 40%.

[0057] In a low eutectic system with 1 mol of choline chloride, 2 mol of ethylene glycol and 2 mol of urea, a low eutectic composite electrolyte is prepared with a molar ratio of ZnCl2:YCl3=1:2, wherein the concentration of ZnCl2 in the system is 0.05 mol / L, and the concentration of YCl3 in the system is 0.1 mol / L.

[0058] The process of preparing rare earth metals or rare earth zinc alloys using the above electrolyte is as follows: add the prepared low-melting electrolyte to the electrolytic cell, use the metal Cu sheet as the working electrode, the metal Pt sheet as the counter electrode, and the Ag / AgCl as the reference electrode. The electrolysis temperature is controlled to be 60°C, and the cathode potential is -1.8V (Ag / Ag+) relative to the Ag / AgCl reference electrode. The electrolysis process is carried out under an argon protective atmosphere for 4 hours. Zn is precipitated on the Cu cathode, and then zinc and yttrium co-deposition occurs on the Zn substrate to form a rare earth zinc alloy, in which the mass fraction of Y is 40%. The cyclic voltammetry test results before electrolysis are as follows: Figure 1 The SEM scanning electron microscopy results of the obtained product are shown in Figure 3 , EDS spectrum analysis results Figure 5 .

[0059] Example 2

[0060] In a low-melting electrolyte of Example 2, the inducing salt is anhydrous zinc chloride (ZnCl2), and the rare earth raw material is anhydrous yttrium chloride (YCl3), which includes: ethylene glycol, choline chloride, urea, an inducing salt and a rare earth compound, the molar fraction of choline chloride is 20%, the molar fraction of urea is 40%, and the molar fraction of ethylene glycol is 40%.

[0061] Among them, in a low eutectic system with a choline chloride content of 1 mol, an ethylene glycol content of 2 mol, and a urea content of 2 mol, a low eutectic composite electrolyte is prepared with a molar ratio of ZnCl2:YCl3=1:4, wherein the concentration of ZnCl2 in the system is 0.05 mol / L.

[0062] The process of preparing rare earth metal or rare earth zinc alloy by using the above electrolyte is as follows: adding the prepared low eutectic electrolyte into an electrolytic cell, using metal Cu as the working electrode, metal Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, controlling the electrolysis temperature to 60°C, and the cathode potential to -1.8V (Ag / AgCl) relative to the Ag / AgCl reference electrode. +The electrolysis process was carried out under an argon protective atmosphere for 4 hours. Zn was precipitated on the Cu cathode, and then zinc and yttrium co-deposited on the Zn substrate to form an alloy with a Y mass fraction of 71%. The cyclic voltammetry test results before electrolysis are as follows: Figure 2 The SEM scanning electron microscopy results of the obtained product are shown in Figure 4 , EDS spectrum analysis results Figure 6 .

[0063] Example 3

[0064] In a low eutectic electrolyte of Example 3, the inducing salt is anhydrous zinc chloride (ZnCl2), and the rare earth raw material is anhydrous ytterbium chloride (YbCl3), which includes: ethylene glycol, choline chloride, urea, an inducing salt and a rare earth compound, the molar fraction of choline chloride is 20%, the molar fraction of urea is 40%, and the molar fraction of ethylene glycol is 40%.

[0065] Among them, in a low-melting eutectic system with a choline chloride content of 1 mol, an ethylene glycol content of 2 mol, and a urea content of 2 mol, a low-melting electrolyte is prepared with a molar ratio of ZnCl2:YbCl3=1:11, wherein the concentration of ZnCl2 in the system is 0.05 mol / L.

[0066] The process of preparing rare earth metals or rare earth zinc alloys using the above electrolyte is as follows: add the prepared eutectic electrolyte to the electrolytic cell, use metal Cu as the working electrode, metal Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, control the electrolysis temperature to 60°C, and the cathode potential relative to the Ag / AgCl reference electrode to be -1.8V (Ag / Ag+). The electrolysis process is carried out under an argon protective atmosphere for 4 hours. Zn is precipitated on the Cu cathode, and then Yb is underpotentially deposited on the Zn substrate to produce black yttrium metal powder. The product is collected and placed on a Si wafer for SEM-EDS detection. It should be noted that the EDS energy spectrum diffraction peaks of Si and Ta are close, and the diffraction peak of Ta appears after deducting the interference of the background Si. The results of the cyclic voltammetry test before electrolysis are as follows Figure 3 The SEM scanning electron microscopy results of the obtained product are shown in Figure 6 , EDS spectrum analysis results Fig. 9 .

[0067] Example 4

[0068] In a low-melting electrolyte of Example 4, the inducing salt is anhydrous lithium nitrate (LiNO3), and the rare earth raw material is anhydrous yttrium nitrate (Y(NO3)3), which includes: ethylene glycol, choline chloride, urea, an inducing salt and a rare earth compound, the molar fraction of choline chloride is 20%, the molar fraction of urea is 40%, and the molar fraction of ethylene glycol is 40%.

[0069] Among them, in a low-melting electrolyte system with a choline chloride content of 1 mol, an ethylene glycol content of 2 mol, and a urea content of 2 mol, a low-melting electrolyte is prepared with a molar ratio of LiNO3:Y(NO3)3=1:11, wherein the concentration of LiNO3 in the system is 0.05 mol / L.

[0070] The process of preparing rare earth metal or rare earth zinc alloy using the above electrolyte is as follows: adding the prepared low eutectic electrolyte into an electrolytic cell, using metal Cu as the working electrode, metal Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, controlling the electrolysis temperature to 60°C, and the cathode potential to -1.8V (Ag / Ag+) relative to the Ag / AgCl reference electrode. The electrolysis process is carried out under an argon protective atmosphere, the electrolysis time is 4 hours, and black yttrium metal powder is precipitated on the Cu cathode.

[0071] Example 5

[0072] In a low-melting electrolyte of Example 5, the inducing salt is anhydrous lithium chloride (LiCl), and the rare earth raw material is anhydrous scandium chloride (ScCl3), which includes: ethylene glycol, choline chloride, urea, an inducing salt and a rare earth compound, the molar fraction of choline chloride is 20%, the molar fraction of urea is 40%, and the molar fraction of ethylene glycol is 40%.

[0073] In a low eutectic system with a choline chloride content of 1 mol, an ethylene glycol content of 2 mol, and a urea content of 2 mol, a low eutectic electrolyte is prepared with a molar ratio of LiCl:YCl3=1:11, wherein the concentration of LiCl in the system is 0.05 mol / L.

[0074] The process of preparing rare earth metal or rare earth zinc alloy using the above electrolyte is as follows: adding the prepared low eutectic electrolyte into an electrolytic cell, using metal Cu as the working electrode, metal Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, controlling the electrolysis temperature to 60°C, and the cathode potential to -1.8V (Ag / Ag+) relative to the Ag / AgCl reference electrode. The electrolysis process is carried out under an argon protective atmosphere, the electrolysis time is 4 hours, and black yttrium metal powder is precipitated on the Cu cathode.

[0075] Example 6

[0076] In a low-melting electrolyte of Example 6, the inducing salt is anhydrous lithium nitrate (LiNO3), and the rare earth raw material is anhydrous yttrium nitrate (Y(NO3)3), which includes: ethylene glycol, choline chloride, urea, an inducing salt and a rare earth compound, the molar fraction of choline chloride is 20%, the molar fraction of urea is 50%, and the molar fraction of ethylene glycol is 30%.

[0077] Among them, in a low eutectic system with a choline chloride content of 2 mol, an ethylene glycol content of 3 mol, and a urea content of 5 mol, a low eutectic electrolyte is prepared with a molar ratio of LiNO3:Y(NO3)3=1:11, wherein the concentration of LiNO3 in the system is 0.05 mol / L.

[0078] The process of preparing rare earth metal or rare earth zinc alloy using the above electrolyte is as follows: adding the prepared low eutectic electrolyte into an electrolytic cell, using metal Cu as the working electrode, metal Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, controlling the electrolysis temperature to 60°C, and the cathode potential to -1.8V (Ag / Ag+) relative to the Ag / AgCl reference electrode. The electrolysis process is carried out under an argon protective atmosphere, the electrolysis time is 4 hours, and black yttrium metal powder is precipitated on the Cu cathode.

[0079] Example 7

[0080] In a low-melting electrolyte of Example 7, the inducing salt is anhydrous lithium nitrate (LiNO3), and the rare earth raw material is anhydrous yttrium nitrate (Y(NO3)3), which includes: ethylene glycol, choline chloride, urea, an inducing salt and a rare earth compound, the molar fraction of choline chloride is 10%, the molar fraction of urea is 40%, and the molar fraction of ethylene glycol is 50%.

[0081] Among them, in a low-melting electrolyte system with a choline chloride content of 1 mol, an ethylene glycol content of 5 mol, and a urea content of 4 mol, a low-melting electrolyte is prepared with a molar ratio of LiNO3:Y(NO3)3=1:11, wherein the concentration of LiNO3 in the system is 0.05 mol / L.

[0082] The process of preparing rare earth metal or rare earth zinc alloy using the above electrolyte is as follows: adding the prepared low eutectic electrolyte into an electrolytic cell, using metal Cu as the working electrode, metal Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, controlling the electrolysis temperature to 60°C, and the cathode potential to -1.8V (Ag / Ag+) relative to the Ag / AgCl reference electrode. The electrolysis process is carried out under an argon protective atmosphere, the electrolysis time is 4 hours, and black yttrium metal powder is precipitated on the Cu cathode.

[0083] Example 8

[0084] In a low-melting electrolyte of Example 8, the inducing salt is anhydrous lithium nitrate (LiNO3), and the rare earth raw material is anhydrous yttrium nitrate (Y(NO3)3), which includes: ethylene glycol, choline chloride, urea, an inducing salt and a rare earth compound, the molar fraction of choline chloride is 30%, the molar fraction of urea is 30%, and the molar fraction of ethylene glycol is 40%.

[0085] Among them, in a low-melting electrolyte system with a choline chloride content of 3 mol, an ethylene glycol content of 4 mol, and a urea content of 3 mol, a low-melting electrolyte is prepared with a molar ratio of LiNO3:Y(NO3)3=1:11, wherein the concentration of LiNO3 in the system is 0.05 mol / L.

[0086] The process of preparing rare earth metal or rare earth zinc alloy using the above electrolyte is as follows: adding the prepared low eutectic electrolyte into an electrolytic cell, using metal Cu as the working electrode, metal Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, controlling the electrolysis temperature to 60°C, and the cathode potential to -1.8V (Ag / Ag+) relative to the Ag / AgCl reference electrode. The electrolysis process is carried out under an argon protective atmosphere, the electrolysis time is 4 hours, and black yttrium metal powder is precipitated on the Cu cathode.

[0087] Example 9

[0088] In a low-melting electrolyte of Example 9, the inducing salt is anhydrous lithium nitrate (LiNO3), and the rare earth raw material is anhydrous yttrium nitrate (Y(NO3)3), which includes: ethylene glycol, choline chloride, urea, an inducing salt and a rare earth compound, the molar fraction of choline chloride is 10%, the molar fraction of urea is 50%, and the molar fraction of ethylene glycol is 40%.

[0089] Among them, in a low-melting electrolyte system with a choline chloride content of 1 mol, an ethylene glycol content of 4 mol, and a urea content of 5 mol, a low-melting electrolyte is prepared with a molar ratio of LiNO3:Y(NO3)3=1:11, wherein the concentration of LiNO3 in the system is 0.05 mol / L.

[0090] The process of preparing rare earth metal or rare earth zinc alloy using the above electrolyte is as follows: adding the prepared low eutectic electrolyte into an electrolytic cell, using metal Cu as the working electrode, metal Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, controlling the electrolysis temperature to 60°C, and the cathode potential to -1.8V (Ag / Ag+) relative to the Ag / AgCl reference electrode. The electrolysis process is carried out under an argon protective atmosphere, the electrolysis time is 4 hours, and black yttrium metal powder is precipitated on the Cu cathode.

[0091] Comparative Example 1

[0092] A low eutectic electrolyte in comparative example 1 does not contain an inducing salt, and the rare earth raw material is anhydrous yttrium chloride (YCl3), which includes: ethylene glycol, choline chloride, urea, and a rare earth compound, and the molar ratio of the choline chloride, urea, and ethylene glycol is 1:2:2.

[0093] Among them, in the low eutectic system with choline chloride content of 1 mol, ethylene glycol content of 2 mol, and urea content of 2 mol, the concentration of YCl3 in the system is 0.1 mol / L.

[0094] The process of preparing rare earth metal or rare earth zinc alloy using the above electrolyte is as follows: add the prepared low eutectic electrolyte to the electrolytic cell, use metal Cu as the working electrode, metal Pt sheet as the counter electrode, Ag / AgCl as the reference electrode, control the electrolysis temperature to 60°C, and the cathode potential relative to the Ag / AgCl reference electrode to -1.8V (Ag / Ag+). The electrolysis process is carried out under an argon protective atmosphere for 4 hours. After electrolysis, a large amount of white flocculent products are produced on the surface of the Cu electrode, such as Fig.10 As shown, side reactions occurred in the system and no metal deposition was observed on the electrode surface.

[0095] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope involved in the present application is not limited to the technical solution formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept, such as a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0096] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A method for preparing a rare earth metal or a rare earth zinc alloy, characterized in that: A low-melting electrolyte is used to carry out constant potential electrodeposition at a temperature of 50 to 80° C. The low-melting electrolyte includes ethylene glycol, choline chloride, urea, an induction salt and a rare earth compound. An electrodeposition product is obtained at the cathode. The induction salt is a Zn salt or a Li salt.

2. The method according to claim 1, characterized in that The Zn salt is chloride, nitrate, carbonate or fluoride of Zn or Li, and the Li salt is chloride, nitrate, carbonate or fluoride of Li.

3. The method according to claim 2, characterized in that When the cathode electrolysis product is a rare earth metal, the induction salt is a Zn salt, and the molar ratio of the rare earth compound to the Zn salt is less than 10.

4. The method according to claim 2, characterized in that: When the cathode electrolysis product is a rare earth alloy, the induction salt is a Zn salt, and the molar ratio of the rare earth compound to the Zn salt is ≥10.

5. The method according to claim 2, characterized in that: When the cathode electrolyzes the product, the induction salt is a lithium salt.

6. The method according to claim 1, characterized in that The rare earth elements include lanthanide elements and one or more of scandium and yttrium. The lanthanide elements include one or more of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

7. The method according to claim 1, characterized in that In the eutectic system, the molar fraction of choline chloride is 10%-30%, the molar fraction of ethylene glycol is 30%-50%, the molar fraction of urea is 30%-50%, and the sum of the molar fractions of choline chloride, ethylene glycol and urea is 100%.

8. The method according to claim 1, characterized in that The cathode potential of the electrodeposition is -1.2 to -2.0 V (vs. Ag / Ag + ), the electrodeposition time is 30min~2h.

9. The method according to claim 1, characterized in that: The electrodeposition is performed in an inert gas atmosphere.

10. The method according to claim 1, characterized in that The constant potential electrodeposition forms a three-electrode system with the participation of a cathode, an anode and a reference electrode and a low-melting electrolyte.

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