Process for the preparation of rare earth metals by electrolysis of oxides in a fluoride system

Abstract

This invention discloses a method for preparing rare earth metals by electrolytic oxides using a fluoride system, belonging to the field of rare earth metal preparation technology. This invention modifies graphite anodes used in rare earth molten salt electrolysis. It improves oxidation and corrosion resistance, reduces anode wear, lowers replacement frequency, and increases production efficiency, yielding high-purity, low-carbon rare earth metal lanthanum. A three-dimensional network framework material is constructed using Prussian blue self-assembly and SiC is deposited to obtain a composite framework material. During pre-calcination with graphite and other materials, the derivatives optimize the crystal structure and interfacial bonding, enhancing the strength of the pre-shaped anode material and ensuring the integrity and performance stability of the electrode structure. Thirdly, the pre-shaped anode material is impregnated with a specific impregnation solution, altering the gas diffusion path and resistance, inhibiting oxidation reactions, and high-temperature sintering generates substances that fill the pores, forming a dense microstructure. Simultaneously, the compounds formed by phosphoric acid enhance cohesion and adhesion, improving oxidation and molten salt corrosion resistance, and extending the service life of the graphite anode.

Description

Technical Field

[0001] This invention belongs to the field of rare earth metal preparation technology, and particularly relates to a method for preparing rare earth metals by electrolytic oxides in a fluoride system. Background Technology

[0002] In traditional electrolytic processes for rare earth metal preparation, graphite is widely chosen as the anode material and high-temperature tank material due to its many excellent properties. Its excellent electrical and thermal conductivity efficiently conducts current and heat, its strong resistance to molten salt corrosion allows it to remain stable in high-temperature molten salt environments, its ease of processing facilitates the construction of electrolytic devices, and its excellent thermal shock resistance further ensures normal operation under electrolytic conditions with drastic temperature changes. In the high-temperature molten salt electrolysis of rare earth fluoride systems, graphite anodes successfully establish stable electrical pathways, effectively ensuring the continuous and stable progress of the electrolytic reaction. However, this traditional process has undeniable drawbacks. The high-temperature environment during electrolysis induces high-temperature oxidation reactions in both the graphite anode and the graphite tank. Since they are mostly made from petroleum coke and coal tar pitch, they exhibit a porous structure, which is a significant disadvantage in high-temperature oxidation environments. On the one hand, the porous structure greatly increases the contact area with oxygen, accelerating the oxidation process and causing rapid consumption of the graphite anode; on the other hand, the synergistic effect of oxidation and high-temperature molten salt corrosion leads to physical damage to the graphite material. These substances, produced by oxidation and damage, inevitably mix into the electrolysis system, with carbon impurities being particularly prominent. This directly leads to a significant increase in the carbon impurity content in the final rare earth metal, severely affecting the purity of the rare earth metal.

[0003] In high-end applications such as semiconductor manufacturing, rare earth metals, as dopants or core materials, play a decisive role in the performance, reliability, and final yield of semiconductor devices. In the field of rare earth permanent magnet materials, the presence of impurities severely disrupts the integrity and order of the magnetic domain structure, thereby weakening the material's magnetic properties. Specifically, this manifests as a significant reduction in coercivity and remanence, making the material unable to meet the stringent requirements of high-end applications. Therefore, the oxidation problem of graphite anodes during electrolysis has become a key factor restricting the improvement of rare earth metal quality, greatly limiting the expansion of rare earth metal applications in high-tech fields. Faced with the ever-increasing demand for high-end rare earth metals, it is crucial to develop a novel electrolytic preparation method that can effectively overcome the high-temperature oxidation problem of graphite anodes and significantly reduce the impurity content of rare earth metals. Summary of the Invention

[0004] To address the above issues and overcome the shortcomings of existing technologies, this invention constructs a SiC-Prussian blue composite framework material. Combined with impregnation solution treatment and specific electrolysis process conditions, it effectively suppresses high-temperature oxidation of graphite anodes and reduces carbon impurity contamination during the electrolytic preparation of rare earth metals in a fluoride system. This significantly improves the purity of rare earth metals, extends the service life of graphite anodes, and enhances overall production efficiency and product quality.

[0005] To achieve the above objectives, the following technical solution is adopted: This invention provides a method for preparing rare earth metals by electrolytic oxidation of fluoride systems, comprising the following steps: S1. Mix 0.1 mol / L potassium ferrocyanide solution and 0.1 mol / L ferric nitrate solution, heat to 60°C, add acrylamide / sodium acrylate copolymer to the mixture and stir until homogeneous. After cooling to room temperature, wash the resulting precipitate with water and ethanol respectively, dry it, and then place it in a high-temperature furnace and introduce argon gas to obtain a three-dimensional network Prussian blue framework material. Then introduce a mixed gas of silicon tetrachloride and hydrogen to deposit SiC on the surface of the Prussian blue framework material to obtain a SiC-Prussian blue composite framework material. S2. Natural flake graphite, artificial graphite, asphalt, and coal char are mixed and then kneaded with SiC-Prussian blue composite skeleton material using a kneader. After pre-calcination, a pre-shaped anode material is obtained. Phosphoric acid, ammonia, ammonium metavanadate, and sodium monofluorophosphate are prepared into an impregnation solution. The pre-shaped anode material is then immersed in the impregnation solution. After impregnation, the pre-shaped anode material is removed from the impregnation solution, excess impregnation solution is wiped off the surface, and the material is dried. It is then placed in a high-temperature sintering furnace for high-temperature sintering. After returning to room temperature, an antioxidant and corrosion-resistant graphite anode is obtained. S3. Using the antioxidant and corrosion-resistant graphite anode prepared in step S2 as the anode electrode, a molybdenum rod as the cathode, and a molybdenum crucible as the receiver, lanthanum oxide is added to the electrolyte system of fluoride molten salt composed of lanthanum fluoride, barium fluoride, and lithium fluoride. Under the action of a DC electric field, liquid lanthanum metal is precipitated on the cathode surface. The produced liquid metal is received by the molybdenum crucible and obtained by casting into an ingot.

[0006] Further, in step S1, the mass ratio of potassium ferrocyanide solution, ferric nitrate solution, and acrylamide / sodium acrylate copolymer is 3:1-2:0.1-0.5.

[0007] Furthermore, in step S1, the temperature of the vacuum furnace is 200℃-350℃, and the flow rate of argon gas is 100-200mL / min.

[0008] Furthermore, in step S1, the mass ratio of silicon tetrachloride to hydrogen is 1:8-10, and the total flow rate of the mixed gas is 200-320 mL / min.

[0009] Furthermore, in step S2, the mass ratio of natural flake graphite, artificial graphite, asphalt, coal char, and SiC-Prussian blue composite skeleton material is 5-8:0.5-3:1.5-3:3-5:0.05-0.2.

[0010] Furthermore, the impregnation solution in step S2 comprises the following components by mass percentage: 20-30% phosphoric acid, 3-5% ammonia, 2-3% sodium monofluorophosphate, and the remainder is water.

[0011] Furthermore, in step S2, the immersion temperature is 60-80℃ and the immersion time is 1-2 hours.

[0012] Furthermore, in step S2, the high-temperature sintering furnace is heated to 600-750℃ at a heating rate of 5-10℃ / min and held at that temperature for 1.5-3 hours.

[0013] Furthermore, in step S3, the mass ratio of lanthanum fluoride, barium fluoride, lithium fluoride, and lanthanum oxide is 1:3-5:0.5-2:50-80.

[0014] Furthermore, the electrolysis temperature in step S3 is 1000-1100℃, the electrolysis current is 4900-5030A, and the electrolysis voltage is 10V.

[0015] The beneficial effects of this invention are: (1) This invention improves the oxidation and corrosion resistance of graphite anodes by modifying graphite anodes used in rare earth molten salt electrolysis, slows down anode wear, reduces the frequency of anode replacement, improves production efficiency, and produces rare earth metal lanthanum with high purity and low carbon content. (2) This invention utilizes the self-assembly mechanism of Prussian blue compounds to construct a Prussian blue framework material with a three-dimensional network structure. Through its spatial topological characteristics, it provides structural support for the performance optimization of subsequent materials. Then, a mixed gas of silicon tetrachloride and hydrogen is introduced to allow SiC to be uniformly deposited on the surface of the Prussian blue framework material, thereby obtaining a SiC-Prussian blue composite framework material. During the synergistic treatment of the composite framework material and raw materials such as graphite through kneading and pre-calcination, the FeC and SiC derived from the Prussian blue framework material microscopically optimize the crystal structure and interfacial bonding force of the material, and macroscopically significantly improve the overall strength of the pre-shaped anode material. This reduces the risk of structural failure caused by insufficient strength in the surface anode material, ensuring the structural integrity and performance stability of the electrode during long-term use. (3) In this invention, an impregnation solution is prepared using phosphoric acid, ammonia, and sodium monofluorophosphate, and a pre-shaped anode material is impregnated in it. The impregnation solution penetrates into the pore channels of the pre-shaped anode material. By filling the pores, the impregnating material changes the path and resistance of gas diffusion, reduces the effective collision frequency between oxidizing gas and the active sites inside the graphite electrode, thereby inhibiting the initiation and propagation of the oxidation reaction at the molecular level and significantly delaying the premature oxidation process of the graphite anode. During the high-temperature sintering process, the impregnation solution undergoes complex chemical reactions to generate substances such as aluminum orthophosphate. These reaction products can further and precisely fill the graphite electrode. The porous structure of the electrode promotes the formation of a dense microstructure, which significantly enhances the oxidation resistance of the graphite anode. Phosphoric acid, when converted to polyphosphate at high temperatures, possesses high viscosity. At the microscale, this effectively binds graphite separation caused by thermal stress or other factors, strengthening the material's cohesion and reducing particle shedding. At the macroscopic level, its excellent adhesion allows it to form a continuous and uniform coating on the graphite surface, hindering oxygen molecule diffusion and molten salt infiltration in a glassy molten state, thus comprehensively improving the graphite anode's oxidation and molten salt corrosion resistance. This enhanced overall performance not only extends the service life of the graphite anode. Attached Figure Description

[0016] Figure 1 The results of rare earth metal content and carbon content detection in various embodiments and comparative examples of the present invention; Figure 2 The graphite anode weight loss rate test results are shown for each embodiment and comparative example of the present invention; Figure 3 The microstructure observation results of graphite after anodizing in various embodiments and comparative examples of the present invention are shown.

[0017] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are all purchased from commercial channels. Example

[0021] A method for preparing rare earth metals by electrolytic oxidation of fluoride systems includes the following steps: S1. Mix 0.1 mol / L potassium ferrocyanide solution and 0.1 mol / L ferric nitrate solution, heat to 60°C, add acrylamide / sodium acrylate copolymer to the mixture and stir until homogeneous. After cooling to room temperature, wash the resulting precipitate with water and ethanol respectively, dry it, and then place it in a high-temperature furnace and introduce argon gas to obtain a three-dimensional network Prussian blue framework material. Then introduce a mixed gas of silicon tetrachloride and hydrogen to deposit SiC on the surface of the Prussian blue framework material to obtain a SiC-Prussian blue composite framework material. S2. Natural flake graphite, artificial graphite, asphalt, and coal char are mixed and then kneaded with SiC-Prussian blue composite skeleton material using a kneader. After pre-calcination, a pre-shaped anode material is obtained. Phosphoric acid, ammonia, ammonium metavanadate, and sodium monofluorophosphate are prepared into an impregnation solution. The pre-shaped anode material is then immersed in the impregnation solution. After impregnation, the pre-shaped anode material is removed from the impregnation solution, excess impregnation solution is wiped off the surface, and the material is dried. It is then placed in a high-temperature sintering furnace for high-temperature sintering. After returning to room temperature, an antioxidant and corrosion-resistant graphite anode is obtained. S3. Using the antioxidant and corrosion-resistant graphite anode prepared in step S2 as the anode electrode, a molybdenum rod as the cathode, and a molybdenum crucible as the receiver, lanthanum oxide is added to the electrolyte system of fluoride molten salt composed of lanthanum fluoride, barium fluoride, and lithium fluoride. Under the action of a DC electric field, liquid lanthanum metal is precipitated on the cathode surface. The produced liquid metal is received by the molybdenum crucible and obtained by casting into an ingot.

[0022] In step S1, the mass ratio of potassium ferrocyanide solution, ferric nitrate solution, and acrylamide / sodium acrylate copolymer is 3:1:0.1.

[0023] In step S1, the temperature of the vacuum furnace is 200℃ and the flow rate of argon gas is 100mL / min.

[0024] In step S1, the mass ratio of silicon tetrachloride to hydrogen is 1:8, and the total flow rate of the mixed gas is 200 mL / min.

[0025] In step S2, the mass ratio of natural flake graphite, artificial graphite, asphalt, coal char, and SiC-Prussian blue composite skeleton material is 5:0.5:1.5:3:0.05.

[0026] The impregnation solution in step S2 comprises the following components by mass percentage: 20% phosphoric acid, 3% ammonia, 2% sodium monofluorophosphate, and the remainder is water.

[0027] In step S2, the immersion temperature is 60°C and the immersion time is 1 hour.

[0028] In step S2, the high-temperature sintering furnace is heated to 600°C at a heating rate of 5°C / min and held at that temperature for 1.5 hours.

[0029] In step S3, the mass ratio of lanthanum fluoride, barium fluoride, lithium fluoride, and lanthanum oxide is 1:3:0.5:50.

[0030] The electrolysis temperature in step S3 is 1000℃, the electrolysis current is 4900A, and the electrolysis voltage is 10V. Example

[0031] A method for preparing rare earth metals by electrolytic oxides in a fluoride system includes the same steps as in Example 1.

[0032] In step S1, the mass ratio of potassium ferrocyanide solution, ferric nitrate solution, and acrylamide / sodium acrylate copolymer is 3:2:0.5.

[0033] In step S1, the temperature of the vacuum furnace is 350℃ and the flow rate of argon gas is 200mL / min.

[0034] In step S1, the mass ratio of silicon tetrachloride to hydrogen is 1:10, and the total flow rate of the mixed gas is 320 mL / min.

[0035] In step S2, the mass ratio of natural flake graphite, artificial graphite, asphalt, coal char, and SiC-Prussian blue composite skeleton material is 8:3:3:5:0.2.

[0036] The impregnation solution in step S2 comprises the following components by mass percentage: 30% phosphoric acid, 5% ammonia, 3% sodium monofluorophosphate, and the remainder is water.

[0037] In step S2, the immersion temperature is 80°C and the immersion time is 2 hours.

[0038] In step S2, the high-temperature sintering furnace is heated to 750°C at a heating rate of 10°C / min and held at that temperature for 3 hours.

[0039] In step S3, the mass ratio of lanthanum fluoride, barium fluoride, lithium fluoride, and lanthanum oxide is 1:5:2:80.

[0040] The electrolysis temperature in step S3 is 1100℃, the electrolysis current is 5030A, and the electrolysis voltage is 10V. Example

[0041] A method for preparing rare earth metals by electrolytic oxides in a fluoride system includes the same steps as in Example 1.

[0042] In step S1, the mass ratio of potassium ferrocyanide solution, ferric nitrate solution, and acrylamide / sodium acrylate copolymer is 3:1.5:0.4.

[0043] In step S1, the temperature of the vacuum furnace is 250℃ and the flow rate of argon gas is 150mL / min.

[0044] In step S1, the mass ratio of silicon tetrachloride to hydrogen is 1:9, and the total flow rate of the mixed gas is 300 mL / min.

[0045] In step S2, the mass ratio of natural flake graphite, artificial graphite, asphalt, coal char, and SiC-Prussian blue composite skeleton material is 6:1.5:2:4:0.1.

[0046] The impregnation solution in step S2 comprises the following components by mass percentage: 25% phosphoric acid, 4% ammonia, 2.5% sodium monofluorophosphate, and the remainder is water.

[0047] In step S2, the immersion temperature is 70°C and the immersion time is 1.5 hours.

[0048] In step S2, the high-temperature sintering furnace is heated to 700°C at a heating rate of 7°C / min and held at that temperature for 2 hours.

[0049] In step S3, the mass ratio of lanthanum fluoride, barium fluoride, lithium fluoride, and lanthanum oxide is 1:4:1:60.

[0050] The electrolysis temperature in step S3 is 1050℃, the electrolysis current is 5000A, and the electrolysis voltage is 10V.

[0051] Comparative Example 1 The anode electrode used in this comparative example is a graphite rod obtained by calcining a mixture of natural flake graphite, artificial graphite, pitch and coal char. Its composition, component content and preparation process are the same as those in Example 3.

[0052] Comparative Example 2 In this comparative example, SiC-Prussian blue composite framework material was not added when preparing the pre-shaped anode material. Instead, natural flake graphite, artificial graphite, pitch and coal char were mixed. The composition, component content and preparation process were the same as in Example 3.

[0053] Results Analysis Experimental Example 1 Rare earth metal content and carbon content detection The rare earth metal content prepared in each example and comparative example was measured using an Agilent 7800 IPC-MS instrument, and the carbon content of the rare earth metals prepared in each example and comparative example was measured using an infrared carbon-sulfur analyzer. The rare earth content bar chart and carbon content line chart are shown below. Figure 1 .

[0054] Depend on Figure 1 It can be seen that the lanthanum content of rare earth metals prepared in Examples 1-3 is significantly higher than that in the comparative example. This is because the present invention optimizes the rare earth molten salt electrolysis process by modifying the graphite anode. The Prussian blue framework material with a three-dimensional network structure and its derived FeC and SiC play a key role at the microstructure level of the material. The spatial topological characteristics of the Prussian blue framework material provide more uniform and stable nucleation sites for the deposition of rare earth metals, enabling the rare earth metals to crystallize and precipitate more efficiently during electrolysis, thereby increasing the yield and content of rare earth metals. At the same time, the carbon content in Examples 1-3 is significantly reduced compared to the comparative example. In the present invention, phosphoric acid, ammonia water and sodium monofluorophosphate are used to prepare the solution. The impregnation solution plays a crucial role. It penetrates the pore channels of the pre-shaped anode material, altering the gas diffusion path and resistance by filling the pores. This reduces the effective collision frequency between oxidizing gases and the active sites inside the graphite electrode, inhibiting graphite oxidation and thus reducing the possibility of carbon contamination into the rare earth metal. Furthermore, the impregnation solution undergoes complex chemical reactions during high-temperature sintering, generating substances such as aluminum orthophosphate. These reaction products further fill the pores of the graphite electrode, promoting the formation of a dense microstructure that prevents the intrusion of external carbon sources and the loss of internal carbon. This effectively reduces the carbon content in the rare earth metal, thereby improving the purity of the rare earth metal lanthanum.

[0055] Experimental Example 2 Graphite anode weight loss rate test The graphite anodes prepared in each embodiment and comparative example were placed in an SR-JX-4-13 muffle furnace and subjected to isothermal oxidation at (1050±10)℃. The oxidation weight loss rate of each embodiment and comparative example at 1050℃ over time was measured, and the results are shown in […]. Figure 2 .

[0056] pass Figure 2It can be seen that under constant temperature oxidation conditions of 1050℃, the oxidation weight loss rate of Examples 1-3 over time is significantly lower than that of the comparative example. This is because the FeC and SiC derived from the Prussian blue framework material prepared in this invention optimize the crystal structure and interfacial bonding force at the microscopic level, and improve the overall strength of the pre-shaped anode material at the macroscopic level, reducing the risk of structural failure caused by insufficient strength. This allows the graphite anode to maintain good structural integrity in the high-temperature oxidation environment, reducing oxidation weight loss caused by structural damage. Furthermore, the use of the impregnation solution changes the gas diffusion path and resistance, reducing the effective collision frequency between oxidizing gas and the active sites inside the graphite electrode, inhibiting the initiation and propagation of the oxidation reaction at the molecular level, thereby significantly delaying the premature oxidation process of the graphite anode. In contrast, the comparative example, lacking these effective protective mechanisms, is more easily oxidized at high temperatures, resulting in a higher weight loss rate.

[0057] Experimental Example 3 Microscopic morphology observation of graphite after anodizing The microstructure of Examples 3 and Comparative Examples 1-2 after oxidation for 1 hour following the weight loss test was observed using a ZEISS G500 scanning electron microscope. The SEM images are shown below. Figure 3 .

[0058] Depend on Figure 3 As can be seen, Example 3 exhibits a relatively dense morphology, with almost no obvious pores and cracks on its surface. The material structure is relatively complete and uniform. This is because the substances generated by the impregnating solution during high-temperature sintering precisely fill the pores of the graphite electrode, promoting the formation of a dense microstructure. This dense structure effectively reduces the intrusion channels of oxidizing gases and molten salts, enhancing the material's resistance to oxidation and molten salt corrosion. Simultaneously, due to the dense structure, the stress distribution within the material is more uniform, reducing structural damage and particle shedding caused by localized stress concentration. In contrast, the microstructure of Comparative Examples 1-2 is relatively loose, with numerous pores and microcracks. This is because the impregnating solution treatment and related synergistic treatment processes of this invention are lacking. During high-temperature oxidation, oxidizing gases and molten salts easily penetrate the material's interior along these pores and cracks, accelerating the oxidation reaction and material loss, leading to gradual structural damage. This makes it impossible to effectively protect the graphite anode and maintain its structural stability as in the Examples.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0060] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing rare earth metals by electrolytic oxide reaction in a fluoride system, characterized in that: Includes the following steps: S1. Mix 0.1 mol / L potassium ferrocyanide solution and 0.1 mol / L ferric nitrate solution, heat to 60°C, add acrylamide / sodium acrylate copolymer to the mixture and stir until homogeneous. After cooling to room temperature, wash the resulting precipitate with water and ethanol respectively, dry it, and then place it in a high-temperature furnace and introduce argon gas to obtain a three-dimensional network Prussian blue framework material. Then introduce a mixed gas of silicon tetrachloride and hydrogen to deposit SiC on the surface of the Prussian blue framework material to obtain a SiC-Prussian blue composite framework material. S2. Natural flake graphite, artificial graphite, asphalt, and coal char are mixed and then kneaded with SiC-Prussian blue composite skeleton material using a kneader. After pre-calcination, a pre-shaped anode material is obtained. Phosphoric acid, ammonia, ammonium metavanadate, and sodium monofluorophosphate are prepared into an impregnation solution. The pre-shaped anode material is then immersed in the impregnation solution. After impregnation, the pre-shaped anode material is removed from the impregnation solution, excess impregnation solution is wiped off the surface, and the material is dried. It is then placed in a high-temperature sintering furnace for high-temperature sintering. After returning to room temperature, an antioxidant and corrosion-resistant graphite anode is obtained. S3. Using the antioxidant and corrosion-resistant graphite anode prepared in step S2 as the anode electrode, a molybdenum rod as the cathode, and a molybdenum crucible as the receiver, lanthanum oxide is added to the electrolyte system of fluoride molten salt composed of lanthanum fluoride, barium fluoride, and lithium fluoride. Under the action of a DC electric field, liquid lanthanum metal is precipitated on the cathode surface. The produced liquid metal is received by the molybdenum crucible and obtained by casting into an ingot.

2. The method for preparing rare earth metals by electrolytic oxide reaction of fluoride system according to claim 1, characterized in that: In step S1, the mass ratio of potassium ferrocyanide solution, ferric nitrate solution, and acrylamide / sodium acrylate copolymer is 3:1-2:0.1-0.

5.

3. The method for preparing rare earth metals by electrolytic oxide reaction of fluoride system according to claim 2, characterized in that: In step S1, the temperature of the vacuum furnace is 200℃-350℃, and the flow rate of argon gas is 100-200mL / min.

4. The method for preparing rare earth metals by electrolytic oxide reaction of fluoride system according to claim 3, characterized in that: In step S1, the mass ratio of silicon tetrachloride to hydrogen is 1:8-10, and the total flow rate of the mixed gas is 200-320 mL / min.

5. The method for preparing rare earth metals by electrolytic oxide reaction of fluoride system according to claim 4, characterized in that: In step S2, the mass ratio of natural flake graphite, artificial graphite, asphalt, coal char, and SiC-Prussian blue composite skeleton material is 5-8:0.5-3:1.5-3:3-5:0.05-0.

2.

6. The method for preparing rare earth metals by electrolytic oxide preparation of fluoride systems according to claim 5, characterized in that: The impregnation solution in step S2 comprises the following components by mass percentage: 20-30% phosphoric acid, 3-5% ammonia, 2-3% sodium monofluorophosphate, and the remainder is water.

7. The method for preparing rare earth metals by electrolytic oxide reaction of fluoride system according to claim 6, characterized in that: In step S2, the immersion temperature is 60-80℃ and the immersion time is 1-2 hours.

8. The method for preparing rare earth metals by electrolytic oxide reaction of fluoride system according to claim 7, characterized in that: In step S2, the high-temperature sintering furnace is heated to 600-750℃ at a heating rate of 5-10℃ / min and held at that temperature for 1.5-3 hours.

9. The method for preparing rare earth metals by electrolytic oxide reaction of fluoride system according to claim 8, characterized in that: In step S3, the mass ratio of lanthanum fluoride, barium fluoride, lithium fluoride, and lanthanum oxide is 1:3-5:0.5-2:50-80.

10. The method for preparing rare earth metals by electrolytic oxide preparation of fluoride systems according to claim 9, characterized in that: The electrolysis temperature in step S3 is 1000-1100℃, the electrolysis current is 4900-5030A, and the electrolysis voltage is 10V.

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