Preparation method of electrolyte for preparing refined aluminum through three-layer liquid electrolysis method

Abstract

The invention belongs to the technical field of refined aluminum preparation, and particularly relates to a preparation method of an electrolyte for preparing refined aluminum through a three-layer liquid electrolysis method. The method comprises the following steps: mixing electrolyte raw materials, and sequentially carrying out melting-pre-purification treatment and electrolytic purification treatment to obtain a purified electrolyte; and carrying out vacuum extraction on the purified electrolyte to obtain the electrolyte for preparing the refined aluminum by the three-layer liquid electrolysis method, the electrolyte is prepared from the following raw materials in percentage by mass: 60 to 61 percent of barium chloride, 23 to 24 percent of cryolite, 12 to 13 percent of aluminum fluoride and 3 to 4 percent of sodium chloride. Impurities are removed through electrolytic purification, the prepared electrolyte has reasonable primary crystal temperature, molecular ratio and electric conductivity, the phenomena of upturning, firing and more precipitates generated in the refined aluminum production process of the electrolyte can be greatly reduced, the quality grade of refined aluminum is improved, and the electricity unit consumption of refined aluminum liquid is reduced.

Description

Technical Field

[0001] This invention belongs to the field of refined aluminum preparation technology, specifically relating to a method for preparing an electrolyte for producing refined aluminum using a three-layer liquid electrolysis method. Background Technology

[0002] In the three-layer electrolysis process for producing refined aluminum, the three layers in the aluminum refining tank, from bottom to top, consist of alloy, electrolyte, and refined aluminum. The three-layer electrolysis process for producing refined aluminum typically uses a relatively mature fluorine-chlorine system electrolyte. Chinese patent CN1487121A discloses a fluorine-chlorine system electrolyte for refined aluminum, which includes barium chloride, cryolite, aluminum fluoride, and sodium fluoride. The main advantages of this electrolyte system are its low melting point, high density, and good conductivity, effectively preventing phenomena such as sparking and boiling over. However, the disadvantages of this electrolyte system are severe hydrolysis problems, leading to increased consumption of each electrolyte component and significant electrolyte precipitation. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for preparing electrolyte for producing refined aluminum by three-layer liquid electrolysis. The electrolyte prepared by this method produces less precipitation, which enables the three-layer liquid electrolysis process for refining refined aluminum to remain stable, improves the quality grade of refined aluminum, and reduces the unit consumption of refined aluminum liquid electrolyte.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing an electrolyte for producing refined aluminum using a three-layer liquid electrolysis method, comprising the following steps:

[0006] The electrolyte raw materials are mixed and subjected to melt-pre-purification treatment and electrolytic purification treatment in sequence to obtain purified electrolyte;

[0007] The purified electrolyte was vacuum extracted to obtain an electrolyte for producing refined aluminum by a three-layer electrolyte electrolysis method.

[0008] The electrolyte raw material comprises the following components in weight percentage:

[0009] Barium chloride: 60-61%, cryolite: 23-24%, aluminum fluoride: 12-13%, sodium chloride: 3-4%.

[0010] Preferably, the barium chloride has a moisture content of ≤0.1%.

[0011] Preferably, the pre-purification process of the molten material is as follows: the temperature is increased from 750°C to 820°C.

[0012] Preferably, the temperature of the electrolytic purification treatment is 820–850°C.

[0013] Preferably, the voltage of the electrolytic purification treatment is 8.0 to 8.5V.

[0014] Preferably, the electrolytic purification process takes 4 to 5 hours.

[0015] Preferably, the heating rate during the melt-pre-purification process is 15-20℃ / h.

[0016] Preferably, during the vacuum extraction process, the pressure difference between the purified electrolyte and the negative pressure environment is -0.06 to -0.08 MPa.

[0017] Preferably, during the vacuum extraction process, the temperature of the purified electrolyte is 800–820°C.

[0018] Preferably, the vacuum extraction device is a vacuum lifter; the suction nozzle of the vacuum lifter penetrates to a depth of 10-15 cm into the purified electrolyte.

[0019] This invention provides a method for preparing an electrolyte for producing refined aluminum using a three-layer electrolyte electrolysis method, comprising the following steps: mixing electrolyte raw materials and sequentially subjecting them to a melt-pre-purification treatment and an electrolytic purification treatment to obtain a purified electrolyte; vacuum-extracting the purified electrolyte to obtain the electrolyte for producing refined aluminum using a three-layer electrolyte electrolysis method; the electrolyte raw materials comprise the following components in mass percentage: barium chloride: 60-61%, cryolite: 23-24%, aluminum fluoride: 12-13%, sodium chloride: 3-4%.

[0020] This invention, through electrolytic purification, involves the precipitation of positively charged ions such as iron, silicon, and copper in the electrolyte formed after the electrolyte raw materials are melted, under the action of direct current, forming slag. This slag is then removed by skimming. The resulting electrolyte possesses a suitable initial crystallization temperature (651–662℃), molecular ratio (1.41–1.45), and conductivity (1.29–1.33 A / Ω·cm). This significantly reduces the phenomena of electrolyte overflow, sparking, and excessive precipitation during refined aluminum production, ensuring the continuous stability of the three-layer electrolytic refining process for refined aluminum, improving the quality grade of refined aluminum, and reducing the unit electricity consumption of refined aluminum liquid. Furthermore, this invention removes the higher Al content from the electrolyte through electrolyte purification. 3+ Electronically corrected impurity ions, compared to Al during this purification process. 3+ Highly ionizable impurity ions Fe 3 + Si 2+ Cu 2+ Mn 2+ Zn 2+Electrolytes preferentially gain electrons and are deposited, then removed by slag removal, thereby improving electrolyte purity. The preparation method of this invention is simple, safer, and more reliable. The refined aluminum production process is easier to manage, effectively avoiding electrolyte ignition and overflow, significantly reducing electrolyte and power consumption, improving refined aluminum quality, and reducing worker workload. Furthermore, because the electrolyte formula of this invention prevents electrolyte overflow, it greatly improves the working environment. Detailed Implementation

[0021] This invention provides a method for preparing an electrolyte for producing refined aluminum using a three-layer liquid electrolysis process, comprising the following steps:

[0022] The electrolyte raw materials are mixed and subjected to melt-pre-purification treatment and electrolytic purification treatment in sequence to obtain purified electrolyte;

[0023] The purified electrolyte was vacuum extracted to obtain an electrolyte for producing refined aluminum by a three-layer electrolyte electrolysis method.

[0024] The electrolyte raw material comprises the following components in weight percentage:

[0025] Barium chloride: 60-61%, cryolite: 23-24%, aluminum fluoride: 12-13%, sodium chloride: 3-4%.

[0026] Unless otherwise specified, the present invention does not have special requirements on the source of the raw materials used in the preparation, and commercially available products well known to those skilled in the art can be used.

[0027] This invention involves mixing electrolyte raw materials and sequentially subjecting them to melting-pre-purification treatment and electrolytic purification treatment to obtain a purified electrolyte.

[0028] In this invention, the electrolyte raw material comprises the following components in weight percentage:

[0029] Barium chloride: 60-61%, cryolite: 23-24%, aluminum fluoride: 12-13%, sodium chloride: 3-4%, preferably barium chloride: 60-60.5%, cryolite: 23-23.5%, aluminum fluoride: 12.5-13%, sodium chloride: 3.5-4%.

[0030] In this invention, the moisture content of the barium chloride is preferably ≤1%.

[0031] Before mixing the electrolyte raw materials, the present invention preferably further includes: drying the barium chloride to a moisture content of ≤0.1%; the drying temperature is preferably 175-180°C, more preferably 180°C.

[0032] The cryolite used in this invention meets the requirements of ordinary cryolite CM-0 in GB / T4291-2017 standard, the sodium chloride meets the requirements of first-grade or above industrial dry salt in refined industrial salt in GB / T5462-2015 standard, and the aluminum fluoride meets the requirements of AF-1 grade products in GB / T4292-2017 standard.

[0033] In this invention, barium chloride is used to adjust the electrolyte density and lower the initial crystallization temperature, but this also reduces the electrolyte conductivity. Cryolite is used to determine the molecular ratio of the electrolyte, thus affecting its conductivity. Aluminum fluoride is used to reduce the molecular ratio of the electrolyte, thereby reducing conductivity, decreasing molten salt density, and reducing the amount of Na+ in the cathode. + The discharge deposition occurs. Sodium chloride's role is to increase the electrolyte's conductivity, lower the primary crystallization temperature, reduce the molten salt density, and prevent the formation of BaF2 (1280℃) on the cathode. In this invention, the barium chloride content is adjusted to 60-61%, ensuring an electrolyte density of 2.68-2.72 g / cm³. 3 This ensures that the initial crystallization temperature is below 670℃; adjusting the cryolite content to 23-24% allows for a molecular ratio range of 1.41-1.45, resulting in a conductivity of 1.29-1.33 A / Ω·cm; and maintaining an aluminum fluoride content of 12-13% ensures an electrolyte density of 2.68-2.72 g / cm³. 3 With a sodium chloride content of 3-4%, it can avoid consuming a large amount of electricity, reduce power consumption, and improve the quality of refined aluminum. This formula is optimal in the production process of three-layer liquid refined aluminum, and the process is easy to control and continuously stable.

[0034] In the three-layer electrolyte method for producing refined aluminum, the products generated by the chemical reaction of four raw materials in the electrolyte are: BaClF, BaAlF3, BaAlF, Al2O3, BaClF5, and Ba3AlO. 11 Substances like these, with high melting points and difficult to melt, deposit as slag on the surface of the anode alloy, commonly known as anode mud. This directly shields the anode current, increases the anode current density, and alters the electrolytic composition, raising the primary crystallization temperature of the electrolyte and reducing conductivity, thus affecting refined aluminum production. This invention addresses this by optimizing the electrolyte formulation and preparation process of the three-layer electrolyte method for producing refined aluminum, thereby reducing the generation of anode mud and avoiding the aforementioned problems caused by it.

[0035] In this invention, the mixing of the electrolyte raw materials is preferably carried out under stirring conditions; the stirring process is not particularly limited in this invention, as long as the electrolyte raw materials are mixed evenly.

[0036] In this invention, both the pre-purification treatment and the electrolytic purification treatment are preferably carried out in a refined aluminum molten material tank; the refined aluminum molten material tank is preferably filled with an anode, a copper-aluminum alloy and molten aluminum in sequence from bottom to top, and a cathode is inserted; the anode is preferably graphite carbon; the cathode is preferably an aluminum rod; after the electrolyte raw materials are mixed, the present invention preferably uses a molten material cart to evenly spread the mixed electrolyte raw materials onto the surface of the molten aluminum, and seals the tank cover plate of the refined aluminum molten material tank.

[0037] In this invention, the preferred process of melting and pre-purification is to raise the temperature from 750°C to 820°C; the preferred heating rate during the melting and pre-purification process is 15–20°C / h, more preferably 20°C / h; and the preferred voltage for the melting and pre-purification process is 8.5–9.5V, more preferably 9–9.5V. This invention does not impose a specific time limit on the melting process, as long as the electrolyte raw material is completely melted.

[0038] In this invention, the preferred temperature for the electrolytic purification treatment is 820–850°C, more preferably 820–830°C; the preferred voltage for the electrolytic purification treatment is 8.0–8.5V, more preferably 8.1–8.4V; and the preferred time for the electrolytic purification treatment is 4–5 hours, more preferably 4–4.5 hours.

[0039] After the electrolytic purification treatment is completed, the present invention preferably performs a slag removal treatment on the electrolyte after the electrolytic purification treatment to obtain a purified electrolyte.

[0040] During the electrolytic purification process, positively charged ions such as iron, silicon, and copper are released from the electrolyte formed after the electrolyte raw materials are melted under the action of direct current, forming slag. The slag is then removed by skimming to obtain a high-quality electrolyte that meets the requirements for producing refined aluminum using the three-layer electrolyte electrolysis method.

[0041] After obtaining the purified electrolyte, the present invention performs vacuum extraction on the purified electrolyte to obtain an electrolyte for producing refined aluminum by three-layer electrolyte electrolysis.

[0042] In this invention, during the vacuum extraction process, the pressure difference between the purified electrolyte and the negative pressure environment is -0.06 to -0.08 MPa, preferably -0.07 MPa; during the vacuum extraction process, the temperature of the purified electrolyte is preferably 800 to 820°C, more preferably 810 to 820°C; the vacuum extraction voltage is preferably 8 to 8.5V, more preferably 8.1 to 8.4V; the vacuum extraction is preferably carried out in a refined aluminum melting tank; the height of the purified electrolyte in the refined aluminum melting tank is preferably ≥15cm, more preferably ≥15.5cm; the suction nozzle of the vacuum lifting bag preferably extends 10 to 15cm below the purified electrolyte, more preferably 12 to 15cm; the suction nozzle of the vacuum lifting bag is preferably above the lower surface of the purified electrolyte, and it is strictly forbidden for the vacuum lifting bag to suck in copper-aluminum alloy liquid; this invention preferably keeps the cathode in the purified electrolyte throughout the extraction process.

[0043] This invention removes substances with a higher concentration of Al from the electrolyte through electrolyte purification. 3+ Electronically corrected impurity ions, compared to Al during this purification process. 3+ Fe, a highly ionizable ion 3+ Si 2+ Cu 2+ Mn 2+ Zn 2+ Electrolytes preferentially gain electrons and are deposited, thereby improving the quality of the electrolyte.

[0044] After the extraction is completed, the present invention preferably further includes: sampling and analyzing the extracted electrolyte. Specifically, the sampling and analysis process involves: according to the technical requirements of the aluminum refinement tank process, slowly adding the extracted electrolyte into the aluminum refinement tank at a rate of 200 kg / h, while simultaneously adjusting the cathode within the aluminum refinement tank, and monitoring the production status of the electrolyte within the tank.

[0045] In this invention, the preferred primary crystallization temperature of the electrolyte used in the three-layer liquid electrolysis method for producing refined aluminum is 651–662°C, and the preferred density is 2.68–2.72 g / cm³. 3 The conductivity is preferably 1.29 to 1.33 A / Ω·cm, and the molecular ratio is preferably 1.41 to 1.45.

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof, but they should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] Barium chloride was dried at 180℃ to a moisture content of ≤0.1%, and then added to a material mixer in a mass percentage ratio of 60%, 23%, 13%, and 4% respectively. After uniform mixing, the mixture was added to the No. 1 aluminum refining tank. The aluminum refining tank was filled from bottom to top with anodes (graphite carbon), copper-aluminum alloy, and molten aluminum, with cathodes (aluminum rods) inserted. When the temperature in the aluminum refining tank reached 750℃, the uniformly mixed material was evenly spread onto the surface using a melting cart at a rate of 500 kg / h. The surface of the molten aluminum is sealed with a cover plate, and the voltage is adjusted to 9V. The pre-purification treatment of the molten material is started. The temperature is increased from 750℃ to 820℃ at a rate of 20℃ / h. During this process, the powder on the surface of the molten aluminum is completely melted and dissolved into the lower layer of the molten aluminum to form an intermediate layer - electrolyte layer. Then the voltage is adjusted to maintain 8.5V and the temperature at 820℃. The voltage and temperature are kept constant and purified for 4 hours. During the purification process, positively charged ions in the electrolyte are precipitated under the action of direct current to form slag. The slag is then removed by slag removal to obtain purified electrolyte.

[0049] The purified electrolyte is extracted using a vacuum pump. During the vacuum extraction process, the pressure difference between the purified electrolyte and the negative pressure environment is -0.07 MPa. The cathode is kept in the purified electrolyte throughout the extraction process. The voltage in the aluminum refinement tank is 8.5V, the temperature of the purified electrolyte is 820℃, and the height of the purified electrolyte in the tank is not less than 15cm. The suction nozzle of the vacuum pump is inserted 15cm below the purified electrolyte and kept above the lower surface of the purified electrolyte. It is strictly forbidden for the vacuum pump to suck in copper-aluminum alloy liquid. The extracted electrolyte is sampled and analyzed. After passing the analysis, the electrolyte for producing refined aluminum by the three-layer electrolyte electrolysis method is obtained.

[0050] The electrolyte for producing refined aluminum using the three-layer liquid electrolysis method was slowly added to the refined aluminum tank No. 6 at a rate of 200 kg / h. The production status of the refined aluminum tank No. 6 was monitored and recorded, as shown in Table 1.

[0051] Table 1. Experimental production status of tank #6

[0052]

[0053] Table 1 shows that, based on the analysis of the electrolyte's conductivity according to the production status tracking results of tank #6, the electrolyte conductivity is 1.31–1.32 A / Ω·cm, and the density is 2.69–2.71 g / cm³. 3 The initial crystallization temperature is between 651 and 657℃. The electrolyte, alloy liquid, and refined aluminum liquid are clearly separated, and electrolyte agglomeration is significantly reduced. A small amount of electrolyte floats to the surface in the initial stage after the electrolyte is added. Through observation over a certain period of time, the electrolyte of this formula significantly improves the process technology conditions in the production of refined aluminum using the three-layer electrolyte electrolysis method. The production process is easy to control and remains stable, and the quality of refined aluminum is consistently improved to above 99.996Al.

[0054] Example 2

[0055] The difference from Example 1 is that the dried barium chloride, which is free of moisture, is mixed with cryolite, aluminum fluoride and sodium chloride in a mass percentage ratio of 60.5%, 23.5%, 12.5% ​​and 3.5%, respectively. The rest of the contents are the same as in Example 1.

[0056] The electrolyte for producing refined aluminum using the three-layer liquid electrolysis method obtained in Example 2 was slowly added to the refined aluminum tank #7 at a rate of 200 kg / h. The production status of the refined aluminum tank #7 was monitored and recorded, as shown in Table 2.

[0057] Table 2. Experimental production status of tank #7

[0058]

[0059] Table 2 shows that, based on the production status tracking results of tank #7, the electrolyte has a molecular weight ratio of 1.41–1.45 and a density of 2.7–2.72 g / cm³. 3 The initial crystallization temperature is between 651 and 660℃. The electrolyte, alloy liquid, and refined aluminum liquid are clearly separated, with no sparking. Electrolyte agglomeration is significantly reduced. A small amount of electrolyte floats to the surface initially after addition, as observed over a certain period. This electrolyte formulation exhibits minimal process fluctuations during the three-layer electrolysis method for refining refined aluminum, resulting in a stable product quality exceeding 99.996Al.

[0060] Example 3

[0061] The difference from Example 1 is that the dried barium chloride, which is free of moisture, is mixed with cryolite, aluminum fluoride and sodium chloride in a mass percentage ratio of 61%, 24%, 12% and 3%, respectively. The rest of the contents are the same as in Example 1.

[0062] The electrolyte for producing refined aluminum using the three-layer liquid electrolysis method obtained in Example 3 was slowly added to the refined aluminum tank #8 at a rate of 200 kg / h. The production status of the refined aluminum tank #8 was monitored and recorded, as shown in Table 3.

[0063] Table 3. Experimental production status of tank #8

[0064]

[0065]

[0066] Table 3 shows that, based on the results of the production tracking experiment in tank #8, the electrolyte conductivity was 1.29–1.33 A / Ω·cm, the molecular ratio was 1.41–1.44, the initial crystallization temperature was between 654 and 662℃, and the electrolyte, alloy liquid, and refined aluminum liquid showed clear stratification. Slight sparking occurred initially after the electrolyte was added. Observations over a certain period showed that the electrolyte formulation produced stable product quality during the three-layer electrolysis method for refining refined aluminum, with a high rate of grades above 99.996 Al.

[0067] Comparative Example 1

[0068] The difference from Example 1 is that the dried barium chloride, which is free of moisture, is mixed with cryolite, aluminum fluoride and sodium chloride in a mass percentage ratio of 58%, 21%, 15% and 6%, respectively. The rest of the contents are the same as in Example 1.

[0069] The electrolyte obtained from Comparative Example 1 for producing refined aluminum by the three-layer liquid electrolysis method was slowly added to the refined aluminum tank #9 at a rate of 200 kg / h. The production status of the refined aluminum tank #9 was statistically monitored, as shown in Table 4.

[0070] Table 4. Experimental production status of tank #9

[0071]

[0072] Table 4 shows that, based on the analysis of the electrolyte according to the production status tracking results of cell #9, the conductivity was 1.15–1.21 A / Ω·cm, the molecular ratio was 1.28–1.32, the initial crystallization temperature was 658–670℃, there were sparking incidents for 5 consecutive days, and there was a lot of agglomeration. The electrolyte floated up more in the early stage after addition, but the floatation was weak in the later stage. This caused instability in the three-layer electrolyte electrolysis refining process of aluminum, increased the difficulty of process control, and led to increased power consumption and production costs. The yield of 99.996AL premium grade was also low.

[0073] Comparative Example 2

[0074] The difference from Example 1 is that the dried barium chloride, which is free of moisture, is mixed with cryolite, aluminum fluoride and sodium chloride in a mass percentage ratio of 63%, 25%, 10% and 2%, respectively. The rest of the contents are the same as in Example 1.

[0075] The electrolyte obtained from the three-layer liquid electrolysis method for producing refined aluminum obtained in Comparative Example 2 was slowly added to the refined aluminum tank No. 10 at a rate of 200 kg / h. The production status of the refined aluminum tank No. 10 was statistically monitored, as shown in Table 5.

[0076] Table 5. Production status of tank #10 during the experiment

[0077]

[0078] Table 5 shows that, based on the results of the production monitoring in tank #10, the electrolyte conductivity was 1.18–1.24 A / Ω·cm, and the electrolyte density was 2.7–2.74 g / cm³. 3 The initial crystallization temperature is between 659 and 669℃. The layers of the alloy and refined aluminum are disordered. There is a continuous sparking when the electrolyte is added, and there are many lumps. The lumps float to the surface for five consecutive days, which increases the difficulty of controlling the three-layer liquid process. In addition, the power consumption increases due to the decrease in electrical conductivity, which increases the production cost. The quality of the refined aluminum produced is low, and the yield of 99.996AL premium grade is low.

[0079] The electrolyte was analyzed by comprehensively comparing the experimental production status tracking results in tanks #6 to #10. The results are shown in Table 6.

[0080] Table 6. Experimental production status of tanks #6 to #10

[0081]

[0082] Table 6 shows that the experiments were conducted in tanks #6, #7, and #8. The experimental analysis is as follows: the electrolyte conductivity was 1.29–1.33 A / Ω·cm, and the density was 2.68–2.72 g / cm³. 3 The initial crystallization temperature is between 651 and 662℃, and the molecular ratio is between 1.41 and 1.45. The electrolyte, alloy solution, and refined aluminum solution in the three electrolytic cells exhibit clear stratification, with significantly reduced electrolyte agglomeration and virtually no sparking or clumping. In the production of refined aluminum using this electrolyte formula, the production process is easy to control and consistently stable, resulting in lower electricity consumption and a stable improvement in refined aluminum quality to above 99.996Al.

[0083] The operating status of #9 and #10 was monitored, with conductivity ranging from 1.15 to 1.24 A / Ω·cm, molecular weight ratio from 1.28 to 1.35, and electrolyte density from 2.7 to 2.77 g / cm³. 3 The initial crystallization temperature is between 658 and 670°C. The electrolyte, alloy liquid, and refined aluminum liquid in the two electrolytic cells are in a disorderly layered state, with continuous sparking, clumping, and floating. This increases the difficulty of controlling the three-layer refined aluminum process. In addition, the increased conductivity leads to an increase in production voltage and production costs, resulting in a low yield of 99.996AL premium grade products.

[0084] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing an electrolyte for producing refined aluminum using a three-layer liquid electrolysis method, characterized in that, Includes the following steps: The electrolyte raw materials are mixed and subjected to melt-pre-purification treatment and electrolytic purification treatment in sequence to obtain purified electrolyte; The purified electrolyte was vacuum extracted to obtain an electrolyte for producing refined aluminum by a three-layer electrolyte electrolysis method. The electrolyte raw material comprises the following components in weight percentage: Barium chloride: 60-61%, cryolite: 23-24%, aluminum fluoride: 12-13%, sodium chloride: 3-4%.

2. The preparation method according to claim 1, characterized in that, The barium chloride has a moisture content of ≤0.1%.

3. The preparation method according to claim 1, characterized in that, The process of melting material pre-purification treatment is as follows: the temperature is raised from 750℃ to 820℃.

4. The preparation method according to claim 1, characterized in that, The temperature for the electrolytic purification process is 820–850°C.

5. The preparation method according to claim 1 or 4, characterized in that, The voltage for the electrolytic purification process is 8.0–8.5V.

6. The preparation method according to claim 1 or 4, characterized in that, The electrolytic purification process takes 4 to 5 hours.

7. The preparation method according to claim 3, characterized in that, The heating rate during the melt-pre-purification process is 15-20℃ / h.

8. The preparation method according to claim 1, characterized in that, During the vacuum extraction process, the pressure difference between the purified electrolyte and the negative pressure environment is -0.06 to -0.08 MPa.

9. The preparation method according to claim 1, characterized in that, During the vacuum extraction process, the temperature of the purified electrolyte is 800–820°C.

10. The preparation method according to claim 1, characterized in that, The vacuum extraction device is a vacuum lifting bag; the suction nozzle of the vacuum lifting bag penetrates to a depth of 10-15 cm into the purified electrolyte.

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