Method for preparing polyaluminum chloride by using lithium hexafluorophosphate byproduct fluorine-containing hydrochloric acid as raw material

Abstract

The invention relates to the technical field of preparation of polyaluminum chloride, and particularly discloses a method for preparing polyaluminum chloride by using lithium hexafluorophosphate byproduct fluorine-containing hydrochloric acid as a raw material, the method comprises the following steps: S1, calcining: calcining kaolinite pyrite tailings to obtain calcined kaolin; s2, leaching reaction: mixing the calcined kaolin with fluorine-containing hydrochloric acid for reaction to obtain an aluminum chloride oligomer mixed solution; s3, polymerization reaction: adding calcium aluminate into the aluminum chloride oligomer mixed solution for polymerization reaction to obtain a polyaluminum chloride mixed solution; s4, filtering: filtering the polyaluminum chloride mixed solution to obtain a polyaluminum chloride solution; and S5, drying: drying the polyaluminum chloride solution to obtain solid polyaluminum chloride. The technical problem that in the prior art, in a technological method for resource utilization of fluorine-containing hydrochloric acid waste water generated in lithium hexafluorophosphate production, calcium salt needs to be added in a pre-sequence or post-sequence process to remove fluorine elements, and consequently the cost is high is solved.

Description

Technical Field

[0001] The invention relates to the technical field of polyaluminium chloride preparation, in particular to a method for preparing polyaluminium chloride by using fluorine-containing hydrochloric acid produced as a by-product of lithium hexafluorophosphate as a raw material. Background Art

[0002] Lithium-ion batteries are widely used in energy storage applications, including new energy vehicle batteries. Lithium-ion battery electrolytes are typically prepared from a combination of lithium salt electrolytes, organic solvents, and additives, all mixed in specific proportions under specific conditions. Currently, lithium hexafluorophosphate (LiPF6) is the most widely used lithium-ion battery electrolyte.

[0003] The mainstream preparation process for lithium hexafluorophosphate is the hydrogen fluoride solvent method, which involves dissolving lithium fluoride (LiF) in anhydrous hydrogen fluoride (HF) liquid, then introducing phosphorus pentafluoride (PF5) gas. The phosphorus pentafluoride reacts with the lithium fluoride to form lithium hexafluorophosphate. The synthesis reaction in this process takes place in the liquid phase, which has the advantages of easy control and fast reaction rate. However, the phosphorus pentafluoride required by this method is in gaseous form, which is inconvenient to store and transport, and the direct purchase cost is high. Therefore, in industrial production, solid phosphorus pentachloride (PCl5) is usually reacted with hydrogen fluoride to directly generate phosphorus pentafluoride on-site for use. This method effectively avoids the series of problems caused by the gaseous state of phosphorus pentafluoride. However, when the reaction produces phosphorus pentafluoride, gaseous byproducts such as hydrogen chloride and hydrogen fluoride are also produced. These gases will follow the phosphorus pentafluoride into the reactor in the system, but do not participate in the reaction and are eventually discharged in the tail gas. Direct discharge of tail gas (containing hydrogen chloride and hydrogen fluoride) can cause environmental pollution. To meet environmental protection requirements, companies pipe the tail gas into a water absorption tower, where the water absorbs the hydrogen chloride and hydrogen fluoride in the tail gas, ensuring that the tail gas meets emission standards. This results in the continuous generation of large amounts of fluorinated hydrochloric acid wastewater during the lithium hexafluorophosphate production process. In addition to fluorine and phosphorus, this fluorinated hydrochloric acid wastewater also contains sodium, potassium, calcium, magnesium, iron, aluminum, sulfur, and arsenic, making it difficult to purify. Therefore, it is difficult to use as a reaction raw material or industrial pickling raw material. As the scale of lithium hexafluorophosphate production continues to expand, the large amount of fluorinated hydrochloric acid wastewater has become a burden for companies, requiring additional disposal costs.

[0004] In the prior art, the treatment of fluorine-containing hydrochloric acid wastewater is mostly carried out by chemical precipitation of calcium salts. The technical solution is to add calcium hydroxide to lithium hexafluorophosphate wastewater, and use a chemical precipitation method to react the fluorine element in the waste acid with calcium to form a calcium fluoride precipitate to achieve the purpose of removing the fluorine element. The calcium chloride generated by the reaction is subsequently concentrated and precipitated as a deicing agent or desiccant. For example, patent document CN220413119U discloses a lithium hexafluorophosphate production wastewater treatment device, which discloses this treatment method. For example, patent documents CN113716731A discloses a lithium hexafluorophosphate industrial wastewater calcium treatment process, and CN110921899A discloses a lithium hexafluorophosphate and low-fluorine lithium phosphate compound wastewater treatment process and device, which also draw on the idea of ​​adding calcium salts.

[0005] In the above-mentioned scheme, only chemical precipitation is used to harmlessly treat the wastewater. Its core idea is to treat the wastewater to the discharge standard without recycling its products. There are still problems such as the need for additional disposal costs and the inability to recycle. Therefore, some process methods that want to recycle fluorine-containing hydrochloric acid wastewater have emerged in the industry, such as a method in patent document CN106865573A that uses lithium salt by-product mixed acid to prepare industrial sodium fluoride and industrial ammonium chloride. It uses fluorine-containing hydrochloric acid as a raw material, and after dephosphorization and sedimentation, it reacts with ammonia water to obtain ammonium fluoride and ammonium chloride; then sodium chloride is added to react to obtain sodium fluoride. After the reaction is completed, calcium chloride is added to deeply defluorinate to produce ammonium chloride and calcium chloride, and then sodium sulfate solution is added to remove calcium to obtain industrial ammonium chloride products. Another example is a method for preparing polyaluminum using fluorine-containing waste acid in patent document CN104649391A. It adds calcium chloride and calcium aluminate powder to the fluorine-containing waste acid, stirs the reaction, and then matures, and filters to remove the fluorine-containing solid waste residue to obtain a polyaluminum solution.

[0006] Although the above technical solutions can recycle the fluorine-containing hydrochloric acid wastewater generated in the production process of lithium hexafluorophosphate to a certain extent, the fluorine element in the fluorine-containing hydrochloric acid wastewater will affect the quality of the final product. Therefore, the above process methods all include a process step of adding calcium chloride to remove fluorine, which makes the recycling process complicated and costly. If a defluorination process is not provided, it is impossible to achieve the goal of not interfering with the final product while also achieving the purpose of defluorination. In particular, in the process of producing polyaluminum chloride using fluorine-containing hydrochloric acid wastewater, while adding calcium chloride to remove fluorine element, the method of directly using calcium aluminate to produce polyaluminum chloride is not only costly, but also leads to insufficient aluminum ions in the solution, making it difficult for collision to occur in the solution, and thus difficult for polymerization to occur. In addition, the excess calcium ions make the produced polyaluminum chloride easily contain impurities such as calcium chloride. Summary of the Invention

[0007] The object of the present invention is to provide a method for preparing polyaluminium chloride using fluorine-containing hydrochloric acid, a by-product of lithium hexafluorophosphate, as a raw material, so as to solve the technical problem mentioned above that in the prior art process for resource utilization of fluorine-containing hydrochloric acid wastewater generated by the production of lithium hexafluorophosphate, calcium salt needs to be added in the preceding or subsequent process to remove the fluorine element, resulting in high cost.

[0008] In order to solve the above problems, the technical solution adopted by the present invention is as follows: a method for preparing polyaluminium chloride using fluorine-containing hydrochloric acid produced as a by-product of lithium hexafluorophosphate as a raw material, comprising the following steps: S1: calcining the kaolinite-type pyrite tailings to obtain amorphous metakaolinite, which is then ground into particles to obtain calcined kaolin; S2: mixing the calcined kaolin obtained in S1 with fluorine-containing hydrochloric acid, heating and reacting under stirring, and obtaining an oligomeric aluminum chloride mixed solution after sufficient reaction; S3: slowly adding calcium aluminate to the oligoaluminum chloride mixed solution obtained in S2 to carry out polymerization reaction, and obtaining a liquid polyaluminum chloride mixed solution after sufficient reaction; S4: filtering the polyaluminium chloride mixed solution obtained in S3 to obtain a pure polyaluminium chloride solution; S5: The liquid polyaluminium solution obtained in S4 is passed into a spray dryer for spray drying to obtain solid polyaluminium chloride.

[0009] The beneficial effects of this embodiment are: Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. In the prior art, the wastewater generated by the production of lithium hexafluorophosphate is mostly defluorinated by calcium salt precipitation. The core idea is to treat it as an impurity and treat it harmlessly without resource utilization. Even if some technologies use it as a reaction raw material to prepare other chemical products, it is necessary to set up a calcium salt defluorination process in the process. The ideas of these schemes are to treat the fluorine element in the fluorine-containing hydrochloric acid as an impurity that needs to be removed, and the only reaction raw material is the hydrogen chloride component in the fluorine-containing hydrochloric acid wastewater. Therefore, it does not maximize the utilization of the effective components in the fluorine-containing hydrochloric acid wastewater. However, when using fluorine-containing hydrochloric acid wastewater, the present application overcomes the technical prejudice of treating hydrogen fluoride in fluorine-containing hydrochloric acid wastewater as an impurity. When the fluorine-containing hydrochloric acid wastewater is reacted with calcined kaolin, hydrogen fluoride will react with the silicon dioxide in the calcined kaolin. The reaction will expose the aluminum element in the kaolin, increasing the Al content in the calcined kaolin. 3+The probability of contact with hydrochloric acid is increased, and the Al2O3 leaching rate is improved. Therefore, the present application not only does not remove hydrogen fluoride as an impurity in fluorine-containing hydrochloric acid, but also utilizes its characteristics to enhance the leaching reaction between hydrochloric acid and kaolin. Compared with the existing technology, the present application does not require an additional calcium salt removal process. The process is simpler and the cost is lower. At the same time, it corrects the prejudice of treating hydrogen fluoride in fluorine-containing hydrochloric acid wastewater as an impurity and fully utilizes the two main components of hydrogen chloride and hydrogen fluoride in fluorine-containing hydrochloric acid.

[0010] 2. In the prior art process of preparing polyaluminium chloride using calcined kaolin as raw material and leaching the aluminium component therein with hydrochloric acid, the process of hydrochloric acid leaching Al2O3 from the calcined kaolin during the leaching reaction is a liquid-solid two-phase leaching reaction process. This type of leaching process is generally composed of three stages: 1. The liquid phase reactant diffuses from the main solution to the solid surface and chemically reacts with the solid reactant on the solid surface; 2. After the solid reactant on the solid surface is consumed by the reaction, the liquid phase reactant diffuses inward through the inert solid layer remaining on the solid and continues to react with the solid reactant inside the solid; 3. The reaction product diffuses outward from the interior of the solid through the inert solid layer and into the main solution. In this process, the liquid phase reactant needs to diffuse into the interior of the solid, but the reaction product needs to diffuse outward from the interior of the solid. The only channel for mutual diffusion is the channel corroded by the leaching reaction on the solid. This means that in one channel, the reaction product needs to exit and the reactant needs to enter, causing the two to collide, which not only leads to a relatively slow leaching reaction. The leaching rate of Al2O3 in kaolin is low because the Al2O3 completely encapsulated by silica in the kaolin cannot be exposed (because hydrochloric acid does not react with silica and cannot break the silica encapsulation). However, the fluorine-containing hydrochloric acid wastewater used in this application contains hydrogen fluoride. During the leaching reaction, hydrogen fluoride reacts with silica, corroding a large number of channels on the solid surface for the liquid phase reactant hydrogen chloride and the reaction product AlCl3 to flow. This accelerates the leaching reaction rate and exposes the Al2O3 completely encapsulated by silica in the kaolin, thereby improving the Al2O3 leaching rate.

[0011] 3. Compared with the prior art process of preparing polyaluminium chloride using calcined kaolin as raw material and leaching the aluminium component therein with hydrochloric acid, the fluorine-containing hydrochloric acid used in this application is wastewater from the production of lithium hexafluorophosphate, and its cost is extremely low compared with purchased hydrochloric acid (usually the fluorine-containing hydrochloric acid wastewater generated in the production of lithium hexafluorophosphate requires additional treatment costs). Therefore, this application greatly reduces the raw material cost of polyaluminium chloride, and compared with hydrochloric acid, its leaching reaction efficiency and Al2O3 leaching rate are higher.

[0012] 4. For the fluorine element in the fluorine-containing hydrochloric acid wastewater, in the leaching reaction stage of this application, hydrogen fluoride will react with silicon dioxide, and the reaction equation is: SiO2+ 4HF→SiF4↑+2H2O; part of the hydrogen fluoride reacts with SiO2+ 6HF → H2SiF6+2H2O. In this step, most of the hydrogen fluoride in the solution is basically released, and part of the fluorosilicic acid remaining in the reaction solution will also react with calcium aluminate in the polymerization stage to generate calcium fluorosilicate or calcium fluoride precipitate. Therefore, adding calcium aluminate in the polymerization stage can not only improve the polymerization degree of polyaluminum chloride, but also serve as a calcium source for fluorine removal. By separating fluorine in two steps, the fluorine removal effect is significant, ensuring that the final product does not contain fluorine element.

[0013] 5. The fluorine-containing hydrochloric acid wastewater generated in the production of lithium hexafluorophosphate has always been a major pain point in the production of lithium hexafluorophosphate. Therefore, a large number of disposal process methods have emerged in the industry, but these methods all have the same problem. Either additional costs are required for harmless disposal, or impurities in the fluorine-containing hydrochloric acid need to be purified, and the input-output of resource utilization is not proportional. However, the value of fluorine-containing hydrochloric acid is fully explored in this application, and the process is simple. It only requires replacing the hydrochloric acid in the process of preparing polyaluminum chloride with calcined kaolin, hydrochloric acid, and calcium aluminate as raw materials in the existing technology with the fluorine-containing hydrochloric acid in this application. The quality of the polyaluminum chloride produced is high and the efficiency is high. No additional investment in other costs is required. It not only reduces the production cost of polyaluminum chloride, but also solves the wastewater disposal problem that has long plagued the lithium hexafluorophosphate production industry.

[0014] Furthermore, the fluorine-containing hydrochloric acid is a by-product mixed acid wastewater of the lithium hexafluorophosphate device, wherein the mass concentration of the hydrochloric acid is 25% to 35% and the fluorine content is 1% to 1.5%.

[0015] Furthermore, in the calcination pretreatment in S1, the calcination temperature is 700-850° C. and the time is 1-2 hours.

[0016] Furthermore, the leaching reaction temperature in S2 is 110-120° C., and the reaction time is 2-3 hours.

[0017] Furthermore, the leaching reaction in S2 is carried out by heating reflux, and the heating method is ultrasonic heating.

[0018] Furthermore, the spray drying temperature in S5 is 130-150°C.

[0019] Furthermore, the sulfur-containing tail gas generated during the calcination of the kaolinite-type pyrite tailings in S1 is absorbed by an alkaline solution and then discharged. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0021] The following is further described in detail through specific implementation methods: The overall approach of this application is as follows: S1: calcining the kaolinite-type pyrite tailings to obtain amorphous metakaolinite, which is then ground into particles to obtain calcined kaolin; Pyrite is primarily found in kaolinite clay rock, with its primary mineral components being kaolinite and pyrite. Therefore, it is also referred to in the industry as kaolinite-type pyrite. The mining and processing of kaolinite-type pyrite ore produces a large amount of pyrite tailings (kaolinite-type pyrite tailings). These tailings are primarily composed of kaolinite, with minor amounts of pyrite, anatase, and other minerals. However, kaolinite has very low acid reactivity, and the Al₂O₃ in the tailings is contained within the kaolinite crystals. Therefore, direct leaching of the Al₂O₃ using hydrochloric acid is extremely difficult. Therefore, kaolinite-type pyrite tailings are placed in a calciner. After calcination (at 800°C for 2 hours), the kaolinite in the tailings transforms into amorphous metakaolinite, increasing its reactivity and facilitating the leaching of Al₂O₃ in hydrochloric acid solutions. In order to enhance the contact of the reaction, the agglomerated metakaolinite needs to be ground and broken into particles after calcination.

[0022] S2: mixing the calcined kaolin obtained in S1 with fluorine-containing hydrochloric acid, heating and reacting under stirring, and obtaining an oligomeric aluminum chloride mixed solution after sufficient reaction; Fluorine-containing hydrochloric acid refers to the fluorine-containing hydrochloric acid wastewater formed by absorbing tail gas in the absorption tower during the production of lithium hexafluorophosphate. This application uses an absorption tower to circulate the wastewater to absorb tail gas until the mass concentration of hydrochloric acid in the wastewater is 25%~35% and the fluorine content is in the range of 1%~1.5%, and then discharge it. It is best to concentrate the mass concentration of hydrochloric acid to 30%. When mixing, it is necessary to ensure that the mixing mass ratio of calcined kaolin and fluorine-containing hydrochloric acid is between 1-2:6-10, and the optimal way is to control it at around 1:8. The leaching reaction temperature is 110~120℃, and the reaction time is 2~3h.

[0023] S3: slowly adding calcium aluminate to the oligoaluminum chloride mixed solution obtained in S2 to carry out polymerization reaction, and obtaining a liquid polyaluminum chloride mixed solution after sufficient reaction; The amount of calcium aluminate added is based on the calcined kaolin mixed in S2, and the mass ratio of the two is 2-4:5. The optimal control is calcium aluminate: calcined kaolin is 4:5.

[0024] S4: filtering the polyaluminium chloride mixed solution obtained in S3 to obtain a pure polyaluminium chloride solution; S5: Drying the liquid polyaluminium solution obtained in S4 to obtain solid polyaluminium chloride. The polyaluminum solution is passed into a spray dryer for spray drying at a spray drying temperature of 130-150° C. After drying, solid polyaluminum chloride is obtained.

[0025] The prepared polyaluminium chloride was tested, wherein the Al2O3 content and basicity were tested according to the test method in GB 15892-2009. The fluorine content was tested as follows: Standard curve drawing 1. Take appropriate amounts of fluoride standard solution and place them in a series of volumetric flasks. Add appropriate amount of TISAB and dilute to the mark with deionized water to prepare a series of standard solutions of different concentrations.

[0026] 2. Insert the fluoride ion selective electrode and saturated calomel electrode into the standard solution, stir with a magnetic stirrer, and read the potential value after the potential stabilizes.

[0027] 3. Draw a standard curve with the logarithm of fluoride ion concentration as the horizontal axis and the potential value as the vertical axis.

[0028] Sample measurement 1. Take an appropriate amount of sample solution and place it in a volumetric flask. Add the same volume of TISAB as used for drawing the standard curve and dilute to the scale with deionized water.

[0029] 2. Insert the electrode into the sample solution and stir with a magnetic stirrer. After the potential stabilizes, read the potential value.

[0030] 3. According to the potential value of the sample solution, find the corresponding fluoride ion concentration from the standard curve.

[0031] Result calculation Calculate the fluoride ion content in the sample based on the concentration and dilution ratio of the sample solution.

[0032] Note: During the entire measurement process, attention should be paid to the maintenance and calibration of the electrode, as well as the impact of factors such as the solution temperature and pH value on the measurement results.

[0033] Experimental Example 1 The kaolinite pyrite tailings were calcined at 850 °C and ground into 10g of calcined kaolin was mixed with 80mL of fluorine-containing hydrochloric acid solution and reacted at 110°C for 3h with a stirring rate of 400rpm. After sufficient reaction, 4g of calcium aluminate was added to the solution and reacted at 90°C for 4h. After the reaction was completed, the solution was filtered and the filtrate was spray-dried at 130°C to obtain solid polyaluminum chloride. After testing, the obtained solid polyaluminum chloride had an Al2O3 content of 26.7%, a basicity of 45.12%, and no fluoride ion content was detected.

[0034] Experimental Example 2 10g of calcined kaolin was reacted with 80mL of fluoride-containing hydrochloric acid solution at 110°C for 3h with a stirring rate of 400rpm. After sufficient reaction, 6g of calcium aluminate was added to the solution and the reaction was continued at 90°C for 4h. After the reaction was completed, the solution was filtered and the filtrate was spray-dried at 130°C to obtain solid polyaluminum chloride. After testing, the obtained solid polyaluminum chloride had an Al2O3 content of 28.4%, a basicity of 57.38%, and no fluoride ion content was detected.

[0035] Experimental Example 3 10g of calcined kaolin was reacted with 80mL of fluoride-containing hydrochloric acid solution at 110°C for 3h with a stirring rate of 400rpm. After sufficient reaction, 8g of calcium aluminate was added to the solution and the reaction was continued at 90°C for 4h. After the reaction was completed, the solution was filtered and the filtrate was spray-dried at 130°C to obtain solid polyaluminum chloride. Testing showed that the Al2O3 content of the obtained solid polyaluminum chloride was 29.9%, the basicity was 67.15%, and the fluoride ion content was undetectable.

[0036] Experimental Example 4 10g of calcined kaolin was reacted with 80mL of fluoride-containing hydrochloric acid solution at 110°C for 3h with a stirring rate of 400rpm. After sufficient reaction, 10g of calcium aluminate was added to the solution and the reaction was continued at 90°C for 4h. After the reaction was completed, the solution was filtered and the filtrate was spray-dried at 130°C to obtain solid polyaluminum chloride. After testing, the obtained solid polyaluminum chloride had an Al2O3 content of 28.8%, a basicity of 70.35%, and no fluoride ion content was detected.

[0037] In the embodiment of the present invention, the key indicators Al2O3 content and basicity were adjusted by changing the amount of calcium aluminate by the above method. The results showed that when the amount of calcium aluminate was 8g (i.e., the mass ratio of calcium aluminate to aluminum source calcined kaolin was 0.8), the optimal polymerization index of solid polyaluminium chloride was obtained, meeting the first-class product requirements of Class II solid polyaluminium chloride in HG / T2677-2009 "Industrial Polyaluminium Chloride".

[0038] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing polyaluminium chloride using fluorine-containing hydrochloric acid produced as a by-product of lithium hexafluorophosphate as a raw material, characterized in that: The following steps are involved: S1. Calcination: calcining the kaolinite pyrite tailings at a temperature of 700-850°C for 1-2 hours to obtain amorphous metakaolinite, which is then ground into particles to obtain calcined kaolin; S2, leaching reaction: mixing the calcined kaolin obtained in S1 with fluorine-containing hydrochloric acid to carry out a leaching reaction, and obtaining an oligomeric aluminum chloride mixed solution after the reaction is completed, wherein the fluorine-containing hydrochloric acid is mixed acid wastewater generated in the production process of lithium hexafluorophosphate, wherein the mass concentration of hydrochloric acid is 25% to 35%, the fluorine content is 1% to 1.5%, and the mixing mass ratio of the calcined kaolin to the fluorine-containing hydrochloric acid is 1-2:6-10; S3, polymerization reaction: slowly adding calcium aluminate to the oligomeric aluminum chloride mixed solution obtained in S2 to carry out polymerization reaction, and obtaining a polyaluminum chloride mixed solution after sufficient reaction, wherein the mass ratio of the calcium aluminate to the calcined kaolin in S2 is 2-4:5; S4, filtration: filtering the polyaluminium chloride mixed solution obtained in S3 to obtain a pure polyaluminium chloride solution; S5, drying: drying the polyaluminium solution in S4 to obtain solid polyaluminium chloride.

2. The electrode sealing device for a yellow phosphorus electric furnace according to claim 1, characterized in that: The mass concentration of hydrochloric acid in the fluorine-containing hydrochloric acid is 30%, and the fluorine content is 1% to 1.5%.

3. The electrode sealing device for a yellow phosphorus electric furnace according to claim 2, characterized in that: The calcination temperature in S1 is 800° C. and the calcination time is 2 h.

4. The electrode sealing device for a yellow phosphorus electric furnace according to claim 2, characterized in that: The leaching reaction temperature in S2 is 110-120° C., and the reaction time is 2-3 hours.

5. The electrode sealing device for a yellow phosphorus electric furnace according to claim 2, characterized in that: The leaching reaction in S2 is carried out by heating reflux, and the heating method is ultrasonic heating.

6. The electrode sealing device for a yellow phosphorus electric furnace according to claim 1, characterized in that: The spray drying temperature in S5 is 130-150°C.

7. The electrode sealing device for a yellow phosphorus electric furnace according to claim 1, characterized in that: The sulfur-containing tail gas generated during the calcination of the kaolinite-type pyrite tailings in S1 is absorbed by an alkaline solution and then discharged.

8. The electrode sealing device for a yellow phosphorus electric furnace according to claim 1, characterized in that: The mass ratio of the calcium aluminate added to S3 to the calcined kaolin mixed with hydrochloric acid in S2 is 4:5.

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