Method for recovering aluminium fluoride from aluminium electrolysis cell cathode carbon blocks

Abstract

The application provides a method for recovering aluminum fluoride from a cathode carbon block of an aluminum electrolysis cell, and the method comprises the following steps: crushing and pulverizing the cathode carbon block to a preset particle size to obtain cathode carbon block powder; adding the cathode carbon block powder into a nitric acid-aluminum nitrate mixed solution for leaching, and performing solid-liquid separation to obtain a leaching solution and a leaching residue; adjusting the pH of the leaching solution to 4.5-5.5 to form a precipitate, and filtering to obtain hydroxy aluminum fluoride and a lithium-containing solution; drying the hydroxy aluminum fluoride, and mixing the dried hydroxy aluminum fluoride with a fluorinated salt at a preset ratio and then calcining to obtain a calcined product; and washing the calcined product with pure water to obtain aluminum fluoride. The application adopts a nitric acid-aluminum nitrate mixed solution for leaching, so that the content of sulfate in the product is reduced; and the aluminum fluoride is obtained by mixing and calcining with a fluorinated salt, in the process of calcining, the fluorinated salt is decomposed thermally, a double decomposition reaction occurs between the fluorinated salt and the aluminum fluoride, the generation of an aluminum oxide phase in the high-temperature calcining process is reduced, and thus the purity of the aluminum fluoride in the product is improved.

Description

Technical Field

[0001] This application relates to the fields of metallurgy and environmental protection, and in particular to a method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell. Background Technology

[0002] Spent carbon cathode (SCC) is one of the main hazardous solid wastes generated during the overhaul of electrolytic cells in aluminum production. It mainly includes bottom and side carbon blocks, cathode paste, refractory materials, and graphite electrodes stripped from the cathode of the aluminum electrolytic cell. Due to the addition of electrolytic additives such as lithium fluoride and cryolite during electrolysis, a large amount of fluoride permeates the cathode surface and the lining of the electrolytic cell. During long-term open-air storage, this generates a large amount of fluoride-containing wastewater. If this highly concentrated fluoride-containing wastewater is discharged directly without treatment, it will not only pollute surface water, soil, and groundwater, but also cause the loss of significant amounts of fluorine resources and other valuable elements.

[0003] Currently, the common method for recycling and processing waste cathodes is to add an aluminum source to produce precipitate to obtain aluminum hydroxy fluoride. However, in practical applications, the purity of the obtained aluminum hydroxy fluoride is not high, and it may contain impurities such as cryolite, which in turn results in insufficient purity of the produced aluminum fluoride product. Summary of the Invention

[0004] This application provides a method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell, which is beneficial for improving the purity of aluminum fluoride.

[0005] In a first aspect, embodiments of this application provide a method for recovering aluminum fluoride from a cathode carbon block in an aluminum electrolysis cell, the method comprising:

[0006] The cathode carbon block is crushed and ground to a preset particle size to obtain cathode carbon block powder;

[0007] The cathode carbon block powder was added to a nitric acid-aluminum nitrate mixed solution for leaching, and the solid and liquid were separated to obtain leaching solution and leaching residue;

[0008] The pH of the leachate was adjusted to 4.5–5.5 to form a precipitate, and the solution was filtered to obtain aluminum hydroxyfluoride and a lithium-containing solution.

[0009] The aluminum hydroxy fluoride is dried, and the dried aluminum hydroxy fluoride is mixed with a fluoride salt in a preset ratio and then calcined to obtain the calcined product.

[0010] The calcined product was washed with pure water to obtain aluminum fluoride.

[0011] According to the first aspect, in one possible implementation, the method further includes:

[0012] The content of F in the cathode carbon block powder was detected;

[0013] Based on the F content in the detected cathode carbon block powder, aluminum nitrate nonahydrate was added to a 2 mol / L nitric acid solution at an F / Al ratio of (2-6):1, and stirred until the aluminum nitrate nonahydrate was completely dissolved to obtain a mixed solution.

[0014] Add pure water to the mixture to adjust the pH to 1 to 3 to obtain a nitric acid-aluminum nitrate mixed solution.

[0015] According to the first aspect, in one possible implementation, the step of adding the cathode carbon block powder to a nitric acid-aluminum nitrate mixed solution for leaching, and separating the solid and liquid to obtain a leachate and a leaching residue includes:

[0016] The cathode carbon block powder is added to the nitric acid-aluminum nitrate mixed solution at a solid-liquid ratio of (10-15):1.

[0017] Heating and stirring for a preset time, solid-liquid separation is achieved to obtain leachate and leachate residue.

[0018] According to the first aspect, in one possible implementation, in the step of heating and stirring for a preset time to separate the solid and liquid to obtain leachate and leach residue, the heating temperature is 60℃~90℃ and the stirring time is 2h~6h.

[0019] According to the first aspect, in one possible implementation, the step of drying the aluminum hydroxy fluoride and then mixing the dried aluminum hydroxy fluoride with a fluoride salt in a predetermined ratio and calcining it to obtain the calcined product includes:

[0020] The aluminum hydroxyfluoride was dried within a temperature range of 120℃ to 150℃.

[0021] The dried aluminum hydroxy fluoride and the fluoride salt are mixed at a ratio of 1:(1-5) to form a mixture;

[0022] The mixture is subjected to a first-stage calcination at a temperature of 200℃ to 300℃ for 0.5h to 3h.

[0023] The mixture after the first stage of calcination is then subjected to a second stage of calcination. The temperature of the second stage of calcination is 550℃~650℃, and the calcination time is 0.5h~3h.

[0024] According to the first aspect, in one possible implementation, the fluoride salt includes one or more of sodium fluoride, sodium hydrogen fluoride, potassium fluoride, potassium hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride.

[0025] According to the first aspect, in one possible implementation, the step of adjusting the pH of the leachate to 4.5–5.5 to form a precipitate, and filtering to obtain aluminum hydroxyfluoride and a lithium-containing solution includes:

[0026] Add alkali solution to the leachate to adjust the pH to 4.5–5.5;

[0027] Stir the leachate at a temperature of 50℃ to 70℃ until sufficient precipitation occurs;

[0028] The solution was obtained by filtration, which yielded aluminum hydroxyfluoride and a lithium-containing solution.

[0029] According to the first aspect, in one possible implementation, the alkaline solution used to adjust the pH is one or more of NH4·H2O, NaOH, and KOH.

[0030] The method for recovering aluminum fluoride from cathode carbon blocks in aluminum electrolytic cells provided in this application uses a mixed leaching method of nitric acid and aluminum nitrate to extract fluorine and lithium from the cathode carbon slag of aluminum electrolytic cells. The fluorine leaching rate can reach 95% to 98%, which greatly reduces the sulfate content in the product. Furthermore, aluminum fluoride is obtained by calcining it with fluoride salts. During the mixed calcination process, the fluoride salts undergo thermal decomposition and undergo a metathesis reaction with the aluminum fluoride to reduce the formation of the alumina phase during high-temperature calcination, thereby improving the purity of aluminum fluoride in the product. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a schematic flowchart of a method for recovering aluminum fluoride from a cathode carbon block in an aluminum electrolysis cell, according to one embodiment.

[0033] Figure 2 This is a detailed flowchart illustrating step S30 of a method for recovering aluminum fluoride from a cathode carbon block in an aluminum electrolysis cell, according to one embodiment.

[0034] Figure 3 This is a detailed flowchart illustrating step S40 of a method for recovering aluminum fluoride from a cathode carbon block in an aluminum electrolysis cell, according to one embodiment.

[0035] Figure 4 This is an XRD diagram of a cathode carbon block according to one embodiment. Detailed Implementation

[0036] The terms "preferred," "more preferably," etc., used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0037] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of the present invention.

[0039] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0040] like Figure 1 As shown, in some embodiments, the method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolysis cell includes the following steps:

[0041] Step S10: Crush and grind the cathode carbon block to a preset particle size to obtain cathode carbon block powder;

[0042] The cathode carbon block is crushed and ground to a preset particle size so that subsequent leaching, extraction and other steps can be carried out more effectively.

[0043] Use a crusher to break the cathode carbon block into smaller particles. Use a ball mill or other grinding equipment to further grind the crushed particles to the preset particle size.

[0044] The particle size after grinding is controlled by sieving. In this example, a 100-200 mesh sieve is required. Selecting an appropriate sieve aperture ensures that the obtained cathode carbon block powder meets the requirements of subsequent processes.

[0045] like Figure 4 As shown, the main components of the cathode carbon block are Na3(AlF6), CaF2, Na3Li3(AlF6)2 and C.

[0046] Step S20: The cathode carbon block powder is added to a nitric acid-aluminum nitrate mixed solution for leaching, and solid-liquid separation is performed to obtain leaching solution and leaching residue;

[0047] The cathode carbon block powder was added to the nitric acid-aluminum nitrate mixed solution at a solid-liquid ratio of 10–15:1. This ratio was chosen to ensure sufficient liquid-solid contact during the leaching process, thereby improving leaching efficiency.

[0048] The mixed solution is heated to 60℃~90℃ and stirred within this temperature range for 2h~6h. Heating can accelerate the chemical reaction rate, while stirring can ensure that the reactants in the solution are in full contact and react.

[0049] After leaching, the leachate and leaching residue are separated using solid-liquid separation techniques such as filtration and centrifugation. The leachate contains dissolved fluorides and other valuable components, while the leaching residue mainly consists of unreacted solids.

[0050] Nitric acid-aluminum nitrate was selected for leaching. The main function of nitric acid is to provide H+ to prevent hydrolysis and to reduce the sulfate content in the product.

[0051] The preparation process of the nitric acid-aluminum nitrate mixed solution is as follows:

[0052] The content of F in the cathode carbon block powder is detected; based on the detected F content in the cathode carbon block powder, aluminum nitrate nonahydrate is added to a 2 mol / L nitric acid solution at an F / Al ratio of (2-6):1, and stirred until the aluminum nitrate nonahydrate is completely dissolved to obtain a mixed solution; pure water is added to the mixed solution to adjust the pH to 1-3, thereby obtaining a nitric acid-aluminum nitrate mixed solution.

[0053] Step S30: Adjust the pH of the leachate to 4.5-5.5 to form a precipitate, and filter to obtain aluminum hydroxyfluoride and a lithium-containing solution;

[0054] like Figure 2 As shown, step S30 includes:

[0055] Step S31: Add alkali solution to the leachate to adjust the pH to 4.5-5.5;

[0056] By adjusting the pH of the leachate to 4.5–5.5, fluorine and aluminum in the solution are precipitated out as aluminum hydroxyfluoride.

[0057] Add an appropriate amount of alkaline solution to the leachate, such as one or more of NH4·H2O (ammonia), NaOH (sodium hydroxide), or KOH (potassium hydroxide). The choice of alkaline solution can be determined based on cost, ease of operation, and subsequent treatment requirements.

[0058] Step S32: Stir the leachate at a temperature of 50℃~70℃ until it is fully precipitated;

[0059] The leachate was stirred within a temperature range of 50℃ to 70℃ to promote precipitate formation. This temperature range helps to accelerate the chemical reaction rate and improve precipitation efficiency.

[0060] The leachate can be thoroughly stirred using a stirring device to ensure that the reactants in the solution are fully in contact and react, forming a uniform precipitate.

[0061] Step S33: Filter to obtain aluminum hydroxyfluoride and lithium-containing solution.

[0062] The resulting aluminum hydroxyfluoride precipitate is separated from the lithium-containing solution by filtration.

[0063] Use appropriate filtration equipment (such as filter press, vacuum filter, etc.) for filtration. During filtration, it is necessary to control the filtration speed and pressure to avoid damage to the precipitate and contamination of the lithium-containing solution.

[0064] The solid product obtained after filtration is aluminum hydroxyfluoride (or a similar form of aluminum fluoride precipitate), while the filtrate is a lithium-containing solution, which may also contain other valuable components.

[0065] Step S40: Dry the aluminum hydroxy fluoride, and then mix the dried aluminum hydroxy fluoride with a fluoride salt in a preset ratio and calcine to obtain the calcined product;

[0066] like Figure 3 As shown, step S40 includes:

[0067] Step S41: Dry the aluminum hydroxyfluoride at a temperature range of 120℃ to 150℃;

[0068] Moisture is removed from aluminum hydroxyfluoride to prepare it for subsequent mixing and calcination steps. Drying is performed within a temperature range of 120℃ to 150℃ to ensure rapid moisture removal while preventing adverse chemical reactions within the aluminum hydroxyfluoride. Appropriate equipment such as ovens or dryers can be used for drying to ensure operational safety and efficiency.

[0069] Step S42: Mix the dried aluminum hydroxy fluoride with the fluoride salt at a ratio of 1:(1-5) to form a mixture;

[0070] By mixing aluminum hydroxyfluoride and fluoride salts, including sodium fluoride, sodium hydrogen fluoride, potassium fluoride, potassium hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride, a mixture with a specific chemical composition is obtained.

[0071] The dried aluminum hydroxy fluoride was mixed with fluoride salts in a ratio of 1:(1-5) to ensure the purity and composition of aluminum fluoride during subsequent calcination.

[0072] Step S43: The mixture is subjected to a first-stage calcination at a temperature of 200℃~300℃ for a duration of 0.5h~3h.

[0073] The first stage of calcination is carried out within a temperature range of 200℃ to 300℃. The first stage of calcination involves AlF₂. x (OH) 3-x The process of removing water of crystallization by mH2O involves aluminum hydroxyfluoride removing most of the water of crystallization, and due to the low temperature, aluminum oxide is basically not formed.

[0074] Step S44: The mixture after the first stage of calcination is subjected to a second stage of calcination. The temperature of the second stage of calcination is 550℃~650℃, and the calcination time is 0.5h~3h.

[0075] The second stage is the transformation of aluminum hydroxyfluoride into α-AlF3. During this process, the fluoride salt undergoes thermal decomposition and undergoes a metathesis reaction with aluminum fluoride, reducing the formation of the alumina phase during high-temperature calcination. Therefore, the purity of aluminum fluoride in the product can be improved.

[0076] Using a two-stage calcination method can reduce the loss of F during calcination and reduce the formation of Al2O3 during calcination, and the purity of the produced aluminum fluoride can reach over 90%.

[0077] Step S50: Wash the calcined product with pure water to obtain aluminum fluoride.

[0078] Removes unreacted substances, fluoride salts, and other soluble impurities from the calcination product. Improves the purity of aluminum fluoride to meet the quality requirements of subsequent applications.

[0079] Methods such as soaking, spraying, or stirring can be used to ensure that the calcined product is in full contact with pure water, thereby effectively removing impurities.

[0080] After washing, the aluminum fluoride is separated from the washing liquid by filtration. Then, the aluminum fluoride is dried to remove residual moisture, yielding the final aluminum fluoride product.

[0081] This embodiment uses a mixed leaching method of nitric acid and aluminum nitrate to extract fluorine and lithium from the cathode carbon slag of aluminum electrolytic cells. The fluorine leaching rate can reach 95% to 98%, which greatly reduces the sulfate content in the product. Furthermore, aluminum fluoride is obtained by calcining it with fluoride salts. During the mixed calcination process, the fluoride salts undergo thermal decomposition and undergo a metathesis reaction with aluminum fluoride to reduce the formation of the alumina phase during high-temperature calcination, thereby improving the purity of aluminum fluoride in the product.

[0082] In the first embodiment, the method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolysis cell includes the following steps:

[0083] 1. Crushing, grinding, and sieving: After crushing the cathode carbon blocks with a crusher, grind them in a vibrating mill for 15 minutes. Sieve the ground cathode carbon blocks through a 200-mesh sieve to obtain cathode carbon block powder.

[0084] 2. Leaching process: Take 60g of powder material, with a fluorine content of approximately 5.7g, according to the original ore ratio. Prepare a nitric acid-aluminum nitrate solution with an F / Al ratio of 3:1. Dissolve 23.4g of aluminum nitrate nonahydrate in 1mol / L HNO3 and stir until fully dissolved. Then add the powder material and adjust the pH to around 2 using pure water, maintaining a liquid-solid ratio of approximately 10:1. Stir at 90℃ for 2 hours. After the reaction is complete, filter to obtain 590ml of leaching solution and 50.2g of leaching residue.

[0085] 3. During the precipitation process, the leachate is placed in a stirring device. NaOH is slowly added during stirring to adjust the pH of the leachate, maintaining it between 4.5 and 5.5. Once the pH no longer decreases, the residue and filtrate are filtered out. The residue is aluminum hydroxyfluoride, and the filtrate is a lithium-containing solution.

[0086] 4. In the calcination process, the obtained aluminum hydroxy fluoride was thoroughly dried at 120℃ and then mixed with sodium fluoride at a ratio of 1:1. The mixture was placed in a muffle furnace and heated to 300℃ for 1 hour, and then heated to 600℃ for 1 hour. After calcination, the mixture was thoroughly rinsed with pure water and dried to obtain 7.98g of AlF3 with a purity of 96.8%.

[0087] In this embodiment, the F recovery rate in the cathode carbon block is 84.2%, and the lithium leaching rate in the final lithium-containing solution reaches 88.7%. After further impurity removal, lithium carbonate can be produced.

[0088] In the second embodiment, the method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolysis cell includes the following steps:

[0089] The aluminum fluoride recovery process in this embodiment is the same as in the first embodiment, except that the F / Al ratio during leaching is changed and the leaching time is extended. The specific implementation method is as follows:

[0090] 1. Crushing, grinding, and sieving: After crushing the cathode carbon blocks with a crusher, grind them in a vibrating mill for 15 minutes. Sieve the ground cathode carbon blocks through a 200-mesh sieve to obtain cathode carbon block powder.

[0091] 2. In the leaching process, a nitric acid-aluminum nitrate solution was prepared with an F / Al ratio of 4:1. 17.6g of aluminum nitrate nonahydrate was dissolved in 1mol / L HNO3 and stirred in a stirring device until fully dissolved. Then, 60g of powdered material was added. The pH was adjusted to about 2 using pure water, and the liquid-solid ratio was maintained at about 10:1. The mixture was stirred at 90℃ for 4 hours. After the reaction was complete, it was filtered to obtain 592ml of leaching solution and 48.6g of leaching residue.

[0092] 3. During the precipitation process, the leachate is placed in a stirring device. NaOH is slowly added during stirring to adjust the pH of the leachate, maintaining it between 4.5 and 5.5. Once the pH no longer decreases, the residue and filtrate are filtered out. The residue is aluminum hydroxyfluoride, and the filtrate is a lithium-containing solution.

[0093] 5. In the calcination process, the obtained aluminum hydroxy fluoride was thoroughly dried at 120℃ and then mixed with sodium fluoride at a ratio of 1:1. The mixture was placed in a muffle furnace and heated to 300℃ for 1 hour, and then heated to 600℃ for 1 hour. After calcination, the mixture was thoroughly rinsed with pure water and dried to obtain 7.68g of AlF3 with a purity of 95.1%.

[0094] In this embodiment, the F recovery rate in the cathode carbon block is 83.6%, and the lithium leaching rate in the final lithium-containing solution reaches 90.1%. After further impurity removal, lithium carbonate can be produced.

[0095] In the third embodiment, the method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolysis cell includes the following steps:

[0096] The process for recovering aluminum fluoride in this embodiment is the same as in the first embodiment, except for the calcination conditions.

[0097] 1. Crushing, grinding, and sieving: After crushing the cathode carbon blocks with a crusher, grind them in a vibrating mill for 15 minutes. Sieve the ground cathode carbon blocks through a 200-mesh sieve to obtain cathode carbon block powder.

[0098] 2. In the leaching process, a nitric acid-aluminum nitrate solution was prepared with an F / Al ratio of 3:1. 23.4 g of aluminum nitrate nonahydrate was dissolved in 1 mol / L HNO3 and stirred in a stirring device until fully dissolved. Then, 60 g of powder was added. The pH was adjusted to about 2 using pure water, and the liquid-solid ratio was maintained at about 10:1. The mixture was stirred at 90°C for 2 hours. After the reaction was complete, it was filtered to obtain 588 ml of leaching solution and 51.0 g of leaching residue.

[0099] 3. During the precipitation process, the leachate is placed in a stirring device. NaOH is slowly added during stirring to adjust the pH of the leachate, maintaining it between 4.5 and 5.5. Once the pH no longer decreases, the residue and filtrate are filtered out. The residue is aluminum hydroxyfluoride, and the filtrate is a lithium-containing solution.

[0100] 6. In the calcination process, the obtained aluminum hydroxy fluoride was thoroughly dried at 120℃ and then mixed with sodium fluoride at a ratio of 1:1. The mixture was placed in a muffle furnace and heated to 300℃ for 3 hours, and then heated to 650℃ for 3 hours. After calcination, the mixture was thoroughly rinsed with pure water and dried to obtain 7.21g of AlF3 with a purity of 93.9%.

[0101] In this embodiment, the F recovery rate in the cathode carbon block is 80.8%.

[0102] The applicant declares that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above detailed methods, that is, it does not mean that the present invention must rely on the above detailed methods to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the methods of the present invention, additions of auxiliary steps, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell, characterized in that, The method includes: The cathode carbon block is crushed and ground to a preset particle size to obtain cathode carbon block powder; The cathode carbon block powder was added to a nitric acid-aluminum nitrate mixed solution for leaching, and the solid and liquid were separated to obtain leaching solution and leaching residue; The pH of the leachate was adjusted to 4.5–5.5 to form a precipitate, and the solution was filtered to obtain aluminum hydroxyfluoride and a lithium-containing solution. The aluminum hydroxy fluoride is dried, and the dried aluminum hydroxy fluoride is mixed with a fluoride salt in a preset ratio and then calcined to obtain the calcined product. The calcined product was washed with pure water to obtain aluminum fluoride.

2. The method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell according to claim 1, characterized in that, The method further includes: The content of F in the cathode carbon block powder was detected; Based on the F content in the detected cathode carbon block powder, aluminum nitrate nonahydrate was added to a 2 mol / L nitric acid solution at an F / Al ratio of (2-6):1, and stirred until the aluminum nitrate nonahydrate was completely dissolved to obtain a mixed solution. Add pure water to the mixture to adjust the pH to 1 to 3 to obtain a nitric acid-aluminum nitrate mixed solution.

3. The method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell according to claim 1, characterized in that, The step of adding the cathode carbon block powder to a nitric acid-aluminum nitrate mixed solution for leaching, and separating the solid and liquid to obtain leaching solution and leaching residue includes: The cathode carbon block powder is added to the nitric acid-aluminum nitrate mixed solution at a solid-liquid ratio of (10-15):

1. Heating and stirring for a preset time, solid-liquid separation is achieved to obtain leachate and leachate residue.

4. The method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell according to claim 3, characterized in that, In the step of heating and stirring for a preset time to separate the solid and liquid to obtain leachate and leachate residue, the heating temperature is 60℃~90℃ and the stirring time is 2h~6h.

5. The method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell according to claim 1, characterized in that, The steps of drying the aluminum hydroxy fluoride and then mixing the dried aluminum hydroxy fluoride with a fluoride salt in a preset ratio and calcining it to obtain the calcined product include: The aluminum hydroxyfluoride was dried within a temperature range of 120℃ to 150℃. The dried aluminum hydroxy fluoride and the fluoride salt are mixed at a ratio of 1:(1-5) to form a mixture; The mixture is subjected to a first-stage calcination at a temperature of 200℃ to 300℃ for 0.5h to 3h. The mixture after the first stage of calcination is then subjected to a second stage of calcination. The temperature of the second stage of calcination is 550℃~650℃, and the calcination time is 0.5h~3h.

6. The method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell according to claim 5, characterized in that, The fluoride salt includes one or more of sodium fluoride, sodium hydrogen fluoride, potassium fluoride, potassium hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride.

7. The method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell according to claim 3, characterized in that, The step of adjusting the pH of the leachate to 4.5-5.5 to form a precipitate, and filtering to obtain aluminum hydroxyfluoride and a lithium-containing solution includes: Add alkali solution to the leachate to adjust the pH to 4.5–5.5; Stir the leachate at a temperature of 50℃ to 70℃ until sufficient precipitation occurs; The solution was obtained by filtration, which yielded aluminum hydroxyfluoride and a lithium-containing solution.

8. The method for recovering aluminum fluoride from the cathode carbon block of an aluminum electrolytic cell according to claim 7, characterized in that, The alkaline solution used to adjust the pH is one or more of NH4·H2O, NaOH, and KOH.

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