A method for recovering aluminum and fluorine elements in an aluminum electrolyte

Abstract

A method for recovering aluminum and fluorine from aluminum electrolytes, belonging to the field of waste resource utilization, includes the following steps: S1. Mixing aluminum electrolyte with alumina, sulfuric acid or sulfate, and calcining to obtain hydrogen fluoride gas and solid 1; S2. Leaching solid 1 with water under certain conditions to obtain solid 2; S3. Adding solid 2 to an alkaline solution, reacting, and filtering to obtain calcium sulfate solid and liquid 3; S4. Adding seed crystals to liquid 3, reacting, and filtering to obtain aluminum hydroxide solid, with the filtrate returned to step S3; S5. Part of the obtained aluminum hydroxide is returned to S4 as seed crystals, and the rest is heated and calcined to obtain alumina product. This method is simple and easy to operate, effectively realizes resource recycling, produces no harmful gases, is environmentally friendly, and achieves a fluorine recovery rate of ≥99% and an aluminum recovery rate of ≥81%.

Description

Technical Field

[0001] This invention belongs to the field of waste resource utilization and specifically relates to a method for recovering aluminum and fluorine elements from aluminum electrolytes. Background Technology

[0002] Aluminum, as an important material, is widely used in construction, aerospace, machinery, and other fields. Currently, the world's aluminum production method still mainly relies on the Hall process. In the electrolytic production process, fluoride molten salts, due to their strong stability, have long been considered the backbone of the molten salt. Simultaneously, to adjust the physical and chemical properties of the electrolyte, fluoride additives containing calcium, magnesium, potassium, etc., are frequently found in industrial production. Furthermore, as production progresses, the content of these additives in the electrolytic cell gradually increases. However, due to the extremely adverse changes in the physical and chemical properties of the melt, replacing the electrolyte requires significant costs. In addition, to maintain the molecular balance of the electrolyte system, continuous electrolytic production processes are usually accompanied by continuous electrolyte removal, including the amounts required for sampling and analysis. Therefore, the aluminum electrolysis production process inevitably generates a large amount of waste electrolyte.

[0003] Currently, research on the recycling of waste aluminum electrolyte is scarce, with only a few similar studies relating to waste linings or furnace bottom waste generated during electrolytic cell shutdowns. However, it's important to note that normally operating electrolytic cells typically last about 5-7 years, resulting in a low frequency of furnace lining waste generation during cell shutdowns. Conversely, the waste electrolyte continuously generated during electrolysis requires appropriate treatment. It has been reported that an average annual aluminum smelter with a production capacity of 200,000 tons generates approximately 2,800 tons of waste electrolyte annually, not including the amount generated due to unstable cell operation, maintenance, anode replacement, etc. Without effective treatment, its large-scale accumulation will significantly occupy land area. Furthermore, because it contains leached fluorides and cyanides, it will cause irreversible damage to the surrounding ecological environment.

[0004] Currently, the most common method for treating aluminum electrolytes is their application in the construction industry, such as cement or road maintenance. However, high Na content in the electrolyte often leads to cracks in cement pavements, resulting in poor application performance. For pyrometallurgy, byproducts are typically in a very stable state after high-temperature calcination, making further recycling difficult. Regarding hydrometallurgy, Chen reported a method using Al / F solution leaching, which leaches waste electrolytes by adjusting the Al / F molar ratio and the pH of the leaching solution. However, waste electrolytes often have complex compositions, requiring further purification of various impurities, increasing process complexity. Furthermore, the large amount of fluoride-containing wastewater generated during this process also requires further complex treatment. Therefore, finding a green, efficient, and high-value-added method for the harmless treatment of waste electrolytes is of great significance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a novel process for recovering fluorine using low-temperature sulfuric acid roasting and alumina as a catalyst, followed by the recycling of the roasted solid with alkaline solution and seed crystals to recover aluminum. In this invention, waste aluminum electrolyte is selected as the main raw material, reacting with alumina and concentrated sulfuric acid at low temperature to generate hydrogen fluoride gas. The roasted solid is then recovered through a series of methods. Besides ensuring cost advantages in terms of low temperature and energy consumption, this process is simple to operate and easy to implement.

[0006] A method for recovering aluminum and fluorine from aluminum electrolytes specifically includes the following steps:

[0007] S1. Aluminum electrolyte, aluminum oxide and sulfuric acid or sulfate solid are mixed and calcined to obtain hydrogen fluoride gas and solid 1;

[0008] S2. Add water to solid 1 and leach it under certain conditions to obtain solid 2;

[0009] S3. Add solid 2 to sodium hydroxide solution, react and filter to obtain calcium sulfate solid and liquid 1;

[0010] S4. Add aluminum hydroxide seed crystals to liquid 1, react and filter to obtain solid aluminum hydroxide, and return the filtrate to step S3;

[0011] S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is heated and calcined to obtain alumina product, of which a portion of the alumina product is returned to step S1.

[0012] in:

[0013] In step S1, the aluminum electrolyte is mainly composed of cryolite and contains at least one of sodium lithium cryolite, calcium fluoride, magnesium fluoride, potassium fluoride, and lithium fluoride; the sulfate is selected from sodium bisulfate and potassium bisulfate.

[0014] In step S1, the mass ratio of alumina to aluminum electrolyte is (0.1-1):1, the calcination time is 100-200 min, and the calcination temperature is 150-300℃.

[0015] In step S1, the mass fraction of sulfuric acid is 95% or higher, and the mass ratio of sulfuric acid to the solid mixture of aluminum electrolyte and aluminum oxide is (2-5):1.

[0016] In step S1, the mass ratio of sodium bisulfate to the solid mixture of aluminum electrolyte and alumina is (3-10):1, and the mass ratio of potassium bisulfate to the solid mixture of aluminum electrolyte and alumina is (4-11):1.

[0017] In step S1, the reaction equation for the reaction between aluminum electrolyte and sulfuric acid / sulfate to produce hydrogen fluoride gas and solid 1 is as follows, where sulfuric acid is used as an example, but sulfate can also be used:

[0018] Na3AlF6+3H2SO4=NaAl(SO4)2+Na2SO4+6HF(g)

[0019] Al2O3+3H2SO4=Al2(SO4)3+3H2O(g)

[0020] In step S2, the leaching temperature is 20-70℃, the leaching time is 20-200 min, and the liquid-solid mass ratio of the added water to solid 1 is (3-7):1.

[0021] In step S3, the concentration of sodium hydroxide solution is 0.5-4 mol / L, the liquid-solid mass ratio of sodium hydroxide solution to solid 2 is (2-8):1, the reaction temperature is 20-90℃, and the reaction time is 10-120 min.

[0022] In step S3, the reaction equation for the reaction between solid 2 and alkaline solution to produce liquid 1 is as follows:

[0023] NaAl(SO4)2+4NaOH=NaAl(OH)4+2Na2SO4

[0024] Al2(SO4)3+8NaOH=2NaAl(OH)4+3Na2SO4

[0025] In step S4, the seed crystal coefficient is 0.05 to 0.5, the reaction temperature is 20 to 90°C, and the reaction time is 3 to 72 hours.

[0026] In step S4, the reaction equation for adding aluminum hydroxide seeds to liquid 1 is as follows:

[0027] NaAl(OH)4=NaOH+Al(OH)3(s)

[0028] In step S5, the calcination temperature is 140–450°C and the calcination time is 1–3 hours.

[0029] In step S5, the reaction equation for the decomposition of aluminum hydroxide is as follows:

[0030] 2Al(OH)3=Al2O3+3H2O(g)

[0031] The fluorine recovery rate obtained using this method is ≥99%, and the aluminum recovery rate is ≥81%.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) The present invention acidifies and roasts waste aluminum electrolytes and then adds alkaline solution and seed crystals to recover valuable aluminum and fluorine elements. The operation is simple and realizes the recycling of resources.

[0034] (2) The present invention recovers and utilizes fluorine by mixing aluminum electrolyte with aluminum oxide and then adding concentrated sulfuric acid or sulfate solid at low temperature, wherein fluorine is converted into hydrogen fluoride, which has high economic benefits and wide application.

[0035] (3) This invention is the first to propose using alumina to catalyze the reaction of aluminum electrolyte with concentrated sulfuric acid, so that the fluorine recovery rate is as high as 99% or more.

[0036] (4) The wet process for treating roasted solids in this invention is simple and produces no harmful gases, making it green and environmentally friendly.

[0037] (5) The solid products and leachate obtained by the wet treatment process of roasting solids of the present invention can be recycled, thereby reducing production costs. Attached Figure Description

[0038] Figure 1 The process flow diagram for recovering aluminum and fluorine elements from aluminum electrolytes according to this invention;

[0039] Figure 2 XRD pattern of the raw material in step S1 of this embodiment of the invention;

[0040] Figure 3 XRD pattern of the product in step S2 of this embodiment of the invention;

[0041] Figure 4 XRD pattern of the product in step S3 of this embodiment of the invention;

[0042] Figure 5 The XRD pattern of the product in step S4 of this embodiment of the invention. Detailed Implementation

[0043] The present invention will be described in detail below with reference to embodiments.

[0044] Example 1

[0045] A method for recovering aluminum and fluorine from aluminum electrolytes, the process flow diagram of which is shown below. Figure 1 As shown, the specific steps include:

[0046] S1. Mix 10g of aluminum electrolyte and 5g of aluminum oxide evenly, and the XRD pattern is as follows. Figure 2 As shown, the aluminum electrolyte phase is mainly sodium hexafluoroaluminate, containing a small amount of calcium fluoride impurities; 45g of concentrated sulfuric acid with a mass fraction of 98.25% was added and stirred evenly, and calcined at 250℃ for 120min to obtain hydrogen fluoride gas and solid 1.

[0047] At S2.25℃, 180mL of water was added to solid 1 and leached for 60min. After filtration, 30g of solid 2 was obtained, and its XRD pattern is shown below. Figure 3 As shown;

[0048] S3. Solid 2 was added to 210 mL of 3 mol / L sodium hydroxide solution, reacted at 60 °C for 60 min, and then filtered to obtain solid 3 and liquid 1. The XRD image of solid 3 is shown below. Figure 4 As shown;

[0049] S4. 2.28 g of aluminum hydroxide seed crystals with a seed coefficient of 0.2 were added to liquid 1 and stirred at 30 °C for 48 h to obtain 11.3 g of solid 4. Its XRD pattern is shown below. Figure 5 As shown, it can be determined that it is aluminum hydroxide; at this time, the decomposition rate of sodium aluminate solution is 81.76%, and the filtrate is returned to step S3 for recycling;

[0050] S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is calcined at 190°C for 2 hours to obtain alumina product, of which a portion of the alumina product is returned to step S1.

[0051] The fluorine recovery rate obtained using this method is 99.59%, and the aluminum recovery rate is 81.76%.

[0052] Example 2

[0053] A method for recovering aluminum and fluorine from aluminum electrolytes specifically includes the following steps:

[0054] S1. Mix 10g of aluminum electrolyte and 6g of aluminum oxide evenly, and the XRD pattern is as follows. Figure 2 As shown, the aluminum electrolyte phase is mainly sodium hexafluoroaluminate, containing a small amount of calcium fluoride impurities; 55g of concentrated sulfuric acid with a mass fraction of 98.09% is added and stirred evenly, and calcined at 250℃ for 150min to obtain hydrogen fluoride gas and solid 1.

[0055] S2.25℃, 220mL of water was added to solid 1 and leached for 120min. After filtration, 36g of solid 2 was obtained, and its XRD is as follows. Figure 3 As shown;

[0056] S3. Solid 2 was added to 260 mL of 3 mol / L sodium hydroxide solution, reacted at 50 °C for 70 min, and then filtered to obtain solid 3 and liquid 1. The XRD pattern of solid 3 is shown below. Figure 4 As shown;

[0057] S4. 2.74 g of aluminum hydroxide seed crystals with a seed coefficient of 0.2 were added to liquid 1 and stirred at 50 °C for 48 h to obtain 14.82 g of solid 4. Its XRD pattern is shown below. Figure 5As shown, it can be determined that it is aluminum hydroxide; at this time, the decomposition rate of sodium aluminate solution is 86.21%, and the filtrate is returned to step S3 for recycling;

[0058] S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is calcined at 220°C for 2.5 hours to obtain alumina product, of which a portion of the alumina product is returned to step S1.

[0059] The fluorine recovery rate obtained using this method is 99.43%, and the aluminum recovery rate is 86.21%.

[0060] Example 3

[0061] A method for recovering aluminum and fluorine from aluminum electrolytes specifically includes the following steps:

[0062] S1. Mix 10g of aluminum electrolyte and 5g of aluminum oxide evenly, and the XRD pattern is as follows. Figure 2 As shown, the aluminum electrolyte phase is mainly sodium hexafluoroaluminate, containing a small amount of calcium fluoride impurities; 60g of concentrated sulfuric acid with a mass fraction of 97.36% was added and stirred evenly, and calcined at 275℃ for 200min to obtain hydrogen fluoride gas and solid 1.

[0063] S2. At 40℃, 300 mL of water was added to solid 1 and leached for 120 min. After filtration, 30 g of solid 2 was obtained, and its XRD pattern is shown below. Figure 3 As shown;

[0064] S3. Solid 2 was added to 315 mL of 2 mol / L sodium hydroxide solution, reacted at 70 °C for 80 min, and then filtered to obtain solid 3 and liquid 1. The XRD pattern of solid 3 is shown below. Figure 4 As shown;

[0065] S4. 2.28 g of aluminum hydroxide seed crystals with a seed coefficient of 0.2 were added to liquid 1 and stirred at 40 °C for 48 h to obtain 11.95 g of solid 4. Its XRD pattern is shown below. Figure 5 As shown, it can be determined that it is aluminum hydroxide; at this time, the decomposition rate of sodium aluminate solution is 83.95%, and the filtrate is returned to step S3 for recycling;

[0066] S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is calcined at 250°C for 2 hours to obtain alumina product, of which a portion of the alumina product is returned to step S1.

[0067] The fluorine recovery rate obtained using this method is 99.79%, and the aluminum recovery rate is 83.95%.

[0068] Example 4

[0069] A method for recovering aluminum and fluorine from aluminum electrolytes specifically includes the following steps:

[0070] S1. Mix 10g of aluminum electrolyte and 6g of aluminum oxide evenly, and the XRD pattern is as follows. Figure 2 As shown, the aluminum electrolyte phase is mainly sodium hexafluoroaluminate, containing a small amount of calcium fluoride impurities; 64g of concentrated sulfuric acid with a mass fraction of 95.18% was added and stirred evenly, and calcined at 275℃ for 180min to obtain hydrogen fluoride gas and solid 1.

[0071] S2. At 50℃, 340 mL of water was added to solid 1 and leached for 140 min. After filtration, 36 g of solid 2 was obtained, and its XRD pattern is shown below. Figure 3 As shown;

[0072] S3. Solid 2 was added to 385 mL of 2 mol / L sodium hydroxide solution, reacted at 80 °C for 50 min, and then filtered to obtain solid 3 and liquid 1. The XRD pattern of solid 3 is shown below. Figure 4 As shown;

[0073] S4. 2.74 g of aluminum hydroxide seed crystals with a seed coefficient of 0.2 were added to liquid 1 and stirred at 35 °C for 72 h to obtain 13.93 g of solid 4. Its XRD pattern is shown below. Figure 5 As shown, it can be determined that it is aluminum hydroxide; at this time, the decomposition rate of sodium aluminate solution is 82.48%, and the filtrate is returned to step S3 for recycling;

[0074] S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is calcined at 300°C for 2.5 hours to obtain alumina product, of which a portion of the alumina product is returned to step S1.

[0075] The fluorine recovery rate obtained using this method is 99.75%, and the aluminum recovery rate is 82.48%.

[0076] Example 5

[0077] A method for recovering aluminum and fluorine from aluminum electrolytes specifically includes the following steps:

[0078] S1. Mix 9g of aluminum electrolyte and 5g of aluminum oxide evenly, and the XRD pattern is as follows. Figure 2 As shown, the aluminum electrolyte phase is mainly sodium hexafluoroaluminate, containing a small amount of calcium fluoride impurities; 45g of concentrated sulfuric acid with a mass fraction of 96.63% was added and stirred evenly, and calcined at 300℃ for 90min to obtain hydrogen fluoride gas and solid 1.

[0079] S2. At 30℃, 260 mL of water was added to solid 1 and leached for 200 min. After filtration, 30 g of solid 2 was obtained, and its XRD pattern is shown below. Figure 3 As shown;

[0080] S3. Solid 2 was added to 162 mL of 4 mol / L sodium hydroxide solution, reacted at 40 °C for 45 min, and then filtered to obtain solid 3 and liquid 1. The XRD image of solid 3 is shown below. Figure 4 As shown;

[0081] S4. 2.54 g of aluminum hydroxide seed crystals with a seed coefficient of 0.22 were added to liquid 1 and stirred at 48 °C for 60 h to obtain 12.41 g of solid 4. Its XRD pattern is shown below. Figure 5 As shown, it can be determined that it is aluminum hydroxide; at this time, the decomposition rate of sodium aluminate solution is 86.45%, and the filtrate is returned to step S3 for recycling;

[0082] S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is calcined at 280°C for 1.5 h to obtain alumina product, of which a portion of the alumina product is returned to step S1.

[0083] The fluorine recovery rate obtained using this method is 99.22%, and the aluminum recovery rate is 86.45%.

[0084] Example 6

[0085] A method for recovering aluminum and fluorine from aluminum electrolytes specifically includes the following steps:

[0086] S1. Mix 8g of aluminum electrolyte and 5g of alumina evenly, and the XRD pattern is as follows. Figure 2 As shown, the aluminum electrolyte phase is mainly sodium hexafluoroaluminate, containing a small amount of calcium fluoride impurities; 52g of concentrated sulfuric acid with a mass fraction of 97.15% was added and stirred evenly, and calcined at 260℃ for 145min to obtain hydrogen fluoride gas and solid 1.

[0087] At 2.55℃, 290 mL of water was added to solid 1 and leached for 160 min. After filtration, 28 g of solid 2 was obtained, and its XRD pattern is shown below. Figure 3 As shown;

[0088] S3. Solid 2 was added to 600 mL of 1 mol / L sodium hydroxide solution, reacted at 75 °C for 65 min, and then filtered to obtain solid 3 and liquid 1. The XRD pattern of solid 3 is shown below. Figure 4 As shown;

[0089] S4. 2.24 g of aluminum hydroxide seed crystals with a seed coefficient of 0.21 were added to liquid 1 and stirred at 55 °C for 62 h to obtain 11.66 g of solid 4. Its XRD pattern is shown below. Figure 5 As shown, it can be determined that it is aluminum hydroxide; at this time, the decomposition rate of sodium aluminate solution is 84.95%, and the filtrate is returned to step S3 for recycling;

[0090] S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is calcined at 260°C for 2 hours to obtain alumina product, of which a portion of the alumina product is returned to step S1.

[0091] The fluorine recovery rate obtained using this method is 99.37%, and the aluminum recovery rate is 84.95%.

[0092] Example 7

[0093] A method for recovering aluminum and fluorine from aluminum electrolytes specifically includes the following steps:

[0094] S1. Mix 8g of aluminum electrolyte and 4g of aluminum oxide evenly, and the XRD pattern is as follows. Figure 2 As shown, the aluminum electrolyte phase is mainly sodium hexafluoroaluminate, containing a small amount of calcium fluoride impurities; 36g of concentrated sulfuric acid with a mass fraction of 95.81% was added and stirred evenly, and calcined at 250℃ for 160min to obtain hydrogen fluoride gas and solid 1.

[0095] At 2.45℃, 210 mL of water was added to solid 1 and leached for 160 min. After filtration, 24 g of solid 2 was obtained, and its XRD pattern is shown below. Figure 3 As shown;

[0096] S3. Solid 2 was added to 252 mL of 2 mol / L sodium hydroxide solution, reacted at 40 °C for 40 min, and then filtered to obtain solid 3 and liquid 1. The XRD image of solid 3 is shown below. Figure 4 As shown;

[0097] S4. 1.81 g of aluminum hydroxide seed crystals with a seed coefficient of 0.2 were added to liquid 1 and stirred at 50 °C for 68 h to obtain 9.86 g of solid 4. Its XRD pattern is shown below. Figure 5 As shown, it can be determined that it is aluminum hydroxide; at this time, the decomposition rate of sodium aluminate solution is 87.43%, and the filtrate is returned to step S3 for recycling;

[0098] S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is calcined at 410°C for 2 hours to obtain alumina product, of which a portion of the alumina product is returned to step S1.

[0099] The fluorine recovery rate obtained using this method is 99.49%, and the aluminum recovery rate is 87.43%.

[0100] Example 8

[0101] A method for recovering aluminum and fluorine from aluminum electrolytes specifically includes the following steps:

[0102] S1. Mix 10g of aluminum electrolyte and 5.5g of aluminum oxide evenly, and the XRD pattern is as follows. Figure 2 As shown, the aluminum electrolyte phase is mainly sodium hexafluoroaluminate, containing a small amount of calcium fluoride impurities; 55g of concentrated sulfuric acid with a mass fraction of 95.47% was added and stirred evenly, and calcined at 270℃ for 120min to obtain hydrogen fluoride gas and solid 1.

[0103] S2. At 40℃, 280 mL of water was added to solid 1 and leached for 190 min. After filtration, 32 g of solid 2 was obtained, and its XRD pattern is as follows. Figure 3 As shown;

[0104] S3. Solid 2 was added to 240 mL of 3 mol / L sodium hydroxide solution, reacted at 55 °C for 50 min, and then filtered to obtain solid 3 and liquid 1. The XRD image of solid 3 is shown below. Figure 4 As shown;

[0105] S4. Add 2.31 g of aluminum hydroxide seed crystals with a seed coefficient of 0.19 to liquid 1, stir at 50 °C for 44 h, and obtain 12.59 g of solid 4. Its XRD pattern is shown below. Figure 5 As shown, it can be determined that it is aluminum hydroxide; at this time, the decomposition rate of sodium aluminate solution is 86.37%, and the filtrate is returned to step S3 for recycling;

[0106] S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is calcined at 370°C for 1.5 h to obtain alumina product, of which a portion of the alumina product is returned to step S1.

[0107] The fluorine recovery rate obtained using this method is 99.56%, and the aluminum recovery rate is 86.37%.

Claims

1. A method for recovering aluminum and fluorine elements from aluminum electrolyte, characterized in that, Specifically, the following steps are included: S1. Aluminum electrolyte, aluminum oxide, and sulfuric acid or an acidic salt of sulfuric acid are mixed and calcined to obtain hydrogen fluoride gas and solid 1; the calcination temperature is 150~300℃; The mass fraction of sulfuric acid is over 98%, and the mass ratio of sulfuric acid to the solid mixture of aluminum electrolyte and alumina is (2~5):1; The acid salt of sulfuric acid is selected from sodium bisulfate and potassium bisulfate. The mass ratio of sodium bisulfate to the solid mixture of aluminum electrolyte and alumina is (3~10):1, and the mass ratio of potassium bisulfate to the solid mixture of aluminum electrolyte and alumina is (4~11):

1. S2. Add water to solid 1 and leach to obtain solid 2; the leaching temperature is 20~70℃, the leaching time is 20~200 min, and the liquid-solid mass ratio of the added water to solid 1 is (3~7):1; solid 2 includes NaAl(SO4)2, Al2(SO4)3, and CaSO4; S3. Add solid 2 to sodium hydroxide solution, filter after reaction to obtain calcium sulfate solid and liquid 1; the concentration of sodium hydroxide solution is 0.5~4 mol / L, the liquid-solid mass ratio of sodium hydroxide solution to solid 2 is (2~8):1, the reaction temperature is 20~90℃, and the reaction time is 10~120 min; S4. Add aluminum hydroxide seed crystals to liquid 1, react and filter to obtain solid aluminum hydroxide, and return the filtrate to step S3; S5. A portion of the obtained aluminum hydroxide is returned to step S4 as seed crystals, and another portion is heated and calcined to obtain alumina product, of which a portion of the alumina product is returned to step S1.

2. The method for recovering aluminum and fluorine elements from aluminum electrolyte according to claim 1, characterized in that, In step S1, the aluminum electrolyte is mainly composed of cryolite and contains at least one of sodium lithium cryolite, calcium fluoride, magnesium fluoride, potassium fluoride, and lithium fluoride.

3. The method for recovering aluminum and fluorine elements from aluminum electrolyte according to claim 1, characterized in that, In step S1, the mass ratio of alumina to aluminum electrolyte is (0.1~1):1, and the calcination time is 100~200 min.

4. The method for recovering aluminum and fluorine elements from aluminum electrolyte according to claim 1, characterized in that, In step S4, the seed crystal coefficient is 0.05~0.5, the reaction temperature is 20~90℃, and the reaction time is 3~72 h.

5. The method for recovering aluminum and fluorine elements from aluminum electrolyte according to claim 1, characterized in that, In step S5, the calcination temperature is 140~450℃ and the calcination time is 1~3 h.

6. The method for recovering aluminum and fluorine elements from aluminum electrolyte according to claim 1, characterized in that, Fluorine recovery rate ≥99%, aluminum recovery rate ≥81%.

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