Method for preparing fluoride from aluminum electrolysis fluorine-containing waste

Abstract

The application relates to a method for preparing fluoride by utilizing aluminum electrolysis fluorine-containing waste, which comprises the following steps: after alkaline leaching of aluminum electrolysis fluorine-containing waste, solid-liquid separation is carried out to obtain filtrate a; evaporation crystallization is carried out on the filtrate a to obtain crystal slurry; NaOH is added into the crystal slurry, so that the initial concentration of NaOH in the solution of the crystal slurry reaches 10-20 mol / L; after stirring and reaction, solid-liquid separation is carried out, washing is carried out, and a filter cake is obtained; the filter cake is uniformly mixed with a reaction agent, roasting is carried out, crushing is carried out, and a roasting product is obtained; wherein the reaction agent is one or several of aluminum sulfate, aluminum chloride, aluminum nitrate and hydrates thereof; the molar ratio of the total amount of fluorine elements to the total amount of aluminum elements in the mixture of the filter cake and the reaction agent is 2-3:1 or 5-6.5:1; after leaching of the roasting product, solid-liquid separation is carried out, washing is carried out, drying is carried out, and a fluoride product is obtained. The purity of the aluminum fluoride product or the cryolite product obtained by the method is high, the purity can reach more than 98%, and the use standard of reagent aluminum fluoride or cryolite can be reached.

Description

Technical Field

[0001] This invention relates to a method for preparing fluorides (such as aluminum fluoride or cryolite) from fluorine-containing waste from aluminum electrolysis, belonging to the field of metallurgical solid waste resource utilization. Background Technology

[0002] Aluminum has a wide range of applications, and it is typically produced through aluminum electrolysis. The process of producing metallic aluminum by aluminum electrolysis continuously generates fluorine-containing waste materials such as overhaul slag, carbon slag, and waste aluminum electrolyte. Producing one ton of aluminum can generate 30-40 kg of overhaul slag, 10-30 kg of carbon slag, and 10-30 kg of waste aluminum electrolyte. For aluminum electrolysis companies with better anode quality, the amount of carbon slag is less, while the amount of waste electrolyte is higher. Typically, the fluorine content in overhaul slag is 3-17 wt%, in carbon slag it is 25-35 wt%, and in waste aluminum electrolyte it is 48-53 wt%. It is evident that the aluminum electrolysis production process generates various fluorine-containing waste materials, and without resource utilization treatment, there will be a serious waste of fluorine resources.

[0003] Because sodium introduced from alumina raw materials continuously accumulates in the electrolytic cell during aluminum electrolysis, leading to an increase in the molecular ratio of aluminum electrolyte, fluorine is often added in the form of aluminum fluoride to adjust or maintain the electrolyte molecular ratio. If the fluorine in the discharged fluorine-containing waste can be recovered and converted into aluminum fluoride, the resource value of fluorine-containing waste from aluminum electrolysis can be significantly improved, and it may even be possible to achieve a closed-loop recycling of fluorine in the aluminum electrolysis industry. Therefore, in recent years, a large number of patents have focused on the development of processes for producing aluminum fluoride from fluorine-containing waste from aluminum electrolysis.

[0004] Chinese invention patent applications CN111485252A, CN113149052A, CN115465876A, CN114804171A, and CN114314625A disclose methods for the resource-based recycling of waste aluminum electrolytes to prepare aluminum fluoride. The core reaction in all these methods involves the roasting of waste aluminum electrolytes and aluminum salts to convert them into aluminum fluoride. These methods are all continuations of the process for preparing aluminum fluoride by roasting fluorine-containing materials with aluminum sulfate, as proposed in Russian patent RU2462418C1. Because waste aluminum electrolytes contain multiple phases such as Na3AlF6, CaF2, Na2LiAlF6, and K2NaAlF6, resulting in a complex composition, high roasting temperatures are typically required to ensure a complete reaction and obtain high-purity aluminum fluoride. For example, the aluminum sulfate roasting process usually requires roasting temperatures above 500℃, leading to high energy consumption. Chinese invention patent applications CN114890447A and CN114853042A propose a waste electrolyte to aluminum fluoride conversion process based on the above-mentioned technology, using low-temperature roasting (50-135℃) or even no roasting. However, under low-temperature conditions, the solid-solid reaction rate is slow and the conversion efficiency is low, resulting in low purity of the aluminum fluoride product. Meanwhile, waste aluminum electrolysis often contains impurities such as Al2O3, SiO2, Fe2O3, and carbon, which are difficult to participate in the reaction and consumption during roasting and subsequent leaching, ultimately entering the aluminum fluoride product and further limiting its purity (typically <97%).

[0005] Chinese invention patents CN117383599B, ​​CN113249582B, CN113501536A, and CN117383599B disclose methods for preparing aluminum fluoride from waste aluminum electrolyte using aluminum hydroxyfluoride as an intermediate. These methods involve leaching the waste aluminum electrolyte into a solution using acid and / or aluminum salt solution, adjusting the pH with an alkaline solution to recover the aluminum-fluoride complex in the solution as aluminum hydroxyfluoride precipitate, and finally reacting the aluminum hydroxyfluoride with HF gas, hydrofluoric acid, or ammonia hydrogen fluoride to obtain aluminum fluoride. While these processes can yield high-purity aluminum fluoride, they are lengthy and involve HF volatilization, requiring sophisticated equipment and environmental protection measures, thus hindering industrial-scale application. If aluminum fluoride is directly calcined to produce aluminum fluoride, the resulting product has low purity (<60%) and low value.

[0006] Chinese invention patent CN109701989B discloses a method for treating waste cathode carbon blocks from aluminum electrolysis using NaOH sub-molten salt. The method involves crushing the waste cathode carbon blocks to obtain cathode carbon block particles, which are then leached in a NaOH sub-molten salt solution. The solid-liquid ratio of the cathode carbon block particles to the NaOH sub-molten salt solution is 1:5 g / ml. The leaching temperature is 120-240℃, the leaching time is 0.5-6 h, the leaching stirring rate is 500-1500 r / min, and the leaching oxygen partial pressure is 0-1.0 MPa. After filtration, a leaching solid product and a filtrate are obtained. The leaching solid product is washed until the filtrate is neutral. The pH of the resulting filtrate is adjusted to neutral, and then evaporated to crystallize out electrolyte powder. This patent can effectively recover carbon materials from waste cathode carbon blocks from aluminum electrolysis, but it cannot directly produce aluminum fluoride.

[0007] Chinese invention patent application CN118047408A discloses a method for preparing aluminum fluoride using waste aluminum electrolyte, comprising the following steps: S1, crushing and sieving the aluminum electrolyte, mixing it with a calcination aid, and calcining it at 500-800℃ to obtain a fluoride; wherein the molar ratio of sodium fluoride to aluminum fluoride in the electrolyte is 1-3, and the calcination aid is one or more of sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate; S2, mixing the fluoride with an additive uniformly, and heat-treating it at a low temperature to obtain a heat-treated product; wherein the additive is aluminum nitrate or its crystalline hydrate, and the heat treatment temperature is 70-135℃; S3, dissolving the heat-treated product in an aqueous solution, filtering it to obtain filter residue and filtrate, and drying the filter residue to obtain aluminum fluoride. The purity of the aluminum fluoride product produced by this patent can only reach 95%, limiting its application. The additive in its S2 can only be aluminum nitrate or its hydrate. Aluminum nitrate cannot be replaced with aluminum sulfate / aluminum chloride. Aluminum nitrate is a hazardous chemical that is easily explosive and is controlled by the public security department. Moreover, it is expensive, which obviously limits the application of this patented technology. Furthermore, waste aluminum electrolytes often inevitably contain carbon materials and α-alumina, and their content is unstable. They hardly react and are consumed during the treatment process, and eventually enter the aluminum fluoride product as impurities, affecting the purity and stability of the product. In addition, the patent has a narrow scope of application and cannot be used to treat fluorine-containing wastes such as overhaul slag and carbon slag.

[0008] In summary, existing processes for preparing aluminum fluoride from fluorine-containing waste from aluminum electrolysis suffer from problems such as long process flow and low purity of aluminum fluoride. Therefore, it is particularly important to further develop new processes for preparing high-purity fluorides from fluorine-containing waste from aluminum electrolysis. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing fluorides using fluorine-containing waste from aluminum electrolysis, in order to obtain fluoride products such as aluminum fluoride or cryolite with higher purity.

[0010] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A method for preparing fluorides from fluorine-containing waste from aluminum electrolysis includes the following steps: S1. After alkaline leaching of fluorine-containing waste from aluminum electrolysis, solid-liquid separation is performed to obtain filtrate a. S2. Evaporate and crystallize the filtrate a to obtain a crystal slurry; then add NaOH to the crystal slurry so that the initial concentration of NaOH in the crystal slurry solution reaches 10-20 mol / L. After stirring and reacting, separate the solid and liquid, wash, and obtain a filter cake. S3. After the filter cake is mixed evenly with the reactant, it is calcined and crushed to obtain the calcined product. The reactant is one or more of aluminum sulfate, aluminum chloride, aluminum nitrate and their hydrates; optionally, the molar ratio of the total amount of fluorine to the total amount of aluminum in the mixture of filter cake and reactant is 2-3:1 or 5-6.5:1; optionally, the mass ratio of filter cake to reactant is 80-110:130-150. S4. After leaching the roasted product, the solid and liquid are separated, washed, and dried to obtain the fluoride product.

[0011] Furthermore, in S1, the fluorine-containing waste from aluminum electrolysis is one or more of the following generated during the aluminum electrolysis process: waste aluminum electrolyte, overhaul slag, waste cathode, carbon slag, anode covering material, trench material, and aluminum ash. And / or, the particle size of fluorine-containing waste from aluminum electrolysis is <0.5 mm, and further, <0.15 mm.

[0012] Optionally, the waste aluminum electrolyte contains 10-28% Al, 40-60% F, 20-30% Na, 0-1.8% Li, and 0-3% K.

[0013] Furthermore, in the waste aluminum electrolyte, the content of Al is 12-25%, the content of F is 45-55%, the content of Na is 22-28%, the content of Li is 0-1.5%, and the content of K is 0-2.5%.

[0014] Optionally, the waste cathode contains 0.5-5% Al, 10-20% F, 5-20% Na, 0-1.5% Li, and 0-0.6% K.

[0015] Furthermore, in S1, during alkaline leaching, the ratio of the sum of the number of moles of alkali added and the number of moles of alkali metal in the aluminum electrolysis fluorine-containing waste to the number of moles of fluorine in the alkaline leaching reaction system is 0.5-2:1, preferably 1-1.5:1, and more preferably 1.2-1.3:1; The alkali is one or more of NaOH, KOH, LiOH and their hydrates; And / or, during alkali leaching, add water to control the initial liquid-to-solid ratio to 8-40 ml / g, or even 10-35 ml / g; And / or, during alkali leaching, stir and react at 30-100℃ for 1-4 hours.

[0016] Optionally, during alkali soaking, the stirring speed is controlled at 100-500 rpm.

[0017] Optionally, in S1, when the aluminum electrolysis fluorine-containing waste contains waste cathodes and / or overhaul slag, H2O2 is added to oxidize the cyanide therein, wherein the amount of H2O2 added is 0.01-0.1% of the mass of the aluminum electrolysis fluorine-containing waste.

[0018] Furthermore, in S2, the volume of the crystal slurry obtained by evaporation and crystallization is 1 / 30-1 / 20 of the volume of filtrate a, preferably 1 / 28-1 / 22, and more preferably 1 / 26-1 / 24.

[0019] Furthermore, in S2, NaOH is added to the crystal slurry so that the initial concentration of NaOH in the crystal slurry solution reaches 15-18 mol / L; And / or, the filtrate b obtained from solid-liquid separation and the washing liquid obtained from washing are mixed to obtain a mixture; the mixture is returned to the alkaline leaching step for reuse; thus, the added NaOH can enter S1 for alkaline leaching without increasing reagent consumption.

[0020] Optionally, in step S2, deionized water is used for washing. During washing, the liquid-to-solid mass ratio is controlled to be 1-3:1 (preferably 1-2:1), and the number of washing cycles is 1-3 (preferably 2).

[0021] Preferably, after the sodium aluminate content in the mixture reaches saturation, calcium hydroxide is added to remove fluoride, followed by filtration. Then, carbon dioxide is bubbled into the filtrate c to adjust the pH of the solution to 7-10, and then filtered again to obtain the aluminum hydroxide product. Preferably, the stirring reaction lasts for 20-40 minutes, more preferably 25-35 minutes.

[0022] Furthermore, before S3, there is also a step of drying the filter cake.

[0023] Furthermore, in S3, the molar ratio of the total amount of fluorine to the total amount of aluminum in the filter cake and reactant is 2.4-2.6:1 or 5.5-6:1; And / or, calcined at 200-600℃ for 1-5 hours, preferably at 350-450℃ for 2-3 hours; and / or, the particle size of the calcined product is ≤100 mesh.

[0024] Furthermore, in S4, when the molar ratio of the total amount of fluorine to the total amount of aluminum in the mixture of filter cake and reactant in S3 is 2-3:1, the calcined product is acid-leached, followed by solid-liquid separation, washing, and drying to obtain aluminum fluoride product. Acid leaching can remove cone cryolite and single cryolite produced in the reaction, resulting in a higher purity aluminum fluoride product.

[0025] When the molar ratio of the total amount of fluorine to the total amount of aluminum in the mixture of filter cake and reactant in S3 is 5-6.5:1, the calcined product is soaked in water, then separated into solid and liquid, washed, and dried to obtain cryolite product. And / or, during leaching, stir and leach at 50-90℃ for 10-60 minutes; And / or, during leaching, control the initial liquid-to-solid ratio of the reaction system to be 1-5 ml / g; And / or, during acid leaching, an inorganic acid is added to maintain the pH of the reaction system <1; The inorganic acid is one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0026] Optionally, in step S4, deionized water is used for washing. During washing, the liquid-to-solid mass ratio is controlled at 1-3:1 (preferably 1.5-2:1), and the number of washing cycles is 1-3 (preferably 2). Optionally, the wash water generated in step S4 is returned to step S1 for use in constructing the alkaline leaching reaction system.

[0027] Further, alkali is added to the filtrate obtained from solid-liquid separation in S4 to adjust the pH value to 5-9 (or even 5.5-6.5), then filtered, and the resulting filtrate d is evaporated and crystallized to obtain sulfate and mother liquor.

[0028] Furthermore, when the mother liquor contains lithium, sodium carbonate is added to the mother liquor to precipitate lithium and obtain lithium carbonate product.

[0029] The following chemical reactions may occur during the alkaline leaching process of this invention: Na3AlF6+ 4NaOH = 6NaF + NaAlO2+ 2H2O; Na2LiAlF6+ 4NaOH = 5NaF + LiF + NaAlO2+ 2H2O; K2NaAlF6+ 4NaOH = 4NaF + 2KF + NaAlO2+ 2H2O; Na5Al3F 14 + 12NaOH = 14NaF + 3NaAlO2 + 6H2O.

[0030] The chemical reaction equations that may occur during the calcination process of this invention are as follows: 12NaF + Al2(SO4)3= 2Na3AlF6+ 3Na2SO4; 6NaF + AlCl3 = Na3AlF6 + 3NaCl; 6NaF + Al(NO3)3= Na3AlF6+ 3NaNO3; 6NaF + Al2(SO4)3= 2AlF3+ 3Na2SO4; 3NaF + AlCl3 = AlF3 + NaCl; 3NaF + Al(NO3)3= AlF3+ 3NaNO3.

[0031] In this invention, fluorine-containing substances such as sodium cryolite, lithium sodium cryolite, and sodium potassium cryolite from aluminum electrolysis fluorine-containing waste are first leached into a solution using alkali, so that fluorine exists mainly in the solution in the form of fluorides such as sodium fluoride, potassium fluoride, and lithium fluoride. Then, through evaporation and concentration, NaF is supersaturated and precipitated. After evaporation, NaOH is added to reduce the solubility of NaF by utilizing the common ion effect, further promoting the selective precipitation of NaF and obtaining NaF with higher purity (corresponding to the filter cake obtained by S2), laying the foundation for obtaining higher purity fluoride products in the future. Then, aluminum salts such as aluminum sulfate are used as reactants to mix with the filter cake and calcine to convert Al and F into aluminum fluoride or cryolite. Finally, the calcined product is acid-leached or water-leached to remove unreacted raw materials and impurities generated by the reaction, obtaining aluminum fluoride products or cryolite products.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The aluminum fluoride or cryolite products obtained by the method of the present invention have high purity, up to 98% or more, which can meet the standards for use of reagent aluminum fluoride or cryolite.

[0033] (2) The method of the present invention obtains NaF with higher purity first, and uses it as an intermediate product to roast with aluminum salt. Compared with directly using waste aluminum electrolyte to roast with aluminum salt, NaF has higher reactivity, higher roasting conversion efficiency, lower roasting temperature, and lower energy consumption.

[0034] (3) The method of the present invention can produce two products, cryolite and aluminum fluoride, by controlling the ratio of filter cake to aluminum salt during roasting, thus broadening the application value of the process.

[0035] (4) The method of the present invention, by adding sodium hydroxide to the crystal slurry obtained by evaporation and crystallization, can reduce the requirement for the evaporation concentration ratio, thereby reducing energy consumption and the corrosion of evaporation equipment by high concentration alkali. At the same time, it can effectively promote the selective precipitation of sodium fluoride, laying the foundation for obtaining higher yield and purity of fluoride products in the future. Therefore, the method of the present invention can reduce processing costs and ensure the yield and purity of fluoride products, resulting in high overall benefits.

[0036] (5) The method of the present invention can realize the full-scale resource recovery of elements such as fluorine, sodium, aluminum and lithium in aluminum electrolysis fluorine-containing waste, with high comprehensive recovery benefits. Attached Figure Description

[0037] Figure 1 This is a phase analysis diagram of the calcined product obtained in Example 1.

[0038] Figure 2 This is a phase analysis diagram of the cryolite product obtained in Example 5. Detailed Implementation

[0039] The present invention will be described in detail below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other. Unless otherwise specified, the relevant percentages refer to mass percentages.

[0040] Example 1 The specific implementation steps of the method for preparing fluorides from fluorine-containing waste from aluminum electrolysis in this embodiment are as follows: (1) Take 100g of waste aluminum electrolyte (Al: 13.5%; F: 50.7%; Na: 24.3%; Li: 1.1%; K: 2.3%) from an aluminum plant in Henan Province, crush and grind it to obtain electrolyte powder of -100 mesh; (2) The above 100.0g electrolyte powder and 70.0g sodium hydroxide were placed in a stirring tank, 2.5L of water was added, and the mixture was stirred at 80℃ for 2h to dissolve. After filtration, filter residue a and filtrate b were obtained. (3) Evaporate and crystallize the above filtrate b until the solution volume is 100 ml. Add 60 g NaOH to the resulting crystal-containing slurry, stir and react for 30 minutes, filter, and wash twice with deionized water to obtain filter cake c. The filtrate obtained from filtration is mixed with the washing solution obtained from washing to obtain a mixture; The filter cake c was dried to obtain 95.4g of NaF powder; During each wash, the liquid-to-solid mass ratio is controlled at 2:1. (4) Mix the 95.4g NaF powder obtained in the above step with 142.5g aluminum sulfate powder evenly, and calcine at 500℃ for 2h to obtain calcined clinker e; (5) After crushing and grinding the roasted clinker e into -100 mesh powder, place it in a stirring tank, add water to adjust the initial liquid-solid ratio to 3 ml / g, add sulfuric acid to control the pH of the solution to be less than 1, stir and leach at 60°C for 30 minutes, filter, wash, and obtain filtrate f and filter cake g. Dry the filter cake g to obtain 60.6 g of aluminum fluoride product. During leaching, sulfuric acid is added to control the solution pH to be less than 1.

[0041] XRF analysis of the aluminum fluoride product was performed according to standard YST 581.4-2024 (the same applies below), and the purity of the aluminum fluoride product was found to be 98.9%. Phase analysis of the aluminum fluoride was also performed, and the results are as follows: Figure 1 As shown, aluminum fluoride diffraction peaks are significant, and there are no obvious impurity diffraction peaks.

[0042] (6) After adding alkali solution to the above-obtained filtrate f to adjust the pH to 6, filter, evaporate the filtrate to crystallize, and obtain mixed sulfate powder; The mixture is returned to step (2) for dissolution of the next batch of electrolyte powder.

[0043] Example 2 Repeat Example 1, except that in step (1), the waste aluminum electrolyte is replaced with waste cathode (Al: 2.3%; F: 15.2%; Na: 12.4%; Li: 1.02%; K: 0.3%).

[0044] The purity of the obtained aluminum fluoride product was found to be 98.5% upon testing.

[0045] Comparative Example 1 Repeat Example 1, except that: in step (3), no NaOH is added; and in step (5), 55.3g of aluminum fluoride product is obtained.

[0046] The purity of the obtained aluminum fluoride product was found to be 98.8% upon testing.

[0047] It is evident that even when the solution volume reaches 100 ml during evaporation and crystallization in step (3), a large amount of sodium fluoride remains in the liquid phase without precipitation, necessitating further evaporation and concentration. However, further evaporation and concentration inevitably leads to greater energy consumption, and higher concentrations of alkali increase the corrosion resistance requirements of the evaporation equipment. By adding NaOH in step (3), this invention can effectively promote the selective precipitation of sodium fluoride, reduce the amount of liquid phase evaporation during the evaporation and crystallization process, help reduce energy consumption and corrosion resistance requirements of the evaporation equipment, and ensure the purity and yield of NaF powder, laying the foundation for obtaining high-purity aluminum fluoride products in the future. At the same time, the mixed solution obtained in step (3) is rich in sodium hydroxide, which can be returned to step (2) for the alkali leaching of the next batch of waste materials without increasing the alkali consumption.

[0048] Example 3 Repeat Example 1, except that in step (3), the amount of NaOH is 40g.

[0049] The tested product yielded 57.6g of aluminum fluoride with a purity of 98.8%.

[0050] Example 4 Repeat Example 1, except that in step (3), the amount of NaOH is 80g.

[0051] The tested product yielded 62.4g of aluminum fluoride with a purity of 99.0%.

[0052] Example 5 Repeat Example 1, except that: 70.6g of aluminum sulfate is added in step (4); sulfuric acid is not added in step (5), and 76.3g of cryolite product is obtained.

[0053] XRF analysis showed that the molecular weight of the cryolite product was 2.87; phase analysis was as follows. Figure 2 As shown, the main phase is cryolite, and there are no impurity diffraction peaks, indicating that the product has high purity.

[0054] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A method for preparing fluorides from fluorine-containing waste from aluminum electrolysis, characterized in that, Includes the following steps: S1. After alkaline leaching of fluorine-containing waste from aluminum electrolysis, solid-liquid separation is performed to obtain filtrate a. During alkaline leaching, the ratio of the sum of the moles of alkali added and the moles of alkali metals in the fluorine-containing waste from aluminum electrolysis to the moles of fluorine in the alkaline leaching reaction system is 0.5-2:1; the alkali is one or more of NaOH, KOH, and their hydrates; during alkaline leaching, water is added to control the initial liquid-to-solid ratio at 8-40 ml / g; during alkaline leaching, the reaction is stirred at 30-100℃ for 1-4 hours. S2. Evaporate and crystallize the filtrate a to obtain a crystal slurry; then add NaOH to the crystal slurry so that the initial concentration of NaOH in the crystal slurry solution reaches 10-20 mol / L. After stirring and reacting, separate the solid and liquid, wash, and obtain a filter cake. The volume of the crystal slurry obtained by evaporation and crystallization is 1 / 28 to 1 / 22 of the volume of filtrate a. S3. After the filter cake is mixed evenly with the reactant, it is calcined and crushed to obtain the calcined product. The reactants are one or more of aluminum sulfate, aluminum chloride, aluminum nitrate and their hydrates; and the mixture is calcined at 450-500℃ for 2-3 hours. S4. After leaching the roasted product, the solid-liquid separation is performed, followed by washing and drying to obtain the fluoride product. In S4, when the molar ratio of the total amount of fluorine to the total amount of aluminum in the mixture of filter cake and reactant in S3 is 2-3:1, the calcined product is acid-leached, then separated into solid and liquid, washed, and dried to obtain aluminum fluoride product. When the molar ratio of the total amount of fluorine to the total amount of aluminum in the mixture of filter cake and reactant in S3 is 5-6.5:1, the calcined product is soaked in water, then separated into solid and liquid, washed, and dried to obtain cryolite product.

2. The method according to claim 1, characterized in that, In S1, the fluorine-containing waste from aluminum electrolysis is one or more of the following generated during the aluminum electrolysis process: waste aluminum electrolyte, overhaul slag, waste cathode, carbon slag, anode covering material, trench material, and aluminum ash. And / or, the particle size of fluorine-containing waste from aluminum electrolysis is <0.5mm.

3. The method according to claim 1, characterized in that, In S1, during alkaline leaching, the ratio of the sum of the number of moles of alkali added and the number of moles of alkali metal in the aluminum electrolysis fluorine-containing waste to the number of moles of fluorine in the alkaline leaching reaction system is 1-1.5:

1.

4. The method according to claim 1, characterized in that, In S2, NaOH is added to the crystal slurry so that the initial concentration of NaOH in the crystal slurry solution reaches 15-18 mol / L; And / or, the filtrate b obtained from solid-liquid separation and the washing solution obtained from washing are mixed to obtain a mixture; the mixture is returned to the alkaline leaching step for reuse.

5. The method according to claim 4, characterized in that, Once the sodium aluminate content in the mixture reaches saturation, calcium hydroxide is added to remove fluoride, followed by filtration. Then, carbon dioxide is bubbled into the filtrate c to adjust the pH of the solution to 7-10, and the solution is filtered again to obtain aluminum hydroxide product.

6. The method according to claim 4, characterized in that, In S2, stir the reaction for 20-40 minutes.

7. The method according to any one of claims 1-6, characterized in that, Before S3, there is also a step of drying the filter cake.

8. The method according to any one of claims 1-6, characterized in that, In S3, the molar ratio of the total amount of fluorine to the total amount of aluminum in the mixture of filter cake and reactant is 2-3:1 or 5-6.5:

1. And / or, the particle size of the calcined product is ≤100 mesh.

9. The method according to claim 8, characterized in that, In the filter cake and reactants, the molar ratio of the total amount of fluorine to the total amount of aluminum is 2.4-2.6:1 or 5.5-6:

1.

10. The method according to any one of claims 1-6, characterized in that, In S4, during leaching, stir and leach for 10-60 minutes at 50-90℃; And / or, during leaching, control the initial liquid-to-solid ratio of the reaction system to be 1-5 ml / g; And / or, during acid leaching, an inorganic acid is added to maintain the pH of the reaction system <1; The inorganic acid is one or more of hydrochloric acid, sulfuric acid, and nitric acid.

11. The method according to any one of claims 1-6, characterized in that, Add alkali to the filtrate obtained from solid-liquid separation in S4, adjust the pH value to 5-9, filter, and evaporate and crystallize the resulting filtrate d to obtain sulfate and mother liquor.

12. The method according to claim 11, characterized in that, When the mother liquor contains lithium, sodium carbonate is added to the mother liquor to precipitate lithium and obtain lithium carbonate product.

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