Method for preparing cryolite from calcium fluoride sludge
By purifying and thermochemically converting calcium fluoride sludge, cryolite was prepared, solving the problems of fluorine resource loss and fluorite resource depletion, and realizing the efficient recycling and harmless disposal of fluorine resources.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-03-13
AI Technical Summary
In existing technologies, the treatment of calcium fluoride sludge leads to the loss of fluorine resources, occupies land resources and poses potential pollution risks, and fluorite resources are depleted, with a lack of efficient fluorine resource recovery and reuse technologies.
By purifying calcium fluoride sludge, extracting calcium fluoride-rich solids using acid leaching, thermochemically converting them into hydrogen fluoride gas, further converting them into cryolite products, and recovering byproducts, the recycling of fluorine resources is achieved.
It achieves efficient recovery and recycling of fluorine resources, provides a harmless disposal solution for calcium fluoride sludge, reduces dependence on fluorite resources, improves the utilization rate of fluorine resources, and reduces environmental pollution.
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Figure CN121651401A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of recycling and reusing fluorine-containing solid waste, and in particular to a method for preparing cryolite using calcium fluoride sludge. Background Technology
[0002] Behind the rapid development of the photovoltaic and optoelectronic semiconductor industries lies the generation of large amounts of high-concentration fluoride-containing wastewater. This wastewater mainly originates from key processes in the manufacturing of chips and solar cells, such as etching and cleaning, which commonly use fluoride-containing chemicals like hydrofluoric acid and ammonium fluoride. To meet stringent environmental emission standards, wastewater treatment companies generally employ the calcium precipitation method for deep treatment. This involves adding compound alkali calcium chloride to the wastewater, causing fluoride ions to precipitate as calcium fluoride, followed by pressure filtration to produce large quantities of calcium fluoride sludge. However, due to excessive amounts of treatment agents added during the water treatment process, its purity is far lower than that of natural fluorite. Calcium fluoride sludge presents challenges such as high recycling costs and technical difficulties. Currently, the vast majority of calcium fluoride sludge can only be disposed of as waste through landfill, which not only occupies land resources and poses a potential risk of leaching pollution but also results in a huge waste of valuable fluoride resources. How to achieve the harmless and resource-based disposal of calcium fluoride sludge has become one of the key environmental challenges restricting the green and sustainable development of this industry.
[0003] With the rapid development of global industrialization, the demand for fluorine resources, as an important strategic mineral resource, is increasing daily. Currently, fluorine resources are mainly found in fluorite and phosphate rock. Global fluorine supply still heavily relies on fluorite mining, but due to over-exploitation in recent years, fluorite reserves are dwindling, highlighting the growing shortage of fluorine resources. Finding suitable alternatives has become an urgent need for the industry. At the same time, the landfilling of calcium fluoride sludge results in the loss of fluorine resources, contradicts the concept of a circular economy, and poses a serious challenge to the sustainable development of related industries. Developing efficient fluorine recovery and reuse technologies to recover fluorine resources from industrial waste can not only alleviate the supply pressure of fluorite resources and reduce dependence on primary minerals, but also promote the green transformation and upgrading of industries such as fluorochemicals, photovoltaics, and semiconductors, possessing significant strategic importance and environmental economic value. Currently, how to overcome the technological bottlenecks in fluorine recovery and achieve high-value utilization of fluorine resources has become a hot topic and a difficult challenge in related fields. This method uses calcium fluoride sludge as raw material, performs simple purification and enrichment, and then generates hydrogen fluoride gas through thermal conversion. The hydrogen fluoride gas is further absorbed and converted to obtain cryolite, which can be used as a flux in aluminum electrolysis. This realizes the recycling of fluorine resources in calcium fluoride solids and provides a new solution for the disposal of calcium fluoride sludge. Summary of the Invention
[0004] To address the existing problem of fluorine resource shortage, particularly the fluorine loss during the disposal of calcium fluoride sludge, this invention aims to provide a method for preparing cryolite from calcium fluoride sludge. This method purifies the calcium fluoride sludge, extracts fluorine through chemical conversion, and absorbs hydrogen fluoride gas to convert it into cryolite, achieving the recycling of fluorine resources in the calcium fluoride sludge. Simultaneously, it yields valuable byproducts, providing a new approach to the disposal of calcium fluoride sludge.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: acid leaching and purification of calcium fluoride sludge to obtain calcium fluoride-rich solid; thorough mixing of the above solid with concentrated sulfuric acid for thermochemical conversion to obtain hydrogen fluoride gas; passing the hydrogen fluoride gas into an alkaline solution containing aluminum and sodium sources for conversion; solid-liquid separation, washing, and drying to obtain cryolite product; washing and drying the remaining solid residue to obtain gypsum by-product; and absorbing and converting the tail gas with alkaline solution to obtain fluorine-containing by-product.
[0006] A method for accurately determining the calcium fluoride content in calcium fluoride sludge includes the following steps: (1) After drying and grinding the calcium fluoride sludge, react it with one of hydrochloric acid, nitric acid, or acetic acid at a concentration of 0.5–3 mol / L, controlling the solid-liquid mass ratio at 1:(2–4), and react at 20–40℃ for 0.5–2 hours to obtain calcium fluoride-rich solid. Taking hydrochloric acid as an example, the main reaction equation is: CaCO3 + 2HCl → CaCl2 + H2O + CO2 Ca(OH)₂ + 2HCl → CaCl₂ + 2H₂O (2) The calcium fluoride solid obtained in step (1) is dried at 100-120℃ to control the solid moisture content to be less than 10wt%, and then pulverized and sieved to control the particle size of the material to be between 100-200μm. The treated solid is reacted with concentrated sulfuric acid at a mass ratio of 1:(1.5-5) at 150-250℃ for 1-4 hours to obtain hydrogen fluoride gas and solid residue. The main reaction equation is as follows: CaF₂ + H₂SO₄ → CaSO₄ + 2HF (3) The hydrogen fluoride gas obtained in step (2) is passed into an alkaline solution containing a 5%–15% sodium aluminate solution and a 5%–15% sodium hydroxide solution. Solid-liquid separation is achieved by reacting the mixture with deionized water or ethanol until the washing solution is neutral. The solution is then dried at 100–120°C to obtain cryolite. The main reaction equation is: 6HF+NaAlO2+2NaOH→Na3AlF6+4H2O (4) The residual tail gas from step (3) is passed into a sodium hydroxide solution with a mass fraction of 10%–30% to obtain sodium fluoride as a byproduct. The main reaction equation is as follows: NaOH + HF → NaF + H₂O (5) Wash the remaining solid residue from step (2) with water until neutral, and dry it at 100-120°C to obtain gypsum byproduct.
[0007] The present invention has the following beneficial effects: 1. Through the acid leaching treatment in step (1), soluble calcium salt impurities such as calcium carbonate and calcium hydroxide in calcium fluoride sludge can be efficiently dissolved and removed, resulting in highly enriched solid calcium fluoride, which increases the subsequent production of hydrogen fluoride gas and greatly improves the fluorine conversion rate, making the subsequent thermochemical conversion more complete.
[0008] 2. Fluorine resources in calcium fluoride sludge can be extracted in one step and converted into high-value cryolite products in the form of hydrogen fluoride. This process is simple, the conversion conditions are mild, and it has strong practicality.
[0009] 3. The hydrogen fluoride gas that is not completely converted during the conversion process is subsequently absorbed and converted to obtain sodium fluoride byproduct, which realizes the full recovery and utilization of fluorine resources. While being environmentally friendly, it greatly improves the utilization rate of fluorine. The remaining solid residue is simply treated to obtain gypsum byproduct, which can be used in the cement industry.
[0010] 4. This method provides a feasible alternative to fluorite minerals in the fluorochemical industry and solves the problem of difficult calcium fluoride sludge disposal. The process is simple, low-cost, clearly controllable, and has a high fluorine recovery rate, demonstrating strong industrial feasibility. Attached Figure Description
[0011] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the process for preparing cryolite using calcium fluoride sludge as described in this invention.
[0012] Figure 2 This is an XRD pattern of the cryolite product obtained in an example of a method for preparing cryolite using calcium fluoride sludge according to the present invention. Detailed Implementation
[0013] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.
[0014] Example 1
[0015] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 0.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 200µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:1.5 and heat-treated at 150℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 30.64g of cryolite product with a purity of 98.21% and a yield of 73.66%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 7.45g of sodium fluoride. The remaining solid residue was washed and dried to obtain 95.02g of gypsum material.
[0016] Example 2
[0017] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 200µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:1.5 and heat-treated at 150℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 32.46g of cryolite product with a purity of 98.53% and a yield of 76.33%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 8.92g of sodium fluoride. The remaining solid residue was washed and dried to obtain 98.47g of gypsum material.
[0018] Example 3
[0019] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 3mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 200µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:1.5 and heat-treated at 150℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 32.09g of cryolite product with a purity of 98.44%, a yield of 76.41%. The remaining tail gas was absorbed with a 10% sodium hydroxide solution, and solid-liquid separation was performed. After washing and drying, 9.40g of sodium fluoride was obtained. The remaining solid residue was washed and dried to obtain 98.57g of gypsum material.
[0020] Example 4
[0021] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 150µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:1.5 and heat-treated at 150℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 33.40g of cryolite product with a purity of 98.73% and a yield of 79.52%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 9.78g of sodium fluoride. The remaining solid residue was washed and dried to obtain 102.58g of gypsum material.
[0022] Example 5
[0023] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:1.5 and heat-treated at 150℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 34.30g of cryolite product with a purity of 98.82%, a yield of 81.67%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 10.04g of sodium fluoride. The remaining solid residue was washed and dried to obtain 105.35g of gypsum material.
[0024] Example 6
[0025] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:3 and heat-treated at 150℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 35.52g of cryolite product with a purity of 98.82%, a yield of 84.57%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 10.40g of sodium fluoride. The remaining solid residue was washed and dried to obtain 109.10g of gypsum material.
[0026] Example 7
[0027] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:5 and heat-treated at 150℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 35.75g of cryolite product with a purity of 98.91%, a yield of 85.11%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 10.47g of sodium fluoride. The remaining solid residue was washed and dried to obtain 109.79g of gypsum material.
[0028] Example 8
[0029] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:3 and heat-treated at 180℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 36.22g of cryolite product with a purity of 98.97%, a yield of 86.23%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 10.608g of sodium fluoride. The remaining solid residue was washed and dried to obtain 111.23g of gypsum material.
[0030] Example 9
[0031] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:3 and heat-treated at 220℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 36.77g of cryolite product with a purity of 98.97% and a yield of 87.56%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 10.77g of sodium fluoride. The remaining solid residue was washed and dried to obtain 112.95g of gypsum material.
[0032] Example 10
[0033] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:3 and heat-treated at 250℃ for 2h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 36.80g of cryolite product with a purity of 98.95%, a yield of 87.61%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 10.78g of sodium fluoride. The remaining solid residue was washed and dried to obtain 113.02g of gypsum material.
[0034] Example 11
[0035] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:3 and heat-treated at 220℃ for 3h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 37.61g of cryolite product with a purity of 98.95% and a yield of 89.55%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 11.02g of sodium fluoride. The remaining solid residue was washed and dried to obtain 115.52g of gypsum material.
[0036] Example 12
[0037] 100g of fluoride-containing sludge A (calcium fluoride content 60%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:3 and heat-treated at 220℃ for 4h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 37.62g of cryolite product with a purity of 98.95%, a yield of 89.59%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 11.03g of sodium fluoride. The remaining solid residue was washed and dried to obtain 115.57g of gypsum material.
[0038] Example 13
[0039] 100g of fluoride-containing sludge B (calcium fluoride content 65%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:3 and heat-treated at 220℃ for 3h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 41.00g of cryolite product with a purity of 98.95%, a yield of 90.11%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 12.01g of sodium fluoride. The remaining solid residue was washed and dried to obtain 125.93g of gypsum material.
[0040] Example 14
[0041] 100g of fluoride-containing sludge C (calcium fluoride content 70%) was dried at 110℃ to a moisture content of 10%, then pulverized and treated with 1.5mol / L hydrochloric acid at a mass ratio of 1:2 at 20℃ for 1h. The resulting calcium fluoride solid was dried, pulverized, and sieved to control the particle size to 100µm. It was then mixed with concentrated sulfuric acid at a mass ratio of 1:3 and heat-treated at 220℃ for 3h. The generated hydrogen fluoride gas was passed into a mixed solution of 10% sodium aluminate and 10% sodium hydroxide. Solid-liquid separation was performed, and the mixture was washed with anhydrous ethanol until the washing liquid was neutral. The mixture was then dried at 110℃ to constant weight, yielding 44.70g of cryolite product with a purity of 98.95%, a yield of 91.23%. The remaining exhaust gas was absorbed with a 10% sodium hydroxide solution. After solid-liquid separation, the solid was washed and dried to obtain 13.09g of sodium fluoride. The remaining solid residue was washed and dried to obtain 137.30g of gypsum material.
[0042] The present invention and its embodiments have been described above. This description is not restrictive. In short, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the spirit of the present invention, such design should fall within the protection scope of the present invention.
Claims
1. A method for preparing cryolite using calcium fluoride sludge, comprising the following steps: (1) The calcium fluoride sludge was purified by acid leaching to obtain calcium fluoride-rich solid; (2) The calcium fluoride solid obtained in step (1) is mixed with concentrated sulfuric acid and reacted under heating conditions to generate hydrogen fluoride gas and solid residue. (3) The hydrogen fluoride gas generated in step (2) is passed into an alkaline solution containing aluminum and sodium sources for absorption reaction. After solid-liquid separation, the resulting solid is washed and dried to obtain cryolite product. (4) The residual tail gas after step (3) is absorbed by an alkaline solution to obtain a fluorine-containing byproduct; (5) The solid residue obtained in step (2) is washed and dried to obtain a byproduct mainly composed of calcium sulfate.
2. The method according to claim 1, characterized in that, The acid used in step (1) for acid leaching and purification is one of hydrochloric acid, nitric acid, or acetic acid.
3. The method according to claim 1, characterized in that, In step (1), the solid-liquid mass ratio of the acid leaching purification is 1:(2-4), the acid concentration is 0.5-3 mol / L, the reaction temperature is 20-40℃, and the reaction time is 0.5-2 hours.
4. The method according to claim 1, characterized in that, In step (1), after acid leaching and purification, the obtained solid is further dried and pulverized; the drying temperature is 100-120℃ until the solid moisture content is less than 10wt%; the particle size of the pulverized material is 100-200μm.
5. The method according to claim 1, characterized in that, In step (2), the mass ratio of the calcium fluoride solid to concentrated sulfuric acid is 1:(2-5); the reaction temperature is 150-250℃; and the reaction time is 1-4 hours.
6. The method according to claim 1, characterized in that, In step (3), the aluminum source is sodium aluminate and the sodium source is sodium hydroxide; in the alkaline solution, the mass fraction of sodium aluminate is 5% to 15% and the mass fraction of sodium hydroxide is 5% to 15%.
7. The method according to claim 1, characterized in that, In step (3), the washing is performed using deionized water or ethanol until the washing solution is neutral, and the drying is performed at 100~110℃ until constant weight.
8. The method according to claim 1, characterized in that, In step (4), the alkaline solution is a sodium hydroxide solution with a mass fraction of 10% to 30%; the fluorine-containing byproduct is sodium fluoride.
9. The method according to claim 1, characterized in that, In step (5), the washing is done by washing with water until neutral; the drying temperature is 100-110°C.