Process method for removing phosphorus from phosphogypsum, enriching fluorine and converting calcium

Abstract

The invention discloses a phosphorus removal and fluorine enrichment calcium conversion process method for phosphogypsum, which comprises five steps of phosphogypsum crushing wet grinding and solid-liquid separation, phosphorus and fluorine element separation in washing water, phosphogypsum solid acid pickling impurity removal, low-temperature calcination and sulfur-containing gas desulfurization treatment, and is used for generating anhydrous calcium sulfate and recycling calcium and sulfur elements in phosphogypsum. In the washing water element separation process, the composite porous hydrogel is prepared, the hydrogel is composed of polyacrylonitrile and a high-entropy metal hydroxide-polyethyleneimine composite membrane on the surface, selective adsorption of phosphate ions can be achieved, fluorine elements are filtered out, and phosphorus elements and fluorine elements in washing water are efficiently separated. According to the method disclosed by the invention, phosphorus and fluorine resources are recovered at the same time on the premise of not generating other wastes, and insoluble calcium is converted into soluble calcium, so that the resource utilization of the phosphogypsum is realized.

Description

Technical Field

[0001] The invention relates to the field of resource and environmental technology, and in particular to a process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium. Background Art

[0002] Phosphogypsum is an industrial byproduct produced during the production of phosphate fertilizers. Its main component is calcium sulfate dihydrate (CaSO4·2H2O), and it also contains a small amount of harmful impurities such as phosphorus and fluorine. The large-scale storage of phosphogypsum will not only occupy land resources, but also cause serious pollution to soil and water bodies. In particular, the phosphorus and fluoride ions in it may cause eutrophication of water bodies and environmental toxicity problems, but its potential resource utilization value cannot be ignored. The calcium and sulfur elements rich in phosphogypsum can be converted into valuable industrial materials such as building gypsum, sulfuric acid and other calcium-based compounds through scientific process treatment. Through reasonable treatment technology, phosphogypsum can not only be harmlessly treated, but also be turned into treasure, fully recover the useful components in it, promote the recycling of resources, and have significant economic and environmental benefits. At present, the treatment methods of phosphogypsum mainly include stockpiling, cement clinker substitution, production of building gypsum, co-production of sulfuric acid and use for soil improvement. However, each of these methods has its own shortcomings. Although the stockpiling method is simple, it occupies a large amount of land and has the risk of environmental pollution; the application of cement clinker substitution and building gypsum production is limited, it is difficult to digest large-scale phosphogypsum, and impurities affect product quality; although the co-production of sulfuric acid can recover sulfuric acid, the process is complex, energy consumption is high, equipment investment is large, and it may cause secondary pollution; the market demand for soil improvement is limited. Therefore, it is urgent to develop a more economical, efficient and environmentally friendly treatment method. Summary of the invention

[0003] Technical problem to be solved: The technical problem to be solved by the present invention is to provide a process method for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium, aiming to solve the problem of harmless treatment of phosphogypsum, and at the same time recycle the calcium and sulfur elements in the phosphogypsum to realize waste utilization.

[0004] Technical solution: A process for removing phosphorus from phosphogypsum and enriching fluorine to calcium, comprising the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation; S2. Adding the composite porous hydrogel to the obtained liquid, stirring it thoroughly to adsorb the phosphorus element and filtering it to separate it, respectively, to obtain a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. Drying the obtained solid, adding it to the acidic leaching solution, stirring and filtering, repeating 5 to 7 times to obtain phosphogypsum solid; S4. Low-temperature calcining the phosphogypsum solid to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a by-product. Preferably, the ratio of phosphogypsum to water in step S1 is 1:3-5. Preferably, the method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to copolymerize acrylonitrile and acrylamide, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water according to a proportion, dropping a strong base to a pH of 9 to 11, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. Dissolve polyethyleneimine and glutaraldehyde in water, add high entropy metal hydroxide and disperse them evenly by ultrasonication, coat them on the polyacrylonitrile porous hydrogel, heat and cross-link and solidify them to form a composite film, and obtain a composite porous hydrogel. Preferably, in step S11, the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:50-80:20-50, and the heating temperature is 55-65°C. Preferably, the high entropy metal hydroxide in step S12 is composed of any five or more of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, lanthanum hydroxide, and cerium hydroxide in equal molar ratios. Preferably, in step S13, the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1-2:5-10, and the heating temperature is 45-60°C. Preferably, the ratio of water to hydrogel in step S2 is 100:1-3. Preferably, the extracting solution in step S3 comprises any one or more of sulfuric acid solution, citric acid solution and oxalic acid solution, and the pH of the extracting solution is 2-4. Preferably, the drying temperature in step S3 is 70-150° C., and the drying time is 5-35 hours. Preferably, the calcination temperature in step S4 is 100-200° C., and the calcination time is 1-5 h. Beneficial effects: The process for removing phosphorus from phosphogypsum and enriching fluorine into calcium according to the present invention first removes phosphorus and fluorine impurities in the phosphogypsum by a water washing method, and separates phosphorus elements in the washing water by adsorption by hydrogel, and simultaneously calcines the washed phosphogypsum at a low temperature, finally obtaining anhydrous calcium sulfate, a fluorine-rich liquid and a phosphorus-enriched hydrogel. The washing water of phosphogypsum contains abundant soluble phosphorus and fluorine. Selective adsorption of phosphorus, separation of phosphorus and fluorine and their recycling are important environmental protection and resource recycling issues. 3- The material with strong selective adsorption is realized by various adsorption effects, and the operation is simple, the design is simple, the cost is low, and the recovery rate of low-concentration phosphorus solution is high. It is one of the commonly used phosphorus treatment processes. There are a large number of amino groups on the surface of polyacrylonitrile, which can effectively adsorb negatively charged phosphate anions through electrostatic action, and it is prepared into a porous hydrogel, increasing the specific surface area, and can effectively improve the adsorption amount, and convenient filtration and separation. However, polyacrylonitrile has a low selectivity for phosphate ions. In order to solve this problem, the present invention prepares a high-entropy metal hydroxide-polyethyleneimine composite membrane on the surface of the hydrogel, and by adjusting the pore size structure of the polyethyleneimine membrane, it is possible to achieve high-selectivity filtration of phosphate ions, and the high-entropy metal hydroxide has a layered structure, a high specific surface area, and the characteristics of exchangeable anions, and the selectivity of oxygen-containing anions is better than that of oxygen-free anions, and is doped into the polyethyleneimine filter membrane, and can selectively adsorb phosphate ions while filtering out fluoride ions, further enhancing the selectivity and adsorption of the membrane, and efficiently separating phosphorus and fluorine in the washing liquid. After washing, the solid phosphogypsum is acid-washed, and multiple stirring and filtering processes can effectively remove the metal impurities therein, which helps to reduce the impact of these impurities on the calcined product and improve the purity of the final product. After acid washing, long-term drying at medium and low temperatures is used to avoid the problems of material decomposition and excessive energy consumption caused by high temperature. Under the premise of ensuring the integrity of the material, the free water and part of the crystal water in the phosphogypsum can be fully removed, providing a suitable material state for the subsequent calcination process. The dried phosphogypsum is calcined at low temperatures to avoid material decomposition caused by high temperature, and effectively decompose the calcium sulfate in the phosphogypsum to extract the required calcium element. The sulfur-containing flue gas generated by the calcination of phosphogypsum is desulfurized, which can efficiently capture sulfur oxides and convert them into valuable sulfur compounds, realize efficient recovery of sulfur elements, and reduce the pollution of sulfur oxides to the environment, further realizing the harmless treatment and resource utilization of phosphogypsum. Compared with the prior art, the present invention has the following advantages and positive effects: The present invention recovers phosphorus and fluorine resources at the same time without generating other wastes, and converts sparingly soluble calcium into soluble calcium, thereby realizing resource utilization of phosphogypsum. The present invention provides a composite porous hydrogel, which can selectively adsorb phosphorus in phosphogypsum washing water, thereby realizing efficient separation and recovery of phosphorus and fluorine in water. The present invention effectively decomposes calcium sulfate in phosphogypsum through a low-temperature calcination method to extract the required calcium element, while efficiently capturing sulfur oxides and converting them into valuable sulfur compounds, thereby achieving efficient recovery of sulfur elements. DETAILED DESCRIPTION In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. Specific preferred examples are as follows: Embodiment 1: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:3; S2. adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:1, stirring thoroughly to adsorb phosphorus and filtering to separate, to obtain a fluorine-rich liquid and a phosphorus-enriched hydrogel, respectively; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:5, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Embodiment 2: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:1, stirring thoroughly to adsorb phosphorus and filtering to separate, to obtain a fluorine-rich liquid and a phosphorus-enriched hydrogel, respectively; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:5, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Embodiment 3: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:5; S2. adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:1, stirring thoroughly to adsorb phosphorus and filtering to separate, to obtain a fluorine-rich liquid and a phosphorus-enriched hydrogel, respectively; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:5, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Embodiment 4: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:5, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Embodiment 5: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:3, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:5, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Embodiment 6: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and uniformly dispersing by ultrasonication, coating on polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:7, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Embodiment 7: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:9, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Embodiment 8: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:10, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Embodiment 9: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:9, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and cerium hydroxide in equal molar ratios. Embodiment 10: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:9, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, zirconium hydroxide, lanthanum hydroxide and cerium hydroxide in equal molar ratios. Embodiment 11: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:9, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, lanthanum hydroxide and cerium hydroxide in equal molar ratios. Embodiment 12: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 130°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:9, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, lanthanum hydroxide and cerium hydroxide in equal molar ratios. Embodiment 13: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 170°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:9, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, lanthanum hydroxide and cerium hydroxide in equal molar ratios. Embodiment 14: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 200°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:9, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, lanthanum hydroxide and cerium hydroxide in equal molar ratios. In order to further illustrate the technical effect of the present invention, the present invention also provides a comparative example, which is as follows: Comparative Example 1: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crush the phosphogypsum and sieve to remove large particles of impurities, add water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:2; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2100:1, stirring the mixture to adsorb phosphorus and filtering the mixture to obtain a fluorine-rich liquid and a phosphorus-enriched hydrogel, respectively; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:5, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Comparative Example 2: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2100:0.5, stirring the mixture to adsorb phosphorus and filtering the mixture to obtain a fluorine-rich liquid and a phosphorus-enriched hydrogel, respectively; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:5, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide and lanthanum hydroxide in equal molar ratios. Comparative Example 3: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. adding a porous hydrogel to the obtained liquid, with the ratio of water to the hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, to obtain a fluorine-rich liquid and a phosphorus-enriched hydrogel, respectively; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the porous hydrogel in step S2 comprises the following steps: Acrylonitrile and acrylamide were dissolved in N,N-dimethylformamide, and ammonium persulfate was added and heated to 60°C to copolymerize acrylonitrile and acrylamide. The mass ratio of ammonium persulfate, acrylonitrile and acrylamide was 1:80:20. The mixture was then freeze-dried to obtain a polyacrylonitrile porous hydrogel. Comparative Example 4: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. Dissolve polyethyleneimine and glutaraldehyde in water, and coat them on the polyacrylonitrile porous hydrogel. The mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5. Heat to 55°C for cross-linking and curing to form a film to obtain a composite porous hydrogel. Comparative Example 5: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 100°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:9, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide and zirconium hydroxide in equal molar ratios. Comparative Example 6: A process for removing phosphorus from phosphogypsum and enriching fluorine to convert it into calcium comprises the following steps: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation, the ratio of phosphogypsum to water is 1:4; S2. Adding a composite porous hydrogel to the obtained liquid, with the ratio of water to hydrogel being 100:2, stirring thoroughly to adsorb phosphorus and filtering to separate, respectively obtaining a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid was dried at a drying temperature of 100 ° C for 20 h, added to a sulfuric acid solution having a pH of 3, stirred and filtered, and repeated 6 times to obtain a phosphogypsum solid; S4. The phosphogypsum solid is calcined at a low temperature of 300°C for 5 hours to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a byproduct; The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to 60°C to copolymerize acrylonitrile and acrylamide, wherein the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:80:20, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water in proportion, dropping a strong base until the pH is 10, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. dissolving polyethyleneimine and glutaraldehyde in water, adding high entropy metal hydroxide and ultrasonically dispersing them uniformly, coating them on the polyacrylonitrile porous hydrogel, wherein the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1.5:9, heating to 55°C for cross-linking and curing to form a composite film, and obtaining a composite porous hydrogel; The high entropy metal hydroxide in step S12 is composed of ferric hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, lanthanum hydroxide and cerium hydroxide in equal molar ratios. According to JC / T 2073-2011, the phosphorus and fluorine contents in phosphogypsum before and after water washing were determined to calculate the removal rate of elements in phosphogypsum; the phosphorus and fluorine contents in the washing water before and after adsorption were determined by molybdenum blue spectrophotometry and ion selective electrode method, respectively, to evaluate the element adsorption effect of hydrogel; The whiteness of the phosphogypsum product before and after treatment was tested using a fully automatic blue light whiteness meter. The samples were tested multiple times after calibration using a black tube and a standard colorimetric plate. The average value was finally taken and the yield of anhydrous phosphogypsum was calculated. The results are shown in Tables 1 to 6. Table 1 Effect of the ratio of phosphogypsum and water in wet grinding on element removal Table 2 Effect of the ratio of hydrogel to washing water on element adsorption Table 3 Effect of composite membrane in hydrogel on element adsorption Table 4 Effect of the ratio of polyethyleneimine to high entropy metal hydroxide in hydrogel composite membrane on element adsorption Table 5 Effect of high entropy metal hydroxide components in hydrogel composite films on element adsorption Table 6 Effect of calcination temperature on the yield of anhydrous calcium sulfate prepared from phosphogypsum name Calcination temperature / ℃ Whiteness / % Yield / % Embodiment 11 100 91 82.5 Example 12 130 91 84.2 Example 13 170 91 85.6 Embodiment 14 200 91 84.8 Comparative Example 6 300 91 75.9 In summary, the present invention realizes the efficient recovery and separation of phosphorus and fluorine resources, and converts the poorly soluble calcium into soluble calcium, and the yield of anhydrous calcium sulfate reaches more than 80%, thus realizing the resource utilization of phosphogypsum.

Claims

1. A process for removing phosphorus from phosphogypsum and enriching fluorine to calcium, characterized in that: The following steps are involved: S1. crushing and sieving the phosphogypsum to remove large particles of impurities, adding water for wet grinding and solid-liquid separation; S2. Adding the composite porous hydrogel to the obtained liquid, stirring it thoroughly to adsorb the phosphorus element and filtering it to separate it, respectively, to obtain a fluorine-rich liquid and a phosphorus-enriched hydrogel; S3. The obtained solid is dried, added to the acidic extract, stirred and filtered, and repeated 5 to 7 times to obtain phosphogypsum solid; S4. The phosphogypsum solid is calcined at low temperature to obtain anhydrous calcium sulfate solid; S5. The gas generated during the calcination process is reacted with lime for desulfurization to obtain anhydrous calcium sulfate as a by-product.

2. The process for removing phosphorus from phosphogypsum and enriching fluorine to calcium according to claim 1, characterized in that: In step S1, the ratio of phosphogypsum to water is 1:3-5.

3. The process for removing phosphorus from phosphogypsum and enriching fluorine to calcium according to claim 1, characterized in that: The method for preparing the composite porous hydrogel in step S2 comprises the following steps: S11. dissolving acrylonitrile and acrylamide in N,N-dimethylformamide, adding ammonium persulfate and heating to copolymerize acrylonitrile and acrylamide, and then freeze-drying to obtain a porous polyacrylonitrile hydrogel; S12. dissolving each metal salt in water according to a proportion, dropping a strong base to a pH of 9 to 11, and precipitating a high entropy metal hydroxide with a nanosheet structure; S13. Dissolve polyethyleneimine and glutaraldehyde in water, add high entropy metal hydroxide and disperse them evenly by ultrasonication, coat them on the polyacrylonitrile porous hydrogel, heat and cross-link and solidify them to form a composite film, and obtain a composite porous hydrogel.

4. The process for removing phosphorus from phosphogypsum and enriching fluorine to calcium according to claim 3, characterized in that: In step S11, the mass ratio of ammonium persulfate, acrylonitrile and acrylamide is 1:50-80:20-50, and the heating temperature is 55-65°C.

5. The process for removing phosphorus from phosphogypsum and enriching fluorine to calcium according to claim 3, characterized in that: In step S12, the high entropy metal hydroxide is composed of any five or more of iron hydroxide, aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, lanthanum hydroxide, and cerium hydroxide in equal molar ratios.

6. The process for removing phosphorus from phosphogypsum and enriching fluorine to calcium according to claim 3, characterized in that: In step S13, the mass ratio of polyethyleneimine, glutaraldehyde and high entropy metal hydroxide is 10:1-2:5-10, and the heating temperature is 45-60°C.

7. The process for removing phosphorus from phosphogypsum and enriching fluorine to calcium according to claim 1, characterized in that: The ratio of water to hydrogel in step S2 is 100:2100:1-3.

8. The process for removing phosphorus from phosphogypsum and enriching fluorine to calcium according to claim 1, characterized in that: The extracting solution in step S3 includes any one or more of sulfuric acid solution, citric acid solution, and oxalic acid solution, and the pH of the extracting solution is 2-4.

9. The process for removing phosphorus from phosphogypsum and enriching fluorine to calcium according to claim 1, characterized in that: The drying temperature in step S3 is 70-150° C., and the drying time is 5-35 hours.

10. The process for removing phosphorus from phosphogypsum and enriching fluorine to calcium according to claim 1, characterized in that: The calcination temperature in step S4 is 100-200° C., and the calcination time is 1-5 hours.

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