Method for preparing calcium sulfate whiskers by ultrasonically leaching ardealite

Abstract

The invention relates to a method for preparing calcium sulfate whiskers by ultrasonically leaching ardealite, which comprises the following steps: S1, levigating ardealite, mixing with a leaching agent, ultrasonically leaching, and filtering to obtain filtrate; wherein the leaching agent comprises an acid and a salt compound, and the hydrogen ion concentration of the leaching agent is 2-8 mol / L; and S2, adding a silane coupling agent solution into the filtrate, purifying, crystallizing, separating and drying to obtain the calcium sulfate whisker. According to the method, the phosphogypsum is finely ground, the particle size of the phosphogypsum is reduced, the contact area of the phosphogypsum and the leaching agent is increased, the solubility of the phosphogypsum is increased by adopting an ultrasonic leaching method, the primary yield of the whisker product is improved, impurity components in the phosphogypsum are deeply removed by adopting the silane coupling agent, and the calcium sulfate whisker with the primary yield reaching 70% or above and the purity reaching 98% or above is obtained. And the method has the advantages of simple steps and low energy consumption, and can reduce the phosphogypsum treatment cost and reduce the environmental pollution generated by phosphogypsum treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste resource utilization, and in particular relates to a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum. Background Art

[0002] Phosphogypsum is a solid waste produced by the wet phosphoric acid process. When phosphoric acid is produced by the wet process, 4.5-5.5 tons of phosphogypsum are produced for every ton of phosphoric acid produced. Phosphogypsum contains a large amount of pollutants such as phosphorus, fluorine, silicon, organic matter and heavy metals, which seriously hinder the resource utilization of phosphogypsum. Therefore, it is necessary to remove impurities to better improve the utilization rate of phosphogypsum.

[0003] On the other hand, calcium sulfate whiskers are fibrous or needle-shaped single crystals, which have a series of advantages such as high temperature resistance, chemical corrosion resistance, strong flame retardancy, extremely high elastic modulus, strong affinity with high molecular polymers, and non-toxicity. They have been widely used in friction materials, asphalt materials, rubber, plastics, PVC and other fields. Using phosphogypsum to prepare calcium sulfate whiskers is one of the most promising ways to consume phosphogypsum.

[0004] Patent CN117758370A discloses "a method for preparing calcium sulfate hemihydrate whiskers using phosphogypsum under normal pressure", wherein phosphogypsum particles are obtained through cumbersome processes such as washing, drying, calcining and crushing, and the crushed granular phosphogypsum is added to a mixed solution of 10%-20% by mass of MgCl2 and 2.5%-7.5% by mass of sulfuric acid at a solid-liquid ratio of 1:5-1:15, heated to 90 ℃-98 ℃, stirred for 1 h-6 h, filtered, washed with boiling water 3 times, washed with anhydrous ethanol once, and the filter cake was placed in a 45 ℃ oven to dry, and phosphogypsum calcium sulfate hemihydrate whiskers with an aspect ratio of 43-130 were obtained. The entire process is washed and dried multiple times, the process is cumbersome, and the washing water and washing ethanol are difficult to handle, and the purity of the calcium sulfate hemihydrate whiskers is not clearly stated. Patent CN118598093A discloses "a method for preparing iron phosphate and calcium sulfate whiskers from phosphogypsum", which obtains iron phosphate dihydrate and calcium sulfate dihydrate whiskers by crushing, acid addition, iron supplementation, low-temperature thermal desorption and high-temperature calcination. The low-temperature thermal desorption has high requirements on equipment, and the formation of calcium sulfate dihydrate whiskers requires multiple washing and impurity removal. In addition, there is a high-temperature calcination link, which is a complex process and high energy consumption, which is an unavoidable problem of this method. Although the above invention has made significant contributions to the purification of phosphogypsum, it has the disadvantages of complex post-processing, high energy consumption of high-temperature calcination, and cumbersome production steps.

[0005] At present, the simplest method for preparing calcium sulfate whiskers using phosphogypsum is the atmospheric pressure acidification method. However, due to the low solubility of calcium sulfate in water and the high impurity content of phosphogypsum, there are two major difficulties in preparing calcium sulfate whiskers using the atmospheric pressure acidification method, namely: the primary yield is less than 70%, and the purity of the whisker product is difficult to meet the standard requirements (greater than 98%). Summary of the invention

[0006] The purpose of the present invention is to overcome the above technical deficiencies, provide a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, and solve the technical problems of low yield and purity of calcium sulfate whiskers in the prior art.

[0007] In order to achieve the above technical purpose, the technical solution provided by the present invention is: In a first aspect, the present invention provides a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, comprising the following steps: S1, grinding the phosphogypsum and mixing it with a leaching agent, filtering it after ultrasonic leaching to obtain a filtrate; wherein the leaching agent includes an acid and a salt compound, and the hydrogen ion concentration of the leaching agent is 2 mol / L to 8 mol / L; S2, adding a silane coupling agent solution to the filtrate, purifying, crystallizing, separating and drying to obtain calcium sulfate whiskers.

[0008] Compared with the prior art, the beneficial effects of the present invention include: The invention grinds phosphogypsum to reduce its particle size, increases the contact area with the leaching agent, adopts an ultrasonic leaching method to increase the solubility of phosphogypsum, improves the primary yield of the whisker product, and adopts a silane coupling agent to deeply remove impurity components in the phosphogypsum, so as to obtain calcium sulfate whiskers with a primary yield of more than 70% and a purity of more than 98%. The invention has simple steps and low energy consumption, can reduce the cost of phosphogypsum treatment, and can reduce the environmental pollution caused by the phosphogypsum treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a schematic diagram of the process of preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum; Figure 2 This is a product photo of calcium sulfate dihydrate whisker of Example 6; Figure 3 The morphology of the calcium sulfate dihydrate whisker of Example 6 under a microscope; Figure 4 This is the XRD pattern of the sample of Example 6. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0011] In view of the defects of low yield and purity of calcium sulfate whisker preparation in the prior art, the present invention provides a method for preparing calcium sulfate whisker by ultrasonic leaching of phosphogypsum, which uses ultrasonic leaching to increase the solubility of phosphogypsum and improve the primary yield of whisker products; uses silane coupling agent to deeply remove impurities in phosphogypsum, and achieves a primary yield of more than 70% and a purity of ≥98% of calcium sulfate dihydrate whisker, which meets the requirements of DB43 / T1155-2016; and the present invention has simple steps and low energy consumption, which can reduce the cost of phosphogypsum treatment and reduce the environmental pollution caused by phosphogypsum treatment. The prepared calcium sulfate whisker can be used as reinforcing fiber for composite materials in the aerospace and automotive industries, realizing resource recycling; the present invention can not only realize the efficient, harmless and resource utilization of phosphogypsum, but also effectively promote the high unity of environmental benefits, economic benefits and social benefits. At the same time, it also has important practical significance for promoting the sustainable green development of the phosphorus chemical industry.

[0012] First, see Figure 1 The present invention provides a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, comprising the following steps: S1. Grind the phosphogypsum and mix it with a leaching agent, perform ultrasonic leaching and filter to obtain a filtrate; wherein the leaching agent includes an acid and a salt compound, and the hydrogen ion concentration of the leaching agent is 2 mol / L to 8 mol / L; S2. Add silane coupling agent solution to the filtrate, and obtain calcium sulfate whiskers through purification, crystallization, separation and drying.

[0013] Preferably, in step S1, the particle size of the ground phosphogypsum is 0.075-0.15 mm, accounting for 60%-80%.

[0014] Further preferably, the particle size distribution of the phosphogypsum is concentrated in the range of 37.5 μm to 400 μm; and the grinding time of the phosphogypsum is 8 min to 15 min.

[0015] Preferably, in step S1, the acid in the leaching agent includes any one of hydrochloric acid, sulfuric acid, nitric acid, and citric acid, or a combination of at least two thereof, and the salt compound includes any one of chloride, sulfate, nitrate, and citrate, or a combination of at least two thereof. In the present invention, the inorganic acid or organic acid is mixed with the salt in a certain ratio to obtain the leaching agent, and the raw material source is wide and the cost is low.

[0016] Preferably, in step S1, the molar ratio of the acid to the salt compound in the leaching agent is (10-20):1.

[0017] Preferably, in step S1, the mass ratio of the ground phosphogypsum to the leaching agent is 1:(8-12).

[0018] Preferably, in step S1, the filtration after ultrasonic leaching is heating and stirring under ultrasound, and then filtering while hot; the conditions for ultrasonic leaching include: ultrasonic frequency of 35 Hz to 45 Hz, heating temperature of 60°C to 100°C, and stirring time of 70 min to 120 min.

[0019] Preferably, in step S2, the mass concentration of the silane coupling agent solution is 3% to 10%.

[0020] Preferably, in step S2, the silane coupling agent includes A-151. In the present invention, by adding the silane coupling agent, the vinyl group in the silane coupling agent has an adsorption effect on impurities such as Si and organic matter in the solution.

[0021] Preferably, in step S2, the mass ratio of the silane coupling agent to the ground phosphogypsum is 1:(10-20).

[0022] Preferably, in step S2, the purification and crystallization is performed by heating and stirring at 75°C to 85°C for 0.5 h to 1 h, filtering while hot, and cooling naturally to precipitate crystals.

[0023] Preferably, in step S2, separation is performed by filtration, and drying is performed by drying.

[0024] More preferably, the drying is carried out at 40-46° C. for 7.5-9 hours.

[0025] The present invention is further described in detail below through specific examples. The main chemical components of the phosphogypsum used are SO337.63%, CaO 26.44%, SiO27.17%, P2O51.88%, F 1.72%, K2O 0.54%, Al2O30.49%, Fe2O30.29%, Na2O 0.17%; its particle size distribution is 37.5 μm to 400 μm. The silane coupling agents used are all A-151 aqueous solutions. The drying is all done at 45°C for 8 hours.

[0026] Example 1 This embodiment provides a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, comprising the following steps: S1. Grinding: Grind the phosphogypsum to obtain a product a having a particle size distribution of 0.075-0.15 mm and accounting for 65%; Preparation of leaching agent: Mix hydrochloric acid and calcium chloride in a molar ratio of 12:1 to obtain product b with a hydrogen ion concentration of 4 mol / L; Ultrasonic extraction: product a and product b were mixed in a mass ratio of 1:10, heated and stirred at 80 °C for 70 min under a 40 Hz ultrasonic field, and filtered while hot to obtain the filtrate product c; S2. Purification and crystallization: Add a 3% silane coupling agent solution to product c at a mass ratio of silane coupling agent to product a of 1:15, heat and stir at 80 °C for 0.5 h, filter while hot, cool naturally to precipitate crystals, filter and dry to obtain calcium sulfate whiskers.

[0027] Example 2 This embodiment provides a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, comprising the following steps: S1. Grinding: Grind the phosphogypsum to obtain a product a with a particle size distribution of 0.075-0.15 mm accounting for 75%; Preparation of leaching agent: Mix hydrochloric acid and calcium chloride in a molar ratio of 12:1 to obtain product b with a hydrogen ion concentration of 4 mol / L; Ultrasonic extraction: product a and product b were mixed in a mass ratio of 1:10, heated and stirred at 80 °C for 70 min under a 40 Hz ultrasonic field, and filtered while hot to obtain the filtrate product c; S2. Purification and crystallization: Add a 3% silane coupling agent solution to product c at a mass ratio of silane coupling agent to product a of 1:15, heat and stir at 80 °C for 0.5 h, filter while hot, cool naturally to precipitate crystals, filter and dry to obtain calcium sulfate whiskers.

[0028] Example 3 This embodiment provides a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, comprising the following steps: S1. Grinding: Grind the phosphogypsum to obtain a product a with a particle size distribution of 0.075-0.15 mm accounting for 75%; Preparation of leaching agent: Mix hydrochloric acid and calcium chloride in a molar ratio of 12:1 to obtain product b with a hydrogen ion concentration of 4 mol / L; Ultrasonic extraction: product a and product b were mixed in a mass ratio of 1:10, heated and stirred at 80 °C for 90 min under a 40 Hz ultrasonic field, and filtered while hot to obtain the filtrate product c; S2. Purification and crystallization: Add a 3% silane coupling agent solution to product c at a mass ratio of silane coupling agent to product a of 1:15, heat and stir at 80 °C for 0.5 h, filter while hot, cool naturally to precipitate crystals, filter and dry to obtain calcium sulfate whiskers.

[0029] Example 4 This embodiment provides a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, comprising the following steps: S1. Grinding: Grind the phosphogypsum to obtain a product a with a particle size distribution of 0.075-0.15 mm accounting for 75%; Preparation of leaching agent: Mix hydrochloric acid and calcium chloride in a molar ratio of 12:1 to obtain product b with a hydrogen ion concentration of 4 mol / L; Ultrasonic extraction: product a and product b were mixed in a mass ratio of 1:10, heated and stirred at 80 °C for 120 min under a 40 Hz ultrasonic field, and filtered while hot to obtain the filtrate product c; S2. Purification and crystallization: Add a 3% silane coupling agent solution to product c at a mass ratio of silane coupling agent to product a of 1:15, heat and stir at 80 °C for 0.5 h, filter while hot, cool naturally to precipitate crystals, filter and dry to obtain calcium sulfate whiskers.

[0030] Example 5 This embodiment provides a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, comprising the following steps: S1. Grinding: Grind the phosphogypsum to obtain a product a with a particle size distribution of 0.075-0.15 mm accounting for 75%; Preparation of leaching agent: Mix hydrochloric acid and calcium chloride in a molar ratio of 12:1 to obtain product b with a hydrogen ion concentration of 4 mol / L; Ultrasonic extraction: product a and product b were mixed in a mass ratio of 1:10, heated and stirred at 80 °C for 90 min under a 40 Hz ultrasonic field, and filtered while hot to obtain the filtrate product c; S2. Purification and crystallization: Add a 3% silane coupling agent solution to product c at a mass ratio of silane coupling agent to product a of 1:15, heat and stir at 80 °C for 1 h, filter while hot, cool naturally to precipitate crystals, filter and dry to obtain calcium sulfate whiskers.

[0031] Example 6 This embodiment provides a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, comprising the following steps: S1. Grinding: Grind the phosphogypsum to obtain a product a with a particle size distribution of 0.075-0.15 mm accounting for 75%; Preparation of leaching agent: Mix hydrochloric acid and calcium chloride in a molar ratio of 12:1 to obtain product b with a hydrogen ion concentration of 4 mol / L; Ultrasonic extraction: product a and product b were mixed in a mass ratio of 1:10, heated and stirred at 80 °C for 90 min under a 40 Hz ultrasonic field, and filtered while hot to obtain the filtrate product c; S2. Purification and crystallization: according to the mass ratio of silane coupling agent to product a of 1:15, add 5% silane coupling agent solution to product c, heat and stir at 80 °C for 1 h, filter while hot, cool naturally to precipitate crystals, filter and dry to obtain calcium sulfate whiskers.

[0032] The actual picture of the obtained calcium sulfate whisker is as follows Figure 2 Its appearance under the microscope is as shown in Figure 3 As shown in the figure, it can be seen that the whiskers are relatively uniform and have a relatively large length diameter. Figure 4 As shown, it shows that the main component is calcium sulfate dihydrate; and there are no other impurity peaks, which means that the product purity is high.

[0033] Example 7 This embodiment provides a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, comprising the following steps: S1. Grinding: Grind the phosphogypsum to obtain a product a with a particle size distribution of 0.075-0.15 mm accounting for 75%; Preparation of leaching agent: Mix hydrochloric acid and calcium chloride in a molar ratio of 12:1 to obtain product b with a hydrogen ion concentration of 4 mol / L; Ultrasonic extraction: product a and product b were mixed in a mass ratio of 1:10, heated and stirred at 80 °C for 90 min under a 40 Hz ultrasonic field, and filtered while hot to obtain the filtrate product c; S2. Purification and crystallization: add 8% silane coupling agent solution to product c at a mass ratio of silane coupling agent to product a of 1:15, heat and stir at 80 °C for 1 h, filter while hot, cool naturally to precipitate crystals, filter and dry to obtain calcium sulfate whiskers.

[0034] Comparative Example 1 The method of this comparative example refers to the method in Example 6, except that the grinding in step S1 is not performed and the original sample is used for ultrasonic leaching.

[0035] Comparative Example 2 The method of this comparative example refers to the method in Example 6, with the only difference being that the grinding time in step S1 is different, and the grinding time of this comparative example is 20 min.

[0036] Comparative Example 3 The method of this comparative example refers to the method in Example 6, with the only difference being that the ultrasonic time in step S1 is different, and the first stirring time of this comparative example is 30 min.

[0037] Comparative Example 4 The method of this comparative example refers to the method in Example 6, with the only difference being that the ultrasonic time in step S1 is different, and the first stirring time of this comparative example is 150 min.

[0038] Comparative Example 5 The method of this comparative example refers to the method in Example 6, with the only difference being that the concentration of the silane coupling agent A-151 in step S2 is different, and the concentration of the silane coupling agent in this comparative example is 1%.

[0039] Comparative Example 6 The method of this comparative example refers to the method in Example 6, with the only difference being that the concentration of the silane coupling agent A-151 in step S2 is different, and the concentration of the silane coupling agent in this comparative example is 10%.

[0040] Comparative Example 7 The method of this comparative example refers to the method in Example 6, with the only difference being that the second stirring time in step S2 is different, and the second stirring time in this comparative example is 20 min.

[0041] Comparative Example 8 The method of this comparative example refers to the method in Example 6, with the only difference being that the second stirring time in step S2 is different, and the second stirring time in this comparative example is 2 h.

[0042] Comparative Example 9 The method of this comparative example refers to the method in Example 6, with the only difference being that the timing of adding the silane coupling agent is different. In this comparative example, the silane coupling agent is added during the ultrasonic leaching in step S1.

[0043] The products obtained in the above embodiments and comparative examples were tested for performance according to standard DB43 / T1155-2016, and the yield was calculated. The results are shown in Table 1.

[0044] Table 1 Product performance table of embodiments and comparative examples

[0045] As can be seen from Table 1, the calcium sulfate whiskers prepared by the method proposed in the present invention have high purity and high yield, with a purity of 98.43% to 99.92% and a yield of 70.23% to 82.06%, and a large aspect ratio of 65 to 71, both of which meet the aspect ratio requirements in standard DB43 / T1155-2016.

[0046] Influence of the particle size of the grinding product a: In Comparative Example 1, since the phosphogypsum is not ground and has a coarse particle size, the contact area with the leaching agent is small, which leads to a decrease in the leaching rate of the phosphogypsum and a decrease in the final yield of calcium sulfate whiskers; in Comparative Example 2, the grinding time is prolonged, the particle size of the product a is further reduced, but the further dissolution effect on the phosphogypsum is not obvious, resulting in no significant improvement in the final yield of calcium sulfate whiskers compared to Example 6.

[0047] Influence of ultrasonic time: In comparative example 3, due to the short ultrasonic time, the amount of phosphogypsum dissolved was reduced, and the final calcium sulfate whisker yield was reduced (from 81.16% to 63.15%). When the ultrasonic time was too long in comparative example 4, the ultrasonic operation had no obvious effect on the further dissolution of phosphogypsum, resulting in the final calcium sulfate whisker yield not being much improved compared with that in example 6 (from 81.16% to 81.30%).

[0048] Regarding the influence of silane coupling agent concentration: because silane coupling agent has an adsorption effect on impurities such as Si and organic matter in the solution, in Comparative Example 5, due to the low concentration of the added silane coupling agent, the impurity removal in the second stirring process was incomplete, affecting the purity of the final calcium sulfate whisker product (from 99.90% to 97.10%); while in Comparative Example 6, when the concentration of the silane coupling agent was too high, the impurity removal effect was weakened by the influence of its concentration, resulting in an insignificant increase in the purity of the final calcium sulfate whisker (from 99.90% to 99.94%), and the yield was lower than that of the 8% silane coupling agent solution in Example 7 (from 81.64% to 81.17%), so the mass concentration of the silane coupling agent solution of the present invention is 3% to 10%, preferably 3% to 8%. Similarly, the amount of silane coupling agent used will also affect the purity and yield of the obtained calcium sulfate whiskers.

[0049] Regarding the influence of the action time of the silane coupling agent: in Comparative Example 7, the second stirring time was too short (i.e., the action time of the silane coupling agent was too short), resulting in incomplete contact between the silane coupling agent and the solution during the second stirring process, resulting in incomplete impurity removal, affecting the purity of the final calcium sulfate whisker product (reduced from 99.90% to 97.20%). In Comparative Example 8, the action time was too long. At this time, the impurity removal effect of the silane coupling agent was little affected by its action time, resulting in no significant improvement in the purity of the final calcium sulfate whisker product (only increased from 99.90% to 99.94%).

[0050] Influence of the timing of adding silane coupling agent: In comparative example 9, silane coupling agent was added during ultrasound. Due to the mutual influence between the dispersion effect of ultrasound on particles and the adsorption effect of silane coupling agent, the purity and yield of the final product decreased significantly.

[0051] Therefore, the calcium sulfate whisker product obtained in the embodiment of the present invention has higher purity; using the method of the present invention can effectively reduce impurities in phosphogypsum, solve the problem of phosphogypsum storage, and improve the utilization rate and added value of phosphogypsum.

[0052] In summary, the present invention proposes a method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, using phosphogypsum as raw material, and using this method, phosphogypsum raw material can be prepared into high-purity calcium sulfate whiskers with a purity greater than 98.4%, which can solve the application limitation problems caused by low whiteness and low purity, and thus improve the added value of phosphogypsum. The present invention considers reaction time, pH, temperature, solid-liquid ratio, acid toxicity, volatility, cost, reusability, structure and properties of solid samples, loss and recovery of materials, safety and environmental protection from multiple angles, through continuous testing and optimization, using ultrasonic leaching, greatly improving the efficiency and purity of calcium sulfate preparation. At the same time, the added silane coupling agent can further remove soluble impurities and further improve the purity of calcium sulfate. The present invention does not require complex equipment or high-pressure conditions, is simple and convenient to operate, is suitable for laboratory-scale preparation, and is also conducive to industrial production. Compared with other complex preparation methods, the equipment and materials used in the present invention are of lower cost and more economical; the present invention can obtain a higher yield in a relatively short time and has higher efficiency; the present invention has strong controllability and can adjust the whisker size, morphology and composition by controlling reaction conditions, such as acid concentration, temperature, etc., to achieve precise control of the product; compared with high-temperature preparation methods, the reaction conditions of the present invention are mild, and the temperature is relatively low during the reaction process, which is conducive to maintaining the structure and properties of the material.

[0053] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum, characterized in that: The following steps are involved: S1. Grind the phosphogypsum and mix it with a leaching agent, perform ultrasonic leaching and filter to obtain a filtrate; wherein the leaching agent includes an acid and a salt compound, and the hydrogen ion concentration of the leaching agent is 2 mol / L to 8 mol / L; S2. Add silane coupling agent solution to the filtrate, and obtain calcium sulfate whiskers through purification, crystallization, separation and drying.

2. The method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum according to claim 1, characterized in that: In step S1, the particle size of the ground phosphogypsum is 0.075-0.15 mm, accounting for 60%-80%.

3. The method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum according to claim 1, characterized in that: In step S1, the acid in the leaching agent includes any one of hydrochloric acid, sulfuric acid, nitric acid, and citric acid, or a combination of at least two of them; the salt compound includes any one of chloride, sulfate, nitrate, and citrate, or a combination of at least two of them; The molar ratio of the acid to the salt compound in the leaching agent is (10-20):

1.

4. The method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum according to claim 1, characterized in that: In step S1, the mass ratio of the ground phosphogypsum to the leaching agent is 1:(8-12).

5. The method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum according to claim 1, characterized in that: In step S1, the filtration after ultrasonic leaching is heating and stirring under ultrasound, and then filtering while hot; the conditions of ultrasonic leaching include: ultrasonic frequency of 35 Hz to 45 Hz, heating temperature of 60°C to 100°C, and stirring time of 70 min to 120 min.

6. The method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum according to claim 1, characterized in that: In step S2, the mass concentration of the silane coupling agent solution is 3% to 10%.

7. The method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum according to claim 1, characterized in that: In step S2, the silane coupling agent includes A-151.

8. The method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum according to claim 1, characterized in that: In step S2, the mass ratio of the silane coupling agent to the ground phosphogypsum is 1:(10-20).

9. The method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum according to claim 1, characterized in that: In step S2, the purification and crystallization is performed by heating and stirring at 75°C to 85°C for 0.5 h to 1 h, filtering while hot, and cooling naturally to precipitate crystals.

10. The method for preparing calcium sulfate whiskers by ultrasonic leaching of phosphogypsum according to claim 1, characterized in that: In step S2, the separation is performed by filtration, and the drying is performed by drying.

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