Method for preparing anhydrite through cooperation of ultrasound and phosphogypsum crystal transformation

Abstract

The invention discloses a method for preparing anhydrite through ultrasound-assisted phosphogypsum crystal transformation, which is characterized in that phosphogypsum is used as a raw material, ammonium persulfate is used as an additive, a dilute sulfuric acid solution is used as a crystal transformation agent, and the anhydrite is prepared by adopting a sulfuric acid method under ultrasound-assisted action. The process for preparing the anhydrous gypsum has the characteristics of low sulfuric acid concentration, low equipment corrosion degree, low heating temperature, low energy consumption, high whiteness of the product anhydrous gypsum and small particle size.

Description

Technical Field

[0001] The invention relates to a method for preparing anhydrous gypsum, in particular to a method for preparing anhydrous gypsum through ultrasonic coordinated crystal transformation of phosphogypsum. Background Art

[0002] Phosphogypsum is a solid waste generated during the production of wet phosphoric acid. The production of 1 ton of phosphoric acid produces about 5 tons of phosphogypsum. Phosphogypsum is mostly composed of calcium sulfate dihydrate with impurities. In addition to silicon dioxide, iron and aluminum oxides, the impurities also contain phosphorus, fluorine and heavy metal elements that are harmful to the environment. In addition, my country is a traditional agricultural country with a large demand for phosphate fertilizers. When producing a large amount of phosphate fertilizers, a large amount of phosphogypsum is produced.

[0003] The large-scale storage of phosphogypsum occupies a large amount of land, and the management and maintenance of the phosphogypsum dam increases the operating costs of enterprises. At the same time, the large-scale storage of phosphogypsum will cause serious damage to the surrounding environment. The leaching of phosphorus and fluoride ions will cause eutrophication of the surrounding water and soil environment, and the leaching of heavy metal ions will pose a serious threat to the personal safety of surrounding residents. The phosphogypsum problem has seriously restricted the development of phosphorus chemical enterprises. Therefore, realizing the resource utilization of phosphogypsum is of great practical significance.

[0004] At present, in addition to selling part of phosphogypsum abroad, the rest is mainly used in agriculture, chemical industry, building materials and other fields. The phosphorus and calcium elements in phosphogypsum can effectively reduce the soil pH of saline-alkali land, improve its physical and chemical properties, and increase the nutrients in the soil. Phosphogypsum contains rich Ca and S resources, which can be used to produce ammonium sulfate, calcium carbonate, potassium sulfate, etc. through chemical reactions.

[0005] In addition, it is noted that the main component of phosphogypsum is dihydrate gypsum, therefore, phosphogypsum is used in the building materials industry as a substitute for natural gypsum. Although phosphogypsum has been used in these fields, the presence of harmful impurities still restricts its further use.

[0006] Anhydrous gypsum is a material obtained by dehydrating dihydrate gypsum at high temperature. Its main component is anhydrous calcium sulfate. Traditional anhydrous gypsum is mainly prepared from natural gypsum. However, with the excessive mining of natural gypsum, the reserves of high-grade natural gypsum are decreasing. In order to alleviate the environmental damage caused by excessive mining of natural gypsum and reduce dependence on natural resources, people are seeking new sources of anhydrous gypsum.

[0007] Since phosphogypsum and natural gypsum have similar main components, both of which are mainly calcium sulfate dihydrate, the use of phosphogypsum as raw material to prepare anhydrous calcium sulfate is currently a research hotspot in the anhydrous gypsum field. It can not only further consume a large amount of stockpiled phosphogypsum and turn it into treasure, but also reduce dependence on natural gypsum.

[0008] However, the current research on the preparation of anhydrous gypsum from phosphogypsum is mainly focused on the calcination method and the sulfuric acid crystallization method. However, the former has too high energy consumption, which is not conducive to industrial promotion. Although the latter has lower energy consumption, it requires the use of a large amount of concentrated sulfuric acid, which causes serious equipment corrosion, and also requires heating to above 70°C for reaction, which involves certain energy consumption. At the same time, impurities such as organic matter in the phosphogypsum are difficult to be effectively removed, resulting in insufficient whiteness of the anhydrous gypsum, which also limits its application. In addition, the anhydrous gypsum prepared by the current sulfuric acid crystallization method is mostly in the form of whiskers, which is not conducive to its application in fillers and other fields.

[0009] Therefore, it is necessary to further study and improve the process of preparing anhydrous gypsum by crystallization of phosphogypsum. Summary of the invention

[0010] In order to solve the above technical problems, the present invention provides a method for preparing anhydrous gypsum by ultrasonic coordinated crystallization of phosphogypsum. The process for preparing anhydrous gypsum of the present invention has the characteristics of low sulfuric acid concentration, low equipment corrosion, low heating temperature, low energy consumption, and high whiteness and small particle size of the product anhydrous gypsum.

[0011] The technical solution of the present invention:

[0012] A method for preparing anhydrous gypsum by ultrasound-assisted crystal transformation of phosphogypsum uses phosphogypsum as a raw material, ammonium persulfate as an additive, and a dilute sulfuric acid solution as a crystal transformation agent, and anhydrous gypsum is prepared by a sulfuric acid method under ultrasound-assisted crystal transformation.

[0013] Preferably, the aforementioned method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization comprises the following steps:

[0014] S1. Prepare dilute sulfuric acid solution;

[0015] S2. ammonium persulfate is added to the dilute sulfuric acid solution to obtain a mixed solution;

[0016] S3. Add phosphogypsum to the mixture and stir evenly to obtain a slurry;

[0017] S4. Place the slurry in an ultrasonic environment and heat it for reaction. After the reaction is completed, filter it to obtain anhydrous gypsum.

[0018] Preferably, in the aforementioned method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization, the phosphogypsum has an average particle size of 80-85 μm, a median particle size of 70-85 μm, and a CaO content of 30-40%.

[0019] Preferably, in the aforementioned method for preparing anhydrous gypsum by ultrasound-assisted crystallization of phosphogypsum, the concentration of the dilute sulfuric acid solution is 25-30%.

[0020] Preferably, in the aforementioned method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization, the concentration of the dilute sulfuric acid solution is 25%.

[0021] Preferably, in the aforementioned method for preparing anhydrous gypsum by ultrasound-assisted crystallization of phosphogypsum, in the mixed solution S2, the mass ratio of ammonium persulfate to dilute sulfuric acid solution is 1:10-15.

[0022] Preferably, in the aforementioned method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization, the mass ratio of the ammonium persulfate to the dilute sulfuric acid solution is 1:15.

[0023] Preferably, in the aforementioned method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization, in the slurry described in S3, the mass ratio of phosphogypsum to dilute sulfuric acid solution is 1:4-6.

[0024] Preferably, in the aforementioned method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization, the mass ratio of the phosphogypsum to the dilute sulfuric acid solution is 1:5.

[0025] Preferably, in the aforementioned method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization, the heating temperature in S4 is 65-75° C., and the reaction time is 5-7 hours.

[0026] Beneficial effects of the present invention:

[0027] 1. The present invention adopts an ultrasonic synergistic method and adds ammonium persulfate as an additive. On the basis of the traditional sulfuric acid method, the method of the present invention further reduces the concentration of sulfuric acid and uses dilute sulfuric acid with a concentration of 25-30%, thereby reducing the corrosion of sulfuric acid to the equipment; at the same time, the reaction temperature is further reduced, the energy consumption is reduced, and the cost is saved.

[0028] 2. The method of the present invention can further remove impurities in phosphogypsum, improve the whiteness of phosphogypsum, and facilitate the promotion and application of anhydrous gypsum made from phosphogypsum.

[0029] 3. The method of the present invention can control the crystal form of anhydrous gypsum to form fine particles, which is beneficial for its application in the fields of fillers and the like.

[0030] The mechanism of the present invention to achieve the above-mentioned effect is that phosphogypsum is dissolved in sulfuric acid solution, releasing phosphorus and fluorine between crystals, and at the same time, ammonium persulfate is activated by ultrasound to generate sulfate free radicals, thereby mineralizing organic matter in phosphogypsum, removing organic matter, and improving whiteness. As the ultrasonic time increases, ammonium persulfate eventually produces sulfate ions, increasing the supersaturation of the solution, allowing the dissolved sulfate and calcium ions to recombine to form anhydrous gypsum crystal nuclei, thereby promoting the crystallization of anhydrous gypsum, thereby reducing the required sulfuric acid concentration and reaction temperature. In addition, the present invention, by utilizing ultrasound, hinders the anhydrous gypsum crystal nuclei in the solution from continuing to grow into larger grains of anhydrous gypsum, so that the generated anhydrous gypsum has a smaller particle size and is in the form of fine particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Attached Figure 1 A physical picture of anhydrous gypsum obtained by the process of the present invention;

[0032] Attached Figure 2 This is a physical picture of the original phosphogypsum;

[0033] Attached Figure 3 The particle size diagrams of original phosphogypsum, anhydrous gypsum prepared without ultrasonic treatment, and anhydrous gypsum prepared with ultrasonic treatment;

[0034] Attached Figure 4 This is the SEM image of anhydrous gypsum produced without ultrasonic treatment;

[0035] Attached Figure 5 This is a SEM image of anhydrous gypsum obtained by ultrasonic treatment of the present invention;

[0036] Attached Figure 6 These are the XRD patterns of original phosphogypsum, anhydrous gypsum prepared without ultrasonic treatment, and anhydrous gypsum prepared with ultrasonic treatment.

[0037] The above-mentioned original phosphogypsum is phosphogypsum that has not been treated in any way;

[0038] The anhydrous gypsum prepared without ultrasonic treatment is: 30g of original phosphogypsum is dissolved in 150g of 25% sulfuric acid solution, and 15g of ammonium persulfate is added, and then heated at 90°C for 6 hours to prepare the obtained sample. The reaction temperature must reach above 90°C at this sulfuric acid concentration. If it is lower than 90°C, the anhydrous gypsum cannot be crystallized.

[0039] The anhydrous gypsum obtained by ultrasonic treatment is as follows: 30 g of original phosphogypsum is dissolved in 150 g of a 25% sulfuric acid solution, and 15 g of ammonium persulfate is added, followed by heating at 70° C. for 6 hours in an ultrasonic environment to prepare the obtained sample.

[0040] from Figure 1-5It can be seen that the initial whiteness of the original phosphogypsum before treatment is 56.7%, and the crystal water content is 18.92%. After treatment by the present invention, the whiteness of the anhydrous gypsum is increased to 91.5%, and the crystal water content is 0.24%. The average particle size of the anhydrous gypsum product obtained without ultrasonic preparation is 13.41 μm, and the average particle size of the anhydrous gypsum product obtained by ultrasonic preparation is 1.944 μm.

[0041] From the SEM images of the anhydrous gypsum products without and after ultrasonic treatment, it can be seen that the anhydrous gypsum without ultrasonic treatment is irregular flake-shaped with a particle size of more than 10 μm, while the anhydrous gypsum product after ultrasonic treatment has a relatively scattered square columnar morphology. Although it is stacked, the particle size is relatively small.

[0042] from Figure 6 It can be seen that the original phosphogypsum is transformed into anhydrous gypsum after being crystallized by sulfuric acid and ammonium persulfate, but the diffraction peak intensity of anhydrous gypsum prepared by ultrasonic synergy is higher than that of anhydrous gypsum prepared without ultrasonic synergy. This shows that ultrasonic synergy makes the crystal particles finer and the crystallization more complete when phosphogypsum is crystallized into anhydrous gypsum. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0044] Embodiments of the present invention

[0045] The phosphogypsum of the embodiment of the present invention is taken from a phosphorus chemical group in Guizhou, with an average particle size of 82.85 μm, a median particle size (D50) of 73.45 μm, and a CaO content of 34.20%. In actual implementation, the average particle size can be 80-85 μm, the median particle size can be 70-85 μm, and the CaO content can be 30-40%.

[0046] Example 1

[0047] A method for preparing anhydrous gypsum by ultrasonic coordinated crystal transformation of phosphogypsum, the steps are as follows:

[0048] S1. Prepare a 25% dilute sulfuric acid solution;

[0049] S2. 15 g of ammonium persulfate was added to 150 g of dilute sulfuric acid solution to obtain a mixed solution;

[0050] S3. Add 30g of phosphogypsum to 150g of the mixture and stir to obtain a slurry;

[0051] S4. Place the slurry in an ultrasonic environment and heat it to 70°C for 6 hours. After the reaction is completed, filter it to obtain anhydrous gypsum.

[0052] Example 2

[0053] A method for preparing anhydrous gypsum by ultrasonic coordinated crystal transformation of phosphogypsum, the steps are as follows:

[0054] S1. Prepare a 26% dilute sulfuric acid solution;

[0055] S2. 13.6 g of ammonium persulfate was added to 150 g of dilute sulfuric acid solution to obtain a mixed solution;

[0056] S3. Add 25g of phosphogypsum to 150g of the mixture and stir to obtain a slurry;

[0057] S4. Place the slurry in an ultrasonic environment and heat it to 70°C for 6 hours. After the reaction is completed, filter it to obtain anhydrous gypsum.

[0058] Example 3

[0059] A method for preparing anhydrous gypsum by ultrasonic coordinated crystal transformation of phosphogypsum, the steps are as follows:

[0060] S1. Prepare a 30% dilute sulfuric acid solution;

[0061] S2. 12.5 g of ammonium persulfate was added to 150 g of dilute sulfuric acid solution to obtain a mixed solution;

[0062] S3. Add 37.5g of phosphogypsum to 150g of the mixture and stir to obtain a slurry;

[0063] S4. Place the slurry in an ultrasonic environment and heat it to 70°C for 6 hours. After the reaction is completed, filter it to obtain anhydrous gypsum.

[0064] Example 4

[0065] A method for preparing anhydrous gypsum by ultrasonic coordinated crystal transformation of phosphogypsum, the steps are as follows:

[0066] S1. Prepare a 27% dilute sulfuric acid solution;

[0067] S2. 11.5 g of ammonium persulfate was added to 150 g of dilute sulfuric acid solution to obtain a mixed solution;

[0068] S3. Add 28g of phosphogypsum to 150g of the mixture and stir to obtain a slurry;

[0069] S4. Place the slurry in an ultrasonic environment and heat it to 70°C for 6 hours. After the reaction is completed, filter it to obtain anhydrous gypsum.

[0070] Example 5

[0071] A method for preparing anhydrous gypsum by ultrasonic coordinated crystal transformation of phosphogypsum, the steps are as follows:

[0072] S1. Prepare a dilute sulfuric acid solution with a concentration of 28%;

[0073] S2. Add 10 g of ammonium persulfate to 150 g of dilute sulfuric acid solution to obtain a mixed solution;

[0074] S3. Add 34g of phosphogypsum to 150g of the mixture and stir to obtain a slurry;

[0075] S4. Place the slurry in an ultrasonic environment and heat it to 70°C for 6 hours. After the reaction is completed, filter it to obtain anhydrous gypsum.

[0076] Example 6

[0077] A method for preparing anhydrous gypsum by ultrasonic coordinated crystal transformation of phosphogypsum, the steps are as follows:

[0078] S1. Prepare a 25% dilute sulfuric acid solution;

[0079] S2. 15 g of ammonium persulfate was added to 150 g of dilute sulfuric acid solution to obtain a mixed solution;

[0080] S3. Add 30g of phosphogypsum to 150g of the mixture and stir to obtain a slurry;

[0081] S4. Place the slurry in an ultrasonic environment and heat it to 65°C for 7 hours. After the reaction is completed, filter it to obtain anhydrous gypsum.

[0082] Example 7

[0083] A method for preparing anhydrous gypsum by ultrasonic coordinated crystal transformation of phosphogypsum, the steps are as follows:

[0084] S1. Prepare a 25% dilute sulfuric acid solution;

[0085] S2. 15 g of ammonium persulfate was added to 150 g of dilute sulfuric acid solution to obtain a mixed solution;

[0086] S3. Add 30g of phosphogypsum to 150g of the mixture and stir to obtain a slurry;

[0087] S4. Place the slurry in an ultrasonic environment and heat it to 75°C for reaction for 5 hours. After the reaction is completed, filter it to obtain anhydrous gypsum.

[0088] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing anhydrous gypsum by ultrasonic assisted crystallization of phosphogypsum, characterized in that: The invention adopts phosphogypsum as raw material, ammonium persulfate as additive, dilute sulfuric acid solution as crystal-changing agent, and adopts sulfuric acid method to prepare anhydrous gypsum under ultrasonic coordination.

2. The method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization according to claim 1, characterized in that: The steps include: S1. Prepare dilute sulfuric acid solution; S2. ammonium persulfate is added to the dilute sulfuric acid solution to obtain a mixed solution; S3. Add phosphogypsum to the mixture and stir evenly to obtain a slurry; S4. Place the slurry in an ultrasonic environment and heat it for reaction. After the reaction is completed, filter it to obtain anhydrous gypsum.

3. The method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization according to claim 1 or 2, characterized in that: The average particle size of the phosphogypsum is 80-85 μm, the median particle size is 70-85 μm, and the CaO content is 30-40%.

4. The method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization according to claim 1 or 2, characterized in that: The concentration of the dilute sulfuric acid solution is 25-30%.

5. The method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization according to claim 4, characterized in that: The concentration of the dilute sulfuric acid solution is 25%.

6. The method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization according to claim 2, characterized in that: In the mixed solution S2, the mass ratio of ammonium persulfate to dilute sulfuric acid solution is 1:10-15.

7. The method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization according to claim 6, characterized in that: The mass ratio of the ammonium persulfate to the dilute sulfuric acid solution is 1:

15.

8. The method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization according to claim 2, characterized in that: In the slurry S3, the mass ratio of phosphogypsum to dilute sulfuric acid solution is 1:4-6.

9. The method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization according to claim 8, characterized in that: The mass ratio of the phosphogypsum to the dilute sulfuric acid solution is 1:

5.

10. The method for preparing anhydrous gypsum by ultrasound-assisted phosphogypsum crystallization according to claim 2, characterized in that: The heating temperature in S4 is 65-75° C., and the reaction time is 5-7 hours.

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