Method for preparing high-purity gypsum from phosphogypsum

Abstract

The application provides a method for preparing high-purity gypsum from phosphogypsum. The method comprises the following steps: dry grinding the phosphogypsum to control the particle size within a certain range; adding the dry-ground phosphogypsum into acid liquor, acid leaching, and filtering; adding water to the filtered phosphogypsum to form a slurry, adding an amine collector to perform positive flotation until the foam is white, and obtaining the product, i.e. the desilicated and purified phosphogypsum; and calcining the desilicated and purified phosphogypsum to obtain gypsum. The method creates necessary acidic conditions for the desilication and purification of the phosphogypsum by acid leaching, and reduces the use of pH adjusting reagents. Compared with the traditional oil acid collector, the amine collector can precisely collect the positively charged gypsum under the condition that the quartz is not charged under the acidic condition, and the amount of the amine collector is small. Compared with the wet purification method, the fire purification method can make the whiteness of the phosphogypsum break through 70% and reach more than 90%.

Description

Technical Field

[0001] This invention relates to the field of solid waste recycling technology, and in particular to a method for preparing high-purity gypsum from phosphogypsum. Background Technology

[0002] Phosphogypsum is an industrial byproduct of wet-process phosphoric acid production. It appears as a grayish-white or grayish-black powder, primarily composed of CaSO4·nH2O, accounting for over 85% of its composition. Other impurities include undecomposed phosphate rock powder, uncleaned phosphoric acid, iron and aluminum compounds, acid-insoluble substances, organic matter, phosphorus (P), sulfur (F), and heavy metals. Current surveys indicate that my country's phosphogypsum stockpile exceeds 600 million tons, with an annual increase of approximately 80 million tons. Despite continuous increases, the utilization rate of existing stock remains low. The presence of impurities in phosphogypsum significantly hinders its resource utilization. Soluble phosphorus and fluorine adhere to the surface of dihydrate gypsum crystals, causing numerous problems when phosphogypsum is used as a building material, such as affecting its setting time, requiring high water consumption, and resulting in low building material strength. While the organic matter content in phosphogypsum is relatively low, generally only around 0.1% to 0.2%, its presence weakens the bonding force between gypsum crystals, leading to a loose structure in the hardened form.

[0003] Current technology discloses a flotation purification method for phosphogypsum, which obtains high-purity phosphogypsum through flotation and physical separation. However, the resulting high-purity phosphogypsum has low whiteness, with a maximum whiteness of only 58.3%, limiting its application scenarios. Furthermore, it does not address the removal of soluble impurities, potentially requiring additional treatment to remove soluble phosphorus and fluorine impurities before further use. Existing technology also discloses a phosphogypsum purification and whitening method, which uses flotation and calcination to remove impurities and purify the phosphogypsum. However, this method does not remove metallic impurities, potentially leading to a reddish tint in the calcined phosphogypsum and affecting its whiteness. Finally, existing technology discloses a calcination purification method for acidic phosphogypsum, which removes or solidifies impurities through rapid calcination at high temperatures. However, this method does not remove SiO2 impurities, resulting in a low CaSO4·2H2O content in the obtained phosphogypsum product.

[0004] Given the shortcomings of the current phosphogypsum flotation method, it is necessary to improve it. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing high-purity gypsum from phosphogypsum to overcome the defects existing in the prior art.

[0006] In a first aspect, the present invention provides a method for preparing high-purity gypsum from phosphogypsum, comprising the following steps:

[0007] Dry grind phosphogypsum until the particle size is controlled to a certain extent;

[0008] Add the dry-ground phosphogypsum to an acid solution, leach, and filter.

[0009] Water was added to the filtered phosphogypsum to make a slurry, and an amine collector was added for positive flotation until the foam turned white. The product obtained was phosphogypsum after desiliconization and purification.

[0010] The phosphogypsum purified by desilication is calcined to obtain gypsum.

[0011] Preferably, in the method for preparing high-purity gypsum from phosphogypsum, the phosphogypsum is dry-ground to a particle size of -0.075 mm, which accounts for 92-94% of the total mass of the phosphogypsum.

[0012] Preferably, in the method for preparing high-purity gypsum from phosphogypsum, the dry-ground phosphogypsum is added to an acid solution. In the acid leaching step, the acid solution is a sulfuric acid solution with a mass concentration of 30-40%, the acid leaching temperature is 40-60°C, and the acid leaching time is 2-3 hours.

[0013] Preferably, in the method for preparing high-purity gypsum from phosphogypsum, in the step of adding water to the filtered phosphogypsum to form a slurry, the mass concentration of the phosphogypsum after adding water to form a slurry is 25-45%.

[0014] Preferably, in the method for preparing high-purity gypsum from phosphogypsum, the amine collector includes at least one of dodecylamine, ethanolamine, and ethylenediamine formate.

[0015] Preferably, in the method for preparing high-purity gypsum from phosphogypsum, the calcination temperature is 500–600°C and the calcination time is 1–2 hours during the step of calcining the desiliconized and purified phosphogypsum.

[0016] Preferably, in the method for preparing high-purity gypsum from phosphogypsum, in the step of dry grinding the phosphogypsum to control the particle size to a certain extent, the mass content of CaSO4·2H2O in the phosphogypsum is 80%–90%, the whiteness is 20%–40%, and the mass content of SiO2 is 10%–15%.

[0017] Secondly, the present invention also provides a gypsum prepared by the method described above.

[0018] The present invention has the following advantages over the prior art:

[0019] The method for preparing high-purity gypsum from phosphogypsum of the present invention includes the following steps: dry grinding phosphogypsum until the particle size is controlled to a certain extent; adding the dry-ground phosphogypsum to acid solution, acid leaching, and filtering; adding water to the filtered phosphogypsum to form a slurry, adding an amine collector for positive flotation until the foam is white, and the obtained product is desilication-purified phosphogypsum; calcining the desilication-purified phosphogypsum to obtain gypsum; the method of the present invention, through acid leaching, creates the necessary acidic conditions for the positive flotation desilication purification of phosphogypsum, reducing the use of pH adjustment agents; compared with the characteristics of traditional oleic acid amine collectors such as large dosage, poor low-temperature collection performance, and poor targeting, the method utilizes the fact that quartz is uncharged under acidic conditions, and amine collectors can be used to accurately collect positively charged gypsum, with a small dosage; compared with wet purification, pyrometallurgical purification can make the whiteness of phosphogypsum exceed 70%, reaching over 90%. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a process flow diagram of the method for preparing high-purity gypsum from phosphogypsum according to the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0024] This application provides a method for preparing high-purity gypsum from phosphogypsum, such as... Figure 1 As shown, it includes the following steps:

[0025] S1. Dry grind the phosphogypsum until the particle size is controlled to a certain extent;

[0026] S2. Add the dry-ground phosphogypsum to the acid solution, acid leaching, and filter;

[0027] S3. Add water to the filtered phosphogypsum to make a slurry, add an amine collector and perform positive flotation until the foam is white. The product obtained is phosphogypsum after desiliconization and purification.

[0028] S4. Calcining the desiliconized and purified phosphogypsum yields gypsum.

[0029] The method for preparing high-purity gypsum from phosphogypsum of the present invention specifically comprises an acid leaching-flotation-calcination combined process. Acid leaching removes soluble phosphorus and fluorine impurities, as well as metallic impurities affecting whiteness; flotation performs desilication purification; and calcination removes organic carbon and other substances. The method for preparing high-purity gypsum from phosphogypsum provided by the present invention utilizes the good solubility of soluble impurities in acidic systems (such as sulfuric acid systems) and the reaction of soluble metallic compounds with sulfuric acid to form water-soluble compounds. The ions in the phosphogypsum are used to remove soluble phosphorus, fluorine, and metallic impurities. For desilication and purification of phosphogypsum, cationic amine collectors are used. Based on electrostatic adsorption theory, minerals with a negative zeta potential can be collected. When the slurry pH > 2.3, both gypsum and quartz minerals are negatively charged and can be collected by cationic amine collectors. When the pH ≤ 2, gypsum minerals are negatively charged and can be electrostatically adsorbed by cationic amine collectors, while quartz surfaces are either charged or uncharged and are not adsorbed. During acid leaching, the pH of the phosphogypsum remains below 2, creating conditions for cationic collection. Under high-temperature conditions, organic carbon and some phosphorus and fluorine compounds in the phosphogypsum will volatilize in gaseous form, thus achieving the whitening and purification process of phosphogypsum.

[0030] Compared with existing processes, the present invention has the following advantages:

[0031] 1. Acid leaching creates the necessary acidic conditions for the desilication and purification of phosphogypsum by positive flotation, reducing the use of pH adjustment reagents;

[0032] 2. Compared with traditional oleic acid-based amine collectors, which have the disadvantages of large dosage, poor low-temperature collection performance, and poor targeting, amine collectors can be used to accurately collect positively charged gypsum by taking advantage of the fact that quartz is uncharged under acidic conditions, and the dosage is small.

[0033] 3. Compared with wet purification, pyrolysis can make the whiteness of phosphogypsum exceed 70% and reach over 90%.

[0034] In some embodiments, the phosphogypsum dry-milled to a particle size of -0.075 mm accounts for 92-94% of the total mass of the phosphogypsum.

[0035] Specifically, a particle size of -0.075mm indicates that the particle size is less than 0.075mm.

[0036] In some embodiments, the dry-ground phosphogypsum is added to an acid solution. In the acid leaching step, the acid solution is a sulfuric acid solution with a mass concentration of 30-40%, an acid leaching temperature of 40-60°C, and an acid leaching time of 2-3 hours.

[0037] In some embodiments, in the step of adding water to the filtered phosphogypsum to form a slurry, the mass concentration of the phosphogypsum after adding water to form a slurry is 25-45%.

[0038] In some embodiments, the amine collector includes at least one of dodecylamine, ethanolamine, and ethylenediamine formate.

[0039] In some embodiments, in the step of calcining the desiliconized and purified phosphogypsum, the calcination temperature is 500-600°C and the calcination time is 1-2 hours.

[0040] In some embodiments, during the step of dry grinding phosphogypsum to control the particle size to a certain extent, the phosphogypsum contains 80%–90% CaSO4·2H2O by mass, 20%–40% whiteness, and 10%–15% SiO2 by mass.

[0041] Based on the same inventive concept, the present invention also provides a gypsum prepared by the above-described method.

[0042] The following detailed embodiments further illustrate the method and procedures for preparing high-purity gypsum from phosphogypsum according to this application. This section further explains the invention in conjunction with specific embodiments, but should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in the art.

[0043] Example 1

[0044] This application provides a method for preparing high-purity gypsum from phosphogypsum, including the following steps:

[0045] S1. The phosphogypsum dry-milled to a particle size of -0.075mm accounts for 92% of the total mass of the phosphogypsum;

[0046] S2. Place 200g of the dry-ground phosphogypsum from S1 in a sulfuric acid solution and acid-soak it at 50℃ for 2 hours, then filter it; wherein, the mass fraction of the sulfuric acid solution is 30%.

[0047] S3. Add water to the phosphogypsum filtered in step S2 to adjust the slurry to a mass concentration of 30% for the phosphogypsum. Then add 0.2 kg / t of dodecylamine (i.e., 0.2 kg of dodecylamine is added to 1 t of phosphogypsum (solid, not slurry)) for positive flotation until the foam is white. The product obtained is phosphogypsum after desilication and purification.

[0048] S4. The phosphogypsum purified by desilication in step S3 is calcined at 600℃ for 1 hour to obtain high-purity gypsum.

[0049] The phosphogypsum used in step S1 is phosphogypsum from a certain place in Hubei Province, with a soluble P2O5 content (mass content) of 1.5%, a soluble fluorine content (mass content) of 0.4%, a CaSO4·2H2O content (mass content) of 90.23%, a SiO2 content (mass content) of 6.13%, and a whiteness of 29.67%.

[0050] The high-purity gypsum prepared according to the method in Example 1 was tested. The soluble P2O5 content (mass content) was 0.01%, the soluble fluorine was below the detection limit, the CaSO4·2H2O content (mass content) was 95.34%, the whiteness was 93%, and the SiO2 content (mass content) was 1.25%.

[0051] The detection method is as follows:

[0052] The CaSO4·2H2O content was tested according to the national standard "Chemical Analysis Methods for Gypsum" (GB / T 5484-2012);

[0053] The soluble P2O5 content was tested according to the national standard "Determination of total phosphorus in water - Ammonium molybdate spectrophotometric method" (GB 11893-90);

[0054] The soluble fluoride content was tested according to the "Determination of Phosphorus and Fluorine in Phosphogypsum" (JC / T 2073);

[0055] The whiteness of the phosphogypsum sample was tested using a WSB-3C whiteness meter manufactured by Hangzhou Qiwei Instrument Co., Ltd.

[0056] Whiteness measurement range is 0%-99%.

[0057] The SiO2 content was tested according to the standard GB / T1873-1995, "Determination of SiO2 Content in Phosphate Rocks and Phosphate Concentrates by Gravimetric and Volumetric Methods".

[0058] In the remaining examples and comparative examples, the testing methods for soluble P2O5 content, soluble fluorine content, CaSO4·2H2O content, whiteness, and SiO2 content are the same as those described above.

[0059] Example 2

[0060] This application provides a method for preparing high-purity gypsum from phosphogypsum, including the following steps:

[0061] S1. The phosphogypsum dry-milled to a particle size of -0.075mm accounts for 93% of the total mass of the phosphogypsum;

[0062] S2. Place 200g of the dry-ground phosphogypsum from S1 in a sulfuric acid solution and acid-leach at 50℃ for 1.5h, then filter; wherein the sulfuric acid solution has a mass fraction of 30%.

[0063] S3. Add water to the phosphogypsum filtered in step S2 to adjust the slurry to a mass concentration of 30% for phosphogypsum. Then add 0.2 kg / t of ethanolamine (i.e., 0.2 kg of ethanolamine is added to 1 t of phosphogypsum (solid, not slurry)) for positive flotation until the foam is white. The product obtained is phosphogypsum after desilication and purification.

[0064] S4. The phosphogypsum purified by desilication in step S3 is calcined at 600℃ for 1.5h to obtain high-purity gypsum.

[0065] The phosphogypsum used in step S1 is from a certain place in Hubei Province, with a soluble P2O5 content (mass content) of 1.41%, a soluble fluorine content (mass content) of 0.35%, a CaSO4·2H2O content (mass content) of 89.51%, a SiO2 content (mass content) of 7.34%, and a whiteness of 27.67%.

[0066] The high-purity gypsum prepared according to the method in Example 1 was tested. The soluble P2O5 content (mass content) was 0.01%, the soluble fluorine was below the detection limit, the CaSO4·2H2O content (mass content) was 96.23%, the whiteness was 92.7%, and the SiO2 content (mass content) was 1.45%.

[0067] Example 3

[0068] This application provides a method for preparing high-purity gypsum from phosphogypsum, including the following steps:

[0069] S1. The phosphogypsum dry-milled to a particle size of -0.075mm accounts for 92% of the total mass of the phosphogypsum;

[0070] S2. Place 200g of the dry-ground phosphogypsum from S1 in a sulfuric acid solution and acid-soak it at 50℃ for 2 hours, then filter it; wherein, the mass fraction of the sulfuric acid solution is 30%.

[0071] S3. Add water to the phosphogypsum filtered in step S2 to adjust the slurry to a mass concentration of 30% for phosphogypsum. Then add 0.2 kg / t of ethylenediamine formate (i.e., 0.2 kg of ethylenediamine formate is added to 1 t of phosphogypsum (solid, not slurry)) for positive flotation until the foam is white. The product obtained is phosphogypsum after desilication and purification.

[0072] S4. The phosphogypsum purified by desilication in step S3 is calcined at 600℃ for 1.5h to obtain high-purity gypsum.

[0073] The phosphogypsum used in step S1 is from a certain place in Hubei Province, with a soluble P2O5 content (mass content) of 1.78%, a soluble fluorine content (mass content) of 0.54%, a CaSO4·2H2O content (mass content) of 85.23%, a SiO2 content (mass content) of 9.24%, and a whiteness of 26.43%.

[0074] The high-purity gypsum prepared according to the method in Example 1 was tested. The soluble P2O5 content (mass content) was 0.01%, the soluble fluorine was below the detection limit, the CaSO4·2H2O content (mass content) was 95.98%, the whiteness was 94%, and the SiO2 content (mass content) was 1.67%.

[0075] Comparative Example 1

[0076] This comparative example provides a method for preparing high-purity gypsum from phosphogypsum, including the following steps:

[0077] S1. The phosphogypsum dry-milled to a particle size of -0.075mm accounts for 92% of the total mass of the phosphogypsum;

[0078] S2. Place 200g of the dry-ground phosphogypsum from S1 in a sulfuric acid solution and acid-soak it at 50℃ for 2 hours, then filter it; wherein, the mass fraction of the sulfuric acid solution is 30%.

[0079] S3. Add water to the phosphogypsum filtered in step S2 to adjust the slurry to a mass concentration of 30% for the phosphogypsum. Then add 0.2 kg / t of dodecylamine (i.e., 0.2 kg of dodecylamine is added to 1 t of phosphogypsum (solid, not slurry)) for positive flotation until the foam is white. The product obtained is phosphogypsum after desilication and purification.

[0080] The phosphogypsum used in step S1 is phosphogypsum from a certain place in Hubei Province, with a soluble P2O5 content (mass content) of 1.5%, a soluble fluorine content (mass content) of 0.4%, a CaSO4·2H2O content (mass content) of 90.23%, a SiO2 content (mass content) of 6.13%, and a whiteness of 29.67%.

[0081] The phosphogypsum raw materials used in Comparative Example 1 and Example 1 are the same. In terms of process, the calcination step in step S4 is removed, and the other steps are the same.

[0082] The phosphogypsum obtained after desilication and purification in step S3 of Comparative Example 1 was tested and found to have a soluble P2O5 content (mass content) of 0.1%, a soluble fluorine content (mass content) of 0.11%, a CaSO4·2H2O content (mass content) of 93.34%, a SiO2 content (mass content) of 1.45%, and a whiteness of 34.21%.

[0083] Compared with Example 1 and Comparative Example 1, it can be found that the uncalcined phosphogypsum has a lower whiteness and a higher content of soluble phosphorus and fluorine than the calcined phosphogypsum.

[0084] Comparative Example 2

[0085] This comparative example provides a method for preparing high-purity gypsum from phosphogypsum, including the following steps:

[0086] S1. The phosphogypsum dry-milled to a particle size of -0.075mm accounts for 93% of the total mass of the phosphogypsum;

[0087] S2. Add water to the dry-ground phosphogypsum in step S1 to adjust the slurry to a mass concentration of phosphogypsum of 30%. Then add 0.2 kg / t of ethanolamine (i.e., 0.2 kg of ethanolamine is added to 1 t of phosphogypsum (solid, not slurry)) for positive flotation until the foam is white. The product obtained is phosphogypsum after desilication and purification.

[0088] S3. The phosphogypsum purified by desilication in step S2 is calcined at 600℃ for 1.5h to obtain high-purity gypsum.

[0089] The phosphogypsum used in step S1 is from a certain place in Hubei Province, with a soluble P2O5 content (mass content) of 1.41%, a soluble fluorine content (mass content) of 0.35%, a CaSO4·2H2O content (mass content) of 89.51%, a SiO2 content (mass content) of 7.34%, and a whiteness of 27.67%.

[0090] The high-purity gypsum prepared was tested according to the method in Comparative Example 2. The soluble P2O5 content (mass content) was 0.87%, the soluble fluorine content (mass content) was 0.28%, the CaSO4·2H2O content (mass content) was 96.62%, the whiteness was 62.23%, and the SiO2 content (mass content) was 5.78%.

[0091] The phosphogypsum raw materials used in Comparative Example 2 and Example 2 were the same. In terms of process, the acid leaching step was removed, while all other steps were the same. It can be found that the phosphogypsum without acid leaching has a lower whiteness and is red. The red color is mainly due to the red appearance of Fe impurities in the phosphogypsum, and the soluble phosphorus and fluorine content is higher than that after acid leaching.

[0092] Comparative Example 3

[0093] This comparative example provides a method for preparing high-purity gypsum from phosphogypsum, including the following steps:

[0094] S1. The phosphogypsum dry-milled to a particle size of -0.075mm accounts for 92% of the total mass of the phosphogypsum;

[0095] S2. Place 200g of the dry-ground phosphogypsum from S1 in a sulfuric acid solution and acid-soak it at 50℃ for 2 hours, then filter it; wherein, the mass fraction of the sulfuric acid solution is 30%.

[0096] S3. Calcine the phosphogypsum filtered in step S2 at a calcination temperature of 600℃ for 1.5h to obtain high-purity gypsum.

[0097] The phosphogypsum used in step S1 is from a certain place in Hubei Province, with a soluble P2O5 content (mass content) of 1.78%, a soluble fluorine content (mass content) of 0.54%, a CaSO4·2H2O content (mass content) of 85.23%, a SiO2 content (mass content) of 9.07%, and a whiteness of 26.43%.

[0098] The high-purity gypsum prepared according to the method in Example 3 was tested. The soluble P2O5 content (mass content) was 0.01%, the soluble fluorine was below the detection limit, the CaSO4·2H2O content (mass content) was 86.44%, the whiteness was 94.22%, and the SiO2 content (mass content) was 8.89%.

[0099] The phosphogypsum raw materials used in Comparative Example 3 and Example 3 were the same. The only difference in the process was the removal of the flotation purification step; all other steps remained the same. It was observed that the SiO2 content of the phosphogypsum without flotation purification did not decrease.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-purity gypsum from phosphogypsum, characterized in that, Includes the following steps: Phosphogypsum is dry-milled until the particle size is controlled to a certain extent; 92-94% of the total mass of phosphogypsum is dry-milled until the particle size is less than 0.075 mm. Add the dry-ground phosphogypsum to an acid solution, leach, and filter. Add water to the filtered phosphogypsum to make a slurry, add 0.2 kg / t of amine collector and perform positive flotation until the foam is white. The product obtained is phosphogypsum after desilication and purification. The phosphogypsum after desiliconization and purification is calcined to obtain gypsum; The dry-ground phosphogypsum is added to an acid solution. In the acid leaching step, the acid solution is a sulfuric acid solution with a mass concentration of 30%, the acid leaching temperature is 50°C, and the acid leaching time is 2 hours. In the step of adding water to the filtered phosphogypsum to form a slurry, the mass concentration of the phosphogypsum after adding water to form a slurry is 30%. The amine collector is any one of dodecylamine, ethanolamine, and ethylenediamine formate; In the step of calcining the desiliconized and purified phosphogypsum, the calcination temperature is 600℃ and the calcination time is 1~1.5h.

2. The method for preparing high-purity gypsum from phosphogypsum as described in claim 1, characterized in that, In the step of dry grinding phosphogypsum to control the particle size to a certain extent, the mass content of CaSO4·2H2O in the phosphogypsum is 80%~90%, the whiteness is 20%~40%, and the mass content of SiO2 is 10%~15%.

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