A method for acidolysis-coupled flotation to whiten phosphogypsum

Abstract

The present invention belongs to the technical field of solid waste resource utilization, and particularly relates to a method for acidolysis coupling flotation to whiten phosphogypsum. The present invention pulverizes and disperses the phosphogypsum aggregates to release impurities such as slime and organic matter on the surface of gypsum crystals; sodium dodecyl glycinate is compounded with pine oil alcohol, and at the same time a foaming agent is added to effectively remove impurities such as slime, organic matter and siliceous minerals; by superimposing an acidolysis solution with a persulfate auxiliary agent, the present invention can not only improve the liquid-phase water activity, effectively release impurities such as eutectic phosphorus in the gypsum lattice, but also effectively promote the dissolution of insoluble impurities in the aqueous solution; according to the precipitation saturation index, the present invention regulates the liquid-phase pH to 8-9 to convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances; the present invention compounded dodecyl trimethyl ammonium chloride with tetradecylamine can effectively adsorb the negatively charged gypsum crystals through electrostatic attraction.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste resource utilization, and particularly relates to a method for acidolysis coupled with flotation to whiten phosphogypsum. Background Art

[0002] Phosphogypsum is a solid waste discharged in the wet-process phosphoric acid process. Its main component is calcium sulfate, and there are also unreacted phosphate rock, residual phosphoric acid, fluorides, acid-insoluble substances, and organic substances, etc. With the rapid development of China's phosphate fertilizer and fine phosphorus chemical industries, phosphogypsum has become a typical bulk solid waste in the Yangtze River Basin area, with a cumulative stockpile exceeding 800 million tons and still increasing year by year. Even more seriously, phosphogypsum contains harmful impurities such as phosphorus, fluorine, and organic matter that are easily leached by rainwater. Therefore, it is urgently necessary to carry out large-scale and high-quality resource treatment on it.

[0003] The types of harmful impurities remaining in phosphogypsum are numerous, and their distribution methods and occurrence forms are complex, which are the technical bottlenecks restricting its resource utilization. For example, the four major harmful impurities such as soluble phosphorus, eutectic phosphorus, soluble fluorine, and organic matter contained in it are likely to cause problems such as unstable quality, poor performance, and easy mildew of downstream products. At present, the main ways to dispose of phosphogypsum are to use it as a cement retarder or to prepare low-end building materials such as building gypsum powder and products, and the comprehensive utilization rate is only 40%. Therefore, comprehensive and in-depth impurity removal and whitening are the key problems that need to be solved urgently to achieve high-quality resource utilization of phosphogypsum.

[0004] At the present stage, the pretreatment technologies of phosphogypsum in China mainly include water washing method, lime neutralization method, flotation method, acid leaching method, etc. Among them, the water washing method can only remove the soluble impurities and part of the organic matter attached to the surface of phosphogypsum crystals, and has limitations in removing eutectic phosphorus and insoluble impurities; the lime neutralization method can only reduce the content of soluble phosphorus and fluorine, and has no purification effect on eutectic phosphorus, organic matter, and insoluble impurities; the flotation method can specifically and efficiently remove organic matter, insoluble impurities, and part of the soluble impurities in phosphogypsum, and has an obvious effect on improving the whiteness of phosphogypsum, but has no purification effect on eutectic phosphorus; the acid leaching method usually uses a single acid solution to transfer part of the insoluble impurities to the liquid phase, and realizes solid-liquid separation by extracting the solute with an organic solvent, but has a poor purification effect on acid-insoluble impurities.

[0005] In summary, the single purification pretreatment processes of phosphogypsum all have defects such as incomplete and non-comprehensive impurity removal, cannot meet the purification index requirements, and are difficult to be applied on a large scale industrially. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for acidolysis coupled with flotation to whiten phosphogypsum. The method provided by the present invention removes impurities and whitens more comprehensively and thoroughly, and the purity of the product is above 95%, and the whiteness is above 83%.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for acidolysis-coupled flotation to whiten phosphogypsum, comprising the following steps:

[0009] (1) Grinding phosphogypsum and then mixing it with water, reverse flotation reagents and a first foaming agent for reverse flotation to obtain a first phosphogypsum slurry; the reverse flotation reagents include sodium dodecyl glycinate and pine oil;

[0010] (2) Mixing the first phosphogypsum slurry with an acidolysis solution and persulfate for acidolysis to obtain a second phosphogypsum solid; the acidolysis solution includes citric acid and sulfuric acid;

[0011] (3) Mixing the second phosphogypsum solid, water and a pH regulator until the pH = 8-9 for a neutralization reaction to obtain a third phosphogypsum slurry;

[0012] (4) Mixing the third phosphogypsum slurry, direct flotation reagents, a second foaming agent and a foam stabilizer for direct flotation to obtain a phosphogypsum concentrate; the direct flotation reagents include dodecyl trimethyl ammonium chloride and tetradecylamine.

[0013] Preferably, in step (1), the mass ratio of sodium dodecyl glycinate to pine oil is 1:0.5-1.5;

[0014] The first foaming agent includes one or more of methyl isobutyl carbinol, sodium lauryl polyoxyethylene ether sulfate and rosin soap foaming agents.

[0015] Preferably, in step (2), the mass ratio of citric acid to sulfuric acid is 7-10:1;

[0016] The total concentration of citric acid and sulfuric acid in the acidolysis solution is 20-30 wt%;

[0017] The persulfate is potassium persulfate.

[0018] Preferably, in step (4), the mass ratio of dodecyl trimethyl ammonium chloride to tetradecylamine is 1:1-2;

[0019] The second foaming agent is methyl isobutyl carbinol;

[0020] The foam stabilizer includes one or more of nano-silica, nano-alumina and nano-zinc oxide.

[0021] Preferably, in step (3), the mass ratio of the second phosphogypsum solid to water is 25-35:65-75.

[0022] Preferably, in step (1), the mass ratio of phosphogypsum to water is 25-35:65-75;

[0023] The mass ratio of the total mass of the phosphogypsum and water to the mass of the reverse flotation reagent is 10,000:1 to 2;

[0024] The mass ratio of the total mass of the phosphogypsum and water to the mass of the first foaming agent is 10,000:2 to 3.

[0025] Preferably, in step (2), the solid content of the first phosphogypsum slurry is 25 to 35 wt%;

[0026] The mass ratio of the first phosphogypsum slurry to the acidolysis solution is 1:1 to 4;

[0027] The mass ratio of the total mass of the first phosphogypsum slurry and the acidolysis solution to the mass of the persulfate is 95 to 97:3 to 5.

[0028] Preferably, in step (4), the solid content of the third phosphogypsum slurry is 20 to 30 wt%;

[0029] The mass ratio of the third phosphogypsum slurry to the positive flotation reagent is 100,000:10 to 15;

[0030] The mass ratio of the third phosphogypsum slurry to the second foaming agent is 100,000:15 to 25;

[0031] The mass ratio of the third phosphogypsum slurry to the foam stabilizer is 100,000:5 to 10.

[0032] Preferably, the temperature of the acidolysis is 75 to 90 °C, and the heat preservation time is 15 to 25 min.

[0033] Preferably, the moisture content of the phosphogypsum is 10 to 20%, and the specific surface area of the ground phosphogypsum is 450 to 600 m 2 / kg.

[0034] The present invention provides a method for acidolysis-coupled flotation to whiten phosphogypsum. In view of the characteristics of the types, distribution rules, and occurrence states of impurities in phosphogypsum, the present invention first grinds and disperses the phosphogypsum aggregates to release impurities such as slime and organic matter on the surface of gypsum crystals, thereby improving the subsequent reverse flotation efficiency;

[0035] The present invention combines sodium dodecyl glycinate containing amino functional groups with pine oil containing hydroxyl functional groups, gives full play to the superposition effect of the reagents, and simultaneously adds a foaming agent to further enhance the reverse flotation efficiency, effectively removing impurities such as slime, organic matter, and siliceous minerals;

[0036] In the present invention, by superimposing persulfate additives on the acidolysis solution, on the one hand, the liquid-phase water activity is improved, the driving force for the dissolution and recrystallization of phosphogypsum is increased, the phase change rate of gypsum dehydration is significantly increased, and impurities such as eutectic phosphorus in the gypsum lattice are effectively released. On the other hand, the provided composite acid liquid-phase environment can effectively promote the dissolution of insoluble impurities in the aqueous solution, providing convenient conditions for the further purification of phosphogypsum.

[0037] In the present invention, the liquid-phase pH is adjusted to 8-9 according to the precipitation saturation index, and the residual soluble phosphorus and soluble fluorine in the liquid phase are converted into insoluble calcium phosphate and calcium fluoride inert substances.

[0038] In the present invention, dodecyltrimethylammonium chloride and tetradecylamine are compounded to give full play to the superimposed effect of the agents. The obtained positive flotation agent, as a composite cationic collector, can effectively adsorb the electro-negative gypsum crystals through electrostatic attraction. Adding a foam stabilizer increases the foam stability and significantly improves the positive flotation efficiency.

[0039] The method provided by the present invention for impurity removal and whitening is comprehensive, thorough and efficient. The present invention effectively couples acidolysis and flotation methods, deeply optimizes purification process parameters such as the molecular structure of flotation agents and the acidolysis liquid-phase environment, removes various impurities successively, and effectively avoids the mutual influence between impurities. It can be used for the efficient impurity removal and whitening of phosphogypsum, boosting the large-scale and high-quality resource utilization of phosphogypsum. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0041] Figure 1 It is a flow chart of the method for acidolysis-coupled flotation and whitening of phosphogypsum provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The present invention provides a method for acidolysis-coupled flotation and whitening of phosphogypsum, comprising the following steps:

[0043] (1) Grinding phosphogypsum and mixing it with water, reverse flotation agents and a first foaming agent for reverse flotation to obtain a first phosphogypsum slurry; the reverse flotation agents include sodium dodecylglycinate and pine oil.

[0044] (2) Mixing the first phosphogypsum slurry with an acidolysis solution and persulfate for acidolysis to obtain a second phosphogypsum solid; the acidolysis solution includes citric acid and sulfuric acid.

[0045] (3) Mix the second phosphogypsum solid, water, and pH regulator until the pH = 8 - 9 for a neutralization reaction to obtain a third phosphogypsum slurry;

[0046] (4) Mix the third phosphogypsum slurry, direct flotation reagent, second foaming agent, and foam stabilizer for direct flotation to obtain phosphogypsum concentrate; the direct flotation reagent includes dodecyl trimethyl ammonium chloride and tetradecylamine.

[0047] In the present invention, the phosphogypsum is ground and then mixed with water, reverse flotation reagent, and first foaming agent for reverse flotation to obtain a first phosphogypsum slurry. In the present invention, the moisture content (target moisture content) of the phosphogypsum is preferably 11 - 18%, more preferably 13 - 16%, and further preferably 15%; the phosphogypsum raw material is preferably dried, water-added, or untreated according to the actual moisture content to reach the target moisture content.

[0048] In the present invention, the grinding is preferably ball milling; the material-to-ball ratio of the ball milling is preferably 2 - 3:1, more preferably 2.3 - 2.7:1, and the ball milling time is preferably 5 - 10 min, more preferably 7 - 9 min; the specific surface area of the ground phosphogypsum is preferably 450 - 600 m 2 / kg, more preferably 500 - 550 m 2 / kg. Through grinding in the present invention, the agglomerated particles in the phosphogypsum can be fully dispersed and ground, and the surface impurities of the gypsum crystals can be released.

[0049] In the present invention, the reverse flotation reagent includes sodium dodecyl glycinate and pine oil; the mass ratio of sodium dodecyl glycinate to pine oil is preferably 1:0.5 - 1.5, more preferably 1:0.7 - 1.3, and further preferably 1:0.9 - 1.1. In the present invention, sodium dodecyl glycinate containing an amino functional group is compounded with pine oil containing a hydroxyl functional group to give full play to the superimposed effect of the reagent and effectively remove impurities such as slime, organic matter, and siliceous minerals.

[0050] In the present invention, the first foaming agent preferably includes one or more of methyl isobutyl carbinol, sodium lauryl polyoxyethylene ether sulfate, and rosin soap foaming agents, and more preferably methyl isobutyl carbinol; the rosin soap foaming agents preferably include one or more of rosin soap and rosin heat polymer. Adding a foaming agent in the present invention can further enhance the reverse flotation efficiency and more effectively remove impurities such as slime, organic matter, and siliceous minerals.

[0051] In the present invention, the mass ratio of the phosphogypsum to water is preferably 25-35:65-75, more preferably 27-32:67-72, and further preferably 29-30:69-70; the mass ratio of the total mass of the phosphogypsum and water to the mass of the reverse flotation reagent is preferably 10000:1-2, more preferably 10000:1.2-1.8, and further preferably 10000:1.4-1.6; the mass ratio of the total mass of the phosphogypsum and water to the mass of the first foaming agent is preferably 10000:2-3, more preferably 10000:2.2-2.8, and further preferably 10000:2.4-2.6.

[0052] In the present invention, the mixing of the ground phosphogypsum with water, the reverse flotation reagent and the first foaming agent is preferably as follows: the ground phosphogypsum is mixed with water to obtain an intermediate phosphogypsum pulp, then the intermediate phosphogypsum pulp is mixed with the reverse flotation reagent to obtain an intermediate phosphogypsum pulp with added reagent, and then the intermediate phosphogypsum pulp with added reagent is mixed with the first foaming agent.

[0053] In the present invention, the time for reverse flotation is preferably 3-5 min, more preferably 4 min; the reverse flotation is preferably carried out under stirring conditions; the rotation speed of the stirring is preferably 2500-3000 r / min, more preferably 2700-3000 r / min. Through the above reverse flotation, impurities such as slime, organic matter and acid-insoluble siliceous minerals in the phosphogypsum are floated and removed in the present invention.

[0054] After obtaining the first phosphogypsum slurry, in the present invention, the first phosphogypsum slurry is mixed with an acidolysis solution and persulfate for acidolysis to obtain a second phosphogypsum solid. In the present invention, the solid content of the first phosphogypsum slurry is preferably 25-35 wt%, more preferably 25-30 wt%, and further preferably 27-30 wt%; the acidolysis solution includes citric acid and sulfuric acid; the mass ratio of citric acid to sulfuric acid is preferably 7-10:1, more preferably 7-9:1, and further preferably 8:1; the total concentration of citric acid and sulfuric acid in the acidolysis solution is preferably 20-30 wt%, more preferably 22-28 wt%, and further preferably 24-26 wt%; the persulfate is preferably potassium persulfate. The added persulfate in the present invention has a coupling effect, which can further reduce the water activity of the solution, promote the dissolution and recrystallization of gypsum, release a large amount of impurities, and lay a foundation for impurity removal.

[0055] In the present invention, the mass ratio of the first phosphogypsum slurry to the acidolysis solution is preferably 1:1-4, more preferably 1:2-3, and further preferably 1:2-2.5; the mass ratio of the total mass of the first phosphogypsum slurry and the acidolysis solution to the mass of the persulfate is preferably 95-97:3-5, more preferably 95.5-96.5:3.5-4.5, and further preferably 96:4.

[0056] In the present invention, the temperature of the acidolysis is preferably 75 - 90°C, more preferably 79 - 88°C, and further preferably 82 - 85°C. The heat preservation time is preferably 15 - 25 min, more preferably 18 - 22 min, and further preferably 20 min. The acidolysis is preferably carried out under stirring conditions. The rotation speed of the stirring is preferably 2500 - 3000 r / min, more preferably 2700 - 3000 r / min. Through the above acidolysis, the present invention can promote the dissolution and recrystallization of phosphogypsum, release impurities such as eutectic phosphorus inside the phosphogypsum lattice, and simultaneously acidolyze some insoluble impurities such as iron oxide and aluminum oxide.

[0057] In the present invention, after the acidolysis, the obtained product is preferably filtered. The filtration is preferably vacuum filtration. The vacuum degree of the vacuum filtration is preferably 0.06 - 0.08 MPa, more preferably 0.06 - 0.07 MPa. After the solid-liquid separation by vacuum filtration in the present invention, an acidolysis solution containing impurities and a phosphogypsum solid with a purity greater than 91% are obtained, and the acidolysis solution can be recycled.

[0058] After obtaining the second phosphogypsum solid, the present invention mixes the second phosphogypsum solid, water and a pH regulator until the pH = 8 - 9 for a neutralization reaction to obtain a third phosphogypsum slurry. In the present invention, the pH regulator is preferably quicklime. The pH is preferably 8.3 - 8.7, and more preferably 8.5.

[0059] In the present invention, the mass ratio of the second phosphogypsum solid to water is preferably 25 - 35:65 - 75, more preferably 27 - 32:68 - 73, and further preferably 29 - 30:70 - 71.

[0060] In the present invention, the mixing of the second phosphogypsum solid, water and a pH regulator is preferably as follows: the second phosphogypsum solid and water are mixed to obtain a second phosphogypsum intermediate slurry, and then the second phosphogypsum intermediate slurry and the pH regulator are mixed.

[0061] In the present invention, the time of the neutralization reaction is preferably 4 - 5 min, more preferably 4.2 - 4.5 min. The neutralization reaction is preferably carried out under stirring conditions. The rotation speed of the stirring is preferably 2500 - 3000 r / min, more preferably 2700 - 3000 r / min. The pH of the third phosphogypsum slurry is preferably 6 - 7. After the neutralization reaction, the obtained product is preferably filtered. Through the neutralization reaction, the present invention converts the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, and then filters to remove the insoluble substances.

[0062] After obtaining the third phosphogypsum slurry, the present invention mixes the third phosphogypsum slurry, a positive flotation reagent, a second foaming agent, and a foam stabilizer for positive flotation to obtain a phosphogypsum concentrate. In the present invention, the solid content of the third phosphogypsum slurry is preferably 20 to 30 wt%, more preferably 22 to 28 wt%, and further preferably 24 to 26 wt%; the positive flotation reagent includes dodecyl trimethyl ammonium chloride and tetradecylamine; the mass ratio of dodecyl trimethyl ammonium chloride to tetradecylamine is preferably 1:1 to 2, more preferably 1:1.2 to 1.8, and further preferably 1:1.4 to 1.6.

[0063] In the present invention, the second foaming agent is preferably methyl isobutyl carbinol; the foam stabilizer preferably includes one or more of nano-silica, nano-alumina, and nano-zinc oxide, and more preferably nano-silica.

[0064] In the present invention, the mass ratio of the third phosphogypsum slurry to the positive flotation reagent is preferably 100,000:10 to 15, more preferably 100,000:11 to 14, and further preferably 100,000:12 to 13; the mass ratio of the third phosphogypsum slurry to the second foaming agent is preferably 100,000:15 to 25, more preferably 100,000:17 to 23, and further preferably 100,000:19 to 21; the mass ratio of the third phosphogypsum slurry to the foam stabilizer is preferably 100,000:5 to 10, more preferably 100,000:6 to 9, and further preferably 100,000:7 to 8.

[0065] In the present invention, the time for positive flotation is preferably 5 to 10 min, more preferably 6 to 9 min, and further preferably 7 to 8 min. The floating product obtained by positive flotation in the present invention is a high-purity phosphogypsum concentrate with a purity of not less than 95%.

[0066] Figure 1The flow chart of the method for acidolysis-coupled flotation to whiten phosphogypsum provided by the present invention. First, the present invention grinds and disperses the aggregates in phosphogypsum to release impurities such as slime and organic matter on the surface of gypsum crystals; secondly, reverse flotation agents and foaming agents are added for reverse flotation to effectively remove impurities such as slime, organic matter and siliceous minerals; then, an acidolysis solution is superimposed with a persulfate auxiliary agent to effectively release impurities such as eutectic phosphorus in the gypsum lattice, and can also effectively promote the dissolution of insoluble impurities in the aqueous solution; then, the pH of the liquid phase is adjusted to 8-9 according to the precipitation saturation index for a neutralization reaction to convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances; then, positive flotation agents are added for positive flotation, which can effectively adsorb the negatively charged gypsum crystals on the surface through electrostatic attraction, and finally obtain a phosphogypsum concentrate. In view of the characteristics of the types, distribution rules and occurrence states of impurities in phosphogypsum, the present invention effectively couples acidolysis and flotation methods, deeply optimizes purification process parameters such as the molecular structure of reagents and the liquid phase environment, and establishes a method for efficient impurity removal and whitening of phosphogypsum by acidolysis-coupled flotation, boosting the large-scale and high-quality resource utilization of phosphogypsum.

[0067] To further illustrate the present invention, the solutions of the present invention will be described in detail below in conjunction with the drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0068] Example 1

[0069] (1) Take the phosphogypsum raw material to be purified and control the moisture content of the phosphogypsum raw material to be 15%;

[0070] (2) Place the phosphogypsum raw material in a grinding device, with a material-ball ratio of 2.5:1, grind for 7 minutes, and control the specific surface area of the phosphogypsum to be 550 m 2 / kg;

[0071] (3) Add water to the ground phosphogypsum fines to adjust the pulp concentration to 30%; add 150 g / t of reverse flotation agent, and the reverse flotation agent is sodium dodecyl glycinate containing an amino functional group and pine oil containing a hydroxyl functional group, which are uniformly mixed in a mass ratio of 1:1; continue to add 250 g / t of foaming agent methyl isobutyl carbinol; control the reverse flotation time to be 5 minutes and the stirring speed to be 3000 r / min, and float up to remove impurities such as slime, organic matter and acid-insoluble siliceous minerals in the phosphogypsum to obtain the first phosphogypsum slurry;

[0072] (4) Compound citric acid and sulfuric acid according to a mass ratio of 8:1, add water to prepare an acidolysis solution with a mass concentration of 25%, add the acidolysis solution to the first phosphogypsum slurry obtained in step (3), and simultaneously add a potassium persulfate auxiliary agent. The mass ratio of the potassium persulfate auxiliary agent to the phosphogypsum ore pulp is 96:4; control the liquid-solid mass ratio of the obtained reaction slurry to be 15:1, the acidolysis temperature to be 80 °C, the stirring speed to be 3000 r / min, and the acidolysis time to be 20 min; then perform vacuum filtration, and after solid-liquid separation, obtain an acidolysis solution containing impurities and a second phosphogypsum solid, wherein the acidolysis solution can be recycled;

[0073] (5) Add water to the second phosphogypsum solid obtained in step (4) to adjust the pulp concentration to 30%, add quicklime and stir, control the pH to be 8.5, the stirring speed to be 3000 r / min, and the neutralization reaction time to be 5 min, convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, filter and separate to obtain a third phosphogypsum slurry;

[0074] (6) Add 120 g / t of a positive flotation reagent to the third phosphogypsum slurry obtained in step (5). The positive flotation reagent is a uniform mixture of dodecyl trimethyl ammonium chloride and tetradecylamine according to a mass ratio of 1:1; continue to add 200 g / t of a foaming agent methyl isobutyl carbinol and 75 g / t of a foam stabilizer nano-silica; control the concentration of the third phosphogypsum slurry to be 25% and the positive flotation time to be 6 min. The floating product obtained is the phosphogypsum concentrate.

[0075] Example 2

[0076] (1) Take the phosphogypsum raw material to be purified and control the moisture content of the phosphogypsum raw material to be 12%;

[0077] (2) Place the phosphogypsum raw material in a grinding equipment, with a material-ball ratio of 2:1, grind for 5 min, and control the specific surface area of the phosphogypsum to be 450 m 2 / kg;

[0078] (3) Add water to the ground phosphogypsum fines to adjust the pulp concentration to 25%; add 100 g / t of a reverse flotation reagent. The reverse flotation reagent is a uniform mixture of sodium dodecyl glycinate containing an amino functional group and pine oil containing a hydroxyl functional group according to a mass ratio of 1:1; continue to add 200 g / t of a foaming agent methyl isobutyl carbinol; control the reverse flotation time to be 3 min and the stirring speed to be 3000 r / min, float and remove impurities such as slime, organic matter and acid-insoluble siliceous minerals in the phosphogypsum to obtain a first phosphogypsum slurry;

[0079] (4) Compound citric acid and sulfuric acid in a mass ratio of 7:1, add water to prepare an acidolysis solution with a mass concentration of 20%, add the acidolysis solution to the first phosphogypsum slurry obtained in step (3), and simultaneously add a potassium persulfate auxiliary agent. The mass ratio of the potassium persulfate auxiliary agent to the phosphogypsum ore pulp is 97:3; control the solid-liquid mass ratio of the reaction slurry to be 10:1, the acidolysis temperature to be 75 °C, the stirring speed to be 3000 r / min, and the acidolysis time to be 15 min; then perform vacuum filtration, and after solid-liquid separation, obtain an acidolysis solution containing impurities and a second phosphogypsum solid, wherein the acidolysis solution can be recycled;

[0080] (5) Add water to the second phosphogypsum solid obtained in step (4) to adjust the pulp concentration to 25%, add quicklime and stir, control the pH to be 8, the stirring speed to be 3000 r / min, and the neutralization reaction time to be 5 min, convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, and perform filtration separation to obtain a third phosphogypsum slurry;

[0081] (6) Add 100 g / t of positive flotation reagent to the third phosphogypsum slurry obtained in step (5). The positive flotation reagent is a uniform mixture of dodecyl trimethyl ammonium chloride and tetradecylamine in a mass ratio of 1:1; continue to add 150 g / t of foaming agent methyl isobutyl carbinol and 50 g / t of foam stabilizer nano-silica; control the concentration of the third phosphogypsum slurry to be 20% and the positive flotation time to be 5 min. The floating product obtained is the phosphogypsum concentrate.

[0082] Example 3

[0083] (1) Take the phosphogypsum raw material to be purified and control the moisture content of the phosphogypsum raw material to be 20%;

[0084] (2) Place the phosphogypsum raw material in a grinding device, with a material-ball ratio of 3:1, grind for 10 min, and control the specific surface area of the phosphogypsum to be 600 m 2 / kg;

[0085] (3) Add water to the ground phosphogypsum fine material to adjust the pulp concentration to 35%; add 200 g / t of reverse flotation reagent. The reverse flotation reagent is a uniform mixture of sodium dodecyl glycinate containing an amino functional group and pine oil containing a hydroxyl functional group in a mass ratio of 1:1; continue to add 300 g / t of foaming agent methyl isobutyl carbinol; control the reverse flotation time to be 5 min and the stirring speed to be 2800 r / min, float and remove impurities such as slime, organic matter, and acid-insoluble siliceous minerals in the phosphogypsum to obtain a first phosphogypsum slurry;

[0086] (4) Compound citric acid and sulfuric acid in a mass ratio of 10:1, add water to prepare an acidolysis solution with a mass concentration of 30%, add the acidolysis solution to the first phosphogypsum slurry obtained in step (3), and simultaneously add a potassium persulfate auxiliary agent. The mass ratio of the potassium persulfate auxiliary agent to the phosphogypsum ore pulp is 95:5; control the solid-liquid mass ratio of the reaction slurry to be 20:1, the acidolysis temperature to be 90 °C, the stirring speed to be 3000 r / min, and the acidolysis time to be 25 min; then perform vacuum filtration, and after solid-liquid separation, obtain an acidolysis solution containing impurities and a second phosphogypsum solid, wherein the acidolysis solution can be recycled;

[0087] (5) Add water to the second phosphogypsum solid obtained in step (4) to adjust the pulp concentration to 35%, add quicklime and stir. The stirring speed is 3000 r / min, control the pH to be 9, and the neutralization reaction time is 5 min to convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, and perform filtration separation to obtain a third phosphogypsum slurry;

[0088] (6) Add 150 g / t of positive flotation reagent to the third phosphogypsum slurry obtained in step (5). The positive flotation reagent is a uniform mixture of dodecyl trimethyl ammonium chloride and tetradecylamine in a mass ratio of 1:1; continue to add 250 g / t of foaming agent methyl isobutyl carbinol and 100 g / t of foam stabilizer nano-silica; control the concentration of the third phosphogypsum slurry to be 30%, and the positive flotation time to be 10 min. The floating product obtained is the phosphogypsum concentrate.

[0089] Example 4

[0090] (1) Take the phosphogypsum raw material to be purified and control the moisture content of the phosphogypsum raw material to be 15%;

[0091] (2) Place the phosphogypsum raw material in a grinding device, with a material-ball ratio of 2.5:1, grind for 7 min, and control the specific surface area of the phosphogypsum to be 550 m 2 / kg;

[0092] (3) Add water to the ground phosphogypsum fine material to adjust the pulp concentration to 30%; add 150 g / t of reverse flotation reagent. The reverse flotation reagent is a uniform mixture of sodium dodecyl glycinate containing an amino functional group and pine oil containing a hydroxyl functional group in a mass ratio of 1:0.5; continue to add 250 g / t of foaming agent sodium lauryl polyoxyethylene ether sulfate; control the reverse flotation time to be 5 min, the stirring speed to be 3000 r / min, and float and remove impurities such as slime, organic matter, and acid-insoluble siliceous minerals in the phosphogypsum to obtain a first phosphogypsum slurry;

[0093] (4) Compound citric acid and sulfuric acid in a mass ratio of 8:1, add water to prepare an acidolysis solution with a mass concentration of 25%, add the acidolysis solution to the first phosphogypsum slurry obtained in step (3), and simultaneously add a potassium persulfate auxiliary agent. The mass ratio of the potassium persulfate auxiliary agent to the phosphogypsum pulp is 96:4; control the liquid-solid mass ratio of the obtained reaction slurry to be 15:1, the acidolysis temperature to be 80 °C, the stirring speed to be 3000 r / min, and the acidolysis time to be 20 min; then perform vacuum filtration, and after solid-liquid separation, obtain an acidolysis solution containing impurities and a second phosphogypsum solid, wherein the acidolysis solution can be recycled;

[0094] (5) Add water to the second phosphogypsum solid obtained in step (4) to adjust the pulp concentration to 30%, add quicklime and stir, control the pH to be 8.5, the stirring speed to be 2500 r / min, and the neutralization reaction time to be 4 min, convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, filter and separate to obtain a third phosphogypsum slurry;

[0095] (6) Add 120 g / t of a positive flotation reagent to the third phosphogypsum slurry obtained in step (5). The positive flotation reagent is a uniform mixture of dodecyltrimethylammonium chloride and tetradecylamine in a mass ratio of 1:1.2; continue to add 200 g / t of a foaming agent, methyl isobutyl carbinol, and 75 g / t of a foam stabilizer, nano-aluminum oxide; control the concentration of the third phosphogypsum slurry to be 25%, and the positive flotation time to be 6 min. The floating product obtained is the phosphogypsum concentrate.

[0096] Example 5

[0097] (1) Take the phosphogypsum raw material to be purified and control the moisture content of the phosphogypsum raw material to be 15%;

[0098] (2) Place the phosphogypsum raw material in a grinding device, with a material-ball ratio of 2.5:1, grind for 7 min, and control the specific surface area of the phosphogypsum to be 550 m 2 / kg;

[0099] (3) Add water to the ground phosphogypsum fine material to adjust the pulp concentration to 30%; add 150 g / t of a reverse flotation reagent. The reverse flotation reagent is a uniform mixture of sodium dodecyl glycinate containing an amino functional group and pine oil containing a hydroxyl functional group in a mass ratio of 1:1; continue to add 250 g / t of a foaming agent, rosin soap; control the reverse flotation time to be 5 min, the stirring speed to be 2600 r / min, and float and remove impurities such as slime, organic matter, and acid-insoluble siliceous minerals in the phosphogypsum to obtain a first phosphogypsum slurry;

[0100] (4) Compound citric acid and sulfuric acid in a mass ratio of 8:1, add water to prepare an acidolysis solution with a mass concentration of 25%, add the acidolysis solution to the first phosphogypsum slurry obtained in step (3), and simultaneously add a potassium persulfate auxiliary agent. The mass ratio of the potassium persulfate auxiliary agent to the phosphogypsum ore pulp is 96:4; control the liquid-solid mass ratio of the obtained reaction slurry to be 15:1, the acidolysis temperature to be 80 °C, the stirring speed to be 2700 r / min, and the acidolysis time to be 20 min; then perform vacuum filtration, and after solid-liquid separation, obtain an acidolysis solution containing impurities and a second phosphogypsum solid, wherein the acidolysis solution can be recycled;

[0101] (5) Add water to the second phosphogypsum solid obtained in step (4) to adjust the pulp concentration to 30%, add quicklime and stir, control the pH to be 8.5, the stirring speed to be 2800 r / min, and the neutralization reaction time to be 5 min, convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, filter and separate to obtain a third phosphogypsum slurry;

[0102] (6) Add 120 g / t of positive flotation reagent to the third phosphogypsum slurry obtained in step (5). The positive flotation reagent is a uniform mixture of dodecyl trimethyl ammonium chloride and tetradecylamine in a mass ratio of 1:1.5; continue to add 200 g / t of foaming agent methyl isobutyl carbinol and 75 g / t of foam stabilizer nano zinc oxide; control the concentration of the third phosphogypsum slurry to be 25% and the positive flotation time to be 6 min. The floating product obtained is the phosphogypsum concentrate.

[0103] Example 6

[0104] (1) Take the phosphogypsum raw material to be purified and control the moisture content of the phosphogypsum raw material to be 15%;

[0105] (2) Place the phosphogypsum raw material in a grinding device, with a material-ball ratio of 2.5:1, grind for 7 min, and control the specific surface area of the phosphogypsum to be 550 m 2 / kg;

[0106] (3) Add water to the ground phosphogypsum fines to adjust the pulp concentration to 30%; add 150 g / t of reverse flotation reagent. The reverse flotation reagent is a uniform mixture of sodium dodecyl glycinate containing an amino functional group and pine oil containing a hydroxyl functional group in a mass ratio of 1:1.5; continue to add 250 g / t of foaming agent methyl isobutyl carbinol; control the reverse flotation time to be 5 min and the stirring speed to be 3000 r / min, and float and remove impurities such as slime, organic matter, and acid-insoluble siliceous minerals in the phosphogypsum to obtain a first phosphogypsum slurry;

[0107] (4) Compound citric acid and sulfuric acid in a mass ratio of 8:1, add water to prepare an acid hydrolysis solution with a mass concentration of 25%, add the acid hydrolysis solution to the first phosphogypsum slurry obtained in step (3), and simultaneously add a potassium persulfate auxiliary agent. The mass ratio of the potassium persulfate auxiliary agent to the phosphogypsum pulp is 96:4; control the liquid-solid mass ratio of the obtained reaction slurry to be 15:1, the acid hydrolysis temperature to be 80 °C, the stirring speed to be 2500 r / min, and the acid hydrolysis time to be 20 min; then perform vacuum filtration, and after solid-liquid separation, obtain an acid hydrolysis solution containing impurities and a second phosphogypsum solid, wherein the acid hydrolysis solution can be recycled;

[0108] (5) Add water to the second phosphogypsum solid obtained in step (4) to adjust the pulp concentration to 30%, add quicklime and stir, control the pH to be 8.5, the stirring speed to be 2900 r / min, and the neutralization reaction time to be 4 min, convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, filter and separate to obtain a third phosphogypsum slurry;

[0109] (6) Add 120 g / t of positive flotation reagent to the third phosphogypsum slurry obtained in step (5). The positive flotation reagent is a uniform mixture of dodecyltrimethylammonium chloride and tetradecylamine in a mass ratio of 1:2; continue to add 200 g / t of foaming agent methyl isobutyl carbinol and 75 g / t of foam stabilizer nano-silica; control the concentration of the third phosphogypsum slurry to be 25%, and the positive flotation time to be 6 min. The floating product obtained is the phosphogypsum concentrate.

[0110] Comparative Example 1

[0111] The main difference from Example 1 is that the phosphogypsum material lacks the pretreatment process of grinding and dispersing agglomerates, and the reverse flotation reagent used is the conventional single pine oil.

[0112] (1) Take the phosphogypsum raw material to be purified, add water to adjust the pulp concentration to 30%; add 150 g / t of reverse flotation reagent. The reverse flotation reagent is pine oil containing hydroxyl functional groups; continue to add 250 g / t of foaming agent methyl isobutyl carbinol; control the reverse flotation time to be 5 min, the stirring speed to be 3000 r / min, float and remove impurities such as slime and organic matter in the phosphogypsum to obtain a first phosphogypsum slurry;

[0113] (2) Mix citric acid and sulfuric acid in a mass ratio of 8:1, add water to prepare an acidolysis solution with a mass concentration of 25%, add the acidolysis solution to the first phosphogypsum slurry obtained in step (1), and at the same time add potassium persulfate as an auxiliary agent. The mass ratio of the potassium persulfate auxiliary agent to the phosphogypsum slurry is 96:4. Control the liquid-solid mass ratio of the resulting reaction slurry to be 15:1, the acidolysis temperature to be 80 °C, the stirring speed to be 3000 r / min, and the acidolysis time to be 20 min. Then, after vacuum filtration and solid-liquid separation, an acidolysis solution containing impurities and a second phosphogypsum solid are obtained, and the acidolysis solution can be recycled;

[0114] (3) Add water to the second phosphogypsum solid obtained in step (2) to adjust the pulp concentration to 30%, add quicklime and stir, control the pH to be 8.5, the stirring speed to be 3000 r / min, and the neutralization reaction time to be 5 min, so as to convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, and then filter and separate to obtain a third phosphogypsum slurry;

[0115] (4) Add 120 g / t of positive flotation reagent to the third phosphogypsum slurry obtained in step (3). The positive flotation reagent is a uniform mixture of dodecyl trimethyl ammonium chloride and tetradecylamine in a mass ratio of 1:1. Continue to add 200 g / t of foaming agent methyl isobutyl carbinol and 75 g / t of foam stabilizer nano-silica. Control the concentration of the third phosphogypsum slurry to be 25% and the positive flotation time to be 6 min. The floating product obtained is the phosphogypsum concentrate.

[0116] Comparative Example 2

[0117] The main difference from Example 1 is that the acid leaching solution used is conventional single sulfuric acid and the potassium persulfate auxiliary agent is missing.

[0118] (1) Take the phosphogypsum raw material to be purified and control the moisture content of the phosphogypsum raw material to be 15%;

[0119] (2) Place the phosphogypsum raw material in a grinding equipment, with a material-ball ratio of 2.5:1, grind for 7 min, and control the specific surface area of the phosphogypsum to be 550 m 2 / kg;

[0120] (3) Add water to the ground phosphogypsum fines to adjust the pulp concentration to 30%; add 150 g / t of reverse flotation reagent. The reverse flotation reagent is a uniform mixture of sodium dodecyl glycinate containing amino functional groups and pine oil containing hydroxyl functional groups in a mass ratio of 1:1. Continue to add 250 g / t of foaming agent methyl isobutyl carbinol; control the reverse flotation time to be 5 min and the stirring speed to be 3000 r / min, float and remove impurities such as slime, organic matter and acid-insoluble siliceous minerals in the phosphogypsum to obtain a first phosphogypsum slurry;

[0121] (4) Prepare an acidolysis solution with a mass concentration of 25% by mixing sulfuric acid with water, and add the acidolysis solution to the first phosphogypsum slurry obtained in step (3); control the liquid-solid mass ratio of the resulting reaction slurry to be 15:1, the acidolysis temperature to be 80 °C, the stirring speed to be 3000 r / min, and the acidolysis time to be 20 min; then, after vacuum filtration and solid-liquid separation, an acidolysis solution containing impurities and a second phosphogypsum solid are obtained, and the acidolysis solution can be recycled;

[0122] (5) Add water to the second phosphogypsum solid obtained in step (4) to adjust the pulp concentration to 30%, add quicklime and stir, control the pH to be 8.5, the stirring speed to be 3000 r / min, and the neutralization reaction time to be 5 min to convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, and then filter and separate to obtain a third phosphogypsum slurry;

[0123] (6) Add 120 g / t of positive flotation reagent to the third phosphogypsum slurry obtained in step (5). The positive flotation reagent is a uniform mixture of dodecyl trimethyl ammonium chloride and tetradecylamine in a mass ratio of 1:1; continue to add 200 g / t of foaming agent methyl isobutyl carbinol and 75 g / t of foam stabilizer nano-silica; control the concentration of the third phosphogypsum slurry to be 25% and the positive flotation time to be 6 min, and the floating product obtained is the phosphogypsum concentrate.

[0124] Comparative Example 3

[0125] The main difference from Example 1 is that the positive flotation reagent used is the conventional single tetradecylamine and the nano-silica foam stabilizer is missing.

[0126] (1) Take the phosphogypsum raw material to be purified and control the moisture content of the phosphogypsum raw material to be 15%;

[0127] (2) Place the phosphogypsum raw material in a grinding equipment, with a material-ball ratio of 2.5:1, grind for 7 min, and control the specific surface area of the phosphogypsum to be 550 m 2 / kg;

[0128] (3) Add water to the ground phosphogypsum fines to adjust the pulp concentration to 30%; add 150 g / t of reverse flotation reagent. The reverse flotation reagent is a uniform mixture of sodium dodecyl glycinate containing an amino functional group and pine oil containing a hydroxyl functional group in a mass ratio of 1:1; continue to add 250 g / t of foaming agent methyl isobutyl carbinol; control the reverse flotation time to be 5 min and the stirring speed to be 3000 r / min, and float and remove impurities such as slime, organic matter, and acid-insoluble siliceous minerals in the phosphogypsum to obtain a first phosphogypsum slurry;

[0129] (4) Compound citric acid and sulfuric acid according to a mass ratio of 8:1, add water to prepare an acidolysis solution with a mass concentration of 25%, add the acidolysis solution to the first phosphogypsum slurry obtained in step (3), and simultaneously add a potassium persulfate auxiliary agent. The mass ratio of the potassium persulfate auxiliary agent to the phosphogypsum ore pulp is 96:4; control the liquid-solid mass ratio of the obtained reaction slurry to be 15:1, the acidolysis temperature to be 80 °C, the stirring speed to be 3000 r / min, and the acidolysis time to be 20 min; then perform vacuum filtration, and after solid-liquid separation, obtain an acidolysis solution containing impurities and a second phosphogypsum solid, wherein the acidolysis solution can be recycled;

[0130] (5) Add water to the second phosphogypsum solid obtained in step (4) to adjust the pulp concentration to 30%, add quicklime and stir, control the pH to be 8.5, the stirring speed to be 3000 r / min, and the neutralization reaction time to be 5 min, convert the residual soluble phosphorus and soluble fluorine in the liquid phase into insoluble calcium phosphate and calcium fluoride inert substances, filter and separate to obtain a third phosphogypsum slurry;

[0131] (6) Add 120 g / t of positive flotation reagent to the third phosphogypsum slurry obtained in step (5), and the positive flotation reagent is tetradecylamine; continue to add 200 g / t of foaming agent methyl isobutyl carbinol; control the concentration of the third phosphogypsum slurry to be 25%, and the positive flotation time to be 6 min. The floating product obtained is the phosphogypsum concentrate.

[0132] Test the impurity removal effects of the phosphogypsum concentrates of Examples 1-3 and Comparative Examples 1-3 of the present invention. Among them, the determination methods of impurities such as soluble phosphorus and soluble fluorine refer to the standard JC / T2073-2011 "Determination Methods of Phosphorus and Fluorine in Phosphogypsum"; the determination methods of impurities such as siliceous minerals, iron oxide and alumina and the purity of phosphogypsum refer to the standard GB / T5484-2012 "Chemical Analysis Methods of Gypsum"; the determination method of organic matter refers to the standard GB / T50123-2019 "Standard for Geotechnical Test Methods"; the whiteness determination method refers to the standard GB / T5950-2008 "Measurement Method of Whiteness of Building Materials and Non-Metallic Mineral Products"; the determination method of eutectic phosphorus is as follows: ① Refer to the standard GB / T5484-2012 "Chemical Analysis Methods of Gypsum", transfer an appropriate volume of potassium hydrogen phthalate solution to prepare a buffer solution with pH = 4.0; ② Weigh 5 g of thoroughly washed and dried phosphogypsum sample, place it in a 100 mL volumetric flask, add a small amount of water and shake, then add 20 mL of buffer solution, and dilute with water to 70 mL, add 20 mL of barium nitrate solution with a mass concentration of 10%, shake, make up the volume, stand for 1 h and then perform dry filtration, accurately transfer 40 mL of the filtrate to a 500 mL beaker; ③ Use the ICP method to determine the content of P2O5 in the solution, and calculate the eutectic phosphorus content according to the obtained data. The test results are shown in Table 1.

[0133] Table 1 Determination Results (%) of Phosphogypsum Concentrates in Examples 1-3 and Comparative Examples 1-3

[0134]

[0135] As can be seen from Table 1, the method for acidolysis-coupled flotation and whitening of phosphogypsum provided by the present invention has very significant effects. The contents of various impurities have decreased significantly, and the purity and whiteness have increased significantly. By comparing Example 1 and Comparative Example 1, the purity and whiteness of Example 1 have increased significantly, especially the whiteness has increased greatly. It can be seen that the grinding and reverse flotation agents used in the present invention have excellent impurity removal and whitening effects; by comparing Example 1 and Comparative Example 2, it shows that the compounding of the acid solution and persulfate used in the present invention can significantly improve the impurity removal efficiency; by comparing Example 1 and Comparative Example 3, it is not difficult to find that the combined action of the direct flotation agent and the foam stabilizer used in the present invention has obvious effects on impurity removal and whitening.

[0136] The test results of Examples 4-6 are similar to those of Examples 1-3.

[0137] From the above examples, it can be seen that the method provided by the present invention has comprehensive and thorough impurity removal and whitening. The purity is above 95%, the whiteness is above 83%, the impurity removal efficiency is high, and it has industrialization prospects, which can boost the large-scale and high-quality resource utilization of phosphogypsum.

[0138] Although the above examples have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for acidolysis-coupled flotation to whiten phosphogypsum, characterized in that, It includes the following steps: (1) Grind phosphogypsum and mix it with water, reverse flotation reagent, and the first foaming agent for reverse flotation to obtain the first phosphogypsum slurry; the reverse flotation reagent includes sodium dodecyl glycinate and pine oil; (2) Mix the first phosphogypsum slurry with acidolysis solution and persulfate for acidolysis to obtain the second phosphogypsum solid; the acidolysis solution includes citric acid and sulfuric acid; (3) Mix the second phosphogypsum solid, water, and pH regulator until the pH = 8 - 9 for neutralization reaction to obtain the third phosphogypsum slurry; (4) Mix the third phosphogypsum slurry, positive flotation reagent, the second foaming agent, and foam stabilizer for positive flotation to obtain phosphogypsum concentrate; the positive flotation reagent includes dodecyl trimethyl ammonium chloride and tetradecylamine.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of sodium dodecyl glycinate to pine oil is 1:0.5 - 1.5; The first foaming agent includes one or more of methyl isobutyl carbinol, sodium lauryl polyoxyethylene ether sulfate, and rosin soap foaming agent.

3. The method according to claim 1, wherein In step (2), the mass ratio of citric acid to sulfuric acid is 7 - 10:1; The total concentration of citric acid and sulfuric acid in the acidolysis solution is 20 - 30 wt%; The persulfate is potassium persulfate.

4. The method according to claim 1, wherein In step (4), the mass ratio of dodecyl trimethyl ammonium chloride to tetradecylamine is 1:1 - 2; The second foaming agent is methyl isobutyl carbinol; The foam stabilizer includes one or more of nano - silica, nano - alumina, and nano - zinc oxide.

5. The method according to claim 1, wherein In step (3), the mass ratio of the second phosphogypsum solid to water is 25 - 35:65 - 75.

6. The method according to claim 1 or 2, characterized in that, In step (1), the mass ratio of phosphogypsum to water is 25 - 35:65 - 75; The mass ratio of the total mass of phosphogypsum and water to the mass of the reverse flotation reagent is 10000:1 - 2; The mass ratio of the total mass of phosphogypsum and water to the mass of the first foaming agent is 10000:2 - 3.

7. The method according to claim 1 or 3, characterized in that, In step (2), the solid content of the first phosphogypsum slurry is 25 - 35 wt%; The mass ratio of the first phosphogypsum slurry to the acidolysis solution is 1:1 - 4; The mass ratio of the total mass of the first phosphogypsum slurry and the acidolysis solution to the mass of the persulfate is 95 - 97:3 - 5.

8. The method according to claim 1, characterized in that, In step (4), the solid content of the third phosphogypsum slurry is 20 - 30 wt%; The mass ratio of the third phosphogypsum slurry to the positive flotation reagent is 100000:10 - 15; The mass ratio of the third phosphogypsum slurry to the second foaming agent is 100000:15 - 25; The mass ratio of the third phosphogypsum slurry to the foam stabilizer is 100000:5 - 10.

9. The method according to claim 1, characterized in that, The temperature of the acidolysis is 75 - 90 °C, and the heat - preservation time is 15 - 25 min.

10. The method according to claim 1 or 6, characterized in that, The moisture content of the phosphogypsum is 10-20%, and the specific surface area of the ground phosphogypsum is 450-600 m 2 / kg.

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