Phosphogypsum flotation impurity removal whitening agent, and preparation method and process thereof

Abstract

The present application relates to a kind of phosphogypsum flotation impurity whitening reagent and its preparation method and process, belong to phosphorus chemical solid waste treatment technical field.Solve the complex synthesis process of phosphogypsum impurity whitening flotation collector in prior art, poor whitening effect, the problem of weak collecting ability.A kind of phosphogypsum flotation impurity whitening reagent, raw material weight portion composition is: vinyl trimethoxysilane 40-60 parts, acetic acid solution 30-45 parts, alkyl trimethylammonium bromide 10-15 parts.The phosphogypsum flotation impurity whitening reagent provided by the present application can adapt to strong acid environment, can capture colored organic matter and silicate impurities at the same time, has the performance of foaming agent, with stable performance, strong collecting ability, fast flotation speed, low dosage and other advantages, after flotation process, the whiteness of phosphogypsum can be increased to about 70%, can be directly used for PVC filler, beta hemihydrate gypsum and building wall material etc..

Description

Technical Field

[0001] This invention belongs to the field of phosphorus chemical solid waste treatment technology, specifically relating to a phosphogypsum flotation impurity removal and whitening agent and its preparation method and process. Background Technology

[0002] Phosphogypsum is a major solid waste product of the phosphate chemical industry. On average, the production of 1 ton of wet-process phosphoric acid generates 4.5-5.5 tons of phosphogypsum. Currently, my country's stockpiled phosphogypsum exceeds 500 billion tons, while the comprehensive utilization rate is only about 40%. Whiteness is an important factor affecting the application of phosphogypsum.

[0003] Phosphogypsum contains impurities such as phosphate and its salts, fluorides, organic matter, quartz, and iron and magnesium oxides, giving it a gray or grayish-black color. This limits its application to low-value-added fields such as cement, chemical raw materials, soil conditioners, and roadbeds. Whitening phosphogypsum by removing impurities can greatly improve its utilization value, allowing it to replace limited natural gypsum reserves, reduce the environmental damage caused by solid waste stockpiling, and improve resource utilization. Flotation can effectively remove organic matter and impurities such as quartz from phosphogypsum, significantly improving its whiteness and expanding its applications in lightweight thermal insulation gypsum boards, phase change energy storage materials, and building decorations, thereby increasing its application value. The flotation collector is crucial to the flotation effect. Patent CN201510930935.4 discloses a phosphogypsum flotation collector prepared using isooctylamine as a raw material. Although it has stable chemical properties and good selectivity, the synthesis process involves hydrogen, hydrogen peroxide, and catalysts, making the process complex. Zhang Lizhen et al. used dodecylamine as a collector and adopted a "one roughing and two cleaning" process to obtain a product with a dihydrate gypsum content of 97.5%, but the whiteness of phosphogypsum did not improve significantly (Inorganic Salt Industry. 2021, 53(06), 171-173+184). Therefore, the demand for a new and efficient phosphogypsum impurity removal and whitening flotation collector is urgent.

[0004] In summary, given the current problems of complex synthesis process, poor whitening effect, and weak collection capacity of phosphogypsum flotation collectors, it is of great significance to develop a phosphogypsum flotation agent for impurity removal and whitening. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a phosphogypsum flotation impurity removal and whitening agent and its preparation method and process, in order to solve at least one of the problems in the prior art of complex synthesis process of phosphogypsum flotation collectors, poor whitening effect, and weak collection ability.

[0006] The main objective of this invention is achieved through the following technical solution:

[0007] This invention provides a phosphogypsum flotation impurity removal and whitening agent, the raw material composition by weight is: 40-60 parts of vinyltrimethoxysilane, 30-45 parts of acetic acid solution, and 10-15 parts of alkyltrimethylammonium bromide.

[0008] Furthermore, the acetic acid solution has a mass fraction of 0.5-5.0%.

[0009] Furthermore, the alkanetrimethylammonium bromide includes one or more of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0010] This invention also provides a method for preparing a phosphogypsum flotation impurity removal and whitening agent, which includes the following steps:

[0011] S1. Mix and stir vinyltrimethoxysilane with acetic acid solution to obtain vinyltrimethoxysilane acetic acid solution system;

[0012] S2. Add alkyltrimethylammonium bromide to the vinyltrimethoxysilane acetic acid solution system and stir.

[0013] Furthermore, in S1, the stirring time is 0.5-3.0 h.

[0014] Furthermore, in step S2, the stirring time is 20-60 minutes.

[0015] This invention also provides a phosphogypsum flotation process for impurity removal and whitening, using the above-mentioned phosphogypsum flotation impurity removal and whitening agent, comprising the following steps:

[0016] Step 1: Mix phosphogypsum and water according to a certain mass percentage, stir and adjust to obtain a slurry;

[0017] Step 2: Add a certain mass of flotation impurity removal and whitening agent to the slurry and continue stirring;

[0018] Step 3: Use a slurry pump to introduce the slurry into the flotation machine for flotation.

[0019] Furthermore, in step 1, the phosphogypsum content in the slurry is 15-35% by mass.

[0020] Furthermore, in step 2, the amount of flotation impurity removal and whitening agent used is 80-300 g / t based on the mass of phosphogypsum.

[0021] Furthermore, in step 3, the flotation time is 4-8 minutes.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] 1. The phosphogypsum flotation impurity removal and whitening agent provided by the present invention is adapted to a strong acid environment and can simultaneously capture colored organic matter and silicate impurities.

[0024] 2. The phosphogypsum flotation impurity removal and whitening agent provided by the present invention also has the properties of a frother, and has the advantages of stable performance, strong collection ability, fast flotation speed and low dosage.

[0025] 3. The phosphogypsum flotation impurity removal and whitening agent provided by the present invention can be directly used for phosphogypsum flotation impurity removal and whitening. After the flotation process, the whiteness can be increased to 70% without the need for a pre-removal of organic matter. It can be directly used for PVC fillers, β hemihydrate gypsum and building wall materials, etc.

[0026] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0028] Figure 1 Flowchart of phosphogypsum flotation in this invention;

[0029] Figure 2 X-ray diffraction analysis results of phosphogypsum flotation tailings in Example 2 of this invention. Detailed Implementation

[0030] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0031] This invention provides a phosphogypsum flotation impurity removal and whitening agent, the raw material composition by weight is: 40-60 parts of vinyltrimethoxysilane, 30-45 parts of acetic acid solution, and 10-15 parts of alkyltrimethylammonium bromide.

[0032] Currently, the synthesis process of phosphogypsum flotation collectors for impurity removal and whitening is complex, resulting in poor whitening effects and weak collection capabilities. Compared with existing technologies, the flotation impurity removal and whitening agent of this invention can simultaneously capture organic matter and silicate impurities; it has strong resistance to acids and heterogeneous ions; it also has the properties of a frother, with low bubble viscosity; it has stable chemical properties and strong collection capabilities; it has a fast flotation speed and low dosage, thus solving the problems of complex synthesis process, poor whitening effects, and weak collection capabilities of phosphogypsum flotation collectors in existing technologies.

[0033] Specifically, the acetic acid solution has a mass fraction of 0.5-5.0%.

[0034] Specifically, alkyltrimethylammonium bromide includes one or more of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0035] It should be noted that the components and their contents in this invention fully leverage the synergistic enhancement effect among them. This invention employs a phosphogypsum flotation impurity removal and whitening agent prepared from vinyltrimethoxysilane, an acetic acid solution with a mass fraction of 0.5-5.0%, and alkanetrimethylammonium bromide. Vinyltrimethoxysilane hydrolyzes in the slurry to generate Si-OH groups, which can bind together the surfaces of organic matter, pyrite, and silicate minerals in the phosphogypsum through dehydration condensation, thereby changing the surface of these impurities from hydrophilic to hydrophobic, thus promoting their flotation separation. The acetic acid solution increases the solubility of vinyltrimethoxysilane in aqueous solution, facilitating better dispersion of vinyltrimethoxysilane in the slurry and its interaction with impurities such as organic matter, pyrite, and silicate minerals. Furthermore, the acetic acid solution can react with alkanetrimethylammonium bromide to generate alkanetrimethylammonium acetate, increasing its collecting and foaming properties. Alkyltrimethylammonium bromide can react with silicate minerals to remove them; on the other hand, it also has foaming properties, promoting the adhesion of vinyltrioxysilane and impurity complexes to bubbles, which then separate as the bubbles rise.

[0036] When the acetic acid solution has a mass fraction below 0.5%, it cannot react completely with vinyltrimethoxysilane and alkyltrimethylammonium bromide in equal proportions, failing to achieve a synergistic effect. When the mass fraction is above 5.0%, even after complete reaction with vinyltrimethoxysilane and alkyltrimethylammonium bromide in equal proportions, there will still be residue. This will affect the pH value of the pulp, which is detrimental to flotation; furthermore, it will waste acetic acid, increase costs, and be uneconomical.

[0037] This invention also provides a method for preparing a phosphogypsum flotation impurity removal and whitening agent, which includes:

[0038] S1. Mix and stir vinyltrimethoxysilane with acetic acid solution to obtain vinyltrimethoxysilane acetic acid solution system;

[0039] S2. Add alkyltrimethylammonium bromide to the vinyltrimethoxysilane acetic acid solution system and stir.

[0040] Specifically, in S1, the stirring time is 0.5-3.0h.

[0041] Specifically, in S2, the stirring time is 20-60 minutes.

[0042] It should be noted that in S1, mixing and stirring vinyltrimethoxysilane with acetic acid solution can, on the one hand, obtain a solution with good solubility of vinyltrimethoxysilane, which facilitates the dispersion of vinyltrimethoxysilane in the phosphogypsum slurry to be treated; on the other hand, during the mixing and stirring process, vinyltrimethoxysilane decomposes with water, and acetic acid solution can promote the decomposition of vinyltrimethoxysilane with water and improve its stability.

[0043] Specifically, vinyltrimethoxysilane has low solubility in water but high solubility in dilute acetic acid solution. Therefore, vinyltrimethoxysilane is first added to acetic acid solution to increase its solubility in solution, which facilitates its better dispersion in slurry. On the other hand, acetic acid solution has the dual effect of promoting the hydrolysis of vinyltrimethoxysilane and improving its stability.

[0044] It should be noted that in S2, alkyltrimethylammonium bromide is readily soluble in water. When added to a vinyltrimethoxysilane acetic acid solution, alkyltrimethylammonium bromide reacts with the acetic acid to form alkyltrimethylammonium acetate, which enhances the foaming properties of the agent.

[0045] In S1 above, the stirring time is 0.5-3.0 h. Within 0.5-3.0 h, vinyltrimethoxysilane is completely dissolved and reacted in acetic acid solution.

[0046] In step S2 above, the stirring time is 20-60 min. Within this timeframe, alkyltrimethylammonium bromide can completely react with acetic acid in the vinyltrimethoxysilane acetic acid solution to form alkyltrimethylammonium acetate, thus improving its foaming properties. If the stirring time is less than 20 min, the reaction between alkyltrimethylammonium bromide and acetic acid is incomplete; if the stirring time is greater than 60 min, the reaction can be guaranteed to be complete.

[0047] This invention also provides a phosphogypsum flotation process for impurity removal and whitening, using the above-mentioned phosphogypsum flotation impurity removal and whitening agent, comprising the following steps:

[0048] Step 1: Mix phosphogypsum and water according to a certain mass percentage, stir and adjust to obtain a slurry;

[0049] Step 2: Add a certain mass of flotation impurity removal and whitening agent to the slurry and continue stirring;

[0050] Step 3: Use a slurry pump to introduce the slurry into the flotation machine for flotation.

[0051] Specifically, in step 1, the phosphogypsum content in the slurry is 15-35% by mass.

[0052] When the phosphogypsum content in the slurry is less than 15%, the processing capacity per unit time is low, resulting in wasted costs and uneconomical practices. Conversely, when the phosphogypsum content in the slurry is higher than 35%, the improvement in whiteness is minimal, and the whitening effect is not significant. In this invention, the phosphogypsum content in the slurry is 15-35% by mass.

[0053] Specifically, the amount of flotation impurity removal and whitening agent added is 80-300 g / t based on the mass of phosphogypsum;

[0054] When the dosage of flotation impurity removal and whitening agent is below 80 g / t, the impurity removal effect is poor, the increase in whiteness is small, and the whitening effect is not obvious. When the dosage of flotation impurity removal and whitening agent is above 300 g / t, on the one hand, calcium sulfate dihydrate and impurities will continue to float to the surface, resulting in waste of calcium sulfate dihydrate; on the other hand, the whiteness of the phosphogypsum flotation product remains almost unchanged, and further increasing the dosage of flotation impurity removal and whitening agent will increase costs and is uneconomical. In this invention, the dosage of flotation impurity removal and whitening agent is 80-300 g / t according to the mass ratio of phosphogypsum.

[0055] Specifically, the flotation process does not require adjustment of the pulp pH value;

[0056] According to experiments, flotation achieves better impurity removal and whitening effects when the pulp pH is between 1.5 and 3.5, resulting in a higher concentrate yield in reverse flotation. Phosphogypsum is derived from the phosphoric acid preparation process, and the original pH of the phosphogypsum pulp is generally between 2.0 and 2.5, which falls within the optimal pH range for flotation. Therefore, the reverse flotation process of this invention does not require adjustment of the pulp pH.

[0057] Specifically, in step 3, the flotation time is 4-8 minutes.

[0058] When the flotation time is less than 4 minutes, the recovery rate of phosphogypsum is insufficient. As the flotation time increases, the recovery rate of phosphogypsum increases, but once the reverse flotation time exceeds 8 minutes, further extending the flotation time no longer improves the recovery rate; instead, it reduces the quality of the concentrate. In this invention, the flotation time is 4-8 minutes.

[0059] In summary, the phosphogypsum flotation impurity removal and whitening agent provided by this invention can be used at room temperature and is suitable for raw phosphogypsum ore (fresh gypsum) and phosphogypsum aged in stockpiles (slag heap gypsum). Both can achieve good impurity removal and whitening effects through flotation.

[0060] In the following embodiments, without changing the preparation method of the flotation impurity removal and whitening agent, only the weight parts of the raw material components are changed.

[0061] In the following examples, phosphogypsum from a certain region of Guizhou Province was used, with a whiteness of 34.0%, a CaSO4·2H2O content of 88.7%, and soluble phosphorus and soluble fluorine contents of 0.24% and 0.28%, respectively. XRF analysis results showed that the main impurities were P2O5 (1.58 wt.%), Fe2O3 (0.255 wt.%), SiO2 (4.25 wt.%), Al2O3 (0.23 wt.%), and colored organic matter.

[0062] To demonstrate the impact of variations in the weight percentage of the raw material components of the flotation impurity removal and whitening reagent on the product indicators of phosphogypsum flotation, flotation tests were conducted on the same phosphogypsum in all examples, and the flotation process was kept completely consistent. Specifically, during the flotation process, the mass percentage of phosphogypsum mixed with water was 25%, the reagent dosage was 150 g / t of phosphogypsum, and the flotation time was 5 minutes. The flotation tailings and phosphogypsum concentrate were dried, weighed, and tested separately. The whiteness and CaSO4·2H2O content of phosphogypsum were used as evaluation indicators to illustrate the performance of the flotation impurity removal and whitening reagent.

[0063] Example 1

[0064] In this embodiment, the raw material composition of the flotation impurity removal and whitening agent is as follows: 40 parts by weight of vinyltrimethoxysilane, 45 parts by weight of 0.5% acetic acid solution, and 15 parts by weight of dodecyltrimethylammonium bromide.

[0065] Test results showed that the whiteness of the phosphogypsum concentrate was 68.2% and the CaSO4·2H2O content was 93.7%.

[0066] Example 2

[0067] In this embodiment, the raw material composition of the flotation impurity removal and whitening agent is as follows: 50 parts by weight of vinyltrimethoxysilane, 35 parts by weight of 1.5% acetic acid solution, and 15 parts by weight of tetradecyltrimethylammonium bromide.

[0068] Test results showed that the whiteness of phosphogypsum was 69.4%, and the CaSO4·2H2O content was 94.3%. X-ray diffraction analysis of the flotation tailings showed the following results: Figure 2 As shown, the tailings contain pyrite, quartz and CaSO4·2H2O.

[0069] Example 3

[0070] In this embodiment, the raw material composition of the flotation impurity removal and whitening agent is as follows: 55 parts by weight of vinyltrimethoxysilane, 35 parts by weight of 2.5% acetic acid solution, and 10 parts by weight of hexadecyltrimethylammonium bromide.

[0071] Test results show that the whiteness of phosphogypsum is 69.9%, the CaSO4·2H2O content is 94.7%, and other main components are shown in Table 1.

[0072] Table 1. X-ray fluorescence analysis results of phosphogypsum concentrate (wt.%)

[0073]

[0074] Example 4

[0075] In this embodiment, the raw material composition of the flotation impurity removal and whitening agent is as follows: 60 parts by weight of vinyltrimethoxysilane, 30 parts by weight of 5.0% acetic acid solution, and 10 parts by weight of octadecyltrimethylammonium bromide.

[0076] Test results showed that the whiteness of phosphogypsum was 70.2% and the CaSO4·2H2O content was 95.2%.

[0077] Comparative Example 1

[0078] In this comparative example, the flotation reagent for removing impurities and brightening the surface is vinyltrimethoxysilane. During the flotation process, vinyltrimethoxysilane can capture colored organic matter to form flocs, but it cannot produce a large amount of uniform foam.

[0079] Test results showed that the whiteness of the phosphogypsum concentrate was 47.1% and the CaSO4·2H2O content was 89.4%.

[0080] Comparative Example 2

[0081] In this comparative example, the raw material composition of the flotation impurity removal and whitening agent was: 60 parts vinyltrimethoxysilane and 40 parts acetic acid solution with a mass fraction of 1.5%. During the flotation process, vinyltrimethoxysilane can capture colored organic matter to form flocs, but it cannot produce a large amount of uniform foam.

[0082] Test results showed that the whiteness of phosphogypsum was 48.4% and the CaSO4·2H2O content was 89.8%.

[0083] Comparative Example 3

[0084] In this comparative example, the flotation reagent for removing impurities and whitening was hexadecyltrimethylammonium bromide. The flotation process can produce a large amount of white, uniform foam, but it cannot effectively capture colored organic matter in the slurry.

[0085] Test results showed that the whiteness of phosphogypsum was 49.7% and the CaSO4·2H2O content was 91.5%.

[0086] Comparative Example 4

[0087] In this comparative example, the raw material composition of the flotation impurity removal and whitening reagent was: 30 parts of 5.0% acetic acid solution and 70 parts of octadecyltrimethylammonium bromide. The flotation process can generate a large amount of uniform foam, but colored organic matter is dispersed in the pulp, which octadecyltrimethylammonium bromide cannot effectively capture.

[0088] Test results showed that the whiteness of phosphogypsum was 54.6% and the CaSO4·2H2O content was 92.3%.

[0089] Comparative Example 5

[0090] In this comparative example, the raw material composition of the flotation impurity removal and whitening reagent is: 60 parts vinyltrimethoxysilane and 40 parts octadecyltrimethylammonium bromide. During the flotation process, vinyltrimethoxysilane has poor dispersibility in the pulp and insufficient ability to capture colored organic matter, producing white, uniform foam.

[0091] Test results showed that the whiteness of phosphogypsum was 55.7% and the CaSO4·2H2O content was 93.4%.

[0092] Comparative Example 6

[0093] The raw material composition of the flotation impurity removal and whitening agent in this comparative example is: a 5.0% (w / w) acetic acid solution. No foam is generated during the flotation process, and no impurities float to the surface.

[0094] Test results showed that the whiteness of phosphogypsum was 41.5% and the CaSO4·2H2O content was 90.8%.

[0095] Comparative Example 7

[0096] In this embodiment, the raw material composition of the flotation impurity removal and whitening collector is as follows: 20 parts by weight of vinyltrimethoxysilane, 75 parts by weight of 5.0% acetic acid solution, and 5 parts by weight of dodecyltrimethylammonium bromide.

[0097] Flotation process: Some colored organic matter adheres to the surface of the bubbles to form black foam, but the black foam is generated in a short time.

[0098] Test results showed that the whiteness of phosphogypsum was 56.6% and the CaSO4·2H2O content was 92.5%.

[0099] Comparing Example 1 and Comparative Example 1, it is evident that while vinyltrimethoxysilane alone can capture colored organic matter in phosphogypsum and form flocs, it lacks foaming properties and cannot generate sufficient foam to float the organic matter flocs. Therefore, the removal rate of colored organic matter is low, and the whiteness and CaSO4·2H2O content of the phosphogypsum concentrate are only 47.1% and 89.4%, respectively.

[0100] Comparing Example 2 and Comparative Example 2, it is evident that using only a mixture of vinyltrimethoxysilane and a 1.5% acetic acid solution in a 60:40 weight ratio as the flotation impurity removal and whitening agent resulted in the same flotation phenomenon as in Comparative Example 1, failing to float impurities by forming a large foam layer. Therefore, the whiteness of the phosphogypsum concentrate was only 48.4%, and the CaSO4·2H2O content was 89.8%.

[0101] Comparing Example 3 and Comparative Example 3, it is evident that using only hexadecyltrimethylammonium bromide as the flotation impurity removal and whitening agent results in good foaming properties, forming a large foam layer. Furthermore, hexadecyltrimethylammonium bromide exhibits a certain ability to capture mineral impurities such as quartz, demonstrating good removal efficiency for these impurities. However, the removal rate of colored organic matter is low, and the whiteness improvement of the phosphogypsum concentrate is only 49.7%, with a CaSO4·2H2O content of 91.5%.

[0102] By comparing Example 4 and Comparative Example 4, it can be seen that using only a mixture of octadecyltrimethylammonium bromide and acetic acid solution with a mass fraction of 5.0% in a weight ratio of 70:30 as a flotation impurity removal and whitening agent results in good foaming properties, dense foam, and good removal effect on mineral impurities such as quartz. However, the removal rate of organic matter is low, resulting in low whiteness of phosphogypsum concentrate, only 54.6%.

[0103] Comparative Example 5 used a mixture of vinyltrimethoxysilane and octadecyltrimethylammonium bromide in a weight ratio of 60:40 as the flotation impurity removal and whitening agent. During the flotation process, vinyltrimethoxysilane showed poor dispersibility in the pulp, resulting in insufficient capture of colored organic matter and the formation of uniform white foam. Comparative Example 6 used a 5.0% acetic acid solution as the flotation impurity removal and whitening agent. No foam was generated during the flotation process, and no impurities floated to the surface. In Comparative Example 7, the weight proportions of vinyltrimethoxysilane, 5.0% acetic acid solution, and dodecyltrimethylammonium bromide in the flotation impurity removal and whitening agent were outside the range specified in this invention. During the flotation process, some colored organic matter adhered to the surface of the bubbles, forming black foam, but the black foam formation time was short. The whiteness of the phosphogypsum concentrate obtained from the three examples was 55.7%, 41.5%, and 56.6%, respectively, significantly lower than that of Examples 1-4.

[0104] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A phosphogypsum flotation agent for impurity removal and whitening that can be directly used for phosphogypsum flotation, characterized in that, The raw material composition by weight is: 40-60 parts of vinyltrimethoxysilane, 30-45 parts of acetic acid solution, and 10-15 parts of alkyltrimethylammonium bromide; The acetic acid solution has a mass fraction of 0.5-5.0%; The phosphogypsum flotation impurity removal and whitening agent can be used for phosphogypsum flotation without adjusting the pulp pH value, and flotation can be carried out directly at the original pH value of the pulp.

2. The phosphogypsum flotation impurity removal and whitening agent according to claim 1, characterized in that, The alkane-trimethylammonium bromide includes one or more of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

3. A method for preparing a phosphogypsum flotation impurity removal and whitening agent, used to prepare the phosphogypsum flotation impurity removal and whitening agent according to claim 1 or 2, characterized in that, Includes the following steps: S1. Mix and stir vinyltrimethoxysilane with acetic acid solution to obtain vinyltrimethoxysilane acetic acid solution system; S2. Add alkyltrimethylammonium bromide to the vinyltrimethoxysilane acetic acid solution system and stir.

4. The preparation method according to claim 3, characterized in that, In step S1, the stirring time is 0.5-3.0 h.

5. The preparation method according to claim 3, characterized in that, In step S1, the stirring time is 20-60 minutes.

6. A phosphogypsum flotation process for impurity removal and whitening, comprising the phosphogypsum flotation impurity removal and whitening agent as described in claim 1 or 2, or the phosphogypsum flotation impurity removal and whitening agent prepared by any one of claims 3-5, characterized in that, Includes the following steps: Step 1: Mix phosphogypsum and water according to a certain mass percentage, stir and adjust to obtain a slurry; Step 2: Add a certain mass of the phosphogypsum flotation impurity removal and whitening agent to the slurry and continue stirring; Step 3: Use a slurry pump to introduce the slurry into the flotation machine for flotation.

7. The impurity removal and whitening process according to claim 6, characterized in that, In step 1, the phosphogypsum content in the slurry is 15-35% by mass.

8. The impurity removal and whitening process according to claim 6, characterized in that, In step 2, the amount of flotation impurity removal and whitening agent used is 80-300 g / t based on the mass of phosphogypsum.

9. The impurity removal and whitening process according to claim 6, characterized in that, In step 3, the flotation time is 4-8 minutes.

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