A solidifying agent for phosphogypsum harmless treatment and a harmless treatment method thereof

Abstract

This invention discloses a solidification agent and a method for the harmless treatment of phosphogypsum, belonging to the field of industrial solid waste treatment technology. The solidification agent of this invention is composed of cationic polyacrylamide and sodium bentonite. The amount of cationic polyacrylamide added is 0.002% of the mass of the original phosphogypsum residue, and the amount of sodium bentonite added is 0.2%~1.5% of the mass of the original phosphogypsum residue. This invention first adjusts the pH of the original phosphogypsum residue to an alkaline environment using fine lime, and then utilizes the synergistic effect of the components in the solidification agent to complete the modification, reducing the fluoride and phosphate content in the phosphogypsum. The treatment method is simple and easy to operate, and can directly meet the treatment needs of existing phosphogypsum storage sites, realizing the long-term harmless disposal and resource utilization of phosphogypsum.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste treatment technology, and more specifically, relates to a solidification agent for the harmless treatment of phosphogypsum and a method for harmless treatment thereof. Background Technology

[0002] Phosphogypsum is a large amount of industrial solid waste generated during the wet process of phosphoric acid production. It contains residual fluorides, phosphates, and heavy metal impurities such as lead, chromium, copper, and cadmium. It is also acidic. Long-term open-air storage will cause harmful substances to leach out with rainwater, polluting the soil and groundwater. At the same time, it occupies a large amount of land resources, becoming a key issue restricting the green development of the phosphoric chemical industry.

[0003] Currently, the main methods for treating phosphogypsum include physical and chemical methods. Physical methods, such as washing and flotation, can remove some soluble impurities, but they suffer from high water consumption, high costs, or limited effectiveness in removing specific pollutants. Furthermore, they cannot improve the mechanical properties of phosphogypsum, making it difficult to achieve resource utilization. Chemical methods, which involve adding reagents to react with pollutants to achieve solidification or removal, are currently the mainstream treatment technology. However, existing chemical solidification technologies still face many insurmountable bottlenecks, directly hindering the harmless and resource-based transformation of phosphogypsum.

[0004] Specifically, existing solidification agents are limited in their specific applications: some agents using lime-based substances can neutralize the acidity of phosphogypsum and precipitate fluorides and phosphates, but their solidification effect on heavy metals is poor, with leaching concentrations far exceeding limits; some dedicated heavy metal solidification agents use a single chelating agent, which can only treat heavy metals and cannot solve fluoride and phosphate pollution, requiring multiple agents for step-by-step treatment, resulting in complex processes and high costs. Meanwhile, a few composite agents attempting to treat multiple pollutants simultaneously have flawed composition design: the addition of expensive components such as rare earth elements and specialized modifiers leads to high costs and difficulty in widespread adoption.

[0005] More importantly, the main challenge in the current phosphogypsum modification industry is the instability of the modified phosphates and fluorides. After being stored in the natural environment, these substances may rebound. Even after initial treatment to meet standards, long-term storage can lead to the decomposition of the solidified products due to rainwater leaching, temperature and humidity fluctuations, and other natural factors, causing the phosphates and fluorides to be released back into the environment, resulting in secondary pollution. These combined problems mean that current technologies ultimately fail to achieve the long-term harmless disposal and resource utilization of phosphogypsum, failing to fundamentally solve the pollution and disposal problems associated with phosphogypsum.

[0006] Therefore, developing a curing agent with reasonable composition that can simultaneously and efficiently reduce fluoride and phosphate in phosphogypsum has important environmental significance and economic value. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, the technical problem this invention aims to solve is to provide a solidifying agent for the harmless treatment of phosphogypsum, which can simultaneously and efficiently reduce the fluoride and phosphate content in phosphogypsum. Another technical problem this invention aims to solve is to provide a method for the harmless treatment of phosphogypsum using the aforementioned solidifying agent, achieving long-term harmless disposal and resource utilization of phosphogypsum.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A curing agent for the harmless treatment of phosphogypsum is composed of cationic polyacrylamide and sodium bentonite, wherein the amount of cationic polyacrylamide added is 0.002% of the mass of the original phosphogypsum residue, and the amount of sodium bentonite added is 0.2% to 1.5% of the mass of the original phosphogypsum residue.

[0010] Preferably, the curing agent is composed of cationic polyacrylamide and sodium bentonite, wherein the amount of cationic polyacrylamide added is 0.002% of the mass of the phosphogypsum residue, and the amount of sodium bentonite added is 0.3% to 1.3% of the mass of the phosphogypsum residue.

[0011] Preferably, the cationic polyacrylamide has a molecular weight of 12,000.

[0012] Preferably, the sodium-based bentonite contains ≥85% montmorillonite and has a cation exchange capacity ≥70 meq / 100g.

[0013] A method for harmlessly treating phosphogypsum using the aforementioned solidifying agent includes the following steps:

[0014] 1) Add refined lime to the phosphogypsum residue and adjust the pH to 11.5~12;

[0015] 2) Add a uniform slurry made of sodium bentonite and water to the phosphogypsum residue obtained in step 1), then add a cationic polyacrylamide solution, stir evenly, and place it in a natural environment for chemical modification to obtain harmless phosphogypsum.

[0016] Preferably, in step 1), the phosphate content in the phosphogypsum residue is 200~1000 mg / L.

[0017] Preferably, in step 1), the amount of refined lime added is 1.4% to 4.1% of the mass of the phosphogypsum residue.

[0018] Preferably, in step 2), the amount of cationic polyacrylamide added is 0.002% of the mass of the phosphogypsum residue, and the amount of sodium bentonite added is 0.2% to 1.5% of the mass of the phosphogypsum residue.

[0019] Preferably, in step 2), the ratio of sodium bentonite to water is 0.1~0.5:1 (g / mL).

[0020] Preferably, in step 2), the time for chemical modification is not less than 4 hours.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0022] 1) This invention first uses fine lime to adjust the pH of the phosphogypsum residue to an alkaline environment, and then utilizes the synergistic effect of the components in the solidification agent to complete the modification, simultaneously and efficiently reducing the fluoride and phosphate content in the phosphogypsum.

[0023] 2) The curing agent of the present invention is inexpensive and environmentally friendly. All the components used are conventional chemical raw materials, which are widely available and low in cost. The preparation and use process does not cause secondary pollution, making it suitable for large-scale industrial promotion.

[0024] 3) This invention utilizes a solidification agent to treat phosphogypsum in a harmless manner. The treatment method is simple and easy to operate, requiring only mixing, stirring, and curing at room temperature. It can directly meet the treatment needs of existing phosphogypsum storage sites, realizing the long-term harmless disposal and resource utilization of phosphogypsum. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is further described below with reference to specific embodiments. Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0026] In the following examples, the phosphogypsum raw material used was hemihydrate phosphogypsum and dihydrate phosphogypsum from Guizhou Yuneng New Energy Battery Materials Co., Ltd.; the effective calcium oxide content of the refined lime used was ≥90%, and the fineness was: the percentage of particles passing through a 200-mesh standard sieve was 90%; the molecular weight of the PAM (cationic polyacrylamide) used was 12000; the fineness of the sodium-based bentonite used was: the percentage of particles passing through a 200-mesh standard sieve was 90%, the montmorillonite content was ≥85%, and the cation exchange capacity was ≥70 meq / 100g.

[0027] The curing agent used in the following examples consists of cationic polyacrylamide and sodium bentonite.

[0028] Example 1

[0029] A method for harmlessly treating phosphogypsum using a solidifying agent includes the following steps:

[0030] 1) Add 14.68g of refined lime directly to 1000g of phosphogypsum residue to adjust the pH of the residue to 11.5~12;

[0031] 2) Add a uniform slurry made by mixing 3g of sodium bentonite and 30mL of water to the phosphogypsum residue obtained in step 1), then add 30mL of PAM solution with a concentration of 0.000667g / mL, stir evenly, and place it in a natural environment for 12h for chemical modification to obtain harmless phosphogypsum.

[0032] Example 2

[0033] A method for harmlessly treating phosphogypsum using a solidifying agent includes the following steps:

[0034] 1) Add 20.6g of refined lime directly to 1000g of phosphogypsum residue to adjust the pH of the residue to 11.5~12;

[0035] 2) Add a uniform slurry made by mixing 3g of sodium bentonite and 30mL of water to the phosphogypsum residue obtained in step 1), then add 30mL of PAM solution with a concentration of 0.000667g / mL, stir evenly, and place it in a natural environment for 12h for chemical modification to obtain harmless phosphogypsum.

[0036] Example 3

[0037] A method for harmlessly treating phosphogypsum using a solidifying agent includes the following steps:

[0038] 1) Add 27.2g of refined lime directly to 1000g of phosphogypsum residue to adjust the pH of the residue to 11.5~12;

[0039] 2) Add a uniform slurry made by mixing 4g of sodium bentonite and 30mL of water to the phosphogypsum residue obtained in step 1), then add 30mL of PAM solution with a concentration of 0.000667g / mL, stir evenly, and place it in a natural environment for 12h for chemical modification to obtain harmless phosphogypsum.

[0040] Example 4

[0041] A method for harmlessly treating phosphogypsum using a solidifying agent includes the following steps:

[0042] 1) Add 31.77g of refined lime directly to 1000g of phosphogypsum residue to adjust the pH of the residue to 11.5~12;

[0043] 2) Add a uniform slurry made by mixing 5g of sodium bentonite and 30mL of water to the phosphogypsum residue obtained in step 1), then add 30mL of PAM solution with a concentration of 0.000667g / mL, stir evenly, and place it in a natural environment for 12h for chemical modification to obtain harmless phosphogypsum.

[0044] Example 5

[0045] A method for harmlessly treating phosphogypsum using a solidifying agent includes the following steps:

[0046] 1) Add 40.17g of refined lime directly to 1000g of phosphogypsum residue to adjust the pH of the residue to 11.5~12;

[0047] 2) Add a uniform slurry made by mixing 7g of sodium bentonite and 30mL of water to the phosphogypsum residue obtained in step 1), then add 30mL of PAM solution with a concentration of 0.000667g / mL, stir evenly, and place it in a natural environment for 12h for chemical modification to obtain harmless phosphogypsum.

[0048] The phosphogypsum residue used in Examples 1-5 and the resulting harmless phosphogypsum were tested for phosphate concentration, fluoride concentration, and pH after 12 hours of modification. The results are shown in Table 1.

[0049] Table 1. Detection results of raw phosphogypsum residue and harmless phosphogypsum from Examples 1-5.

[0050] As shown in Table 1, the phosphate and fluoride content in the original phosphogypsum residue can be effectively reduced by using the curing agent of the present invention.

[0051] Example 6

[0052] A method for harmlessly treating phosphogypsum using a solidifying agent includes the following steps:

[0053] 1) Add 30.45g of refined lime directly to 1000g of phosphogypsum residue to adjust the pH of the residue to 11.5~12;

[0054] 2) Add a uniform slurry made by mixing 5g of sodium bentonite and 30mL of water to the phosphogypsum residue obtained in step 1), then add 30mL of PAM solution with a concentration of 0.000667g / mL, stir evenly, and place it in a natural environment for 7h for chemical modification to obtain harmless phosphogypsum.

[0055] Example 7

[0056] When using a solidifying agent to treat phosphogypsum in a harmless manner, in step 2), a uniform slurry prepared by mixing 10g of sodium bentonite and 30mL of water is added. The remaining treatment methods and parameters are the same as in Example 6.

[0057] Example 8

[0058] When using a solidifying agent to treat phosphogypsum in a harmless manner, in step 2), a uniform slurry prepared by mixing 12.5g of sodium bentonite and 30mL of water is added. The remaining treatment methods and parameters are the same as in Example 6.

[0059] Example 9

[0060] When using a solidifying agent to treat phosphogypsum in a harmless manner, 29.93g of refined lime is added in step 1), and the mixture is placed in a natural environment for 12 hours to undergo chemical modification. The remaining treatment methods and parameters are the same as in Example 6.

[0061] Example 10

[0062] When using a solidifying agent to treat phosphogypsum in a harmless manner, 20g of refined lime is added in step 1), and the mixture is placed in a natural environment for 12 hours for chemical modification. The remaining treatment methods and parameters are the same as in Example 7.

[0063] Example 11

[0064] When using a solidifying agent to treat phosphogypsum in a harmless manner, 30g of refined lime is added in step 1), and the mixture is placed in a natural environment for 12 hours for chemical modification. The remaining treatment methods and parameters are the same as in Example 6.

[0065] Example 12

[0066] When using a solidifying agent to treat phosphogypsum for harmlessness, 30g of refined lime is added in step 1), and the mixture is placed in a natural environment for 12 hours for chemical modification. The remaining treatment methods and parameters are the same as in Example 7.

[0067] Example 13

[0068] A method for harmlessly treating phosphogypsum using a solidifying agent includes the following steps:

[0069] 1) Add 25g of refined lime directly to 1000g of phosphogypsum residue to adjust the pH of the residue to 11.5~12;

[0070] 2) Add a uniform slurry made by mixing 3g of sodium bentonite and 30mL of water to the phosphogypsum residue obtained in step 1), then add 30mL of PAM solution with a concentration of 0.000667g / mL, stir evenly, and place it in a natural environment for 12h for chemical modification to obtain harmless phosphogypsum.

[0071] The phosphate concentration, fluoride concentration, and pH of the harmless phosphogypsum from Examples 6-13 were tested at different modification times, and the results are shown in Tables 2-4. The phosphate concentration of the phosphogypsum residue used in Examples 6-13 was 207.57 mg / L, the fluoride concentration was 223.24 mg / L, and the pH was 2.64.

[0072] Table 2. Test results of harmless phosphogypsum in Examples 6-9 at different modification times.

[0073] Table 3. Detection results of harmless phosphogypsum in Examples 9-12 at different modification times.

[0074] Note: “—” in this table indicates that the performance index was not detected at that time point.

[0075] Table 4. Detection results of harmless phosphogypsum in Example 13 at different modification times.

[0076] As shown in Tables 2 to 4, the curing agent of the present invention provides a high-efficiency, stable and long-lasting treatment of high-phosphorus, high-fluorine, and strongly acidic phosphogypsum residue.

[0077] Example 14

[0078] A method for harmlessly treating phosphogypsum using a solidifying agent includes the following steps:

[0079] 1) Add 40g of refined lime directly to 2000g of phosphogypsum residue to adjust the pH of the residue to 11.5~12;

[0080] 2) Add a uniform slurry made by mixing 6g of sodium bentonite and 60mL of water to the phosphogypsum residue obtained in step 1), then add 60mL of PAM solution with a concentration of 0.000667g / mL, stir evenly, and place it in a natural environment for 12h for chemical modification to obtain harmless phosphogypsum.

[0081] Comparative Example 1

[0082] When treating phosphogypsum to render it harmless, only a uniform slurry prepared by mixing 6g of sodium bentonite and 60mL of water is added, without adding PAM solution. The other treatment methods and parameters are the same as in Example 14.

[0083] Comparative Example 2

[0084] When treating phosphogypsum to render it harmless, only 60 mL of PAM solution with a concentration of 0.000667 g / mL was added, and the remaining treatment methods and parameters were the same as in Example 14.

[0085] The phosphate concentration, fluoride concentration, and pH of the harmless phosphogypsum from Example 14 and Comparative Examples 1-2 were tested at different modification times, and the results are shown in Table 5. The phosphate concentration of the phosphogypsum residue used in Example 14 and Comparative Examples 1-2 was 166.76 mg / L, the fluoride concentration was 143.03 mg / L, and the pH was 2.75.

[0086] Table 5. Test results of phosphogypsum in Example 14 and Comparative Examples 1-2 at different modification times.

[0087] As shown in Table 5, the present invention has a significantly better effect on the harmless modification of phosphogypsum than Comparative Examples 1 and 2, and the long-term stability of the modification effect is better. At the same time, the pH of Example 14 drops to a mildly weakly alkaline range of 8.13 as the modification time progresses, which is more suitable for the subsequent resource utilization needs of phosphogypsum compared to the slightly alkaline Comparative Examples 1 and 2.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A curing agent for the harmless treatment of phosphogypsum, characterized in that, It is composed of cationic polyacrylamide and sodium bentonite, wherein the amount of cationic polyacrylamide added is 0.002% of the mass of phosphogypsum residue, and the amount of sodium bentonite added is 0.2% to 1.5% of the mass of phosphogypsum residue.

2. The curing agent for the harmless treatment of phosphogypsum according to claim 1, characterized in that, The curing agent is composed of cationic polyacrylamide and sodium bentonite. The amount of cationic polyacrylamide added is 0.002% of the mass of the phosphogypsum residue, and the amount of sodium bentonite added is 0.3% to 1.3% of the mass of the phosphogypsum residue.

3. The curing agent for the harmless treatment of phosphogypsum according to claim 1, characterized in that, The cationic polyacrylamide has a molecular weight of 12,000.

4. The curing agent for the harmless treatment of phosphogypsum according to claim 1, characterized in that, The sodium-based bentonite contains ≥85% montmorillonite and has a cation exchange capacity ≥70 meq / 100g.

5. A method for harmlessly treating phosphogypsum using the curing agent according to any one of claims 1-4, characterized in that, Includes the following steps: 1) Add refined lime to the phosphogypsum residue and adjust the pH to 11.5~12; 2) Add a uniform slurry made of sodium bentonite and water to the phosphogypsum residue obtained in step 1), then add a cationic polyacrylamide solution, stir evenly, and place it in a natural environment for chemical modification to obtain harmless phosphogypsum.

6. The method for harmlessly treating phosphogypsum using a solidifying agent according to claim 5, characterized in that, In step 1), the phosphate content in the phosphogypsum residue is 200~1000 mg / L.

7. The method for harmlessly treating phosphogypsum using a solidifying agent according to claim 5, characterized in that, In step 1), the amount of refined lime added is 1.4% to 4.1% of the mass of the phosphogypsum residue.

8. The method for harmless treatment of phosphogypsum using a solidifying agent according to claim 5, characterized in that, In step 2), the amount of cationic polyacrylamide added is 0.002% of the mass of the phosphogypsum residue, and the amount of sodium bentonite added is 0.2% to 1.5% of the mass of the phosphogypsum residue.

9. The method for harmlessly treating phosphogypsum using a solidifying agent according to claim 5, characterized in that, In step 2), the ratio of sodium bentonite to water is 0.1~0.5:1 (g / mL).

10. The method for harmless treatment of phosphogypsum using a solidifying agent according to claim 5, characterized in that, In step 2), the time for chemical modification is not less than 4 hours.

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