Phosphogypsum stabilized material and application thereof

Abstract

The invention provides a phosphogypsum stabilized material and application thereof, and belongs to the technical field of harmless treatment of solid wastes. The phosphogypsum stabilizing material is prepared from hydrotalcite, calcium formate, calcium bentonite, limestone powder and metakaolin, and the problem that in the prior art, the comprehensive utilization pH value of phosphogypsum and the leaching concentration of soluble phosphorus and soluble fluorine cannot reach the standard is solved. According to the invention, through reasonable compatibility, by utilizing the characteristics of materials and hydration products formed after reaction, and through ion exchange, chemical precipitation and adsorption, the fluoride content is less than 10mg / L, the phosphate content is less than 0.5 mg / L and the pH value is 6-9 after the phosphogypsum is treated, the related requirements of the current national standard GB 8978 Integrated Wastewater Discharge Standard are met, the use amount of stabilizing materials is reduced by 20-30%, and the production cost is reduced. And engineering economic indexes are met, the comprehensive construction cost of engineering is reduced, and wide application prospects are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of harmless waste treatment, and in particular to a phosphogypsum stabilization material and application thereof. Background Art

[0002] Phosphogypsum is an industrial by-product of the wet phosphoric acid leaching process. Its main component is calcium sulfate dihydrate. Phosphogypsum is acidic and contains many impurity elements. Large-scale storage will cause groundwater pollution, water eutrophication, air pollution and other problems, seriously threatening human health and life safety. At present, a large amount of phosphogypsum has been stored, and the stock continues to increase. In addition to its use in building materials, roads, and mine backfill, a large amount of phosphogypsum is still stored in slag yards.

[0003] Chinese patent CN111377632A discloses a phosphogypsum treatment agent, a phosphogypsum treatment method, a phosphogypsum filling material preparation method and a phosphogypsum filling material, wherein the treatment agent comprises the following components in percentage by mass: 27.7% to 96.7% of calcined phosphate tailings, 0.3% to 1% of ammonium sulfate, 3% to 68% of solid waste powder, and 0% to 3.5% of alkaline activator, wherein the calcined phosphate tailings are the calcined products of high-magnesium phosphate tailings. The phosphogypsum treatment agent based on the invention can realize the harmless treatment of phosphogypsum and the effective utilization of solid waste high-magnesium phosphate tailings, while ensuring the strength requirements of phosphogypsum as an engineering filling material.

[0004] However, the comprehensive utilization of phosphogypsum in the prior art has the defect that the pH value, soluble phosphorus and soluble fluorine leaching concentration cannot meet the standards. Summary of the invention

[0005] The purpose of the present invention is to provide a phosphogypsum stabilization material and its application, which solves the problem in the prior art that the pH value, soluble phosphorus and soluble fluorine leaching concentration of phosphogypsum comprehensive utilization cannot meet the standards.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a phosphogypsum stabilization material, which comprises the following components in parts by weight:

[0008] 1-5 parts of hydrotalcite, 2-5 parts of calcium formate, 15-20 parts of calcium-based bentonite, 25-30 parts of limestone and 50-60 parts of metakaolin.

[0009] Preferably, the anion exchange capacity of the hydrotalcite is greater than 3.0 meq. / g.

[0010] Preferably, the hydrotalcite is a magnesium-aluminum-chloride type hydrotalcite compound.

[0011] Preferably, the specific surface area of ​​the limestone powder is 600m2 / kg or more.

[0012] Preferably, the calcium carbonate content of the limestone powder is above 90%.

[0013] Preferably, the calcination temperature of the metakaolin is 750-800°C.

[0014] Preferably, the metakaolin has a 45 μm sieve residue of ≤5%.

[0015] Preferably, the 28d strength activity index of the metakaolin is above 90%.

[0016] The present invention also provides the use of the above-mentioned phosphogypsum stabilization material in reducing the fluoride content of phosphogypsum, reducing the phosphate content of phosphogypsum or neutralizing the pH value of phosphogypsum.

[0017] The present invention also provides a method for stabilizing phosphogypsum, comprising the following steps:

[0018] Mixing the phosphogypsum stabilized material with water to obtain a phosphogypsum stabilized slurry;

[0019] mixing the phosphogypsum stabilized slurry with the phosphogypsum;

[0020] The mass concentration of the phosphogypsum stabilized slurry is 3-8%.

[0021] Technical effects and advantages of the present invention:

[0022] The phosphogypsum stabilization material provided by the present invention is composed of hydrotalcite (Mg6Al2(OH) 16 Cl2·4H2O), calcium formate, calcium-based bentonite, limestone powder and metakaolin. Hydrotalcite is a layered double metal hydroxide, alkaline, and is a compound assembled by the interaction of positively charged main layers and interlayer anions through non-covalent bonds. Since the layers and interlayer anions are connected by hydrogen bonds, the interlayer anions of hydrotalcite are exchangeable, and can be exchanged with soluble fluorine in phosphogypsum to reduce the soluble fluorine content after phosphogypsum treatment; calcium formate (C2H2O4Ca) is an organic calcium salt that provides Ca 2+ At the same time, it can achieve chemical precipitation of soluble phosphorus and soluble fluorine in phosphogypsum without increasing the pH value of the system; calcium-based bentonite provides Ca through cation exchange 2+ , combining soluble phosphorus and soluble fluorine, and adsorbing other harmful substances in phosphogypsum; limestone powder (CaCO3) and metakaolin ((Al2O3)·2(SiO2)) react in an alkaline environment to form hydration products such as monocarbonate calcium aluminate, which adsorb harmful substances such as fluoride ions. The relevant reaction equation is as follows:

[0023] Mg6Al2(OH) 16 Cl2H2O+F - →Mg6Al2(OH) 16 F2H2O+Cl -

[0024] Ca 2+ +2F - →CaF2; 3Ca 2+ +2PO4 3- →Ca3(PO4)2

[0025] Al2O3+CaCO3+Ca 2+ +OH - →3CaO·Al2O3·CaCO3·11H2O(C4A C H 11 )

[0026] CaO·Al2O3·CaCO3·11H2O+2F - →CaO·Al2O3·CaF2·11H2O+CO3 2-

[0027] The above five components are reasonably matched, and the characteristics of the materials and the hydration products formed after the reaction are utilized, and through ion exchange, chemical precipitation and adsorption, the fluoride content of the phosphogypsum after treatment is less than 10 mg / L, the phosphate (in terms of P) is less than 0.5 mg / L, and the pH is 6-9, which meets the relevant requirements of the current national standard GB8978 "Comprehensive Sewage Discharge Standard", and achieves a reduction of 20%-30% in the amount of stabilization materials. The present invention can not only adapt to the characteristics of phosphogypsum and meet the requirements of actual engineering on the pH, soluble phosphorus and soluble fluorine of phosphogypsum, but also meet the engineering economic indicators, reduce the comprehensive engineering cost, and has a wide range of application prospects. DETAILED DESCRIPTION

[0028] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0029] Example 1

[0030] (1) Prepare a stabilizing material according to the following ratio: 5% hydrotalcite, 5% calcium formate, 20% calcium-based bentonite, 30% limestone powder, and 40% metakaolin. Weigh the above stabilizing material according to 2.0% of the mass of dry phosphogypsum, mix it with 38.0g water to make a slurry with a mass concentration of 5%, and then mix it with 100g of phosphogypsum (dry basis) from a certain place in Yunnan, and stir it evenly using a high-speed mixer.

[0031] (2) After the mixture formed by adding stabilizing materials to phosphogypsum is aged for 72 hours, the pH value, fluoride and phosphate content of the phosphogypsum mixture are determined in accordance with the current national standard GB8978 "Integrated Wastewater Discharge Standard".

[0032] Example 2

[0033] (1) Prepare a stabilizing material according to the following ratio: 2.5% hydrotalcite, 5% calcium formate, 18.5% calcium-based bentonite, 30% limestone powder, and 44% metakaolin. Weigh the above stabilizing material at 2.2% of the mass of dry phosphogypsum, mix it with 41.8g water to make a slurry with a mass concentration of 5%, and then mix it with 100g of phosphogypsum (dry basis) from a certain place in Guizhou, and stir it evenly using a high-speed mixer.

[0034] (2) After the mixture formed by adding stabilizing materials to phosphogypsum is aged for 72 hours, the pH value, fluoride and phosphate content of the phosphogypsum mixture are determined in accordance with the current national standard GB8978 "Integrated Wastewater Discharge Standard".

[0035] Example 3

[0036] (1) Prepare a stabilizing material according to the following ratio: 3.5% hydrotalcite, 3.5% calcium formate, 16% calcium-based bentonite, 27% limestone powder, and 50% metakaolin. Weigh the above stabilizing material at 2.4% of the mass of dry phosphogypsum, mix it with 45.6g water to make a slurry with a mass concentration of 5%, and then mix it with 100g of phosphogypsum (dry basis) from a certain place in Sichuan, and stir it evenly using a high-speed mixer.

[0037] (2) After the mixture formed by adding stabilizing materials to phosphogypsum is aged for 72 hours, the pH value, fluoride and phosphate content of the phosphogypsum mixture are determined in accordance with the current national standard GB8978 "Integrated Wastewater Discharge Standard".

[0038] Example 4

[0039] (1) Prepare a stabilizing material according to the following ratio: 4% hydrotalcite, 2.5% calcium formate, 15% calcium-based bentonite, 20% limestone powder, and 58.5% metakaolin. Weigh the above stabilizing material at 2.6% of the mass of dry phosphogypsum, mix it with 49.4g water to make a slurry with a mass concentration of 5%, and then mix it with 100g of phosphogypsum (dry basis) from a certain place in Hubei, and stir it evenly using a high-speed mixer.

[0040] (2) After the mixture formed by adding stabilizing materials to phosphogypsum is aged for 72 hours, the pH value, fluoride and phosphate content of the phosphogypsum mixture are determined in accordance with the current national standard GB8978 "Integrated Wastewater Discharge Standard".

[0041] Example 5

[0042] (1) Prepare a stabilizing material according to the following ratio: 5% hydrotalcite, 2% calcium formate, 12% calcium-based bentonite, 26% limestone powder, and 55% metakaolin. Weigh the above stabilizing material at 2.8% of the mass of dry phosphogypsum, mix it with 53.2g water to make a slurry with a mass concentration of 5%, and then mix it with 100g of phosphogypsum (dry basis) from a certain place in Anhui Province, and stir it evenly using a high-speed mixer.

[0043] (2) After the mixture formed by adding stabilizing materials to phosphogypsum is aged for 72 hours, the pH value, fluoride and phosphate content of the phosphogypsum mixture are determined in accordance with the current national standard GB8978 "Integrated Wastewater Discharge Standard".

[0044] Example 6

[0045] (1) Prepare a stabilizing material according to the following ratio: 1% hydrotalcite, 4% calcium formate, 15% calcium-based bentonite, 30% limestone powder, and 60% metakaolin. Weigh the above stabilizing material according to 3.0% of the mass of dry phosphogypsum, mix it with 57.0g water to make a slurry with a mass concentration of 5%, and then mix it with 100g of phosphogypsum (dry basis) from a certain place in Jiangsu, and stir it evenly using a high-speed mixer.

[0046] (2) After the mixture formed by adding stabilizing materials to phosphogypsum is aged for 72 hours, the pH value, fluoride and phosphate content of the phosphogypsum mixture are determined in accordance with the current national standard GB8978 "Integrated Wastewater Discharge Standard".

[0047] Comparative Example 1

[0048] (1) 3 g of ordinary silicate 42.5 cement and 57 g of water were mixed to prepare a slurry with a mass concentration of 5%, and then mixed with 100 g of phosphogypsum (dry basis) from a certain place in Hubei Province, and stirred evenly using a high-speed mixer.

[0049] (2) After aging the mixture of phosphogypsum and ordinary Portland cement for 72 hours, the pH value, fluoride and phosphate content of the phosphogypsum mixture were determined in accordance with the current national standard GB8978 "Integrated Wastewater Discharge Standard".

[0050] Comparative Example 2

[0051] (1) 3 g of quicklime and 57 g of water were mixed to prepare a slurry with a mass concentration of 5%, and then mixed with 100 g of phosphogypsum (dry basis) from a certain place in Yunnan, and stirred evenly using a high-speed mixer.

[0052] (2) After the mixture of phosphogypsum and quicklime is aged for 72 hours, the pH value, fluoride and phosphate content of the phosphogypsum mixture are determined in accordance with the current national standard GB8978 "Integrated Wastewater Discharge Standard".

[0053] Table 1 Application performance test results of phosphogypsum stabilized materials

[0054] Example No. pH Fluoride mg / L Phosphate (P) mg / L Example 1 7.25 8.20 0.30 Example 2 6.75 7.66 0.19 Example 3 6.88 7.46 0.10 Example 4 7.02 7.04 0.05 Example 5 7.35 8.69 0.02 Example 6 7.55 8.40 0.02 Comparative Example 1 10.15 7.22 16.12 Comparative Example 2 10.83 7.67 0.49

[0055] From the results of the comparison of the examples and the comparative examples in Table 1, it can be seen that the pH value of the phosphogypsum mixture obtained by using the phosphogypsum stabilization material in the examples of the present invention is less than 9, the fluoride is less than 10 mg / L, and the phosphate is less than 0.5 mg / L; while the pH value of the phosphogypsum mixture obtained by using simple cement or quicklime and other materials in the comparative example is greater than 9 and the phosphate exceeds the standard. The stabilization materials provided in Examples 1-6 of the present invention can efficiently stabilize phosphogypsum in different regions, and the effect is significantly better than that of cement or lime, and can meet the needs of ecological restoration or further treatment of phosphogypsum.

[0056] In the material for stabilizing phosphogypsum provided by the embodiment of the present invention, the adsorption component has a double-layer structure, can combine with fluoride ions in the system to form hydration products, reduce the fluoride concentration in the system, and has stable binding ability, which can keep the phosphogypsum mixture in a stable state; at the same time, the calcium ions in the material can produce chemical precipitation with the fluoride and phosphate in the phosphogypsum, and the synergistic adsorption components react quickly, shortening the aging time of the phosphogypsum, generating insoluble hydration products such as calcium phosphate and calcium fluoride, and further reducing the concentration of fluoride and phosphate in the phosphogypsum. Through the synergistic effect of the various components in the stabilization material, the problems of excessive pH value and substandard leaching of harmful substances when treating phosphogypsum with materials such as cement or lime are solved, and the relevant requirements of the current national standard GB 8978 "Comprehensive Sewage Discharge Standard" are met. While meeting the ecological restoration of phosphogypsum, the use of stabilization materials is reduced by about 20%-30%, saving 15%-25% of the project cost. It has good environmental and economic benefits, reduces the use of cement or quicklime, and indirectly reduces the carbon emissions of engineering projects, which is conducive to the promotion of the "dual carbon" goals.

[0057] It can be seen from the above embodiments that the present invention provides a material for stabilizing phosphogypsum, which has the following application prospects and significance:

[0058] 1. In terms of the comprehensive utilization of phosphogypsum, the stabilized material of the present invention can effectively reduce the content of fluoride and phosphate in phosphogypsum to meet environmental protection standards, thereby broadening the application scope of phosphogypsum, including but not limited to building materials, soil conditioners, landscaping, etc.

[0059] 2. During the treatment of phosphogypsum, the stabilizing material of the present invention not only reduces the leaching of harmful substances, but also lowers the pH value of the treated phosphogypsum mixture, making it closer to neutral, which is beneficial to the subsequent resource utilization.

[0060] 3. Since the stabilizing material of the present invention has good adsorption and precipitation properties, it can reduce the dependence on other chemical additives in the stabilization treatment of phosphogypsum, simplify the treatment process, and reduce the complexity of operation.

[0061] 4. In practical applications, the stabilizing material of the present invention can significantly reduce engineering costs, improve economic benefits, and at the same time reduce the amount of cement or quicklime used, which helps to reduce carbon emissions and meets the national requirements for environmental protection and sustainable development.

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A phosphogypsum stabilized material, characterized in that: In parts by weight, it includes the following components: 1-5 parts of hydrotalcite, 2-5 parts of calcium formate, 15-20 parts of calcium-based bentonite, 25-30 parts of limestone and 50-60 parts of metakaolin.

2. The phosphogypsum stabilized material according to claim 1, characterized in that: The anion exchange capacity of the hydrotalcite is greater than 3.0 meq. / g.

3. The phosphogypsum stabilized material according to claim 1, characterized in that: The hydrotalcite is a magnesium-aluminum-chloride type hydrotalcite compound.

4. The phosphogypsum stabilized material according to claim 1, characterized in that: The specific surface area of ​​the limestone powder is 600m 2 / kg or more.

5. The phosphogypsum stabilized material according to claim 1, characterized in that: The calcium carbonate content of the limestone powder is above 90%.

6. The phosphogypsum stabilized material according to claim 1, characterized in that: The calcination temperature of the metakaolin is 750-800°C.

7. The phosphogypsum stabilized material according to claim 1, characterized in that: The metakaolin has a 45 μm sieve residue of ≤5%.

8. The phosphogypsum stabilized material according to claim 1, characterized in that: The 28d strength activity index of the metakaolin is above 90%.

9. Use of the phosphogypsum stabilization material according to any one of claims 1 to 8 in reducing the fluoride content of phosphogypsum, reducing the phosphate content of phosphogypsum or neutralizing the pH value of phosphogypsum.

10. A method for stabilizing phosphogypsum, characterized in that: The following steps are involved: Mixing the phosphogypsum stabilized material according to any one of claims 1 to 8 with water to obtain a phosphogypsum stabilized slurry; mixing the phosphogypsum stabilized slurry with the phosphogypsum; The mass concentration of the phosphogypsum stabilized slurry is 3-8%.