Hexavalent chromium repairing material based on phosphogypsum and preparation method thereof

Abstract

The invention discloses a hexavalent chromium repairing material based on ardealite and a preparation method of the hexavalent chromium repairing material. Aiming at the dilemma that a large amount of solid waste phosphogypsum is low in resource utilization rate and easy to cause environmental pollution, separation of phosphogypsum pollution impurities and modification and improvement of physicochemical properties are achieved through the processes of compound washing, reduction calcination and cross-linking strengthening, and the prepared heavy metal hexavalent chromium repairing material is environmentally friendly, free of pollution and capable of being recycled. The method also has a good hexavalent chromium removal effect, and can provide support for ardealite absorption and remediation of hexavalent chromium polluted soil and underground water.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste treatment, and particularly relates to a hexavalent chromium repair material based on phosphogypsum and a preparation method thereof. Background Art

[0002] Phosphogypsum is a by-product generated from the reaction of phosphate rock and sulfuric acid during the production of wet-process phosphoric acid, and its main component is calcium sulfate dihydrate (CaSO4·2H2O, with a mass fraction of 75% - 95%). Phosphogypsum belongs to the second category of general industrial solid waste, and the leachate generated has characteristics such as strong acidity, high total phosphorus and fluoride concentrations. A large amount of stockpiled phosphogypsum not only occupies land resources and damages the ecological environment, but also causes soil, groundwater and surface water pollution problems, seriously threatening human health and life safety.

[0003] At present, the main ways of comprehensive utilization of phosphogypsum are cement retarders, gypsum building materials and mine filling. The comprehensive utilization rate of cement retarders and gypsum building materials for phosphogypsum accounts for more than 50%, but it is at an obvious disadvantage in the regional competition with natural gypsum and desulfurized gypsum. In addition, with the slowdown of the real estate industry, the utilization amount of cement retarders will decrease significantly. The lack of high-value-added products in gypsum building materials leads to serious homogeneous competition, and the utilization amount of gypsum building materials grows slowly. Hexavalent chromium pollution is one of the typical pollution problems. There is an urgent need to actively explore repair materials for hexavalent chromium pollution to support large-scale hexavalent chromium pollution repair.

[0004] At present, the main problems of heavy metal repair materials based on phosphogypsum are incomplete impurity removal (poor removal effect of insoluble and hardly soluble impurities) and weak heavy metal removal ability (especially in the removal of hexavalent chromium). There is an urgent need to actively explore new coupling processes to strengthen the removal of impurities in phosphogypsum, improve the heavy metal removal rate, and avoid secondary pollution of the environment by resource-based products. Summary of the Invention

[0005] Aiming at the problems of incomplete impurity removal and weak heavy metal removal ability of heavy metal repair materials based on phosphogypsum in the prior art, the present invention provides a hexavalent chromium repair material based on phosphogypsum and a preparation method thereof. After removing insoluble and hardly soluble impurities in phosphogypsum with an acidic compound detergent, the decontaminated phosphogypsum is mixed with straw, cast iron powder and polyvinyl alcohol and subjected to reduction calcination. On the one hand, this process promotes the conversion of CaSO4·2H2O in phosphogypsum into calcium sulfide with the function of reducing hexavalent chromium. On the other hand, through the iron-carbon microelectrolysis reaction of the calcination products of cast iron powder and straw, the reduction effect of calcium sulfide on hexavalent chromium is synergistically enhanced. Adding polyvinyl alcohol not only improves the dispersibility of the mixed system, but also further enhances the reduction effect of calcium sulfide and iron powder by increasing the specific surface area.

[0006] Meanwhile, by crosslinking with calcium ions in phosphogypsum, while reducing the dosage of calcium chloride, the specific surface area of the phosphogypsum - cast iron powder reaction system is significantly increased, thereby greatly enhancing the reaction rate and removal rate of hexavalent chromium.

[0007] One of the technical solutions of the present invention is to provide a preparation method of a hexavalent chromium repair material based on phosphogypsum, which has the following steps: (1) Mix 10 - 12 wt% of NaCl aqueous solution, 10 - 15 wt% of HCl aqueous solution, and 5 - 10 wt% of H2C2O4 aqueous solution evenly according to a volume ratio of 1:1:1 to obtain a compound detergent; (2) Add 10 g of phosphogypsum to 10 - 30 ml of the compound detergent, stir and mix evenly, heat to 80 - 85 °C, stir for 30 - 45 min, and filter after cooling to obtain a filter residue; (3) Take the filter residue obtained in step 2 and mix it evenly with crushed rice straw and cast iron powder according to a mass ratio of 2:1:0.2; (4) Add 1 ml of 2 wt% polyvinyl alcohol solution to the product obtained in step 3, stir and mix evenly to obtain a mixture; (5) Bake the mixture at 600 - 650 °C for 1 h under a reducing atmosphere to obtain solid A; (6) Add 2 - 4 g of sodium alginate to 100 ml of water, stir well, place it in an incubator at 85 °C and heat for 2 h, let it stand for 2 hours after complete dissolution to obtain solution A; (7) Add 0.5 g of calcium chloride to 100 ml of distilled water, stir and dissolve to obtain solution B; (8) Mix solid A and solution A evenly, drop solution B while stirring, and let it stand for more than 4 h to obtain a hexavalent chromium repair material based on phosphogypsum.

[0008] Further, the filtration in step 1 is vacuum filtration.

[0009] Further, the phosphogypsum in step 2 is obtained through a 200 - mesh steel sieve.

[0010] Further, the rice straw and cast iron powder in step 3 are obtained through a 200 - mesh steel sieve.

[0011] Further, the baking in step 5 is carried out in a tube resistance furnace.

[0012] Further, the reducing atmosphere in step 5 is CO.

[0013] Another technical solution of the present invention is to provide a hexavalent chromium repair material based on phosphogypsum prepared by the above - mentioned preparation method.

[0014] The beneficial effects of the present invention are as follows: (1) During reduction calcination, the dispersibility of the mixed system was improved by adding polyvinyl alcohol, and the specific surface area of the mixed system was increased, thereby further enhancing the reduction effect of calcium sulfide and iron powder on hexavalent chromium.

[0015] (2) The unique combined process of compound washing and calcination not only achieved the efficient removal of polluting impurities in phosphogypsum, but also realized the efficient activation of the components for reducing hexavalent chromium.

[0016] (3) The cross-linking strengthening process was introduced to fully disperse the modified phosphogypsum-based material, greatly enhancing its ability to remove hexavalent chromium, thereby reducing the repair cost. Specific Embodiments

[0017] The following examples are used to further illustrate the present invention, and the purpose is to explain the present invention rather than to limit the scope of the present invention. Unless otherwise specified, all are in parts by weight and weight percentages.

[0018] The raw materials used in the present invention are all conventional commercially available products unless otherwise specified; the methods used in the present invention are all conventional methods in the art unless otherwise specified.

[0019] The following further illustrates the embodiments of the present invention in multiple examples.

[0020] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative work belong to the scope protected by the present application.

[0021] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "the" and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0022] Example 1 (1) Pass the phosphogypsum through a 200-mesh steel sieve, and weigh 10 g of the sieve residue and place it in a 100-ml beaker for later use; (2) Prepare a 10% (by mass) NaCl solution, a 10% (by mass) HCl solution, and a 5% (by mass) H2C2O4 solution, and compound them in a dosage ratio of 1:1:1 by volume to form a compound detergent for later use; (3) Measure 10 ml of the compound detergent in step 2, add it to the beaker in step (1), stir well for 1 min, then put it into a magnetic heating stirrer, heat to 80 °C, stir for 30 min, filter under vacuum after cooling, take out the filter residue and dry it naturally for later use; (4) Mix the filter residue after natural drying in step (3) with crushed rice straw and cast iron powder (passing through a 200-mesh steel sieve) in a mass ratio of 2:1:0.2; (5) Prepare 10 ml of a polyvinyl alcohol solution with a mass concentration of 2% for later use; (6) Measure 1 ml of the solution prepared in step (5) and mix it with the mixture in step (4). After stirring well, place it in a crucible for later use; (7) Place the crucible in step (6) into a tube resistance furnace for roasting. Control the temperature at 600 °C and the roasting time at 1 h. Introduce a CO reducing atmosphere during the roasting process. The roasted product is for later use; (8) Add sodium alginate at a concentration of 0.02 g / mL to 100 mL of distilled water. After stirring well, heat it in an incubator at 85 °C for 2 h. After complete dissolution, let it stand for 2 hours for later use; (9) Add 0.5 g of calcium chloride to 100 ml of distilled water. After stirring well and dissolving, it is for later use; (10) Mix the roasted product in step (7) with 10 ml of the solution prepared in step (8) and stir well. While stirring, slowly drop it into the solution prepared in step (10) and cure for 4 h to obtain a hexavalent chromium repair material based on phosphogypsum.

[0023] Add the material prepared in this example and 3 materials for experimental comparison (pure iron powder, 1% bimetallic copper plating, 1% bimetallic Fe-Cu copper plating immobilized by calcium alginate) to 1 L of Cr(Ⅵ)-containing wastewater with an initial concentration of 50 mg / L. The iron powder content in all the above fillers is 0.5 g, and the iron powder in the 4 fillers is all cast iron powder.

[0024] Through static beaker experiments, it was found that after 24 hours, the removal rates of pure iron powder, 1.0% bimetallic copper plating, 1% bimetallic Fe-Cu copper plating immobilized by calcium alginate, and the hexavalent chromium repair material based on phosphogypsum for Cr(Ⅵ)-containing wastewater were 10%, 18%, 34%, 70%, and 100% respectively. And after detection, the concentrations of impurity ions such as fluoride and other heavy metals in the Cr(Ⅵ)-containing wastewater after repair were lower than the third-class water quality standards of the Surface Water Environment Quality Standard and the third-class water quality standards of the Groundwater Quality Standard, and would not cause secondary pollution to surface water and groundwater.

[0025] Example 2 (1) Pass phosphogypsum through a 200-mesh steel sieve and weigh 10 g of the sifted material and place it in a 100-ml beaker for later use; (2) Prepare an NaCl solution with a mass concentration of 12%, an HCl solution with a mass concentration of 15%, and an H2C2O4 solution with a mass concentration of 10%, and compound them in a dosage ratio of 1:1:1 to form a compound detergent for later use; (3) Measure 30 ml of the compounded detergent in step 2, add it to the beaker in step (1), stir well for 1 min, then put it into a magnetic heating stirrer, heat it to 85 °C, stir for 45 min, filter it under vacuum after cooling, take out the filter residue, and let it dry naturally for later use; (4) Mix the filter residue dried naturally in step (3) with the crushed rice straw and cast iron powder (passing through a 200-mesh steel sieve) in a mass ratio of 2:1:0.2; (5) Prepare 10 ml of a polyvinyl alcohol solution with a mass concentration of 2% for later use; (6) Measure 1 ml of the solution prepared in step (5) and the mixture in step (4), stir well, and then put it into a crucible for later use; (7) Put the crucible in step (6) into a tube resistance furnace for roasting, control the temperature at 650 °C, control the roasting time at 1 h, introduce a CO reducing atmosphere during the roasting process, and let the roasted product be for later use; (8) Add sodium alginate at a concentration of 0.04 g / mL to 100 mL of distilled water, stir well, place it in an incubator and heat it at 85 °C for 2 h, let it stand for 2 h after complete dissolution for later use; (9) Add 0.5 g of calcium chloride to 100 ml of distilled water, stir well until dissolved for later use; (10) Mix the roasted product in step (7) with 10 ml of the solution prepared in step (8) and stir well, and slowly drip it into the solution prepared in step (10) while stirring, and cure for 6 h to obtain the hexavalent chromium repair material based on phosphogypsum.

[0026] Add the material prepared in this example (the iron powder content is 0.5 g) to 1 L of Cr(Ⅵ)-containing wastewater with an initial concentration of 50 mg / L. Through a static beaker experiment, it is found that after 24 h, the Cr(Ⅵ) removal rate reaches 100%, and after detection, the concentrations of impurity ions such as fluoride and other heavy metals in the Cr(Ⅵ)-containing wastewater after repair are lower than the third-class water quality standards of the Surface Water Environment Quality Standard and the third-class water quality standards of the Groundwater Quality Standard, and will not cause secondary pollution to surface water and groundwater.

[0027] Comparative Example 1 (1) Pass phosphogypsum through a 200-mesh steel sieve, and weigh 10 g of the sifted material and place it in a 100 ml beaker for later use; (2) Prepare a NaCl solution with a mass concentration of 12%, an HCl solution with a mass concentration of 15%, and an H2C2O4 solution with a mass concentration of 10%, and compound them in a dosage ratio of 1:1:1 by volume to form a compounded detergent for later use; (3) Measure 30 ml of the compounded detergent in step 2, add it to the beaker in step (1), stir well for 1 min, then place it in a magnetic heating stirrer, heat to 85 °C, stir for 45 min, filter under vacuum after cooling, take out the filter residue, and dry it naturally for later use; (4) Take the filter residue dried naturally in step (3), mix it with crushed rice straw and iron powder (passing through a 200-mesh steel sieve), with a mass ratio of 2:1:0.2; (5) After stirring the mixture in step (4) evenly, place it in a crucible for later use; put the crucible into a tube resistance furnace for roasting, control the temperature at 650 °C, control the roasting time at 1 h, introduce a CO reducing atmosphere during the roasting process, and use the roasted product for later use; (6) Add sodium alginate at a concentration of 0.04 g / mL to 100 mL of distilled water, stir well, then place it in an incubator and heat at 85 °C for 2 h. After complete dissolution, let it stand for 2 hours for later use; (7) Add 0.5 g of calcium chloride to 100 ml of distilled water, stir well until dissolved for later use; (8) Mix the roasted product in step (5) with 10 ml of the solution prepared in step (6) and stir well, and slowly drip it into the solution prepared in step (7) while stirring, and cure for 4 h. Add the prepared material (the iron powder content is 0.5 g) to the Cr(Ⅵ)-containing wastewater with an initial concentration of 50 mg / L and a volume of 1 L. After a static beaker experiment, it is found that after 24 hours, the Cr(Ⅵ) removal rate reaches 85.7%.

[0028] Comparative Example 2 (1) Pass the phosphogypsum through a 200-mesh steel sieve, and weigh 10 g of the sifted material and place it in a 100 ml beaker for later use; (2) Prepare a NaCl solution with a mass concentration of 12%, an HCl solution with a mass concentration of 15%, and an H2C2O4 solution with a mass concentration of 10%, and compound them in a dosage ratio of 1:1:1 to form a compounded detergent for later use; (3) Measure 30 ml of the compounded detergent in step 2, add it to the beaker in step (1), stir well for 1 min, then place it in a magnetic heating stirrer, heat to 85 °C, stir for 45 min, filter under vacuum after cooling, take out the filter residue, and dry it naturally for later use; (4) Take the filter residue dried naturally in step (3), mix it with crushed rice straw and iron powder (passing through a 200-mesh steel sieve), with a mass ratio of 2:1:0.2; (5) Prepare 10 ml of a polyvinyl alcohol solution with a mass concentration of 2% for later use; (6) Measure 1 ml of the solution prepared in step (5) and mix it with the mixture in step (4), stir well evenly, then place it in a crucible for later use; (7) Place the crucible from step (6) into a tube resistance furnace for roasting. Control the temperature at 650 °C and the roasting time at 1 h. Introduce a CO reducing atmosphere during the roasting process. After roasting, the product is obtained. Add the prepared materials (each with an iron powder content of 0.5 g) to 1 L of Cr(VI)-containing wastewater with an initial concentration of 50 mg / L. Through static beaker experiments, it is found that after 24 hours, the Cr(VI) removal rate reaches 65%.

[0029] Comparative Example 3 (1) Pass phosphogypsum through a 200-mesh steel sieve, and weigh 10 g of the sieve residue and mix it with crushed rice straw and cast iron powder (passed through a 200-mesh steel sieve) in a mass ratio of 2:1:0.2; (2) After thoroughly stirring the mixture from step (1) evenly, place it in a crucible for later use. Place the crucible in a tube resistance furnace for roasting. Control the temperature at 650 °C and the roasting time at 1 h. Introduce a CO reducing atmosphere during the roasting process. The roasted product is for later use; (3) Add sodium alginate at a concentration of 0.04 g / mL to 100 mL of distilled water. After thorough stirring, place it in an incubator and heat it at 85 °C for 2 h. After complete dissolution, let it stand for 2 hours for later use; (4) Add 0.5 g of calcium chloride to 100 ml of distilled water. After thorough stirring and dissolution, it is for later use; (5) Mix and stir evenly the roasted product from step (2) with 10 ml of the solution prepared in step (3), and slowly drip it into the solution prepared in step (4) while stirring, and cure for 4 h. Add the prepared materials (each with an iron powder content of 0.5 g) to 1 L of Cr(VI)-containing wastewater with an initial concentration of 50 mg / L. Through static beaker experiments, it is found that after 24 hours, the Cr(VI) removal rate reaches 100%, but the concentrations of impurity ions such as fluoride and phosphate in the Cr(VI)-containing wastewater after remediation are higher than the Class III water quality standards of the Surface Water Environment Quality Standard and the Class III water quality standards of the Groundwater Quality Standard, which is likely to cause secondary pollution to surface water and groundwater.

[0030] The above embodiments have detailed the structure, characteristics, and function effects of the present invention. The above are only the preferred embodiments of the present invention. Any changes made according to the concept of the present invention, or equivalent embodiments modified into equivalent changes, still within the scope covered by the specification, should be within the protection scope of the present invention.

Claims

1. A preparation method of a hexavalent chromium repair material based on phosphogypsum, characterized in that, It has the following steps: (1) Mix 10 - 12 wt% aqueous NaCl solution, 10 - 15 wt% aqueous HCl solution, and 5 - 10 wt% aqueous H2C2O4 solution evenly according to a volume ratio of 1:1:1 to obtain a compound detergent; (2) Add 10 g of phosphogypsum to 10 - 30 ml of the compound detergent, stir and mix evenly, heat to 80 - 85 °C, stir for 30 - 45 min, and filter after cooling to obtain a filter residue; (3) Take the filter residue obtained in step 2 and mix it evenly with crushed rice straw and cast iron powder according to a mass ratio of 2:1:0.2; (4) Add 1 ml of 2 wt% polyvinyl alcohol solution to the product obtained in step 3, stir and mix evenly to obtain a mixture; (5) Bake the mixture in a reducing atmosphere at 600 - 650 °C for 1 h to obtain solid A; (6) Add 2 - 4 g of sodium alginate to 100 ml of water, stir well, place it in an incubator at 85 °C and heat for 2 h. After complete dissolution, let it stand for 2 hours to obtain solution A; (7) Add 0.5 g of calcium chloride to 100 ml of distilled water, stir and dissolve to obtain solution B; (8) Mix solid A and solution A evenly, drop solution B while stirring, and let it stand for more than 4 h to obtain a hexavalent chromium repair material based on phosphogypsum.

2. The preparation method according to claim 1, characterized in that The filtration described in step 1 is vacuum filtration.

3. The preparation method according to claim 1, characterized in that, The phosphogypsum described in step 2 is obtained through a 200 - mesh steel sieve.

4. The preparation method according to claim 1, characterized in that, The rice straw and cast iron powder described in step 3 are obtained through a 200 - mesh steel sieve.

5. The preparation method according to claim 1, characterized in that, The baking in step 5 is carried out in a tube resistance furnace.

6. The preparation method according to claim 1, wherein, The reducing atmosphere described in step 5 is CO.

7. A hexavalent chromium repair material based on phosphogypsum prepared by the preparation method as described in claim 1.