Preparation method for modifying phosphogypsum based on cooperation of curing agent and calcium hydroxide

Abstract

The invention discloses a preparation method of phosphogypsum modified based on a curing agent synergistic calcium hydroxide, and the phosphogypsum modified curing agent based on calcium hydroxide comprises calcium hydroxide and an anionic polymer composite modifier. The industrial calcium hydroxide and the modifier can be used for treating the ardealite raw slag, a stable macromolecular complex is formed in the ardealite raw slag, and the stable macromolecular complex and the added calcium hydroxide are co-precipitated under the effects of colloid destabilization, adsorption bridging and the like, so that ardealite phosphate and fluorine ions are efficiently induced and captured, and the phosphogypsum phosphate and fluorine ions are effectively recovered. Through targeting reaction of special materials, soluble phosphate radicals and fluorine ions in the phosphogypsum are converted into inorganic minerals such as insoluble calcium phosphate or hydroxyapatite and calcium fluoride, so that the aim of harmlessly treating the phosphogypsum at lower cost is fulfilled.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial solid waste treatment, and in particular relates to a preparation method of phosphogypsum based on the coordinated use of a curing agent and calcium hydroxide. Background Art

[0002] Phosphogypsum is a by-product of the wet process for producing phosphoric acid. Existing harmless treatment technologies include composite solidification technology.

[0003] The calcium-based composite agent used in composite curing technology is a calcium alkoxide-calcium composite synthesized from calcium oxide and ethanol. After reacting for 14 days at a 20% moisture content, it achieves a phosphorus and fluorine removal rate exceeding 90%, and its volume is reduced by 30% after curing, making it suitable for large-scale slag dump remediation. While composite curing technology effectively reduces phosphorus and fluorine concentrations and prevents aquatic pollution, ethanol itself, as a chemical substance, can pose air pollution and biosafety risks if not handled properly. During use, ethanol can evaporate, forming volatile organic compounds (VOCs), which can pollute the atmosphere and pose health risks. The ethanol production process can involve significant energy consumption and resource waste, increasing the overall environmental burden. Ethanol is a flammable liquid, requiring strict control during its production and use, increasing transportation and storage costs. The disposal of ethanol waste also requires proper management to prevent soil and groundwater contamination.

[0004] Therefore, a method for treating phosphogypsum with low environmental impact, low cost and good treatment effect is needed.

[0005] The patent application document with the announcement number CN116571534A discloses a harmless agent for phosphogypsum and its engineering application method. The agent consists of a powder component and a liquid component; wherein the powder component consists of an alkaline component and talcum powder, and the alkaline component is at least one of calcium oxide, magnesium oxide, calcium hydroxide, and magnesium hydroxide; the liquid component is an aqueous solution of at least one of soluble iron salts, aluminum salts, and calcium salts. The method is to use a lime neutralization method including calcium oxide. The lime neutralization method is considered to be a simple and low-cost method for treating phosphogypsum, and is suitable for phosphogypsum with relatively stable quality and low organic matter content. The lime neutralization method will produce insoluble calcium phosphate (Ca3(PO4)2) and calcium fluoride (CaF2) precipitates with rough crystal morphology and unstable performance, requiring secondary treatment. The treatment process needs to be further optimized to improve resource utilization and avoid secondary pollution problems. In addition, some acidic substances (such as H + ) is neutralized, which increases the pH value of the solution and increases the difficulty of treatment.

[0006] Patent application publication number CN117819849A discloses a method for purifying and classifying low-quality, compacted phosphogypsum to produce building materials. The method comprises the following steps: 1) grinding the low-quality, compacted phosphogypsum in a ceramic ball mill to produce a phosphogypsum slurry; 2) subjecting the phosphogypsum slurry to ultrasonic cleaning in an ultrasonic cleaning machine; 3) obtaining a foam product, which is a high-silicon tailings product, and a high-purity phosphogypsum slurry, as an underflow product; 4) subjecting the high-silicon tailings to filtration in a filter, where fly ash and an alkali activator are added to produce a phosphogypsum-based polymer; and 5) filtering the high-purity phosphogypsum slurry through a filter, drying it in an oven, and finally calcining it in a calciner to produce high-quality β-hemihydrate gypsum powder. This method requires ultrasonic cleaning and high-temperature calcination, resulting in a processing cost exceeding 200 yuan per ton of phosphogypsum, making it relatively cost-effective. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides a preparation method of phosphogypsum based on the cooperation of a curing agent and calcium hydroxide.

[0008] The present invention is achieved through the following technical solutions.

[0009] The present invention provides a preparation method of phosphogypsum based on a curing agent and calcium hydroxide modification, comprising a process of mixing calcium hydroxide and an anionic polymer composite modifier with phosphogypsum to prepare the modified phosphogypsum.

[0010] Preferably, the mass ratio of the calcium hydroxide to the anionic polymer composite modifier is 5-30:3-10.

[0011] Preferably, the anionic polymer composite modifier comprises the following components: polyaluminum chloride, polyaluminum ferric chloride, magnesium sulfate, N,0-carboxymethyl chitosan, a coagulant aid and purified water.

[0012] Preferably, the anionic polymer composite modifier comprises the following components in mass percentage: 20% to 25% polyaluminum chloride, 15% to 19% polyaluminum ferric chloride, 7% to 10% magnesium sulfate, 5% to 7% N,0-carboxymethyl chitosan, 2% to 4% coagulant aid and 30% to 50% purified water.

[0013] Preferably, the coagulant aid is polyferric sulfate.

[0014] Preferably, the calcium hydroxide is a powder, with a calcium hydroxide content greater than 90%, a moisture content less than 2.0%, and a 325 mesh sieving rate greater than or equal to 95%.

[0015] Preferably, the preparation method of the anionic polymer composite modifier comprises the following steps:

[0016] A1: Add polyaluminium chloride, polyaluminium ferric chloride, magnesium sulfate, N,0-carboxymethyl chitosan and coagulant aid into purified water;

[0017] A2: By adjusting the amount of purified water, the density, pH value and mass fraction of water-insoluble matter of the obtained anionic polymer composite modifier can reach the usage standards.

[0018] Preferably, in step A2, the amount of purified water is adjusted so that the density of the anionic polymer composite modifier is 1.2-1.3 g / cm 3 , pH value 1.5-3.5, the mass fraction of water-insoluble matter ≤0.3% meets the use standard.

[0019] Preferably, the preparation method of phosphogypsum modified by a curing agent in collaboration with calcium hydroxide comprises the following steps:

[0020] B1: adding calcium hydroxide to phosphogypsum and stirring evenly to obtain a mixture;

[0021] B2: adding the anionic polymer composite modifier to water for dilution, stirring and dissolving to prepare a modifier solution, and then adding the solution to the mixture and stirring and mixing to obtain a modified mixture;

[0022] B3: Let the modified mixture stand and complete the phosphogypsum treatment.

[0023] Preferably, in step B1, calcium hydroxide is added to the phosphogypsum and stirred evenly, and the pH of the phosphogypsum is adjusted to 9-12;

[0024] In step B2, the mass ratio of the anionic polymer composite modifier to water is 0.8-5:5-12, and the modifier solution is added to the mixture and stirred for 1-3 minutes at a stirring speed of 100-200 rpm;

[0025] In step B3, the modified mixture is allowed to stand for 24 hours to complete the phosphogypsum treatment.

[0026] The beneficial effects of the present invention are:

[0027] The present invention can use industrial calcium hydroxide and a modifier to treat phosphogypsum slag, form a stable macromolecular complex in the phosphogypsum slag, produce co-precipitation with the added calcium hydroxide through the effects of colloidal destabilization, adsorption bridging, etc., so that phosphates and fluoride ions in the phosphogypsum are efficiently induced and captured, and through the targeted reaction of exclusive materials, the soluble phosphate radicals and fluoride ions in the phosphogypsum are converted into insoluble inorganic minerals such as calcium phosphate or hydroxyapatite and calcium fluoride, thereby achieving the purpose of harmless disposal of phosphogypsum at a relatively low cost. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0029] Example 1:

[0030] A preparation method of phosphogypsum based on the coordination of a curing agent and calcium hydroxide comprises the process of mixing calcium hydroxide and an anionic polymer composite modifier with phosphogypsum to prepare the modified phosphogypsum.

[0031] Adding an anionic polymer composite modifier as a curing agent further enhances the fluoride removal effect by complexing and adsorbing fluoride ions. For example, polyaluminum chloride hydrolyzes in water to produce aluminum hydroxide colloid, which can adsorb fluoride ions. At the same time, aluminum ions can also form stable complexes with fluoride ions, thereby achieving the purpose of fluoride removal.

[0032] The main function of adding calcium hydroxide is to adjust the pH of phosphogypsum, making it alkaline. Calcium ions react chemically with fluoride ions to form calcium fluoride precipitates, thereby removing some fluoride ions. It also reacts with impurities to form insoluble substances, thereby removing or converting them. For example, the reaction of calcium hydroxide with fluoride to form calcium fluoride precipitates can reduce the fluoride content in phosphogypsum, reducing its harmful effects on the environment and human health.

[0033] The mass ratio of the calcium hydroxide to the anionic polymer composite modifier is 5-30:3-10.

[0034] The anionic polymer composite modifier comprises the following components in mass percentage: 20% polyaluminium chloride, 15% polyaluminium ferric chloride, 7% magnesium sulfate, 5% N,0-carboxymethyl chitosan, 2% polyferric sulfate and 50% purified water.

[0035] The calcium hydroxide is powder, the calcium hydroxide content is greater than 90%, the moisture content is less than 2.0%, and the 325 mesh sieving rate is greater than 95%.

[0036] The preparation method of the anionic polymer composite modifier comprises the following steps:

[0037] A1: Add polyaluminium chloride, polyaluminium ferric chloride, magnesium sulfate, N,0-carboxymethyl chitosan and coagulant aid into purified water;

[0038] A2: By adjusting the amount of purified water, the density, pH value and mass fraction of water-insoluble matter of the obtained anionic polymer composite modifier can reach the usage standards.

[0039] In step A2, the amount of purified water is adjusted to make the density of the anionic polymer composite modifier 1.2 g / cm 3, pH value 1.5, the mass fraction of water-insoluble matter ≤ 0.3% meets the use standard.

[0040] A preparation method based on curing agent and calcium hydroxide modified phosphogypsum comprises the following steps:

[0041] B1: adding calcium hydroxide to phosphogypsum and stirring evenly to obtain a mixture;

[0042] B2: adding the anionic polymer composite modifier to water for dilution, stirring and dissolving to prepare a modifier solution, and then adding the solution to the mixture and stirring and mixing to obtain a modified mixture;

[0043] B3: Let the modified mixture stand and complete the phosphogypsum treatment.

[0044] In step B1, calcium hydroxide is added to the phosphogypsum and stirred evenly, and the pH of the phosphogypsum is adjusted to 9;

[0045] In step B2, the mass ratio of the anionic polymer composite modifier to water is 0.8:5, and the modifier solution is added to the mixture and stirred for 1 minute at a stirring speed of 100 rpm;

[0046] In step B3, the modified mixture is allowed to stand for 24 hours to complete the phosphogypsum treatment.

[0047] Example 2:

[0048] A preparation method of phosphogypsum based on the coordination of a curing agent and calcium hydroxide comprises the process of mixing calcium hydroxide and an anionic polymer composite modifier with phosphogypsum to prepare the modified phosphogypsum.

[0049] Adding an anionic polymer composite modifier as a curing agent further enhances the fluoride removal effect by complexing and adsorbing fluoride ions. For example, polyaluminum chloride hydrolyzes in water to produce aluminum hydroxide colloid, which can adsorb fluoride ions. At the same time, aluminum ions can also form stable complexes with fluoride ions, thereby achieving the purpose of fluoride removal.

[0050] The main function of adding calcium hydroxide is to adjust the pH of phosphogypsum, making it alkaline. Calcium ions react chemically with fluoride ions to form calcium fluoride precipitates, thereby removing some fluoride ions. It also reacts with impurities to form insoluble substances, thereby removing or converting them. For example, the reaction of calcium hydroxide with fluoride to form calcium fluoride precipitates can reduce the fluoride content in phosphogypsum, reducing its harmful effects on the environment and human health.

[0051] The mass ratio of the calcium hydroxide to the anionic polymer composite modifier is 5-30:3-10.

[0052] The anionic polymer composite modifier comprises the following components in mass percentage: 25% polyaluminium chloride, 19% polyaluminium ferric chloride, 10% magnesium sulfate, 7% N,0-carboxymethyl chitosan, 4% polyferric sulfate and 50% purified water.

[0053] The calcium hydroxide is powder, the calcium hydroxide content is greater than 90%, the moisture content is less than 2.0%, and the 325 mesh sieving rate is greater than 95%.

[0054] The preparation method of the anionic polymer composite modifier comprises the following steps:

[0055] A1: Add polyaluminium chloride, polyaluminium ferric chloride, magnesium sulfate, N,0-carboxymethyl chitosan and coagulant aid into purified water;

[0056] A2: By adjusting the amount of purified water, the density, pH value and mass fraction of water-insoluble matter of the obtained anionic polymer composite modifier can reach the usage standards.

[0057] In step A2, the amount of purified water is adjusted to make the density of the anionic polymer composite modifier 1.3 g / cm 3 , pH value 3.5, the mass fraction of water-insoluble matter ≤ 0.3% meets the use standard.

[0058] A preparation method based on curing agent and calcium hydroxide modified phosphogypsum comprises the following steps:

[0059] B1: adding calcium hydroxide to phosphogypsum and stirring evenly to obtain a mixture;

[0060] B2: adding the anionic polymer composite modifier to water for dilution, stirring and dissolving to prepare a modifier solution, and then adding the solution to the mixture and stirring and mixing to obtain a modified mixture;

[0061] B3: Let the modified mixture stand and complete the phosphogypsum treatment.

[0062] In step B1, calcium hydroxide is added to the phosphogypsum and stirred evenly, and the pH of the phosphogypsum is adjusted to 12;

[0063] In step B2, the mass ratio of the anionic polymer composite modifier to water is 5:12, and the modifier solution is added to the mixture and stirred for 3 minutes at a stirring speed of 200 rpm;

[0064] In step B3, the modified mixture is allowed to stand for 24 hours to complete the phosphogypsum treatment.

[0065] Example 3:

[0066] A preparation method of phosphogypsum based on the coordination of a curing agent and calcium hydroxide comprises the process of mixing calcium hydroxide and an anionic polymer composite modifier with phosphogypsum to prepare the modified phosphogypsum.

[0067] Adding an anionic polymer composite modifier as a curing agent further enhances the fluoride removal effect by complexing and adsorbing fluoride ions. For example, polyaluminum chloride hydrolyzes in water to produce aluminum hydroxide colloid, which can adsorb fluoride ions. At the same time, aluminum ions can also form stable complexes with fluoride ions, thereby achieving the purpose of fluoride removal.

[0068] The main function of adding calcium hydroxide is to adjust the pH of phosphogypsum, making it alkaline. Calcium ions react chemically with fluoride ions to form calcium fluoride precipitates, thereby removing some fluoride ions. It also reacts with impurities to form insoluble substances, thereby removing or converting them. For example, the reaction of calcium hydroxide with fluoride to form calcium fluoride precipitates can reduce the fluoride content in phosphogypsum, reducing its harmful effects on the environment and human health.

[0069] The mass ratio of the calcium hydroxide to the anionic polymer composite modifier is 16:7.

[0070] The anionic polymer composite modifier comprises the following components in mass percentage: 23% polyaluminium chloride, 16% polyaluminium ferric chloride, 8% magnesium sulfate, 6% N,0-carboxymethyl chitosan, 3% polyferric sulfate and 42% purified water.

[0071] The calcium hydroxide is powder, the calcium hydroxide content is greater than 90%, the moisture content is less than 2.0%, and the 325 mesh sieving rate is greater than 95%.

[0072] The preparation method of the anionic polymer composite modifier comprises the following steps:

[0073] A1: Add polyaluminium chloride, polyaluminium ferric chloride, magnesium sulfate, N,0-carboxymethyl chitosan and coagulant aid into purified water;

[0074] A2: By adjusting the amount of purified water, the density, pH value and mass fraction of water-insoluble matter of the obtained anionic polymer composite modifier can reach the usage standards.

[0075] In step A2, the amount of purified water is adjusted to make the density of the anionic polymer composite modifier 1.2 g / cm 3 , pH value 2.2, mass fraction of water-insoluble matter ≤ 0.3% meets the use standard.

[0076] A preparation method based on curing agent and calcium hydroxide modified phosphogypsum comprises the following steps:

[0077] B1: adding calcium hydroxide to phosphogypsum and stirring evenly to obtain a mixture;

[0078] B2: adding the anionic polymer composite modifier to water for dilution, stirring and dissolving to prepare a modifier solution, and then adding the solution to the mixture and stirring and mixing to obtain a modified mixture;

[0079] B3: Let the modified mixture stand and complete the phosphogypsum treatment.

[0080] In step B1, calcium hydroxide is added to the phosphogypsum and stirred evenly, and the pH of the phosphogypsum is adjusted to 10;

[0081] In step B2, the mass ratio of the anionic polymer composite modifier to water is 2.4:7.8, and the modifier solution is added to the mixture and stirred for 1 to 3 minutes at a stirring speed of 200 rpm;

[0082] In step B3, the modified mixture is allowed to stand for 24 hours to complete the phosphogypsum treatment.

[0083] Comparative Example 1

[0084] Use calcium hydroxide as powder and add it to phosphogypsum, stir evenly, and then let it stand for 24 hours.

[0085] The calcium hydroxide powder has the following specifications: calcium hydroxide content > 90%, moisture < 2.0%, and 325 mesh screening rate > 95%.

[0086] Comparative Example 2

[0087] The same anionic polymer composite modifier as in Example 3 was added to water for dilution, stirred and dissolved to prepare a modifier solution, which was then added to the phosphogypsum and stirred and mixed evenly to obtain a modified mixture; the modified mixture was allowed to stand for 24 hours to complete the phosphogypsum treatment.

[0088] In the step, the mass ratio of the anionic polymer composite modifier to water is 2.4:7.8, and the modifier solution is added to the mixture and stirred for 1 to 3 minutes at a stirring speed of 200 rpm.

[0089] The methods of Examples 1-3 and Comparative Examples 1-2 were used to treat phosphogypsum with total phosphorus contents of 98.3 mg / L, 351.9 mg / L, and 707.9 mg / L, respectively. The proportions of the components are shown in Table 1, and the results are shown in Table 2.

[0090] Table 1 Ratio of Examples 1-3, Comparative Examples 1-2 and phosphogypsum

[0091]

[0092]

[0093] Table 2 Phosphogypsum treatment results

[0094]

[0095] As shown in Table 2, the combined use of anionic polymer composite modifiers and calcium hydroxide exhibits a synergistic effect. Phosphogypsum treated using the methods of Examples 1-3 achieved total phosphorus levels of ≤ 0.5 mg / L, fluoride levels of ≤ 10 mg / L, and a pH of 6-9, meeting the requirements for Class I solid waste. Using the methods of Examples 1-3, phosphogypsum with a total phosphorus (P₂O₅) level as high as 707.9 mg / L was treated at a cost of less than 40 yuan per ton, demonstrating high cost-effectiveness.

Claims

1. A method for preparing phosphogypsum based on a curing agent and calcium hydroxide modification, characterized in that: The invention comprises a process of preparing modified phosphogypsum by mixing calcium hydroxide and anionic polymer composite modifier with phosphogypsum.

2. The method for preparing phosphogypsum based on a curing agent in collaboration with calcium hydroxide as claimed in claim 1, wherein: The mass ratio of the calcium hydroxide to the anionic polymer composite modifier is 5-30:3-10.

3. The method for preparing phosphogypsum based on a curing agent and calcium hydroxide modification according to claim 1, wherein: The anionic polymer composite modifier comprises the following components: polyaluminum chloride, polyaluminum ferric chloride, magnesium sulfate, N,0-carboxymethyl chitosan, a coagulant aid and purified water.

4. The method for preparing phosphogypsum based on a curing agent in collaboration with calcium hydroxide as claimed in claim 3, characterized in that: The anionic polymer composite modifier comprises the following components in mass percentage: 20% to 25% of polyaluminum chloride, 15% to 19% of polyaluminum ferric chloride, 7% to 10% of magnesium sulfate, 5% to 7% of N,0-carboxymethyl chitosan, 2% to 4% of a coagulant aid and 30% to 50% of purified water.

5. A method for preparing phosphogypsum based on a curing agent in collaboration with calcium hydroxide as claimed in claim 4, characterized in that: The coagulant aid is polyferric sulfate.

6. The method for preparing phosphogypsum based on a curing agent in collaboration with calcium hydroxide as claimed in claim 1, characterized in that: The calcium hydroxide is powder, the calcium hydroxide content is greater than 90%, the moisture content is less than 2.0%, and the 325 mesh sieving rate is greater than or equal to 95%.

7. The method for preparing phosphogypsum based on a curing agent in collaboration with calcium hydroxide as claimed in claim 4, characterized in that: The preparation method of the anionic polymer composite modifier comprises the following steps: A1: Add polyaluminium chloride, polyaluminium ferric chloride, magnesium sulfate, N,0-carboxymethyl chitosan and coagulant aid into purified water; A2: By adjusting the amount of purified water, the density, pH value and mass fraction of water-insoluble matter of the obtained anionic polymer composite modifier can reach the usage standards.

8. The method for preparing phosphogypsum based on a curing agent in collaboration with calcium hydroxide as claimed in claim 7, characterized in that: In step A2, the amount of purified water is adjusted to make the density of the anionic polymer composite modifier 1.2-1.3 g / cm 3 , pH value 1.5-3.5, the mass fraction of water-insoluble matter ≤0.3% meets the use standard.

9. The method for preparing phosphogypsum based on a curing agent in collaboration with calcium hydroxide as claimed in claim 1, wherein: The following steps are involved: B1: adding calcium hydroxide to phosphogypsum and stirring evenly to obtain a mixture; B2: adding the anionic polymer composite modifier to water for dilution, stirring and dissolving to prepare a modifier solution, and then adding the solution to the mixture and stirring and mixing to obtain a modified mixture; B3: Let the modified mixture stand and complete the phosphogypsum treatment.

10. The method for preparing phosphogypsum based on a curing agent in collaboration with calcium hydroxide as claimed in claim 9, characterized in that: In step B1, calcium hydroxide is added to the phosphogypsum and stirred evenly, and the pH of the phosphogypsum is adjusted to 9-12; In step B2, the mass ratio of the anionic polymer composite modifier to water is 0.8-5:5-12, and the modifier solution is added to the mixture and stirred for 1-3 minutes at a stirring speed of 100-200 rpm; In step B3, the modified mixture is allowed to stand for 24 hours to complete the phosphogypsum treatment.

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