High-purity Ca-MOF fluorine fixing agent as well as preparation method and application thereof

Abstract

The invention discloses a high-purity Ca-MOF fluorine fixing agent and a preparation method and application thereof.The preparation method comprises the steps that water is added into ardealite for size mixing, the pH value is adjusted, then filtering is conducted, a calcium ion solution is obtained, then an organic ligand and a solvent are added into the calcium ion solution, and MOF-1 is obtained through a reaction; and then mixing the MOF-1 with an activating agent, and activating to obtain the high-purity Ca-MOF fluorine fixing agent. Calcium ions are taken as a metal center to react with an organic ligand, and a crystal material with a three-dimensional porous structure is formed through in-situ polymerization self-assembly, so that a space is provided for precipitation reaction of the calcium ions and fluorine, and efficient capture and stable curing of the fluorine ions are realized.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization technology, specifically relating to a high-purity Ca-MOF fluorine-fixing agent, its preparation method, and its application. Background Technology

[0002] Phosphogypsum is a large-scale industrial solid waste generated during the wet-process phosphoric acid production. Its main component is calcium sulfate dihydrate (CaSO4·2H2O). With the expansion of wet-process phosphoric acid production capacity, phosphogypsum production has also increased exponentially. Currently, the treatment method for phosphogypsum is stockpiling, which not only occupies a large amount of land resources, but more seriously, it contains harmful impurities such as soluble fluoride, soluble phosphorus, and heavy metals. These impurities can seep into water bodies and soil under rainwater immersion, causing serious environmental pollution. At the same time, soluble fluoride (mainly in the form of hydrogen fluoride, fluorosilicates, etc.) in phosphogypsum is also one of the key factors restricting the resource utilization of phosphogypsum. It not only delays the setting time of cement (when phosphogypsum is used as a cement setting regulator), but also slowly precipitates during the use of phosphogypsum products, posing a long-term potential risk to the environment. Therefore, one of the core tasks of harmless treatment of phosphogypsum is to solidify the soluble fluoride in it.

[0003] Currently, the most commonly used industrial technology for fluoride fixation in phosphogypsum is the lime neutralization method. This involves adding lime (calcium hydroxide) to phosphogypsum, causing soluble fluoride to react with calcium ions to form calcium fluoride (CaF2) precipitate. While this method is simple to operate, it has significant drawbacks: First, the amount of lime added is difficult to control precisely; excessive addition can lead to alkalization of the phosphogypsum, affecting its subsequent utilization performance. Second, the efficiency of lime in solidifying fluoride is limited, especially in scenarios with low fluoride concentrations or complex phosphogypsum compositions, where the solidification rate is often low (traditional methods typically achieve solidification rates below 80%). Furthermore, the calcium fluoride precipitate generated during the reaction may coat the surface of the phosphogypsum particles, hindering further solidification of the internal fluoride and resulting in incomplete solidification.

[0004] Chinese patent CN115872641B discloses a curing agent for curing and removing soluble phosphorus and soluble fluoride from phosphogypsum and its application. The curing agent is a mixed aqueous solution containing polyacrylamide and calcium hydroxide. When using this curing agent to cure and remove soluble phosphorus and soluble fluoride from phosphogypsum, experiments have shown that good curing and removal effects can be achieved whether the curing agent is mixed and stirred with phosphogypsum for reaction, or whether in-situ leaching or heap leaching processes are used for treatment.

[0005] Chinese patent CN119683922A discloses a composite formulation for solidifying fluorine and phosphorus in phosphogypsum and its application. It utilizes the high specific surface area and active groups of modified clay minerals to adsorb fluorine and phosphorus. However, its preparation process is complex and depends on the quality stability of the mineral raw materials. Although these methods offer some improvements, they still fail to fundamentally solve the problems of insufficient reaction sites and low mass transfer efficiency in fluorine-fixing agents.

[0006] Metal-organic frameworks (MOFs) are a class of porous crystalline materials that have attracted widespread attention in recent years. They are formed by the self-assembly of metal ions and organic ligands through coordination bonds. MOFs possess high specific surface area, tunable pore structure, and abundant surface functional groups, showing great potential in adsorption, catalysis, and other fields. Among various MOFs, calcium-based metal-organic frameworks (Ca-MOFs) are considered to have unique advantages in environmental remediation due to the low toxicity and low cost of their metal source (calcium), and the fact that calcium ions can form stable calcium fluoride with fluoride ions. Studies have shown that Ca-MOFs are not only structurally stable, but also often contain unsaturated calcium metal sites within their pores, exhibiting strong selective adsorption capacity for anions such as fluoride ions. Currently, phosphogypsum is commonly used to prepare Ca-MOF materials, but the recycling of Ca-MOF materials into phosphogypsum for efficient and stable fluoride fixation has not been explored in depth. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a high-purity Ca-MOF fluorine-fixing agent, its preparation method, and its application. The agent uses calcium ions as the metal center to react with organic ligands, forming a crystalline material with a three-dimensional porous structure through in-situ polymerization and self-assembly. This material can undergo a precipitation reaction with fluorine, and the porous structure of the MOF provides space for the reaction, achieving efficient capture and stable solidification of fluoride ions.

[0008] To achieve the above objectives, the present invention provides a method for preparing a high-purity Ca-MOF fluorine-fixing agent, comprising the following steps: (1) Add organic ligands and solvent to calcium ion solution, and after reaction, wash with water, filter and dry to obtain MOF; (2) Mix MOF with activator to carry out activation reaction, wash and dry to obtain Ca-MOF fluorine fixative.

[0009] Preferably, the mass ratio of the calcium ion solution to the complex organic ligand and solvent in step (1) is 37-40:0.56-1.85:900-950.

[0010] More preferably, the calcium ion solution is prepared by dispersing phosphogypsum in water, adjusting the pH to 4-5 with dilute hydrochloric acid, stirring to dissolve, and filtering to obtain the calcium ion solution.

[0011] More preferably, the mass ratio of the phosphogypsum to water is 1:1.5-2.5.

[0012] More preferably, the phosphogypsum is dried to a CaSO4 content of 85-90%.

[0013] More preferably, the composite organic ligand is composed of terephthalaldehyde and 2-aminoterephthalic acid in a mass ratio of 0.21-0.31:0.85:1.0.

[0014] More preferably, the solvent is a mixture of DMF and any one or more of anhydrous ethanol and 1,4-dioxane.

[0015] More preferably, the solvent is a mixed solution of DMF and anhydrous ethanol; the volume ratio of DMF to anhydrous ethanol is 10-9:1.

[0016] Preferably, the reaction conditions in step (1) are 130-140℃ for 30-38h.

[0017] Preferably, the mass ratio of MOF to activator in step (2) is 1:8-10; the activation conditions are 180-230℃ and activation under an inert atmosphere for 2-4 hours.

[0018] More preferably, the activator is one or more of sodium hydroxide and calcium hydroxide.

[0019] More preferably, the activator is composed of sodium hydroxide and calcium hydroxide in a volume ratio of 8-9:1.

[0020] This invention also provides a high-purity Ca-MOF fluorine-fixing agent prepared according to the above-described method, wherein the high-purity Ca-MOF fluorine-fixing agent has a specific surface area ≥200 m². 2 / g, with a pore size range of 0.5-5nm.

[0021] The present invention also provides an application of high-purity Ca-MOF fluoride-fixing agent in the harmless treatment of phosphogypsum, wherein the amount of high-purity Ca-MOF fluoride-fixing agent used in the application is 0.3-0.5% of the mass of phosphogypsum.

[0022] The beneficial effects of this invention are as follows: 1. By regulating the functional groups of organic ligands (such as -COOH, -NH2), this invention can endow Ca-MOF with high selective adsorption capacity for fluoride ions, effectively reducing the competitive interference of anions such as phosphate and sulfate coexisting in phosphogypsum.

[0023] 2. The Ca-MOF material prepared by this invention has a huge specific surface area and a highly ordered pore structure, providing abundant diffusion channels and reaction space for fluoride ions. The unsaturated calcium sites on its framework can directly coordinate with fluoride ions and rapidly form calcium fluoride precipitate, with a solidification rate of over 97%, significantly better than the traditional lime neutralization method.

[0024] 3. The Ca-MOF material prepared by this invention is non-toxic and harmless. The calcium fluoride generated by the curing reaction is stably fixed in the MOF channels, avoiding the risk of secondary leaching. The treated phosphogypsum can be used to prepare mine pit filling materials, ecological restoration materials or cement setting modifiers. Its mechanical properties and durability are improved, realizing the resource utilization of waste.

[0025] 4. The preparation process of this invention is simple, the reaction conditions are mild, and the calcium source can be obtained from industrial by-products, which conforms to the principles of green chemistry and realizes "treating waste with waste".

[0026] 5. The Ca-MOF material prepared by this invention has high purity and requires a small amount (less than 0.5%) when used for fluorine fixation with phosphogypsum, which can reduce the cost of fluorine fixation. Detailed Implementation

[0027] The technical solution of the present invention will be further explained and described below with reference to specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0028] In the following examples, the phosphogypsum was sourced from Yidu Xingfa Chemical Co., Ltd., with a water content of 10-15% and a CaSO4 content of 89%.

[0029] Example 1 (1) Disperse phosphogypsum in 2 times its mass of deionized water, add 0.1 mol / L dilute hydrochloric acid to adjust the pH to 5, stir to dissolve and filter to obtain calcium ion solution; (2) According to the mass ratio of calcium ion filtrate: terephthalaldehyde: 2-aminoterephthalic acid: calcium ion filtrate of 37:0.21:0.85:900, terephthalaldehyde, 2-aminoterephthalic acid and solvent were added to the calcium ion solution, placed in a reaction vessel, and reacted at 120°C for 30 h. The product was collected, washed three times with ethanol, washed three times with water, and dried at 80°C for 10 h to obtain MOF-1. The solvent consisted of DMF and anhydrous ethanol in a volume ratio of 8:1. (3) The prepared MOF-1: sodium hydroxide: calcium hydroxide were mixed in a mass ratio of 1:8:2, and then placed in a tube furnace. The mixture was activated at 200°C for 2 hours under a nitrogen atmosphere. After washing with water three times, the mixture was dried at 80°C for 10 hours to obtain Ca-MOF-1 curing agent.

[0030] Example 2 (1) Disperse phosphogypsum in 2 times its mass of deionized water, add 0.1 mol / L dilute hydrochloric acid to adjust the pH to 4.5, stir to dissolve and filter to obtain calcium ion solution; (2) According to the mass ratio of calcium ion filtrate: terephthalaldehyde: 2-aminoterephthalic acid: calcium ion filtrate of 40:0.21:0.85:900, terephthalaldehyde, 2-aminoterephthalic acid and solvent were added to the calcium ion solution, placed in a reaction vessel, and reacted at 130°C for 36 h. The product was collected, washed with water and dried at 80°C for 10 h to obtain MOF-2. The solvent consisted of DMF and anhydrous ethanol in a volume ratio of 9:1. (3) Mix MOF-2, sodium hydroxide and calcium hydroxide in a mass ratio of 1:9:1, then place them in a tube furnace, activate them at 210°C for 3 hours in a nitrogen atmosphere, wash them three times with water, and then dry them at 80°C for 10 hours to obtain Ca-MOF-2 curing agent.

[0031] Example 3 (1) Disperse phosphogypsum in 2 times its mass of deionized water, add 0.1 mol / L dilute hydrochloric acid to adjust the pH to 4, stir to dissolve and filter to obtain calcium ion solution; (2) According to the mass ratio of calcium ion filtrate: terephthalaldehyde: 2-aminoterephthalic acid: calcium ion filtrate of 40:0.31:0.85:950, terephthalaldehyde, 2-aminoterephthalic acid and solvent were added to the calcium ion solution, placed in a reaction vessel, and reacted at 130°C for 36 h. The product was collected, washed with water and dried at 80°C for 10 h to obtain MOF-3. The solvent consisted of DMF and ethanol in a volume ratio of 10:1. (3) Mix MOF-3, sodium hydroxide and calcium hydroxide in a mass ratio of 1:9:1, then place them in a tube furnace, activate them at 230°C for 4 hours in a nitrogen atmosphere, wash them three times with water, and then dry them at 80°C for 10 hours to obtain Ca-MOF-3 curing agent.

[0032] Example 4 (1) Disperse phosphogypsum in 2 times its mass of deionized water, add 0.1 mol / L dilute hydrochloric acid to adjust the pH to 4, stir to dissolve and filter to obtain calcium ion solution; (2) According to the mass ratio of calcium ion filtrate: terephthalaldehyde: 2-aminoterephthalic acid: calcium ion filtrate of 40:0.31:1.0:950, terephthalaldehyde, 2-aminoterephthalic acid and solvent were added to the calcium ion solution, placed in a reaction vessel, and reacted at 140℃ for 36h. The product was collected, washed with water and dried at 80℃ for 10h to obtain MOF-4. The solvent consisted of DMF and anhydrous ethanol in a volume ratio of 10:1. (3) Mix MOF-4, sodium hydroxide and calcium hydroxide in a mass ratio of 1:9:1, then place them in a tube furnace, activate them at 230°C for 4 hours in a nitrogen atmosphere, wash them three times with water, and then dry them at 80°C for 10 hours to obtain Ca-MOF-4 curing agent.

[0033] Example 5 (1) Disperse phosphogypsum in 2 times its mass of deionized water, add 0.1 mol / L dilute hydrochloric acid to adjust the pH to 4, stir to dissolve and filter to obtain calcium ion solution; (2) Calcium ion filtrate: terephthalaldehyde: 2-aminoterephthalic acid: calcium ion filtrate in a mass ratio of 40:0.21:1.0:950. Terephthalaldehyde, 2-aminoterephthalic acid and solvent were added to the calcium ion solution and placed in a reaction vessel. After reacting at 140°C for 38 h, the product was collected, washed with water and dried at 80°C for 10 h to obtain MOF-5. The solvent consisted of DMF and anhydrous ethanol in a volume ratio of 10:1. (3) Mix MOF-5, sodium hydroxide and calcium hydroxide in a mass ratio of 1:9:1, then place them in a tube furnace, activate them at 230°C for 4 hours in a nitrogen atmosphere, wash them three times with water, and then dry them at 80°C for 10 hours to obtain Ca-MOF-5 curing agent.

[0034] Example 6 (1) Disperse phosphogypsum in 2 times its mass of deionized water, add 0.1 mol / L dilute sulfuric acid to adjust the pH to 4, stir to dissolve and filter to obtain calcium ion solution; (2) According to the mass ratio of calcium ion filtrate: terephthalaldehyde: 2-aminoterephthalic acid: calcium ion filtrate of 40:0.31:0.85:950, terephthalaldehyde, 2-aminoterephthalic acid and solvent were added to the calcium ion solution, placed in a reaction vessel, and reacted at 140°C for 38 h. The product was collected, washed with water and dried at 80°C for 10 h to obtain MOF-6. The solvent was composed of DMF and anhydrous ethanol in a volume ratio of 10:1. (3) Mix MOF-6, sodium hydroxide and calcium hydroxide in a mass ratio of 1:9:1, then place them in a tube furnace, wash and activate them at 230°C for 4 hours in a nitrogen atmosphere, wash them three times with water, and then dry them at 80°C for 10 hours to obtain Ca-MOF-6 curing agent.

[0035] Comparative Example 1 (1) Disperse phosphogypsum in 2 times its mass of deionized water, add 0.1 mol / L dilute hydrochloric acid to adjust the pH to 4, stir to dissolve and filter to obtain calcium ion solution; (2) Calcium ion filtrate: terephthalaldehyde: 2-aminoterephthalic acid: calcium ion filtrate in a mass ratio of 35:0.5:0.85:800. Terephthalaldehyde, 2-aminoterephthalic acid and solvent were added to the calcium ion solution and placed in a reaction vessel. After reacting at 140°C for 38 h, the product was collected, washed with water and dried at 80°C for 10 h to obtain MOF-1-1. The solvent was composed of DMF and anhydrous ethanol in a volume ratio of 10:1. (3) Mix MOF-1 with sodium hydroxide at a mass ratio of 1:10, then place it in a tube furnace, wash and activate it at 230°C for 4 hours under a nitrogen atmosphere, wash it three times with water, and then dry it at 80°C for 10 hours to obtain Ca-MOF-1-1 curing agent.

[0036] Comparative Example 2 (1) Prepare a calcium chloride solution with the same concentration of calcium ions as in Example 3, add 0.1 mol / L dilute hydrochloric acid to adjust the pH to 4, stir to dissolve and filter to obtain a calcium ion solution; (2)-(3): Same as in Example 3, the curing agent Ca-MOF-2-1 was prepared.

[0037] Comparative Example 3 (1) Same as Example 3; (2) According to the mass ratio of calcium ion filtrate: terephthalaldehyde: 2-aminoterephthalic acid: calcium ion filtrate of 40:0.31:1.5:950, terephthalaldehyde, 2-aminoterephthalic acid and solvent were added to the calcium ion solution, placed in a reaction vessel, and reacted at 130°C for 36 h. The product was collected, washed with water and dried at 80°C for 10 h to obtain MOF-3-3. (3) Same as in Example 3, the curing agent Ca-MOF-3-1 was prepared.

[0038] Comparative Example 4 (1) Same as Example 3; (2) According to the mass ratio of calcium ion filtrate: 2-aminoterephthalic acid: calcium ion filtrate of 40:1.1:950, 2-aminoterephthalic acid and solvent were added to the calcium ion solution and placed in a reaction vessel. After reacting at 140°C for 38 h, the product was collected, washed with water and dried at 80°C for 10 h to obtain MOF-4-1; wherein the solvent was composed of DMF and anhydrous ethanol in a volume ratio of 7:1. (3) Same as in Example 3, the curing agent Ca-MOF-4-1 was prepared.

[0039] Comparative Example 5 (1) Same as Example 3; (2) According to the mass ratio of calcium ion filtrate: terephthalaldehyde: calcium ion filtrate of 40:1.1:950, terephthalaldehyde and solvent were added to the calcium ion solution, placed in a reaction vessel, and reacted at 120°C for 38 h. The product was collected, washed with water, and dried at 80°C for 10 h to obtain MOF-5-1. The solvent was composed of DMF and anhydrous ethanol in a volume ratio of 10:1. (3) Same as in Example 3, the curing agent Ca-MOF-5-1 was prepared.

[0040] Comparative Example 6 (1)-(2): Same as Example 3; (3) MOF-6 was placed in a tube furnace and activated at 210°C for 3 hours in a nitrogen atmosphere. After washing with water three times, it was dried at 80°C for 10 hours to obtain Ca-MOF-6-1.

[0041] Comparative Example 7 (1)-(2): Same as Example 3; (3) Mix MOF-1, sodium hydroxide and calcium hydroxide in a mass ratio of 1:7:3, then place them in a tube furnace, wash and activate them at 210°C for 3 hours under a nitrogen atmosphere, wash them three times with water, and then dry them at 80°C for 10 hours to obtain Ca-MOF-7-1.

[0042] Results Testing: 0.5g of the curing agent prepared in the above examples and comparative examples was added to 100g of phosphogypsum (initial soluble fluorine content was 76 mg / g, phosphorus content was 200 mg / g). A small amount of water was added to keep the moisture content of the phosphogypsum below 20%. The mixture was stirred for 2 minutes and then aged at room temperature for 24 hours. The leaching toxicity of the treated phosphogypsum was then tested according to the "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" (HJ557-2010). The results are shown in Table 1. Table 1. Physicochemical properties and fluorine fixation effect of curing agent

[0043] Table 2 shows the effect of fluoride fixation after phosphogypsum treatment.

[0044] The results, as shown in Tables 1-2, indicate that the Ca-MOF curing agents prepared in Examples 1-6 reduced the leaching concentration of fluoride ions from 76 mg / L before treatment to below 3 mg / L, achieving a curing rate of 96%. The leached fluoride content was far below the limit requirements of the "Standard for Pollution Control of General Industrial Solid Waste Storage and Landfill" (GB 18599), demonstrating excellent curing effects. Furthermore, testing after 30 days showed even better fluoride fixation effects in phosphogypsum. Compared to Comparative Example 2, Examples 1-6 show that the Ca-MOF curing agent prepared using calcium filtrate from phosphogypsum exhibits the same fluoride fixation effect as analytical grade calcium solution. The curing agents prepared in Comparative Examples 1, 3, 4, 5, 6, and 7 showed significantly reduced fluoride curing rates. While the use of fluoride-fixing ash resulted in good curing effects after 2 days, it was unstable, and the cured fluoride was released over time.

Claims

1. A method for preparing a high-purity Ca-MOF fluorine-fixing agent, characterized in that: Includes the following steps: (1) Add a complex organic ligand and solvent to a calcium ion solution, and after the reaction, wash with water, filter and dry to obtain MOF; (2) Mix MOF with activator to carry out activation reaction, wash and dry to obtain Ca-MOF fluorine fixative.

2. The method for preparing a high-purity Ca-MOF fluorine-fixing agent according to claim 1, characterized in that: The mass ratio of the calcium ion solution to the complex organic ligand and solvent in step (1) is 37-40:0.56-1.85:900-950.

3. The method for preparing a high-purity Ca-MOF fluorine-fixing agent according to claim 2, characterized in that: The calcium ion solution is prepared by dispersing phosphogypsum in water, adjusting the pH to 4-5, stirring to dissolve, and filtering to obtain the calcium ion solution.

4. The method for preparing a high-purity Ca-MOF fluorine-fixing agent according to claim 2, characterized in that: The composite organic ligand is composed of terephthalaldehyde and 2-aminoterephthalic acid in a mass ratio of 0.21-0.31:0.85:1.

0.

5. The method for preparing a high-purity Ca-MOF fluorine-fixing agent according to claim 2, characterized in that: The solvent is a mixture of DMF and any one or more of anhydrous ethanol and 1,4-dioxane.

6. The method for preparing a high-purity Ca-MOF fluorine-fixing agent according to claim 2, characterized in that: The reaction temperature is 130-150℃, and the reaction time is 25-38h.

7. The method for preparing a high-purity Ca-MOF fluorine-fixing agent according to claim 1, characterized in that: The mass ratio of MOF to activator in step (2) is 1:8-10; the activation conditions are 180-230℃ and activation in an inert atmosphere for 2-4 hours.

8. The method for preparing a high-purity Ca-MOF fluorine-fixing agent according to claim 7, characterized in that: The activator is one or more of sodium hydroxide and calcium hydroxide.

9. A high-purity Ca-MOF fluorine-fixing agent prepared by the method described in any one of claims 1-8, characterized in that: The specific surface area of ​​the high-purity Ca-MOF fluorine-fixing agent is ≥200m². 2 / g, with a pore size range of 0.5-5nm.

10. The application of the high-purity Ca-MOF fluoride-fixing agent as described in claim 9 in the harmless treatment of phosphogypsum, characterized in that: The amount of high-purity Ca-MOF fluorine-fixing agent used in the application is 0.2-0.5% of the mass of phosphogypsum.

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