Method for converting ardealite into metal-organic framework material by utilizing aqueous solution stirring

Abstract

The invention belongs to the technical field of ardealite upgrading chemical recovery, and discloses a method for converting ardealite into a metal-organic framework material by utilizing aqueous solution stirring, which comprises the following steps: (1) adding a strong alkali compound into water, and uniformly dispersing to obtain a first dispersion system; then adding an organic carboxylic acid ligand, dissolving and reacting to obtain a second dispersion system; (2) adding ardealite into the second dispersion system in a stirring state, and stirring and reacting at normal temperature; and carrying out suction filtration, washing and drying on the product to obtain the Ca-MOF material. The high-added-value MOF material is prepared by using ardealite as a raw material through a simple method, firstly, an organic carboxylic acid ligand reacts with a strong alkali compound to promote carboxylic acid dissociation, then carboxylate ions and calcium ions derived from ardealite are in full contact under the stirring effect and are subjected to a coordination reaction, and the high-added-value MOF material is obtained. The method is green and environment-friendly, the reaction is efficient, and the cost is low.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical recycling of phosphogypsum upgrades, and more specifically, relates to a method for converting phosphogypsum into a metal-organic framework material by stirring an aqueous solution, thereby providing an effective recycling pathway for the waste phosphogypsum. Background Art

[0002] Phosphogypsum is a byproduct of the wet-process phosphoric acid production process. Its primary components are calcium sulfate dihydrate, followed by free water, organic matter, heavy metals, rare earth elements, and possibly radioactive elements. Phosphogypsum also contains impurities such as surfactants introduced during beneficiation processes and adsorbed phosphoric acid dissolved in the water. Generally, every ton of phosphoric acid produced produces approximately 5 tons of phosphogypsum. The presence of various impurities in phosphogypsum limits its feasibility as a direct gypsum. Currently, the comprehensive utilization of phosphogypsum is primarily focused on four pathways: cement retarder, external sales and supply, ecological restoration, and construction plaster. Natural gypsum is typically added to cement at a rate of 3% to 5% (by mass) as a retarder. Phosphogypsum, with dihydrate gypsum as its primary component, can, in principle, replace natural gypsum as a retarder in cement. Phosphogypsum is heated in a two-step process to remove moisture to produce building plaster powder, or it can be calcined at high temperatures (750-800°C) to substantially volatilize soluble P₂O₅ and F to produce building plaster powder with a pH of 6-7. Gypsum powder can be sold directly, or it can be further processed to make products such as building blocks, boards, stucco gypsum, plastering gypsum, self-leveling mortar and suspended ceilings. Phosphogypsum is mixed with cement and fly ash in appropriate proportions for cementation and filling, or various materials such as quicklime, sodium hydroxide and Glauber's salt are added to prepare phosphogypsum-based composite filling materials. However, since phosphogypsum contains a small amount of impurities such as P and F, it will reduce the early strength of the filling body, which makes the application of phosphogypsum as a filling material have certain limitations. The above methods of recycling and utilizing phosphogypsum have the disadvantages of low product added value, complicated process flow and high energy consumption. Therefore, the efficient and green upgraded chemical recovery of phosphogypsum and its preparation into high-value-added products are the key to solving the large-scale accumulation of phosphogypsum.

[0003] MOF materials are porous crystalline materials with regular network structures composed of metal ions and organic ligands. They possess advantages such as large specific surface area, rich pores, and customizable structures. Based on the different metal ions, organic ligands, pore size, and crystal structure, over 20,000 MOFs have been discovered and are widely used in environmental pollution control, energy storage and conversion, polymer nanocomposites, gas separation, storage, and catalysis. Converting phosphogypsum waste into high-value-added MOF materials is a new avenue for its recycling and reuse. Unfortunately, research in this area is limited, with only one reported work to date. Yimer et al. used the residue (mainly calcium hydroxide) after alkaline dissolution of phosphogypsum in water as a metal ion source, and used 1,2,4,5-tetrakis(4-carboxyphenyl)benzene, terephthalic acid, and trimesic acid as ligands, respectively, to prepare three MOF materials, SBMOF-2, Ca-BDC, and Ca-BTC, by a solvent thermal method (AM Yimer, A H Assen, I E Mghaimimi, O. Lakbita, K. Adil, Y. Belmabkhout, Unlocking the potential of phosphogypsum waste: Unified synthesis of functional metal-organic frameworks and zeolite via a sustainable valorization route. Chemical Engineering Journal 2024, 479, 147902). The study showed that phosphogypsum waste can be used as a raw material to prepare MOF. However, this method requires high temperature, high pressure and other conditions, a long reaction time, and the use of a large amount of organic solvents, high cost and energy consumption, making it difficult to achieve large-scale production.

[0004] In summary, converting phosphogypsum waste into high-value-added MOF materials is a new avenue for its upcycling and utilization; however, this area is understudied and still in its infancy. Currently, the main methods for recycling phosphogypsum waste are its use as a cement retarder, building plaster material, and filler. However, these recycling methods suffer from low product value-added, complex processes, and high energy consumption, which contradict the concept of environmental protection. Reported methods for preparing MOF materials using phosphogypsum waste as a precursor require high temperatures, high pressures, and the use of large amounts of organic solvents, resulting in high costs and energy consumption. Therefore, a green, efficient, and low-cost method is urgently needed to prepare phosphogypsum waste into MOF materials on a large scale, achieving the goal of "turning waste into treasure." This would also help address the environmental pollution caused by the long-term accumulation of phosphogypsum and contribute to sustainable development. Summary of the Invention

[0005] In response to the above-mentioned deficiencies or improvements in the prior art, the present invention aims to provide a method for converting phosphogypsum into a metal-organic framework material using aqueous solution stirring. By improving the overall process design of the method, an organic carboxylic acid ligand is first reacted with a strong base compound based on aqueous solution stirring to promote the dissociation of the carboxylic acid. Subsequently, under stirring, the carboxylate ions fully contact and coordinate with the calcium ions derived from the phosphogypsum, thereby generating a calcium-based MOF material with good crystallinity. This invention achieves the recycling and reuse of waste phosphogypsum and the efficient preparation of high-value-added MOF materials through an environmentally friendly, efficient, and low-cost method.

[0006] To achieve the above object, according to the present invention, a method for converting phosphogypsum into a metal-organic framework material by stirring an aqueous solution is provided, characterized in that it comprises the following steps:

[0007] (1) adding a strong base compound to water and dispersing it uniformly to obtain a first dispersion; then adding an organic carboxylic acid ligand to the first dispersion, dissolving and reacting the organic carboxylic acid ligand to obtain a second dispersion;

[0008] (2) adding phosphogypsum to the second dispersion under stirring, and reacting under stirring at room temperature; the product is filtered, washed, and dried to obtain the Ca-MOF material.

[0009] As a further preference of the present invention, in step (1), the strong base compound is one or more of sodium hydroxide and potassium hydroxide.

[0010] As a further preferred embodiment of the present invention, in step (1), the organic carboxylic acid ligand is one or more of terephthalic acid, trimesic acid and pyromellitic acid.

[0011] As a further preferred embodiment of the present invention, in step (1), the molar ratio of the strong base compound to the organic carboxylic acid ligand is 2:1 to 4:1.

[0012] As a further preferred embodiment of the present invention, the molar ratio of the organic carboxylic acid ligand in step (1) to the calcium sulfate dihydrate contained in the phosphogypsum in step (2) is 1:3 to 2:1.

[0013] As a further preference of the present invention, in step (2), the reaction time of the stirring reaction is 4 to 20 hours, and the stirring speed is 50 to 600 r / min.

[0014] As a further preferred embodiment of the present invention, in step (2), the mass percentage of calcium sulfate dihydrate in the phosphogypsum is greater than 90%.

[0015] The above technical solution conceived by the present invention, compared with existing technologies, first adds an organic carboxylic acid ligand to a strong alkaline solution. Stirring to promote mass transfer accelerates the reaction between the two and promotes the dissociation of the carboxylic acid. Phosphogypsum is then added under stirring, allowing the carboxylate ions to fully contact and coordinate with the metal ions provided by the phosphogypsum, producing a calcium-based MOF material with good crystallinity. This method offers advantages such as high product added value, simple process, low cost, and high reaction efficiency. Furthermore, it adheres to the concept of green environmental protection and can be used to prepare a variety of crystalline metal-organic framework (MOF) materials.

[0016] Specifically, the method of the present invention can achieve the following beneficial effects:

[0017] (1) The method of the present invention includes a two-step series process, namely, the acid-base reaction of the organic carboxylic acid ligand and the strong base and the growth of the MOF material under the stirring of the aqueous solution. This is because the organic carboxylic acid ligand is first reacted with the strong base compound to promote the dissociation of the carboxylic acid, and then the carboxylate ions are fully contacted with the calcium ions from the phosphogypsum under the stirring action and a coordination reaction occurs to generate a MOF material with good crystallinity. The present invention uses a method of stirring the aqueous solution to convert the phosphogypsum into the MOF material. The reaction conditions are mild, the operation is simple, easy to control, the reaction time is short, no organic solvent is used, it is green and environmentally friendly, and the cost is low. It effectively avoids the high temperature and high pressure conditions required for the reported preparation of phosphogypsum into MOF materials by the solvent thermal method, and at the same time avoids the use of a large amount of organic solvents. The reaction efficiency is significantly improved, and the obtained MOF material has good crystallinity, is suitable for large-scale production, and has the potential for industrial application.

[0018] (2) The present invention converts phosphogypsum into high-value-added MOF materials, thereby realizing the upgraded chemical recycling of phosphogypsum. The preparation process is environmentally friendly, the reaction is efficient, and the cost is low. Compared with recycling methods such as using phosphogypsum as a cement retarder, building gypsum material, and filling material, the present invention has a simple process, low energy consumption, and the prepared product has high added value. The economic value of phosphogypsum is significantly improved, while reducing resource waste and alleviating environmental burdens, providing new ideas for the upgraded recycling of phosphogypsum.

[0019] (3) The present invention utilizes industrial waste such as phosphogypsum and reports for the first time that high-value-added MOF materials are prepared by a simple method using phosphogypsum as a raw material. The method of the present invention uses phosphogypsum as a source of metal ions, and organic carboxylic acid ligands react with metal ions under the action of stirring an aqueous solution to prepare MOF materials. This is a new way to upgrade and recycle phosphogypsum. Compared with commercial metal salts such as calcium nitrate, calcium sulfate, and calcium chloride, which have purchase costs, the cost of phosphogypsum is extremely low and can even be obtained free of charge, significantly reducing the cost of raw materials for MOF material preparation, turning waste into treasure, and reducing resource waste. The use of phosphogypsum to prepare MOF materials fully utilizes industrial waste and reduces dependence on natural mineral resources, thus complying with the concept of sustainable development.

[0020] The key to this invention lies in utilizing phosphogypsum to prepare high-value-added calcium-based MOF materials. Phosphogypsum recycling is typically focused on engineering applications (for use as cement retarders, building materials, and fillers), while the preparation of MOF materials falls within the realm of chemistry. The preparation of phosphogypsum into MOF materials spans a wide range of fields. However, this invention utilizes a simple and efficient method to prepare phosphogypsum into high-value-added Ca-MOF materials.

[0021] (4) The method of the present invention can preferably control the molar ratio of the organic carboxylic acid ligand to the calcium sulfate dihydrate contained in the phosphogypsum to be preferably 1:3 to 2:1, and the molar ratio of the strong base compound to the organic carboxylic acid ligand to be preferably controlled to be 2:1 to 4:1, thereby promoting the full deprotonation of the organic acid ligand, effectively ensuring the formation of coordination bonds and MOF coordination networks, and avoiding the possible formation of metal clusters or metal oxide precipitation, thereby effectively ensuring the crystallinity of the product MOF.

[0022] (5) The stirring speed of the present invention can be preferably controlled to 50-600 r / min to accelerate the diffusion of the reactants, ensure uniform mixing of the reactants, increase the nucleation rate, promote crystal formation, and ensure the yield of the MOF material. In addition, the stirring time can be preferably set to 4-20 h to ensure sufficient reaction and obtain a MOF material with good porosity.

[0023] In summary, the present invention adopts an aqueous solution stirring method to convert phosphogypsum into MOF material, thereby realizing the upgraded chemical recycling and reuse of phosphogypsum. Compared with traditional physical or chemical recovery methods, this method has the advantages of high product added value, simple process, low cost, high reaction efficiency, etc., and is in line with the concept of green environmental protection, and can prepare a variety of crystalline MOF materials. This method solves the difficult problems of harmless treatment and resource utilization of industrial phosphogypsum waste, provides a new green way for the upgraded chemical recycling of large amounts of phosphogypsum waste, realizes "turning waste into treasure", helps to solve the environmental pollution problem caused by the long-term accumulation of phosphogypsum, and has significant environmental, economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The X-ray diffraction spectrum and infrared spectrum of Ca-BDC prepared by using phosphogypsum and terephthalate in Example 1 are shown; wherein, Figure 1 The a in corresponds to the X-ray diffraction spectrum, Figure 1 b in the figure corresponds to the infrared spectrum.

[0025] Figure 2 The X-ray diffraction spectrum and infrared spectrum of Ca-BTC prepared by using phosphogypsum and trimesic acid salt in Example 2 are shown; wherein, Figure 2 The a in corresponds to the X-ray diffraction spectrum, Figure 2 b in the figure corresponds to the infrared spectrum.

[0026] Figure 3 The X-ray diffraction spectrum and infrared spectrum of Ca-BTEC prepared by using phosphogypsum and pyromellitic tetracarboxylate in Example 3 are shown; wherein, Figure 3 The a in corresponds to the X-ray diffraction spectrum, Figure 3 b in the figure corresponds to the infrared spectrum.

[0027] Figure 4 This is the X-ray diffraction spectrum of Ca-BTC prepared using phosphogypsum and trimesic acid salt in Example 4.

[0028] Figure 5 This is the X-ray diffraction spectrum of Ca-BDC prepared using phosphogypsum and terephthalate in Example 5.

[0029] Figure 6 The X-ray diffraction spectrum and scanning electron microscope image of Ca-BDC prepared using phosphogypsum and terephthalate in Example 6; wherein, Figure 6 The a in corresponds to the X-ray diffraction spectrum, Figure 6 b in FIG corresponds to a scanning electron microscope image.

[0030] Figure 7 The X-ray diffraction spectrum and scanning electron microscope image of Ca-BTEC prepared using phosphogypsum and pyromellitic tetracarboxylate in Example 7; wherein, Figure 7 The a in corresponds to the X-ray diffraction spectrum, Figure 7 b in FIG corresponds to a scanning electron microscope image.

[0031] Figure 8 The X-ray diffraction spectrum and scanning electron microscope image of Ca-BTC prepared by using phosphogypsum and trimesic acid salt in Example 8; wherein, Figure 8 The a in corresponds to the X-ray diffraction spectrum, Figure 8 b in FIG corresponds to a scanning electron microscope image.

[0032] Figure 9 The X-ray powder diffraction spectrum of the product in Comparative Example 1 is shown. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0034] The aqueous solution stirring method for preparing MOF materials using phosphogypsum in the present invention can be carried out according to the following steps:

[0035] First, a strong base compound is added to water and dissolved to obtain solution A (or dispersion A), and then an organic carboxylic acid ligand is added to solution A (or dispersion A) and stirred to obtain solution B (or dispersion B).

[0036] Secondly, solution B (or dispersion B) is placed on a magnetic stirrer, and phosphogypsum (e.g., phosphogypsum waste) is added to solution B (or dispersion B) under stirring to react, and the product is filtered, washed, and dried to obtain MOF material.

[0037] The phosphogypsum used in the following examples is waste phosphogypsum powder provided by phosphate fertilizer production enterprises (phosphogypsum is a by-product of the phosphate fertilizer industry), and the content of calcium sulfate dihydrate contained therein is 95wt%, and the impurities mainly include silicon dioxide, magnesium, phosphoric acid, etc.

[0038] The following are specific embodiments:

[0039] Example 1

[0040] (1) Weigh 5.61 g of potassium hydroxide (0.10 mol) and add it to 60 mL of water to dissolve. Then weigh 8.31 g of terephthalic acid (0.05 mol) and add it to the newly prepared potassium hydroxide solution to dissolve to obtain a dipotassium terephthalate solution.

[0041] (2) The salt solution was placed on a magnetic stirrer and 9.06 g of phosphogypsum (corresponding to 0.05 mol of calcium sulfate dihydrate) was added to the solution while stirring. Stirring was continued at room temperature for 8 h at a speed of 500 r / min. The product was filtered, washed, and dried to obtain Ca-BDC with a yield of 90.3 wt%.

[0042] Figure 1 a in the figure is the X-ray diffraction spectrum of Ca-BDC. Figure 1Figure b is the infrared spectrum of Ca-BDC. The X-ray diffraction spectrum shows that Ca-BDC exhibits significant characteristic diffraction peaks, indicating successful synthesis. Ca-O stretching vibrations are also observed in the infrared spectrum, confirming successful synthesis of Ca-BDC.

[0043] Example 2

[0044] The addition amount of potassium hydroxide in step (1) of the above Example 1 was changed to 8.42 g (0.15 mol), terephthalic acid was changed to trimesic acid and the addition amount was 10.51 g (0.05 mol), and other parameter conditions (including other reagents and amounts) remained unchanged to obtain Ca-BTC with a yield of 72.1 wt%.

[0045] Figure 2 a in the figure is the X-ray diffraction spectrum of Ca-BTC. Figure 2 Figure b is the infrared spectrum of Ca-BTC. The X-ray diffraction spectrum shows that Ca-BTC exhibits significant characteristic diffraction peaks, indicating successful synthesis. Ca-O stretching vibrations are also observed in the infrared spectrum, confirming successful synthesis of Ca-BTC.

[0046] Example 3

[0047] (1) Weigh 4.00 g of sodium hydroxide (0.10 mol) and add it to 60 mL of water to dissolve it. Then weigh 6.35 g of pyromellitic acid (0.025 mol) and add it to the newly prepared sodium hydroxide solution to dissolve it to obtain a tetrasodium pyromellitic acid solution.

[0048] (2) The salt solution was placed on a magnetic stirrer and 9.06 g of phosphogypsum (corresponding to 0.05 mol of calcium sulfate dihydrate) was added to the solution while stirring. Stirring was continued at room temperature for 12 h at a speed of 400 rpm. The product was filtered, washed, and dried to obtain Ca-BTEC with a yield of 88.3 wt%.

[0049] Figure 3 a in the figure is the X-ray diffraction spectrum of Ca-BTEC. Figure 3 Figure b is the infrared spectrum of Ca-BTEC. The X-ray diffraction spectrum shows that Ca-BTEC exhibits significant characteristic diffraction peaks, indicating successful synthesis. Ca-O stretching vibrations are also observed in the infrared spectrum, confirming the successful synthesis of Ca-BTEC.

[0050] Example 4

[0051] (1) Weigh 3.00 g of sodium hydroxide (0.075 mol) and add it to 60 mL of water to dissolve. Then weigh 5.25 g of trimesic acid (0.025 mol) and add it to the newly prepared sodium hydroxide solution to dissolve to obtain a solution of trisodium trimesic acid.

[0052] (2) The salt solution was placed on a magnetic stirrer and 9.06 g of phosphogypsum (corresponding to 0.05 mol of calcium sulfate dihydrate) was added to the solution while stirring. Stirring was continued at room temperature for 8 h at a speed of 400 r / min. The product was filtered, washed, and dried to obtain Ca-BTC with a yield of 80.6 wt%.

[0053] Figure 4 The X-ray diffraction spectrum of Ca-BTC is shown in Figure 2. As can be seen from the X-ray diffraction spectrum, Ca-BTC has significant characteristic diffraction peaks, indicating the successful synthesis of Ca-BTC.

[0054] Example 5

[0055] (1) Weigh 8.00 g of sodium hydroxide (0.20 mol) and add it to 60 mL of water to dissolve. Then weigh 16.61 g of terephthalic acid (0.10 mol) and add it to the newly prepared sodium hydroxide solution to dissolve to obtain a disodium terephthalate solution.

[0056] (2) The salt solution was placed on a magnetic stirrer and 9.06 g of phosphogypsum (corresponding to 0.05 mol of calcium sulfate dihydrate) was added to the solution while stirring. Stirring was continued at room temperature for 4 h at a speed of 600 rpm. The product was filtered, washed, and dried to obtain Ca-BDC with a yield of 86.7 wt%.

[0057] Figure 5 The X-ray diffraction spectrum of Ca-BDC is shown in Figure 2. As can be seen from the X-ray diffraction spectrum, Ca-BDC has significant characteristic diffraction peaks, indicating that Ca-BDC was successfully synthesized.

[0058] Example 6

[0059] (1) Weigh 8.42 g of potassium hydroxide (0.15 mol) and add it to 60 mL of water to dissolve. Then weigh 12.46 g of terephthalic acid (0.075 mol) and add it to the newly prepared potassium hydroxide solution to dissolve to obtain a dipotassium terephthalate solution.

[0060] (2) The salt solution was placed on a magnetic stirrer and 9.06 g of phosphogypsum (corresponding to 0.05 mol of calcium sulfate dihydrate) was added to the solution while stirring. Stirring was continued at room temperature for 20 h at a speed of 50 r / min. The product was filtered, washed, and dried to obtain Ca-BDC with a yield of 83.4 wt%.

[0061] Figure 6 a in the figure is the X-ray diffraction spectrum of Ca-BDC. Figure 6 Figure b is a scanning electron micrograph of Ca-BDC. The X-ray diffraction spectrum shows that Ca-BDC exhibits distinct characteristic diffraction peaks, confirming its successful synthesis. The scanning electron micrograph reveals a relatively regular, rod-like morphology.

[0062] Example 7

[0063] (1) Weigh 11.22 g of potassium hydroxide (0.20 mol) and add it to 60 mL of water to dissolve it. Then weigh 12.71 g of pyromellitic acid (0.05 mol) and add it to the newly prepared potassium hydroxide solution to dissolve it to obtain a tetrapotassium pyromellitic acid solution.

[0064] (2) The salt solution was placed on a magnetic stirrer and 9.06 g of phosphogypsum (corresponding to 0.05 mol of calcium sulfate dihydrate) was added to the solution while stirring. Stirring was continued at room temperature for 4 h at a speed of 200 r / min. The product was filtered, washed, and dried to obtain Ca-BTEC with a yield of 91.2 wt%.

[0065] Figure 7 a in the figure is the X-ray diffraction spectrum of Ca-BTEC. Figure 7 Figure b is a scanning electron micrograph of Ca-BTEC. The X-ray diffraction spectrum shows that Ca-BTEC exhibits distinct characteristic diffraction peaks, confirming its successful synthesis. The scanning electron micrograph reveals a relatively regular, rod-like morphology.

[0066] Example 8

[0067] (1) Weigh 2.00 g of sodium hydroxide (0.05 mol) and add it to 60 mL of water to dissolve. Then weigh 3.57 g of trimesic acid (0.0167 mol) and add it to the newly prepared sodium hydroxide solution to dissolve to obtain a solution of trisodium trimesic acid.

[0068] (2) The salt solution was placed on a magnetic stirrer and 9.06 g of phosphogypsum (corresponding to 0.05 mol of calcium sulfate dihydrate) was added to the solution while stirring. Stirring was continued at room temperature for 12 h at a speed of 400 r / min. The product was filtered, washed, and dried to obtain Ca-BTC with a yield of 75.6 wt%.

[0069] Figure 8 a in the figure is the X-ray diffraction spectrum of Ca-BTC. Figure 8Figure b is a scanning electron micrograph of Ca-BTC. The X-ray diffraction spectrum shows that Ca-BTC exhibits distinct characteristic diffraction peaks, confirming its successful synthesis. The scanning electron micrograph reveals a prismatic structure.

[0070] Comparative Example 1

[0071] (1) Weigh 8.31 g of terephthalic acid (0.05 mol) and add it to water to dissolve it to obtain a terephthalic acid solution.

[0072] (2) The solution was placed on a magnetic stirrer and 9.06 g of phosphogypsum (corresponding to 0.05 mol of calcium sulfate dihydrate) was added to the solution while stirring. The mixture was stirred at room temperature for 8 h at a speed of 500 r / min. A gray product was obtained after filtration, washing, and drying.

[0073] Figure 9 The X-ray diffraction spectrum of the product shows that the product is a mixture of terephthalic acid and phosphogypsum, and no Ca-BDC is generated.

[0074] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for converting phosphogypsum into a metal-organic framework material by stirring an aqueous solution, characterized in that: The following steps are involved: (1) adding a strong base compound to water and dispersing it uniformly to obtain a first dispersion; then adding an organic carboxylic acid ligand to the first dispersion, dissolving and reacting the organic carboxylic acid ligand to obtain a second dispersion; (2) adding phosphogypsum to the second dispersion under stirring, and reacting under stirring at room temperature; the product is filtered, washed, and dried to obtain the Ca-MOF material.

2. The method according to claim 1, wherein: In step (1), the strong base compound is one or more of sodium hydroxide and potassium hydroxide.

3. The method according to claim 1, wherein: In step (1), the organic carboxylic acid ligand is one or more of terephthalic acid, trimesic acid and pyromellitic acid.

4. The method according to claim 1, wherein: In step (1), the molar ratio of the strong base compound to the organic carboxylic acid ligand is 2:1 to 4:

1.

5. The method according to claim 1, wherein: The molar ratio of the organic carboxylic acid ligand in step (1) to the calcium sulfate dihydrate contained in the phosphogypsum in step (2) is 1:3 to 2:

1.

6. The method according to claim 1, wherein: In step (2), the reaction time of the stirring reaction is 4 to 20 hours, and the stirring speed is 50 to 600 r / min.

7. The method according to claim 1, wherein: In step (2), the mass percentage of calcium sulfate dihydrate in the phosphogypsum is greater than 90%.

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