Fluorine removal agent for fluorine-containing industrial wastewater and preparation method thereof

Abstract

This invention relates to the field of water treatment agents, specifically to a defluoridator for fluoride-containing industrial wastewater and its preparation method. The invention discloses a defluoridator for fluoride-containing industrial wastewater and its preparation method, which involves compounding aluminum sulfate, magnesium sulfate, and calcium-chitosan-grafted hydroxyapatite powder to obtain a highly efficient defluoridator, overcoming the shortcomings of single defluoridation materials in deep treatment. This defluoridator is suitable for the deep treatment of fluoride-containing industrial wastewater, achieving a defluoridation efficiency of over 98%, and the effluent fluoride concentration can be stably controlled below 2 mg / L. The preparation process of this invention is simple and easy to implement, with a fast reaction rate, strong operational stability, and a wide range of applicable water qualities. It can effectively adapt to fluoride-containing wastewater treatment scenarios in industries such as metallurgy, chemical engineering, and electroplating, and has good potential for industrial application and promotion.

Description

Technical Field

[0001] This invention relates to the field of water treatment agents, specifically to a defluoridating agent for fluoride-containing industrial wastewater and its preparation method. Background Technology

[0002] Fluoride pollutants mainly originate from chemical production processes, commonly found in metal processing industries such as aluminum and steel, and electroplating. Conventional treatment methods often fail to efficiently and stably meet discharge standards for this type of industrial fluoride wastewater, resulting in significant fluctuations in effluent fluoride concentrations. This not only impacts the stable operation of subsequent industrial wastewater treatment plants but may also cause fluoride levels in receiving water bodies to exceed the limits set by the "Surface Water Environmental Quality Standard." Fluoride in wastewater accumulates in organisms through the water cycle. Excessive ingestion by livestock such as cattle and sheep can lead to symptoms such as swollen joints, elongated hooves, osteoporosis, and even paralysis. In humans, excessive fluoride can interfere with the activity of various enzymes, disrupt calcium and phosphorus metabolism, causing fluorosis symptoms such as brittle teeth, discoloration, and bone and joint deformities, and may even increase the risk of cancer.

[0003] Currently, methods for treating fluoride in wastewater mainly include precipitation (chemical precipitation, coagulation precipitation), adsorption, electrocoagulation, electrodialysis, reverse osmosis, and ion exchange. These methods require the addition of defluorinating agents to the fluoride-containing wastewater. The defluorinating agents react with fluoride ions in the water through adsorption, complexation, or flocculation to form precipitates, thus achieving effective separation of fluoride ions. Chinese patent application CN201910258256.5 discloses a defluorinating agent for water treatment, comprising raw material components such as calcium salts, polyaluminum salts, polyferric salts, magnesium salts, copper salts, and sodium iminodisuccinate. Although this method shows good defluorination effects, the introduction of copper ions in the process causes new pollution to the water body. Therefore, it is essential to provide a defluorinating agent for fluoride-containing industrial wastewater. Summary of the Invention

[0004] The purpose of this invention is to provide a defluorinating agent for fluoride-containing industrial wastewater and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a defluorinating agent for fluoride-containing industrial wastewater, comprising the following steps: Step 1: Add calcium nitrate tetrahydrate, ferric nitrate nonahydrate, and zirconium nitrate pentahydrate to deionized water and stir to dissolve. Add diammonium hydrogen phosphate solution at 20~30℃ and stir to obtain the precursor solution. Step 2: Add nitric acid solution and urea solution to the precursor solution and control the pH of the system to 2-3; stir for 5-10 min and then carry out hydrothermal synthesis reaction of the precursor solution at 150-160℃ for 3-5 h; after the hydrothermal reaction is completed, cool, centrifuge to collect the crude product and wash with deionized water until the washing solution is neutral, freeze-dry to obtain Fe-Zr dual-ion co-doped hydroxyapatite; Step 3: S1: 3-Aminopropyltriethoxysilane was added dropwise to an aqueous ethanol solution, hydrolyzed for 30-60 min, and Fe-Zr dual-ion co-doped hydroxyapatite was added. The mixture was stirred at 25-30℃ for 8-10 h, filtered, and dried to obtain amino-modified hydroxyapatite. S2: Chitosan powder is added to acetic acid solution and stirred to dissolve to obtain chitosan solution. Calcium chloride solid is added to chitosan solution and stirred to dissolve to obtain calcium-chitosan mixed solution. Amino-modified hydroxyapatite is added to the calcium-chitosan mixed solution. Glutaraldehyde solution is used as a crosslinking agent. After reacting at 25~30℃ for 5~6h, the precipitate is collected by centrifugation, washed with deionized water until neutral, freeze-dried, pulverized, and sieved to obtain calcium-chitosan-grafted hydroxyapatite powder. Step 4: Mix aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder to obtain a fluoride removal agent.

[0006] Furthermore, in step 1, the molar ratio of (calcium + iron + zirconium) / phosphorus in the precursor solution is (1.55~1.67):1.

[0007] Furthermore, in step 1, the concentration of the diammonium hydrogen phosphate solution is 0.5~0.6 mol / L.

[0008] Furthermore, in step 2, the concentration of the nitric acid solution is 10~10.5 mol / L.

[0009] Furthermore, in step 2, the concentration of the urea solution is 0.5~0.6 mol / L.

[0010] Furthermore, in S1, the mass ratio of 3-aminopropyltriethoxysilane to Fe-Zr dual-ion co-doped hydroxyapatite is (1~3):100.

[0011] Furthermore, in S1, the volume concentration of the ethanol aqueous solution is 90%.

[0012] Furthermore, in S2, the mass ratio of chitosan, calcium chloride, and amino-modified hydroxyapatite is (1~2):1:(7~8).

[0013] Furthermore, in step 4, the mass ratio of aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder in the defluorinating agent is 10:(1~5):(5~10).

[0014] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: The defluorinating agent provided by this invention is a compound of aluminum sulfate, magnesium sulfate, and calcium-chitosan-grafted hydroxyapatite powder. Aluminum sulfate, as a conventional defluorinating component, can remove fluoride ions through the hydrolysis of aluminum ions to form aluminum hydroxide colloids via complexation precipitation and adsorption co-precipitation. However, when used alone, it suffers from defects such as loose floc structure and poor defluorination stability. The introduction of magnesium sulfate constructs a dual-metal ion defluorination system: magnesium ions can directly form magnesium fluoride precipitate with fluoride ions, and the magnesium hydroxide flocs produced by its hydrolysis can also combine with aluminum hydroxide colloids to form a more dense and stable magnesium-aluminum composite hydroxide floc, significantly increasing the specific surface area of ​​the floc and the number of fluoride ion adsorption sites, thereby improving the defluorination rate and floc settling performance.

[0015] However, in the aluminum sulfate-magnesium sulfate system, sulfate ions readily compete with fluoride ions for adsorption, making it difficult to treat fluoride ions to the emission standard (≤2 mg / L). This invention introduces calcium-chitosan-grafted hydroxyapatite powder as a functional enhancement component. The material uses Fe-Zr dual-ion co-doped hydroxyapatite as a matrix, which, after amination modification, is grafted with a chitosan-calcium chloride complex under the action of glutaraldehyde. Simultaneously, under the action of glutaraldehyde, the chitosan-calcium chloride complex undergoes further self-crosslinking, improving its stability in wastewater treatment. Calcium-chitosan grafting not only improves the dispersibility of hydroxyapatite in the aqueous phase but also endows the material with richer adsorption sites and pH response characteristics. In the pH range of 5–7, Fe-Zr co-doped hydroxyapatite exhibits excellent selective adsorption capacity for fluoride ions, enhancing the deep removal of low-concentration fluoride ions. In a weakly alkaline environment (pH 8-9), calcium-chitosan ionizes to generate -NH3+ and -OH2+, which can efficiently adsorb sulfate ions in the system, alleviating the competitive adsorption between sulfate and fluoride ions and creating favorable conditions for deep defluorination. Simultaneously, calcium-chitosan slowly releases calcium ions, which further combine with fluoride ions to form fluorides. In the presence of low concentrations of free sulfate ions, the sulfate ions doped in the calcium fluoride crystals can effectively neutralize the positive charge of the fluorides, thereby reducing the repulsive force between fluoride crystals and promoting crystal aggregation. Ultimately, deep defluorination is achieved through the synergistic effect of multiple factors. Furthermore, in the preparation of calcium-chitosan-grafted hydroxyapatite powder, excessive chitosan grafting can reduce the active sites on the hydroxyapatite surface that react with fluoride ions, affecting the defluorination effect. Through repeated experiments, it was found that the optimal defluorination effect was achieved when the mass ratio of chitosan, calcium chloride, and amino-modified hydroxyapatite was (1-2):1:(7-8).

[0016] This invention's defluoridator utilizes a ternary compound of aluminum sulfate, magnesium sulfate, and calcium-chitosan-grafted hydroxyapatite to achieve a coupling of multiple mechanisms including complexation precipitation, co-precipitation, selective adsorption, and crystalline precipitation. It achieves a defluoridation efficiency of over 98% for fluoride-containing industrial wastewater, with the treated wastewater exhibiting a stable fluoride ion concentration that meets emission standards. This defluoridator also boasts a wider applicable pH range, excellent flocculent properties, high defluoridation efficiency, and good stability, demonstrating promising industrial application prospects in the treatment of fluoride-containing industrial wastewater from metallurgical, chemical, and electroplating industries. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] All materials used in this invention are commercially available products.

[0019] Example 1: A method for preparing a defluoridating agent for fluoride-containing industrial wastewater, comprising the following steps: Step 1: Add calcium nitrate tetrahydrate, ferric nitrate nonahydrate, and zirconium nitrate pentahydrate to deionized water and stir to dissolve. Add diammonium hydrogen phosphate solution at 20°C and stir to obtain a precursor solution. The concentration of the diammonium hydrogen phosphate solution is 0.5 mol / L. In the precursor solution, the molar ratio of (calcium + iron + zirconium) / phosphorus is 1.55:1. Step 2: Add nitric acid solution and urea solution to the precursor solution and control the pH of the system to 2; after stirring for 5 min, carry out hydrothermal synthesis reaction of the precursor solution at 150℃ for 3 h; after the hydrothermal reaction is completed, cool, collect the crude product by centrifugation, and wash with deionized water until the washing solution is neutral, and freeze-dry to obtain Fe-Zr dual-ion co-doped hydroxyapatite; wherein, the concentration of nitric acid solution is 10 mol / L and the concentration of urea solution is 0.5 mol / L; Step 3: S1: 3-Aminopropyltriethoxysilane was added dropwise to an aqueous ethanol solution with a volume concentration of 90%, hydrolyzed for 30 min, and Fe-Zr dual-ion co-doped hydroxyapatite was added. The mixture was stirred at 25 °C for 8 h, filtered, and dried to obtain amino-modified hydroxyapatite. S2: Chitosan powder was added to acetic acid solution and stirred to dissolve, obtaining a chitosan solution. Calcium chloride solid was added to the chitosan solution and stirred to dissolve, obtaining a calcium-chitosan mixed solution. Amino-modified hydroxyapatite was added to the calcium-chitosan mixed solution. Glutaraldehyde solution was used as a crosslinking agent. After reacting at 25℃ for 5 hours, the precipitate was collected by centrifugation, washed with deionized water until neutral, freeze-dried, pulverized, and sieved to obtain calcium-chitosan-grafted hydroxyapatite powder; wherein: In S1, the mass ratio of 3-aminopropyltriethoxysilane to Fe-Zr dual-ion co-doped hydroxyapatite is 1:100. In S2, the mass ratio of chitosan, calcium chloride, and amino-modified hydroxyapatite is 1:1:8. Step 4: Mix aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder to obtain a defluorinating agent; wherein the mass ratio of aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder is 10:1:5.

[0020] Example 2: A method for preparing a defluorinating agent for fluoride-containing industrial wastewater, comprising the following steps: Step 1: Add calcium nitrate tetrahydrate, ferric nitrate nonahydrate, and zirconium nitrate pentahydrate to deionized water and stir to dissolve. Add diammonium hydrogen phosphate solution at 25°C and stir to obtain a precursor solution. The concentration of the diammonium hydrogen phosphate solution is 0.55 mol / L. In the precursor solution, the molar ratio of (calcium + iron + zirconium) / phosphorus is 1.63:1. Step 2: Add nitric acid solution and urea solution to the precursor solution, and control the pH of the system to 2.5; after stirring for 8 min, carry out hydrothermal synthesis reaction of the precursor solution at 155℃ for 4 h; after the hydrothermal reaction is completed, cool, collect the crude product by centrifugation, and wash with deionized water until the washing solution is neutral, and freeze-dry to obtain Fe-Zr dual-ion co-doped hydroxyapatite; wherein, the concentration of nitric acid solution is 10.3 mol / L and the concentration of urea solution is 0.55 mol / L; Step 3: S1: 3-Aminopropyltriethoxysilane was added dropwise to a 90% (v / v) aqueous ethanol solution, hydrolyzed for 45 min, and Fe-Zr dual-ion co-doped hydroxyapatite was added. The mixture was stirred at 27 °C for 9 h, filtered, and dried to obtain amino-modified hydroxyapatite. S2: Chitosan powder was added to acetic acid solution and stirred to dissolve, obtaining a chitosan solution. Calcium chloride solid was added to the chitosan solution and stirred to dissolve, obtaining a calcium-chitosan mixed solution. Amino-modified hydroxyapatite was added to the calcium-chitosan mixed solution, and glutaraldehyde solution was used as a crosslinking agent. After reacting at 27℃ for 5.5 h, the precipitate was collected by centrifugation, washed with deionized water until neutral, freeze-dried, pulverized, and sieved to obtain calcium-chitosan-grafted hydroxyapatite powder; wherein: In S1, the mass ratio of 3-aminopropyltriethoxysilane to Fe-Zr dual-ion co-doped hydroxyapatite is 2:100. In S2, the mass ratio of chitosan, calcium chloride, and amino-modified hydroxyapatite is 1.5:1:7.5. Step 4: Mix aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder to obtain a fluoride removal agent; wherein the mass ratio of aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder is 10:3:7.

[0021] Example 3: A method for preparing a defluoridating agent for fluoride-containing industrial wastewater, comprising the following steps: Step 1: Add calcium nitrate tetrahydrate, ferric nitrate nonahydrate, and zirconium nitrate pentahydrate to deionized water and stir to dissolve. Add diammonium hydrogen phosphate solution at 30°C and stir to obtain a precursor solution. The concentration of the diammonium hydrogen phosphate solution is 0.6 mol / L. In the precursor solution, the molar ratio of (calcium + iron + zirconium) / phosphorus is 1.67:1. Step 2: Add nitric acid solution and urea solution to the precursor solution and control the pH of the system to 3; after stirring for 10 min, carry out hydrothermal synthesis reaction of the precursor solution at 160℃ for 5 h; after the hydrothermal reaction is completed, cool, collect the crude product by centrifugation, and wash with deionized water until the washing solution is neutral, and freeze-dry to obtain Fe-Zr dual-ion co-doped hydroxyapatite; wherein, the concentration of nitric acid solution is 10.5 mol / L and the concentration of urea solution is 0.6 mol / L; Step 3: S1: 3-Aminopropyltriethoxysilane was added dropwise to a 90% (v / v) aqueous ethanol solution, hydrolyzed for 60 min, Fe-Zr dual-ion co-doped hydroxyapatite was added, stirred at 30 °C for 10 h, filtered and dried to obtain amino-modified hydroxyapatite. S2: Chitosan powder was added to an acetic acid solution and stirred to dissolve, obtaining a chitosan solution. Calcium chloride solid was added to the chitosan solution and stirred to dissolve, obtaining a calcium-chitosan mixed solution. Amino-modified hydroxyapatite was added to the calcium-chitosan mixed solution, and glutaraldehyde solution was used as a crosslinking agent. After reacting at 30°C for 6 hours, the precipitate was collected by centrifugation, washed with deionized water until neutral, freeze-dried, pulverized, and sieved to obtain calcium-chitosan-grafted hydroxyapatite powder; wherein: In S1, the mass ratio of 3-aminopropyltriethoxysilane to Fe-Zr dual-ion co-doped hydroxyapatite is 3:100. In S2, the mass ratio of chitosan, calcium chloride, and amino-modified hydroxyapatite is 2:1:7. Step 4: Mix aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder to obtain a defluorinating agent; wherein the mass ratio of aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder is 10:5:10.

[0022] Comparative Example 1: The defluorinating agent did not contain calcium-chitosan-grafted hydroxyapatite powder, and the other parameters were the same as in Example 1.

[0023] Aluminum sulfate and magnesium sulfate are mixed to obtain a defluorinating agent; the mass ratio of aluminum sulfate to magnesium sulfate is 10:1.

[0024] Comparative Example 2: Hydroxyapatite was used instead of Fe-Zr dual-ion co-doped hydroxyapatite, and the other parameters were the same as in Example 2.

[0025] Step 1: Add calcium nitrate tetrahydrate to deionized water and stir to dissolve. Add diammonium hydrogen phosphate solution at 25°C and stir to obtain a precursor solution. The concentration of the diammonium hydrogen phosphate solution is 0.55 mol / L. The molar ratio of calcium to phosphorus in the precursor solution is 1.63:1. Step 2: Add nitric acid solution and urea solution to the precursor solution, and control the pH of the system to 2.5; after stirring for 8 min, carry out a hydrothermal synthesis reaction on the precursor solution at 155℃ for 4 h; after the hydrothermal reaction is completed, cool, collect the crude product by centrifugation, and wash with deionized water until the washing solution is neutral, and freeze-dry to obtain hydroxyapatite; wherein, the concentration of nitric acid solution is 10.3 mol / L and the concentration of urea solution is 0.55 mol / L; Step 3: S1: 3-Aminopropyltriethoxysilane was added dropwise to a 90% (v / v) aqueous ethanol solution, hydrolyzed for 45 min, hydroxyapatite was added, and the mixture was stirred at 27 °C for 9 h. After filtration and drying, amino-modified hydroxyapatite was obtained. S2: Chitosan powder was added to acetic acid solution and stirred to dissolve, obtaining a chitosan solution. Calcium chloride solid was added to the chitosan solution and stirred to dissolve, obtaining a calcium-chitosan mixed solution. Amino-modified hydroxyapatite was added to the calcium-chitosan mixed solution, and glutaraldehyde solution was used as a crosslinking agent. After reacting at 27℃ for 5.5 h, the precipitate was collected by centrifugation, washed with deionized water until neutral, freeze-dried, pulverized, and sieved to obtain calcium-chitosan-grafted hydroxyapatite powder; wherein: In S1, the mass ratio of 3-aminopropyltriethoxysilane to hydroxyapatite is 2:100; In S2, the mass ratio of chitosan, calcium chloride, and amino-modified hydroxyapatite is 1.5:1:7.5. Step 4: Mix aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder to obtain a fluoride removal agent; wherein the mass ratio of aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder is 10:3:7.

[0026] Comparative Example 3: The content of chitosan in calcium-chitosan-grafted hydroxyapatite powder was increased, and the other parameters were the same as in Example 3.

[0027] Step 1: Add calcium nitrate tetrahydrate, ferric nitrate nonahydrate, and zirconium nitrate pentahydrate to deionized water and stir to dissolve. Add diammonium hydrogen phosphate solution at 30°C and stir to obtain a precursor solution. The concentration of the diammonium hydrogen phosphate solution is 0.6 mol / L. In the precursor solution, the molar ratio of (calcium + iron + zirconium) / phosphorus is 1.67:1. Step 2: Add nitric acid solution and urea solution to the precursor solution and control the pH of the system to 3; after stirring for 10 min, carry out hydrothermal synthesis reaction of the precursor solution at 160℃ for 5 h; after the hydrothermal reaction is completed, cool, collect the crude product by centrifugation, and wash with deionized water until the washing solution is neutral, and freeze-dry to obtain Fe-Zr dual-ion co-doped hydroxyapatite; wherein, the concentration of nitric acid solution is 10.5 mol / L and the concentration of urea solution is 0.6 mol / L; Step 3: S1: 3-Aminopropyltriethoxysilane was added dropwise to a 90% (v / v) aqueous ethanol solution, hydrolyzed for 60 min, Fe-Zr dual-ion co-doped hydroxyapatite was added, stirred at 30 °C for 10 h, filtered and dried to obtain amino-modified hydroxyapatite. S2: Chitosan powder was added to an acetic acid solution and stirred to dissolve, obtaining a chitosan solution. Calcium chloride solid was added to the chitosan solution and stirred to dissolve, obtaining a calcium-chitosan mixed solution. Amino-modified hydroxyapatite was added to the calcium-chitosan mixed solution, and glutaraldehyde solution was used as a crosslinking agent. After reacting at 30°C for 6 hours, the precipitate was collected by centrifugation, washed with deionized water until neutral, freeze-dried, pulverized, and sieved to obtain calcium-chitosan-grafted hydroxyapatite powder; wherein: In S1, the mass ratio of 3-aminopropyltriethoxysilane to Fe-Zr dual-ion co-doped hydroxyapatite is 3:100. In S2, the mass ratio of chitosan, calcium chloride, and amino-modified hydroxyapatite is 5:1:7. Step 4: Mix aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder to obtain a defluorinating agent; wherein the mass ratio of aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder is 10:5:10.

[0028] Experiment: Fluorine-containing industrial wastewater from a factory was sampled and tested. The fluoride ion concentration (C0) in the wastewater was measured to be 113 mg / L. The pH value of the wastewater was controlled between 5 and 7. The defluorinating agents prepared in Examples 1-3 and Comparative Examples 1-3 were added, with a dosage of 750 mg / L. After stirring for 5 hours, the pH value was adjusted to 8.0-9.0 using 10 wt.% sodium hydroxide solution and 10 wt.% hydrochloric acid solution, and the reaction was continued for another 5 hours. The fluoride ion concentration was measured, and the results are shown in Table 1. The fluoride ion concentration was detected using a spectrophotometer. The fluoride ion concentration (Cn) in the treated industrial wastewater was calculated using the formula: η = (C0 - Cn) / C0 × 100%. The results are shown in Table 1.

[0029] Table 1.

[0030] Conclusion: The data in Table 1 show that the defluorinating agent prepared in this invention can effectively achieve deep defluorination of fluoride-containing industrial wastewater, with a defluorination efficiency of over 98%. After treatment, the concentration of fluoride ions in the wastewater is reduced to below 2 mg / L, meeting the discharge standards.

[0031] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0032] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a defluorinating agent for fluoride-containing industrial wastewater, characterized in that: Includes the following steps: Step 1: Add calcium nitrate tetrahydrate, ferric nitrate nonahydrate, and zirconium nitrate pentahydrate to deionized water and stir to dissolve. Add diammonium hydrogen phosphate solution at 20~30℃ and stir to obtain the precursor solution. Step 2: Add nitric acid solution and urea solution to the precursor solution and control the pH of the system to 2-3; stir for 5-10 min and then carry out hydrothermal synthesis reaction of the precursor solution at 150-160℃ for 3-5 h; after the hydrothermal reaction is completed, cool, centrifuge to collect the crude product and wash with deionized water until the washing solution is neutral, freeze-dry to obtain Fe-Zr dual-ion co-doped hydroxyapatite; Step 3: S1: 3-Aminopropyltriethoxysilane was added dropwise to an aqueous ethanol solution, hydrolyzed for 30-60 min, and Fe-Zr dual-ion co-doped hydroxyapatite was added. The mixture was stirred at 25-30℃ for 8-10 h, filtered, and dried to obtain amino-modified hydroxyapatite. S2: Chitosan powder is added to acetic acid solution and stirred to dissolve to obtain chitosan solution. Calcium chloride solid is added to chitosan solution and stirred to dissolve to obtain calcium-chitosan mixed solution. Amino-modified hydroxyapatite is added to the calcium-chitosan mixed solution. Glutaraldehyde solution is used as a crosslinking agent. After reacting at 25~30℃ for 5~6h, the precipitate is collected by centrifugation, washed with deionized water until neutral, freeze-dried, pulverized, and sieved to obtain calcium-chitosan-grafted hydroxyapatite powder. Step 4: Mix aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder to obtain a fluoride removal agent.

2. The method for preparing a defluorinating agent for fluoride-containing industrial wastewater according to claim 1, characterized in that: In step 1, the molar ratio of (calcium + iron + zirconium) / phosphorus in the precursor solution is (1.55~1.67):

1.

3. The method for preparing a defluorinating agent for fluoride-containing industrial wastewater according to claim 1, characterized in that: In step 1, the concentration of diammonium hydrogen phosphate solution is 0.5~0.6 mol / L.

4. The method for preparing a defluorinating agent for fluoride-containing industrial wastewater according to claim 1, characterized in that: In step 2, the concentration of the nitric acid solution is 10~10.5 mol / L.

5. The method for preparing a defluorinating agent for fluoride-containing industrial wastewater according to claim 1, characterized in that: In step 2, the concentration of the urea solution is 0.5~0.6 mol / L.

6. The method for preparing a defluorinating agent for fluoride-containing industrial wastewater according to claim 1, characterized in that: In S1, the mass ratio of 3-aminopropyltriethoxysilane to Fe-Zr dual-ion co-doped hydroxyapatite is (1~3):

100.

7. The method for preparing a defluorinating agent for fluoride-containing industrial wastewater according to claim 1, characterized in that: In S1, the volume concentration of the aqueous ethanol solution is 90%.

8. The method for preparing a defluorinating agent for fluoride-containing industrial wastewater according to claim 1, characterized in that: In S2, the mass ratio of chitosan, calcium chloride, and amino-modified hydroxyapatite is (1~2):1:(7~8).

9. The method for preparing a defluorinating agent for fluoride-containing industrial wastewater according to claim 1, characterized in that: In step 4, the mass ratio of aluminum sulfate, magnesium sulfate and calcium-chitosan-grafted hydroxyapatite powder in the defluorinating agent is 10:(1~5):(5~10).

10. The defluorinating agent prepared by any one of claims 1 to 9.

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