Compound defluorination agent, its preparation method and its application in industrial wastewater
By combining the synergistic effects of components A and B in the compound defluorinating agent with flocculation and adsorption technologies, the problems of slow calcium salt precipitation and deep defluorination are solved, achieving a highly efficient defluorination effect for industrial wastewater, and ensuring that the fluoride content of the effluent meets the standards.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING LVLIAN ENVIRONMENTAL TECH DEV CO LTD
- Filing Date
- 2026-05-11
- Publication Date
- 2026-06-09
AI Technical Summary
In existing technologies, the fluorides generated by the reaction of calcium salts with fluoride ions have high solubility and a slow precipitation process. Furthermore, calcium salts alone cannot achieve deep defluorination, and the fluoride ion content in the effluent cannot meet the discharge standards. Existing composite defluorinating agents are difficult to produce industrially.
A compound defluorinating agent is used, including component A and component B. Component A is a compound of polyaluminum ferric chloride, aluminum salt, and magnesium salt, while component B is a lanthanum-doped biochar-montmorillonite composite material. The coarse flocculation and fine adsorption are achieved through stepwise feeding. The highly active lanthanum sites and abundant pore structure of the lanthanum-doped biochar-montmorillonite composite material are used for deep defluorination.
It achieves highly efficient fluoride ion removal, with the fluoride content in the effluent steadily reduced to below 1 mg/L and the fluoride removal rate reaching over 99%, demonstrating promising application prospects.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of water treatment agents, specifically to a compound defluoridating agent, its preparation method, and its application in industrial wastewater. Background Technology
[0002] Fluorine, a common element, has wide applications in industrial production in metallurgy, semiconductors, chemicals, and pharmaceuticals. Due to its significant biotoxicity, fluorine poses serious risks to the environment and human health, making the treatment of fluoride-containing industrial wastewater crucial. Traditional methods for treating fluoride-containing industrial wastewater involve adding chemical agents such as calcium, aluminum, and magnesium salts. These agents react chemically to rapidly combine with fluoride ions, forming insoluble fluoride precipitates, which are then removed through solid-liquid separation, thus achieving defluorination. However, this process has the following problems: First, the fluorides formed by the reaction of calcium salts with fluoride ions have high solubility, resulting in a slow precipitation process and affecting defluorination efficiency; second, calcium salts alone cannot achieve deep defluorination, and the fluoride ion content in the effluent fails to meet discharge standards.
[0003] Chinese Patent Application No. CN202111218039.7 discloses a composite defluorinating agent and its preparation method. The composite defluorinating agent comprises polyaspartic acid-sulfonated styrene copolymer, zinc salt, acid, iron salt, cationic starch ether quaternary ammonium salt, and water, combining the strong coagulation and flocculation function of cationic starch ether quaternary ammonium salt with the adsorption and complexation capabilities of zinc and iron salts for fluoride ions. Chinese Patent Application No. CN202311521782.9 discloses a method for preparing a defluorinating agent by loading hydroxyapatite onto porous nanofibers. This method involves loading hydroxyapatite onto fibers and then preparing the loaded fibers into highly porous adsorption microspheres, thereby improving the adsorption performance of the defluorinating agent for fluoride ions and its regeneration and recycling performance. The defluorination effects of the above technical solutions all rely on organic polymer additives, which are currently difficult to industrialize. Therefore, it is essential to propose a highly efficient and easily prepared composite defluorinating agent and apply it to industrial wastewater treatment. Summary of the Invention
[0004] The purpose of this invention is to provide a compound defluorinating agent, its preparation method, and its application in industrial wastewater, 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: On one hand, the present invention provides a method for preparing a compound defluorinating agent, wherein the compound defluorinating agent comprises component A and component B; wherein: The preparation method of component A is as follows: Component A is obtained by mixing polyaluminum ferric chloride, aluminum salt, and magnesium salt; The preparation method of component B includes the following steps: S1: Chitosan was added to acetic acid solution to obtain chitosan solution; montmorillonite was added to deionized water and ultrasonically dispersed to obtain montmorillonite dispersion; the pH of chitosan solution was adjusted to 5-6 with sodium hydroxide solution and then montmorillonite dispersion was added. The mixture was stirred at 50-60℃ for 6-8 hours and then filtered. The product was washed with deionized water until the washing liquid was neutral and then vacuum dried to obtain chitosan-montmorillonite intercalation material. S2: Lanthanum chloride was added to deionized water to obtain a lanthanum chloride solution; chitosan-montmorillonite intercalation material was added to the lanthanum chloride solution, the pH was adjusted to 10-11 with sodium hydroxide solution, and the mixture was stirred at 25-30℃ for 3-5 hours. After filtration, drying, pulverization and sieving, lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was obtained; the lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was heat-treated under nitrogen atmosphere to obtain lanthanum-doped biochar-montmorillonite composite material. S3: Add calcium chloride to deionized water to obtain a calcium chloride solution; add lanthanum-doped biochar-montmorillonite composite material to the calcium chloride solution at a solid-liquid ratio of 1:(20~30); let stand for 48~60h, filter, and dry at 100~120℃ to constant weight to obtain component B.
[0006] Furthermore, in component A, the mass ratio of polyaluminum ferric chloride, aluminum salt, and magnesium salt is (8~10):(5~7):(1~2).
[0007] Furthermore, the aluminum salt is any one or more of aluminum sulfate, aluminum chloride, calcium aluminate, and sodium aluminate.
[0008] Furthermore, the magnesium salt is any one or more of magnesium chloride, magnesium sulfate, magnesium acetate, and magnesium citrate.
[0009] Further, in S1, the montmorillonite dispersion is added to the chitosan solution at a chitosan to montmorillonite mass ratio of (1.5~2):1.
[0010] Further, in S2, chitosan-montmorillonite intercalation material is added to lanthanum chloride solution at a solid-liquid ratio of 1:(45~50).
[0011] Furthermore, in S2, the heat treatment temperature is 400~500℃ and the heat treatment time is 4~6h.
[0012] Furthermore, in S3, lanthanum-doped biochar-montmorillonite composite material is added to the calcium chloride solution at a solid-liquid ratio of 1:(20~30).
[0013] Furthermore, in S3, the concentration of calcium chloride solution is 20~30 wt.%.
[0014] On the other hand, the present invention provides the application of the compound defluorinating agent, comprising the following steps: Step 1: Adjust the pH of the fluoride-containing industrial wastewater to 5-6, add component A at a dosage of 10-20g per liter of wastewater; stir at a constant speed for 1-2 hours, then transfer to a primary sedimentation tank for 1-2 hours of settling, and obtain the supernatant after sludge-water separation. Step 2: Adjust the pH of the supernatant obtained in Step 1 to 8-9, add component B to the supernatant at a dosage of 5-15g per liter of wastewater, stir at a constant speed for 30-45 minutes, then transfer to a secondary sedimentation tank for settling for 1-2 hours. After sludge-water separation, defluorinated industrial wastewater is obtained.
[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The compound defluorinating agent provided by the present invention includes component A and component B, which work synergistically. Component A is obtained by compounding polyaluminum ferric chloride, aluminum salt, and magnesium salt; component B includes a lanthanum-doped biochar-montmorillonite composite material and calcium chloride loaded in the pores of the biochar. The lanthanum-doped biochar-montmorillonite composite material is prepared by chitosan intercalation, lanthanum hydroxide loading, and high-temperature treatment of montmorillonite.
[0016] In application, this invention employs a step-by-step feeding method to achieve segmented defluorination, synergistically combining coarse flocculation removal and fine adsorption removal, significantly improving the treatment efficiency of fluoride-containing industrial wastewater. First, the pH of the fluoride-containing industrial wastewater is adjusted to 5-6, and component A is added. Through complexation precipitation of fluoride ions with polyaluminum ferric chloride, aluminum salts, and magnesium salts, as well as ion exchange, the majority of fluoride ions in the water are rapidly removed, significantly reducing the fluoride load in the system. This creates favorable conditions for subsequent deep defluorination and improves the overall process stability.
[0017] After coarse defluorination, the precipitate is separated, and the pH of the supernatant is adjusted to 8-9. Component B is then added for further defluorination. The weakly alkaline environment effectively reduces the competitive adsorption of hydroxide ions and fluoride ions on the material surface, fully utilizing the specific complexing ability of lanthanum with fluoride ions. It also promotes the reaction between calcium salts and fluoride ions, increasing the crystal formation rate. During the further defluorination process, the lanthanum-doped biochar-montmorillonite composite material in component B, with its large specific surface area, abundant porous structure, and highly active lanthanum sites, further facilitates the physical adsorption and pore trapping of residual fluoride ions after coarse defluorination. The lanthanum active sites on the surface of the lanthanum-doped biochar-montmorillonite composite material exhibit a strong specific binding ability for fluoride ions, forming highly stable, insoluble complexes. Meanwhile, the highly active lanthanum sites within the biochar channels, after enriching for fluoride ions, effectively restrict the free diffusion of fluoride ions, increasing the contact frequency between fluoride ions and calcium chloride, and promoting the formation of calcium fluoride crystals. Simultaneously, the lanthanum active sites promote the transformation of the generated calcium fluoride crystals from homogeneous nucleation to heterogeneous nucleation, lowering the nucleation energy barrier and overcoming the difficulty in calcium fluoride nucleation due to insufficient reaction driving force at low fluoride content. Furthermore, the inventors discovered in experiments that if calcium chloride is directly blended with the lanthanum-doped biochar-montmorillonite composite material, the crystals formed by heterogeneous nucleation will grow on the surface of the lanthanum-doped biochar-montmorillonite composite material and continuously accumulate to form a "crystal shell" covering the surface of the composite material, reducing the composite material's adsorption capacity for fluoride ions and ultimately leading to poor deep fluoride removal.
[0018] The compound defluoridator prepared by this invention fully combines the advantages of fast treatment speed and large treatment capacity of component A with the characteristics of strong selectivity and deep defluoridation of component B, realizing the coupling of coarse removal of high concentration of fluoride and fine removal of low concentration of residual fluoride. The fluoride content of the effluent is stably reduced to below 1 mg / L, and the defluoridation rate can reach more than 99%, which has good application prospects. Detailed Implementation
[0019] 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.
[0020] Materials and sources used in this invention: Montmorillonite is from NANOCOR Corporation, USA, and all other products are from Sinopharm Chemical Reagent Co., Ltd.
[0021] Example 1: A compound defluorinating agent, comprising component A and component B; The preparation method of component A is as follows: polyaluminum ferric chloride, aluminum salt, and magnesium salt are mixed to obtain component A; in component A, the mass ratio of polyaluminum ferric chloride, aluminum salt, and magnesium salt is 8:5:1; the aluminum salt is aluminum sulfate, and the magnesium salt is magnesium sulfate. The preparation method of component B includes the following steps: S1: Chitosan was added to acetic acid solution to obtain a 1 wt.% chitosan solution; montmorillonite was added to deionized water and ultrasonically dispersed to obtain a 3 wt.% montmorillonite dispersion; the pH of the chitosan solution was adjusted to 5 with 1 mol / L sodium hydroxide solution, and then the montmorillonite dispersion was added. The mixture was stirred at 50℃ for 6 h, filtered, and the product was washed with deionized water until the washing liquid was neutral. The product was then vacuum dried to obtain the chitosan-montmorillonite intercalation material; wherein the mass ratio of chitosan to montmorillonite was 1.5:1. S2: Lanthanum chloride was added to deionized water to obtain a 0.5 wt.% lanthanum chloride solution; chitosan-montmorillonite intercalation material was added to the lanthanum chloride solution at a solid-liquid ratio of 1:45, the pH was adjusted to 10 with 1 mol / L sodium hydroxide solution, and the mixture was stirred at 25℃ for 3 h. After filtration, drying, pulverization, and passing through a 50-mesh sieve, lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was obtained; the lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was heat-treated at 400℃ in a nitrogen atmosphere for 4 h to obtain a lanthanum-doped biochar-montmorillonite composite material. S3: Add calcium chloride to deionized water to obtain a 20 wt.% calcium chloride solution; add lanthanum-doped biochar-montmorillonite composite material to the calcium chloride solution at a solid-liquid ratio of 1:20; let stand for 48 h, filter, and dry at 100℃ to constant weight to obtain component B.
[0022] Example 2: A compound defluorinating agent, comprising component A and component B; The preparation method of component A is as follows: Component A is obtained by mixing polyaluminum ferric chloride, aluminum salt, and magnesium salt; in component A, the mass ratio of polyaluminum ferric chloride, aluminum salt, and magnesium salt is 9:6:1.2; the aluminum salt is aluminum sulfate, and the magnesium salt is magnesium sulfate. The preparation method of component B includes the following steps: S1: Chitosan was added to acetic acid solution to obtain a 1 wt.% chitosan solution; montmorillonite was added to deionized water and ultrasonically dispersed to obtain a 3 wt.% montmorillonite dispersion; the pH of the chitosan solution was adjusted to 5.5 with 1 mol / L sodium hydroxide solution, and then the montmorillonite dispersion was added. The mixture was stirred at 55℃ for 7 h, filtered, and the product was washed with deionized water until the washing liquid was neutral. The product was then vacuum dried to obtain the chitosan-montmorillonite intercalated material; wherein the mass ratio of chitosan to montmorillonite was 1.8:1. S2: Lanthanum chloride was added to deionized water to obtain a 0.5 wt.% lanthanum chloride solution; chitosan-montmorillonite intercalation material was added to the lanthanum chloride solution at a solid-liquid ratio of 1:48, the pH was adjusted to 10.5 with 1 mol / L sodium hydroxide solution, and the mixture was stirred at 28℃ for 4.5 h. After filtration, drying, pulverization, and passing through a 50-mesh sieve, lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was obtained; the lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was heat-treated at 480℃ for 5.5 h in a nitrogen atmosphere to obtain a lanthanum-doped biochar-montmorillonite composite material. S3: Add calcium chloride to deionized water to obtain a 25 wt.% calcium chloride solution; add lanthanum-doped biochar-montmorillonite composite material to the calcium chloride solution at a solid-liquid ratio of 1:25; let stand for 54 h, filter, and dry at 110 °C to constant weight to obtain component B.
[0023] Example 3: A compound defluorinating agent, comprising component A and component B; The preparation method of component A is as follows: polyaluminum ferric chloride, aluminum salt, and magnesium salt are mixed to obtain component A; in component A, the mass ratio of polyaluminum ferric chloride, aluminum salt, and magnesium salt is 10:7:2; the aluminum salt is aluminum sulfate, and the magnesium salt is magnesium sulfate. The preparation method of component B includes the following steps: S1: Chitosan was added to acetic acid solution to obtain a 1 wt.% chitosan solution; montmorillonite was added to deionized water and ultrasonically dispersed to obtain a 3 wt.% montmorillonite dispersion; the pH of the chitosan solution was adjusted to 6 with 1 mol / L sodium hydroxide solution, and then the montmorillonite dispersion was added. The mixture was stirred at 55℃ for 7 h, filtered, and the product was washed with deionized water until the washing liquid was neutral. The product was then vacuum dried to obtain the chitosan-montmorillonite intercalation material; wherein the mass ratio of chitosan to montmorillonite was 2:1. S2: Lanthanum chloride was added to deionized water to obtain a 0.5 wt.% lanthanum chloride solution; chitosan-montmorillonite intercalation material was added to the lanthanum chloride solution at a solid-liquid ratio of 1:50, the pH was adjusted to 11 with 1 mol / L sodium hydroxide solution, and the mixture was stirred at 30℃ for 5 h. After filtration, drying, pulverization, and passing through a 50-mesh sieve, lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was obtained; the lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was heat-treated at 500℃ for 6 h in a nitrogen atmosphere to obtain a lanthanum-doped biochar-montmorillonite composite material. S3: Add calcium chloride to deionized water to obtain a 30 wt.% calcium chloride solution; add lanthanum-doped biochar-montmorillonite composite material to the calcium chloride solution at a solid-liquid ratio of 1:30; let stand for 60 h, filter, and dry at 120 °C to constant weight to obtain component B.
[0024] Comparative Example 1: The difference from Example 1 is that the defluorinating agent contains only component A.
[0025] The method for preparing the defluorinating agent is as follows: mixing polyaluminum ferric chloride, aluminum salt, and magnesium salt to obtain component A; in component A, the mass ratio of polyaluminum ferric chloride, aluminum salt, and magnesium salt is 8:5:1; the aluminum salt is aluminum sulfate, and the magnesium salt is magnesium sulfate.
[0026] Comparative Example 2: The difference from Example 2 is that chitosan-montmorillonite intercalation material is used in component B instead of lanthanum-doped biochar-montmorillonite composite material.
[0027] A compound defluorinating agent, comprising component A and component B; The preparation method of component A is as follows: Component A is obtained by mixing polyaluminum ferric chloride, aluminum salt, and magnesium salt; in component A, the mass ratio of polyaluminum ferric chloride, aluminum salt, and magnesium salt is 9:6:1.2; the aluminum salt is aluminum sulfate, and the magnesium salt is magnesium sulfate. The preparation method of component B includes the following steps: S1: Chitosan was added to acetic acid solution to obtain a 1 wt.% chitosan solution; montmorillonite was added to deionized water and ultrasonically dispersed to obtain a 3 wt.% montmorillonite dispersion; the pH of the chitosan solution was adjusted to 5.5 with 1 mol / L sodium hydroxide solution, and then the montmorillonite dispersion was added. The mixture was stirred at 55℃ for 7 h, filtered, and the product was washed with deionized water until the washing liquid was neutral. The product was then vacuum dried to obtain the chitosan-montmorillonite intercalated material; wherein the mass ratio of chitosan to montmorillonite was 1.8:1. S2: Chitosan-montmorillonite intercalated material was heat-treated at 480℃ for 5.5 h in a nitrogen atmosphere to obtain biochar-montmorillonite composite material; S3: Add calcium chloride to deionized water to obtain a 25 wt.% calcium chloride solution; add lanthanum-doped biochar-montmorillonite composite material to the calcium chloride solution at a solid-liquid ratio of 1:25; let stand for 54 h, filter, and dry at 110 °C to constant weight to obtain component B.
[0028] Comparative Example 3: The difference from Example 3 is that calcium chloride in component B is directly mixed with lanthanum-doped biochar-montmorillonite composite material.
[0029] The preparation method of component A is as follows: polyaluminum ferric chloride, aluminum salt, and magnesium salt are mixed to obtain component A; in component A, the mass ratio of polyaluminum ferric chloride, aluminum salt, and magnesium salt is 10:7:2; the aluminum salt is aluminum sulfate, and the magnesium salt is magnesium sulfate. The preparation method of component B includes the following steps: S1: Chitosan was added to acetic acid solution to obtain a 1 wt.% chitosan solution; montmorillonite was added to deionized water and ultrasonically dispersed to obtain a 3 wt.% montmorillonite dispersion; the pH of the chitosan solution was adjusted to 6 with 1 mol / L sodium hydroxide solution, and then the montmorillonite dispersion was added. The mixture was stirred at 55℃ for 7 h, filtered, and the product was washed with deionized water until the washing liquid was neutral. The product was then vacuum dried to obtain the chitosan-montmorillonite intercalation material; wherein the mass ratio of chitosan to montmorillonite was 2:1. S2: Lanthanum chloride was added to deionized water to obtain a 0.5 wt.% lanthanum chloride solution; chitosan-montmorillonite intercalation material was added to the lanthanum chloride solution at a solid-liquid ratio of 1:50, the pH was adjusted to 11 with 1 mol / L sodium hydroxide solution, and the mixture was stirred at 30℃ for 5 h. After filtration, drying, pulverization, and passing through a 50-mesh sieve, lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was obtained; the lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was heat-treated at 500℃ for 6 h in a nitrogen atmosphere to obtain a lanthanum-doped biochar-montmorillonite composite material. S3: Calcium chloride and lanthanum-doped biochar-montmorillonite composite material were mixed at a mass ratio of 1:1 to obtain component B.
[0030] Experiment: Industrial wastewater from a factory was collected, and the fluoride ion concentration (C0) was measured to be 118 mg / L. Samples were taken in 1L increments, and the compound defluorinating agents prepared in Examples 1-3 and Comparative Examples 1-3 were applied to the samples for defluorination. The application methods are as follows: Step 1: Adjust the pH of the fluoride-containing industrial wastewater to 5, add component A at a dosage of 15g per liter of wastewater; stir at a constant speed for 1 hour, then transfer to a primary sedimentation tank for 1 hour of settling, and obtain the supernatant after sludge-water separation. Step 2: Adjust the pH of the supernatant obtained in Step 1 to 8, add component B to the supernatant at a dosage of 8g per liter of wastewater, stir at a constant speed for 45 minutes, then transfer to a secondary sedimentation tank for settling for 2 hours. After sludge-water separation, defluorinated industrial wastewater is obtained.
[0031] The defluoridation industrial wastewater treated as described above was tested (since the defluorinating agent in Comparative Example 1 only contained component A, the supernatant obtained after sedimentation and sludge-water separation was used as the test object). Referring to the "Determination of Fluoride in Water - Fluoride Reagent Spectrophotometric Method" (HJ488-2009), the fluoride ion concentration C in the defluoridation industrial wastewater was determined using a spectrophotometer. n And calculate the defluorination rate η = (C0 - C n The result is shown in Table 1.
[0032] Table 1.
[0033] Conclusion: The data in Table 1 show that the defluorination efficiency of the compound defluorinating agent prepared in this invention reaches over 99%, and can effectively reduce the fluoride ion concentration to below 1 mg / L.
[0034] 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.
[0035] 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 compound defluorinating agent, wherein the compound defluorinating agent comprises component A and component B; characterized in that: The preparation method of component A is as follows: Component A is obtained by mixing polyaluminum ferric chloride, aluminum salt, and magnesium salt; The preparation method of component B includes the following steps: S1: Chitosan was added to acetic acid solution to obtain chitosan solution; montmorillonite was added to deionized water and ultrasonically dispersed to obtain montmorillonite dispersion; the pH of chitosan solution was adjusted to 5-6 with sodium hydroxide solution and then montmorillonite dispersion was added. The mixture was stirred at 50-60℃ for 6-8 hours and then filtered. The product was washed with deionized water until the washing liquid was neutral and then vacuum dried to obtain chitosan-montmorillonite intercalation material. S2: Lanthanum chloride was added to deionized water to obtain a lanthanum chloride solution; chitosan-montmorillonite intercalation material was added to the lanthanum chloride solution, the pH was adjusted to 10-11 with sodium hydroxide solution, and the mixture was stirred at 25-30℃ for 3-5 hours. After filtration, drying, pulverization and sieving, lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was obtained; the lanthanum hydroxide-doped chitosan-montmorillonite intercalation material was heat-treated under nitrogen atmosphere to obtain lanthanum-doped biochar-montmorillonite composite material. S3: Add calcium chloride to deionized water to obtain a calcium chloride solution; add lanthanum-doped biochar-montmorillonite composite material to the calcium chloride solution; let stand for 48-60 h, filter, and dry at 100-120℃ to constant weight to obtain component B.
2. The method for preparing the compound defluorinating agent according to claim 1, characterized in that: In component A, the mass ratio of polyaluminum ferric chloride, aluminum salt, and magnesium salt is (8~10):(5~7):(1~2).
3. The method for preparing the compound defluorinating agent according to claim 1, characterized in that: The aluminum salt is any one or more of aluminum sulfate, aluminum chloride, calcium aluminate, and sodium aluminate.
4. The preparation method of the compound defluorinating agent according to claim 1, characterized in that: The magnesium salt is any one or more of magnesium chloride, magnesium sulfate, magnesium acetate, and magnesium citrate.
5. The method for preparing the compound defluorinating agent according to claim 1, characterized in that: In S1, the montmorillonite dispersion is added to the chitosan solution at a mass ratio of chitosan to montmorillonite (1.5~2):
1.
6. The method for preparing the compound defluorinating agent according to claim 1, characterized in that: In S2, chitosan-montmorillonite intercalation material is added to lanthanum chloride solution at a solid-liquid ratio of 1:(45~50).
7. The method for preparing the compound defluorinating agent according to claim 1, characterized in that: In S2, the heat treatment temperature is 400~500℃ and the heat treatment time is 4~6h.
8. The method for preparing the compound defluorinating agent according to claim 1, characterized in that: In S3, lanthanum-doped biochar-montmorillonite composite material is added to calcium chloride solution at a solid-liquid ratio of 1:(20~30), wherein the concentration of calcium chloride solution is 20~30 wt.%.
9. The compound defluorinating agent prepared by any one of claims 1 to 8.
10. The application of a compound defluorinating agent as described in claim 9, characterized in that: Includes the following steps: Step 1: Adjust the pH of the fluoride-containing industrial wastewater to 5-6, add component A at a dosage of 10-20g per liter of wastewater; stir at a constant speed for 1-2 hours, then transfer to a primary sedimentation tank for 1-2 hours of settling, and obtain the supernatant after sludge-water separation. Step 2: Adjust the pH of the supernatant obtained in Step 1 to 8-9, add component B to the supernatant at a dosage of 5-15g per liter of wastewater, stir at a constant speed for 30-45 minutes, then transfer to a secondary sedimentation tank for settling for 1-2 hours. After sludge-water separation, defluorinated industrial wastewater is obtained.