Deep fluoride removal agent with wide pH range and preparation method thereof

Abstract

The application relates to a deep fluorine removal agent with a wide pH range and a preparation method thereof. The fluorine removal agent comprises polyaluminum chloride, aluminum / zirconium bimetal modified biochar, cerium dioxide modified chitosan hydrogel, acrylamide-alkenyl quaternary ammonium salt copolymer and calcium chloride, and is obtained by mixing through a mixer. The polyaluminum chloride with low price is used as the main material, the aluminum / zirconium bimetal modified biochar is matched with the polyaluminum chloride to provide adsorption and fluorine removal under a wide pH range; the small amount of cerium dioxide modified chitosan hydrogel further enhances the adsorption selectivity and adsorption capacity of the fluorine ion, the chitosan raw material is widely sourced and environment-friendly; the small amount of acrylamide-alkenyl quaternary ammonium salt copolymer simultaneously plays the dual functions of an organic flocculant and a quaternary ammonium salt, and simplifies the formula composition; the fluorine removal agent obtained by mixing has good stability, when the fluorine removal agent is used in a fluorine removal process, the pH does not need to be intentionally adjusted and a washing step does not need to be performed, the process flow is simplified, waste water is avoided, the metal utilization rate is high, and industrialized production is facilitated.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment agent technology, specifically to a deep defluorination agent with a wide pH range and its preparation method. Background Technology

[0002] With the acceleration of industrialization, the discharge of fluoride-containing wastewater has been increasing year by year, posing a serious threat to the ecological environment and human health. Fluoride-containing wastewater is mostly found in wastewater from pesticide and fertilizer production, electroplating, and non-ferrous metal smelting. Currently, the most common defluoridation technology is chemical precipitation, using reagents such as lime, calcium chloride, and polyferric chloride. It is simple to operate and low in cost. However, the fluoride content after treatment is usually reduced to 20-30 mg / L, which is difficult to meet discharge standards and is greatly affected by pH. Other defluoridation technologies include coagulation, adsorption, ion exchange, and membrane separation. These methods are either inefficient or costly and cannot be sustained for long periods. Summary of the Invention

[0003] In order to improve processing efficiency and save costs, this invention relates to a deep defluorinating agent with a wide pH range, which combines the advantages of chemical precipitation and adsorption methods, and has good treatment effect and strong adaptability.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a deep defluorinating agent with a wide pH range includes the following steps: S1. Preparation of aluminum / zirconium bimetallic modified biochar S1-1. Disperse microcrystalline cellulose and tannic acid in deionized water and stir evenly. Perform hydrothermal reaction and cool for later use. S1-2. Add aluminum chloride and zirconium oxychloride to the reaction flask, add deionized water and stir to dissolve them, then slowly add them dropwise to step S1-1, adjust the pH to weakly acidic, stir evenly at room temperature, then add biochar, stir in a 60°C water bath for 3-6 hours, centrifuge and calcine to obtain the product. S2. Preparation of cerium dioxide modified chitosan hydrogel Chitosan was dissolved in an aqueous acetic acid solution, and cerium dioxide was ultrasonically dispersed in deionized water. The cerium dioxide dispersion was slowly added to the chitosan solution while stirring, followed by the addition of glutaraldehyde to initiate a cross-linking reaction, thus obtaining the product. S3. Preparation of acrylamide-alkenyl quaternary ammonium salt copolymer Acrylamide and dimethyl diallyl ammonium chloride are added to a reaction flask, and a polymerization reaction is carried out using potassium persulfate as an initiator to obtain the product. S4. Preparation of defluorinating agent Weigh out 25-35 parts by weight of polyaluminum chloride, 20-30 parts by weight of aluminum / zirconium bimetallic modified biochar, 3-6 parts by weight of cerium dioxide modified chitosan hydrogel, 1-5 parts by weight of acrylamide-alkenyl quaternary ammonium salt copolymer and 3-6 parts by weight of calcium chloride, and mix them by a mixer.

[0005] The functions of each component in the defluorinating agent formulation of this invention are described below: Polyaluminum chloride: As a primary flocculant and defluorinating agent, aluminum ions can undergo a complexation reaction with fluoride ions to form aluminum fluoride complexes. At the same time, the hydrolysis products of polyaluminum chloride can remove fluoride ions through electrostatic adsorption.

[0006] Aluminum / Zirconium Bimetallic Modified Biochar: Using biochar as a carrier and a cellulose-tannin complex as a template and coordination agent, the abundant phenolic hydroxyl groups in the tannin molecule form stable coordination complexes with aluminum and zirconium, dispersing on the cellulose surface and preventing sedimentation in solution. During impregnation, the biochar acts as a porous carrier, adsorbing the metal complexes. During pyrolysis, the organic template is removed, creating pores and increasing the specific surface area, forming oxygen vacancies. Simultaneously, the metal salt is converted in situ into nano-metal oxides and uniformly anchored on the carbon skeleton of the biochar. In this invention, the number of active sites of aluminum and zirconium is comparable, and the adsorption mechanism changes from a single aluminum complexation-dominated mechanism to a triple synergistic mechanism of aluminum complexation + zirconium coordination + ion exchange. Zirconium has stronger Lewis acidity and a higher coordination number for fluorine, enabling it to form more stable inner-layer complexes with fluorine. The pH response ranges of aluminum and zirconium are superimposed—aluminum is highly active under weakly acidic to neutral conditions, while zirconium maintains activity over a wider pH range (including weakly basic conditions). This complementarity allows the material to maintain high adsorption activity within a pH range of 3–9.

[0007] Cerium dioxide-modified chitosan hydrogel: Chitosan is a naturally occurring alkaline polysaccharide. The abundant amino groups on its molecular chain provide the possibility for hydrogel construction. It is non-toxic, harmless, widely available, and readily biodegradable. Modifying chitosan hydrogel with cerium dioxide nanoparticles can further enhance its adsorption selectivity and adsorption capacity for fluoride ions.

[0008] Acrylamide-alkenyl quaternary ammonium salt copolymer: Composed of acrylamide units and alkenyl quaternary ammonium salt units, it simultaneously performs the dual functions of organic flocculant and quaternary ammonium salt, maintaining good flocculation activity and stability over a wide pH range.

[0009] Calcium chloride: Calcium ions react with fluoride ions to form calcium fluoride precipitate, and the effect of removing fluoride is particularly significant under alkaline conditions.

[0010] Furthermore, in step S1-1, the mass ratio of microcrystalline cellulose to tannic acid is 1:1~1.2, the solid content in deionized water is 5wt%; the hydrothermal reaction temperature is 140℃, and the reaction time is 2~4h.

[0011] Further, in steps S1-2, aluminum chloride and zirconium oxychloride are mixed in a molar ratio of Al:Zr=1:0.5~1.5.

[0012] Furthermore, in steps S1-2, the biochar is obtained by crushing agricultural straw, carbonizing it at 400-500℃ for 3-5 hours under nitrogen protection, and then acidifying it; the total mass ratio of the biochar to cellulose-tannin is 4-5:1.

[0013] Further, in step S1-2, the calcination process is as follows: the temperature is increased to 220℃ at a rate of 5℃ / min and held for 1 hour, then increased to 450℃ at a rate of 3℃ / min and held for 2 hours, and finally increased to 600℃ at a rate of 5℃ / min and held for 1 hour.

[0014] Furthermore, in step S2, the mass ratio of chitosan to cerium dioxide and glutaraldehyde is 10:2~5:0.8~1.5; the crosslinking reaction temperature is 50~60℃, and the reaction time is 2~3h.

[0015] Furthermore, the specific process of step S3 is as follows: Acrylamide and dimethyl diallyl ammonium chloride were dissolved in deionized water at a molar ratio of 1:0.4~0.8. Nitrogen gas was introduced for 30 min, potassium persulfate initiator was added, and the temperature was raised to 60℃. The polymerization reaction was carried out for 12 h. After the reaction was completed, the product was washed with anhydrous ethanol and filtered 4 times, dried, and ground to obtain the final product.

[0016] Furthermore, in step S4, the mixing machine speed is set to 10~20 rpm, and the mixing time is 3~12 hours.

[0017] A second objective of this invention is to provide a deep defluorinating agent with a wide pH range prepared according to the preparation method described above.

[0018] The beneficial effects of this invention are as follows: It uses inexpensive polyaluminum chloride as the main flocculant and defluorinator, combined with an appropriate amount of aluminum / zirconium bimetallic modified biochar to provide adsorption and defluorination performance over a wide pH range; a small amount of cerium dioxide-modified chitosan hydrogel further enhances the adsorption selectivity and capacity for fluoride ions; chitosan raw materials are widely available and environmentally friendly; a small amount of acrylamide-alkenyl quaternary ammonium salt copolymer simultaneously functions as both an organic flocculant and a quaternary ammonium salt, simplifying the formulation; the resulting defluorinator has good stability, and when used in the defluorination process, it does not require deliberate pH adjustment or washing steps, simplifying the process and avoiding wastewater generation; it also has high metal utilization, facilitating industrial production. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 The graphs show the defluorination rates of the defluorinating agents in the embodiments and comparative examples of the present invention at different pH values. Detailed Implementation

[0021] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0022] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] Example 1: A wide pH range deep defluorinating agent S1. Preparation of aluminum / zirconium bimetallic modified biochar S1-1. Disperse 1 g of microcrystalline cellulose and 1.2 g of tannic acid in 44 mL of deionized water and stir at room temperature for 1 h. Then transfer to a reaction vessel and hydrothermally react at 140 °C for 3 h. After cooling, use directly for the next step. S1-2. After crushing the corn stalks, wash and dry them with water. Carbonize them at 500℃ for 3 hours under nitrogen protection. After natural cooling, grind and sieve them, add them to 0.1mol / L dilute hydrochloric acid and soak for 2 hours. Take them out, wash them with water until the supernatant is neutral, dry and grind them to obtain biochar. S1-3. Add 0.64g AlCl3·6H2O and 0.86g ZrOCl2·8H2O (Al:Zr=1:1) to the reaction flask, add 50mL of deionized water and stir to dissolve, then slowly add dropwise to step S1-1, adjust the pH to 5.0 with dilute hydrochloric acid, and stir at room temperature for 4h. S1-4. Add 10g of biochar to the reaction system of S1-3, stir in a water bath at 60℃ for 5 h, centrifuge and then calcine; raise the temperature to 220℃ at a rate of 5℃ / min and hold for 1 h, then raise the temperature to 450℃ at a rate of 3℃ / min and hold for 2 h, and finally raise the temperature to 600℃ at a rate of 5℃ / min and hold for 1 h.

[0024] S2. Preparation of cerium dioxide modified chitosan hydrogel Dissolve 10g of chitosan in 200mL of 2v / v% acetic acid aqueous solution, and ultrasonically disperse 3g of cerium dioxide in 50mL of deionized water; while stirring, slowly add the cerium dioxide dispersion to the chitosan solution, then add 1g of glutaraldehyde, and perform a crosslinking reaction at 60℃ for 2 h to obtain the final product.

[0025] S3. Preparation of acrylamide-alkenyl quaternary ammonium salt copolymer Acrylamide and dimethyl diallyl ammonium chloride were dissolved in deionized water at a molar ratio of 1:0.5. Nitrogen gas was introduced for 30 min, potassium persulfate initiator was added, and the temperature was raised to 60℃. The polymerization reaction was carried out for 12 h. After the reaction was completed, the product was washed with anhydrous ethanol and filtered 4 times, dried, and ground to obtain the final product.

[0026] S4. Preparation of defluorinating agent Weigh out 30 parts by weight of polyaluminum chloride, 25 parts by weight of aluminum / zirconium bimetallic modified biochar, 5 parts by weight of cerium dioxide modified chitosan hydrogel, 2 parts by weight of acrylamide-alkenyl quaternary ammonium salt copolymer and 4 parts by weight of calcium chloride, and mix them in a mixer at 15 rpm for 10 h.

[0027] Example 2: A wide pH range deep defluorination agent S1. Preparation of aluminum / zirconium bimetallic modified biochar S1-1. Disperse 1 g of microcrystalline cellulose and 1 g of tannic acid in 40 mL of deionized water and stir at room temperature for 1 h. Then transfer to a reaction vessel and hydrothermally react at 140 °C for 3 h. Cool and set aside. S1-2. After crushing the corn stalks, wash and dry them with water. Carbonize them at 500℃ for 3 hours under nitrogen protection. After natural cooling, grind and sieve them, add them to 0.1mol / L dilute hydrochloric acid and soak for 2 hours. Take them out, wash them with water until the supernatant is neutral, dry and grind them to obtain biochar. S1-3. Add 0.64g AlCl3·6H2O and 0.86g ZrOCl2·8H2O (Al:Zr=1:1) to the reaction flask, add 50mL of deionized water and stir to dissolve, then slowly add dropwise to step S1-1, adjust the pH to 5.0 with dilute hydrochloric acid, and stir at room temperature for 4h. S1-4. Add 9 g of biochar to the reaction system of S1-3, stir in a water bath at 60℃ for 5 h, centrifuge and then calcine; raise the temperature to 220℃ at a rate of 5℃ / min and hold for 1 h, then raise the temperature to 450℃ at a rate of 3℃ / min and hold for 2 h, and finally raise the temperature to 600℃ at a rate of 5℃ / min and hold for 1 h.

[0028] S2. Preparation of cerium dioxide modified chitosan hydrogel Dissolve 10g of chitosan in 200mL of 2v / v% acetic acid aqueous solution, and ultrasonically disperse 4g of cerium dioxide in 50mL of deionized water; while stirring, slowly add the cerium dioxide dispersion to the chitosan solution, then add 1.1g of glutaraldehyde, and perform a crosslinking reaction at 50℃ for 2.5 h to obtain the final product.

[0029] S3. Preparation of acrylamide-alkenyl quaternary ammonium salt copolymer Acrylamide and dimethyl diallyl ammonium chloride were dissolved in deionized water at a molar ratio of 1:0.5. Nitrogen gas was introduced for 30 min, potassium persulfate initiator was added, and the temperature was raised to 60℃. The polymerization reaction was carried out for 12 h. After the reaction was completed, the product was washed with anhydrous ethanol and filtered 4 times, dried, and ground to obtain the final product.

[0030] S4. Preparation of defluorinating agent Weigh out 28 parts by weight of polyaluminum chloride, 28 parts by weight of aluminum / zirconium bimetallic modified biochar, 5 parts by weight of cerium dioxide modified chitosan hydrogel, 3 parts by weight of acrylamide-alkenyl quaternary ammonium salt copolymer and 3 parts by weight of calcium chloride, and mix them in a mixer with the mixer speed set at 15 rpm and the mixing time at 10 h.

[0031] Example 3: A wide pH range deep defluorination agent S1. Preparation of aluminum / zirconium bimetallic modified biochar S1-1. Disperse 1 g of microcrystalline cellulose and 1 g of tannic acid in 40 mL of deionized water and stir at room temperature for 1 h. Then transfer to a reaction vessel and hydrothermally react at 140 °C for 3 h. Cool and set aside. S1-2. After crushing the corn stalks, wash and dry them with water. Carbonize them at 500℃ for 3 hours under nitrogen protection. After natural cooling, grind and sieve them, add them to 0.1mol / L dilute hydrochloric acid and soak for 2 hours. Take them out, wash them with water until the supernatant is neutral, dry and grind them to obtain biochar. S1-3. Add 0.64g AlCl3·6H2O and 0.7g ZrOCl2·8H2O (Al:Zr=1:0.8) to the reaction flask, add 50mL of deionized water and stir to dissolve, then slowly add dropwise to step S1-1, adjust the pH to 5.0 with dilute hydrochloric acid, and stir at room temperature for 4h. S1-4. Add 8 g of biochar to the reaction system of S1-3, stir in a water bath at 60℃ for 5 h, centrifuge and then calcine; raise the temperature to 220℃ at a rate of 5℃ / min and hold for 1 h, then raise the temperature to 450℃ at a rate of 3℃ / min and hold for 2 h, and finally raise the temperature to 600℃ at a rate of 5℃ / min and hold for 1 h.

[0032] S2. Preparation of cerium dioxide modified chitosan hydrogel Dissolve 10g of chitosan in 200mL of 2v / v% acetic acid aqueous solution, and ultrasonically disperse 3g of cerium dioxide in 50mL of deionized water; while stirring, slowly add the cerium dioxide dispersion to the chitosan solution, then add 1g of glutaraldehyde, and perform a crosslinking reaction at 60℃ for 2 h to obtain the final product.

[0033] S3. Preparation of acrylamide-alkenyl quaternary ammonium salt copolymer Acrylamide and dimethyl diallyl ammonium chloride were dissolved in deionized water at a molar ratio of 1:0.5. Nitrogen gas was introduced for 30 min, potassium persulfate initiator was added, and the temperature was raised to 60℃. The polymerization reaction was carried out for 12 h. After the reaction was completed, the product was washed with anhydrous ethanol and filtered 4 times, dried, and ground to obtain the final product.

[0034] S4. Preparation of defluorinating agent Weigh out 25 parts by weight of polyaluminum chloride, 20 parts by weight of aluminum / zirconium bimetallic modified biochar, 3 parts by weight of cerium dioxide modified chitosan hydrogel, 1 part by weight of acrylamide-alkenyl quaternary ammonium salt copolymer and 3 parts by weight of calcium chloride, and mix them in a mixer with the mixer speed set at 10 rpm and the mixing time at 12 h.

[0035] Example 4: A deep defluorinating agent with a wide pH range S1. Preparation of aluminum / zirconium bimetallic modified biochar S1-1. Disperse 1 g of microcrystalline cellulose and 1.2 g of tannic acid in 44 mL of deionized water and stir at room temperature for 1 h. Then transfer to a reaction vessel and hydrothermally react at 140 °C for 3 h. Cool and set aside. S1-2. After crushing the corn stalks, wash and dry them with water. Carbonize them at 500℃ for 3 hours under nitrogen protection. After natural cooling, grind and sieve them, add them to 0.1mol / L dilute hydrochloric acid and soak for 2 hours. Take them out, wash them with water until the supernatant is neutral, dry and grind them to obtain biochar. S1-3. Add 0.64g AlCl3·6H2O and 1.4g ZrOCl2·8H2O (Al:Zr=1:1.4) to the reaction flask, add 50mL of deionized water and stir to dissolve, then slowly add it dropwise to step S1-1, adjust the pH to 5.0 with dilute hydrochloric acid, and stir at room temperature for 4h. S1-4. Add 10g of biochar to the reaction system of S1-3, stir in a water bath at 60℃ for 5 h, centrifuge and then calcine; raise the temperature to 220℃ at a rate of 5℃ / min and hold for 1 h, then raise the temperature to 450℃ at a rate of 3℃ / min and hold for 2 h, and finally raise the temperature to 600℃ at a rate of 5℃ / min and hold for 1 h.

[0036] S2. Preparation of cerium dioxide modified chitosan hydrogel Dissolve 10g of chitosan in 200mL of 2v / v% acetic acid aqueous solution, and ultrasonically disperse 5g of cerium dioxide in 50mL of deionized water; while stirring, slowly add the cerium dioxide dispersion to the chitosan solution, then add 1.5g of glutaraldehyde, and perform a crosslinking reaction at 60℃ for 2 h to obtain the final product.

[0037] S3. Preparation of acrylamide-alkenyl quaternary ammonium salt copolymer Acrylamide and dimethyl diallyl ammonium chloride were dissolved in deionized water at a molar ratio of 1:0.8. Nitrogen gas was introduced for 30 min, potassium persulfate initiator was added, and the temperature was raised to 60℃. The polymerization reaction was carried out for 12 h. After the reaction was completed, the product was washed with anhydrous ethanol and filtered 4 times, dried, and ground to obtain the final product.

[0038] S4. Preparation of defluorinating agent Weigh out 35 parts by weight of polyaluminum chloride, 30 parts by weight of aluminum / zirconium bimetallic modified biochar, 5 parts by weight of cerium dioxide modified chitosan hydrogel, 5 parts by weight of acrylamide-alkenyl quaternary ammonium salt copolymer and 6 parts by weight of calcium chloride, and mix them by mixing in a mixer with the mixer speed set to 20 rpm and the mixing time set to 8 h.

[0039] Comparative Example 1: Same as Example 1, except that the defluorinating agent does not contain aluminum / zirconium bimetallic modified biochar.

[0040] Comparative Example 2: Same as Example 1, except that the defluorinating agent does not contain cerium dioxide-modified chitosan hydrogel during preparation.

[0041] Comparative Example 3: Same as Example 1, except that the defluorinating agent does not contain acrylamide-alkenyl quaternary ammonium salt copolymer during preparation.

[0042] Comparative Example 4: S1, Preparation of Aluminum / Zirconium Bimetallic Modified Biochar S1-1. After crushing the corn stalks, wash and dry them with water. Carbonize them at 500℃ for 3 hours under nitrogen protection. After natural cooling, grind and sieve them, add them to 0.1mol / L dilute hydrochloric acid and soak for 2 hours. Take them out, wash them with water until the supernatant is neutral, dry and grind them to obtain biochar. S1-2. Add 0.64g AlCl3·6H2O and 0.86g ZrOCl2·8H2O (Al:Zr=1:1) to the reaction flask, add 50mL of deionized water and stir to dissolve. Adjust the pH to 5.0 with dilute hydrochloric acid and stir at room temperature for 4h. Add 10g of biochar, stir in a 60℃ water bath for 5h, centrifuge and calcine. Increase the temperature to 220℃ at a rate of 5℃ / min and hold for 1h, then increase the temperature to 450℃ at a rate of 3℃ / min and hold for 2h, and finally increase the temperature to 600℃ at a rate of 5℃ / min and hold for 1h.

[0043] The remaining steps are the same as in Example 1.

[0044] Performance testing: Fluoride-containing solutions with different pH values ​​were prepared to simulate fluoride-containing wastewater with a fluoride ion concentration of 100 mg / L. Fluoride-containing wastewater with pH values ​​of 3 / 5 / 6.5 / 8 / 9 was prepared respectively.

[0045] Add 30 mg of the defluorinating agent from Example 1 to 100 mL of fluoride-containing wastewater with different pH values, stir, let stand for 30 min, take the supernatant to test the fluoride content, and calculate the defluorination rate.

[0046] The remaining embodiments and comparative examples were carried out in accordance with the above method, and the defluorination rate results are as follows: Figure 1 As shown in the figure, the defluorinating agent of Example 1 exhibits excellent removal effects on fluoride ions at different pH levels, with the best effect observed at pH=6.5. By changing some preparation conditions or the proportions of the defluorinating agent formulation, deep defluorinating agents with a wide pH range can be obtained within reasonable limits (Examples 2-3). The effect of Example 4 is observed to be relatively optimal. Comparative Example 1, without the addition of aluminum / zirconium bimetallic modified biochar, showed poor defluorination performance, especially with the most significant decrease in defluorination rate under acidic and alkaline conditions. Although Comparative Example 4 added aluminum / zirconium bimetallic modified biochar, the absence of a cellulose-tannin template during its preparation resulted in a significant decrease in defluorination rate, indicating that the template pore-forming and metal dispersion effects of the cellulose-tannin hydrothermal carbon precursor are crucial for defluorination performance. Comparative Examples 2 and 3 investigated the effects of cerium dioxide-modified chitosan hydrogel and acrylamide-alkenyl quaternary ammonium salt copolymer on defluorination efficiency, respectively. It was observed that the decrease in defluorination rate in Comparative Example 3 compared to Example 1 was smaller than that in Comparative Example 1. This is because the defluorination effect of Comparative Example 1 was mainly due to the aluminum / zirconium bimetallic modified biochar and other main components in the formulation system. During actual testing, it was found that the flocculation and sedimentation rate of Comparative Example 3 was slower, indicating that the acrylamide-alkenyl quaternary ammonium salt copolymer has flocculation and defluorination-assisting effects. Comparative Example 2 fell between Comparative Examples 1 and 3. Due to the presence of aluminum / zirconium bimetallic modified biochar in Comparative Example 2, its defluorination rate under both acidic and alkaline conditions was significantly higher than that of Comparative Example 1.

[0047] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a deep defluorination agent with a wide pH range, characterized in that, Includes the following steps: S1. Preparation of aluminum / zirconium bimetallic modified biochar S1-1. Disperse microcrystalline cellulose and tannic acid in deionized water and stir evenly. Perform hydrothermal reaction and cool for later use. S1-2. Add aluminum chloride, zirconium oxychloride and deionized water to the reaction flask, stir to dissolve, and then slowly add dropwise to the product obtained in step S1-1. Adjust the pH to weakly acidic, stir evenly at room temperature, then add biochar, stir in a 60°C water bath for 3-6 hours, centrifuge and calcine to obtain the product. S2. Preparation of cerium dioxide modified chitosan hydrogel Chitosan was dissolved in an aqueous acetic acid solution, and cerium dioxide was ultrasonically dispersed in deionized water. The cerium dioxide dispersion was slowly added to the chitosan solution while stirring, followed by the addition of glutaraldehyde to initiate a cross-linking reaction, thus obtaining the product. S3. Preparation of acrylamide-alkenyl quaternary ammonium salt copolymer Acrylamide and dimethyl diallyl ammonium chloride are added to a reaction flask, and a polymerization reaction is carried out using potassium persulfate as an initiator to obtain the product. S4. Preparation of defluorinating agent Weigh out 25-35 parts by weight of polyaluminum chloride, 20-30 parts by weight of aluminum / zirconium bimetallic modified biochar, 3-6 parts by weight of cerium dioxide modified chitosan hydrogel, 1-5 parts by weight of acrylamide-alkenyl quaternary ammonium salt copolymer and 3-6 parts by weight of calcium chloride, and mix them by a mixer.

2. The method for preparing the wide pH range deep defluorination agent according to claim 1, characterized in that, In step S1-1, the mass ratio of microcrystalline cellulose to tannic acid is 1:1~1.2, the solid content in deionized water is 5wt%, the hydrothermal reaction temperature is 140℃, and the reaction time is 2~4h.

3. The method for preparing the wide pH range deep defluorination agent according to claim 1, characterized in that, In steps S1-2, aluminum chloride and zirconium oxychloride are mixed in a molar ratio of Al:Zr=1:0.5~1.

5.

4. The method for preparing the wide pH range deep defluorination agent according to claim 1, characterized in that, In steps S1-2, the biochar is obtained by crushing agricultural straw, carbonizing it at 400-500℃ for 3-5 hours under nitrogen protection, and then acidifying it; the total mass ratio of the biochar to cellulose-tannin is 4-5:

1.

5. The method for preparing the wide pH range deep defluorination agent according to claim 1, characterized in that, In step S1-2, the calcination process is as follows: the temperature is increased to 220℃ at a rate of 5℃ / min and held for 1 hour, then increased to 450℃ at a rate of 3℃ / min and held for 2 hours, and finally increased to 600℃ at a rate of 5℃ / min and held for 1 hour.

6. The method for preparing the wide pH range deep defluorination agent according to claim 1, characterized in that, In step S2, the mass ratio of chitosan to cerium dioxide and glutaraldehyde is 10:2~5:0.8~1.5; the crosslinking reaction temperature is 50~60℃, and the reaction time is 2~3h.

7. The method for preparing the wide pH range deep defluorination agent according to claim 1, characterized in that, The specific process of step S3 is as follows: Acrylamide and dimethyl diallyl ammonium chloride were dissolved in deionized water at a molar ratio of 1:0.4~0.

8. Nitrogen gas was introduced for 30 min, potassium persulfate initiator was added, and the temperature was raised to 60℃. The polymerization reaction was carried out for 12 h. After the reaction was completed, the product was washed with anhydrous ethanol and filtered 4 times, dried, and ground to obtain the final product.

8. The method for preparing the wide pH range deep defluorination agent according to claim 1, characterized in that, In step S4, the mixer speed is set to 10~20 rpm, and the mixing time is 3~12 hours.

9. A wide pH range deep defluorinating agent prepared by any one of claims 1-8.

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