Defluorination material applied to industrial wastewater treatment

Abstract

The invention relates to the technical field of sewage purification, in particular to a defluorination material applied to industrial wastewater treatment. According to the defluorination material applied to industrial wastewater treatment, a hierarchical construction strategy of'biochar substrate-main adsorption phase (magnesium oxide / aluminum oxide) loading-rare earth La / Ce and metal Sr co-doping 'is adopted, so that the diversification and function complementation of adsorption sites are realized; the common technical problems of limited adsorption capacity, poor selectivity, low mechanical strength, difficult regeneration and the like of a traditional defluorination material in a complex industrial wastewater environment are solved.

Description

Technical Field

[0001] This invention relates to the field of wastewater purification technology, specifically to a defluorination material used in industrial wastewater treatment. Background Technology

[0002] Fluoride pollution in industrial wastewater is a significant challenge in environmental remediation, especially wastewater from industries such as metallurgy, electroplating, semiconductors, and phosphate fertilizer production. This wastewater exhibits high fluoride ion concentrations and complex compositions, posing a serious threat to ecosystems and human health. High concentrations of fluoride increase water toxicity, affect crop growth, and accumulate through the food chain, leading to diseases such as skeletal fluorosis and dental fluorosis in humans. Therefore, developing efficient, stable, and selective fluoride removal materials is of great importance for the advanced treatment of industrial wastewater.

[0003] Currently, common defluoridation technologies mainly include precipitation, adsorption, ion exchange, and membrane separation. Among them, adsorption is widely studied and applied due to its simple operation, low cost, and ease of integration. Traditional adsorption materials such as activated alumina, bone char, hydroxyapatite, and certain clay minerals, while having some defluoridation effect, still have significant shortcomings in actual industrial wastewater treatment: limited adsorption capacity: most traditional materials have low adsorption capacity for fluoride ions, especially when treating high-fluoride-concentration wastewater, requiring large amounts of material to be added, leading to increased operating costs and solid waste volume; poor selectivity: industrial wastewater often contains Cl... - SO4 2- NO3 - Coexisting anions, they will react with F - Competing for adsorption sites significantly reduces the selective adsorption efficiency of the material for fluorine; insufficient mechanical strength and stability: powder materials are easily lost under water scouring, and molded materials often suffer structural collapse and dissolution of active components due to poor loading of active components or low skeleton strength, resulting in performance degradation during long-term operation or acid-base fluctuations.

[0004] Biochar, as a porous, inexpensive, and environmentally friendly carbon matrix, is widely used as an adsorption carrier. However, its original surface functional groups are limited, its anchoring ability for metal active components is weak, and the improvement in the functionality and stability of the material after direct loading is limited. How to utilize biochar to prepare a highly efficient industrial wastewater defluoridation material is the technical problem to be solved by this invention. Summary of the Invention

[0005] To address the problems of existing technologies, this invention provides a defluorination material for industrial wastewater treatment. This defluorination material employs a hierarchical construction strategy of "biochar substrate → main adsorption phase (magnesium oxide / alumina) loading → rare earth La / Ce and metal Sr co-doping," achieving diversification of adsorption sites and functional complementarity. This solves the technical problems of traditional defluorination materials, such as limited adsorption capacity, low adsorption efficiency, and low mechanical strength.

[0006] The technical solution of the present invention to solve the above problems is as follows:

[0007] A defluoridation material for industrial wastewater treatment is prepared by the following method:

[0008] Step 1: Add biochar to deionized water, add hydrochloric acid solution while stirring, heat to 60-70℃ and stir for 1.5-3 hours, filter, wash with deionized water until the pH of the filtrate is 6-7, dry at 100-110℃ for 10-14 hours to obtain acid-washed activated biochar.

[0009] Step 2: Add the acid-washed activated biochar obtained in Step 1 to a magnesium nitrate solution, stir at 25-40℃ for 1.5-3h, dry at 100-110℃ for 10-14h, and calcine at 380-450℃ for 1-2h to obtain magnesium oxide supported biochar.

[0010] Step 3: Add the magnesium oxide-supported biochar obtained in Step 2 to the aluminum nitrate solution, stir at 25-40℃ for 1.5-3h, dry at 100-110℃ for 10-14h, and calcine at 450-550℃ for 1.5-3h to obtain magnesium oxide-alumina composite supported biochar.

[0011] Step 4: Lanthanum nitrate, cerium nitrate, and strontium nitrate are added to water to prepare a mixed nitrate solution. The magnesium oxide-alumina composite supported biochar obtained in Step 3 is added to the mixed nitrate solution. The mixture is stirred at 25-40℃ for 1.5-3 hours, dried at 60-80℃ for 5-8 hours, and then calcined at 280-350℃ for 1-2 hours to obtain a rare earth co-doped composite adsorbent.

[0012] Step 5: Add a binder aqueous solution to the rare earth co-doped composite adsorbent powder obtained in Step 4, granulate to obtain particles with a particle size of 1.5-2.5 mm, and dry at 140-180℃ for 1.5-3 h to obtain the final product.

[0013] Preferably, in step 1, the mass ratio of biochar, deionized water, and hydrochloric acid solution is 1:2-4:0.01-0.03, and the concentration of hydrochloric acid solution is 30-40%.

[0014] Preferably, in step 2, the mass ratio of the acid-washed activated biochar to the magnesium nitrate solution is 1:1.5-2.5, and the concentration of the magnesium nitrate solution is 5-10%.

[0015] Preferably, in step 3, the mass ratio of magnesium oxide-supported biochar obtained in step 2 to aluminum nitrate solution is 1:1.5-2.5, and the concentration of aluminum nitrate solution is 15-20%.

[0016] Preferably, in step 4, the mass ratio of the magnesium oxide-alumina composite supported biochar to the mixed nitrate solution is 1:0.8-1.2, and the concentrations of lanthanum nitrate, cerium nitrate, and strontium nitrate in the mixed nitrate solution are 0.005-0.015 mol / L, 0.005-0.015 mol / L, and 0.01-0.03 mol / L, respectively.

[0017] Preferably, in step 5, the mass ratio of the rare earth co-doped composite adsorbent powder to the binder aqueous solution is 100:3-5, the mass concentration of the binder aqueous solution is 8-12%, and the binder is PVA or sodium silicate.

[0018] Preferably, the acid-washed and activated biochar obtained in step 1 is pre-modified with composite materials. The preparation method of the composite-modified biochar is as follows:

[0019] Step a: The acid-washed activated biochar is heated to 340-360℃ at 5-8℃ / min and kept at the same temperature for 40-60min for pre-oxidation. After completion, it is naturally cooled to below 80℃ to obtain pre-oxidized biochar.

[0020] Step b: Disperse the pre-oxidized biochar in deionized water, add vinylphosphonic acid and potassium persulfate in sequence, adjust the pH of the reaction system to 4.0-4.8 with dilute sodium hydroxide solution, bubble nitrogen gas under the liquid surface to remove oxygen for 20-30 minutes, then maintain the reaction system in a slightly positive nitrogen atmosphere, raise the temperature to 35-45℃, and stir the reaction at a constant temperature for 5-8 hours. After the reaction is completed, cool the material to below 40℃ and filter it. Wash the filter cake with hot water at 60-70℃ countercurrently, and finally dry the washed material at 90-105℃ for 10-14 hours to obtain phosphorylated biochar.

[0021] Step c: Disperse the phosphate-modified biochar in deionized water, add pre-dried sodium propylene sulfonate and ammonium persulfate sequentially, adjust the pH of the reaction system to 2.5-3.5 with a 3% dilute hydrochloric acid solution, heat to 40-50℃, and stir for 3-6 hours. After the reaction is complete, add hydrochloric acid solution to the system again and continue stirring for 0.5-1.0 hours to complete the sulfonic acid group conversion. Then filter, and wash the filter cake as follows: First, alkali rinsing: rinse with a 0.5-1.0% sodium carbonate solution at 50-60℃ for 20-30 minutes with stirring, and then filter; then hot water rapid washing: wash with hot water at 60-70℃ with rapid stirring 3-4 times, with the washing solution volume to filter cake mass ratio of 1-1.5:1 each time; finally, rinse once with room temperature deionized water; dry the washed wet material at 100-110℃ for 12-16 hours to obtain composite modified biochar.

[0022] Preferably, in step b, the mass ratio of the pre-oxidized biochar to deionized water, vinylphosphonic acid, and potassium persulfate is 100:600-800:15-25:1.8-4.5.

[0023] Preferably, in step c, the mass ratio of the phosphoric acid biochar, deionized water, sodium propylene sulfonate, and ammonium persulfate is 100:400-500:9-14:1.0-2.5, the concentration of the hydrochloric acid solution used for sulfonic acid group conversion is 2-4%, and the mass ratio of the hydrochloric acid solution used for sulfonic acid group conversion to the phosphoric acid biochar is 50-100:100.

[0024] The present invention has the following beneficial effects:

[0025] The fluoride removal material for industrial wastewater treatment described in this invention successfully solves the technical problems of limited adsorption capacity, poor selectivity, and low mechanical strength of traditional fluoride removal materials through innovative material design and a step-by-step functionalization preparation process. It adopts a hierarchical construction strategy of "pre-modified biochar substrate → main adsorption phase (magnesium oxide / alumina) loading → rare earth La / Ce and metal Sr co-doping," achieving diversification of adsorption sites and functional complementarity. The material uses porous biochar as a framework, successively loading high-capacity magnesium oxide and highly selective alumina, forming a composite adsorption system that combines physical and chemical adsorption. Subsequently, Sr is introduced for co-doping modification with rare earth elements La and Ce, utilizing La... 3+ With F - Strong coordination ability, Ce 3 + / Ce 4+ Redox properties and Sr 2+The lattice modulation effect constructs multi-layered, highly active fluoride removal sites on the material surface and within the material. This method enables the material to exhibit not only a large adsorption capacity for high concentrations of fluoride but also extremely high adsorption affinity for low concentrations of fluoride, and effectively resists common coexisting anions in wastewater (such as Cl-). - SO4 2- Interference from ).

[0026] Specifically, in the adsorbent material of this invention, strontium and rare earth metals are co-doped using three nitrates: lanthanum nitrate, cerium nitrate, and strontium nitrate. 2+ The dispersed F is "widely enriched" by electrostatic attraction with low charge density. - Solving the problem of rare earth metals (such as La) 3+ The problem of low efficiency in local enrichment; La 3+ With Ce 3+ / 4+ F is precisely fixed by strong coordination complexes (such as LaF3, Ce-F). - This forms a hierarchical pathway of enrichment and fixation, resulting in an increased adsorption capacity compared to a single system. Secondly, Sr... 2+ Dominant electrostatic attraction and ion exchange, La 3+ / Ce 3+ Responsible for coordination and complexation, the three work synergistically to cover a variety of complex water qualities, further improving the fluoride removal rate. Meanwhile, Sr... 2+ Large radius can isolate La 3+ / Ce 3+ The aggregation of these molecules allows them to exist in a monodisperse or small cluster form, increasing the exposure rate of active sites and thus improving the adsorption rate.

[0027] This invention employs an impregnation-drying-calcination process, which allows the active components to grow firmly or embed themselves in the pores and surface of biochar, resulting in a tight bond that is not easily detached during long-term hydraulic erosion or acid-base fluctuations. The final granulation step further enhances the mechanical strength (wear resistance) and uniformity of the material.

[0028] Furthermore, the biochar undergoes deep chemical modification by introducing bifunctional groups of phosphate and sulfonic acid groups onto its surface. This not only significantly enhances the anchoring ability of the substrate for active metal components but also provides an additional specific adsorption pathway for fluoride ions. Specifically, step a, pre-oxidation at 340-360℃ introduces more oxygen-containing groups onto the biochar surface and moderately expands the pores, providing abundant anchoring sites for subsequent grafting reactions, improving the thermal stability and chemical inertness of the biochar framework, and ensuring structural integrity during subsequent high-temperature calcination and strong acid treatment. Step b, by grafting vinylphosphonic acid, stable POC covalent bonds are formed on the biochar surface. Its phosphate group has a strong affinity for fluoride ions and can serve as a specific adsorption site. The introduced polar phosphate group improves the hydrophilicity of the biochar, making it easier to disperse in solution and improving mass transfer efficiency. Step c, by grafting sodium propylene sulfonate, high-density strongly acidic sulfonic acid groups are introduced. The strong acidity helps maintain the surface positive charge over a wide pH range, enhancing fluoride ion enrichment through electrostatic attraction. Through the above modifications, a dual-function synergy of "phosphate + sulfonate" is achieved: phosphate is responsible for specific complexation, and sulfonate is responsible for electrostatic enrichment. The synergistic effect of the two significantly improves the adsorption capacity and rate.

[0029] Furthermore, the phosphate and sulfonate groups on the surface of the composite modified biochar can react with the supported Mg. 2+ Al 3+ Coordination or ion exchange occurs, forming a bridging structure of organic ligands, metal ions, and fluoride ions, enhancing chemisorption. Simultaneously, the metal oxide is firmly anchored, preventing leaching and ensuring the long-term stability of the material. The pre-modified multidentate ligand environment (phosphate and sulfonate groups) provides a suitable environment for La... 3+ Ce 3+ Rare earth ions provide an ideal coordination platform, promoting the formation of more stable rare earth-fluorine complexes, thereby enhancing adsorption capacity and selectivity for fluorine. Pre-modification improves the hydrophilicity and dispersibility of biochar, making it easier to form uniform and high-strength particles during subsequent granulation, avoiding agglomeration and pore blockage problems. Attached Figure Description

[0030] Figure 1 The changes in fluoride concentration in water at different times during the defluorination process of the defluorination material samples of Examples 1-5 and Comparative Examples 1-3 are shown.

[0031] Figure 2 The results show the defluorination rate test results of the defluorination materials in Examples 1-5 and Comparative Examples 1-3. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] All of the following raw materials are commercially available.

[0034] Biochar, appearance: granular columnar honeycomb, material: fruit shell, ash content ≤5%, Gongyi City Jiajinkou Hengchang Water Purification Packing Factory.

[0035] Example 1

[0036] A defluoridation material for industrial wastewater treatment is prepared by the following method:

[0037] Step 1: Add biochar to deionized water, add hydrochloric acid solution while stirring, heat to 65℃ and stir for 2 hours, filter, wash with deionized water until the pH of the filtrate is 6-7, and dry at 105℃ for 12 hours to obtain acid-washed activated biochar; wherein, the mass ratio of biochar, deionized water and hydrochloric acid solution is 1:3:0.02, and the concentration of hydrochloric acid solution is 37%;

[0038] Step 2: Add the acid-washed activated biochar obtained in Step 1 to a magnesium nitrate solution, stir at 30°C for 2.5 h, dry at 105°C for 12 h, and calcine at 420°C for 1.5 h to obtain magnesium oxide-supported biochar; wherein, the mass ratio of the acid-washed activated biochar to the magnesium nitrate solution is 1:2, and the concentration of the magnesium nitrate solution is 7%;

[0039] Step 3: Add the magnesium oxide-supported biochar obtained in Step 2 to an aluminum nitrate solution, stir at 32℃ for 2 hours; dry at 105℃ for 12 hours, and calcine at 500℃ for 2.5 hours to obtain magnesium oxide-alumina composite supported biochar; wherein, the mass ratio of the magnesium oxide-supported biochar obtained in Step 2 to the aluminum nitrate solution is 1:2, and the concentration of the aluminum nitrate solution is 18%;

[0040] Step 4: Lanthanum nitrate, cerium nitrate, and strontium nitrate are added to water to prepare a mixed nitrate solution. The magnesium oxide-alumina composite supported biochar obtained in Step 3 is added to the mixed nitrate solution. The mixture is stirred at 32°C for 2 hours, dried at 70°C for 6 hours, and calcined at 320°C for 1.5 hours to obtain a rare earth co-doped composite adsorbent. The mass ratio of the magnesium oxide-alumina composite supported biochar to the mixed nitrate solution is 1:1. The concentrations of lanthanum nitrate, cerium nitrate, and strontium nitrate in the mixed nitrate solution are 0.01 mol / L, 0.005 mol / L, and 0.02 mol / L, respectively.

[0041] Step 5: Add the rare earth co-doped composite adsorbent powder obtained in Step 4 to the binder PVA aqueous solution, granulate to a particle size of 1.5-2.5 mm, and dry at 160℃ for 2 hours to obtain the final product; wherein, the mass ratio of the rare earth co-doped composite adsorbent powder to the PVA aqueous solution is 100:4, and the mass concentration of the binder PVA aqueous solution is 10%.

[0042] Example 2

[0043] A defluoridation material for industrial wastewater treatment is prepared by the following method:

[0044] Step 1: Add biochar to deionized water, add hydrochloric acid solution while stirring, heat to 60℃ and stir for 3 hours, filter, wash with deionized water until the pH of the filtrate is 6-7, and dry at 110℃ for 10 hours to obtain acid-washed activated biochar; wherein, the mass ratio of biochar, deionized water and hydrochloric acid solution is 1:4:0.01, and the concentration of hydrochloric acid solution is 37%;

[0045] Step 2: Add the acid-washed activated biochar obtained in Step 1 to a magnesium nitrate solution, stir at 25°C for 3 hours, dry at 100°C for 14 hours, and calcine at 450°C for 1 hour to obtain magnesium oxide-supported biochar; wherein, the mass ratio of the acid-washed activated biochar to the magnesium nitrate solution is 1:1.5, and the concentration of the magnesium nitrate solution is 8%;

[0046] Step 3: Add the magnesium oxide-supported biochar obtained in Step 2 to the aluminum nitrate solution, stir at 25°C for 3 hours; dry at 100°C for 14 hours; calcine at 450°C for 3 hours to obtain magnesium oxide-alumina composite supported biochar; wherein, the mass ratio of the magnesium oxide-supported biochar obtained in Step 2 to the aluminum nitrate solution is 1:2.5, and the concentration of the aluminum nitrate solution is 15%;

[0047] Step 4: Lanthanum nitrate, cerium nitrate, and strontium nitrate are added to water to prepare a mixed nitrate solution. The magnesium oxide-alumina composite supported biochar obtained in Step 3 is added to the mixed nitrate solution. The mixture is stirred at 40°C for 1.5 h, dried at 80°C for 5 h, and calcined at 280°C for 2 h to obtain a rare earth co-doped composite adsorbent. The mass ratio of the magnesium oxide-alumina composite supported biochar to the mixed nitrate solution is 1:0.8. The concentrations of lanthanum nitrate, cerium nitrate, and strontium nitrate in the mixed nitrate solution are 0.005 mol / L, 0.01 mol / L, and 0.03 mol / L, respectively.

[0048] Step 5: Add the rare earth co-doped composite adsorbent powder obtained in Step 4 to the binder PVA aqueous solution, granulate to a particle size of 1.5-2.5 mm, and dry at 140℃ for 3 hours to obtain the final product; wherein, the mass ratio of the rare earth co-doped composite adsorbent powder to the PVA aqueous solution is 100:5, and the mass concentration of the binder PVA aqueous solution is 8%.

[0049] Example 3

[0050] A defluoridation material for industrial wastewater treatment is prepared by the following method:

[0051] Step 1: Add biochar to deionized water, add hydrochloric acid solution while stirring, heat to 70℃ and stir for 1.5 h, filter, wash with deionized water until the pH of the filtrate is 6-7, and dry at 100℃ for 14 h to obtain acid-washed activated biochar; wherein, the mass ratio of biochar, deionized water and hydrochloric acid solution is 1:2:0.03, and the concentration of hydrochloric acid solution is 37%;

[0052] Step 2: Add the acid-washed activated biochar obtained in Step 1 to a magnesium nitrate solution, stir at 40°C for 1.5 h, dry at 110°C for 10 h, and calcine at 380°C for 2 h to obtain magnesium oxide-supported biochar; wherein, the mass ratio of the acid-washed activated biochar to the magnesium nitrate solution is 1:2.5, and the concentration of the magnesium nitrate solution is 10%;

[0053] Step 3: Add the magnesium oxide-supported biochar obtained in Step 2 to the aluminum nitrate solution, stir at 40℃ for 1.5 h; dry at 110℃ for 10 h; calcine at 550℃ for 1.5 h to obtain magnesium oxide-alumina composite supported biochar; wherein, the mass ratio of the magnesium oxide-supported biochar obtained in Step 2 to the aluminum nitrate solution is 1:1.5, and the concentration of the aluminum nitrate solution is 20%;

[0054] Step 4: Lanthanum nitrate, cerium nitrate, and strontium nitrate are added to water to prepare a mixed nitrate solution. The magnesium oxide-alumina composite supported biochar obtained in Step 3 is added to the mixed nitrate solution. The mixture is stirred at 25°C for 3 hours, dried at 60°C for 8 hours, and calcined at 350°C for 1 hour to obtain a rare earth co-doped composite adsorbent. The mass ratio of the magnesium oxide-alumina composite supported biochar to the mixed nitrate solution is 1:1.2. The concentrations of lanthanum nitrate, cerium nitrate, and strontium nitrate in the mixed nitrate solution are 0.015 mol / L, 0.015 mol / L, and 0.01 mol / L, respectively.

[0055] Step 5: Add the rare earth co-doped composite adsorbent powder obtained in Step 4 to the PVA aqueous solution as a binder, granulate to a particle size of 1.5-2.5 mm, and dry at 180℃ for 1.5 h to obtain the final product; wherein, the mass ratio of the rare earth co-doped composite adsorbent powder to the PVA aqueous solution is 100:3, and the mass concentration of the PVA aqueous solution as a binder is 12%.

[0056] Example 4

[0057] A defluorination material for industrial wastewater treatment, wherein the acid-washed and activated biochar obtained in step 1 is pre-modified before being applied in step 2, and the method for preparing the composite-modified biochar is as follows:

[0058] Step a: The acid-washed activated biochar is heated to 360°C at 8°C / min and kept at the same temperature for 40min for pre-oxidation. After completion, it is naturally cooled to below 80°C to obtain pre-oxidized biochar.

[0059] Step b: Disperse the pre-oxidized biochar in deionized water, add vinylphosphonic acid and potassium persulfate sequentially, adjust the pH of the reaction system to 4.0-4.8 with a 4% dilute sodium hydroxide solution, bubble nitrogen gas under the liquid surface to remove oxygen for 30 minutes, then maintain the reaction system in a slightly positive nitrogen atmosphere, raise the temperature to 45°C, and stir the reaction at a constant temperature for 5 hours. After the reaction is completed, cool the material to below 40°C and filter it. Wash the filter cake countercurrently with 70°C hot water, and finally dry the washed material at 105°C for 14 hours to obtain phosphorylated biochar; wherein, the mass ratio of the pre-oxidized biochar to deionized water, vinylphosphonic acid, and potassium persulfate is 100:800:15:4.5;

[0060] Step c: Disperse the phosphate-esterified biochar in deionized water, add pre-dried sodium propylene sulfonate and ammonium persulfate sequentially, adjust the pH of the reaction system to 2.5-3.5 with a 3% dilute hydrochloric acid solution, heat to 50℃, and stir for 4 hours. After the reaction is complete, add hydrochloric acid solution again and continue stirring for 0.8 hours to complete the sulfonic acid group conversion. Then filter, and wash the filter cake as follows: First, alkali rinsing: rinse with a 0.8% sodium carbonate solution at 55℃ for 25 minutes with stirring, then filter; then hot water rapid washing… Washing: Wash three times with rapid stirring in 65℃ hot water, with the washing liquid volume to filter cake mass ratio of 1.2:1 each time; finally, rinse once with room temperature deionized water; dry the washed wet material at 105℃ for 14 hours to obtain composite modified biochar; wherein, the mass ratio of the phosphoric acid esterified biochar, deionized water, sodium propylene sulfonate, and ammonium persulfate is 100:500:9:2.5, the concentration of hydrochloric acid solution used for sulfonic acid group transformation is 2%, and the mass ratio of hydrochloric acid solution used for sulfonic acid group transformation to phosphoric acid esterified biochar is 100:100.

[0061] The rest is the same as in Example 1.

[0062] Example 5

[0063] A defluoridation material for industrial wastewater treatment, in the preparation process,

[0064] The acid-washed and activated biochar obtained in step 1 is further modified before being applied in step 2. The preparation method of the modified biochar is as follows:

[0065] Step a: The acid-washed activated biochar is heated to 340℃ at 5℃ / min and kept at the same temperature for 60min for pre-oxidation. After completion, it is naturally cooled to below 80℃ to obtain pre-oxidized biochar.

[0066] Step b: Disperse the pre-oxidized biochar in deionized water, add vinylphosphonic acid and potassium persulfate sequentially, adjust the pH of the reaction system to 4.0-4.8 with a 3-5% dilute sodium hydroxide solution, bubble nitrogen gas under the liquid surface to remove oxygen for 20-30 minutes, then maintain the reaction system under a slightly positive nitrogen atmosphere, raise the temperature to 35°C, and stir the reaction at a constant temperature for 8 hours. After the reaction is completed, cool the material to below 40°C and filter it. Wash the filter cake countercurrently with 60°C hot water, and finally dry the washed material at 95°C for 12 hours to obtain phosphate-esterified biochar; wherein, the mass ratio of the pre-oxidized biochar to deionized water, vinylphosphonic acid, and potassium persulfate is 100:600:25:1.8;

[0067] Step c: Disperse the phosphate-esterified biochar in deionized water, add pre-dried sodium propylene sulfonate and ammonium persulfate sequentially, adjust the pH of the reaction system to 2.5-3.5 with a 3% dilute hydrochloric acid solution, raise the temperature to 40℃, and stir for 4 hours. After the reaction is complete, add hydrochloric acid solution to the system again and continue stirring for 0.8 hours to complete the sulfonic acid group conversion. Then filter, and wash the filter cake as follows: First, alkali rinsing: rinse with a 0.8% sodium carbonate solution at 55℃ for 25 minutes with stirring, then filter; then hot water... Quick wash: Wash three times with 65℃ hot water by rapid stirring, with the washing liquid volume to filter cake mass ratio of 1.2:1 each time; finally, rinse once with room temperature deionized water; dry the washed wet material at 105℃ for 14 hours to obtain composite modified biochar; wherein, the mass ratio of the phosphoric acid esterified biochar, deionized water, sodium propylene sulfonate, and ammonium persulfate is 100:450:12:2, the concentration of hydrochloric acid solution used for sulfonic acid group transformation is 3%, and the mass ratio of hydrochloric acid solution used for sulfonic acid group transformation to phosphoric acid esterified biochar is 80:100.

[0068] The rest is the same as in Example 1.

[0069] Comparative Example 1: A defluorination material applied to industrial wastewater treatment, wherein step 4 is omitted in the preparation method of the defluorination material, and step 5 granulation is carried out directly after step 3, and the rest is the same as in Example 1.

[0070] Comparative Example 2

[0071] A defluorination material for industrial wastewater treatment, wherein in step 4, the mixed nitrate is replaced with a single lanthanum nitrate solution (only La(NO3)3 is added, concentration 0.015mol / L, other parameters are the same as in Example 1: composite loaded biochar to solution mass ratio 1:1, dried at 70℃ for 6h, calcined at 320℃ for 1.5h, other parameters are the same as in Example 1).

[0072] Comparative Example 3

[0073] A defluorination material for industrial wastewater treatment, wherein step c is omitted in the preparation method of composite modified biochar, and the rest is the same as in Example 4.

[0074] Performance testing:

[0075] Prepare 700 mL of a fluoride-containing aqueous solution with a fluoride concentration of 50 mg / L, adjust the pH to 6-7, and use the defluorination materials obtained in Examples 1-5 and Comparative Examples 1-3 for defluorination, respectively, at a dosage of 0.15 g / L. Stir the reaction at room temperature, and detect the fluoride concentration of the liquid at 0.5 h, 1 h, 1.5 h, and 2 h, respectively. Calculate the final defluorination rate. The fluoride concentration and defluorination rate after treatment are shown in Table 1.

[0076] Table 1. Test Results

[0077]

[0078] From Table 1 and Figure 1 , Figure 2As can be seen, in Examples 1, 2, and 3, the fluoride concentrations at 2.5 h were 0.50, 0.52, and 0.48 mg / L, respectively, corresponding to fluoride removal rates of 98.9%-99.0%, indicating that the basic rare earth co-doped composite adsorbent possesses the characteristics of rapid adsorption and high removal rate. In Examples 4 and 5, due to the introduction of phosphoric acid-sulfonic acid bifunctional modification, the adsorption performance was further improved, with the fluoride concentration decreasing to 0.30 and 0.35 mg / L at 2.5 h, respectively, and the fluoride removal rate reaching 99.3%-99.4%. This indicates that the phosphate ester groups and sulfonic acid groups can provide additional strong coordination and electrostatic adsorption sites, significantly accelerating the initial adsorption rate and reducing the equilibrium concentration. The comparative results show that Comparative Example 1, which omits Sr and rare earth co-doping, had a fluoride concentration as high as 5.0 mg / L at 2.5 h, with a removal rate of only 90.0%, proving that composite doping can effectively increase the active centers and ion exchange capacity, which is key to achieving efficient fluoride removal. Comparative Example 2, using only lanthanum nitrate, achieved a yield of 92.6%, which was better than the sample without rare earth elements but lower than Example 1, indicating that the synergistic effect of multi-component rare earth doping is superior to single rare earth doping. Comparative Example 3, lacking sulfonic acid group modification, achieved a yield of 95.0%, which was higher than Comparative Examples 1 and 2 but still lower than Examples 4 and 5, demonstrating the significant improvement effect of bifunctional modification on adsorption performance.

[0079] 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.

[0080] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A defluoridation material for industrial wastewater treatment, characterized in that, It is prepared by the following method: Step 1: Add biochar to deionized water, add hydrochloric acid solution while stirring, heat to 60-70℃ and stir for 1.5-3 hours, filter, wash with deionized water until the pH of the filtrate is 6-7, dry at 100-110℃ for 10-14 hours to obtain acid-washed activated biochar. Step 2: Add the acid-washed activated biochar obtained in Step 1 to a magnesium nitrate solution, stir at 25-40℃ for 1.5-3h, dry at 100-110℃ for 10-14h, and calcine at 380-450℃ for 1-2h to obtain magnesium oxide supported biochar. Step 3: Add the magnesium oxide-supported biochar obtained in Step 2 to the aluminum nitrate solution, stir at 25-40℃ for 1.5-3h, dry at 100-110℃ for 10-14h, and calcine at 450-550℃ for 1.5-3h to obtain magnesium oxide-alumina composite supported biochar. Step 4: Lanthanum nitrate, cerium nitrate, and strontium nitrate are added to water to prepare a mixed nitrate solution. The magnesium oxide-alumina composite supported biochar obtained in Step 3 is added to the mixed nitrate solution. The mixture is stirred at 25-40℃ for 1.5-3 hours, dried at 60-80℃ for 5-8 hours, and then calcined at 280-350℃ for 1-2 hours to obtain a rare earth co-doped composite adsorbent. Step 5: Add a binder aqueous solution to the rare earth co-doped composite adsorbent powder obtained in Step 4 to prepare particles with a particle size of 1.5-2.5 mm, and then dry at 140-180℃ for 1.5-3 hours to obtain the final product.

2. The defluoridation material for industrial wastewater treatment according to claim 1, characterized in that, In step 1, the mass ratio of biochar, deionized water, and hydrochloric acid solution is 1:2-4:0.01-0.03, and the concentration of hydrochloric acid solution is 30-40%.

3. The defluoridation material for industrial wastewater treatment according to claim 1, characterized in that, In step 2, the mass ratio of the acid-washed activated biochar to the magnesium nitrate solution is 1:1.5-2.5, and the concentration of the magnesium nitrate solution is 5-10%.

4. The defluoridation material for industrial wastewater treatment according to claim 1, characterized in that, In step 3, the mass ratio of magnesium oxide-supported biochar obtained in step 2 to aluminum nitrate solution is 1:1.5-2.5, and the concentration of aluminum nitrate solution is 15-20%.

5. The defluoridation material for industrial wastewater treatment according to claim 1, characterized in that, In step 4, the mass ratio of the magnesium oxide-alumina composite supported biochar to the mixed nitrate solution is 1:0.8-1.2, and the concentrations of lanthanum nitrate, cerium nitrate, and strontium nitrate in the mixed nitrate solution are 0.005-0.015 mol / L, 0.005-0.015 mol / L, and 0.01-0.03 mol / L, respectively.

6. The defluoridation material for industrial wastewater treatment according to claim 1, characterized in that, In step 5, the mass ratio of the rare earth co-doped composite adsorbent powder to the binder aqueous solution is 100:3-5, the mass concentration of the binder aqueous solution is 8-12%, and the binder is PVA or sodium silicate.

7. The defluoridation material for industrial wastewater treatment according to claim 1, characterized in that, The acid-washed and activated biochar obtained in step 1 is pre-modified with composite materials. The preparation method of the composite-modified biochar is as follows: Step a: The acid-washed activated biochar is heated to 340-360℃ at 5-8℃ / min and kept at the temperature for 40-60min for pre-oxidation, and then cooled to below 80℃ to obtain pre-oxidized biochar; Step b: Disperse the pre-oxidized biochar in deionized water, add vinylphosphonic acid and potassium persulfate in sequence, adjust the pH of the reaction system to 4.0-4.8, bubble nitrogen gas under the liquid surface to remove oxygen, raise the temperature to 35-45℃, stir the reaction at a constant temperature for 5-8 hours, after the reaction is completed, filter, wash and dry to obtain phosphoric acid esterified biochar. Step c: Disperse the phosphate-modified biochar in deionized water, add pre-dried sodium propylene sulfonate and ammonium persulfate in sequence, adjust the pH of the reaction system to 2.5-3.5, raise the temperature to 40-50℃, and stir the reaction at a constant temperature for 3-6 hours. After the reaction is completed, add hydrochloric acid solution and continue stirring for 0.5-1.0 hours. Then filter, wash and dry to obtain composite modified biochar.

8. The defluoridation material for industrial wastewater treatment according to claim 7, characterized in that, In step b, the mass ratio of the pre-oxidized biochar to deionized water, vinylphosphonic acid, and potassium persulfate is 100:600-800:15-25:1.8-4.

5.

9. The defluoridation material for industrial wastewater treatment according to claim 7, characterized in that, In step c, the mass ratio of the phosphoric acid biochar, deionized water, sodium propylene sulfonate, and ammonium persulfate is 100:400-500:9-14:1.0-2.5, the concentration of the hydrochloric acid solution is 2-4%, and the mass ratio of the hydrochloric acid solution to the phosphoric acid biochar is 50-100:100.

Images