Fluorine-containing wastewater treatment agent and method for preparing the same

Abstract

This invention discloses a fluoride-containing wastewater treatment agent and its preparation method. The preparation method includes the following steps: adding mesoporous silica and lanthanum nitrate solution respectively, reacting in a water bath at 80-90℃, and then activating the modified mesoporous silica at 500-550℃ in an air atmosphere to obtain modified mesoporous silica. The modified silica is then immersed in a sodium alginate mixture and homogenized by ultrasonication in an ice bath at 300-350W. Next, it is sequentially immersed in a calcium chloride solution and a chitosan mixture, and then shaken at room temperature to obtain gel microspheres. A dopamine solution is pre-saturated in an air atmosphere, and then the gel microspheres are added. The mixture is then shaken at 120 times / min in the dark at room temperature to obtain polydopamine-coated microcapsules. The activated microcapsules are then immersed in a carboxybetaine grafting solution and shaken in a water bath at 50-55℃ under nitrogen protection to obtain the fluoride-containing wastewater treatment agent. This results in a fluoride-containing wastewater treatment agent with high adsorption efficiency, easy recycling, and long service life.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment agents, and in particular to a fluoride-containing wastewater treatment agent and its preparation method. Background Technology

[0002] With the vigorous development of industrial society, various environmental problems such as industrial waste gas and wastewater have also emerged. In particular, the steel industry or integrated circuit manufacturing industry produces a large amount of fluoride-containing wastewater, with fluoride concentrations as high as 2000 ppm, which significantly exceeds the legal emission standard of 15 ppm. It must be properly treated before it can be discharged. Although there are many defluorinating agents on the market that can reduce fluoride to below 1 mg / L, the dosage is very large. Moreover, the defluorinating agents have a very low pH and high acidity, which means that after being added to the wastewater, alkali needs to be added to adjust the pH, making it troublesome to use. Therefore, people have begun to study related fluoride-containing wastewater treatment agents to solve the problems of excessive dosage and low pH of existing defluorinating agents, which require adjusting the pH of the wastewater.

[0003] Fluoride-containing wastewater treatment agents are chemical agents or materials specifically designed to remove fluoride ions from wastewater. They reduce fluoride concentrations to national or industry emission standards through chemical reactions, adsorption, precipitation, or ion exchange. Existing fluoride-containing wastewater treatment agents mainly include precipitants, flocculants, and adsorbents. Precipitants primarily include calcium-based and magnesium-based precipitants; however, calcium-based precipitants are highly sensitive to pH and produce high levels of residual fluoride and large amounts of sludge after use, while magnesium-based precipitants are expensive and unsuitable for widespread use. Flocculants are mainly aluminum-based flocculants, but they are significantly affected by pH, produce difficult-to-treat aluminum sludge, and are costly, making them unsuitable for widespread use. Adsorbents are mainly activated alumina and rare earth materials, offering strong deep treatment capabilities and regenerability, but are generally only suitable for low-concentration fluoride wastewater and are greatly affected by water quality.

[0004] While current fluoride-containing wastewater treatment agents have solved the problems of large dosage and high acidity, their applicable pH range is narrow, the sludge volume is large and difficult to treat, and there are still many shortcomings in terms of defluorination efficiency, recyclability, and anti-interference. Therefore, developing a new type of fluoride-containing wastewater treatment agent that can effectively broaden the applicable pH range, reduce the amount of sludge produced by traditional precipitation methods, effectively solve the problem of difficult sludge treatment, while having high adsorption efficiency, anti-interference, easy recovery, and effectively extending the service life of the fluoride-containing wastewater treatment agent is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a fluoride-containing wastewater treatment agent and its preparation method. This fluoride-containing wastewater treatment agent, by constructing a microcapsule structure, effectively broadens the applicable pH range of the treatment agent, reduces the amount of sludge produced by traditional precipitation methods, effectively solves the problem of difficult sludge treatment, and utilizes multiple functional groups and multiple adsorption mechanisms for synergistic adsorption, effectively improving the adsorption selectivity and adsorption capacity of the treatment agent, enhancing the adsorption efficiency of the treatment agent, achieving high-efficiency adsorption while effectively shielding the interference of competing ions on active sites, facilitating recovery, and effectively extending the service life of the fluoride-containing wastewater treatment agent.

[0006] To achieve the above objectives, this invention proposes a method for preparing a fluoride-containing wastewater treatment agent, comprising the following steps: S1. Mesoporous silica and lanthanum nitrate solution were added separately, and after reaction in a water bath at 80~90℃, the mixture was activated at 500~550℃ in an air atmosphere to obtain modified mesoporous silica. The silica was then immersed in a sodium alginate mixture and homogenized by ultrasonication in an ice bath at 300~350W. After that, it was immersed in calcium chloride solution and chitosan mixture in sequence and then shaken at room temperature to obtain gel microspheres. S2. After pre-saturating the dopamine solution in an air atmosphere, add gel microspheres and perform room temperature light-proof shaking treatment at a speed of 120 times / min to obtain polydopamine-coated microcapsules. S3. Microcapsules were activated by adding carbodiimide and N-hydroxysuccinimide respectively, and then immersed in carboxybetaine grafting solution. Under nitrogen protection, the microcapsules were subjected to water bath shaking at 50~55℃ to obtain a fluoride-containing wastewater treatment agent.

[0007] In some embodiments of the present invention, in step S1, the mesoporous silica has a particle size of 5-8 nm, the lanthanum nitrate solution is an aqueous solution of high-purity lanthanum nitrate dissolved in deionized water, with the pH adjusted to 4.0 using 0.1 M nitric acid solution, the sodium alginate mixture is a mixed aqueous solution of sodium alginate and carboxybetaine at a mass ratio of 3:1, and the calcium chloride solution is a mixture of 0.1 M calcium chloride aqueous solution and 0.05 M tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution at a volume ratio of 1:1. The chitosan mixture is a mixture of 0.5% chitosan solution and 0.1% calcium chloride solution. The chitosan solution is chitosan dissolved in acetic acid solution, and the pH is adjusted to 5.0 with 1M sodium hydroxide solution. The mass ratio of mesoporous silica to lanthanum nitrate is 1~2:4~9. The mass-volume ratio of the modified mesoporous silica and sodium alginate mixture, the calcium chloride solution and the chitosan mixture is 1g:10~15mL:10~20mL:10~12mL.

[0008] In some embodiments of the present invention, step S1 includes: S1.1. Mesoporous silica is slowly added to a lanthanum nitrate solution and pretreated with ultrasound at 40-50 kHz and 100-200 W for 10 min. Then, it is reacted in a water bath at 80-90℃ with a stirring speed of 700-800 rpm for 6-8 h. After centrifugation, washing, and vacuum drying, it is calcined and activated at 500-550℃ for 1-2 h in an air atmosphere at a rate of 5℃ / min to obtain modified mesoporous silica. S1.2. The modified mesoporous silica was immersed in a sodium alginate mixture and homogenized by ultrasonication in an ice bath at 25-28°C for 20-30 min at 20-30 kHz, 300-350 W, and a pulse mode of 5 s on / 2 s off. Then, it was dropped into a calcium chloride solution at a flow rate of 2 mL / min and magnetically stirred at 200-300 rpm for 30-40 min. After that, it was immersed in a chitosan mixture and oscillated at room temperature for 10-15 min to obtain gel microspheres.

[0009] In some embodiments of the present invention, in step S2, the dopamine solution is a mixed aqueous solution of dopamine hydrochloride and tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a pH of 8.5, and the mass-to-volume ratio of the gel microspheres to the dopamine solution is 1g:5~10mL.

[0010] In some embodiments of the present invention, step S2 includes: pre-saturating the dopamine solution in an air atmosphere of 0.5 L / min for 10-15 min, adding gel microspheres, maintaining oscillation at 120 times / min with an amplitude of 5 cm at room temperature for 12 h under light-protected conditions, and obtaining polydopamine-coated microcapsules after washing and vacuum drying.

[0011] In some embodiments of the present invention, step S3 includes: S3.1 Add 2-(N-morpholino)ethanesulfonic acid buffer, carbodiimide and N-hydroxysuccinimide respectively, stir magnetically at 500~600rpm for 5~10min, add polydopamine-coated microcapsules, shake at 120~150rpm at room temperature in the dark for 30~45min, and obtain activated microcapsules after centrifugation and washing. S3.2 Add the carboxybetaine graft solution to the activated microcapsules, and under nitrogen protection, shake in a water bath at 50-55℃ at a speed of 150-180 rpm for 6-8 hours. After centrifugation, washing, and vacuum drying, the fluoride-containing wastewater treatment agent is obtained.

[0012] In some embodiments of the present invention, in step S3, the carboxybetaine grafting solution is a solution in which carboxybetaine is dissolved in a phosphate buffer solution with a pH of 7.4 and the pH is finely adjusted to 7.4 with a 0.1M sodium hydroxide / hydrochloric acid solution. The mass ratio of the carbodiimide to the N-hydroxysuccinimide is 2~7:1~3. The mass-to-volume ratio of the polydopamine-coated microcapsules to the 2-(N-morpholino)ethanesulfonic acid buffer solution is 1g:50~80mL. The mass ratio of the carboxybetaine to the activated microcapsules is 0.05~0.2:1~3.

[0013] This invention proposes a fluoride-containing wastewater treatment agent, prepared by the method described above, comprising mesoporous silica, lanthanum nitrate, sodium alginate, calcium chloride, chitosan, dopamine hydrochloride, carbodiimide, N-hydroxysuccinimide, and carboxybetaine; wherein, The mesoporous silica is used to provide a porous support structure with a high specific surface area, enhance the loading capacity and mass transfer efficiency of the adsorbent, and improve the dispersibility of lanthanum ions through the mesoporous confinement effect, thereby increasing the fluoride adsorption capacity of the fluoride-containing wastewater treatment agent. The lanthanum nitrate, as a lanthanum source, reacts with the silanol groups on the surface of mesoporous silica to provide fluorine-specific coordination sites, thereby enhancing the selective adsorption capacity of fluoride ions by the fluoride-containing wastewater treatment agent. The sodium alginate, used as the microcapsule wall matrix, forms an "egg box" gel structure through cross-linking of carboxyl groups and calcium ions, giving the microcapsules pH responsiveness and improving their mechanical strength. The calcium chloride provides calcium ion crosslinking ions, which form a three-dimensional network structure with the carboxyl groups of sodium alginate, solidify the shape of the microcapsules, control their porosity, and balance the adsorption and diffusion rates. The chitosan forms a dense shell by electrostatically combining protonated amino groups with the carboxyl groups of sodium alginate, reducing surface defects of the microcapsules and lowering their breakage rate during recycling. The dopamine hydrochloride is oxidized and polymerized into polydopamine under alkaline conditions. The polydopamine is then covalently bonded to the surface of the microcapsules through phenolic hydroxyl / amino groups to form a coating structure, thereby increasing the surface zeta potential of the microcapsules and enhancing their repulsion of organic pollutants. The carbodiimide is used to activate the carboxyl group of polydopamine to generate an O-acyl isourea intermediate, which promotes the efficiency of the carboxybetaine grafting reaction of the microcapsules and shortens the reaction time. The N-hydroxysuccinimide is used to stabilize the carboxyl group activated by carbodiimide to form N-hydroxysuccinimide ester, reduce hydrolysis side reactions, increase the amide bond formation rate of the microcapsules, and increase their grafting density. The carboxybetaine forms a hydrophilic, antifouling surface through zwitterionic groups, reducing the contact angle of the fluoride-containing wastewater treatment agent and decreasing the rate of decrease in its fluoride adsorption in high-organic-content wastewater.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention uses lanthanum-modified mesoporous silica as the core material, sodium alginate-calcium "egg carton" gel as the inner shell, chitosan-sodium alginate composite layer as the outer shell, and polydopamine-carboxybetaine composite layer as the coating to prepare a microcapsule structure for treating fluoride-containing wastewater. Lanthanum ions on the silica surface form strong coordination bonds with fluoride ions to generate insoluble lanthanum fluoride, effectively removing fluoride ions from wastewater. It has high selectivity and is not affected by common anions in wastewater. Furthermore, the mesoporous structure of silica produces a mesoporous confinement effect, which enriches fluoride ions through physical adsorption, increases their local concentration, promotes the chemical adsorption of fluoride ions, and significantly improves the adsorption efficiency of fluoride ions. The chitosan-sodium alginate composite layer forms a cross-linked network, allowing selective passage of fluoride ions while repelling large organic molecules or colloidal particles. This effectively shields the active sites from interference by competing ions. Simultaneously, the zwitterionic structure of carboxybetaine maintains the electroneutrality of the microcapsule surface across a wide pH range through intramolecular charge self-balancing, further preventing interference from competing ions such as hydroxide or chloride ions on fluoride ion adsorption. This enhances the material's pH adaptability, effectively stabilizes the microcapsule pore structure, and repels organic matter, forming an anti-fouling barrier. It also effectively prevents blockage of lanthanum ion active sites, ensuring stable fluoride removal in wastewater with varying pH levels. Furthermore, the chitosan and polydopamine surfaces... The amino groups on the surface of the microcapsules protonate under acidic conditions, capturing fluoride ions through electrostatic attraction and hydrogen bonding. The hydroxyl groups on the surface of polydopamine or silica undergo ion exchange with fluoride ions under neutral conditions. The carboxylate ions of carboxybetaine form hydrogen bonds with fluoride ions under neutral / alkaline conditions. This synergistic effect significantly improves the defluorination efficiency of the treatment agent, achieving highly efficient defluorination. Moreover, the large particle size of the microcapsules makes them easy to recover, and the sodium hydroxide / hydrochloric acid solution can desorb the fluoride, enabling the regeneration of the treatment agent. Furthermore, the hydrophilic layer of carboxybetaine promotes the release of fluoride ions during desorption, effectively improving the microcapsule regeneration efficiency and extending the service life of the fluoride-containing wastewater treatment agent. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] This invention proposes a method for preparing a fluoride-containing wastewater treatment agent, comprising the following steps: S1. Mesoporous silica and lanthanum nitrate solution were added separately, and after reacting in a water bath at 80~90℃, the mixture was heated to 500~550℃ in an air atmosphere for activation treatment to obtain modified mesoporous silica. The silica was then immersed in a sodium alginate mixture and homogenized by ultrasonication in an ice bath at 300~350W. After that, it was immersed in calcium chloride solution and chitosan mixture in sequence, and then shaken at room temperature to obtain gel microspheres.

[0017] In step S1, the mesoporous silica has a particle size of 5-8 nm. The lanthanum nitrate solution is an aqueous solution of high-purity lanthanum nitrate dissolved in deionized water, with the pH adjusted to 4.0 using 0.1 M nitric acid solution. The sodium alginate mixture is an aqueous solution of sodium alginate and carboxybetaine in a mass ratio of 3:1. The calcium chloride solution is a mixture of 0.1 M calcium chloride aqueous solution in a volume ratio of 1:1 and 0.05 M tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution at pH 8.5. The chitosan mixture is a mixture of 0.5% chitosan solution and 0.1% calcium chloride. The chitosan solution is chitosan dissolved in acetic acid solution, and the pH is adjusted to 5.0 with 1M sodium hydroxide solution. The mass ratio of mesoporous silica to lanthanum nitrate is 1~2:4~9. The mass-volume ratio of the modified mesoporous silica and sodium alginate mixture, calcium chloride solution and chitosan mixture is 1g:10~15mL:10~20mL:10~12mL.

[0018] Step S1 includes: S1.1. Slowly add mesoporous silica to a lanthanum nitrate solution and pretreat with ultrasound at 40-50 kHz and 100-200 W for 10 min. Then, react in a water bath at 80-90℃ for 6-8 h with stirring at 700-800 rpm. After centrifugation, washing, and vacuum drying, calcine and activate at 500-550℃ for 1-2 h in an air atmosphere at a rate of 5℃ / min to obtain modified mesoporous silica.

[0019] Lanthanum nitrate-modified mesoporous silica was used. In an acidic solution with a pH of 4.0, lanthanum ions mainly exist as hexacoordinate hydrated ions, which undergo ligand exchange reactions with hydroxyl groups on the surface of mesoporous silica. After high-temperature calcination, lanthanum-modified mesoporous silica is formed. The mesoporous structure of silica produces a mesoporous confinement effect, and the pore space of the mesopores can promote the diffusion of lanthanum ions into the pores, increasing their loading and providing highly active sites for subsequent fluorine adsorption.

[0020] Ultrasonic pretreatment breaks up silica particle agglomeration, promotes uniform loading of lanthanum ions, and accelerates the diffusion of lanthanum ions into the mesopores through cavitation, enhancing mass transfer efficiency. Controlling the frequency at 40-50 kHz represents the optimal cavitation threshold, effectively avoiding energy waste caused by excessively high frequencies. A power of 100-200 W balances the dispersion effect with the integrity of the material structure, preventing damage to the mesoporous structure from excessive power. Ultrasonic pretreatment for 10 minutes at this power and frequency effectively disperses mesoporous silica, laying the foundation for subsequent uniform modification. Controlling the stirring rate at 700-800 rpm ensures thorough solid-liquid mixing, preventing localized lanthanum ion supersaturation and precipitation. Maintaining the water bath temperature at 80-90℃ promotes the dehydration condensation of lanthanum ions with the silanol groups on the silica surface, while avoiding violent hydrolysis caused by boiling water. A water bath reaction at this stirring speed and temperature for 6-8 hours effectively balances the reaction rate and modification effect, promoting uniform loading of lanthanum ions on the mesoporous silica surface. Controlling the calcination temperature at 500~550℃ can effectively decompose residual nitrates while avoiding mesoporous collapse. Controlling the heating rate at 5℃ / min and slowly heating up prevents thermal stress from causing cracks and ensures the stable formation of chemical bonds.

[0021] S1.2. The modified mesoporous silica was immersed in a sodium alginate mixture and homogenized by ultrasonication in an ice bath at 25-28°C for 20-30 min at 20-30 kHz, 300-350 W, and a pulse mode of 5 s on / 2 s off. Then, it was dropped into a calcium chloride solution at a flow rate of 2 mL / min and magnetically stirred at 200-300 rpm for 30-40 min. After that, it was immersed in a chitosan mixture and oscillated at room temperature for 10-15 min to obtain gel microspheres.

[0022] Lanthanum ions on the surface of modified mesoporous silica weakly coordinate with the carboxyl groups of sodium alginate, while the carboxyl groups of sodium alginate react with calcium ions to form an "egg-box" gel structure, achieving physical encapsulation of the modified mesoporous silica. At pH 5.0, the amino groups of chitosan are protonated and interact electrostatically with the carboxyl ions of sodium alginate. The hydroxyl groups of chitosan react with the carboxyl groups of sodium alginate to form hydrogen bonds, effectively enhancing the toughness of the microcapsule material. At the same time, long-chain chitosan and sodium alginate molecules intertwine during cross-linking to form an interpenetrating network, effectively improving the mechanical strength of the microcapsules. After high-temperature calcination, the modified mesoporous silica system has a pH range of 5-8. Its surface is negatively charged and will interact electrostatically with the uncrosslinked protonated amino groups in chitosan. Furthermore, the hydroxyl groups of the modified mesoporous silica will form a hydrogen bond network with the hydroxyl groups of chitosan, which significantly improves the bonding strength between the modified mesoporous silica adsorbent and the chitosan-sodium alginate composite layer, thus achieving an effective bond between the microcapsule shell and the core material.

[0023] The optimal cavitation effect range is 20-30kHz, which promotes the uniform dispersion of modified mesoporous silica in the sodium alginate mixture and avoids chain breakage caused by high frequencies. The power is controlled at 300-350W to ensure sufficient power to break up the agglomeration of modified mesoporous silica while avoiding localized overheating. A pulse mode of 5s on / 2s off is used for intermittent ultrasound to reduce heat accumulation and protect the molecular structure of sodium alginate. An ice bath method is used to control the ultrasound temperature at 25-28℃, ensuring effective energy transfer while preventing thermal degradation of sodium alginate. Ultrasonic homogenization at this temperature for 20-30 minutes generates sufficient cavitation bubbles to break up the agglomeration of modified mesoporous silica and ensure its uniform distribution in the sodium alginate mixture. Controlling the flow rate at 2 mL / min ensures uniform droplet size and prevents excessive flow that could cause the gel microspheres to stick together. Maintaining the stirring rate at 200–300 rpm balances mixing efficiency and shear force. Magnetic stirring at this rate for 30–40 min ensures effective cross-linking of sodium alginate and calcium ions while preventing excessive surface cross-linking. Shaking at room temperature for 10–15 min ensures adequate chitosan coating and prevents the microspheres from swelling and rupturing due to prolonged shaking.

[0024] In step S2, the dopamine solution is a mixed aqueous solution of dopamine hydrochloride and tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a pH of 8.5, and the mass-volume ratio of gel microspheres to dopamine solution is 1g:5~10mL.

[0025] S2. After pre-saturating the dopamine solution in an air atmosphere, add gel microspheres and perform room temperature light-proof shaking treatment at a speed of 120 times / min to obtain polydopamine-coated microcapsules.

[0026] Step S2 includes: The dopamine solution was pre-saturated in air at a speed of 0.5 L / min for 10-15 min, and then gel microspheres were added. The mixture was kept in the dark and oscillated at 120 times / min with an amplitude of 5 cm at room temperature for 12 h. After washing and vacuum drying, polydopamine-coated microcapsules were obtained.

[0027] Under oxygen and alkaline conditions, the catechol structure of dopamine is oxidized by oxygen to dopaquinone, which then forms dihydroxyindole through intramolecular Michael addition reaction. This dihydroxyindole then forms a disordered polydopamine polymer network through π-π stacking, hydrogen bonding, and covalent cross-linking. The quinone group reacts with the amino group of chitosan in a Schiff base reaction and with the hydroxyl group of sodium alginate in a Michael addition reaction, effectively enhancing the binding strength between polydopamine and microspheres. At the same time, the phenolic hydroxyl and amino groups of polydopamine react with the polar groups on the surface of microspheres to form hydrogen bonds, further enhancing the binding strength between polydopamine and microspheres, thus achieving effective encapsulation of polydopamine on the surface of microspheres.

[0028] Controlling the airflow rate at 0.5 L / min provides a constant dissolved oxygen level, effectively driving the oxidative polymerization of dopamine. Pre-saturation at this airflow rate for 10-15 min ensures the dissolved oxygen in the solution reaches saturation, guaranteeing consistency during the polymerization initiation phase. Controlling the oscillation speed at 120 oscillations / min ensures the microspheres tumble sufficiently, preventing deposition or adhesion. Controlling the amplitude at 5 cm provides moderate shear force, promoting uniform polydopamine deposition while avoiding mechanical damage. Oscillation at room temperature for 12 hours at this speed and amplitude conforms to reaction kinetics, ensuring coating integrity while preventing excessive polydopamine deposition that could clog pores.

[0029] S3. Microcapsules were activated by adding carbodiimide and N-hydroxysuccinimide respectively, and then immersed in carboxybetaine grafting solution. Under nitrogen protection, the microcapsules were subjected to water bath shaking at 50~55℃ to obtain a fluoride-containing wastewater treatment agent.

[0030] Step S3 includes: S3.1 Add 2-(N-morpholino)ethanesulfonic acid buffer, carbodiimide and N-hydroxysuccinimide respectively, stir magnetically at 500~600rpm for 5~10min, add polydopamine-coated microcapsules, shake at 120~150rpm at room temperature in the dark for 30~45min, and obtain activated microcapsules after centrifugation and washing.

[0031] Polydopamine-coated microcapsules were activated using 2-(N-morpholino)ethanesulfonic acid buffer, carbodiimide, and N-hydroxysuccinimide. Carbodiimide reacted with the carboxyl groups of polydopamine to generate an unstable O-acylisourea intermediate. N-hydroxysuccinimide reacted with the highly reactive O-acylisourea intermediate to generate a more stable N-hydroxysuccinimide ester, effectively activating the carboxyl groups on the surface of polydopamine and promoting subsequent covalent coupling with carboxybetaine.

[0032] Maintaining a stirring speed of 500–600 rpm ensures rapid dispersion of carbodiimide / N-hydroxysuccinimide, preventing excessively high local concentrations that could lead to self-crosslinking side reactions. Magnetic stirring at this speed for 5–10 min ensures uniform dispersion of both carbodiimide and N-hydroxysuccinimide, laying the foundation for subsequent microcapsule activation. Shaking at 120–150 rpm provides adequate mixing, promoting sufficient contact between carbodiimide / N-hydroxysuccinimide and the carboxyl groups on the polydopamine surface to generate active intermediates, while avoiding high shear forces that could damage the microcapsule structure. Shaking at this speed at room temperature in the dark for 30–45 min increases the maximum grafting rate of N-hydroxysuccinimide on the microcapsule surface while maintaining the integrity of the microcapsule structure.

[0033] S3.2 Add the carboxybetaine graft solution to the activated microcapsules, and under nitrogen protection, shake in a water bath at 50-55℃ at a speed of 150-180 rpm for 6-8 hours. After centrifugation, washing, and vacuum drying, the fluoride-containing wastewater treatment agent is obtained.

[0034] By treating activated microcapsules with carboxybetaine graft solution, the amino groups on the surface of carboxybetaine undergo nucleophilic substitution with N-hydroxysuccinimide ester to form amide bonds. These amide bonds covalently graft carboxybetaine onto the polydopamine surface, retaining carboxylate and quaternary ammonium groups. The carboxylate groups react with metal ions in wastewater to form metal-carboxylic acid complexes, further adsorbing fluoride ions. The quaternary ammonium groups attract fluoride ions through electrostatic attraction, effectively enhancing the defluorination efficiency of the treatment agent. Simultaneously, the zwitterionic structure of carboxybetaine effectively inhibits microbial adhesion and maintains the electroneutrality of the microcapsule surface across a wide pH range through intramolecular charge self-balancing, effectively repelling organic matter in wastewater and shielding against interference from competing ions such as hydroxide ions, forming an anti-pollution and anti-interference barrier. This effectively prevents blockage of lanthanum ion active sites, reducing their ineffective utilization. Furthermore, the hydration of its hydrophilic layer accelerates the diffusion of fluoride ions to lanthanum ion sites, synergistically achieving highly efficient nitrogen removal by the treatment agent.

[0035] Maintaining the rotation speed at 150-180 rpm ensures uniform suspension of the microcapsules, preventing deposition, while simultaneously maintaining appropriate shear force to promote the diffusion of carboxybetaine molecules to the activation sites. This prevents mechanical damage to the microcapsules and the shearing detachment of grafted carboxybetaine chains due to excessive rotation speed. Controlling the water bath temperature at 50-55℃ effectively increases the amide bond formation rate and prevents thermal degradation of the carboxybetaine side chains due to excessive temperature. Irrigating in the water bath at this temperature for 6-8 hours promotes the slow diffusion of carboxybetaine into the microcapsule pores, achieving deep grafting and increasing the grafting rate on the microcapsule surface.

[0036] In step S3, the carboxybetaine grafting solution is a solution in which carboxybetaine is dissolved in phosphate buffer at pH 7.4 and the pH is finely adjusted to 7.4 with 0.1M sodium hydroxide / hydrochloric acid solution. The mass ratio of carbodiimide to N-hydroxysuccinimide is 2~7:1~3. The mass-volume ratio of polydopamine-coated microcapsules to 2-(N-morpholino)ethanesulfonic acid buffer is 1g:50~80mL. The mass ratio of carboxybetaine to activated microcapsules is 0.05~0.2:1~3.

[0037] This invention proposes a fluoride-containing wastewater treatment agent, prepared by the method described above, comprising mesoporous silica, lanthanum nitrate, sodium alginate, calcium chloride, chitosan, dopamine hydrochloride, carbodiimide, N-hydroxysuccinimide, and carboxybetaine; wherein, Mesoporous silica is used to provide a porous support structure with high specific surface area, which enhances the loading capacity and mass transfer efficiency of the adsorbent, and improves the dispersibility of lanthanum ions through the mesoporous confinement effect, thereby increasing the fluoride adsorption capacity of the fluoride wastewater treatment agent. Lanthanum nitrate, as a lanthanum source, reacts with silanol groups on the surface of mesoporous silica, providing fluorine-specific coordination sites and enhancing the selective adsorption capacity of fluoride ions in fluoride-containing wastewater treatment agents. Sodium alginate, as a microcapsule wall matrix, forms an "egg box" gel structure through cross-linking of carboxyl groups and calcium ions, giving the microcapsules pH responsiveness and improving their mechanical strength. Calcium chloride provides calcium ions for cross-linking, which form a three-dimensional network structure with the carboxyl groups of sodium alginate, solidifying the shape of the microcapsules, controlling their porosity, and balancing adsorption and diffusion rates. Chitosan forms a dense shell by electrostatically combining protonated amino groups with the carboxyl groups of sodium alginate, reducing surface defects in microcapsules and lowering their breakage rate during recycling. Dopamine hydrochloride undergoes oxidative self-polymerization under alkaline conditions to form polydopamine, which covalently bonds with the surface of microcapsules through phenolic hydroxyl / amino groups to form a coating structure, thereby increasing the surface zeta potential of the microcapsules and enhancing their repulsion of organic pollutants. Carbodiimide is used to activate the carboxyl group of polydopamine to generate an O-acyl isourea intermediate, which promotes the efficiency of the carboxybetaine grafting reaction of microcapsules and shortens the reaction time. N-hydroxysuccinimide is used to stabilize the carboxyl group activated by carbodiimide to form N-hydroxysuccinimide ester, reduce hydrolysis side reactions, increase the amide bond formation rate of microcapsules, and increase their grafting density. Carboxybetaine constructs a hydrophilic and antifouling surface through zwitterionic groups, reducing the contact angle of fluoride-containing wastewater treatment agents and decreasing the rate of fluoride adsorption in high-organic wastewater.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a fluoride-containing wastewater treatment agent, characterized in that the steps include... include: S1. Mesoporous silica and lanthanum nitrate solution were added separately, and after reaction in a water bath at 80~90℃, the mixture was activated at 500~550℃ in an air atmosphere to obtain modified mesoporous silica. The silica was then immersed in a sodium alginate mixture and homogenized by ultrasonication in an ice bath at 300~350W. After that, it was immersed in calcium chloride solution and chitosan mixture in sequence and then shaken at room temperature to obtain gel microspheres. The mesoporous silica has a particle size of 5~8 nm; The lanthanum nitrate solution is an aqueous solution of high-purity lanthanum nitrate dissolved in deionized water, with the pH adjusted to 4.0 using 0.1M nitric acid solution. The sodium alginate mixture is an aqueous solution of sodium alginate and carboxybetaine in a mass ratio of 3:

1. The calcium chloride solution is a mixture of 0.1M calcium chloride aqueous solution (volume ratio 1:1) and 0.05M tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with pH 8.

5. The chitosan mixture is a mixture of 0.5% chitosan solution and 0.1% calcium chloride; the chitosan solution is a solution in which chitosan is dissolved in acetic acid solution and the pH is adjusted to 5.0 with 1M sodium hydroxide solution. The mass ratio of the mesoporous silica to the lanthanum nitrate is 1~2:4~9; The mass-volume ratio of the modified mesoporous silica and the sodium alginate mixture, the calcium chloride solution and the chitosan mixture is 1g:10~15mL:10~20mL:10~12mL; S2. After pre-saturating the dopamine solution in an air atmosphere, add gel microspheres and perform room temperature light-proof shaking treatment at a speed of 120 times / min to obtain polydopamine-coated microcapsules. S3. Microcapsules were activated by adding carbodiimide and N-hydroxysuccinimide respectively, and then immersed in carboxybetaine grafting solution. Under nitrogen protection, the microcapsules were subjected to water bath shaking at 50~55℃ to obtain a fluoride-containing wastewater treatment agent.

2. The method for preparing a fluoride-containing wastewater treatment agent according to claim 1, characterized in that, Step S1 includes: S1.

1. Mesoporous silica is slowly added to a lanthanum nitrate solution and pretreated with ultrasound at 40-50 kHz and 100-200 W for 10 min. Then, it is reacted in a water bath at 80-90℃ with a stirring speed of 700-800 rpm for 6-8 h. After centrifugation, washing, and vacuum drying, it is calcined and activated at 500-550℃ for 1-2 h in an air atmosphere at a rate of 5℃ / min to obtain modified mesoporous silica. S1.

2. The modified mesoporous silica was immersed in a sodium alginate mixture and homogenized by ultrasonication in an ice bath at 25-28°C for 20-30 min at 20-30 kHz, 300-350 W, and a pulse mode of 5 s on / 2 s off. Then, it was dropped into a calcium chloride solution at a flow rate of 2 mL / min and magnetically stirred at 200-300 rpm for 30-40 min. After that, it was immersed in a chitosan mixture and oscillated at room temperature for 10-15 min to obtain gel microspheres.

3. The method for preparing a fluoride-containing wastewater treatment agent according to claim 1, characterized in that, In step S2, the dopamine solution is a mixed aqueous solution of dopamine hydrochloride and tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution with a pH of 8.5; the mass-to-volume ratio of the gel microspheres to the dopamine solution is 1g:5~10mL.

4. The method for preparing a fluoride-containing wastewater treatment agent according to claim 1, characterized in that, Step S2 includes: pre-saturating the dopamine solution in an air atmosphere of 0.5 L / min for 10-15 min, adding gel microspheres, maintaining a shaking rate of 120 times / min and an amplitude of 5 cm at room temperature for 12 h under light-protected conditions, and obtaining polydopamine-coated microcapsules after washing and vacuum drying.

5. The method for preparing a fluoride-containing wastewater treatment agent according to claim 1, characterized in that, Step S3 includes: S3.1 Add 2-(N-morpholino)ethanesulfonic acid buffer, carbodiimide and N-hydroxysuccinimide respectively, stir magnetically at 500~600rpm for 5~10min, add polydopamine-coated microcapsules, shake at 120~150rpm at room temperature in the dark for 30~45min, and obtain activated microcapsules after centrifugation and washing. S3.2 Add the carboxybetaine graft solution to the activated microcapsules, and under nitrogen protection, shake in a water bath at 50-55℃ at a speed of 150-180 rpm for 6-8 hours. After centrifugation, washing, and vacuum drying, the fluoride-containing wastewater treatment agent is obtained.

6. The method for preparing a fluoride-containing wastewater treatment agent according to claim 5, characterized in that, In step S3, the carboxybetaine grafting solution is a solution in which carboxybetaine is dissolved in a phosphate buffer solution with a pH of 7.4, and the pH is finely adjusted to 7.4 with a 0.1M sodium hydroxide / hydrochloric acid solution; the mass ratio of the carbodiimide to the N-hydroxysuccinimide is 2~7:1~3; the mass-to-volume ratio of the polydopamine-coated microcapsules to the 2-(N-morpholino)ethanesulfonic acid buffer solution is 1g:50~80mL; and the mass ratio of the carboxybetaine to the activated microcapsules is 0.05~0.2:1~3.

7. A fluoride-containing wastewater treatment agent, characterized in that, The fluoride-containing wastewater treatment agent is prepared by the method described in any one of claims 1-6, comprising mesoporous silica, lanthanum nitrate, sodium alginate, calcium chloride, chitosan, dopamine hydrochloride, carbodiimide, N-hydroxysuccinimide, and carboxybetaine; wherein, The mesoporous silica is used to provide a porous support structure with a high specific surface area, enhance the loading capacity and mass transfer efficiency of the adsorbent, and improve the dispersibility of lanthanum ions through the mesoporous confinement effect, thereby increasing the fluoride adsorption capacity of the fluoride-containing wastewater treatment agent. The lanthanum nitrate, as a lanthanum source, reacts with the silanol groups on the surface of mesoporous silica to provide fluorine-specific coordination sites, thereby enhancing the selective adsorption capacity of fluoride ions by the fluoride-containing wastewater treatment agent. The sodium alginate, used as the microcapsule wall matrix, forms an "egg box" gel structure through cross-linking of carboxyl groups and calcium ions, giving the microcapsules pH responsiveness and improving their mechanical strength. The calcium chloride provides calcium ion crosslinking ions, which form a three-dimensional network structure with the carboxyl groups of sodium alginate, solidify the shape of the microcapsules, control their porosity, and balance the adsorption and diffusion rates. The chitosan forms a dense shell by electrostatically combining protonated amino groups with the carboxyl groups of sodium alginate, reducing surface defects of the microcapsules and lowering their breakage rate during recycling. The dopamine hydrochloride is oxidized and polymerized into polydopamine under alkaline conditions. The polydopamine is then covalently bonded to the surface of the microcapsules through phenolic hydroxyl / amino groups to form a coating structure, thereby increasing the surface zeta potential of the microcapsules and enhancing their repulsion of organic pollutants. The carbodiimide is used to activate the carboxyl group of polydopamine to generate an O-acyl isourea intermediate, which promotes the efficiency of the carboxybetaine grafting reaction of the microcapsules and shortens the reaction time. The N-hydroxysuccinimide is used to stabilize the carboxyl group activated by carbodiimide to form N-hydroxysuccinimide ester, reduce hydrolysis side reactions, increase the amide bond formation rate of the microcapsules, and increase their grafting density. The carboxybetaine forms a hydrophilic, antifouling surface through zwitterionic groups, reducing the contact angle of the fluoride-containing wastewater treatment agent and decreasing the rate of decrease in its fluoride adsorption in high-organic-content wastewater.