A fluorine removing agent and a method for preparing the same

Abstract

The application discloses a fluorine removal agent and a preparation method thereof, and relates to the technical field of fluorine removal agents, and comprises the following components in parts by weight: 5-10 parts of an aluminum salt, 5-10 parts of an iron salt, 15-20 parts of a rare earth material, sodium citrate and beta-cyclodextrin; the addition amount of the sodium citrate is 5%-10% of the total mass of the aluminum salt, the iron salt and the rare earth material; and the addition amount of the beta-cyclodextrin is 30%-50% of the mass of the sodium citrate. Through the introduction of the synergistic system of sodium citrate and beta-cyclodextrin, the metal ion precipitation sequence is regulated, meanwhile, the beta-cyclodextrin captures competitive anions through molecular recognition and constructs a hydrogen bond network to block interference, and the combination of the microsphere type and the porous particle type further realizes dynamic directional transmission of pollutants and nuclear pore limited crystallization, and the active site distribution is reconstructed at the molecular level, so that a technical scheme with universality, economy and reliability is provided for the treatment of complex fluorine-containing wastewater.

Description

Technical Field

[0001] This invention relates to the field of defluorinating agents, and in particular to a defluorinating agent and its preparation method. Background Technology

[0002] Fluoride-containing wastewater is common in the electronics industry, characterized by large volumes and high biological toxicity. Fluoride removal agents, as key water treatment chemicals, play a crucial role in the treatment of fluoride-containing wastewater in the electronics industry and other fields. Addressing the limitations of traditional fluoride removal methods such as chemical precipitation and coagulation sedimentation, including unstable treatment effects, poor sludge settling performance, and secondary pollution caused by metal ion back-dissolution, several novel fluoride removal agents have been developed in recent years.

[0003] Although the novel defluoridating agent improves the problems of metal ion back-dissolution and floc loosening in the traditional process by loading aluminum, iron and rare earth metal co-precipitates with chitosan skeleton, it still has defects such as the mismatch of metal ion precipitation time leading to the encapsulation of rare earth active sites, the interference of competing ions such as phosphate in high salinity wastewater on the adsorption process, and the loose structure of sludge and slow settling, which restrict its stability in the application of complex water quality. Summary of the Invention

[0004] This application provides a defluorinating agent and its preparation method, solving the problems of disordered metal ion precipitation, poor anti-interference, and loose flocs in existing defluorinating agents. By introducing a synergistic system of sodium citrate and β-cyclodextrin, the precipitation sequence of metal ions is regulated. At the same time, β-cyclodextrin captures competitive anions through molecular recognition and constructs a hydrogen bond network to block interference. The combination of its microsphere and porous particle types further realizes the dynamic directional transport of pollutants and the core-pore confined crystallization, reconstructing the distribution of active sites at the molecular level, improving the stability of the defluorinating agent, and providing a universal, economical, and reliable technical solution for the treatment of complex fluoride-containing wastewater.

[0005] This application provides a defluorinating agent, comprising, by weight:

[0006] 5-10 parts aluminum salt, 5-10 parts iron salt, 15-20 parts rare earth materials, sodium citrate and β-cyclodextrin;

[0007] The amount of sodium citrate added is 5%-10% of the total mass of aluminum salts, iron salts, and rare earth materials;

[0008] The amount of β-cyclodextrin added is 30%-50% of the mass of sodium citrate;

[0009] The β-cyclodextrin includes microspherical β-cyclodextrin and porous particulate β-cyclodextrin, with a mass ratio of 1:4.

[0010] The microsphere-type β-cyclodextrin has a particle size of 0.45-0.55 μm and its surface is modified with sulfonic acid groups;

[0011] The porous granular β-cyclodextrin has a particle size of 140-160 μm and a pore size of 2-10 nm.

[0012] Furthermore, the microsphere-type β-cyclodextrin is prepared by spray drying at an inlet temperature of 75-85℃, the sulfonating agent is propanesulfonate lactone, and the molar ratio of β-cyclodextrin to propanesulfonate lactone is 1:1.1-1.3.

[0013] Furthermore, the porous particulate β-cyclodextrin is cross-linked with glutaraldehyde after calcination at 450°C using 20nm silica as a template, and the molar ratio of β-cyclodextrin to glutaraldehyde is 1:0.55-0.65.

[0014] Furthermore, the porous particulate β-cyclodextrin is coated to form a core-shell structure, including a core layer and a shell layer;

[0015] The core layer is a porous particulate β-cyclodextrin cross-linked with glutaraldehyde;

[0016] The shell is a pH-responsive layer formed by embedding sodium citrate in calcium alginate.

[0017] Furthermore, the aluminum salt is aluminum chloride, the iron salt is polyferric chloride, and the rare earth material is at least one of lanthanum nitrate and cerium chloride.

[0018] A method for preparing a defluorinating agent specifically includes the following steps:

[0019] (a) Dissolve aluminum salts, iron salts, rare earth materials, sodium citrate, and β-cyclodextrin in water and stir;

[0020] (b) Add the mixture dropwise to the NaOH solution, control the endpoint pH, and a precipitate will form;

[0021] (c) Centrifuge to separate the precipitate, wash and dry it to obtain powder;

[0022] (d) Dissolve chitosan in acetic acid, add the powder from step (c) and stir to obtain a mixture;

[0023] (e) The mixture is pre-frozen and then freeze-dried under vacuum to obtain the final product.

[0024] Further, in step (b), the mixture is added dropwise to a 10% NaOH solution at a rate of ≤10 mL / min, and the final pH is controlled to be 8.0-8.5.

[0025] Furthermore, in step (a), aluminum salt, iron salt, and rare earth materials are first dissolved in water, then porous granular β-cyclodextrin is added and stirred for 30 minutes, and finally microsphere β-cyclodextrin is added and stirred for 2 hours, while maintaining the water temperature at 25±3℃.

[0026] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0027] By using sodium citrate and β-cyclodextrin, the precipitation sequence is reconstructed at the molecular level, ion competition is blocked, and the crystallization process is optimized, achieving a triple breakthrough in fluoride removal efficiency, sludge performance, and stability. This solves the defects of metal precipitation stratification and lack of anti-interference mechanism, which leads to insufficient utilization of active sites, loose floc structure, and difficulty in achieving stable standards in complex water quality.

[0028] By introducing a combination of 0.5μm microsphere-type β-cyclodextrin and 150μm porous particulate-type β-cyclodextrin, the problem of single β-cyclodextrin affecting colloidal PO4 was solved. 3- Low retention, weak shear resistance of traditional flocs, low temperature La 3+ Addressing issues such as slow nucleation, the system has achieved significant improvements in fluoride removal efficiency, sludge settling performance, increased tolerance to colloidal pollutants, and extended cycle life.

[0029] By constructing a core-shell structured β-CD and sodium citrate composite carrier, calcium ions are loaded onto a 150μm cross-linked porous β-cyclodextrin core layer to form precipitation microcavities. A pH-responsive shell layer of sodium citrate is then formed by encapsulating sodium citrate with calcium alginate. Through a cascade reaction of pH-triggered targeted slow release and energy feedback closed loop, the comprehensive performance of the defluorinating agent is further improved. When the system pH is >7.5, the carrier intelligently swells and releases sodium citrate into the core pores, matching the rare earth precipitation process. Simultaneously, 0.5μm sulfonated microspheres of β-cyclodextrin dynamically capture pollutants and release reaction heat. The heat energy is conducted through the core and shell to increase the temperature inside the pores, driving the increase of lanthanum ion nucleation rate and guiding the confined directional deposition of aluminum iron hydroxide within 2-10nm pores, forming a single-crystal active structure with LaF3 nuclei and Al(OH)3 coating. Detailed Implementation

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] Example 1: A defluorinating agent, comprising the following components by weight:

[0032] Aluminum salt (aluminum chloride): 5-10 parts;

[0033] Iron salt (polyferric chloride): 5-10 parts;

[0034] Rare earth materials (lanthanum nitrate / cerium chloride, etc.): 15-20 parts;

[0035] Sodium citrate (C6H5Na3O7): 5%-10% of the total mass of aluminum salts, iron salts, and rare earth materials;

[0036] β-Cyclodextrin (β-CD): 30%-50% of sodium citrate by mass;

[0037] The preparation method of the defluorinating agent includes the following steps:

[0038] Step 1. Add aluminum salt, iron salt, rare earth materials, sodium citrate, and β-CD to deionized water; stir at 200~300 rpm for 3 hours at a water temperature of 25±3℃ to form a homogeneous solution;

[0039] Step 2. Add the mixture obtained in Step 1 dropwise to a 10% NaOH solution at a rate of ≤10 mL / min; monitor the pH in real time and control the final pH to be 8.0~8.5; continue stirring for 30 minutes after the addition is complete;

[0040] Step 3. Centrifuge to separate the precipitate (10,000 rpm, 10 minutes); wash with deionized water until the filtrate pH is 6.5-7.5 and the conductivity is ≤100 μS / cm;

[0041] Dry at 70~80℃ to constant weight, then grind to 100~200 mesh powder;

[0042] Step 4. Add chitosan (degree of deacetylation 80%-95%) to acetic acid at a mass ratio of chitosan:acetic acid = 1:0.5; add deionized water to dilute to a solid content of 10% and stir to dissolve.

[0043] Add the powder from step 3 to the chitosan solution and stir at 200 rpm for 12 hours;

[0044] Step 5: Pour the mixture into the mold and freeze at -80℃ for 6 hours;

[0045] The freeze dryer is set to -45℃ and vacuum degree ≤10 Pa for 24 hours to obtain a loose powdery defluorinating agent.

[0046] Experiments were conducted on the technical solution of this embodiment:

[0047] 1. The total mass of the metals is 40g (aluminum salts + iron salts + rare earth elements), aluminum chloride: 10.0g, polyferric chloride: 10.0g, and lanthanum nitrate: 20.0g.

[0048] The experimental groups and additive dosages (fixed total metal amount = 40g) are shown in Table 1 below:

[0049] Table 1

[0050]

[0051] 2. Performance testing methods:

[0052] (1) Defluorination efficiency test:

[0053] Simulated wastewater: Ca 2+ Pre-treated to contain F - =10mg / L, add Na2SO4 (SO4) 2- =100mg / L) and Na3PO4 (PO4 3- =5mg / L) simulated competing ions;

[0054] operate:

[0055] Take 500 mL of simulated wastewater and add defluoridating agent to a concentration of 300 ppm;

[0056] Stir rapidly (300 rpm, 30 min), then stir slowly (100 rpm, 10 min), and then let it stand to settle for 30 min.

[0057] The supernatant was used to determine F using the fluoride ion electrode method (GB 7484-87). - concentration.

[0058] (2) Sludge settling performance test:

[0059] Take 100 mL of effluent from the flocculation tank into a graduated cylinder, record the change in sludge interface height over time, and calculate the settling velocity (m / h).

[0060] Take the settled sludge, dry it at 105℃ to constant weight, and calculate the sludge moisture content (%).

[0061] The test results are shown in Table 2 below:

[0062] Table 2

[0063]

[0064] The technical solutions described in the embodiments of this application have at least the following technical effects or advantages:

[0065] By introducing sodium citrate and β-cyclodextrin (β-CD), the problems of uneven metal coprecipitation, interference from multivalent anion competition, and loose sludge floc structure are synergistically solved. At the molecular level, the precipitation sequence is reconstructed, ion competition is blocked, and the crystallization process is optimized, thereby improving the defluorination efficiency, sludge performance, and stability.

[0066] Sodium citrate regulates the precipitation sequence of metals through selective complexation; citrate ions react with Al... 3+ / Fe 3+ It forms highly stable complexes, delaying their complete precipitation from pH 4-6 to above 8.5; while rare earth ions with weaker complexing ability preferentially precipitate as crystal nuclei at pH 7.5-8.5, thus forming an ordered structure of rare earth core-aluminum-iron shell, significantly improving the utilization rate of rare earth active sites, broadening the application range of defluoridating agents, and enhancing their resistance to water quality fluctuations.

[0067] β-cyclodextrin avoids competitive interference through molecular recognition, and the hydrophobic cavity of β-CD encapsulates PO4 through hydrogen bonds. 3- Its outer wall hydroxyl groups form a hydrogen bond network with citrate ions, which enhances the stability of the aluminum ion-citric acid complex. PO4 3- The residual amount of defluorinating agent in SO4 is reduced. 2- ≤200mg / L, PO4 3- It remains highly efficient even in high-salt wastewater with a concentration of ≤10 mg / L;

[0068] The combination of sodium citrate and β-CD produces a synergistic effect:

[0069] β-CD captures PO4 3- Subsequently, the hydroxyl groups on its outer wall form a hydrogen bond network with the citrate ion, significantly increasing the binding energy of the aluminum ion-citric acid complex and blocking anion competition. This process converts PO4 into a hydrogen bond network. 3- The fluoride removal efficiency under interference increased from 1.2 mg / L (sodium citrate alone) to 0.4 mg / L;

[0070] β-CD inclusion of PO4 3- The reaction releases heat, and the system locally heats up by 5°C, promoting the reaction of La. 3+ The nucleation rate is significantly increased at 35℃, and a highly crystalline LaF3 rigid framework is formed first. At this temperature, sodium citrate still binds Al... 3+ / Fe 3+ Stable in the dissolved state, after rare earth crystal nuclei are formed, Al 3+ / Fe 3+ The sludge is redeposited on the surface of the crystal nucleus, forming a dense core-shell structure; this process drives the sludge settling velocity to increase from 0.7 m / h to 1.3 m / h, and reduces the water content.

[0071] β-CD adsorbs at the precipitation interface, and its rigid ring structure prevents Al(OH)3 colloids from encapsulating rare earth particles, ensuring that aluminum-iron hydroxide is loaded onto the surface of rare earth crystal nuclei, forming a uniform core-shell structure, thus reducing the sludge floc density from 1.2 g / cm³. 3 Increased to 1.8 g / cm³ 3 The volume of sludge decreases.

[0072] The following effects are produced by introducing sodium citrate and β-CD:

[0073] 1. Improved fluoride removal efficiency, doubled utilization of active sites, increased exposure of rare earth crystal nuclei, and Al / Fe shell providing auxiliary adsorption sites, resulting in a significant increase in adsorption capacity; enhanced resistance to interference, particularly in PO4. 3- =10mg / L, SO4 2- Under extreme conditions of 200 mg / L, the effluent F⁻ is consistently ≤0.5 mg / L;

[0074] 2. Sludge improvement and increased floc density: Thermally driven LaF3 crystal nuclei form the framework, encapsulated with Al(OH)3, increasing the overall floc density from 1.2 g / cm³. 3 Increased to 1.8 g / cm³ 3 Improved moisture content and settling velocity: sludge moisture content decreased from 98.5% to 91.5%, and settling velocity increased.

[0075] 3. Extended cycle life and enhanced pore stability: the 2-5nm mesopores generated by the decomposition of β-CD during freeze-drying increase the specific surface area by 30%, delaying CaF2 blockage; metal dissolution is inhibited, and the dense core-shell structure protects Al... 3+ The dissolution concentration should be controlled below 0.05 mg / L.

[0076] Example 2: The above Example 1, through the action of sodium citrate and β-cyclodextrin, reconstructs the precipitation sequence at the molecular level, blocks ion competition, and optimizes the crystallization process, achieving a triple breakthrough in defluoridation efficiency, sludge performance, and stability. It solves the defects of metal precipitation stratification and lack of anti-interference mechanism, which leads to insufficient utilization of active sites, loose floc structure, and difficulty in achieving stable compliance in complex water quality. To further improve the comprehensive performance of the defluoridator, further improvements are made based on Example 1.

[0077] The β-CD includes microsphere β-CD and porous granular β-CD; the mass ratio of microsphere β-CD to porous granular β-CD is 1:4;

[0078] Among them, the average particle size of the microsphere β-CD is 0.5 μm, and the particle size distribution range is 0.45~0.55 μm; the surface is modified with sulfonic acid groups (-SO3H);

[0079] Microsphere-type β-CD was prepared by spray drying, with the inlet temperature controlled at 75~85℃. Propanolactone was used as the sulfonating agent, and the molar ratio of β-cyclodextrin to propanelactone was 1:1.1~1.3.

[0080] The porous β-CD particles have an average particle size of 150 μm and a particle size distribution range of 140–160 μm; the porosity is 35 ± 5% and the pore size is 2–10 nm; they are cross-linked with glutaraldehyde (cross-linking degree 0.55–0.65 mol / mol).

[0081] Porous granular β-CD was prepared using silica nanospheres with a particle size of 20 nm as templates. The templates were removed by calcination at 450 °C, and then cross-linked with glutaraldehyde. The molar ratio of β-cyclodextrin to glutaraldehyde was 1:0.55~0.65.

[0082] The addition of microsphere-type β-CD and porous particle-type β-CD specifically involves...

[0083] Step 1. Add aluminum salt, iron salt, and rare earth elements to 200mL of deionized water and stir at 200rpm to dissolve.

[0084] First, add porous granular β-CD and stir at 200 rpm for 30 minutes to build a macroscopic framework;

[0085] Then add microsphere β-CD, stir at 300 rpm for 2 hours, the system temperature rises to 32±1℃, and the β-CD inclusion is exothermic;

[0086] Add sodium citrate, maintain water temperature at 25±3℃, and stir for a total of 3 hours.

[0087] Based on Experiment D2 of Embodiment 1, an experiment was conducted on the technical solution of the above embodiments. Experiment D4 was conducted. The difference between D4 and D2 is that β-CD in D4 includes microsphere β-CD and porous particle β-CD. The mass ratio of microsphere β-CD to porous particle β-CD is 1:4. The detection results are shown in Table 3 below.

[0088]

[0089] The technical solutions described in the embodiments of this application above have at least the following technical effects or advantages:

[0090] A single β-cyclodextrin can only capture dissolved PO4. 3- For colloidal PO4 3- Low retention rate, weak shear resistance of traditional flocs, easy breakage at high flow velocities leading to decreased settling efficiency, and La under low temperature conditions 3+ Slow nucleation affects the efficiency of active site generation. This problem is solved by introducing a combination of 0.5μm microsphere β-cyclodextrin and 150μm porous particulate β-cyclodextrin.

[0091] A technological breakthrough was achieved by combining 0.5 μm sulfonated microspheres of β-cyclodextrin with 150 μm cross-linked porous particles of β-cyclodextrin, and constructing a mechanism for dynamic capture, directional transport, and confined precipitation. The sulfonic acid groups on the surface of the microspheres instantaneously capture dissolved phosphate ions through electrostatic attraction, and simultaneously release reaction heat to drive rare earth ion nucleation. The particles physically trap colloidal pollutants with a rigid framework and precise pore size. The pre-placed citrate-aluminum ion complex traps in the pores achieve irreversible locking of pollutants. The two work synergistically through a Brownian motion-mediated directional transport pathway. Under the guidance of the sodium citrate hydrogen bond network, aluminum ions are precisely positioned in the particle pore reaction zone, avoiding competitive interference while ensuring complete exposure of rare earth crystal nuclei and confined deposition of aluminum-iron hydroxide.

[0092] 0.5μm microsphere-type β-cyclodextrin efficiently captures dissolved phosphate ions through strong electrostatic attraction generated by its surface sulfonic acid groups. Its nanoscale size ensures an ultra-high diffusion rate, while the heat released by the inclusion reaction drives the local temperature to 35℃, significantly improving the nucleation rate of lanthanum ions. Meanwhile, 150μm porous particulate β-cyclodextrin forms a micron-scale trapping network with a cross-linked reinforced rigid framework and pore size, physically capturing colloidal contaminants. Its high-porosity framework provides an irreversible precipitation reaction chamber for the citrate-aluminum ion complex trap.

[0093] The combination of microsphere-type β-cyclodextrin and porous particulate-type β-cyclodextrin enables dynamic capture and directional transport to a fixed depth, with the microspheres adsorbing PO4. 3- The particles are transported into the pores via Brownian motion and locked by pre-placed citrate-aluminum ion complex traps within the pores, thus avoiding competitive interference caused by the escape of colloidal contaminants in traditional processes. The microspheres exothermically conduct heat to the particle skeleton, uniformly increasing the temperature rise within the pores and simultaneously optimizing the kinetic matching degree of lanthanum ion nucleation and aluminum ion precipitation. Meanwhile, the particle skeleton resists the shear force of water flow, protecting the complete growth of rare earth crystal nuclei.

[0094] The carboxyl groups of sodium citrate form a hydrogen bond network with the hydroxyl groups on the surface of particulate β-cyclodextrin, guiding aluminum ions into the particle pores and forming a citrate-aluminum ion-β-cyclodextrin composition, thus blocking PO4. 3- Competition for active sites;

[0095] The synergy between microsphere-type β-cyclodextrin and porous particulate-type β-cyclodextrin is not a functional superposition, but a directional transport pathway of pollutants achieved through Brownian motion. The dissolved phosphate ions captured by the microspheres are directionally transported into the pores of the particles. Guided by the hydrogen bond network constructed by sodium citrate, aluminum ions are located in the pore reaction zone, avoiding colloidal interference while achieving complete exposure of rare earth crystal nuclei and confined deposition of aluminum iron hydroxide, thereby reconstructing the pollutant removal pathway at the molecular level.

[0096] The combined use of microspherical β-cyclodextrin and porous granular β-cyclodextrin further enhances the performance of the defluoridator. In terms of defluoridation efficiency, the staged capture of dissolved and colloidal phosphate ions significantly improves the total removal rate, increasing it from 84% to 94%, and reducing the residual phosphate concentration to below 0.3 mg / L. The directional sedimentation process ensures the exposure of rare earth active sites, further reducing the effluent fluoride concentration and increasing the adsorption capacity. Regarding sludge performance, the granular skeleton imparts a dense, concrete-like structure to the flocs, increasing the settling rate. The permanent skeleton formed by confined crystallization within the pores prevents the flocs from becoming loose. In terms of system tolerance, the upper limit of colloidal pollutant tolerance is expanded, further improving the applicable range. The granular skeleton is cross-linked with glutaraldehyde, and the cross-linked and strengthened granular skeleton extends the cycle life. The constructed mechanism of dynamic capture, directional transport, and confined sedimentation provides a technical solution for the treatment of highly toxic fluoride-containing wastewater that is universal, economical, and engineering reliable.

[0097] Example 3: Example 2 solved the problem of single β-cyclodextrin affecting colloidal PO4 by introducing a combination of 0.5μm microsphere-type β-cyclodextrin and 150μm porous particulate-type β-cyclodextrin. 3- Low retention, weak shear resistance of traditional flocs, low temperature La 3+ To address issues such as slow nucleation, this study achieved a significant improvement in defluorination efficiency, improved sludge settling performance, increased system tolerance to colloidal pollutants, and extended cycle life. Further improvements were made based on Example 2 to further enhance the defluorination effect.

[0098] The porous particulate β-cyclodextrin is coated to form a core-shell structure, including a core layer and a shell layer. The core layer is porous particulate β-cyclodextrin cross-linked with glutaraldehyde, and the shell layer is a pH-responsive layer formed by calcium alginate encapsulating sodium citrate.

[0099] The specific steps for preparing the core-shell structure are as follows:

[0100] (1) Core layer pretreatment:

[0101] Take 150μm porous β-CD particles and crosslink them with glutaraldehyde;

[0102] Vacuum impregnation with 0.1M CaCl2 solution for 30 minutes results in calcium ions being loaded into the pores and surface, forming pre-calcified β-CD particles.

[0103] (2) Shell covering:

[0104] Precalcified β-CD particles were placed in a fluidized bed and kept suspended by hot air at 40°C.

[0105] Atomized spray coating solution, 10% sodium alginate and 5% sodium citrate:

[0106] The shell solution is a mixture of 10% sodium alginate and 5% sodium citrate; the atomization pressure is 0.2 MPa; the spraying rate is 2 g / min; and the number of spraying rounds is 8, with a 3-minute interval between each round.

[0107] (3) Steam crosslinking and curing:

[0108] The sodium alginate was treated with 0.1 M CaCl2 steam (65 °C) for 20 minutes to crosslink and form a gel network, thus forming core-shell structured particles.

[0109] The core-shell structure particles have a particle size of 185±5μm.

[0110] In the preparation of the defluorinating agent after introducing core-shell structured particles, in step 2, the mixture obtained in step 1 is added dropwise to a 10% NaOH solution at a rate of ≤5 mL / min; the pH is monitored in real time, and the pH is controlled to slowly rise from 6.0 to 8.5; after the addition is completed, stirring is continued for 30 minutes.

[0111] In step 3, the precipitate is separated by centrifugation (8000 rpm, 8 minutes); without grinding, the core-shell functional powder is obtained directly.

[0112] Based on Experiment D4 of Embodiment 2, an experiment was conducted on the technical solution of the above embodiments. Experiment D5 was conducted, and the difference between D5 and D4 is that the porous β-CD particles are core-shell structured particles. The test results are shown in Table 4 below.

[0113]

[0114] The technical solutions described in the embodiments of this application have at least the following technical effects or advantages:

[0115] By modifying the core-shell structure of porous particulate β-cyclodextrin, a composite carrier of β-CD core and sodium citrate shell is constructed. Based on the dual-particle-size synergistic mechanism, the combination of targeted sustained release and energy feedback is further introduced to solve the problems of metal ion precipitation timing mismatch and low reaction heat energy utilization in traditional processes.

[0116] The core-shell structure achieves spatial isolation and intelligent response of functional components. 150μm porous β-CD particles serve as a rigid carrier core layer, whose cross-linked framework and precise pore size (2-10nm) provide a physical retention network and confined precipitation space. The shell layer embeds sodium citrate through a sodium alginate-calcium ion cross-linking network to form a pH-responsive intelligent slow-release unit. When the system pH>7.5, the shell layer swells, and sodium citrate is released into the core pores at a controllable rate, matching rare earth precipitation. Meanwhile, the reaction heat of the microsphere β-CD capturing pollutants is efficiently conducted through the core-shell interface, driving the temperature inside the core pores to rise, further improving the nucleation rate of lanthanum ions and simultaneously optimizing the directional deposition path of aluminum iron hydroxide.

[0117] At the molecular level, the on-demand release of sodium citrate avoids the disordered precipitation sequence caused by premature complexation of aluminum and iron ions, ensuring the exposure of rare earth crystal nuclei. At the mesoscopic level, the confined space of the core-pore allows aluminum-iron hydroxide to deposit orderly within 2-10 nm pores, forming composite active sites of LaF3 and Al(OH)3 with a near-single-crystal structure. The increased binding energy leads to a further improvement in fluoride ion adsorption capacity. At the macroscopic level, the mechanical strength and thermal feedback of the core-shell carrier increase the sludge skeleton density to 2.4 g / cm³. 3 This achieves a further breakthrough in moisture content. Specifically, the thermal energy released by the microspheres dynamically capturing pollutants is efficiently converted through the core-shell structure, further improving utilization. This process involves pollutant capture, heat release, thermal energy feedback, and directional sedimentation, solving the problems of energy dissipation and disordered sedimentation in discrete component processes.

[0118] The core-shell carrier's targeted and controlled release of sodium citrate reduced phosphate residue to the 0.05 mg / L level, further improving the fluoride ion removal depth; the thermal energy closed-loop drive further improved sludge moisture content; and the cross-linked core-shell framework's resistance to centrifugal breakage further extended the cycle life.

[0119] By constructing a core-shell structured β-CD and sodium citrate composite carrier, calcium ions are loaded onto a 150μm cross-linked porous β-cyclodextrin core layer to form precipitation microcavities. A pH-responsive shell layer of sodium citrate is then formed by encapsulating sodium citrate with calcium alginate. Through a cascade reaction of pH-triggered targeted slow release and energy feedback closed loop, the comprehensive performance of the defluorinating agent is further improved. When the system pH is >7.5, the carrier intelligently swells and releases sodium citrate into the core pores, matching the rare earth precipitation process. Simultaneously, 0.5μm sulfonated microspheres of β-cyclodextrin dynamically capture pollutants and release reaction heat. The heat energy is conducted through the core and shell to increase the temperature inside the pores, driving the increase of lanthanum ion nucleation rate and guiding the confined directional deposition of aluminum iron hydroxide within 2-10nm pores, forming a single-crystal active structure with LaF3 nuclei and Al(OH)3 coating.

[0120] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A defluorinating agent, characterized in that, Included by weight: 5-10 parts aluminum salt, 5-10 parts iron salt, 15-20 parts rare earth materials, sodium citrate and β-cyclodextrin; The amount of sodium citrate added is 5%-10% of the total mass of aluminum salts, iron salts, and rare earth materials; The amount of β-cyclodextrin added is 30%-50% of the mass of sodium citrate; The β-cyclodextrin includes microspherical β-cyclodextrin and porous particulate β-cyclodextrin, with a mass ratio of 1:

4. The microsphere-type β-cyclodextrin has a particle size of 0.45-0.55 μm and its surface is modified with sulfonic acid groups; The porous granular β-cyclodextrin has a particle size of 140-160 μm and a pore size of 2-10 nm.

2. The defluorinating agent as described in claim 1, characterized in that, The microsphere-type β-cyclodextrin was prepared by spray drying at an inlet temperature of 75-85℃. The sulfonating agent was propanesulfonate lactone, and the molar ratio of β-cyclodextrin to propanesulfonate lactone was 1:1.1-1.

3.

3. The defluorinating agent as described in claim 1, characterized in that, The porous particulate β-cyclodextrin is coated to form a core-shell structure, including a core layer and a shell layer; The core layer is a porous particulate β-cyclodextrin cross-linked with glutaraldehyde; The shell is a pH-responsive layer formed by embedding sodium citrate in calcium alginate.

4. The defluorinating agent as described in claim 1, characterized in that, The aluminum salt is aluminum chloride, the iron salt is polyferric chloride, and the rare earth material is at least one of lanthanum nitrate and cerium chloride.

5. A method for preparing the defluorinating agent according to any one of claims 1-4, characterized in that, Specifically, the following steps are included: (a) Dissolve aluminum salts, iron salts, rare earth materials, sodium citrate, and β-cyclodextrin in water and stir; (b) Add the mixture dropwise to the NaOH solution, control the endpoint pH, and a precipitate will form; (c) Centrifuge to separate the precipitate, wash and dry it to obtain powder; (d) Dissolve chitosan in acetic acid, add the powder from step (c) and stir to obtain a mixture; (e) The mixture is pre-frozen and then freeze-dried under vacuum to obtain the final product.

6. The method for preparing the defluorinating agent as described in claim 5, characterized in that, Step (b) Add the mixture dropwise to the 10% NaOH solution at a rate of ≤10 mL / min, and control the endpoint pH to be 8.0-8.5.

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