Aluminum-based high-efficiency fluoride removal agent, and preparation method and application thereof

Abstract

The application discloses an aluminum-based high-efficiency fluorine removal agent and a preparation method and application thereof, and belongs to the technical field of water treatment agents. The fluorine removal agent is mainly prepared from polyaluminum sulfate with a salt base of 45-65% and an Al2O3 content of 8-12%, and is compounded with a silicon-aluminum hybrid, a calcium / magnesium active coordination component, a hydroxyl enhancer, multiple stability aids and a cationic organic modified porous inorganic framework. A polyaluminum hydroxide activation solution is first prepared, then a silicon-aluminum hybrid is introduced to perform in-situ co-curing to obtain a precursor, the modified inorganic framework and the stabilizer are compounded, and the liquid or powder product is prepared through curing and impurity removal. The application relies on a layered calcium-aluminum-silicon acid hybrid structure to construct multi-stage fluorine capture sites in cooperation with a double-metal hydroxyl complex, has a wide pH interval, excellent flocculation and sedimentation separation performance, low reagent dosage load and low sludge output, can realize deep fluorine removal of various fluorine-containing water bodies to meet the standards, has no organic residue risk, and has strong engineering adaptability.

Description

Technical Field

[0001] This invention relates to the field of water treatment agents, and more specifically, to an aluminum-based high-efficiency defluoridator, its preparation method, and its application. Background Technology

[0002] Fluorine is an essential trace element for the human body, but long-term excessive concentrations of fluoride ions in water can harm human health, easily leading to conditions such as dental fluorosis and skeletal fluorosis. my country's drinking water hygiene standards and integrated wastewater discharge standards both impose strict limits on fluoride content in water. With the rapid development of industries such as photovoltaics, lithium batteries, electrolytic aluminum, coal chemicals, and electroplating, the volume and concentration of industrial fluoride-containing wastewater discharged are large, creating an urgent need for stable, efficient, and low-cost deep fluoride removal technologies.

[0003] Currently, the treatment of fluoride-containing water mainly employs chemical precipitation, adsorption, and coagulation-precipitation methods. Among these, metal salts, represented by aluminum and iron salts, are the most widely used due to their combined coagulation and fluoride removal functions. Polyaluminum sulfate (PAS) has attracted attention due to its high basicity, good flocculation performance, and strong adaptability to water quality. However, conventional aluminum and iron salt fluoride removal agents still have many shortcomings in practical applications. Single aluminum salts are difficult to fully polymerize during hydrolysis, resulting in a low content of active aluminum hydroxyl species and insufficient active sites for complexation and adsorption with fluoride ions, thus limiting the fluoride ion capture capacity and removal rate. Furthermore, these agents have a narrow effective range; their fluoride removal efficiency decreases significantly under neutral and weakly alkaline conditions, often requiring substantial pre-adjustment of the water's pH, increasing agent consumption and operational burden. In addition, the flocs formed by conventional aluminum salt agents are small and loose, with slow settling speed, making solid-liquid separation difficult, and the effluent is prone to residual turbidity, resulting in a high load on the sedimentation unit. In order to ensure that the effluent meets the standards, the dosage is increased, which further leads to problems such as high sludge production, difficulty in dewatering, and increased operating costs.

[0004] While polyaluminum sulfate (PAS) outperforms single aluminum salts, its surface active sites are insufficient for direct deep defluorination, resulting in slow fluoride complexation kinetics and difficulty in achieving stable deep purification levels of fluoride ions in the effluent. To improve its defluorination performance, existing modification techniques often introduce high-valence metal salts such as zirconium and titanium salts into the agent, or utilize organic polymeric flocculants to enhance flocculation and sedimentation. However, the former suffers from high raw material costs, complex preparation processes, and poor product stability, while the latter easily leads to organic residues and secondary pollution, making it unsuitable for high-standard water bodies such as drinking water. Both approaches hinder large-scale engineering applications. Therefore, this invention provides an aluminum-based high-efficiency defluorinating agent, its preparation method, and its application to solve the aforementioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide an aluminum-based high-efficiency defluoridator, its preparation method, and its application. It can construct multi-level fluoride capture sites by relying on the layered calcium-aluminum-silica hybrid structure and the synergistic bimetallic hydroxyl complexation. It has a wide pH range adaptability to water quality, excellent floc settling and separation performance, low agent dosage, and low sludge production. It can achieve deep defluoridation of various fluoride-containing water bodies to meet standards, with no risk of organic residue, and strong engineering adaptability.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0007] This invention provides an aluminum-based high-efficiency defluorinating agent, which, by weight, comprises the following raw material components: 60-85 parts of polyaluminum sulfate, 3-15 parts of silicon-aluminum hybrid, 5-15 parts of active coordination component, 3-10 parts of hydroxyl enhancer, 0.5-2 parts of stabilizing agent, and 2-8 parts of modified inorganic framework component.

[0008] The polyaluminum sulfate has an Al2O3 content of 8-12% and a basicity of 45-65%; the active coordinating component is one or a compound of calcium chloride and magnesium chloride in any proportion; the hydroxyl enhancer is one or a compound of calcium aluminate powder and aluminum hydroxide in any proportion; and the stabilizing agent is one or a compound of sodium dihydrogen phosphate, sodium citrate, sodium hexametaphosphate, and sodium gluconate in any proportion.

[0009] This invention also provides a method for preparing the above-mentioned aluminum-based high-efficiency defluorinating agent, comprising the following preparation steps:

[0010] (1) Dissolve polyaluminum sulfate in water to prepare a solution with a mass concentration of 25%-40%, and slowly add hydroxyl enhancer at 50-65℃ and 240-300rpm to adjust the basicity of the system to 45-65%. Continue to mature for 30-90min to allow polyaluminum sulfate to undergo controlled hydrolysis and hydroxyl polymerization reaction, forming a polyaluminum hydroxyl activated solution with polyaluminum hydroxyl polymer active species as the main body;

[0011] (2) After the basicity of the above system stabilizes, add the silicon-aluminum hybrid at 50-65℃ and add the active coordination component. Stir at 240-300 rpm and co-mature in situ at constant temperature for 60-120 min to form a precursor solution.

[0012] (3) Add the modified inorganic framework component to the above hydroxyl hybrid and disperse it fully for 30-60 min. Then add the stabilizing agent and continue stirring for 20-40 min until the system is fully and uniformly dispersed. After aging at room temperature for 2-6 h, remove coarse particulate impurities through a 100-200 mesh sieve to obtain a liquid defluorinating agent, or obtain a powder defluorinating agent by spray drying.

[0013] Preferably, the preparation step (2) of the silicon-aluminum hybrid is as follows:

[0014] S1. Prepare an aluminum salt solution with a mass concentration of 4-10% (Al2O3) by aluminum sulfate. Slowly add a composite precipitant at 60-75℃ and 250-400 rpm to adjust the pH of the system to 7.5-8.5, generate aluminum hydroxyl gel, and cure at a constant temperature for 1-3 hours to convert it into boehmite gel. After washing to remove soluble sulfate, add acetic acid to adjust the pH of the system to 3.5-4.5, and gel at 70-85℃ and 300-500 rpm for 0.5-2 hours to obtain boehmite sol.

[0015] S2. Using the pseudoboehmite sol obtained in step S1 as the aluminum source, calcium chloride is added at a calcium to aluminum molar ratio of 1.5-2.5. The pH of the system is adjusted to 10.0-11.5 at 70-85℃ and 300-500rpm, and the system is crystallized at a constant temperature for 3-6 hours to obtain an active calcium aluminum layered hydroxide slurry.

[0016] S3. Sodium silicate is diluted to prepare a water glass solution with a mass concentration of 3-6% based on SiO2. Sulfuric acid is added for activation and the pH is adjusted to 5.0-6.0. After aging for 0.5-1h, active silicic acid is obtained. The active silicic acid is added to the above calcium-aluminum layered hydroxide slurry at a mass ratio of SiO2 to Al2O3 of 0.10-0.40. The mixture is reacted at 60-80℃ and 300-500rpm for 1-3h. After filtration and drying, a silicon-aluminum hybrid is obtained.

[0017] Preferably, the composite precipitant in step S1 is a mixture of ammonia and ammonium bicarbonate, with a mass ratio of ammonia to ammonium bicarbonate of (1.5-2.5):1 and an ammonia concentration of 20-25 wt%.

[0018] Preferably, the preparation steps of the modified inorganic framework component in step (3) are as follows:

[0019] A1. The inorganic framework component is immersed in hydrochloric acid with a concentration of 0.5-3 mol / L for acid activation, with a solid-liquid mass ratio of 1:(5-8). The activation is carried out at 50-80℃ for 1-4 hours. After washing with water until it is nearly neutral, it is calcined at 350-550℃ for 1-3 hours to obtain the acidified framework.

[0020] A2. Disperse the acidified skeleton in water at a solid-liquid mass ratio of 1:(5-8), add 1-10% of polydimethyldiallylammonium chloride by mass of the acidified skeleton, adjust the pH of the system to 5.0-7.0, and react at 50-80℃ and 200-400rpm for 1-3h. After solid-liquid separation, drying and pulverization, the modified inorganic skeleton component is obtained.

[0021] Preferably, the inorganic framework raw material in step A1 is at least one of diatomaceous earth, zeolite powder, bentonite, attapulgite, and kaolin, and the acid used for acidification and activation is hydrochloric acid.

[0022] Preferably, in step (1), the polyaluminum sulfate is prepared into an aqueous solution with a mass concentration of 25-40%, and the basicity is adjusted under the conditions of temperature control at 50-65℃ and stirring at 240-300rpm, and then aged at a constant temperature for 30-90min.

[0023] Preferably, in step (2), the constant temperature co-curing temperature is 50-65℃, the stirring speed is 240-300rpm, and the curing time is 60-120min; in step (3), the skeleton dispersion time is 30-60min, the additive stirring time is 20-40min, the room temperature curing time is 2-6h, and impurities are removed by using a 100-200 mesh sieve.

[0024] This invention also provides an application method for an aluminum-based high-efficiency defluoridating agent, which is directly added to various industrial fluoride-containing wastewaters to efficiently adsorb, complex, and fix fluoride ions in the water, rapidly reduce the fluoride ion concentration in the water, and stably achieve deep purification treatment of fluoride-containing water.

[0025] In summary, the present invention has the following beneficial effects:

[0026] 1. This invention uses polyaluminum sulfate with specific basicity and Al2O3 content as the main component. A process route is employed: first, a polyaluminum hydroxide activation solution is prepared by adjusting the basicity; then, functional components are introduced through in-situ co-curing. This constructs an aluminum-based high-efficiency defluorination agent, effectively overcoming the shortcomings of existing aluminum salt agents, such as insufficient active sites, limited fluoride complexation capacity, and difficulty in consistently achieving deep defluorination standards. Precise control of the basicity allows for the complete hydrolysis and polymerization of polyaluminum sulfate, generating polyaluminum hydroxide active species rich in surface hydroxyl groups. During in-situ co-curing, these species continuously couple with the surface hydroxyl groups of the silicon-aluminum hybrid, significantly increasing the density of active hydroxyl sites. This allows for sufficient ligand exchange and complexation fixation of fluoride ions, thereby achieving deep purification standards under low dosage.

[0027] 2. The silica-alumina hybrid used in this invention is derived stepwise from the alkaline crystallization of boehmite sol and the condensation of active silica. It works synergistically with calcium and magnesium active coordination components, enabling the reagent to possess multiple fluoride removal capabilities, including ligand exchange, interlayer anion exchange, silica-alumina framework fixation, and bimetallic hydroxyl complexation. This overcomes the shortcomings of existing technologies, which have a single fluoride removal mechanism and a narrow applicable acid-base range. The boehmite sol provides a high density of active aluminum hydroxyl groups, while the active calcium-aluminum layered hydroxides construct multi-level fluoride capture sites through interlayer exchangeable anions and slow-release of structural calcium. The condensation of active silica introduces a silica-alumina framework, both adding fluoride fixation channels and supporting the layered structure to resist acid-base fluctuations. The complementary and superimposed acid-base activity ranges of each mechanism allow the reagent to effectively remove fluoride under neutral and weakly alkaline conditions without requiring significant adjustment of water pH, thus exhibiting a wide range of water quality adaptability.

[0028] 3. This invention introduces a porous inorganic framework modified by acid activation and cation grafting, and combines it with various stabilizing agents to produce dense, coarse flocs that settle rapidly, achieve thorough solid-liquid separation, and ensure stable storage. This overcomes the shortcomings of conventional aluminum salt agents, which produce small, loose flocs, settle slowly, and generate high sludge production. The porous inorganic framework, after acid activation, acts as a weighting and nucleation core to increase floc density and particle size. The cation groups grafted onto its surface electrostatically adsorb and bridge fine flocs and fluorine-containing particles, working in conjunction with the charge neutralization and sweeping action of polyaluminum sulfate to form a dense, easily settling matrix floc. The stabilizing agents inhibit excessive hydrolysis of polyaluminum species, ensuring long-term homogeneity of the agent and preventing stratification during storage.

[0029] 4. The overall process of this invention starts with inexpensive aluminum salts, combined with common inorganic raw materials and trace amounts of cationic modifiers. Each stage of precursors is continuously derived through common aqueous phase operations such as precipitation, solution, alkali crystallization, condensation, and co-curing. It has the advantages of simple preparation, low cost, and low risk of secondary pollution. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used, unless otherwise specified, were all purchased from conventional biochemical reagent stores. All quantitative experiments in the following examples were performed in triplicate, and the data are the average of the three replicates or the average ± standard deviation.

[0032] Diatomaceous earth, purchased from Shandong Zhengxing New Materials Co., Ltd., item number CG8;

[0033] Zeolite powder, purchased from Wuhan Jiyesheng Chemical Co., Ltd.;

[0034] Bentonite, purchased from Hubei Xinhongli Chemical Co., Ltd.;

[0035] Attapulgite clay, purchased from Shanghai Jieshikai Biotechnology Co., Ltd.;

[0036] Polydiallyl ammonium chloride, purchased from Taian Jiangzhou Biotechnology Co., Ltd., CAS No. ;

[0037] The following examples use a uniform water sample to evaluate the defluoridation performance, with fluoride-containing wastewater containing fluoride ions at a concentration of 100 mg / L, a pH of 7.0, and an initial turbidity of 31 NTU as the treatment target.

[0038] Example 1

[0039] This embodiment provides a method for preparing an aluminum-based high-efficiency defluorination agent, using the following technical solution:

[0040] Preparation of silicon-aluminum hybrid: Aluminum sulfate was prepared into an aluminum salt solution with a mass concentration of 6% (Al2O3). A composite precipitant with a mass ratio of ammonia to ammonium bicarbonate of 2.0:1 and ammonia concentration of 22 wt% was slowly added at 68℃ and 320 rpm. The pH of the system was adjusted to 8.0, generating an aluminum hydroxyl gel. After constant temperature aging for 2 h, it was converted into a pseudoboehmite gel. Soluble sulfate was washed away, and acetic acid was added to adjust the pH to 4.0. The pseudoboehmite sol was obtained by gelation at 80℃ and 400 rpm for 1 h. This sol was used as... An aluminum source was used, and calcium chloride was added at a calcium to aluminum molar ratio of 2.0. The pH was adjusted to 11.0 at 80℃ and 400 rpm, and the mixture was crystallized at this temperature for 4 hours to obtain an active calcium-aluminum layered hydroxide slurry. Sodium silicate was diluted to a water glass solution with a mass concentration of 4% (SiO2). Sulfuric acid was added to activate the solution, and the pH was adjusted to 5.5. The solution was aged for 0.5 hours to obtain active silicic acid. The active silicic acid was added to the above slurry at a SiO2 to Al2O3 mass ratio of 0.25. The mixture was reacted at 70℃ and 400 rpm for 2 hours, and then filtered and dried to obtain a silicon-aluminum hybrid.

[0041] Preparation of modified inorganic framework components: Diatomaceous earth was immersed in 1 mol / L hydrochloric acid and activated at 65℃ for 2 h at a solid-liquid mass ratio of 1:6. After washing with water until near neutral, it was calcined at 450℃ for 2 h to obtain an acidified framework. The acidified framework was dispersed in water at a solid-liquid mass ratio of 1:6, and 5% by weight of polydimethyldiallylammonium chloride was added to adjust the pH of the system to 6.0. The reaction was carried out at 65℃ and 300 rpm for 2 h. After solid-liquid separation, drying at 110℃ and pulverizing, modified diatomaceous earth was obtained.

[0042] Preparation of defluorinating agent: By weight, 70 parts of polyaluminum sulfate with an Al2O3 content of 10% were dissolved in water to prepare a solution with a mass concentration of 32%. At 58℃ and 270 rpm, 5 parts of calcium aluminate powder were added to adjust the basicity of the system to 55%, and the solution was aged at a constant temperature for 60 min to obtain polyaluminum hydroxide activated solution. At 58℃ and 270 rpm, 8 parts of the above-mentioned silicon-aluminum hybrid and 9 parts of calcium chloride were added to it, and the solution was aged in situ at a constant temperature for 90 min to obtain precursor solution. Then, 4 parts of the above-mentioned modified diatomaceous earth were added, and the solution was dispersed with ultrasonic frequency of 40 kHz and power of 300 W and mechanically stirred for 45 min. Then, 1 part of sodium dihydrogen phosphate was added and stirred continuously for 30 min until the system was uniform. After aging at room temperature for 4 h, the solution was filtered through a 150-mesh sieve to obtain liquid defluorinating agent.

[0043] Application and Effects: The defluoridating agent prepared in this embodiment was used to treat the above-mentioned fluoride-containing wastewater. It was added at a dosage of 1.5 g / L, mixed at 250 rpm for 2 min with rapid stirring, flocculated at 50 rpm for 12 min with slow stirring, and allowed to settle for 20 min. The fluoride ion concentration in the water was measured to be 0.48 mg / L, the fluoride ion removal rate was 99.52%, the average interfacial settling velocity from 0 to 10 min was 1.92 cm / min, the turbidity of the supernatant after 30 min of sedimentation was 0.62 NTU, and the dry sludge content was 121 mg / L.

[0044] Example 2

[0045] This embodiment provides a method for preparing an aluminum-based high-efficiency defluorination agent, using the following technical solution:

[0046] Preparation of silicon-aluminum hybrid: Aluminum sulfate was prepared into an aluminum salt solution with a mass concentration of 7% (Al2O3). A composite precipitant with a mass ratio of ammonia to ammonium bicarbonate of 2.2:1 and ammonia concentration of 23 wt% was slowly added at 72℃ and 380 rpm. The pH of the system was adjusted to 8.2, generating an aluminum hydroxyl gel. After constant temperature aging for 1.5 h, it was converted into a pseudoboehmite gel. Soluble sulfate was washed away, and acetic acid was added to adjust the pH to 3.8. The pseudoboehmite sol was obtained by gelation at 82℃ and 450 rpm for 0.8 h. This sol was used as... An aluminum source was used, and calcium chloride was added at a calcium to aluminum molar ratio of 2.0. The pH was adjusted to 11.2 at 82℃ and 450 rpm, and the mixture was crystallized at this temperature for 3.5 h to obtain an active calcium-aluminum layered hydroxide slurry. Sodium silicate was diluted to a water glass solution with a mass concentration of 5% (SiO2). Sulfuric acid was added to activate the solution, and the pH was adjusted to 5.5. The solution was aged for 0.8 h to obtain active silicic acid. The active silicic acid was added to the above slurry at a SiO2 to Al2O3 mass ratio of 0.30, and the mixture was reacted at 75℃ and 450 rpm for 1.5 h. After filtration and drying, a silicon-aluminum hybrid was obtained.

[0047] Preparation of modified inorganic framework components: Zeolite powder was immersed in 1.5 mol / L hydrochloric acid and activated at 70℃ for 1.5 h at a solid-liquid mass ratio of 1:6. After washing with water until near neutral, it was calcined at 500℃ for 1.5 h to obtain an acidified framework. The acidified framework was dispersed in water at a solid-liquid mass ratio of 1:6, and 6% by weight of polydimethyldiallylammonium chloride was added to adjust the pH of the system to 6.2. The reaction was carried out at 70℃ and 350 rpm for 1.5 h. After solid-liquid separation, drying at 110℃ and pulverizing, modified zeolite powder was obtained.

[0048] Preparation of defluorinating agent: By weight, 75 parts of polyaluminum sulfate with an Al2O3 content of 10% were dissolved in water to prepare a solution with a mass concentration of 35%. At 60℃ and 285 rpm, 6 parts of calcium aluminate powder were added to adjust the basicity of the system to 58%, and the solution was aged at a constant temperature for 50 min to obtain polyaluminum hydroxide activated solution. At 60℃ and 285 rpm, 10 parts of the above-mentioned silicon-aluminum hybrid and 10 parts of calcium chloride were added to the solution, and the solution was aged in situ at a constant temperature for 80 min to obtain precursor solution. Then, 5 parts of the above-mentioned modified zeolite powder were added, and the solution was dispersed with ultrasonic frequency of 40 kHz and power of 320 W and mechanically stirred for 40 min. Subsequently, 1.5 parts of a stability additive composed of sodium dihydrogen phosphate and sodium citrate in a mass ratio of 2:1 were added and stirred continuously for 28 min until the system was homogeneous. After aging at room temperature for 3.5 h, the solution was filtered through a 160-mesh sieve to obtain liquid defluorinating agent.

[0049] Application and Effects: The defluoridating agent prepared in this embodiment was used to treat the above-mentioned fluoride-containing wastewater. It was added at a dosage of 1.5 g / L, mixed at 250 rpm for 2 min with rapid stirring, flocculated at 50 rpm for 12 min with slow stirring, and allowed to settle for 20 min. The fluoride ion concentration in the water was measured to be 0.31 mg / L, the fluoride ion removal rate was 99.69%, the average interface settling velocity from 0 to 10 min was 2.06 cm / min, the turbidity of the supernatant after 30 min of sedimentation was 0.47 NTU, and the dry sludge content was 112 mg / L.

[0050] Example 3

[0051] This embodiment provides a method for preparing an aluminum-based high-efficiency defluorination agent, using the following technical solution:

[0052] Preparation of silicon-aluminum hybrid: Aluminum sulfate was prepared into an aluminum salt solution with a mass concentration of 5% (Al2O3). A composite precipitant with a mass ratio of 1.6:1 (ammonium bicarbonate, 20 wt% ammonia) was slowly added at 62℃ and 270 rpm. The pH of the system was adjusted to 7.6, generating an aluminum hydroxyl gel. After constant temperature aging for 2.8 h, it was converted into a pseudoboehmite gel. Soluble sulfate was washed away, and acetic acid was added to adjust the pH to 4.3. The pseudoboehmite sol was obtained by gelation at 72℃ and 320 rpm for 1.8 h. This sol was used as... An aluminum source was used, and calcium chloride was added at a calcium to aluminum molar ratio of 1.6. The pH was adjusted to 10.3 at 72°C and 320 rpm, and the mixture was crystallized at this temperature for 5.5 h to obtain an active calcium-aluminum layered hydroxide slurry. Sodium silicate was diluted to a water glass solution with a SiO2 mass concentration of 3.5%, activated with sulfuric acid, and the pH was adjusted to 5.2. The solution was aged for 1 h to obtain active silicic acid. The active silicic acid was added to the above slurry at a SiO2 to Al2O3 mass ratio of 0.15, and the mixture was reacted at 62°C and 320 rpm for 2.8 h. After filtration and drying, a silicon-aluminum hybrid was obtained.

[0053] Preparation of modified inorganic framework components: Bentonite was immersed in 0.8 mol / L hydrochloric acid and activated at 55℃ for 3.5 h at a solid-liquid mass ratio of 1:5. After washing with water until near neutral, it was calcined at 380℃ for 2.8 h to obtain an acidified framework. The acidified framework was dispersed in water at a solid-liquid mass ratio of 1:5, and 3% by weight of polydimethyldiallylammonium chloride was added to adjust the pH of the system to 5.5. The reaction was carried out at 55℃ and 220 rpm for 2.8 h. After solid-liquid separation, drying at 105℃ and pulverizing, modified bentonite was obtained.

[0054] Preparation of defluorinating agent: By weight, 62 parts of polyaluminum sulfate with an Al2O3 content of 9% were dissolved in water to prepare a solution with a mass concentration of 27%. At 52℃ and 250rpm, 3 parts of aluminum hydroxide were added to adjust the basicity of the system to 48%, and the solution was aged at a constant temperature for 85min to obtain polyaluminum hydroxide activated solution. At 52℃ and 250rpm, 4 parts of the above-mentioned silicon-aluminum hybrid and 6 parts of magnesium chloride were added to the solution, and the solution was aged in situ at a constant temperature for 115min to obtain precursor solution. Then, 2.5 parts of the above-mentioned modified bentonite were added, and the solution was dispersed with ultrasonic frequency of 40kHz and power of 270W and mechanically stirred for 55min. Then, 0.6 parts of sodium hexametaphosphate were added and stirred continuously for 38min until the system was uniform. After aging at room temperature for 5.5h, the solution was filtered through a 120-mesh sieve and spray-dried to obtain powder defluorinating agent.

[0055] Application and Effects: The defluoridating agent prepared in this embodiment was used to treat the above-mentioned fluoride-containing wastewater. It was added at a dosage of 1.5 g / L, mixed at 250 rpm for 2 min with rapid stirring, flocculated at 50 rpm for 12 min with slow stirring, and allowed to settle for 20 min. The fluoride ion concentration in the water was measured to be 0.74 mg / L, the fluoride ion removal rate was 99.26%, the average interfacial settling velocity from 0 to 10 min was 1.77 cm / min, the turbidity of the supernatant after 30 min of sedimentation was 0.83 NTU, and the dry sludge content was 108 mg / L.

[0056] Example 4

[0057] This embodiment provides a method for preparing an aluminum-based high-efficiency defluorination agent, using the following technical solution:

[0058] Preparation of silicon-aluminum hybrid: Aluminum sulfate was prepared into an aluminum salt solution with a mass concentration of 9% (Al2O3). A composite precipitant with a mass ratio of 2.4:1 (ammonium bicarbonate, 24 wt% ammonia) was slowly added at 74℃ and 390 rpm. The pH of the system was adjusted to 8.4, generating an aluminum hydroxyl gel. After constant temperature aging for 1.2 h, it was converted into a pseudoboehmite gel. Soluble sulfate was washed away, and acetic acid was added to adjust the pH to 3.6. The solution was then gelled at 84℃ and 480 rpm for 0.6 h to obtain a pseudoboehmite sol. This sol was used as the aluminum source. Calcium chloride was added at a calcium to aluminum molar ratio of 2.4, and the pH was adjusted to 11.4 at 84℃ and 480 rpm. The mixture was then crystallized at this temperature for 3.2 h to obtain an activated calcium-aluminum layered hydroxide slurry. Sodium silicate was diluted to a water glass solution with a SiO2 mass concentration of 5.5%, activated with sulfuric acid, and the pH was adjusted to 5.8. The solution was then aged for 0.8 h to obtain activated silicic acid. The activated silicic acid was added to the above slurry at a SiO2 to Al2O3 mass ratio of 0.35, and the mixture was reacted at 78℃ and 480 rpm for 1.2 h. After filtration and drying, a silicon-aluminum hybrid was obtained.

[0059] Preparation of modified inorganic framework components: Attapulgite was immersed in 2.5 mol / L hydrochloric acid and activated at 78℃ for 1.2 h at a solid-liquid mass ratio of 1:8. After washing with water until near neutral, it was calcined at 540℃ for 1.2 h to obtain an acidified framework. The acidified framework was dispersed in water at a solid-liquid mass ratio of 1:8, and 8% by weight of polydimethyldiallylammonium chloride was added to adjust the pH of the system to 6.5. The reaction was carried out at 78℃ and 380 rpm for 1.2 h. After solid-liquid separation, drying at 120℃ and pulverizing, modified attapulgite was obtained.

[0060] Preparation of defluorinating agent: By weight, 84 parts of polyaluminum sulfate with an Al2O3 content of 11% were dissolved in water to prepare a solution with a mass concentration of 38%. At 64℃ and 295 rpm, 6 parts of calcium aluminate powder and 3 parts of aluminum hydroxide were added to adjust the basicity of the system to 63%, and the solution was aged at a constant temperature for 35 min to obtain polyaluminum hydroxide activated solution. At 64℃ and 295 rpm, 14 parts of the above-mentioned silicon-aluminum hybrid, 10 parts of calcium chloride, and 4 parts of magnesium chloride were added to the solution, and the solution was aged in situ at a constant temperature for 65 min to obtain precursor solution. Then, 7.5 parts of the above-mentioned modified attapulgite were added, and the solution was dispersed with ultrasonic frequency of 40 kHz and power of 350 W and mechanically stirred for 32 min. Then, 1.8 parts of sodium gluconate were added and stirred continuously for 22 min until the system was homogeneous. After aging at room temperature for 2.5 h, the solution was filtered through a 200-mesh sieve to obtain liquid defluorinating agent.

[0061] Application and Effects: The defluoridating agent prepared in this embodiment was used to treat the above-mentioned fluoride-containing wastewater. It was added at a dosage of 1.5 g / L, mixed at 250 rpm for 2 min with rapid stirring, flocculated at 50 rpm for 12 min with slow stirring, and allowed to settle for 20 min. The fluoride ion concentration in the water was measured to be 0.43 mg / L, the fluoride ion removal rate was 99.57%, the average interfacial settling velocity from 0 to 10 min was 1.98 cm / min, the turbidity of the supernatant after 30 min of sedimentation was 0.57 NTU, and the dry sludge content was 129 mg / L.

[0062] Comparative Example 1

[0063] The difference between this comparative example and Example 2 is that no silicon-aluminum hybrid is added during the preparation of the defluorinating agent, and an equal part by weight of polyaluminum sulfate is used to make up the difference.

[0064] The obtained defluoridating agent was used to treat the same fluoride-containing wastewater. The measured fluoride ion concentration in the water was 2.35 mg / L, the fluoride ion removal rate was 97.65%, the average interfacial settling velocity from 0 to 10 min was 1.58 cm / min, the turbidity of the supernatant after 30 min of sedimentation was 1.28 NTU, and the dry sludge content was 143 mg / L.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 2 is that step S1 is omitted in the preparation of the silicon-aluminum hybrid. Instead of using boehmite sol as the aluminum source, aluminum hydroxide of equal Al2O3 is used as the aluminum source. It is directly crystallized with calcium chloride at a calcium to aluminum molar ratio of 2.0. The remaining steps are the same as in Example 2.

[0067] The obtained defluoridating agent was used to treat the same fluoride-containing wastewater. The measured fluoride ion concentration in the water was 0.86 mg / L, the fluoride ion removal rate was 99.14%, the average interface settling velocity was 1.85 cm / min from 0 to 10 min, the turbidity of the supernatant after 30 min of sedimentation was 0.71 NTU, and the dry sludge content was 122 mg / L.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 2 is that the calcium-aluminum alkali crystallization step S2 is omitted in the preparation of the silicon-aluminum hybrid. That is, the pseudo-boehmite sol obtained in step S1 does not undergo calcium-aluminum alkali crystallization to form a layered structure, and directly reacts with the active silica obtained in step S3. The remaining steps are the same as in Example 2.

[0070] The obtained defluoridating agent was used to treat the above-mentioned fluoride-containing wastewater. The measured concentration of fluoride ions in the water was 1.12 mg / L, the fluoride ion removal rate was 98.88%, the average interfacial settling velocity was 1.79 cm / min from 0 to 10 min, the turbidity of the supernatant after 30 min of sedimentation was 0.78 NTU, and the dry sludge content was 126 mg / L.

[0071] Comparative Example 4

[0072] The difference between this comparative example and Example 2 is that the active silica condensation modification in step S3 is omitted during the preparation of the silicon-aluminum hybrid. That is, the active calcium-aluminum layered hydroxide slurry obtained in step S2 is used as the silicon-aluminum hybrid after being filtered and dried directly without active silica condensation. The remaining steps are the same as in Example 2.

[0073] The obtained defluoridating agent was used to treat the above-mentioned fluoride-containing wastewater. The measured concentration of fluoride ions in the water was 0.79 mg / L, the fluoride ion removal rate was 99.21%, the average interface settling velocity was 1.74 cm / min from 0 to 10 min, the turbidity of the supernatant after 30 min of sedimentation was 0.85 NTU, and the dry sludge content was 120 mg / L.

[0074] Comparative Example 5

[0075] The difference between this comparative example and Example 2 is that the modified inorganic framework component used in the preparation of the defluorinating agent is replaced by an equal weight of raw material zeolite powder that has not been acid activated and cationic grafted modified. That is, the steps A1 acid activation calcination and A2 cationic grafting modification of the framework are omitted. The other raw materials and steps are the same as in Example 2.

[0076] The obtained defluoridating agent was used to treat the above-mentioned fluoride-containing wastewater. The concentration of fluoride ions in the water was measured to be 0.58 mg / L, the fluoride ion removal rate was 99.42%, the average interface settling velocity was 1.55 cm / min from 0 to 10 min, the turbidity of the supernatant after 30 min of sedimentation was 1.12 NTU, and the dry sludge content was 120 mg / L.

[0077] The aluminum-based high-efficiency defluoridating agents prepared in Examples 1-4 all exhibited excellent deep defluoridation and solid-liquid separation performance. Under the same water sample condition with an influent fluoride concentration of 100 mg / L, the effluent fluoride concentration was stably reduced to below 1 mg / L, and the fluoride removal rate was not less than 99.2%. The floc settling speed and supernatant turbidity also showed good performance. The aforementioned superior effects are attributed to the synergistic effect between the components of this invention. The pseudoboehmite sol provides high-density active aluminum hydroxyl groups for ligand exchange of fluoride ions. The active calcium-aluminum layered hydroxide obtained by alkali crystallization facilitates interlayer anion exchange and constructs multi-level fluoride capture sites through slow-release nucleation of structural calcium. The condensation of active silica introduces a silica-alumina framework, which not only adds fluoride-fixing channels but also stabilizes the layered structure to broaden the applicable acid-base range. Furthermore, basicity regulation and in-situ co-maturation enable continuous coupling between polyhydroxyaluminum species and hydroxyl groups on the surface of the silica-alumina hybrid. The addition of cation-grafted modified porous framework further aids in sedimentation and bridging, thereby achieving efficient fluoride ion capture and dense and rapid sedimentation of flocs under low loading conditions.

[0078] The performance data of the comparative examples were significantly lower than those of the examples. Comparative Example 1 did not introduce a silicon-aluminum hybrid, resulting in the complete absence of multi-stage fluoride capture sites. Relying solely on the coagulation and sweeping of polyaluminum sulfate, the effluent fluoride ion concentration increased significantly, and the amount of sludge also increased. Comparative Example 2 replaced the self-made pseudoboehmite sol with commercially available aluminum hydroxide, which reduced the density of active aluminum hydroxyl groups and the crystallinity of the layered structure, thus decreasing the fluoride capacity. Comparative Example 3 omitted calcium-aluminum alkali-adjusting crystallization, resulting in the absence of interlayer anion exchange and structural calcium nucleation mechanisms, weakening the fluoride removal capacity. Comparative Example 4 omitted active silica condensation, resulting in the loss of the fixed sites of the silicon-aluminum framework and the stable support of the layered structure, leading to a simultaneous deterioration in both fluoride removal and sedimentation performance. Comparative Example 5 used a raw material framework that was not acid-activated and cation-grafted modified, resulting in the loss of the framework's weighting and sedimentation-aiding functions and electrostatic bridging functions, significantly worsening the floc settling speed and supernatant turbidity.

[0079] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. An aluminum-based high-efficiency defluorinating agent, characterized in that, Based on weight, it includes the following raw material components: 60-85 parts of polyaluminum sulfate, 3-15 parts of silicon-aluminum hybrid, 5-15 parts of active coordination component, 3-10 parts of hydroxyl enhancer, 0.5-2 parts of stabilizing agent, and 2-8 parts of modified inorganic framework component. The polyaluminum sulfate has an aluminum oxide content of 8-12% and a basicity of 45-65%; the active coordinating component is one or a compound of calcium chloride and magnesium chloride; the hydroxyl enhancer is one or a compound of calcium aluminate powder and aluminum hydroxide; and the stabilizing agent is one or a compound of sodium dihydrogen phosphate, sodium citrate, sodium hexametaphosphate, and sodium gluconate.

2. A method for preparing an aluminum-based high-efficiency defluorination agent, used to prepare the aluminum-based high-efficiency defluorination agent according to claim 1, characterized in that, Includes the following steps: (1) Mix the polyaluminum sulfate aqueous solution with a hydroxyl enhancer to adjust the basicity, and after aging reaction, obtain polyaluminum hydroxyl activated solution; (2) Add silicon-aluminum hybrid and active coordination component to polyhydroxyaluminum activation solution, and perform constant temperature co-curing reaction to obtain precursor solution; (3) Modified inorganic framework components and stabilizing agents are added sequentially to the precursor solution, dispersed and mixed, and then aged at room temperature. After removing impurities, liquid defluorinating agent or powder defluorinating agent is obtained respectively.

3. The preparation method of the aluminum-based high-efficiency defluorinating agent according to claim 2, characterized in that, The method for preparing the silicon-aluminum hybrid includes the following steps: S1. Aluminum salt solution is mixed with composite precipitant and reacted. After pH adjustment, it is matured to generate pseudoboehmite gel. After washing and gel treatment, pseudoboehmite sol is obtained. S2. Using boehmite sol as the aluminum source, and mixing it with calcium source to adjust the alkali and crystallize, an active calcium-aluminum layered hydroxide slurry is obtained. S3. The activated active silica is mixed with the active calcium aluminum layered hydroxide slurry for condensation reaction, and then post-processed to obtain a silicon aluminum hybrid.

4. The preparation method of the aluminum-based high-efficiency defluorinating agent according to claim 3, characterized in that, In step S1, the composite precipitant is a mixture of ammonia and ammonium bicarbonate, with a mass ratio of ammonia to ammonium bicarbonate of (1.5-2.5):1 and an ammonia concentration of 20-25 wt%.

5. The preparation method of an aluminum-based high-efficiency defluorinating agent according to claim 2, characterized in that, The preparation method of the modified inorganic framework component includes the following steps: A1. The inorganic framework raw material is activated with dilute acid, washed with water, and calcined at 350-550℃ to obtain the acidified framework; A2. Disperse the acidified skeleton in water, add polydimethyldiallylammonium chloride for grafting modification reaction, and obtain the modified inorganic skeleton component after separation, drying and pulverization.

6. The method for preparing an aluminum-based high-efficiency defluorinating agent according to claim 5, characterized in that, In step A1, the inorganic framework raw material is at least one of diatomaceous earth, zeolite powder, bentonite, attapulgite, and kaolin, and the acid used for acidification and activation is hydrochloric acid.

7. The preparation method of an aluminum-based high-efficiency defluorinating agent according to claim 2, characterized in that, In step (1), the polyaluminum sulfate is prepared into an aqueous solution with a mass concentration of 25-40%, and the basicity is adjusted under the conditions of temperature control at 50-65℃ and stirring at 240-300rpm, and then aged at a constant temperature for 30-90min.

8. The preparation method of an aluminum-based high-efficiency defluorinating agent according to claim 2, characterized in that, The constant temperature co-curing temperature in step (2) is 50-65℃, the stirring speed is 240-300rpm, and the curing time is 60-120min; in step (3), the skeleton dispersion time is 30-60min, the additive stirring time is 20-40min, the room temperature curing time is 2-6h, and impurities are removed by using a 100-200 mesh sieve.

9. The application of the aluminum-based high-efficiency defluorinating agent as described in claim 1, characterized in that, The aluminum-based high-efficiency defluoridating agent is added to fluoride-containing wastewater to adsorb and complex fluoride ions in the water, thereby achieving the purification treatment of fluoride-containing water.