Activated carbon-based fluorine removal agent and preparation method thereof

Abstract

The invention discloses an activated carbon-based fluorine removal agent and a preparation method thereof, and relates to the technical field of water treatment. The activated carbon-based fluorine removal agent comprises the following raw material components in parts by mass: 50-70 parts of activated carbon, 10-20 parts of nano aluminum hydroxide, 5-15 parts of chitosan, 3-8 parts of calcium chloride, 2-8 parts of polyvinyl alcohol, 3-5 parts of sodium carboxymethyl cellulose and 6-12 parts of polyethyleneimine. According to the invention, the active carbon, the nano aluminum hydroxide, the chitosan, the calcium chloride and other materials are subjected to composite modification, so that the adsorption performance of the fluorine removal agent on fluorine ions is greatly improved, and the prepared fluorine removal agent has the characteristics of rapid adsorption and high adsorption capacity, and also has excellent cycle stability and long-term storage stability. The preparation process is simple, the cost is low, the obvious environmental protection advantage is achieved, the novel activated carbon-based fluorine removal agent has wide application prospects in the fields of drinking water treatment, industrial wastewater treatment and the like, and an efficient solution is provided for high-fluorine water treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, in particular to an activated carbon-based defluoridating agent and a preparation method thereof. Background Art

[0002] Fluorine is an essential trace element for the human body and plays a vital role in human health. However, excessive fluoride levels in drinking water can pose serious risks to human health. Long-term consumption of high-fluoride water can lead to a variety of diseases, such as dental fluorosis and skeletal fluorosis. These conditions not only affect quality of life but can also cause long-term damage to physical health. Therefore, developing an efficient, environmentally friendly, and economically viable fluoride removal technology is crucial for ensuring drinking water safety and human health.

[0003] Currently, methods for removing fluoride ions from water primarily include adsorption, ion exchange, and chemical precipitation. Adsorption is widely used in water treatment due to its simplicity, effectiveness, and environmental friendliness. This method effectively removes fluoride ions from water by adsorbing them onto the surfaces of specific materials. Due to its numerous advantages in practical applications, adsorption has become a key area of ​​research and practice.

[0004] Adsorption is a water treatment technology based on physical or chemical effects, the core of which lies in the selection of suitable adsorption materials. The key to this technology lies in the selection of adsorption materials and the optimization of their performance. Activated carbon, as a commonly used adsorption material, has been widely used in the field of water treatment because of its large specific surface area and rich pore structure. In addition, activated carbon also has good stability and durability and can adapt to different water quality conditions. However, although activated carbon has shown many advantages in water treatment, the adsorption capacity of ordinary activated carbon for fluoride ions is still limited. This is mainly because the interaction between fluoride ions and the surface of activated carbon is weak, making it difficult to form an effective bond. Therefore, in practical applications, ordinary activated carbon often cannot meet the needs of deep treatment of high-fluoride water. In order to overcome this problem, researchers have tried a variety of modification methods to improve the adsorption performance of activated carbon for fluoride ions.

[0005] To address the problem of insufficient fluoride ion adsorption capacity of ordinary activated carbon, existing technologies generally use modification methods such as metal oxide loading. These methods significantly improve its adsorption performance for fluoride ions by introducing active sites on the surface of activated carbon or enhancing its surface chemical properties. For example, some studies have shown that the adsorption efficiency of activated carbon for fluoride ions can be significantly improved by loading metal oxides (such as Al2O3, Fe2O3, etc.). This is because metal oxides can form strong chemical bonds with fluoride ions, thereby enhancing the adsorption effect. However, these modification methods also have some obvious limitations: First, the modification process is complex, which limits its large-scale production and practical application. For example, the process of loading metal oxides requires multiple chemical reactions and high-temperature treatment, which places high demands on equipment and technology and increases production costs. Second, the high cost of these methods further limits their promotion in actual water treatment. Finally, the loaded metal is easy to fall off, which may cause secondary pollution problems. The detached metal particles may re-enter the water body, causing new environmental risks. The existence of these problems shows that although existing modification technologies can improve the adsorption performance of activated carbon to a certain extent, they still face many challenges in practical application.

[0006] Therefore, the development of an activated carbon-based defluoridation agent that is efficient, environmentally friendly, and has a simple preparation process is of great practical significance. It has positive significance for achieving higher fluorine adsorption efficiency, lower production costs, and promoting the advancement of water treatment technology and the development of practical applications. Summary of the Invention

[0007] The purpose of the present invention is to provide an activated carbon-based defluoridating agent and a preparation method thereof, so as to solve the problems existing in the above-mentioned prior art and achieve effective removal of fluoride in water.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] One of the technical solutions of the present invention is to provide an activated carbon-based defluoridating agent, comprising the following raw material components in parts by weight:

[0010] 50-70 parts of activated carbon, 10-20 parts of nano-aluminum hydroxide, 5-15 parts of chitosan, 3-8 parts of calcium chloride, 2-8 parts of polyvinyl alcohol, 3-5 parts of sodium carboxymethyl cellulose and 6-12 parts of polyethyleneimine.

[0011] The second technical solution of the present invention is to provide a method for preparing the above-mentioned activated carbon-based defluorination agent, comprising the following steps:

[0012] (1) soaking the activated carbon in a mixed solution of nitric acid and hydrogen peroxide, washing it to neutrality, and drying it to obtain pretreated activated carbon;

[0013] (2) adding sodium carboxymethyl cellulose and polyethyleneimine to deionized water and adjusting the pH to 9 to obtain a mixed solution 1;

[0014] (3) adding nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol into deionized water and adjusting the pH to 6-7 to obtain a mixed solution 2;

[0015] (4) mixing the mixed solution 1 and the mixed solution 2 to obtain a loaded solution;

[0016] (5) adding the pretreated activated carbon into the loading solution and soaking;

[0017] (6) heat-treating the activated carbon obtained in step (5) and cooling it to obtain the activated carbon-based defluorination agent.

[0018] As a further preferred embodiment of the present invention, the heat treatment temperature is 400-500° C. and the time is 2-3 hours.

[0019] As a further preference of the present invention, the heat treatment is carried out under a protective atmosphere.

[0020] As a further preferred embodiment of the present invention, in step (1), the volume concentration of the mixed solution of nitric acid and hydrogen peroxide is 15%, wherein the volume ratio of nitric acid to hydrogen peroxide is 1:1.

[0021] As a further preferred embodiment of the present invention, in step (1), the soaking temperature is 60° C. More preferably, ultrasound is combined during the soaking process, and the soaking time is 2 hours.

[0022] As a further preference of the present invention, in step (2), sodium carboxymethyl cellulose and polyethyleneimine are added to 30-50 times the mass of deionized water.

[0023] As a further preferred embodiment of the present invention, in step (3), nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol are added to 30-50 times the mass of deionized water.

[0024] The third technical solution of the present invention: provides the application of the above-mentioned activated carbon-based defluoridating agent in water treatment.

[0025] The activated carbon-based defluoridant of the present invention rapidly adsorbs fluoride ions. The rich pore structure of the activated carbon provides a rapid diffusion pathway for fluoride ions, allowing them to quickly reach adsorption sites. Simultaneously, the loaded active substances further enhance their reaction with fluoride ions, thereby achieving rapid fluoride adsorption. Furthermore, nano-aluminum hydroxide can undergo a complexation reaction with fluoride ions, and chitosan, rich in functional groups such as amino and hydroxyl groups, can generate electrostatic adsorption and hydrogen bonding with fluoride ions, significantly improving the defluoridant's adsorption capacity and selectivity for fluoride ions.

[0026] Calcium chloride provides Ca 2+ It can form ionic bonds with the amino groups between chitosan molecules to enhance the adhesion stability of chitosan on the surface of activated carbon. The cross-linked chitosan forms a tighter network structure, which wraps and fixes the nano-aluminum hydroxide particles in the pores of activated carbon, preventing them from falling off or agglomerating, and improving the loading efficiency. 2+ Adsorption on the surface of activated carbon can promote the adsorption of negatively charged fluoride ions to the surface of the defluoridant through electrostatic action.

[0027] In the mixed solution, polyvinyl alcohol molecules can be adsorbed on the surface of nano-aluminum hydroxide particles, preventing the particles from agglomerating through the steric hindrance effect, making them evenly dispersed in the solution, and ensuring that the nanoparticles can fully cover the activated carbon surface during the subsequent loading process.

[0028] During the high-temperature activation stage (400-500°C) under nitrogen protection, polyvinyl alcohol and polyethyleneimine are carbonized to form a carbon skeleton structure, further enhancing the stability of the particles and introducing additional adsorption sites (such as oxygen-containing functional groups) to improve fluoride removal performance. The CO2 produced by the decomposition of sodium carboxymethyl cellulose forms a microporous structure, further increasing the specific surface area and ensuring the adsorption of fluorine.

[0029] The activated carbon-based defluoridation agent of the present invention has a simple preparation method, does not require complex equipment and harsh reaction conditions, is easy to industrialize, and reduces production costs. The activated carbon-based defluoridation agent of the present invention does not generate harmful substances during preparation and use, and has good stability and does not cause secondary pollution.

[0030] The present invention discloses the following technical effects:

[0031] This invention provides an activated carbon-based defluoridant that successfully addresses the problem of insufficient fluoride ion adsorption capacity of activated carbon. By modifying the activated carbon with materials such as nano-aluminum hydroxide, chitosan, and calcium chloride, its fluoride adsorption performance is significantly improved. The defluoridant exhibits rapid adsorption and high adsorption capacity, while also possessing excellent cyclic stability and long-term storage stability.

[0032] The preparation process of the present invention is simple, low-cost, and has significant environmental advantages. This new activated carbon-based defluoridant has broad application prospects in drinking water treatment, industrial wastewater treatment and other fields, and provides an efficient solution for the treatment of high-fluoride water. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0035] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0036] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0037] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0038] At present, some studies have directly used activated carbon to treat fluoride-containing wastewater. However, when activated carbon is used directly, due to the weak interaction between fluoride ions and the surface of activated carbon, the adsorption capacity and removal rate of fluoride ions are relatively low, which makes it difficult to meet the needs of deep treatment of high-fluoride water.

[0039] Existing technologies have modified activated carbon in various ways to improve its fluoride ion adsorption performance, for example:

[0040] 1. Metal modification

[0041] Iron-based modified activated carbon primarily removes fluoride by loading iron salts and iron oxides onto the activated carbon, where they undergo ion exchange and electrostatic adsorption with fluoride ions. One study used pretreated coal-based activated carbon soaked in FeC3 solution to produce modified coal-based activated carbon. This modification effectively improved the activated carbon's pore structure and specific surface area, making it more conducive to iron salt loading and increasing fluoride removal. The adsorption mechanism of aluminum-based modified activated carbon is complex, involving electrostatic interactions, ion exchange, and complexation between metal ions and fluoride ions.

[0042] 2. Non-metal modification

[0043] Blending hydroxyapatite (HAP) with activated carbon or loading it onto activated carbon can improve fluoride removal. Studies have shown that this modification increases activated carbon's fluoride removal capacity by 5.3-14 times. The calcium ions in HAP exchange with fluoride ions, forming less soluble calcium fluoride, thereby enhancing the activated carbon's fluoride removal effectiveness.

[0044] 3. Acid-base modification

[0045] Activated carbon is commonly treated with acids such as nitric acid and hydrochloric acid. Acid treatment removes ash and impurities from the activated carbon's surface, expands its pore structure, and increases its specific surface area. Acid treatment also alters the nature and quantity of surface functional groups, increasing the content of surface acidic functional groups and enhancing its adsorption capacity for fluoride ions. For example, Wang Guozhen et al. washed activated carbon granules three times with distilled water, then soaked them in 10% HNO₃ for 12 hours, rinsed them with deionized water until neutral, and dried them at 100°C for later use. The modified activated carbon showed improved adsorption of fluoride ions.

[0046] Alkali modification typically involves treating activated carbon with a strong alkaline solution, such as sodium hydroxide. Alkali treatment can etch the activated carbon surface, further expanding its pores, and also modulate surface functional groups, increasing the number of alkaline groups. Lin Hao et al. conducted regeneration experiments on modified activated carbon using NaOH solutions of varying concentrations and found that, within a certain range, higher NaOH concentrations resulted in better regeneration. This suggests that alkaline treatment may enhance the interaction between activated carbon and fluoride ions, improving adsorption performance.

[0047] 4. Composite modification

[0048] To fully leverage the advantages of different modification methods, a combined modification approach is often employed. For example, metal modification can be combined with acid-base or non-metal modification. One study first treated activated carbon with an iron-based base followed by acid treatment. The results showed that the modified activated carbon significantly optimized its pore structure, surface functional groups, and adsorption properties, significantly increasing both its adsorption capacity and removal rate for fluoride ions. This combined modification approach combines the advantages of multiple modification methods to more effectively enhance the fluoride removal performance of activated carbon.

[0049] Some modification processes involve complex chemical reactions and high-temperature treatments, placing high demands on equipment and technology. This increases production costs and limits large-scale application. For example, some metal modification processes require precise control of reaction conditions, increasing production difficulty and cost. Furthermore, the material's fluorine adsorption performance needs to be improved.

[0050] One of the objects of the present invention is to provide an activated carbon-based defluoridation agent comprising the following raw material components in parts by weight:

[0051] 50-70 parts of activated carbon, 10-20 parts of nano-aluminum hydroxide, 5-15 parts of chitosan, 3-8 parts of calcium chloride, 2-8 parts of polyvinyl alcohol, 3-5 parts of sodium carboxymethyl cellulose and 6-12 parts of polyethyleneimine.

[0052] A second object of the present invention is to provide a method for preparing the above-mentioned activated carbon-based defluorination agent, comprising the following steps:

[0053] (1) soaking the activated carbon in a mixed solution of nitric acid and hydrogen peroxide, washing it to neutrality, and drying it to obtain pretreated activated carbon;

[0054] (2) adding sodium carboxymethyl cellulose and polyethyleneimine to deionized water and adjusting the pH to 9 to obtain a mixed solution 1;

[0055] (3) adding nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol into deionized water and adjusting the pH to 6-7 to obtain a mixed solution 2;

[0056] (4) mixing the mixed solution 1 and the mixed solution 2 to obtain a loaded solution;

[0057] (5) adding the pretreated activated carbon into the loading solution and soaking;

[0058] (6) heat-treating the activated carbon obtained in step (5) and cooling it to obtain the activated carbon-based defluorination agent.

[0059] Preferably, the heat treatment temperature is 400-500° C. and the time is 2-3 hours.

[0060] Preferably, the heat treatment is performed under a protective atmosphere.

[0061] Preferably, in step (1), the volume concentration of the mixed solution of nitric acid and hydrogen peroxide is 15%, wherein the volume ratio of nitric acid to hydrogen peroxide is 1:1.

[0062] Preferably, in step (1), the soaking temperature is 60°C.

[0063] Preferably, in step (2), sodium carboxymethyl cellulose and polyethyleneimine are added to 30-50 times the mass of deionized water.

[0064] Preferably, in step (3), nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol are added to 30-50 times the mass of deionized water.

[0065] As a specific embodiment of the present invention, the drying temperature in step (1) is 120°C.

[0066] As a specific embodiment of the present invention, step (1) adopts vacuum drying for 8 hours.

[0067] As a specific embodiment of the present invention, in step (2), sodium carboxymethyl cellulose and polyethyleneimine are dissolved in water at 30-35°C.

[0068] As a specific embodiment of the present invention, in step (2), the pH is adjusted to 9 using sodium hydroxide solution.

[0069] As a specific embodiment of the present invention, the stirring speed of step (3) is 300-500 r / min, and the stirring time is 30-60 min.

[0070] As a specific embodiment of the present invention, in step (3), acetic acid is used to adjust the pH to 6-7.

[0071] As a specific embodiment of the present invention, in step (5), the soaking time is 1-2 hours.

[0072] As a specific embodiment of the present invention, in step (5), the temperature is raised to 400-500°C at a heating rate of 5-10°C / min, kept at this temperature for 2-3 hours, and then naturally cooled to room temperature to obtain an activated carbon-based defluorination agent.

[0073] A third object of the present invention is to provide the use of the above-mentioned activated carbon-based defluoridating agent in water treatment.

[0074] The present invention will be further described in detail below with reference to the embodiments.

[0075] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0076] The activated carbon used in the present invention is wood activated carbon with a specific surface area of ​​800-1200m 2 / g, and the average pore size is 2-5nm.

[0077] Example 1

[0078] The raw materials used in the activated carbon-based defluorination agent of this embodiment and their mass proportions are as follows:

[0079] 50 parts of activated carbon, 15 parts of nano-aluminum hydroxide, 13 parts of chitosan, 5 parts of calcium chloride, 3 parts of polyvinyl alcohol, 4 parts of sodium carboxymethyl cellulose and 8 parts of polyethyleneimine.

[0080] The preparation steps of activated carbon-based defluoridation agent are as follows:

[0081] (1) Activated carbon pretreatment: The activated carbon was immersed in a 15% volume concentration of nitric acid-hydrogen peroxide (volume ratio 1:1) mixed solution, ultrasonically treated at 60°C for 2 h, then washed with deionized water until neutral, and vacuum dried at 120°C for 8 h.

[0082] (2) In a constant temperature water bath at 30°C, sodium carboxymethyl cellulose and polyethyleneimine were dissolved in 30 times the mass of deionized water, the pH was adjusted to 9 with sodium hydroxide solution, and the mixture was stirred for 4 hours to obtain a mixed solution 1;

[0083] (3) Under stirring conditions, nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol were added in sequence to 50 times the mass of deionized water, and the pH was adjusted to 6 with acetic acid solution. The stirring speed was controlled at 400 r / min and the stirring time was 30 min to obtain a mixed solution 2;

[0084] (4) mixing the mixed solution 1 with the mixed solution 2 to obtain a loaded solution;

[0085] (5) Add the pretreated activated carbon to the loading solution and soak for 1 h;

[0086] (6) The activated carbon obtained in step (5) is placed in a muffle furnace, and under a nitrogen protective atmosphere, the temperature is increased to 400° C. at a heating rate of 10° C. / min, kept at this temperature for 2 h, and then naturally cooled to room temperature to obtain an activated carbon-based defluorination agent.

[0087] Example 2

[0088] The raw materials used in the activated carbon-based defluorination agent of this embodiment and their mass proportions are as follows:

[0089] 65 parts of activated carbon, 17 parts of nano-aluminum hydroxide, 13 parts of chitosan, 6 parts of calcium chloride, 3 parts of polyvinyl alcohol, 4 parts of sodium carboxymethyl cellulose and 7 parts of polyethyleneimine.

[0090] The preparation steps of activated carbon-based defluoridation agent are as follows:

[0091] (1) Activated carbon pretreatment: The activated carbon was immersed in a 15% volume concentration of nitric acid-hydrogen peroxide (volume ratio 1:1) mixed solution, ultrasonically treated at 60°C for 2 h, then washed with deionized water until neutral, and vacuum dried at 120°C for 8 h.

[0092] (2) In a constant temperature water bath at 30°C, sodium carboxymethyl cellulose and polyethyleneimine were dissolved in 30 times the mass of deionized water, the pH was adjusted to 9 with sodium hydroxide solution, and the mixture was stirred for 4 hours to obtain a mixed solution 1;

[0093] (3) Under stirring conditions, nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol were added in sequence to 50 times the mass of deionized water, and the pH was adjusted to 6 with acetic acid solution. The stirring speed was controlled at 400 r / min and the stirring time was 30 min to obtain a mixed solution 2;

[0094] (4) mixing the mixed solution 1 with the mixed solution 2 to obtain a loaded solution;

[0095] (5) Add the pretreated activated carbon to the loading solution and soak for 1 h;

[0096] (6) The activated carbon obtained in step (5) is placed in a muffle furnace, and the temperature is increased to 450° C. at a heating rate of 10° C. / min under a nitrogen protective atmosphere, kept at this temperature for 2 h, and then naturally cooled to room temperature to obtain an activated carbon-based defluorination agent.

[0097] Example 3

[0098] The raw materials used in the activated carbon-based defluorination agent of this embodiment and their mass proportions are as follows:

[0099] 55 parts of activated carbon, 10 parts of nano-aluminum hydroxide, 12 parts of chitosan, 5 parts of calcium chloride, 3 parts of polyvinyl alcohol, 4 parts of sodium carboxymethyl cellulose and 10 parts of polyethyleneimine.

[0100] The preparation steps of activated carbon-based defluoridation agent are as follows:

[0101] (1) Activated carbon pretreatment: The activated carbon was immersed in a 15% volume concentration of nitric acid-hydrogen peroxide (volume ratio 1:1) mixed solution, ultrasonically treated at 60°C for 2 h, then washed with deionized water until neutral, and vacuum dried at 120°C for 8 h.

[0102] (2) In a constant temperature water bath at 30°C, sodium carboxymethyl cellulose and polyethyleneimine were dissolved in 30 times the mass of deionized water, the pH was adjusted to 9 with sodium hydroxide solution, and the mixture was stirred for 4 hours to obtain a mixed solution 1;

[0103] (3) Under stirring conditions, nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol were added in sequence to 50 times the mass of deionized water, and the pH was adjusted to 6 with acetic acid solution. The stirring speed was controlled at 400 r / min and the stirring time was 30 min to obtain a mixed solution 2;

[0104] (4) mixing the mixed solution 1 with the mixed solution 2 to obtain a loaded solution;

[0105] (5) Add the pretreated activated carbon to the loading solution and soak for 1 h;

[0106] (6) The activated carbon obtained in step (5) is placed in a muffle furnace, and under a nitrogen protective atmosphere, the temperature is increased to 400° C. at a heating rate of 5° C. / min, kept at this temperature for 2 h, and then naturally cooled to room temperature to obtain an activated carbon-based defluorination agent.

[0107] Example 4

[0108] The raw materials used in the activated carbon-based defluorination agent of this embodiment and their mass proportions are as follows:

[0109] 70 parts of activated carbon, 20 parts of nano-aluminum hydroxide, 13 parts of chitosan, 5 parts of calcium chloride, 8 parts of polyvinyl alcohol, 3 parts of sodium carboxymethyl cellulose and 8 parts of polyethyleneimine.

[0110] The preparation steps of activated carbon-based defluoridation agent are as follows:

[0111] (1) Activated carbon pretreatment: The activated carbon was immersed in a 15% volume concentration of nitric acid-hydrogen peroxide (volume ratio 1:1) mixed solution, ultrasonically treated at 60°C for 2 h, then washed with deionized water until neutral, and vacuum dried at 120°C for 8 h.

[0112] (2) In a constant temperature water bath at 30°C, sodium carboxymethyl cellulose and polyethyleneimine were dissolved in 30 times the mass of deionized water, the pH was adjusted to 9 with sodium hydroxide solution, and the mixture was stirred for 4 hours to obtain a mixed solution 1;

[0113] (3) Under stirring conditions, nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol were added in sequence to 50 times the mass of deionized water, and the pH was adjusted to 6 with acetic acid solution. The stirring speed was controlled at 400 r / min and the stirring time was 30 min to obtain a mixed solution 2;

[0114] (4) mixing the mixed solution 1 with the mixed solution 2 to obtain a loaded solution;

[0115] (5) Add the pretreated activated carbon to the loading solution and soak for 1 h;

[0116] (6) The activated carbon obtained in step (5) is placed in a muffle furnace, and the temperature is increased to 450° C. at a heating rate of 10° C. / min under a nitrogen protective atmosphere, kept at this temperature for 2 h, and then naturally cooled to room temperature to obtain an activated carbon-based defluorination agent.

[0117] Comparative Example 1

[0118] Unmodified activated carbon (the same as the raw activated carbon in Example 1) was used as a defluorination agent.

[0119] Comparative Example 2

[0120] The only difference from Example 1 is that the treatment in step (2) is not performed; the preparation method of the activated carbon-based defluoridating agent is as follows:

[0121] (1) Activated carbon pretreatment: The activated carbon was immersed in a 15% volume concentration of nitric acid-hydrogen peroxide (volume ratio 1:1) mixed solution, ultrasonically treated at 60°C for 2 h, then washed with deionized water until neutral, and vacuum dried at 120°C for 8 h.

[0122] (2) Under stirring conditions, nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol were added in sequence to 50 times the mass of deionized water, the pH was adjusted to 6 with acetic acid solution, the stirring speed was controlled at 400 r / min, and the stirring time was 30 min to obtain a mixed solution;

[0123] (3) Add the pretreated activated carbon to the mixed solution and soak for 1 hour;

[0124] (4) placing the activated carbon obtained in step (3) in a muffle furnace, heating it to 400°C at a heating rate of 10°C / min under a nitrogen atmosphere, keeping it warm for 2 hours, and then naturally cooling it to room temperature to obtain an activated carbon-based defluorination agent.

[0125] Comparative Example 3

[0126] The only difference from Example 1 is that step (3) is not performed; the preparation method of the activated carbon-based defluorination agent is as follows:

[0127] (1) Activated carbon pretreatment: The activated carbon was immersed in a 15% volume concentration of nitric acid-hydrogen peroxide (volume ratio 1:1) mixed solution, ultrasonically treated at 60°C for 2 h, then washed with deionized water until neutral, and vacuum dried at 120°C for 8 h.

[0128] (2) In a constant temperature water bath at 30°C, sodium carboxymethyl cellulose and polyethyleneimine were dissolved in 30 times the mass of deionized water, the pH was adjusted to 9 with sodium hydroxide solution, and the mixture was stirred for 4 h to obtain a mixed solution;

[0129] (3) Add the pretreated activated carbon to the mixed solution and soak for 1 hour;

[0130] (4) placing the activated carbon obtained in step (3) in a muffle furnace, heating it to 400°C at a heating rate of 10°C / min under a nitrogen atmosphere, keeping it warm for 2 hours, and then naturally cooling it to room temperature to obtain an activated carbon-based defluorination agent.

[0131] Effect verification example:

[0132] Sodium fluoride was dissolved in deionized water to prepare a solution with an initial fluoride ion concentration of 20 mg / L for adsorption experiments.

[0133] 1. Adsorption saturation determination

[0134] 1 g of the defluoridant from Example 1 was added to 100 mL of simulated wastewater with an initial fluoride ion concentration of 20 mg / L. The mixture was shaken at 25°C and 150 rpm for 30, 60, 120, and 180 minutes, respectively. Sampling was performed afterward. The results showed that the adsorption capacity reached 55.3 mg / g after 120 minutes, and there was no significant increase in the adsorption capacity (≤1%) after 180 minutes, indicating that the defluoridant reached adsorption saturation within 120 minutes.

[0135] The defluoridation agents of Examples 2-4 and Comparative Examples 1-3 were tested in the same manner as above. The results showed that the defluoridation agents of Examples 1-4 of the present invention all reached adsorption saturation at 120 minutes, while those of Comparative Examples 1-3 reached adsorption saturation at 180 minutes.

[0136] 2. Adsorption capacity test

[0137] 1g of each defluoridant prepared in the Examples and Comparative Examples was added to 100mL of simulated fluoride-containing wastewater with an initial fluoride ion concentration of 20mg / L. The mixture was shaken and adsorbed for 2h at 25°C and 150rpm. The fluoride ion concentration in the solution after adsorption was measured, and the fluoride ion adsorption capacity of the defluoridant was calculated. The test was repeated three times, and the average values ​​were calculated. The results are shown in Table 1.

[0138] Table 1

[0139] Adsorption capacity (mg / g) Example 1 55.3 Example 2 54.9 Example 3 54.3 Example 4 55.1 Comparative Example 1 40.3 Comparative Example 2 46.8 Comparative Example 3 47.6

[0140] 3. Cyclic stability test

[0141] 1 g of each defluoridant prepared in the example and the comparative example was taken and added to 100 mL of simulated fluoride-containing wastewater with an initial fluoride ion concentration of 20 mg / L. The mixture was oscillated and adsorbed at 25°C and 150 r / min for 2 h. The concentration of fluoride ions in the solution after adsorption was measured, and the adsorption amount of fluoride ions by the defluoridant was calculated. The defluoridants of the example and the comparative example after adsorption were regenerated by the following regeneration method: soaking in 0.1 mol / L NaOH solution for 2 h, washing with water until neutral, drying at 100°C, and then heat-treating at 300°C in a nitrogen atmosphere for 1 h.

[0142] The adsorption-regeneration process was repeated 10 times, and the retention rate after 10 cycles was calculated. The test was repeated 3 times, and the average value was calculated. The results are shown in Table 2.

[0143] Adsorption amount retention rate = 10th adsorption amount / 1st adsorption amount × 100%.

[0144] Table 2

[0145] Retention rate after 10 cycles (%) Example 1 86.6 Example 2 87.1 Example 3 87.5 Example 4 87.2 Comparative Example 1 43.3 Comparative Example 2 59.8 Comparative Example 3 60.3

[0146] After 10 adsorption-regeneration cycles, the adsorption capacity retention rates of the defluoridants of Examples 1 to 4 of the present invention all exceeded 86%, indicating that the defluoridants of the present invention have excellent cyclic stability.

[0147] 4. Long-term storage stability test

[0148] The defluoridating agents prepared in the examples and comparative examples were sealed and stored in a desiccator (temperature 25°C ± 1°C, humidity <40% RH). Samples were taken after 30 days and 90 days, respectively, to test the adsorption retention rate. The samples were taken 5 times and the average value was calculated.

[0149] Adsorption capacity retention rate = fluorine adsorption capacity before storage / fluorine adsorption capacity after storage × 100%.

[0150] Table 3

[0151]

[0152]

[0153] After 90 days of sealed storage, the adsorption capacity retention rate of the defluoridating agents of Examples 1-4 still exceeded 96%, while that of the unmodified activated carbon (Comparative Example 1) was only 41.2%, indicating that the materials of the present invention have excellent long-term storage stability.

[0154] The defluorination agent of the present invention can be stored for a long time at room temperature, is suitable for transportation and inventory management after industrial production, and reduces storage costs and performance risks in practical applications.

[0155] 5. Ion Selectivity Test

[0156] Control group: weigh NaF and dissolve it in deionized water to prepare F - Solution with a concentration of 20 mg / L;

[0157] Experimental group: NaF, NaCL, Na2SO4, NaHCO3, KNO3 were added to deionized water, among which the interfering ions (Cl-, SO4 2- 、HCO3 - 、NO3 - ) total concentration is 200 mg / L, F - Concentration 20mg / L.

[0158] Take 100 mL of the experimental solution, add the defluoridation agent prepared in Example 1, and shake at 25°C and 150 r / min for 2 h. After filtration, determine the F content in the filtrate. - The adsorption attenuation rate was calculated and repeated 3 times to calculate the average value. The results showed that the adsorption attenuation rate was less than 5.2%.

[0159] Wherein, adsorption decay rate = (fluorine adsorption amount of control group - fluorine adsorption amount of experimental group) / fluorine adsorption amount of control group × 100%.

[0160] During the water treatment process, the activated carbon-based defluoridating agents prepared in the embodiments of the present invention and the comparative examples release heavy metal ions (such as aluminum, lead, cadmium, etc.) in a manner that meets the requirements of the "Standards for Drinking Water Quality" (GB 5749-2022), wherein the aluminum ion release concentration is ≤0.1 mg / L (far below the safety limit of 0.2 mg / L), and trace heavy metals such as lead and cadmium are not detected or their concentrations are significantly lower than the standard limits. There is no risk of secondary pollution, and the safety is good.

[0161] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. An activated carbon-based defluoridating agent, characterized in that: The invention comprises the following raw material components in parts by weight: 50-70 parts of activated carbon, 10-20 parts of nano-aluminum hydroxide, 5-15 parts of chitosan, 3-8 parts of calcium chloride, 2-8 parts of polyvinyl alcohol, 3-5 parts of sodium carboxymethyl cellulose and 6-12 parts of polyethyleneimine.

2. The method for preparing an activated carbon-based defluoridating agent according to claim 1, wherein: The following steps are involved: (1) soaking the activated carbon in a mixed solution of nitric acid and hydrogen peroxide, washing it to neutrality, and drying it to obtain pretreated activated carbon; (2) adding sodium carboxymethyl cellulose and polyethyleneimine to deionized water and adjusting the pH to 9 to obtain a mixed solution 1; (3) adding nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol into deionized water and adjusting the pH to 6-7 to obtain a mixed solution 2; (4) mixing the mixed solution 1 and the mixed solution 2 to obtain a loaded solution; (5) adding the pretreated activated carbon into the loading solution and soaking; (6) heat-treating the activated carbon obtained in step (5) and cooling it to obtain the activated carbon-based defluorination agent.

3. The method for preparing an activated carbon-based defluoridating agent according to claim 2, wherein: The heat treatment temperature is 400-500° C. and the time is 2-3 hours.

4. The method for preparing an activated carbon-based defluoridating agent according to claim 2, wherein: The heat treatment is carried out under a protective atmosphere.

5. The method for preparing an activated carbon-based defluoridating agent according to claim 2, wherein: In step (1), the volume concentration of the mixed solution of nitric acid and hydrogen peroxide is 15%.

6. The method for preparing an activated carbon-based defluoridating agent according to claim 2, wherein: In step (1), the soaking temperature is 60°C.

7. The method for preparing an activated carbon-based defluoridating agent according to claim 2, wherein: In step (2), sodium carboxymethyl cellulose and polyethyleneimine are added to 30-50 times the mass of deionized water.

8. The method for preparing an activated carbon-based defluoridating agent according to claim 2, wherein: In step (3), nano-aluminum hydroxide, chitosan, calcium chloride and polyvinyl alcohol are added into deionized water with a mass of 30-50 times.

9. Use of the activated carbon-based defluoridating agent according to claim 1 in water treatment.

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