Composite fluorine removal agent and preparation method thereof

Abstract

The invention discloses a composite fluorine removal agent and a preparation method thereof, and belongs to the technical field of water treatment. The preparation method of the composite fluorine removal agent comprises the following steps: dipping biomass charcoal in a lanthanum-containing solution, and calcining to obtain a La2O3 / charcoal carrier; the La2O3 / carbon carrier, nano-hydroxyapatite, MgO and magnetic Fe3O4 particles are mixed and then subjected to heat treatment, and a composite material is obtained; mixing the composite material, tetraethoxysilane and a solvent, dropwise adding ammonia water into the mixture for catalytic hydrolysis, and then annealing to obtain a SiO2-coated composite material; and mixing and granulating the SiO2 coated composite material and a binder, and then activating to obtain the composite fluorine removal agent. The method realizes the preparation of the composite fluorine removal agent which is wide in pH application range, can be recycled and can be suitable for efficient treatment of low-concentration fluorine wastewater.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and more particularly relates to a composite defluoridating agent and a preparation method thereof. Background Art

[0002] Fluoride ions (F - Excessive fluoride concentrations (>1.5 mg / L, according to the WHO standard) can lead to diseases such as dental fluorosis and skeletal fluorosis. With the development of industry, fluoride ion pollution in drinking water has significantly increased, and efficient, low-cost fluoride removal technologies are urgently needed.

[0003] The current mainstream fluoride removal methods and their limitations are as follows: Adsorption is a common method, but the adsorbents used in existing adsorption methods are significantly insufficient. For example, activated alumina has a low adsorption capacity and requires a strict pH control of 5.5-6.5. Zeolite-modified materials experience a significant drop in adsorption efficiency after regeneration, achieving only 50% adsorption efficiency. Metal oxides (such as iron oxide) are expensive and prone to agglomeration. Sedimentation produces large amounts of sludge, which is difficult to handle and significantly increases subsequent treatment costs. Membrane separation requires large equipment investments and is unsuitable for decentralized water supply.

[0004] To address the challenges of the aforementioned adsorption methods, researchers have studied various composite adsorbents. However, these still suffer from limited pH ranges, high costs associated with recycling, and poor adaptability to low-concentration fluoride wastewater. Therefore, developing a composite defluoridation agent with a wide pH range, recyclability, and high efficiency for treating low-concentration fluoride wastewater is of great significance. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite defluoridating agent and a preparation method thereof, so as to solve the problems existing in the above-mentioned prior art and realize the preparation of a composite defluoridating agent with a wide pH range of application, recyclability and applicability to the efficient treatment of low-concentration fluoride wastewater.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is to provide a method for preparing a composite defluoridating agent, comprising the following steps:

[0008] The biomass carbon is impregnated in a lanthanum-containing solution and then calcined to obtain a La2O3 / carbon support;

[0009] The La2O3 / carbon support, nano-hydroxyapatite, MgO and magnetic Fe3O4 particles are mixed and then heat-treated to obtain a composite material;

[0010] The composite material, tetraethyl orthosilicate and a solvent are mixed, and ammonia water is added dropwise thereto for catalytic hydrolysis, followed by annealing to obtain a SiO2-coated composite material;

[0011] The SiO2-coated composite material and a binder are mixed and granulated, and then activated to obtain the composite defluoridating agent.

[0012] Preferably, the biochar is obtained by pyrolysis of waste biomass; the pyrolysis temperature is 550-650° C., and the time is 1-2 hours.

[0013] Furthermore, the waste biomass includes straw, hemp stalks, wood chips, bark, bamboo chips, bamboo powder, branches, walnut shells, palm shells, coconut shells and rice husks.

[0014] Furthermore, the preparation steps of the biochar are as follows:

[0015] The waste biomass is washed and dried, and then pyrolyzed to obtain porous biochar; the porous biochar is soaked in 1-1.5 mol / L HCl for 24 hours to remove ash, washed to neutrality, dried, ground, and sieved to obtain biochar with a particle size of ≤200 μm.

[0016] Preferably, the lanthanum-containing solution includes a lanthanum nitrate aqueous solution and / or a lanthanum chloride aqueous solution; the concentration of the lanthanum-containing solution is 0.5 to 1 mol / L; the impregnation time is 1 to 2 hours; the calcination is carried out under a nitrogen atmosphere, the calcination temperature is 500 to 600° C., and the time is 2 to 3 hours.

[0017] Preferably, the mass ratio of the La2O3 / carbon carrier, nano-hydroxyapatite, MgO and magnetic Fe3O4 particles is 5-8:5-8:3-4:2-3.

[0018] Furthermore, the La2O3 / carbon carrier, MgO and magnetic Fe3O4 particles are all ground and sieved before use, wherein the particle size of the La2O3 / carbon carrier is ≤200μm, the particle size of MgO is ≤500nm, and the particle size of the magnetic Fe3O4 particles is ≤30nm; the nano-hydroxyapatite is rod-shaped particles with an aspect ratio of 1:3 to 5 and a length of 20 to 100nm.

[0019] Furthermore, the magnetic Fe3O4 particles are prepared by a co-precipitation method, and the specific steps are as follows:

[0020] FeCl3 and FeSO4 are dissolved in water in a molar ratio of 2:1, nitrogen is introduced into the reactor to remove oxygen, and while the nitrogen is being introduced, ammonia water is added dropwise at 50-55°C until the pH value reaches 10 to generate a black Fe3O4 precipitate. After magnetic separation, the precipitate is washed and dried to obtain the magnetic Fe3O4 particles.

[0021] Preferably, the heat treatment parameters are: nitrogen or argon atmosphere, heating rate 5-5.5°C / min, temperature 500-550°C, and holding time 2-3h.

[0022] Preferably, the solvent is an ethanol aqueous solution; the volume ratio of ethanol to water in the ethanol aqueous solution is 1:1-2; the amount ratio of the composite material to the solvent is 1g:3-4mL, the amount of the tetraethyl orthosilicate is 3-3.2% of the mass of the composite material, and the amount of the ammonia water is 1-2% of the total volume of the mixed solution obtained by mixing the composite material, tetraethyl orthosilicate and the solvent.

[0023] Preferably, the catalytic hydrolysis time is 12 to 14 hours; the annealing temperature is 300 to 350° C., and the time is 0.5 to 1 hour.

[0024] Preferably, the binder comprises sodium carboxymethyl cellulose; the amount of the binder is 2-3% of the mass of the SiO2-coated composite material; the activation temperature is 350-400° C., and the activation time is 1-1.5 hours.

[0025] The second technical solution of the present invention is to provide a composite defluoridating agent prepared by the above preparation method.

[0026] The third technical solution of the present invention is to provide an application of the above-mentioned composite defluoridating agent in the treatment of fluorine-contaminated water.

[0027] Furthermore, the fluorine-contaminated water sources in the fluorine-contaminated water treatment include industrial wastewater, domestic sewage and agricultural sewage; the industrial wastewater includes industrial wastewater generated in the fields of metallurgy and metal processing, semiconductors and photovoltaics.

[0028] The technical mechanism of the present invention is as follows:

[0029] The preparation process of the composite defluoridant of the present invention is divided into four stages: the formation of La2O3 and its loading in biochar → the formation of La2O3 / charcoal-HAP-MgO-Fe3O4 composite → the surface coating of SiO2 → the subsequent activation.

[0030] In the first stage (La2O3 formation and loading in biochar), agricultural waste is used to replace some metal salts, and a porous adsorption framework is formed through pyrolysis activation to reduce costs. Simultaneously, the biochar is modified with the inexpensive rare earth oxide lanthanum (La) to increase its complexing strength with fluorine and enhance its selective adsorption.

[0031] In the second stage (formation of La2O3 / carbon-HAP-MgO-Fe3O4 composite), La2O3 / carbon support: heat treatment makes La2O3 nanoparticles evenly dispersed in the carbon pores, avoids agglomeration, and exposes more La 3+Active sites. At the same time, the carbon skeleton is partially graphitized, which enhances conductivity and promotes La 3+ With F - Nanohydroxyapatite (HAP): HAP partially decomposes into β-tricalcium phosphate (β-TCP, Ca3(PO4)2) and CaO at high temperature, and the newly added Ca 2+ Active site, with F - CaF2 precipitates are formed. The retained HAP crystal structure provides stable -OH groups, which adsorb F through hydrogen bonds. - MgO: After heat treatment, defect sites (such as oxygen vacancies) are formed on the surface of MgO, which enhances the - Chemical adsorption. It cooperates with CaO produced by HAP decomposition to adjust pH to avoid local over-acidity / over-alkalinity affecting adsorption. Fe3O4: During the heat treatment process, Fe3O4 is partially oxidized to γ-Fe2O3, which retains its magnetic properties (facilitating subsequent recovery by magnetic adsorption) while increasing the surface Fe-OH groups. The Fe-OH groups can exchange with F through ligands. - Forming a stable inner complex (Fe-F) significantly improves the - complexing ability.

[0032] La2O3 / carbon-HAP-MgO-Fe3O4 composite was prepared under specific parameters by La2O3-Ca 2+ -MgO multi-metal synergy forms a "adsorption-precipitation" dual mechanism, which significantly enhances the - The complexing ability effectively improves the removal effect of fluorine.

[0033] The heat treatment parameters defined in the present invention are: nitrogen or argon atmosphere, heating rate 5-5.5°C / min, temperature 500-550°C, and holding time 2-3h. When the temperature is lower than 500°C, the uniformity of La2O3 loading is poor; when the temperature is higher than 550°C, the carbon is excessively burned and most of the Fe3O4 is oxidized to α-Fe2O3, resulting in loss of magnetism and inability to recover it by magnetic adsorption in the later stage. At the same time, the composite material is susceptible to F - The complexing ability is weakened. This holding time ensures sufficient crystallization of La2O3 and HAP while preventing over-sintering of MgO. A nitrogen or argon protective atmosphere prevents carbon oxidation and maintains the magnetic properties of Fe3O4. Slowly increasing the temperature (5-5.5°C / min) can prevent structural collapse of the composite material.

[0034] In addition, the present invention introduces nano-hydroxyapatite and MgO, which release OH under acidic conditions. - Can neutralize H + , under alkaline conditions, through Ca 2+ / Mg 2+Fluoride ions are precipitated to achieve a wide range of pH values ​​from 3 to 13, ensuring efficient treatment of industrial wastewater with large pH fluctuations, such as acidic metallurgical wastewater or alkaline semiconductor wastewater.

[0035] The present invention ensures efficient compounding of Fe3O4 and biochar by limiting the amount of each raw material used in the preparation process of the La2O3 / charcoal-HAP-MgO-Fe3O4 composite and combining it with specific preparation parameters. Fe3O4 particles can act as a pore-forming agent and form macroporous-mesoporous channels after pyrolysis, further increasing the diffusion rate of fluorine therein and ensuring efficient absorption of fluorine.

[0036] In the third stage (SiO2 surface coating), the SiO2 protective layer is coated on the surface of the composite material to effectively prevent the loss and oxidation of rare earth components, ensuring that the composite defluoridation agent still has excellent performance after recycling. At the same time, SiO2 can also be combined with unconverted Fe3O4 to form Fe3O4@SiO2 composite, which has a great effect on F - The adsorption capacity of Fe3O4 can be increased by about 30%.

[0037] In the fourth stage (late activation), the regeneration stability of the composite defluoridating agent can be improved through late activation.

[0038] The present invention discloses the following technical effects:

[0039] 1. High-efficiency fluorine removal performance: Through the combination of multiple raw materials, it combines the advantages of multiple substances, not only improving the adsorption effect of fluorine, but also achieving a wide range of applicability of pH = 3 to 13, ensuring efficient treatment of industrial wastewater with large pH fluctuations such as acidic metallurgical wastewater or alkaline semiconductor wastewater.

[0040] 2. Good regeneration performance: The composite defluoridating agent obtained by the present invention can be reused many times, which reduces the use cost and improves the resource utilization rate.

[0041] 3. Environmentally friendly: Biochar is a widely available and renewable raw material, and the reagents used in the entire preparation process are relatively environmentally friendly, with minimal environmental pollution. Furthermore, the defluorination agent does not generate secondary pollution during use, thus meeting environmental protection requirements.

[0042] 4. Easy to separate and recycle: Since the composite material contains magnetic Fe3O4 particles, it can be easily separated from the treated solution under the action of an external magnetic field, avoiding the problems of difficult filtration and large loss that may occur in the separation process of traditional defluorination agents, thereby improving the operability and economy of the defluorination process. DETAILED DESCRIPTION

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0048] 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.

[0049] The preparation steps of the magnetic Fe3O4 particles used in the following examples and comparative examples of the present invention are as follows:

[0050] FeCl3·6H2O and FeSO4·7H2O were dissolved in water at a molar ratio of 2:1. Nitrogen was introduced into the reactor to remove oxygen. While nitrogen was being introduced, aqueous ammonia was added dropwise at 50°C until the pH reached 10 to generate a black Fe3O4 precipitate. After magnetic separation, the precipitate was washed and dried, ground and sieved to obtain magnetic Fe3O4 particles with a particle size of ≤30 nm.

[0051] Example 1

[0052] A composite defluoridating agent is provided, and the preparation steps are as follows:

[0053] The coconut shell was washed and dried, and then pyrolyzed in a muffle furnace at 550°C for 1 hour to obtain porous biochar. The porous biochar was soaked in 1 mol / L HCl for 24 hours to remove ash, washed to neutrality, dried, ground, and sieved to obtain biochar with a particle size of ≤200 μm.

[0054] The biochar was immersed in a 1 mol / L lanthanum nitrate aqueous solution for 2 h, and then calcined at 500 °C for 2 h under a nitrogen atmosphere to obtain a La2O3 / carbon support.

[0055] Prepare La2O3 / carbon support with a particle size of ≤200μm, MgO with a particle size of ≤500nm, prepared magnetic Fe3O4 particles and nanohydroxyapatite (rod-shaped particles with an aspect ratio of 1:3-5 and a length of 60-80nm);

[0056] La2O3 / carbon support, nano-hydroxyapatite, MgO and magnetic Fe3O4 particles were mixed in a mass ratio of 8:5:4:3 and then heat-treated. The heat treatment parameters were: nitrogen atmosphere, heating rate 5°C / min, temperature 500°C, and holding time 2h to obtain a composite material.

[0057] 100 g of the composite material, 3 g of tetraethyl orthosilicate, and 300 mL of an ethanol-water solution (the volume ratio of ethanol to water is 1:1) were mixed, and aqueous ammonia (the amount of aqueous ammonia was 2% of the total volume of the mixture of the composite material, tetraethyl orthosilicate, and solvent) was added dropwise thereto for catalytic hydrolysis for 12 h, followed by annealing at 300° C. for 1 h to obtain a SiO2-coated composite material;

[0058] The SiO2-coated composite material and sodium carboxymethyl cellulose are mixed, with the amount of sodium carboxymethyl cellulose being 3% of the mass of the SiO2-coated composite material, and granulated in a granulator to obtain 3 mm particles, which are then activated at 350° C. for 1 hour to obtain a composite defluoridant.

[0059] Example 2

[0060] A composite defluoridating agent is provided, and the preparation steps are as follows:

[0061] The corn stalks were washed, dried, and pyrolyzed in a muffle furnace at 600°C for 1 h to obtain porous biochar. The porous biochar was soaked in 1 mol / L HCl for 24 h to remove ash, washed to neutrality, dried, ground, and sieved to obtain biochar with a particle size of ≤200 μm.

[0062] The biochar was immersed in a 1 mol / L lanthanum chloride aqueous solution for 1 h, and then calcined at 580 °C for 2 h under a nitrogen atmosphere to obtain a La2O3 / carbon support.

[0063] Prepare La2O3 / carbon support with a particle size of ≤200μm, MgO with a particle size of ≤500nm, prepared magnetic Fe3O4 particles and nanohydroxyapatite (rod-shaped particles with an aspect ratio of 1:3-5 and a length of 80-100nm);

[0064] La2O3 / carbon support, nano-hydroxyapatite, MgO and magnetic Fe3O4 particles were mixed in a mass ratio of 5:5:3:2 and then heat-treated. The heat treatment parameters were: nitrogen atmosphere, heating rate 5.5℃ / min, temperature 550℃, and holding time 3h to obtain a composite material.

[0065] 100 g of the composite material, 3 g of tetraethyl orthosilicate, and 300 mL of an ethanol-water solution (the volume ratio of ethanol to water is 1:1) were mixed, and aqueous ammonia (the amount of aqueous ammonia was 2% of the total volume of the mixture of the composite material, tetraethyl orthosilicate, and solvent) was added dropwise thereto for catalytic hydrolysis for 12 h, followed by annealing at 300° C. for 1 h to obtain a SiO2-coated composite material;

[0066] The SiO2-coated composite material and sodium carboxymethyl cellulose are mixed, with the amount of sodium carboxymethyl cellulose being 3% of the mass of the SiO2-coated composite material, and granulated in a granulator to obtain 3 mm particles, which are then activated at 350° C. for 1 hour to obtain a composite defluoridant.

[0067] Example 3

[0068] A composite defluoridating agent is provided, and the preparation steps are as follows:

[0069] The rice husk was washed and dried, and then pyrolyzed in a muffle furnace at 600°C for 1 hour to obtain porous biochar; the porous biochar was soaked in 1 mol / L HCl for 24 hours to remove ash, washed to neutrality, dried, ground, and sieved to obtain biochar with a particle size of ≤200 μm;

[0070] The biochar was immersed in a 1 mol / L lanthanum chloride aqueous solution for 1 h, and then calcined at 580 °C for 2 h under a nitrogen atmosphere to obtain a La2O3 / carbon support.

[0071] Prepare La2O3 / carbon support with a particle size of ≤200μm, MgO with a particle size of ≤500nm, prepared magnetic Fe3O4 particles and nanohydroxyapatite (rod-shaped particles with an aspect ratio of 1:3-5 and a length of 40-50nm);

[0072] La2O3 / carbon support, nano-hydroxyapatite, MgO and magnetic Fe3O4 particles were mixed in a mass ratio of 8:8:4:2 and then heat-treated. The heat treatment parameters were: nitrogen atmosphere, heating rate 5°C / min, temperature 600°C, and holding time 3h to obtain a composite material.

[0073] 100 g of the composite material, 3 g of tetraethyl orthosilicate, and 300 mL of an ethanol-water solution (the volume ratio of ethanol to water is 1:1) were mixed, and aqueous ammonia (the amount of aqueous ammonia was 2% of the total volume of the mixture of the composite material, tetraethyl orthosilicate, and solvent) was added dropwise thereto for catalytic hydrolysis for 12 h, followed by annealing at 300° C. for 1 h to obtain a SiO2-coated composite material;

[0074] The SiO2-coated composite material and sodium carboxymethyl cellulose are mixed, with the amount of sodium carboxymethyl cellulose being 3% of the mass of the SiO2-coated composite material, and granulated in a granulator to obtain 3 mm particles, which are then activated at 350° C. for 1 hour to obtain a composite defluoridant.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that the addition of nano-hydroxyapatite is omitted, and the amount of MgO is increased to make up for the omitted amount of nano-hydroxyapatite. Other steps are the same as Example 1.

[0077] Comparative Example 2

[0078] The difference from Example 1 is that the addition of MgO is omitted, and the amount of nano-hydroxyapatite is increased to make up for the omitted amount of MgO. Other steps are the same as Example 1.

[0079] Comparative Example 3

[0080] The difference from Example 1 is that the addition of magnetic Fe3O4 particles is omitted, and the rest is the same as Example 1.

[0081] Comparative Example 4

[0082] The difference from Example 1 is that the preparation steps of the La2O3 / carbon support are adjusted, and the rest are the same as Example 1. Specifically, the biochar is immersed in a 1 mol / L lanthanum chloride aqueous solution for 1 hour, and then dried at 200°C for 1 hour to obtain the La2O3 / carbon support.

[0083] Comparative Example 5

[0084] The difference from Example 1 is that the SiO2 coating process is omitted, and the rest is the same as Example 1.

[0085] Comparative Example 6

[0086] The difference from Example 1 is that the activation process is omitted, and the rest is the same as Example 1.

[0087] Comparative Example 7

[0088] The difference from Example 1 is that the amount of magnetic Fe3O4 particles is adjusted to ensure that the mass ratio of La2O3 / carbon carrier, nanohydroxyapatite, MgO and magnetic Fe3O4 particles is 8:5:4:5 or 8:5:4:1. The rest is the same as Example 1.

[0089] Comparative Example 8

[0090] The difference from Example 1 is that the heat treatment temperature is adjusted to 600° C. or 400° C., and the rest is the same as Example 1.

[0091] Comparative Example 9

[0092] The difference from Example 1 is that the heating rate of the heat treatment is adjusted to 15° C. / min, and the rest is the same as Example 1.

[0093] Application Example 1

[0094] The defluorination agents obtained in the examples and comparative examples were used to treat acidic metallurgical wastewater, which was collected from a local metallurgical plant. - The concentration is 200mg / L.

[0095] Acidic metallurgical wastewater was divided into 14 equal parts. 1 g / L of the defluoridating agent obtained in each example and comparative example was added to the acidic metallurgical wastewater. The water was stirred at room temperature for 12 days at a stirring speed of 150 r / min. The water quality of the water source was tested after the experiment. The results are shown in Table 1.

[0096] Table 1 Water quality of the water source after the experiment

[0097]

[0098] Application Example 2

[0099] The defluorination agents obtained in each example and comparative example were used to treat alkaline semiconductor wastewater, which was collected from a local semiconductor production plant. - The concentration is 80mg / L.

[0100] The alkaline semiconductor wastewater was divided into 14 equal portions. 1.2 g / L of the defluoridating agent obtained in each example and comparative example was added to the alkaline semiconductor wastewater. The water was stirred at room temperature for 12 days at a stirring speed of 150 r / min. The water quality of the water source was tested after the experiment. The results are shown in Table 2.

[0101] Table 2 Water quality of the water source after the experiment

[0102]

[0103] Application Example 3

[0104] The defluoridating agents obtained in each embodiment and comparative example were used to treat agricultural sewage, which was obtained from the wastewater outlet of a local livestock and poultry breeding base. - The concentration is 4mg / L.

[0105] Agricultural wastewater was divided into 14 equal portions and subjected to a dynamic filter column test. 0.5 g / L of the defluoridating agent obtained in each example and comparative example was added to the agricultural wastewater. The filter was filled to a height of 50 cm and flowed at a rate of 5 BV / h for 30 days. The water quality of the source water was tested after the experiment. The results are shown in Table 3.

[0106] Table 3 Water quality of the water source after the experiment

[0107]

[0108]

[0109] As can be seen from Tables 1 to 3, the composite defluoridant obtained by the present invention is applicable to a wide range of pH values ​​of 3 to 13, ensuring efficient treatment of industrial wastewater with large pH fluctuations, such as acidic metallurgical wastewater or alkaline semiconductor wastewater. Moreover, since the pH value needs to be adjusted first during the conventional acidic wastewater treatment process, and the treatment process mainly relies on the flocculation effect of precipitation to remove fluorine, a large amount of sludge will be generated after treatment by conventional methods. However, the composite defluoridant obtained by the present invention does not require pH adjustment when treating acidic wastewater. The reaction process mainly relies on interfacial reactions such as adsorption and does not produce a large amount of sludge. At the same time, the composite defluoridant obtained by the present invention is also excellent in removing fluoride ions from agricultural wastewater with low fluoride ion content.

[0110] Application Example 4

[0111] Verify the recycling and reuse effect of the composite defluorination agent obtained in each embodiment and comparative example:

[0112] 0.1g of the composite defluoridating agent obtained in each example and comparative example was added into 100mL of F-containing - Solution (10 mg / L, pH = 7), shake for 30 min;

[0113] Use magnets to absorb composite defluoridation agents;

[0114] Immerse the composite defluoridant in 0.1 mol / L NaOH solution for 10 min, then wash with water until neutral, and dry at 60°C;

[0115] Repeat the above steps 10 times in total.

[0116] The adsorption capacity and regeneration rate were tested according to the following formula: Adsorption capacity (Q e ): (Unit: mg / g); Regeneration rate: (n is the number of cycles). Where C0 is the initial concentration of F in the solution. - Concentration, C e is the F in the solution after each cycle - concentration, V is the volume of the solution, m is the mass of the composite defluoridant, Q e,n is the adsorption capacity after 10 cycles, Q e,1 is the adsorption capacity after the first cycle.

[0117] The results are shown in Table 4.

[0118] Table 4

[0119]

[0120] As shown in Table 4, the composite defluoridating agent obtained by the present invention has an excellent regeneration effect and can be recycled multiple times.

[0121] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0122] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a composite defluoridating agent, characterized in that: The steps include: The biomass carbon is impregnated in a lanthanum-containing solution and then calcined to obtain a La2O3 / carbon support; The La2O3 / carbon support, nano-hydroxyapatite, MgO and magnetic Fe3O4 particles are mixed and then heat-treated to obtain a composite material; The composite material, tetraethyl orthosilicate and a solvent are mixed, and ammonia water is added dropwise thereto for catalytic hydrolysis, followed by annealing to obtain a SiO2-coated composite material; The SiO2-coated composite material and a binder are mixed and granulated, and then activated to obtain the composite defluoridating agent.

2. The preparation method according to claim 1, characterized in that The biomass charcoal is obtained by pyrolysis of waste biomass; the pyrolysis temperature is 550-650° C., and the time is 1-2 hours.

3. The preparation method according to claim 1, characterized in that The lanthanum-containing solution includes a lanthanum nitrate aqueous solution and / or a lanthanum chloride aqueous solution; and / or the concentration of the lanthanum-containing solution is 0.5 to 1 mol / L; and / or the impregnation time is 1 to 2 hours; and / or the calcination is carried out under a nitrogen atmosphere, the calcination temperature is 500 to 600° C., and the time is 2 to 3 hours.

4. The preparation method according to claim 1, characterized in that The mass ratio of the La2O3 / carbon carrier, nano-hydroxyapatite, MgO and magnetic Fe3O4 particles is 5-8:5-8:3-4:2-3.

5. The preparation method according to claim 1, characterized in that The heat treatment parameters are: nitrogen or argon atmosphere, heating rate 5-5.5°C / min, temperature 500-550°C, and holding time 2-3h.

6. The preparation method according to claim 1, characterized in that The solvent is an ethanol-water solution; the volume ratio of ethanol to water in the ethanol-water solution is 1:1-2; and / or the amount ratio of the composite material to the solvent is 1g:3-4mL, the amount of the tetraethyl orthosilicate used is 3-3.2% of the mass of the composite material, and the amount of the ammonia water used is 1-2% of the total volume of the mixed solution obtained by mixing the composite material, tetraethyl orthosilicate and the solvent.

7. The preparation method according to claim 1, characterized in that The catalytic hydrolysis time is 12 to 14 hours; and / or the annealing temperature is 300 to 350° C. and the time is 0.5 to 1 hour.

8. The preparation method according to claim 1, characterized in that The binder includes sodium carboxymethyl cellulose; and / or, the amount of the binder is 2-3% of the mass of the SiO2-coated composite material; and / or, the activation temperature is 350-400° C., and the activation time is 1-1.5 hours.

9. A composite defluoridating agent prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the composite defluoridating agent according to claim 9 in the treatment of fluorine-contaminated water.

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