A modified biochar-based heavy metal adsorption material and a preparation method thereof
Patent Information
- Application Number
- CN202610724689.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-25
- Publication Date
- 2026-08-28
AI Technical Summary
然而，现有技术中多采用分步改性策略，导致工艺复杂、成本高昂，且各组分间协同作用有限，难以兼顾高吸附容量与便捷分离的需求
[0015]本发明提供了一种改性生物炭基重金属吸附材料及其制备方法，相较于现有技术，该材料在组分设计、微观结构构筑以及制备工艺路线等方面均表现出显著的优势和有益效果。
Abstract
Description
Technical Field
[0001] This invention belongs to the field of adsorbent preparation technology, and relates to a modified biochar-based heavy metal adsorbent material and its preparation method. Background Technology
[0002] With the increase in industrial wastewater discharge, heavy metal pollution in water bodies, such as lead, cadmium, and copper, is becoming increasingly serious. Developing efficient and low-cost heavy metal adsorption materials has become a research hotspot in the environmental field.
[0003] Biochar, with its porous structure and large specific surface area, is widely used for heavy metal adsorption. However, its limited surface functional groups and poor adsorption selectivity restrict its practical application. To improve the adsorption performance of biochar, researchers have attempted to modify it by doping with heteroatoms or composite metal compounds. For example, sulfur doping can introduce specific adsorption sites such as thiol groups, enhancing its affinity for heavy metals; hydroxyapatite has good chemical precipitation properties for heavy metal ions; and iron oxide imparts magnetic separation properties, facilitating recycling and reuse. However, existing technologies often employ stepwise modification strategies, resulting in complex processes, high costs, and limited synergistic effects between components, making it difficult to simultaneously meet the requirements of high adsorption capacity and convenient separation.
[0004] Therefore, there is an urgent need to develop a modified biochar-based heavy metal adsorbent material that is simple to process, low in cost, and has excellent comprehensive performance. Summary of the Invention
[0005] The purpose of this invention is to provide a modified biochar-based heavy metal adsorbent material and its preparation method, which has the characteristics of high adsorption efficiency.
[0006] The objective of this invention can be achieved through the following technical solutions: A modified biochar-based heavy metal adsorbent material, comprising the following components by mass percentage: Sulfur-doped biochar matrix: 55%–80%; Nano-hydroxyapatite 15%~35%; 5%~10% of ferric oxide magnetic particles; The sulfur-doped biochar matrix has a specific surface area of 300-600 m² / g and a sulfur content of 1.5%-5.0% by mass. The sulfur mainly exists on the surface and in the framework of biochar in the form of mercapto, thioether and / or thiocarbonyl functional groups. The nano-hydroxyapatite and ferric oxide magnetic particles are loaded on the surface and inside the pores of the sulfur-doped biochar matrix, and the two are distributed together on the matrix.
[0007] Furthermore, the precursor biochar raw material of the sulfur-doped biochar matrix is selected from one or more of straw, fruit shells or lignocellulose; The preparation conditions of the precursor biochar are as follows: under a nitrogen atmosphere, the temperature is increased to 400-600 °C at a heating rate of 5-10 °C / min for pyrolysis, held at the temperature for 1-2 h, and then cooled and ground through a 60-100 mesh sieve to obtain biochar powder.
[0008] Furthermore, the nano-hydroxyapatite is distributed in the form of nanoparticles or thin layers on the surface and pore walls of the sulfur-doped biochar matrix. The magnetic particles of the iron oxide have a particle size of 10~50 nm and a saturation magnetization of 12~25 emu / g, and at least some of the magnetic particles of the iron oxide are embedded or attached to the surface or gaps of the nano-hydroxyapatite.
[0009] A method for preparing a modified biochar-based heavy metal adsorbent material includes the following steps: S1: After cleaning, drying and crushing the biomass raw materials, high-temperature pyrolysis is carried out under a nitrogen atmosphere. After cooling, the biochar powder is obtained by grinding and sieving. S2: Immerse the biochar powder obtained in step S1 in a 0.1~1 mol / L sulfur-containing compound solution, and then perform impregnation-heat treatment to dope sulfur into the biochar framework, thereby obtaining sulfur-doped biochar. S3: Disperse the sulfur-doped biochar obtained in step S2 in a calcium chloride solution to form suspension A; separately dissolve diammonium hydrogen phosphate, ferrous salt, and ferric salt in water to form solution B; S4: Under nitrogen protection and stirring conditions, solution B is slowly added dropwise to suspension A. At the same time, the pH value of the system is adjusted to 9-11 using 5% ammonia water. The reaction is carried out at 30-60℃ for 1-3 hours to allow nano-hydroxyapatite and ferric oxide magnetic particles to precipitate together on the sulfur-doped biochar. S5: The mixture obtained in step S4 is aged at room temperature for 6-12 hours, solid-liquid separation is performed using a magnet, and the mixture is washed with deionized water until the filtrate is neutral. Then, it is vacuum dried at 60-80°C for 6-12 hours, and finally calcined at 300-400°C for 1-2 hours under an inert atmosphere to obtain the modified biochar-based heavy metal adsorbent material.
[0010] Furthermore, in step S2, the sulfur-containing compound is selected from one or more of thiourea, sodium sulfide, thioacetamide, L-cysteine, or ammonium sulfate.
[0011] Furthermore, in step S2, the process parameters for the impregnation-heat treatment method are as follows: Biochar powder and sulfur-containing compound solution are mixed at a solid-liquid ratio of 1:10~30, stirred and impregnated at 60~90℃ for 2~6h, then dried at 80~120℃, and finally heat-treated at 150~250℃ for 1~3h under nitrogen protection.
[0012] Furthermore, in step S3, the concentration of the calcium chloride solution is 0.5~1.0 mol / L.
[0013] Furthermore, in step S3, the molar ratio of the ferrous salt to the ferric salt is 1:1~2, and the total iron ion concentration is 0.2~0.5 mol / L.
[0014] Furthermore, in step S3, the molar ratio of phosphorus in diammonium hydrogen phosphate, calcium in calcium chloride, and iron in iron salt is (3~5):(4~6):1.
[0015] This invention provides a modified biochar-based heavy metal adsorbent material and its preparation method. Compared with the prior art, this material shows significant advantages and beneficial effects in terms of component design, microstructure construction and preparation process.
[0016] First, this invention constructs a heavy metal adsorption system with multiple synergistic effects through specific component selection and proportioning. The adsorption material uses a sulfur-doped biochar matrix as its main framework, with its mass percentage controlled between 55% and 80%. This proportion ensures sufficient mechanical strength and abundant pore structure in the material, while also guaranteeing conductivity and the stability of the carbon matrix of the biochar itself. In this invention, the specific surface area of the sulfur-doped biochar matrix is 300–600 m² / g. This specific surface area range avoids the problems of drastically increased preparation costs and easy pore collapse caused by excessively high specific surface areas, while ensuring that the material has sufficient physical adsorption sites. More importantly, by controlling the mass content of sulfur to 1.5%–5.0%, and ensuring that it mainly exists in the form of mercapto (-SH), thioether (-CSC-), and / or thiocarbonyl (-C=S) functional groups on the surface and in the framework of the biochar, the chemical adsorption capacity of the material for heavy metal ions is significantly enhanced. Sulfur-containing functional groups such as thiol groups exhibit extremely strong coordination affinity and specific adsorption capacity for heavy metal ions such as mercury, lead, and cadmium. They can form stable sulfur-metal complexes with these heavy metal ions. This chemical bonding is far superior to the electrostatic attraction or ion exchange force of functional groups such as carboxyl and hydroxyl groups on the surface of traditional biochar, thus fundamentally improving adsorption selectivity and adsorption capacity. Furthermore, the porous structure of the biochar matrix itself provides physical retention space for heavy metal ions, achieving an organic combination of physical and chemical adsorption.
[0017] Secondly, this invention introduces nano-hydroxyapatite and magnetite (Fe3O4) magnetic particles as key functional modifying components, strictly controlling their mass percentages to 15-35% and 5-10%, respectively. Nano-hydroxyapatite exhibits excellent ion exchange capacity and chemical precipitation properties for heavy metal ions, generating more stable phosphate precipitates through a dissolution-precipitation mechanism or by undergoing a displacement reaction with heavy metal ions. In this invention, controlling the content of nano-hydroxyapatite at 15-35% fully utilizes its chemical fixation effect on heavy metals while avoiding problems such as overfilling of biochar pores, a sharp decrease in specific surface area, and poor dispersibility due to excessive material density caused by excessive addition. The introduction of magnetite magnetic particles endows the material with convenient magnetic separation properties; controlling their mass percentage at 5-10% allows the material to maintain high adsorption efficiency while achieving a saturation magnetization of 12-25. The magnetization range of emu / g ensures that the material can be quickly and completely separated from the aqueous solution under the action of an external magnetic field, effectively solving the problem that traditional powdered adsorbents are difficult to separate into solid and liquid and are prone to secondary pollution, greatly facilitating the recycling and regeneration of the material and its practical application. Through a specific preparation process, this invention enables nano-hydroxyapatite and magnetite magnetic particles to achieve a tight bond and reasonable spatial distribution on a sulfur-doped biochar matrix. Specifically, nano-hydroxyapatite is distributed in the form of nanoparticles or thin layers on the surface and pore walls of the sulfur-doped biochar matrix, while the particle size of the magnetite magnetic particles is controlled at 10-50 nm and is at least partially embedded or attached to the surface or interstices of the nano-hydroxyapatite. This microstructure design forms a unique "core-shell" or "interpenetrating" composite structure, which maximizes the interfacial contact area between the three components and makes the electron transfer path smoother, thus producing a significant synergistic effect: on the one hand, the precipitation effect of hydroxyapatite can quickly capture a large number of heavy metal ions, forming primary enrichment; on the other hand, the exposed sulfur-containing functional groups such as thiol groups can further chelate the unprecipitated fine ions or ions on the surface of the precipitated particles, forming a double protection; at the same time, the presence of magnetite not only provides magnetism, but the iron ions on its surface may also participate in the adsorption or catalytic oxidation process of specific heavy metals, and the tight binding with hydroxyapatite effectively inhibits the oxidation and loss of magnetic particles, improving the overall stability and cycle life of the material.
[0018] The preparation method provided by this invention has significant technological advantages. In step S1, readily available and inexpensive biomass raw materials such as straw, fruit shells, or lignocellulose are selected. By controlling the pyrolysis conditions, a biochar precursor with a suitable pore structure is prepared. This not only reduces raw material costs but also aligns with the environmental protection concept of waste resource utilization. The impregnation-heat treatment method in step S2 is the key step in achieving sulfur doping in this invention. By mixing biochar powder with a sulfur-containing compound solution at a specific solid-liquid ratio, and then impregnating at 60-90℃, drying at 80-120℃, and performing low-temperature heat treatment at 150-250℃, sulfur can be efficiently doped into the biochar framework, rather than merely adhering to the surface. This doping method ensures the thermal and chemical stability of the sulfur-containing functional groups, making them less prone to detachment during adsorption, thereby maintaining long-term adsorption performance. Steps S3 and S4 constitute the co-precipitation loading process of nano-hydroxyapatite and magnetic iron oxide particles. Suspension A was formed by dispersing sulfur-doped biochar in a calcium chloride solution, and solution B was formed by mixing diammonium hydrogen phosphate with ferrous and ferric salts. Solution B was then added dropwise to suspension A under nitrogen protection and stirring. The pH value was precisely controlled within the range of 9-11 using ammonia water. This pH environment is conducive to the nucleation and growth of hydroxyapatite and the co-precipitation of Fe²⁺ and Fe³⁺ to form iron(III) oxide. During this process, the molar ratio of phosphorus in diammonium hydrogen phosphate, calcium in calcium chloride, and iron in ferric salts was strictly controlled at (3-5):(4-6):1. This ratio is key to ensuring the formation of pure phase hydroxyapatite and spinel-structured iron(III) oxide, avoiding the formation of impurity phases, and ensuring the crystallinity and reactivity of the product. At the same time, in-situ precipitation in the presence of sulfur-doped biochar allows the generated nanoparticles to nucleate and grow directly on the surface and inside the pores of the biochar, effectively inhibiting the aggregation of nanoparticles and achieving uniform dispersion on the carrier. The aging, magnetic separation washing, drying, and calcination under an inert atmosphere in step S5 further optimize the crystal structure and surface properties of the material. Aging at room temperature for 6-12 hours helps to perfect and grow the crystals. Magnetic separation washing to neutrality ensures the removal of residual reactants and byproducts, avoiding interference with the subsequent adsorption environment. Vacuum drying at 60-80℃ removes moisture and prevents oxidation of magnetic particles. Finally, calcination at 300-400℃ under an inert atmosphere for 1-2 hours not only further stabilizes the carbon structure and removes residual organic impurities, but also promotes the fusion and bonding of the interfaces of various components, improving the overall mechanical strength and thermal stability of the material. Detailed Implementation
[0019] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below. Example
[0020] A modified biochar-based heavy metal adsorbent material, comprising the following components by mass percentage: 75% sulfur-doped biochar matrix; Nano-hydroxyapatite 17%; 8% of ferric oxide magnetic particles; The specific preparation method is as follows. S1: The washed, dried and crushed straw is heated to 500℃ under a nitrogen atmosphere at a heating rate of 5℃ / min for pyrolysis, kept at the temperature for 2 h, and then ground through a 100-mesh sieve after cooling to obtain biochar powder. S2: Immerse the biochar powder obtained in step S1 in a 5 mol / L thiourea solution, and then perform impregnation-heat treatment to dope sulfur into the biochar framework, thereby obtaining sulfur-doped biochar. The process parameters for the impregnation-heat treatment method are as follows: Biochar powder and sulfur-containing compound solution were mixed at a solid-liquid ratio of 1:20, stirred and impregnated at 75°C for 4 hours, then dried at 100°C, and finally heat-treated at 200°C for 2 hours under nitrogen protection. S3: Disperse the sulfur-doped biochar obtained in step S2 in a calcium chloride solution with a concentration of 0.5 mol / L to form suspension A; separately dissolve diammonium hydrogen phosphate, ferrous salt, and ferric salt in water to form solution B, wherein the molar ratio of ferrous salt to ferric salt is 1:1, the total iron ion concentration is 0.2 mol / L, and the molar ratio of phosphorus in diammonium hydrogen phosphate, calcium in calcium chloride, and iron in ferric salt is 4:5:1; S4: Under nitrogen protection and stirring conditions, solution B is slowly added dropwise to suspension A. At the same time, the pH value of the system is adjusted to 10 using 5% ammonia water. The reaction is carried out at 45℃ for 2 hours, so that nano-hydroxyapatite and ferric oxide magnetic particles are co-precipitated on the sulfur-doped biochar. S5: The mixture obtained in step S4 is aged at room temperature for 8 hours, solid-liquid separation is performed using a magnet, and the mixture is washed with deionized water until the filtrate is neutral. Then, it is vacuum dried at 80°C for 6 hours, and finally calcined at 300°C for 1 hour under an inert atmosphere to obtain the modified biochar-based heavy metal adsorbent material. Example
[0021] A modified biochar-based heavy metal adsorbent material, comprising the following components by mass percentage: Sulfur-doped biochar matrix 55%; Nano-hydroxyapatite 35%; 10% ferric oxide magnetic particles; The specific preparation method is as follows. S1: The washed, dried and crushed straw is heated to 400℃ under a nitrogen atmosphere at a heating rate of 5℃ / min for pyrolysis, kept at the temperature for 1 hour, cooled and then ground through a 60-mesh sieve to obtain biochar powder. S2: Immerse the biochar powder obtained in step S1 in a 5 mol / L sodium sulfide solution, and then perform impregnation-heat treatment to dope sulfur into the biochar framework, thereby obtaining sulfur-doped biochar. The process parameters for the impregnation-heat treatment method are as follows: Biochar powder and sulfur-containing compound solution were mixed at a solid-liquid ratio of 1:10, stirred and impregnated at 60°C for 2 hours, then dried at 80°C, and finally heat-treated at 150°C for 1 hour under nitrogen protection. S3: Disperse the sulfur-doped biochar obtained in step S2 in a calcium chloride solution with a concentration of 0.5 mol / L to form suspension A; separately dissolve diammonium hydrogen phosphate, ferrous salt, and ferric salt in water to form solution B, wherein the molar ratio of ferrous salt to ferric salt is 1:1, the total iron ion concentration is 0.2 mol / L, and the molar ratio of phosphorus in diammonium hydrogen phosphate, calcium in calcium chloride, and iron in ferric salt is 3:4:1; S4: Under nitrogen protection and stirring conditions, solution B is slowly added dropwise to suspension A. At the same time, the pH value of the system is adjusted to 9 using 5% ammonia water. The reaction is carried out at 30℃ for 1 hour, so that nano-hydroxyapatite and magnetite magnetic particles are co-precipitated on the sulfur-doped biochar. S5: The mixture obtained in step S4 is aged at room temperature for 6 hours, solid-liquid separation is performed using a magnet, and the mixture is washed with deionized water until the filtrate is neutral. Then, it is vacuum dried at 60°C for 6 hours, and finally calcined at 300°C for 1 hour under an inert atmosphere to obtain the modified biochar-based heavy metal adsorbent material. Example
[0022] A modified biochar-based heavy metal adsorbent material, comprising the following components by mass percentage: Sulfur-doped biochar matrix: 80%; Nano-hydroxyapatite 15%; 5% magnetic particles of ferric oxide; The specific preparation method is as follows. S1: The washed, dried and crushed fruit shells were heated to 600 °C under a nitrogen atmosphere at a heating rate of 10 °C / min for pyrolysis, held at the temperature for 2 h, cooled and then ground through a 100-mesh sieve to obtain biochar powder. S2: Immerse the biochar powder obtained in step S1 in a 1 mol / L thioacetamide solution, and then perform impregnation-heat treatment to dope sulfur into the biochar framework, thereby obtaining sulfur-doped biochar. The process parameters for the impregnation-heat treatment method are as follows: Biochar powder and sulfur-containing compound solution were mixed at a solid-liquid ratio of 1:30, stirred and impregnated at 90°C for 6 hours, then dried at 120°C, and finally heat-treated at 250°C for 3 hours under nitrogen protection. S3: Disperse the sulfur-doped biochar obtained in step S2 in a calcium chloride solution with a concentration of 1.0 mol / L to form suspension A; separately dissolve diammonium hydrogen phosphate, ferrous salt, and ferric salt in water to form solution B, wherein the molar ratio of ferrous salt to ferric salt is 1:2, the total iron ion concentration is 0.5 mol / L, and the molar ratio of phosphorus in diammonium hydrogen phosphate, calcium in calcium chloride, and iron in ferric salt is 5:6:1; S4: Under nitrogen protection and stirring conditions, solution B is slowly added dropwise to suspension A. At the same time, the pH value of the system is adjusted to 11 using 5% ammonia water. The reaction is carried out at 60℃ for 3 hours, so that nano-hydroxyapatite and ferric oxide magnetic particles are co-precipitated on the sulfur-doped biochar. S5: The mixture obtained in step S4 is aged at room temperature for 12 hours, solid-liquid separation is performed using a magnet, and the mixture is washed with deionized water until the filtrate is neutral. Then, it is vacuum dried at 80°C for 12 hours, and finally calcined at 400°C for 2 hours under an inert atmosphere to obtain the modified biochar-based heavy metal adsorbent material.
[0023] Comparative Example 1 This comparative example does not involve sulfur doping of the biochar; the remaining steps are the same as in Example 1.
[0024] Comparative Example 2 This comparative example does not add magnetite particles; the remaining steps are the same as in Example 1.
[0025] Comparative Example 3 This comparative example was prepared by physical mixing, that is, sulfur-doped biochar and magnetic composite were prepared separately and then mechanically mixed. The remaining steps were the same as in Example 1.
[0026] The specific surface area, saturation magnetization, and adsorption performance of the above embodiments and comparative examples were tested. A 100 mg / L Pb(NO3)2 solution was prepared as a simulated heavy metal wastewater, and the pH was adjusted to 5.0 with dilute nitric acid or sodium hydroxide. 0.05 g of adsorbent material was weighed and added to 100 mL of simulated wastewater, and the mixture was shaken and adsorbed for 2 hours at 25℃ and 150 rpm. After adsorption, solid-liquid separation was performed using an external magnet, and the concentration of heavy metal ions in the remaining solution was determined using inductively coupled plasma optical emission spectrometry (ICP-OES).
[0027] The experimental results are summarized in the table below. Experimental data show that the present invention significantly improves the overall performance of the material through a ternary in-situ composite strategy of sulfur doping-hydroxyapatite-Fe3O4: Comparing Example 1 with Comparative Example 1, sulfur doping significantly increases the adsorption capacity of Pb²⁺ from 98.7 mg / g to 189.6 mg / g, indicating that the introduced sulfur-containing functional groups have a strong specific adsorption effect on heavy metal ions; Comparing Example 1 with Comparative Example 2, although the adsorption capacities are similar, Comparative Example 2 has a saturation magnetization close to 0 due to the lack of magnetic particles, making magnetic separation impossible, thus verifying the necessity of the magnetic component; Example 1 shows a higher adsorption capacity than the physically mixed Comparative Example 3, and combined with BET data, it shows that the in-situ composite process can effectively maintain the pore structure of the material and promote synergistic effects among the components.
[0028] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.
Claims
1. A modified biochar-based heavy metal adsorbent material, characterized in that, It consists of the following components by mass percentage: Sulfur-doped biochar matrix: 55%–80%; Nano-hydroxyapatite 15%~35%; 5%~10% of magnetic particles of ferric oxide; The sulfur-doped biochar matrix has a specific surface area of 300-600 m² / g and a sulfur content of 1.5%-5.0% by mass. The sulfur mainly exists on the surface and in the framework of biochar in the form of mercapto, thioether and / or thiocarbonyl functional groups. The nano-hydroxyapatite and ferric oxide magnetic particles are loaded on the surface and inside the pores of the sulfur-doped biochar matrix, and the two are distributed together on the matrix.
2. The modified biochar-based heavy metal adsorbent material according to claim 1, characterized in that, The precursor biochar raw material of the sulfur-doped biochar matrix is selected from one or more of straw, fruit shells or lignocellulose. The preparation conditions of the precursor biochar are as follows: under a nitrogen atmosphere, the temperature is increased to 400-600 °C at a heating rate of 5-10 °C / min for pyrolysis, held at the temperature for 1-2 h, and then cooled and ground through a 60-100 mesh sieve to obtain biochar powder.
3. The modified biochar-based heavy metal adsorbent material according to claim 1, characterized in that, The nano-hydroxyapatite is distributed in the form of nanoparticles or thin layers on the surface and pore walls of the sulfur-doped biochar matrix. The magnetic particles of the iron oxide have a particle size of 10~50 nm and a saturation magnetization of 12~25 emu / g, and at least some of the magnetic particles of the iron oxide are embedded or attached to the surface or gaps of the nano-hydroxyapatite.
4. A method for preparing a modified biochar-based heavy metal adsorbent material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: After cleaning, drying and crushing the biomass raw materials, high-temperature pyrolysis is carried out under a nitrogen atmosphere. After cooling, the biochar powder is obtained by grinding and sieving. S2: Immerse the biochar powder obtained in step S1 in a 0.1~1 mol / L sulfur-containing compound solution, and then perform impregnation-heat treatment to dope sulfur into the biochar framework, thereby obtaining sulfur-doped biochar. S3: Disperse the sulfur-doped biochar obtained in step S2 in a calcium chloride solution to form suspension A; separately dissolve diammonium hydrogen phosphate, ferrous salt, and ferric salt in water to form solution B; S4: Under nitrogen protection and stirring conditions, solution B is slowly added dropwise to suspension A. At the same time, the pH value of the system is adjusted to 9-11 using 5% ammonia water. The reaction is carried out at 30-60℃ for 1-3 hours to allow nano-hydroxyapatite and ferric oxide magnetic particles to precipitate together on the sulfur-doped biochar. S5: The mixture obtained in step S4 is aged at room temperature for 6-12 hours, solid-liquid separation is performed using a magnet, and the mixture is washed with deionized water until the filtrate is neutral. Then, it is vacuum dried at 60-80°C for 6-12 hours, and finally calcined at 300-400°C for 1-2 hours under an inert atmosphere to obtain the modified biochar-based heavy metal adsorbent material.
5. The preparation method according to claim 4, characterized in that, In step S2, the sulfur-containing compound is selected from one or more of thiourea, sodium sulfide, thioacetamide, L-cysteine, or ammonium sulfate.
6. The preparation method according to claim 4, characterized in that, In step S2, the process parameters for the impregnation-heat treatment method are as follows: Biochar powder and sulfur-containing compound solution are mixed at a solid-liquid ratio of 1:10~30, stirred and impregnated at 60~90℃ for 2~6h, then dried at 80~120℃, and finally heat-treated at 150~250℃ for 1~3h under nitrogen protection.
7. The preparation method according to claim 4, characterized in that, In step S3, the concentration of the calcium chloride solution is 0.5~1.0 mol / L.
8. The preparation method according to claim 4, characterized in that, In step S3, the molar ratio of the ferrous salt to the ferric salt is 1:1~2, and the total iron ion concentration is 0.2~0.5 mol / L.
9. The preparation method according to claim 4, characterized in that, In step S3, the molar ratio of phosphorus in diammonium hydrogen phosphate, calcium in calcium chloride, and iron in iron salt is (3~5):(4~6):1.