Preparation method and application of magnetic biochar adsorption material

Abstract

The invention provides a preparation method and application of a magnetic biochar adsorption material, and relates to the technical field of biochar adsorption materials. The adsorption material is prepared by taking three kinds of biomass including municipal sludge, straw and antimony ore waste residues as biochar sources and further loading magnetic nano gamma-Fe2O3 particles. In the process, by controlling the mass of the municipal sludge, the straw and the antimony ore waste residues, the composition and performance of the biochar base material in the adsorption material can be regulated and controlled, rich active sites in the sludge and the straw are fully utilized, loading of the magnetic nano gamma-Fe2O3 particles is achieved, and the adsorption efficiency is improved. A microfibril structure in the straw and a high-activity mesoporous carrier in the antimony ore waste residue not only can improve the load rate of the magnetic nano gamma-Fe2O3 particles to a certain extent, but also can be beneficial to diffusion and capture of heavy metal ions in the application process, so that the adsorption rate of the material to the heavy metal ions is improved on the whole.

Description

Technical Field

[0001] The present invention relates to the technical field of biochar adsorption materials, and particularly to a preparation method and application of a magnetic biochar adsorption material. Background Art

[0002] Antimony (Sb) and its associated heavy metals (Pb(II), Cd(II)) are globally controlled environmental pollutants. Due to the complex rainfall characteristics, yard characteristics, geological and hydrological conditions in antimony mining areas, and the complex chemical composition of antimony ore slag and the release of heavy metals under rainfall leaching in the yard, resulting in complex antimony-containing multi-metal wastewater, there is less research on the slag reduction - resource utilization of multi-source solid wastes in antimony mining areas and the treatment technology of yard antimony-containing multi-metal wastewater. For the treatment technologies of heavy metal wastewater at home and abroad, adsorption composite materials are regarded as effective and economical methods due to their advantages such as simple operation, high adsorption capacity, and sustainability. In the process of material selection, magnetic iron oxide shows significant advantages due to its excellent stability and outstanding metal adsorption ability, becoming an ideal magnetic-based material. And γ-Fe2O3 shows broad application potential in the treatment of heavy metal pollution, especially in the adsorption process of Sb, due to its stable structure and high adsorption efficiency. In the process of selecting carbon-based materials, biochar is a porous solid material formed by the pyrolysis and carbonization of organic matter in an anaerobic or anoxic environment, with a high specific surface area and carbon content. In recent years, due to its excellent adsorption performance, biochar has been widely used to remove heavy metals, organic pollutants, and nutrients in water. Domestic and foreign scholars have successfully developed some mineral-based and magnetic modified mineral-based nano-adsorption materials with good economy, strong selectivity, recyclability, and large adsorption capacity, and they show significant efficacy in treating single heavy metal wastewater. However, there are difficulties in treating multi-heavy metal wastewater, and the adsorption materials are prone to loss, difficult to separate and recycle, and there is a lack of development of composite materials using a wide range of and low-cost multi-source solid wastes in mining areas.

[0003] In view of this, it is necessary to design an improved preparation method and application of a magnetic biochar adsorption material to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method and application of a magnetic biochar adsorption material.

[0005] To achieve the above invention purpose, the present invention provides a preparation method of a magnetic biochar adsorption material, including the following steps:

[0006] S1. Mix the biomass mixture with an aqueous carboxymethyl cellulose solution and dry to obtain a biochar precursor; the biomass mixture is composed of municipal sludge, straw, and antimony ore waste residue;

[0007] S2. After mixing the biochar precursor obtained in step S1 with the magnetic γ-Fe₂O₃ precursor solution, perform a hydrothermal reaction at 160 - 180 °C for 15 - 17 h. After subjecting the reaction product to segmented pyrolysis treatment, a magnetic biochar adsorbent material is prepared.

[0008] Preferably, in step S1, the mass ratio of municipal sludge, straw, and antimony ore waste residue is (3 - 5)∶(2 - 4)∶(1 - 3).

[0009] Preferably, in step S2, the magnetic γ-Fe₂O₃ precursor solution is obtained by dissolving FeCl₃·6H₂O and urea in a molar ratio of 1∶(1 - 3) in 40 - 60 mL of ethylene glycol.

[0010] Preferably, in step S2, the segmented pyrolysis treatment is carried out as follows: in a nitrogen atmosphere, keep the temperature at 100 - 200 °C for 30 min, then keep the temperature at 200 - 300 °C for 30 min, and finally, keep the temperature at 300 - 400 °C for 60 min.

[0011] Preferably, in step S1, the municipal sludge needs to be pretreated. The pretreatment is carried out as follows: add FeSO₄·7H₂O and H₂O₂ to the municipal sludge to be treated. The addition amount of FeSO₄·7H₂O is 0.15 mol / kg, and the addition amount of H₂O₂ is 0.75 mol / kg. The pH of the solution after adding H₂O₂ is 3.0. After reacting for 1 h, add Ca(OH)₂ until the pH of the solution = 7.0. The obtained precipitate is dried to obtain the pretreated municipal sludge.

[0012] Preferably, in step S1, the antimony ore waste residue needs to be pretreated. The pretreatment is carried out as follows: crush the antimony ore waste residue to be treated into particles with a particle size less than 0.5 cm, then perform acid washing on the particles. The eluent for acid washing is 1 M HCl, the flow rate is 2 BV / h, the liquid-solid ratio is 10:1, and the number of acid washing times is 3 times; then, use zirconia balls as grinding balls to perform ball milling activation on the acid-washed particles. The ball-to-material ratio is 10:1, the rotation speed is 300 rpm, and the ball milling time is 2 h; after the ball milling is completed, dry at 80 °C for 12 h to obtain the pretreated antimony ore waste residue.

[0013] Preferably, in step S1, the mass ratio of municipal sludge, straw, and antimony ore waste residue is 4:3:2.

[0014] Preferably, in step S2, the segmented pyrolysis treatment is carried out as follows: in a nitrogen atmosphere, keep the temperature at 100 °C for 30 min, then keep the temperature at 200 °C for 30 min, and finally, keep the temperature at 300 °C for 60 min.

[0015] The magnetic biochar adsorption material prepared by the preparation method proposed in the present invention includes:

[0016] Biochar, which serves as a substrate;

[0017] Magnetic nano-γ-Fe2O3 particles, which are distributed inside and on the surface of the pore structure of the biochar, with a particle size of 200 - 500 nm, and the specific surface area of the magnetic biochar adsorption material is 20 - 80 m 2 / g. The magnetic biochar adsorption material can be applied to the adsorption of Sb(V), Pb(II) and Cd(II) in wastewater.

[0018] The beneficial effects of the present invention are:

[0019] 1. The preparation method of the magnetic biochar adsorption material provided by the present invention uses municipal sludge, straw, and antimony ore waste residue as the sources of biochar, and further loads magnetic nano-γ-Fe2O3 particles, which can make full use of the structural and compositional characteristics of the three to achieve the loading of magnetic nano-γ-Fe2O3 particles. In the above process, by controlling the masses of municipal sludge, straw, and antimony ore waste residue, the composition and properties of the biochar substrate in the adsorption material can be regulated, making full use of the abundant active sites in the sludge and straw to achieve the loading of magnetic nano-γ-Fe2O3 particles. Moreover, the microfibril structure in the straw and the highly active mesoporous carrier in the antimony ore waste residue can not only improve the loading rate of magnetic nano-γ-Fe2O3 particles to a certain extent, but also facilitate the diffusion and capture of heavy metal ions during the application process, thus overall enhancing the adsorption rate of the material to heavy metal ions.

[0020] 2. The preparation method provided by the present invention realizes the loading of magnetic nano-γ-Fe2O3 particles in the biochar precursor by means of hydrothermal treatment and staged pyrolysis, which can avoid the aggregation of nanoparticles, and at the same time effectively enhance the binding force between the γ-Fe2O3 precursor and the biochar precursor, making it easier to achieve loading, ensuring the effective combination of the loaded particles and the biochar precursor together, enhancing the overall stability of the material, and avoiding the instability of the material performance caused by the shedding of nanoparticles during the application process. Description of the Drawings

[0021] Figure 1 is the process flow chart of the preparation method of the magnetic biochar adsorption material proposed by the present invention;

[0022] Figure 2 is the XRD pattern of the magnetic biochar adsorption material prepared in Example 1 of the present invention;

[0023] Figure 3 is the FTIR pattern of the magnetic biochar adsorption material prepared in Example 1 of the present invention;

[0024] Figure 4 BET result diagram of the magnetic biochar adsorption material prepared in Example 1 of the present invention;

[0025] Figure 5 VSM characterization diagram of the magnetic biochar adsorption material prepared in Example 1 of the present invention;

[0026] Figure 6 SEM diagram of the magnetic biochar adsorption material prepared in Example 1 of the present invention;

[0027] Figure 7 is Figure 6 partial enlarged view of;

[0028] Figure 8 Cyclic adsorption experiment results of the magnetic biochar adsorption material prepared in Example 1 of the present invention for Sb(V), Pb(II) and Cd(II);

[0029] Figure 9 Adsorption results of the magnetic biochar adsorption material prepared in Example 1 of the present invention for Sb(V) in the presence of interfering ions;

[0030] Figure 10 Adsorption results of the magnetic biochar adsorption material prepared in Example 1 of the present invention for Pb(II) in the presence of interfering ions;

[0031] Figure 11 Adsorption results of the magnetic biochar adsorption material prepared in Example 1 of the present invention for Cd(II) in the presence of interfering ions. Detailed implementation manners

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Here, it should also be noted that in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0034] In addition, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0035] On the one hand, the present invention provides a magnetic biochar adsorption material, which includes:

[0036] Biochar, which serves as a substrate;

[0037] Magnetic nano γ-Fe2O3 particles are distributed within and on the surface of the pore structure of biochar, with a particle size of 200 - 500 nm. The specific surface area of the magnetic biochar adsorption material is 20 - 80 m 2 / g.

[0038] Please refer to Figure 1 as shown. The present invention provides a preparation method of a magnetic biochar adsorption material, which includes the following steps:

[0039] S1. After mixing the pretreated municipal sludge, straw and antimony ore waste residue, mix with an aqueous solution of carboxymethyl cellulose and dry to obtain a biochar precursor;

[0040] S2. After mixing the biochar precursor obtained in step S1 with a magnetic γ-Fe2O3 precursor solution, carry out a hydrothermal reaction at 160 - 180 °C for 15 - 17 h. After the reaction product is subjected to segmented pyrolysis treatment, a magnetic biochar adsorption material is obtained.

[0041] In the above technical solution, the γ-Fe2O3 precursor (iron hydroxide and related products) is synthesized through a hydrothermal reaction between FeCl3·6H2O (as the magnetic component) and urea (as the alkaline reaction agent), and is uniformly loaded onto the biochar precursor. Then, through pyrolysis treatment, the γ-Fe2O3 precursor is transformed into magnetic nano γ-Fe2O3, effectively ensuring the uniformity and stability of the loading. This is because after directly loading the γ-Fe2O3 precursor into the biochar precursor and then transforming the precursor into magnetic nano-ions, the aggregation of nanoparticles can be avoided. At the same time, compared with the method of directly loading nano γ-Fe2O3 on biochar, the binding force between the γ-Fe2O3 precursor and the biochar precursor is stronger, making it easier to achieve loading, ensuring the effective combination of the loaded particles and the biochar precursor, improving the overall stability of the material, and avoiding the instability of the material performance caused by the shedding of nanoparticles during application.

[0042] The preparation mechanism and application of the magnetic biochar adsorption material provided by the present invention are as follows: After sludge carbonization, active oxygen-containing functional groups such as –COOH and –OH are exposed on the surface, which can not only provide binding sites for the loading process of γ-Fe2O3, but also provide complexation and electrostatic adsorption sites for metal ions to be adsorbed during subsequent applications; after straw carbonization, a developed microfiber pore structure is formed inside, significantly improving the specific surface area and mass transfer performance. During the preparation stage, it is beneficial for the precursor solution of γ-Fe2O3 to penetrate into the interior of the carbon precursor, and during the application process, it can play a certain enrichment role in the solution to be treated, improving the adsorption effect of target metal ions; after the antimony ore waste residue is carbonized, a mineral skeleton containing a large amount of SiO2, Al2O3, etc. is formed inside, providing a stable support structure and mineral-based adsorption sites for the whole adsorption material. The three carbon source precursors cooperate to endow the adsorption material with good pore structure, chemical stability and interfacial reaction activity. During the application process, the three types of metal ions are adsorbed through different mechanisms: Sb(V) is preferentially combined with Fe–OH sites in the form of anions through electrostatic adsorption and surface coordination to form an Fe–O–Sb complex structure, which can further adjust the surface charge and functional group arrangement, promoting the complexation and precipitation adsorption of subsequent Pb(II) and Cd(II), thereby realizing the synergistic enrichment and mutual promotion effect among the three, and finally significantly improving the removal rate of metal ions and the application stability of the material.

[0043] In some embodiments, in step S1, the pretreatment of municipal sludge is carried out as follows: Add FeSO4·7H2O and H2O2 with a mass percentage of 30% to the municipal sludge to be treated, and the molar ratio of the two is 1:5. The addition amount of FeSO4·7H2O is 0.15 mol / kg, and the addition amount of H2O2 is 0.75 mol / kg. That is, the addition amount of FeSO4·7H2O in 1 kg of dry-based municipal sludge is 0.15 mol, and the addition amount of H2O2 in 1 kg of dry-based municipal sludge is 0.75 mol. The pH of the solution in the early stage of treatment is 3.0, and the reaction is carried out for 1 h. Use the Fenton reaction between Fe 2+ and H2O2 to generate hydroxyl radicals ·OH. The strongly oxidizing ·OH can destroy the organic matter structure in the sludge, improve the dewatering performance, and degrade toxic and harmful substances; subsequently, add Ca(OH)2 until the pH = 7.0, and let it stand for 30 min to precipitate the residual Fe 3+ , and dehydrate it by means of pressure filtration to ensure that the moisture content of the filter residue is less than 65%; crush the filter residue to a particle size of 100 mesh and dry it at 60 °C until the moisture content is less than 10%, and the pretreated municipal sludge is obtained. Among them, the conditions for the pressure filtration process are: pressure 0.8 MPa, time 30 min.

[0044] Furthermore, the pretreatment of straw is carried out as follows: The alkali treatment-mechanical crushing combined process is adopted for treatment, and the specific treatment steps are as follows: The straw to be treated is put into a 1% NaOH solution, soaked at room temperature for 12 h according to a liquid-solid ratio of 10:1 to remove part of the lignin and expand the fiber structure in the straw. The straw is turned over every 3 h during the treatment process to ensure that the straw is fully treated. After the soaking treatment, it is thoroughly rinsed with deionized water until the pH of the filtrate is close to neutral (6.5 - 7.0), and then dried for standby; The dried straw is crushed into straw segments with a length of 5 - 10 cm to reduce the energy consumption of subsequent treatment. After crushing, the segmented straw is rinsed with deionized water to avoid affecting the conductivity of the material. Then, the segmented straw is processed to a D90 of less than 2 mm and vacuum dried until the moisture content of the straw is less than 10%.

[0045] The pretreatment of antimony ore waste residue is carried out according to the following method: First, the waste residue is crushed into particles with a particle size of less than 0.5 cm, and then the particles are pickled with a percolation column. The pickling eluent is 1 M HCl, the flow rate is 2 BV / h, the liquid-solid ratio is 10:1, and the number of pickling times is 3 times; Then, zirconia balls with a diameter of 5 mm are used as grinding balls to ball-mill and activate the pickled particles. The ball-to-material ratio is 10:1, the rotation speed is 300 rpm, and the ball-milling time is 2 h. During the ball-milling process, the forward and reverse rotations are alternated every 10 min to ensure sufficient ball-milling; After the ball-milling is completed, it is rinsed with an alkali solution to remove the adsorbed acidic solution on the surface of the particles. Finally, it is dried at 80 °C for 12 h to obtain the pretreated antimony ore waste residue. Among them, the size of the percolation column is: inner diameter 10 cm, height 50 cm, and the internal filling height of the waste residue bed layer is 30 cm.

[0046] By selecting antimony ore waste residue as the source of carbon precursor, its active mineral components can be utilized to construct a functional framework. This is because antimony ore waste residue is rich in mineral components such as SiO2, Al2O3, and Fe2O3, which can be transformed into silica-alumina-based neutral frameworks with strong stability and surface reaction activity during pyrolysis and activation, helping to enhance the structural strength and pore stability of the material; Secondly, there may be trace amounts of Sb or Sb oxidation state species remaining in the antimony ore waste residue, which can participate in doping or surface coordination during the construction of the composite material, regulating the electron distribution and surface charge of the material, thereby enhancing the electron affinity between the adsorbent and the metal ions to be removed (especially Sb(V)), and improving the selective recognition ability for the target metal; Moreover, some metal oxides in the antimony ore waste residue, such as Fe-O, Al-O and Sb-O, have the potential for synergistic complexation or coprecipitation, which helps to form a stable surface coordination structure during the adsorption process, effectively enhancing the synergistic enrichment and selective adsorption effects on coexisting heavy metal ions such as Sb(V), Pb(II), and Cd(II).

[0047] In the above technical solution, by using the Fenton method to pretreat municipal sludge, the active sites in the sludge can be exposed (-COOH, -OH, etc.), providing more active sites for the adsorption of heavy metal ions and simultaneously improving the surface chemical properties and hydrophilicity of the material; by using an alkali treatment method to treat straw, its microfibril structure can be exposed, and the surface of this structure is rich in active hydroxyl groups -OH, providing a template for the loading of magnetic nanoparticles; by ball-milling and pickling antimony ore waste residue, the iron and manganese minerals in it can be converted into highly active mesoporous carriers, which is beneficial to the loading of magnetic nanoparticles. When used for the adsorption of heavy metal ions subsequently, the presence of the mesoporous structure is conducive to the diffusion and capture of heavy metal ions, enhancing the adsorption of heavy metal ions by the material.

[0048] In some embodiments, in step S1, the mass ratio of municipal sludge, straw, and antimony ore waste residue is (3 - 5)∶(2 - 4)∶(1 - 3); carboxymethyl cellulose aqueous solution is used as an adhesive, and its mass percentage in all raw materials is 2 wt%, that is, the ratio of the mass of the carboxymethyl cellulose aqueous solution to the sum of the masses of municipal sludge, straw, antimony ore waste residue, and carboxymethyl cellulose aqueous solution is 2%. The straw is the stems and leaves of crops such as rice, corn, and wheat.

[0049] In the above technical solution, by controlling the masses of municipal sludge, straw, and antimony ore waste residue, the composition and properties of the biochar substrate in the adsorption material can be regulated, making full use of the abundant active sites in the sludge and straw to achieve the loading of magnetic nano γ-Fe2O3 particles. The microfibril structure in the straw and the highly active mesoporous carriers in the antimony ore waste residue can not only improve the loading rate of magnetic nano γ-Fe2O3 particles to a certain extent but also facilitate the diffusion and capture of heavy metal ions during the application process, overall enhancing the adsorption rate of the material for heavy metal ions.

[0050] In some embodiments, in step S2, the magnetic γ-Fe2O3 precursor solution is obtained by dissolving FeCl3·6H2O and urea in a molar ratio of 1∶(1 - 3) in 40 - 60 mL of ethylene glycol.

[0051] In some embodiments, in step S2, the staged pyrolysis treatment includes the following stages: in a nitrogen environment, keep the temperature at 100 - 200 °C for 30 min, then keep the temperature at 200 - 300 °C for 30 min, and finally, keep the temperature at 300 - 400 °C for 60 min.

[0052] In the above technical solution, at 100-200 °C, hemicellulose in straw can be cracked to generate microporous structures, and protein functional groups in sludge can be retained; at 200-300 °C, the carbonization of biochar precursors can be promoted to form mesoporous networks, and the silicon-aluminum components in the waste residue can be used to construct mineral skeletons; at 300-400 °C, the formation of adsorption structures is facilitated. Through staged temperature control and atmosphere regulation, the pore structure, surface chemical properties and magnetic nanoparticle loading of biochar can be optimized, endowing the material with excellent adsorption performance.

[0053] The preparation method and application of the magnetic biochar adsorption material proposed by the present invention will be further described below in conjunction with specific embodiments:

[0054] Example 1

[0055] In this example, a magnetic biochar adsorption material was prepared, and the preparation method included the following steps:

[0056] S1. Mix municipal sludge with FeSO4·7H2O and 30% H2O2 by mass percentage. The addition amount of FeSO4·7H2O is 0.15 mol / kg, and the addition amount of H2O2 is 0.75 mol / kg. That is, the addition amount of FeSO4·7H2O in 1 kg of dry-based municipal sludge is 0.15 mol, and the addition amount of H2O2 in 1 kg of dry-based municipal sludge is 0.75 mol. The pH of the solution in the early stage of treatment is 3.0. Use the Fenton reaction between Fe 2+ and H2O2 to generate hydroxyl radicals ·OH. The strongly oxidizing ·OH can destroy the organic matter structure in the sludge, improve the dewatering performance, and degrade toxic and harmful substances; subsequently, add Ca(OH)2 until pH = 7.0 to precipitate residual Fe 3 + , and dehydrate by pressure filtration to ensure that the moisture content of the filter residue is less than 65%; crush the filter residue to a particle size of 100 mesh and dry it at 60 °C until the moisture content is less than 10%, that is, the pretreated municipal sludge is obtained; among them, the conditions of the pressure filtration process are: pressure 0.8 MPa, time 30 min. The municipal sludge is taken from the dewatered sludge of the sewage treatment plant in Baodaxing Mining Area, Xikuangshan, Hunan. Its total solid (TS) is 35.6%, and the volatile solid (VS) is 52.7%;

[0057] The treatment is carried out by using the combined process of alkali treatment and mechanical crushing, including coarse crushing, washing, fine crushing and drying. Coarse crushing is to cut the rice straw into sections with a length of 5 - 10 cm to reduce the energy consumption of subsequent treatment. After coarse crushing, the sectioned straw is rinsed with deionized water to avoid affecting the conductivity of the material. Then, the sectioned straw is processed to a D90 of less than 2 mm and vacuum dried to a moisture content of less than 10% to obtain the pretreated rice straw. The rice straw is taken from the rice straw around the mining area, with a cellulose content of 35%, a hemicellulose content of 25%, and a lignin content of 20%.

[0058] First, the antimony ore waste residue is crushed into particles with a particle size of less than 0.5 cm, and then the particles are pickled with a percolation column. The pickling eluent is 1 M HCl, the flow rate is 2 BV / h, the liquid-solid ratio is 10:1, and the pickling times are 3 times. Then, using zirconia balls with a diameter of 5 mm as grinding balls, the pickled particles are ball-milled and activated with a ball-to-material ratio of 10:1, a rotation speed of 300 rpm, and a ball-milling time of 2 h. During the ball-milling process, the rotation direction is reversed every 10 minutes to ensure sufficient ball-milling. After ball-milling, it is rinsed with an alkali solution to remove the adsorbed acidic solution on the surface of the particles, and finally dried at 80 °C for 12 h to obtain the pretreated antimony ore waste residue. Among them, the size of the percolation column is: inner diameter 10 cm, height 50 cm, and its internal filling height of the waste residue bed layer is 30 cm. The antimony ore waste residue is taken from the surface weathered waste residue of the slag yard of Baodaxing Mining Area in Xikuangshan, Hunan. Its particle size is 1 - 5 cm, and the main minerals are 45% quartz, 30% calcite, 15% limonite, and the balance is impurities.

[0059] After mixing the pretreated municipal sludge, rice straw and antimony ore waste residue according to the mass ratio of 4:3:2, it is mixed with 1.8 mL of carboxymethyl cellulose aqueous solution. The obtained mixed solution is kneaded in a kneader for 30 min to form a plastic blank, and then pressed into a Φ20×10 mm cylindrical blank by a hydraulic press at a pressure of 20 MPa and cured and dried at room temperature for 12 h to obtain the biochar precursor. The mass percentage of the carboxymethyl cellulose aqueous solution in the mixed solution is 2 wt%.

[0060] S2. After mixing the biochar precursor obtained in step S1 with the magnetic γ-Fe₂O₃ precursor solution, perform a hydrothermal reaction at 170 °C for 16 h. Collect the reaction product, wash it 3 - 5 times each with ethanol and deionized water, dry it in an environment at 60 °C, then place the sample in a three-stage tubular furnace. Under the condition of T1 = 100 °C, keep it warm for 30 min, then under the condition of T2 = 200 °C, keep it warm for 30 min, and then under the condition of T3 = 300 °C, keep it warm for 60 min to perform segmented pyrolysis treatment on the sample, thus obtaining the magnetic biochar adsorbent material. The whole process of pyrolysis treatment is carried out in a nitrogen environment, and the gas flow rate is 200 mL / min. Among them, the magnetic γ-Fe₂O₃ precursor solution is obtained by adding FeCl₃·6H₂O and urea into 50 mL of ethylene glycol (analytical pure), and the molar ratio of FeCl₃·6H₂O to urea is 1:2.

[0061] The XRD pattern of the magnetic biochar adsorbent material is as Figure 2 shown. By comparing it with the XRD standard card of γ-Fe₂O₃, it can be seen that the diffraction peaks of the adsorbent material mainly include the characteristic peaks of γ-Fe₂O₃ (2θ = 35.7°, 57.3°, 62.9°, etc.) and the broad peak of biochar, indicating that γ-Fe₂O₃ is successfully loaded on the biochar. The FTIR pattern of the adsorbent material is as Figure 3 shown. In the figure, characteristic absorption peaks of hydroxyl (–OH) and carboxyl (–COOH) appear at 3385.54 cm -1 and 1150.83 cm -1 respectively, which originate from the biochar. The BET result graph of the adsorbent material is as Figure 4 shown. The results show that there is a micropore-mesopore-macropore hierarchical structure in the adsorbent material, and it is mainly mesoporous (pore size 2 - 10 nm). After calculation, the specific surface area of the adsorbent material is 60.808 m 2 / g. The VSM characterization graph of the adsorbent material is as Figure 5 shown. The results show that the adsorbent material exhibits typical superparamagnetism and can aggregate when approaching magnetic substances, indicating that the material has excellent magnetic recovery performance. The SEM graph of the adsorbent material is as Figure 6 shown. The partial enlarged view of the part circled in red in this figure is as Figure 7 shown. It can be seen from the figure that several wrinkles are formed on the surface of the material, and a high specific surface area loading area is formed between adjacent two wrinkles, and spherical γ-Fe₂O₃ particles with nanoscale size are loaded in this area.

[0062] Furthermore, this embodiment also explored the application of magnetic biochar adsorbent materials in heavy metal adsorption. The specific test method is as follows: 50 mL of a composite pollution solution with an initial concentration of 20 mg / L of Sb(V), Pb(II), and Cd(II) was adjusted to pH 5. 200 mg of magnetic biochar adsorbent material was added to the above solution, and it was oscillated at 150 rpm for 240 min at 25°C. 10 mL of samples were taken every 30 min, filtered through a 0.45 μm filter membrane, and the residual concentrations of Sb(V), Pb(II), and Cd(II) in the solution were measured. After calculation, under the above conditions, the adsorption rates of the adsorbent material for Sb(V), Pb(II), and Cd(II) were 91.25%, 82.76%, and 85.63% respectively. The XRD pattern and FTIR pattern of the adsorbent material after adsorption saturation are respectively as Figure 2 , Figure 3 shown. Comparing the XRD curves of the adsorbent material before and after adsorption in Figure 2 , it can be found that the positions of the characteristic diffraction peaks of the two are almost the same, and the change of the wave peaks is not obvious, indicating that the adsorbent material has excellent stability. Comparing the FTIR patterns of the adsorbent material before and after adsorption in Figure 3 , it can be seen that after adsorption, the characteristic peak of the material at 1200 - 1500 cm -1 becomes relatively flat due to stretching vibration. This is because the C=C and C=O double bonds are broken, and Fe can coordinate through oxygen bonds to form Fe-O active sites and Fe-O-Cl active sites, which can better combine with biochar and act on target metal ions, and is related to the complex formation with Sb(V), Pb(II), and Cd(II).

[0063] The above-mentioned adsorbent material after adsorption saturation was taken out and eluted with 0.1 mol / L NaOH solution, centrifuged and washed repeatedly until the supernatant was neutral, and then dried at 60°C for reuse. The results of the cyclic adsorption experiment of the adsorbent material for Sb(V), Pb(II), and Cd(II) are as Figure 8 shown. The results show that by the fifth cyclic experiment, the adsorption rates of the adsorbent material for Sb(V), Pb(II), and Cd(II) still exceeded 65%, indicating that the adsorbent material prepared in this embodiment has excellent ability to adsorb Sb(V), Pb(II), and Cd(II).

[0064] Particularly, this embodiment also explored the adsorption ability of the adsorbent material for target ions in complex water bodies containing various interfering ions. During the test process, the adsorbent material was used to adsorb the solution containing Na + , Ca 2+ , Mg 2+ , Cl - , CO 2- , PO 3-Sb(V), Pb(II) and Cd(II) in the heavy metal wastewater solution, the adsorption results of Sb(V) are as Figure 9 shown, the adsorption results of Pb(II) are as Figure 10 shown, the adsorption results of Cd(II) are as Figure 11 shown. The results show that PO 3- has the greatest influence on the adsorption process. However, in the presence of high-concentration interfering ions, the adsorption rates of the adsorption material for Sb(V), Pb(II) and Cd(II) can all be maintained above 70%, indicating that the adsorption material has excellent anti-interference ability and the co-adsorption ability for Sb(V), Pb(II) and Cd(II).

[0065] Examples 2 to 5

[0066] The differences between Examples 2 to 5 and Example 1 are only as follows: in step S1, the mass ratios of municipal sludge, rice straw and antimony ore waste residue in the biochar precursor are different from those in Example 1, and the remaining experimental parameters are the same as those in Example 1, which will not be elaborated here.

[0067] The mass ratio settings of municipal sludge, straw and antimony ore waste residue in the biochar precursors of Examples 1 to 5 and the adsorption performances of the adsorption materials prepared under the corresponding conditions are shown in Table 1. Analyzing the data in the table, it can be seen that the adsorption abilities of the adsorption material for Sb(V), Pb(II) and Cd(II) are related to the ratios of the three carbon sources in the biochar precursor. This is because the three carbon sources play different roles in the adsorption process. In the later stage of sludge carbonization, the surface is rich in oxygen-containing functional groups such as –COOH and –OH, which can provide abundant complexation and electrostatic adsorption sites for metal ions; the unique wrinkled structure formed after straw carbonization significantly improves the mass transfer rate of metal ions and is conducive to promoting the adsorption process of metal ions; after the antimony ore waste residue is carbonized, the Fe / Mn co-adsorption sites in the skeleton are exposed, which not only provides a stable carrier for γ-Fe2O3 nanoparticles but also has a selective complexation effect on Sb(V). When the ratios of the three carbon sources are too large or too small, the synergistic effect between the three cannot be maximally exerted, resulting in a decrease in the adsorption rate. That is, only when the three carbon sources are mixed in a specific ratio can the high-efficiency co-adsorption performance for the three metal ions be simultaneously exerted.

[0068] Table 1 The mass ratio settings of municipal sludge, straw and antimony ore waste residue in the biochar precursors of Examples 1 to 5 and the adsorption performances of the adsorption materials prepared under the corresponding conditions

[0069]

[0070] Examples 6 to 7

[0071] Examples 6 to 7 are different from Example 1 only in that: in step S2, the molar ratio of FeCl3·6H2O to urea in the magnetic γ-Fe2O3 precursor solution is different from that in Example 1, and the remaining experimental parameters are the same as those in Example 1, which will not be elaborated here.

[0072] The molar ratio settings of FeCl3·6H2O to urea in Example 1 and Examples 6 to 7 and the adsorption performance of the adsorbent materials prepared under the corresponding conditions are shown in Table 2. The results show that as the molar ratio of FeCl3·6H2O and urea increases, the adsorption capacity of the adsorbent material gradually increases. However, when the loading amount is too high, the increase in adsorption efficiency tends to level off. This is because: in the hydrothermal reaction, FeCl3·6H2O hydrolyzes to form Fe(OH)3, and then γ-Fe2O3 precursor is generated through further oxidation. The reaction equations involved in the reaction process are as follows: , , and the subsequent pyrolysis process forms magnetic nano γ-Fe2O3 particles. The specific reaction equation is ; the molar ratio of FeCl3·6H2O and urea directly affects the quantity, size, and distribution of the final γ-Fe2O3 precursor. Too low urea concentration may lead to insufficient hydrolysis of Fe 3+ ions, incomplete formation of γ-Fe2O3 precursor or larger particles, which is not conducive to the adsorption reaction. Too high concentration is likely to cause aggregation of nanoparticles, thereby affecting the performance of magnetic nano γ-Fe2O3 adsorption.

[0073] Table 2 Molar ratio settings of FeCl3·6H2O to urea in Example 1 and Examples 6 to 7 and the adsorption performance of the adsorbent materials prepared under the corresponding conditions

[0074]

[0075] Examples 8 to 10

[0076] Examples 8 to 10 are different from Example 1 only in that: in step S2, the temperature settings of the three stages during the segmented pyrolysis treatment are different from those in Example 1, and the remaining experimental parameters are the same as those in Example 1, which will not be elaborated here.

[0077] The temperature settings for the staged pyrolysis treatment in Example 1 and Examples 8 to 10 and the adsorption performance of the adsorbent materials prepared under the corresponding conditions are shown in Table 3. Analyzing the data in the table, it can be seen that the adsorption performance of the adsorbent material prepared under the conditions of Example 1 is the best. This is because pyrolysis treatment at a specific temperature can form a unique pore structure (micropore-mesopore-macropore hierarchical structure) in the material. The pore structures of different scales not only provide abundant adsorption sites but also ensure the smoothness of the ion mass transfer channels, and the adsorption efficiency is the highest at this time. When the temperature during the pyrolysis treatment process is too high and the span is too large, the carbon precursor is prone to collapse or fusion, and a pore structure and adsorption area conducive to the adsorption of metal ions cannot be formed.

[0078] Table 3 Temperature settings for the staged pyrolysis treatment in Example 1 and Examples 8 to 10 and the adsorption performance of the adsorbent materials prepared under the corresponding conditions

[0079]

[0080] Comparative Example 1

[0081] The difference between Comparative Example 1 and Example 1 is only that: in step S1, the carbon source composition of the biochar precursor is different. Specifically, the biochar precursor is prepared by using pretreated municipal sludge and rice straw, and the mass ratio of sludge to straw is 4.74:3.19. The sum of their masses is the same as the total mass of municipal sludge, rice straw, and antimony ore waste residue in Example 1, and the remaining experimental parameters are the same as those in Example 1, which will not be elaborated here.

[0082] Comparative Example 2

[0083] The difference between Comparative Example 2 and Example 1 is only that: in step S1, the carbon source composition of the biochar precursor is different. Specifically, the biochar precursor is prepared by using pretreated municipal sludge and antimony ore waste residue, and the mass ratio of municipal sludge to antimony ore waste residue is 3.19:2.24. The sum of their masses is the same as the total mass of municipal sludge, rice straw, and antimony ore waste residue in Example 1, and the remaining experimental parameters are the same as those in Example 1, which will not be elaborated here.

[0084] The adsorption effects of the adsorbent materials prepared in Example 1 and Comparative Examples 1-2 are shown in Table 4. The results show that the adsorption effect of Example 1 is far better than that of Comparative Examples 1-2. This is because: for the adsorbent material prepared from sludge and straw in Comparative Example 1, although it has a certain adsorption capacity, due to its low surface activity and non-optimized pore structure, its removal effect on heavy metal ions is relatively weak.

[0085] The main reason for the significantly better adsorption effect of Example 1 than that of Comparative Example 1 and Comparative Example 2 is that the material obtained after optimizing the composite carbon source ratio has a more abundant pore structure and a larger specific surface area. Specifically, the carbon-based precursor jointly constructed by municipal sludge, rice straw, and antimony ore waste residue in Example 1 formed an excellent pore structure during the pyrolysis process. The surface of the material has more wrinkles and the pores are evenly distributed, endowing it with a higher specific surface area and a more complex three-dimensional adsorption channel. This enables heavy metal ions to obtain more active sites when contacting the material surface, achieving rapid and efficient enrichment. In Comparative Example 1, due to the lack of the mineral template effect of antimony ore waste residue, the pore structure tends to be single and the surface is relatively flat, restricting the ion adsorption channel and diffusion efficiency. In Comparative Example 2, the straw microfiber structure was not introduced, the overall structure of the material is dense, the wrinkles are reduced, and the specific surface area is low, which is also not conducive to the entry and full adsorption of metal ions. Therefore, the material prepared in Example 1 exhibits more wrinkles, a higher specific surface area, and a better pore system at the microstructural level, which is the key to its significantly better adsorption performance than that of Comparative Examples 1 and 2.

[0086] Table 4 Adsorption effects of the adsorption materials prepared in Example 1 and Comparative Examples 1-2

[0087]

[0088] The above examples are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of a magnetic biochar adsorption material, characterized in that, It includes the following steps: S1. Mix the biomass mixture with an aqueous carboxymethyl cellulose solution and dry it to obtain a biochar precursor; the biomass mixture is composed of municipal sludge, straw, and antimony ore waste residue. S2. After mixing the biochar precursor obtained in step S1 with a magnetic γ-Fe2O3 precursor solution, perform a hydrothermal reaction at 160 - 180 °C for 15 - 17 h. After subjecting the reaction product to staged pyrolysis treatment, a magnetic biochar adsorption material is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of municipal sludge, straw, and antimony ore waste residue is (3 - 5)∶(2 - 4)∶(1 - 3).

3. The preparation method according to claim 1, characterized in that, In step S2, the magnetic γ-Fe2O3 precursor solution is obtained by dissolving FeCl3·6H2O and urea in a molar ratio of 1∶(1 - 3) in 40 - 60 mL of ethylene glycol.

4. The preparation method according to claim 1, characterized in that, In step S2, the staged pyrolysis treatment is carried out as follows: in a nitrogen environment, keep it at 100 - 200 °C for 30 min, then keep it at 200 - 300 °C for 30 min, and finally, keep it at 300 - 400 °C for 60 min.

5. The preparation method according to claim 1, characterized in that, In step S1, the municipal sludge needs to be pretreated, and the pretreatment is carried out as follows: add FeSO4·7H2O and H2O2 to the municipal sludge to be treated. The addition amount of FeSO4·7H2O is 0.15 mol / kg, and the addition amount of H2O2 is 0.75 mol / kg. The pH of the solution after adding H2O2 is 3.

0. After reacting for 1 h, add Ca(OH)2 until the solution pH = 7.

0. The obtained precipitate is dried to obtain the pretreated municipal sludge.

6. The preparation method according to claim 1, characterized in that, In step S1, the antimony ore waste residue needs to be pretreated, and the pretreatment is carried out as follows: crush the antimony ore waste residue to be treated into particles with a particle size less than 0.5 cm, and then perform acid washing on the particles. The eluent for acid washing is 1 M HCl, the flow rate is 2 BV / h, the liquid-solid ratio is 10:1, and the number of acid washing times is 3 times; then, use zirconia balls as grinding balls to perform ball milling activation on the acid-washed particles, the ball-to-material ratio is 10:1, the rotation speed is 300 rpm, and the ball milling time is 2 h; after the ball milling is completed, dry it at 80 °C for 12 h to obtain the pretreated antimony ore waste residue.

7. The preparation method according to claim 2, wherein, In step S1, the mass ratio of municipal sludge, straw, and antimony ore waste residue is 4:3:

2.

8. The preparation method according to claim 4, characterized in that In step S2, the staged pyrolysis treatment is carried out as follows: in a nitrogen environment, keep it at 100 °C for 30 min, then keep it at 200 °C for 30 min, and finally, keep it at 300 °C for 60 min.

9. A magnetic biochar adsorption material prepared by the preparation method according to any one of claims 1-8, characterized in that, It includes: Biochar, which serves as a substrate. Magnetic nano γ-Fe₂O₃ particles, which are distributed in the pore structure and on the surface of the biochar, with a particle size of 200 - 500 nm, and the specific surface area of the magnetic biochar adsorbent is 20 - 80 m 2 / g.

10. Application of the magnetic biochar adsorption material prepared by the preparation method according to any one of claims 1 - 8 or the magnetic biochar adsorption material according to claim 9 in adsorbing Sb(V), Pb(II), and Cd(II) in wastewater.

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