Preparation method and application of magnetic biochar adsorption material

Abstract

The present invention provides a preparation method and application of a magnetic biochar adsorption material, and relates to the technical field of biochar adsorption materials. The above-mentioned adsorption material is prepared by using three kinds of biomass, namely municipal sludge, straw and antimony mine waste residue, as biochar sources, and further loading magnetic nano-γ-Fe2O3 particles. In the above process, by controlling the quality of municipal sludge, straw and antimony mine waste residue, the composition and performance of the biochar substrate in the adsorption material can be regulated, and the rich active sites in the sludge and straw can be fully utilized to achieve the loading of magnetic nano-γ-Fe2O3 particles. The microfibril structure in the straw and the high-activity mesoporous carrier in the antimony mine waste residue can not only improve the loading rate of the magnetic nano-γ-Fe2O3 particles to a certain extent, but also facilitate the diffusion and capture of heavy metal ions during the application process, thereby improving the adsorption rate of the material to heavy metal ions as a whole.

Description

Technical Field

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

[0002] Antimony (Sb) and its associated heavy metals (Pb(II) and Cd(II)) are globally controlled environmental pollutants. Due to the complex rainfall patterns, stockpile characteristics, geology, and hydrological conditions in antimony mining areas, as well as the complex chemical composition of antimony slag and the release of heavy metals from stockpiles during rainfall leaching, resulting in complex antimony-containing and multi-metal wastewater, research on synergistic wastewater treatment technologies for slag reduction and resource utilization, as well as for the treatment of antimony-containing and multi-metal wastewater from stockpiles, has been limited. Adsorption composite materials are considered effective and economical approaches for heavy metal wastewater treatment both domestically and internationally due to their ease of operation, high adsorption capacity, and sustainability. Magnetic iron oxide, with its exceptional stability and excellent metal adsorption capacity, has emerged as an ideal magnetic-based material. γ-Fe₂O₃, with its stable structure and high adsorption efficiency, has shown broad application potential in heavy metal pollution control, particularly for Sb adsorption. In the selection process of carbon-based materials, biochar is a porous solid material formed by high-temperature cracking and carbonization of organic matter under anaerobic or anoxic conditions, with a high specific surface area and carbon content. In recent years, due to its excellent adsorption properties, biochar has been widely used to remove heavy metals, organic pollutants and nutrients from water bodies. Domestic and foreign scholars have successfully developed some mineral-based and magnetically modified mineral-based nano-adsorbent materials with good economy, strong selectivity, recyclability and large adsorption capacity, and have shown significant efficiency in treating single heavy metal wastewater. However, there are difficulties in treating multiple heavy metal wastewaters, and the adsorption materials are easy to lose, difficult to separate and recycle, and the development of composite materials using multi-solid waste from mining areas with a wide range of sources and low prices is poor.

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

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

[0005] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing a magnetic biochar adsorption material, comprising the following steps:

[0006] S1. Mixing a biomass mixture with a carboxymethyl cellulose aqueous solution and drying the mixture to produce a biochar precursor; the biomass mixture comprises municipal sludge, straw, and antimony mine waste residue;

[0007] S2. The biochar precursor obtained in step S1 is mixed with a magnetic γ-Fe2O3 precursor solution, and the mixture is subjected to a hydrothermal reaction at 160-180° C. for 15-17 h. The reaction product is subjected to a staged pyrolysis treatment to obtain a magnetic biochar adsorption material.

[0008] Preferably, in step S1, the mass ratio of municipal sludge, straw and antimony mine 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 40-60 mL of ethylene glycol in a molar ratio of 1:(1-3).

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

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

[0012] Preferably, in step S1, the antimony ore waste needs to be pretreated, and the pretreatment is carried out as follows: the antimony ore waste to be treated is crushed into particles with a particle size of less than 0.5 cm, and then the particles are pickled, 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, the pickled particles are ball milled and activated using zirconia balls as grinding balls, 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, it is dried at 80°C for 12 h to obtain the pretreated antimony ore waste.

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

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

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

[0016] biochar, which serves as a substrate;

[0017] Magnetic nano-γ-Fe2O3 particles are distributed in the pore structure and surface of the biochar, with a particle size of 200-500 nm. The specific surface area of ​​the magnetic biochar adsorption material is 20-80 m 2 The magnetic biochar adsorption material can be used to adsorb 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 mine waste as biochar sources, and further loads magnetic nano-γ-Fe2O3 particles, which can fully utilize 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 quality of municipal sludge, straw, and antimony mine waste, the composition and performance of the biochar substrate in the adsorption material can be regulated, and the abundant active sites in the sludge and straw can be fully utilized to achieve the loading of magnetic nano-γ-Fe2O3 particles. The microfibril structure in the straw and the highly active mesoporous carrier in the antimony mine waste can not only improve the loading rate of the magnetic nano-γ-Fe2O3 particles to a certain extent, but also facilitate the diffusion and capture of heavy metal ions during the application process, thereby improving the adsorption rate of the material to heavy metal ions as a whole.

[0020] 2. The preparation method provided by the present invention realizes the loading of magnetic nano γ-Fe2O3 particles in the biochar precursor by adopting hydrothermal treatment and segmented pyrolysis, which can avoid the aggregation of nanoparticles and effectively improve the binding force between the γ-Fe2O3 precursor and the biochar precursor, making it easier to achieve loading and ensure that the loaded particles and the biochar precursor are effectively combined together, thereby improving the overall stability of the material and avoiding the shedding of nanoparticles during the application process, which leads to unstable material performance. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

[0026] Figure 6 This is an SEM image of the magnetic biochar adsorption material prepared in Example 1 of the present invention;

[0027] Figure 7 for Figure 6 A partial enlarged view of

[0028] Figure 8 The results of the cyclic adsorption experiments of Sb(V), Pb(II) and Cd(II) by the magnetic biochar adsorption material prepared in Example 1 of the present invention are shown;

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

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

[0031] Figure 11 The adsorption results of Cd(II) by the magnetic biochar adsorption material prepared in Example 1 of the present invention in the presence of interfering ions. DETAILED DESCRIPTION

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

[0033] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0034] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0035] In one aspect, the present invention provides a magnetic biochar adsorption material comprising:

[0036] biochar, which serves as a substrate;

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

[0038] See also Figure 1 As shown, the present invention provides a method for preparing a magnetic biochar adsorption material, comprising the following steps:

[0039] S1, mixing pretreated municipal sludge, straw and antimony mine waste residue, mixing with a carboxymethyl cellulose aqueous solution, and drying to prepare a biochar precursor;

[0040] S2. The biochar precursor obtained in step S1 is mixed with the magnetic γ-Fe2O3 precursor solution, and the mixture is hydrothermally reacted at 160-180° C. for 15-17 h. The reaction product is subjected to staged pyrolysis treatment to obtain a magnetic biochar adsorption material.

[0041] In the above technical solution, a γ-Fe2O3 precursor (ferric hydroxide and related products) is synthesized by a hydrothermal reaction between FeCl3·6H2O (as a magnetic component) and urea (as an alkaline reactant), and is evenly loaded onto a biochar precursor. The γ-Fe2O3 precursor is then converted into magnetic nano-γ-Fe2O3 by pyrolysis treatment, effectively ensuring the uniformity and stability of the load. This is because after the γ-Fe2O3 precursor is directly loaded into the biochar precursor, the precursor is converted into magnetic nano-ions, which can avoid the aggregation of nanoparticles. 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, and loading is easier to achieve, ensuring that the loaded particles and the biochar precursor are effectively combined together, thereby improving the overall stability of the material and avoiding the shedding of nanoparticles during application, which leads to unstable material performance.

[0042] The preparation mechanism and application of the magnetic biochar adsorption material provided by the present invention are as follows: after carbonization of sludge, 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 the metal ions to be adsorbed in the subsequent application process; after carbonization of straw, a developed microfiber pore structure is formed inside, which significantly improves the specific surface area and mass transfer performance. The preparation stage is conducive to the immersion of the precursor solution of the γ-Fe2O3 loading process into the carbon precursor. The application process can play a certain enrichment role on the treated solution and improve the adsorption effect of the target metal ions; and after carbonization of antimony ore waste slag, a mineral skeleton containing a large amount of SiO2, Al2O3, etc. is formed inside it, which provides a stable support structure and mineral-based adsorption sites for the adsorption material as a whole. The three carbon source precursors synergistically give the adsorption material 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) preferentially binds to the Fe–OH site in the form of anions through electrostatic adsorption and surface coordination to form a Fe–O–Sb complex structure. This structure can further regulate the surface charge and functional group arrangement, promote the subsequent complexation and precipitation adsorption of Pb(II) and Cd(II), thereby achieving synergistic enrichment and mutual promotion effects among the three, and ultimately significantly improving the metal ion removal rate and the application stability of the material.

[0043] In some embodiments, in step S1, the pretreatment of municipal sludge is carried out as follows: FeSO4·7H2O and 30% by mass of H2O2 are added to the municipal sludge to be treated, and the molar ratio of the two is 1:5. The amount of FeSO4·7H2O added is 0.15 mol / kg, and the amount of H2O2 added is 0.75 mol / kg, that is, the amount of FeSO4·7H2O added to 1 kg of dry municipal sludge is 0.15 mol, and the amount of H2O2 added to 1 kg of dry 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 hour. 2+ The Fenton reaction between sludge and H2O2 generates hydroxyl radicals ·OH. The strong oxidizing ·OH can destroy the organic matter structure in the sludge, improve the dewatering performance, and degrade toxic and harmful substances. Subsequently, Ca(OH)2 is added to pH=7.0, and the residual Fe is precipitated after standing for 30 minutes. 3+ , dehydration is carried out by filter pressing to ensure that the moisture content of the filter residue is less than 65%; the filter residue is crushed to a particle size of 100 mesh and dried at 60°C until the moisture content is less than 10%, thereby obtaining the pretreated municipal sludge. The conditions of the filter pressing process are: pressure 0.8 MPa, time 30 min.

[0044] Furthermore, the straw was pretreated as follows: an alkali treatment-mechanical crushing combined process was used for treatment, and the specific treatment steps were as follows: the straw to be treated was placed in a 1% NaOH solution and soaked at room temperature for 12 hours at a liquid-to-solid ratio of 10:1 to remove part of the lignin and expanded fiber structure in the straw. The straw was turned over every 3 hours during the treatment process to ensure that the straw was fully treated. After soaking, the straw was fully rinsed with deionized water until the pH of the filtrate was close to neutral (6.5-7.0), and dried for later use; the dried straw was crushed into 5-10 cm segments to reduce the energy consumption of subsequent processing. After crushing, the segments were rinsed with deionized water to avoid affecting the conductivity of the material. The segments were then treated until D90 was less than 2 mm and vacuum dried until the moisture content of the straw was less than 10%.

[0045] The pretreatment of antimony ore waste was carried out as follows: the waste was first crushed into particles less than 0.5 cm in size. The particles were then acid-washed using a percolation column with 1 M HCl at a flow rate of 2 BV / h, a liquid-to-solid ratio of 10:1, and three acid washes. The acid-washed particles were then ball-milled using 5 mm diameter zirconia balls at a 10:1 ball-to-solid ratio, a rotation speed of 300 rpm, and a milling time of 2 h. The milling process alternated between forward and reverse rotation every 10 min to ensure thorough milling. After milling, the particles were rinsed with alkaline solution to remove adsorbed acidic solution from the surface. Finally, the particles were dried at 80°C for 12 h to obtain the pretreated antimony ore waste. The percolation column dimensions were: 10 cm inner diameter, 50 cm height, and filled with a 30 cm high waste slag bed.

[0046] By selecting antimony ore waste as a source of carbon precursor, it can be used to provide active mineral components for constructing a functional framework. This is because antimony ore waste is rich in mineral components such as SiO2, Al2O3, and Fe2O3, which can be converted into a neutral silicon-aluminum framework with strong stability and surface reactivity during pyrolysis and activation, helping to enhance the structural strength and pore stability of the material. Secondly, trace amounts of Sb or Sb oxidation species may remain in the antimony ore waste. During the construction of the composite material, they can participate in doping or surface coordination, 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 of the target metal. Thirdly, some metal oxides in the antimony ore waste, such as Fe-O and Al-O, have the potential for synergistic complexation or coprecipitation with Sb-O, which helps to form a stable surface coordination structure during the adsorption process, effectively enhancing the synergistic enrichment and selective adsorption of coexisting heavy metal ions such as Sb(V), Pb(II), and Cd(II).

[0047] In the above technical solution, by pre-treating municipal sludge with the Fenton method, the active sites in the sludge (-COOH, -OH, etc.) can be exposed, providing more active sites for the adsorption of heavy metal ions, and at the same time improving the surface chemical properties and hydrophilicity of the material; by treating the straw with alkali, its microfibril structure can be exposed, and the surface of the structure is rich in active hydroxyl -OH, which provides a template for the loading of magnetic nanoparticles; by ball milling and acid washing the antimony mine waste, the iron and manganese minerals therein can be converted into highly active mesoporous carriers, which are beneficial to the loading of magnetic nanoparticles. When used for the subsequent adsorption of heavy metal ions, the presence of the mesoporous structure is beneficial to the diffusion and capture of heavy metal ions, thereby improving 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 mine waste residue is (3-5): (2-4): (1-3); carboxymethyl cellulose aqueous solution is used as a binder, and its mass percentage in all raw materials is 2 wt%, that is, the ratio of the mass of carboxymethyl cellulose aqueous solution to the sum of the masses of municipal sludge, straw, antimony mine waste residue, and carboxymethyl cellulose aqueous solution is 2%, and straw refers to the stems and leaves of crops, such as rice, corn, wheat, etc.

[0049] In the above technical scheme, by controlling the quality of municipal sludge, straw and antimony mine waste, the composition and performance of the biochar substrate in the adsorption material can be regulated, and the rich active sites in the sludge and straw can be fully utilized to achieve the loading of magnetic nano γ-Fe2O3 particles. The microfibril structure in the straw and the highly active mesoporous carrier in the antimony mine waste 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, thereby improving the overall adsorption rate of the material for heavy metal ions.

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

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

[0052] In this technical solution, temperatures of 100-200°C can pyrolyze the hemicellulose in straw to create a microporous structure while retaining the protein-like functional groups in the sludge. Temperatures of 200-300°C promote carbonization of the biochar precursor to form a mesoporous network, while utilizing the silicon and aluminum components in the waste residue to construct a mineral framework. Temperatures of 300-400°C facilitate the formation of an adsorption structure. This process, through staged temperature and atmosphere control, optimizes the biochar's pore structure, surface chemistry, and magnetic nanoparticle loading, imparting the material with excellent adsorption properties.

[0053] The preparation method and application of the magnetic biochar adsorption material proposed by the present invention are further described below with reference to specific examples:

[0054] Example 1

[0055] This embodiment prepares a magnetic biochar adsorption material, and the preparation method includes the following steps:

[0056] S1. Mix municipal sludge with FeSO4·7H2O and 30% by mass of H2O2. The amount of FeSO4·7H2O added is 0.15 mol / kg and the amount of H2O2 added is 0.75 mol / kg. That is, the amount of FeSO4·7H2O added to 1 kg of dry municipal sludge is 0.15 mol, and the amount of H2O2 added to 1 kg of dry municipal sludge is 0.75 mol. The pH of the solution in the early stage of treatment is 3.0. 2+ The Fenton reaction between hydroxyl radicals and H2O2 generates hydroxyl radicals ·OH. The strong oxidizing ·OH can destroy the organic matter structure in the sludge, improve the dewatering performance, and degrade toxic and harmful substances. Subsequently, Ca(OH)2 is added to pH=7.0 to precipitate the residual Fe 3 + The sludge was dehydrated by filter pressing to ensure that the moisture content of the filter residue was less than 65%. The filter residue was crushed to a particle size of 100 mesh and dried at 60°C until the moisture content was less than 10%, thereby obtaining pretreated municipal sludge. The filter pressing process conditions were: pressure 0.8 MPa, time 30 min. The municipal sludge was obtained from the dewatered sludge of the wastewater treatment plant in the Baodaxing mining area of ​​Hunan Xikuangshan, with a total solids (TS) of 35.6% and a volatile solids (VS) of 52.7%.

[0057] The rice straw was processed using a combined alkali treatment and mechanical crushing process, including coarse crushing, washing, fine crushing, and drying. Coarse crushing involves cutting the rice straw into 5-10 cm segments to reduce energy consumption for subsequent processing. After coarse crushing, the segments were rinsed with deionized water to avoid affecting the material's conductivity. The segments were then processed to a D90 value below 2 mm and vacuum dried to a moisture content below 10%, obtaining pretreated rice straw. The rice straw was obtained from rice straw grown near the mining area and had a cellulose content of 35%, a hemicellulose content of 25%, and a lignin content of 20%.

[0058] First, the antimony ore waste slag was crushed into particles with a particle size of less than 0.5 cm, and then the particles were pickled using a filtration column. The pickling eluent was 1 M HCl, the flow rate was 2 BV / h, the liquid-to-solid ratio was 10:1, and the number of pickling times was 3 times; then, the pickled particles were ball-milled and activated using zirconia balls with a diameter of 5 mm as grinding balls, 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 positive and negative rotations were alternated every 10 minutes to ensure sufficient ball milling; after the ball milling, the particles were rinsed with alkaline solution to remove the acidic solution adsorbed on the surface of the particles, and finally dried at 80°C for 12 h to obtain the pretreated antimony ore waste slag; the dimensions of the filtration column were: inner diameter 10 cm, height 50 cm, and a waste slag bed layer with a height of 30 cm inside. The antimony ore waste slag was taken from the surface weathered waste slag of the slag dump in the Daxing mining area of ​​Shanbao, Hunan Province, with a particle size of 1-5 cm, the main minerals are 45% quartz, 30% calcite, 15% limonite, and the rest are impurities;

[0059] Pretreated municipal sludge, rice straw, and antimony mine waste residue were mixed in a mass ratio of 4:3:2 and then mixed with 1.8 mL of carboxymethyl cellulose aqueous solution. The resulting mixture was kneaded in a kneader for 30 minutes to form a plastic billet. The billet was then pressed into a Φ20×10 mm cylindrical body using a hydraulic press at a pressure of 20 MPa. The body was then cured and dried at room temperature for 12 hours to produce a biochar precursor. The mass percentage of the carboxymethyl cellulose aqueous solution in the mixture was 2 wt%.

[0060] S2. The biochar precursor obtained in step S1 was mixed with a magnetic γ-Fe2O3 precursor solution and subjected to a hydrothermal reaction at 170°C for 16 h. The reaction product was collected, washed 3-5 times with ethanol and deionized water, and dried at 60°C. The sample was then placed in a three-stage tube furnace and held at T1 = 100°C for 30 min, then at T2 = 200°C for 30 min, and then at T3 = 300°C for 60 min to perform a staged pyrolysis of the sample to produce a magnetic biochar adsorption material. The pyrolysis process was performed entirely in a nitrogen atmosphere at a gas flow rate of 200 mL / min. The magnetic γ-Fe2O3 precursor solution was prepared by adding FeCl3·6H2O and urea to 50 mL of ethylene glycol (analytical grade), with a molar ratio of FeCl3·6H2O to urea of ​​1:2.

[0061] The XRD pattern of magnetic biochar adsorption material is shown in Figure 2 As 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 peaks of biochar, indicating that γ-Fe2O3 is successfully loaded on biochar. The FTIR graph of the adsorbent material is shown in Figure 1. Figure 3 As shown in the figure, 3385.54 cm -1 and 1150.83 cm -1 The characteristic absorption peaks of hydroxyl (–OH) and carboxyl (–COOH) appear at the bottom, which are derived from biochar. The BET results of the adsorption material are shown in the figure below. Figure 4 The results show that there is a micropore-mesopore-macroporous multi-level structure in the adsorption material, and the mesopores (pore size 2-10 nm) are the main ones. The specific surface area of ​​the adsorption material is calculated to be 60.808 m 2 / g. The VSM characterization diagram of the adsorption material is as follows Figure 5 As shown in the results, the adsorption material exhibits typical superparamagnetism and can aggregate when close to magnetic substances, indicating that the material has excellent magnetic recovery performance. Figure 6 As shown in the figure, the local enlarged picture of the red circle is as follows Figure 7 As shown in the figure, it can be seen that several wrinkles are formed on the surface of the material, and a loading area with a high specific surface area is formed between two adjacent wrinkles, which is loaded with nano-sized spherical γ-Fe2O3 particles.

[0062] Furthermore, this embodiment also explores the application of magnetic biochar adsorption materials in heavy metal adsorption. The specific test method is as follows: 50 mL of Sb(V), Pb(II) and Cd(II) composite contaminated solution with an initial concentration of 20 mg / L was adjusted to pH 5, 200 mg of magnetic biochar adsorption material was added to the above solution, and the mixture was shaken at 150 rpm for 240 min at 25°C. 10 mL was sampled every 30 min, and the residual concentrations of Sb(V), Pb(II) and Cd(II) in the solution were determined after filtering with a 0.45 μm filter membrane. It was calculated that under the above conditions, the adsorption rates of the adsorption material for Sb(V), Pb(II) and Cd(II) were 91.25%, 82.76% and 85.63%, respectively. The XRD patterns and FTIR patterns of the adsorption material after adsorption saturation were as shown below. Figure 2 、 Figure 3 As shown, compared Figure 2 From the XRD curves of the adsorbent material before and after adsorption, it can be found that the positions of the characteristic diffraction peaks of the two are almost the same, and the peak changes are not obvious, indicating that the adsorbent material has excellent stability; Figure 3 The FTIR graph of the adsorbed material before and after adsorption shows that after adsorption, the material has a wavelength of 1200-1500 cm -1 The characteristic peak at is stretched and vibrated to be relatively gentle. 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. It is related to the complex formation of Sb(V), Pb(II) and Cd(II).

[0063] The adsorbent material after saturation was taken out and eluted with 0.1 mol / L NaOH solution. The supernatant was washed repeatedly by centrifugation until it was neutral. After drying at 60℃, it was reused. The results of the cyclic adsorption experiment of the adsorbent material for Sb(V), Pb(II) and Cd(II) are shown in the figure. Figure 8 As shown in the figure, the results show that by the fifth cycle experiment, the adsorption rate of the adsorption material for Sb(V), Pb(II) and Cd(II) is still over 65%, indicating that the adsorption material prepared in this example has excellent ability to adsorb Sb(V), Pb(II) and Cd(II).

[0064] In particular, this example also explores the adsorption capacity of the adsorbent material for target ions in complex water bodies containing multiple interfering ions. During the test, the adsorbent material was used to adsorb Na + , Ca 2+ Mg 2+ 、Cl - 、CO 2- , PO 3-The adsorption results of Sb(V), Pb(II) and Cd(II) in heavy metal wastewater solutions are as follows: Figure 9 As shown in Figure 2, the adsorption results of Pb(II) are as follows: Figure 10 As shown in Figure 2, the adsorption results of Cd(II) are as follows: Figure 11 As shown, the results show that PO 3- The greatest impact on the adsorption process, but in the presence of high concentrations of interfering ions, the adsorption rates of the adsorption material for Sb(V), Pb(II) and Cd(II) can be maintained above 70%, indicating that the adsorption material has excellent anti-interference ability and synergistic adsorption ability for Sb(V), Pb(II) and Cd(II).

[0065] Examples 2 to 5

[0066] The only difference between Examples 2 to 5 and Example 1 is that in step S1, the mass ratio of municipal sludge, rice straw and antimony mine waste residue in the biochar precursor is different from that in Example 1. The other experimental parameters are the same as those in Example 1 and are not repeated here.

[0067] The mass ratios of municipal sludge, straw and antimony mine waste residue in the biochar precursors of Examples 1 to 5 and the adsorption properties of the adsorption materials prepared under the corresponding conditions are shown in Table 1. From the analysis of the data in the table, it can be seen that the adsorption capacity of the adsorption material for Sb(V), Pb(II) and Cd(II) is related to the ratio of the three carbon sources in the biochar precursor. This is because the three carbon sources play different roles in the adsorption process. The surface of the sludge is rich in oxygen-containing functional groups such as –COOH and –OH in the late stage of carbonization, which can provide abundant complexation and electrostatic adsorption sites for metal ions; the unique wrinkled structure formed after carbonization of the straw significantly improves the mass transfer rate of metal ions, which is conducive to promoting the adsorption process of metal ions; after carbonization of the antimony mine waste residue, the Fe / Mn 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 ratio of the three carbon sources is too large or too small, the synergistic effect between the three cannot be maximized, resulting in a decrease in the adsorption rate. That is, only when the three carbon sources are mixed in a specific ratio can they simultaneously exert efficient synergistic adsorption performance for the three metal ions.

[0068] Table 1 Mass ratios of municipal sludge, straw, and antimony mine waste residue in the biochar precursors of Examples 1 to 5 and the adsorption properties of the adsorption materials prepared under the corresponding conditions

[0069]

[0070] Examples 6 to 7

[0071] The only difference between Examples 6 and 7 and Example 1 is 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. The other experimental parameters are the same as those in Example 1 and are not repeated here.

[0072] The molar ratios of FeCl3·6H2O to urea in Examples 1 and 6 to 7 and the adsorption properties 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 to urea increases, the adsorption capacity of the adsorbent material gradually increases. However, when the loading amount is too high, the improvement in adsorption efficiency tends to be flat. This is because: in the hydrothermal reaction, FeCl3·6H2O is hydrolyzed to form Fe(OH)3, which is then further oxidized to form a γ-Fe2O3 precursor. The reaction equation involved in the reaction process is as follows: , , 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 a urea concentration may lead to Fe 3+ Insufficient ion hydrolysis will result in incomplete generation of the γ-Fe2O3 precursor or large particles, which is not conducive to the adsorption reaction. Excessive concentration will easily cause nanoparticle aggregation, thereby affecting the adsorption performance of magnetic nano-γ-Fe2O3.

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

[0074]

[0075] Examples 8 to 10

[0076] The only difference between Examples 8 to 10 and Example 1 is that in step S2, the temperature settings of the three stages during the staged pyrolysis treatment are different from those in Example 1. The remaining experimental parameters are the same as those in Example 1 and will not be repeated here.

[0077] The temperature settings of the segmented pyrolysis treatment in Examples 1 and 8 to 10 and the adsorption properties of the adsorption materials obtained under the corresponding conditions are shown in Table 3. From the analysis of the data in the table, it can be seen that the adsorption performance of the adsorption material obtained under the conditions of Example 1 is the best. This is because the pyrolysis treatment is carried out at a specific temperature, and a unique pore structure (micropore-mesopore-macroporous multi-level structure) can be formed in the material. The pore structures of different scales provide rich adsorption sites and ensure the smooth flow of ion mass transfer channels. The adsorption efficiency is the highest at this time. When the temperature of the pyrolysis treatment process is too high and the span is too large, the carbon precursor is prone to collapse or fusion, and it is impossible to form a pore structure and adsorption area that are conducive to the adsorption of metal ions.

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

[0079]

[0080] Comparative Example 1

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

[0082] Comparative Example 2

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

[0084] The adsorption effects of the adsorption 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 superior to that of Comparative Examples 1-2. This is because: the adsorption material prepared from sludge and straw in Comparative Example 1, although having a certain adsorption capacity, has a relatively low surface activity and an insufficiently optimized pore structure, resulting in a relatively weak removal effect of heavy metal ions.

[0085] The main reason why the adsorption effect of Example 1 is significantly better than that of Comparative Examples 1 and 2 is that the material obtained after the optimization of the composite carbon source ratio has a richer pore structure and a larger specific surface area. Specifically, the carbon-based precursor constructed by the synergistic combination of municipal sludge, rice straw and antimony mine waste in Example 1 forms an excellent pore structure during the pyrolysis process. The material surface has more wrinkles and the pores are evenly distributed, giving it a higher specific surface area and more complex three-dimensional adsorption channels. This allows heavy metal ions to obtain more active sites when they contact the material surface, achieving rapid and efficient enrichment. However, due to the lack of the mineral template effect of antimony mine waste, Comparative Example 1 has a single pore structure and a relatively flat surface, which limits the adsorption channels and diffusion efficiency of the ions. Comparative Example 2 does not introduce the straw microfiber structure, and the overall structure of the material is dense, with fewer wrinkles and a low specific surface area, which is not conducive to the entry and sufficient adsorption of metal ions. Therefore, the material prepared in Example 1 presents more wrinkles, a higher specific surface area and a better pore system in the microstructure, which is the key to its significantly better adsorption performance than Comparative Examples 1 and 2.

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

[0087]

[0088] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a magnetic biochar adsorption material, characterized in that: The steps include: S1. Mixing a biomass mixture with a carboxymethyl cellulose aqueous solution and drying the mixture to produce a biochar precursor; the biomass mixture comprises municipal sludge, straw, and antimony mine waste residue, wherein the mass ratio of the municipal sludge, straw, and antimony mine waste residue is 4:3:2; S2. The biochar precursor obtained in step S1 is mixed with a magnetic γ-Fe2O3 precursor solution, and the mixture is subjected to a hydrothermal reaction at 160-180° C. for 15-17 h. The reaction product is subjected to a staged pyrolysis treatment to obtain a magnetic biochar adsorption material. The magnetic γ-Fe2O3 precursor solution is prepared by dissolving FeCl3·6H2O and urea in a molar ratio of 1:(1-3) in 40-60 mL of ethylene glycol. The staged pyrolysis treatment is carried out as follows: in a nitrogen environment, the solution is kept at 100°C for 30 minutes, then kept at 200°C for 30 minutes, and finally kept at 300°C for 60 minutes.

2. 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: FeSO4·7H2O and H2O2 are added to the municipal sludge to be treated, the amount of FeSO4·7H2O added is 0.15 mol / kg, the amount of H2O2 added is 0.75 mol / kg, the pH of the solution after adding H2O2 is 3.0, after reacting for 1 hour, Ca(OH)2 is added to the solution until the pH value is 7.0, and the obtained precipitate is dried to obtain the pretreated municipal sludge.

3. The preparation method according to claim 1, characterized in that In step S1, the antimony ore waste needs to be pretreated, and the pretreatment is carried out as follows: the antimony ore waste to be treated is crushed into particles with a particle size of less than 0.5 cm, and then the particles are pickled, 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; then, the pickled particles are ball milled and activated using zirconia balls as grinding balls, 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, the antimony ore waste is dried at 80°C for 12 h to obtain the pretreated antimony ore waste.

4. A magnetic biochar adsorption material prepared by the preparation method according to any one of claims 1 to 3, characterized in that: include: biochar, which serves as a substrate; Magnetic nano-γ-Fe2O3 particles are distributed in the pore structure and surface of the biochar, with a particle size of 200-500nm. The specific surface area of ​​the magnetic biochar adsorption material is 20-80m 2 / g.

5. Use of the magnetic biochar adsorption material obtained by the preparation method according to any one of claims 1 to 3 or the magnetic biochar adsorption material according to claim 4 in adsorbing Sb(V), Pb(II) and Cd(II) in wastewater.

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