Preparation method of magnetic magnesium-iron co-modified biochar and application of magnetic magnesium-iron co-modified biochar in lead ion adsorption

Abstract

The invention discloses a preparation method of magnetic magnesium-iron co-modified biochar and application of the magnetic magnesium-iron co-modified biochar in lead ion adsorption, and belongs to the technical field of environmental functional materials.According to the magnetic magnesium-iron co-modified biochar adsorbent prepared through the method, Mg and Fe are successfully loaded to the surfaces of corn straw by increasing the surface roughness of the magnetic magnesium-iron co-modified biochar adsorbent, and the magnetic magnesium-iron co-modified biochar adsorbent is prepared. The maximum adsorption capacity of the biochar to lead ions Pb (II) is effectively improved, the biochar has magnetism and excellent separation and recovery performance, the biochar can be efficiently recovered from a solution and reused, the adsorption process follows a quasi-second-order kinetic model and a Langmuir adsorption model, and the adsorption efficiency is greatly improved. The main mechanism of the adsorption process is electrostatic attraction, H bond adsorption, pi-pi interaction, surface complexation and ion exchange, the adsorption efficiency of the lead ions Pb (II) is effectively improved, and an efficient, low-cost and environment-friendly solution is provided for lead pollution treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental functional materials, and specifically refers to a preparation method of magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption. Background Art

[0002] In recent years, heavy metal pollution in water resources has become increasingly serious due to the influence of industrial production, smelters and landfills. Lead ions Pb(II) are particularly toxic, and even trace amounts can cause health problems. Moreover, lead ions are difficult to be excreted from the body and are bioaccumulative. Long-term exposure can cause headaches, diarrhea, liver disorders and nervous system damage. Therefore, it is particularly important to use green and environmentally friendly methods to remove lead ions from water.

[0003] Methods for removing heavy metals from water include evaporation, adsorption, membrane separation, biological treatment, chemical precipitation, etc. Among them, the adsorption method is widely used because of its low cost, simple operation and environmental friendliness. Biochar has a strong lead ion adsorption capacity. Among them, biochar made from raw materials such as agricultural waste such as corn straw has been proven to be an efficient, low-cost and environmentally friendly heavy metal adsorbent. However, traditional biochar adsorption materials have problems such as low specific surface area, underdeveloped pore structure, and insufficient surface functional groups, resulting in insufficient adsorption efficiency for heavy metals. Existing modification technologies mostly use single metal modification, with limited improvement in adsorption capacity, and the material is difficult to recycle, which easily causes secondary pollution. Summary of the Invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a preparation method of magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption, which effectively solves the problems of low lead ion adsorption efficiency and separation difficulty of biochar made from corn straw as raw material in the current market, and provides an efficient, low-cost and environmentally friendly solution for lead pollution control.

[0005] The technical solution adopted by the present invention is as follows: The present invention proposes a preparation method of magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption, comprising the following preparation steps: Corn straw was crushed, cleaned and dried, then ground and sieved to obtain unmodified biochar (BC); the unmodified biochar was soaked in citric acid, dried and washed to neutrality, and placed in a muffle furnace for pyrolysis to obtain acid-modified biochar (HBC); the acid-modified biochar was ultrasonically mixed with MgCO3 and Fe3O4, and a modified lignin-silk peptide complex was added. The mixture was transferred to a high-pressure reactor for high-pressure reaction, and the product was washed with anhydrous ethanol and deionized water and then dried to obtain magnetic magnesium-iron co-modified biochar (MBC).

[0006] Furthermore, the preparation of the modified lignin-silk fibroin peptide complex comprises the following steps: Bombyx mori silk fibroin was dissolved in LiBr solution, and trypsin was added to hydrolyze and retain components with a molecular weight of 500-1000Da. The silk fibroin peptide fragments were separated and collected, and freeze-dried for later use. Ethyl gallate and laccase were added to sodium lignin sulfonate borate buffer to react and generate a quinone-type structure graft body. ZnCl2 solution was added dropwise to form a blue metal complex precipitate. The resulting product was mixed with deionized water, ultrasonically treated at 4°C, and quickly freeze-dried to obtain a powdered modified lignin-silk fibroin peptide complex.

[0007] Furthermore, the concentration of citric acid is 0.8-1.5 mol / L.

[0008] Furthermore, the citric acid soaking time is 12-36 hours.

[0009] Furthermore, the muffle furnace pyrolysis heating rate is 8-15°C / min.

[0010] Furthermore, the mass ratio of the acid-modified biochar to MgCO3 and Fe3O4 is (3-5): (3-5):1.

[0011] Furthermore, the mass ratio of trypsin to substrate is 1:(45-55).

[0012] Furthermore, the molar ratio of ZnCl2 to gallic acid is 1:2.

[0013] Furthermore, the mass ratio of the silk peptide to the blue metal complex precipitate is 1:(2.5-3.5).

[0014] Furthermore, the magnetic magnesium-iron co-modified biochar was added to the lead ion aqueous solution, and the mass ratio of the biochar to the lead ion aqueous solution was 1:1000.

[0015] The beneficial effects achieved by the present invention using the above structure are as follows: This study proposes a method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption. The biochar surface exhibits a loose, rough and porous structure, which can remove Pb(II) from aqueous solutions. Mg and Fe are loaded on the biochar made from corn straw in the form of oxides, and the maximum adsorption capacity for Pb(II) is significantly improved.

[0016] The adsorption process of magnetic magnesium-iron co-modified biochar follows the pseudo-secondary, intraparticle diffusion and Langmuir models at the same time, which indicates that chemical adsorption on the homogeneous monolayer is the main adsorption mechanism; the biochar achieves the adsorption of Pb(II) through multiple mechanisms such as electrostatic attraction, H-bond adsorption, π-π interaction, surface complexation and ion exchange, effectively improving the adsorption effect of Pb(II), and the biochar is easy to separate and reuse, and can still maintain its effectiveness after multiple cycles.

[0017] By adding modified lignin-silk peptide complex, the grain size of the loaded Mg / Fe oxide is limited to below 60nm, so that the metal oxide forms a monomolecular layer coverage on the biochar surface, increasing the Pb(II) binding sites per unit area and improving the structural stability, thereby increasing the adsorption capacity of biochar for Pb(II); the phenolic hydroxyl groups in lignin are anchored to the crystal surface of Fe3O4 through hydrogen bonds, and the sulfonic acid groups generate a negative potential, preventing particle aggregation through electrostatic repulsion; the arginine guanidine group in the tripeptide sequence of the silk peptide component captures magnesium / iron ions in the solution through strong electrostatic interaction, and the predetermined sites promote uniform nucleation. The phenolic hydroxyl (-OH) and carboxyl (-COOH) groups provide additional Pb(II) binding sites, further improving the adsorption capacity for Pb(II).

[0018] In summary, the biochar exhibited superior adsorption capacity and excellent regeneration potential, making it a promising, cost-effective, and environmentally friendly Pb(II) adsorbent. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 These are SEM images of a magnetic magnesium-iron co-modified biochar proposed in the present invention. Figures a, b, and c are SEM images of unmodified biochar (BC), acid-modified biochar (HBC), and magnetic magnesium-iron co-modified biochar (MBC), respectively. Figures d, e, f, g, h, and i are elemental images of Mg, Al, Fe, C, Ca, and O, respectively. Figure 2 This is a bar graph showing the effect of biochar dosage on the adsorption capacity of a magnetic magnesium-iron co-modified biochar proposed in the present invention.

[0020] Figure 3 This is a fitting curve of the effect of contact time between biochar and Pb(Ⅱ) on Pb(Ⅱ) in a magnetic magnesium-iron co-modified biochar proposed in the present invention.

[0021] Figure 4 This is the effect of the initial Pb(Ⅱ) concentration on the adsorption capacity of a magnetic magnesium-iron co-modified biochar proposed in the present invention (a) and the Pb(b, c) adsorption isotherm fitting curve.

[0022] Figure 5This is a histogram of the regeneration cycle of the magnetic magnesium-iron co-modified biochar proposed in the present invention. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] Example 1: A method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption.

[0025] To prepare the modified lignin-silk peptide complex, 10 g of Bombyx mori silk protein was dissolved in 0.1 M LiBr solution, trypsin was added with an enzyme-to-substrate mass ratio of 1:45, hydrolyzed at 37°C for 2 h, and the component with a molecular weight of 500-1000 Da was retained. The silk peptide fragments were separated and collected, and freeze-dried for later use. 2 g of ethyl gallate and 500 U of laccase were added to the sodium lignin sulfonate borate buffer to react and generate a quinone-type structure graft body. A ZnCl2 solution with a molar concentration of 0.1 M was added dropwise to form a blue metal complex precipitate. 1 g of silk peptide and 2.5 g of the blue metal complex precipitate were mixed in deionized water, ultrasonically treated at 4°C for 15 min, and quickly freeze-dried to obtain a powdered modified lignin-silk peptide complex.

[0026] The corn straw raw material was pulverized and then cleaned to remove surface impurities, and then fully dried at 80°C to reduce the influence of the raw material moisture content on subsequent processes. After drying, it was ground and then sieved through a 60-mesh standard sieve for particle size control to obtain unmodified biochar basic material (BC); 20g of unmodified biochar sample was taken and soaked in a 0.8mol / L citric acid solution for 12h. This step can effectively activate the surface functional groups. The modified material was dried and repeatedly washed until it reached a neutral pH, and then transferred to a muffle furnace for pyrolysis reaction. The heating rate was set to 8°C / min, and finally maintained at a constant temperature of 500°C for 3h to complete the preparation process of acid-modified biochar and obtain acid-modified biochar (HBC); in the final stage, 1g of acid-modified biochar was mixed with MgCO3 and 0.3g of Fe3O4, and 2 The wt% modified lignin-silk peptide complex was uniformly dispersed by ultrasonication for 30 minutes and then reacted in a high-pressure reactor at 150°C for 5 hours. The product was thoroughly washed with anhydrous ethanol and deionized water, and finally dried in an oven at 80°C to obtain magnetic magnesium-iron co-modified biochar (MBC) for subsequent applications.

[0027] Example 2: A method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption.

[0028] To prepare a modified lignin-silk peptide complex, 10 g of Bombyx mori silk protein was dissolved in a 0.1 M LiBr solution, and trypsin was added with an enzyme-to-substrate mass ratio of 1:50. The mixture was hydrolyzed at 37°C for 2 h and the component with a molecular weight of 500-1000 Da was retained. The silk peptide fragments were separated and collected, and freeze-dried for later use. 2 g of ethyl gallate and 500 U of laccase were added to a sodium lignin sulfonate borate buffer solution to react and generate a quinone-type structure graft body. A ZnCl2 solution with a molar concentration of 0.1 M was added dropwise to form a blue metal complex precipitate. 1 g of silk peptide and 3 g of the blue metal complex precipitate were mixed in deionized water, ultrasonically treated at 4°C for 15 min, and quickly freeze-dried to obtain a powdered modified lignin-silk peptide complex.

[0029] The corn straw raw material was pulverized and then cleaned to remove surface impurities, and then fully dried at 80°C to reduce the influence of the raw material moisture content on subsequent processes. After drying, it was ground and then sieved through a 60-mesh standard sieve for particle size control to obtain unmodified biochar basic material (BC); 20g of unmodified biochar sample was taken and soaked in a citric acid solution with a concentration of 1.2mol / L for 24h. This step can effectively activate the surface functional groups. The modified material was dried and repeatedly washed until it reached a neutral pH, and then transferred to a muffle furnace for pyrolysis reaction. The heating rate was set to 10°C / min, and finally maintained at a constant temperature of 500°C for 2h to complete the preparation process of acid-modified biochar and obtain acid-modified biochar (HBC); in the final stage, 1g of acid-modified biochar was mixed with MgCO3 and 0.25g of Fe3O4, and 2 The wt% modified lignin-silk peptide complex was uniformly dispersed by ultrasonication for 30 minutes and then reacted in a high-pressure reactor at 150°C for 5 hours. The product was thoroughly washed with anhydrous ethanol and deionized water, and finally dried in an oven at 80°C to obtain magnetic magnesium-iron co-modified biochar (MBC) for subsequent applications.

[0030] Example 3: A method for preparing magnetic magnesium-iron co-modified biochar and its application in lead ion adsorption.

[0031] To prepare the modified lignin-silk peptide complex, 10 g of Bombyx mori silk protein was dissolved in 0.1 M LiBr solution, trypsin was added with an enzyme-to-substrate mass ratio of 1:55, hydrolyzed at 37°C for 2 h, and the component with a molecular weight of 500-1000 Da was retained. The silk peptide fragments were separated and collected, and freeze-dried for later use. 2 g of ethyl gallate and 500 U of laccase were added to the sodium lignin sulfonate borate buffer to react and generate a quinone-type structure graft body. A ZnCl2 solution with a molar concentration of 0.1 M was added dropwise to form a blue metal complex precipitate. 1 g of silk peptide and 3.5 g of the blue metal complex precipitate were mixed in deionized water, ultrasonically treated at 4°C for 15 min, and quickly freeze-dried to obtain a powdered modified lignin-silk peptide complex.

[0032] The corn straw raw material was pulverized and then cleaned to remove surface impurities, and then fully dried at 80°C to reduce the influence of the raw material moisture content on subsequent processes. After drying, it was ground and then sieved through a 60-mesh standard sieve for particle size control to obtain unmodified biochar basic material (BC); 20g of unmodified biochar sample was taken and soaked in a citric acid solution with a concentration of 1.5mol / L for 36h. This step can effectively activate the surface functional groups. The modified material was dried and repeatedly washed until it reached a neutral pH, and then transferred to a muffle furnace for pyrolysis reaction. The heating rate was set to 15°C / min, and finally maintained at a constant temperature of 500°C for 1.5h to complete the preparation process of acid-modified biochar and obtain acid-modified biochar (HBC); in the final stage, 1g of acid-modified biochar was mixed with MgCO3 and 0.2g of Fe3O4, and 2 The wt% modified lignin-silk peptide complex was uniformly dispersed by ultrasonication for 30 minutes and then reacted in a high-pressure reactor at 150°C for 5 hours. The product was thoroughly washed with anhydrous ethanol and deionized water, and finally dried in an oven at 80°C to obtain magnetic magnesium-iron co-modified biochar (MBC) for subsequent applications.

[0033] Comparative Example 1: The corn straw raw material was crushed and then washed to remove surface impurities. It was then fully dried at 80°C to reduce the impact of the raw material moisture content on subsequent processes. After drying, it was ground and then sieved through a 60-mesh standard sieve for particle size control to obtain unmodified biochar base material (BC).

[0034] Comparative Example 2: The corn straw raw material was pulverized and then washed to remove surface impurities, and then fully dried at 80°C to reduce the impact of the raw material moisture content on subsequent processes. After drying, it was ground and then sieved through a 60-mesh standard sieve for particle size control to obtain unmodified biochar basic material (BC); 20g of the unmodified biochar sample was taken and soaked in a citric acid solution with a concentration of 1.5mol / L for 36h. This step can effectively activate the surface functional groups. The modified material was dried and repeatedly washed until it reached a neutral pH, and then transferred to a muffle furnace for pyrolysis reaction. The heating rate was set to 15°C / min, and finally maintained at a constant temperature of 500°C for 1.5h to complete the preparation process of acid-modified biochar and obtain acid-modified biochar (HBC).

[0035] Experimental Example 1: Scanning electron microscopy-energy dispersive spectrometry (SEM-Mapping) was used to measure the appearance and morphology of the sample and observe the distribution of the material components of the sample; a specific surface area analyzer (BET) was used to measure the surface area and pore structure of the material.

[0036] The results are as follows Figure 1 As shown in the figure, compared with the unmodified corn straw biochar, the pores of the corn straw with the modified lignin-silk peptide complex increased, the surface became rougher, and the specific surface area increased. The elemental map found the presence of Fe and Mg elements, and MgO particles were clearly visible. The above results show that Mg and Fe were successfully loaded onto the surface of corn straw, its specific surface area increased, and more active sites were obtained, thereby improving its adsorption capacity for Pb(Ⅱ).

[0037] Experimental Example 2: 20 mL of a 100 mg / L Pb(II) solution and 0.02 g of an adsorbent were placed in a 50 mL conical flask, and the pH value was adjusted to 6. An adsorption experiment was conducted using a constant temperature shaker at 298 K and 180 rpm to study the effect of adsorbent dosage (5-50 g / L) on adsorption. After the experiment, samples were taken to measure the Pb(II) concentration. Three average experiments were performed, and the average value was taken. The adsorption capacity (Equation 1) and removal rate (Equation 2) were calculated using the following formulas:

[0038] Where: R is the removal rate, unit is %; C0 is the initial concentration of heavy metals, unit is mg / L; C is the residual concentration of heavy metals in the solution after adsorption equilibrium, unit is mg / L; q is the adsorption amount, unit is mg / g; V is the solution volume, unit is mL; m is the mass of the adsorbent, unit is mg.

[0039] The adsorption capacity of biochar dosage on Pb(Ⅱ) was tested by intermittent adsorption test. The results are as follows Figure 2As shown in the data, when the dosage of the adsorbent increased to 10 mg / L, the adsorption capacity of MBC, HBC and BC for Pb(Ⅱ) reached the maximum, which were 95.54 mg / g, 71.40 mg / g and 61.42 mg / g, respectively. Among them, the effect of magnetic magnesium-iron co-modified biochar (MBC) was much higher than that of unmodified BC and HBC without magnesium-iron co-modification, indicating that with the increase of adsorbent dosage, the active sites increased, and the removal rate of Pb(Ⅱ) was significantly improved; when the dosage of the adsorbent continued to increase to 50 mg / L, the adsorption capacity gradually decreased, indicating that at high dosage, the aggregation of adsorbent particles would reduce the surface area. It was concluded that the magnetic magnesium-iron co-modified biochar (MBC) had the best effect on Pb(Ⅱ) removal, and considering the adsorption capacity and economic cost, 10 mg / L was the optimal dosage.

[0040] Experimental Example 3: Weigh 0.02 g of magnetic magnesium-iron co-modified biochar (MBC) in a 50 mL conical flask, add 20 mL of Pb(Ⅱ) solution with a mass concentration of 100 mg / L, place the conical flask in a constant temperature oscillator at 25 ° C, the speed is 180 r / min, the pH value is 6, and the concentration of Pb(Ⅱ) is measured by atomic absorption spectrometer at 5, 10, 30, 60, 90, 120 and 150 min. Three average experiments are performed and the average value is taken. The pseudo-first-order kinetic model (Equation 3), pseudo-second-order kinetic model (Equation 4) and intraparticle diffusion model (Equation 5) are used to explore the adsorption mechanism of modified biochar for Pb(Ⅱ).

[0041]

[0042]

[0043] Where: qt is the adsorption amount of heavy metals by modified biochar at time t, in mg / g; t is the adsorption time, in min; k1 is the adsorption rate constant, in min; k2 is the adsorption rate constant, in g / (mg·min); Kdi is the intra-particle diffusion constant, in mg / g·min 1 / 2 ; Ci is the boundary layer constant.

[0044] Table 1 Kinetic fitting parameters

[0045] Through adsorption kinetics experiments, the pseudo-first-order kinetic model, pseudo-second-order kinetic model and intra-particle diffusion model were used to study the adsorption capacity of Pb(Ⅱ) on different biochars. As shown in Table 1, the pseudo-second-order kinetic model R 2 All of them are higher than pseudo-first-order kinetics, indicating that the adsorption of Pb(Ⅱ) by biochar products at each stage of the present invention is mainly chemical adsorption; Figure 3As shown in the data, the adsorption of Pb(Ⅱ) by all biochars showed a trend of rapid adsorption first and then tending to equilibrium, and basically reached equilibrium within 150 minutes, all showing adsorption effect, and the adsorption effect showed a trend of MBC being the best, HBC being the second, and BC being the weakest, indicating that the final product, magnetic magnesium-iron co-modified biochar (MBC), had the best adsorption effect for Pb(Ⅱ).

[0046] Experimental Example 4: 0.02 g of adsorbent was added to 20 mL of Pb(II) solutions with mass concentrations of 20 mg / L, 40 mg / L, 60 mg / L, 80 mg / L, 100 mg / L, 200 mg / L, 300 mg / L, 350 mg / L, 400 mg / L and 450 mg / L, and oscillated at 180 r / min for 120 min at a pH of 6 at 298 K. After the experiment, samples were taken to measure the concentration of Pb(II). Three average experiments were performed, the average value was taken, and the Langmuir model (Equation 6) and the Freundlich model (Equation 7) were used for fitting.

[0047]

[0048] Where: qm is the maximum adsorption capacity, the unit is mg / g; KL is the Langmuir adsorption equilibrium constant; KF is the Freundlich adsorption equilibrium constant; n is the Freundlich constant.

[0049] Table 2 Adsorption isotherm fitting parameters

[0050] The experimental data were fitted using the Langmuir isotherm model and the Freundlich isotherm model, as shown in Figure 4 As shown in Table 2, the Langmuir isotherm model reflects the monolayer adsorption effect of pollutants on homogeneous adsorbents, and the Freundlich isotherm model usually reflects the multilayer adsorption effect of pollutants on homogeneous adsorbents. Both show good fitting effects, among which the R 2 The values ​​are all higher than those of the Freundlich isotherm model, indicating that the Langmuir isotherm model can better explain the process of biochar removing Pb(Ⅱ) from groundwater, and the process belongs to a uniform monolayer chemical adsorption; According to the Langmuir fitting data, the n values ​​of the three adsorbents are all greater than 1, indicating that each biochar is conducive to the Pb(Ⅱ) adsorption process, and the maximum adsorption capacity of MBC, HBC and BC for Pb(Ⅱ) is 578.381 mg / g, 466.078 mg / g and 364.704 mg / g, among which the adsorption capacity of MBC is much greater than that of HBC and BC; According to Figure 4As shown in the figure, the Pb(Ⅱ) adsorbed on all biochars increased with the increase of initial Pb(Ⅱ) concentration, and then gradually reached a stable state. The maximum adsorption capacity of Pb(Ⅱ) by MBC, HBC and BC were 253.6 mg / g, 191.2 mg / g and 167.9 mg / g, respectively, proving that magnetic magnesium-iron co-modified biochar (MBC) had the best adsorption effect.

[0051] Experimental Example 5: The dried adsorbed material was shaken with 0.1 mol / L HCl at room temperature for 30 min, washed with distilled water until neutral, dried and tested for adsorption effect again. The adsorption-desorption test was repeated five times, three parallel experiments were performed, and the average value was taken.

[0052] The results of the regeneration experiment are as follows Figure 5 As shown in the data, after five cycles, the adsorption capacity of magnetic magnesium-iron co-modified biochar (MBC) for Pb(Ⅱ) decreased from 99.51 mg / g to 86.95 mg / g. The rate of decrease of adsorption capacity was slow after the reaction, and it still had a high adsorption capacity after five cycles. The results showed that magnetic magnesium-iron co-modified biochar had good recyclability.

[0053] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0054] The present invention and its embodiments are described above. Such description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if a person skilled in the art is inspired by the above, and does not deviate from the purpose of the present invention, without inventive design, a structure and embodiment similar to the technical solution should fall within the scope of protection of the present invention.

Claims

1. A magnetic magnesium-iron co-modified biochar, characterized by: The preparation of magnetic magnesium-iron co-modified biochar includes the following steps: Corn straw was crushed, cleaned and dried, then ground and sieved to obtain unmodified biochar (BC); the unmodified biochar was soaked in citric acid, dried and washed to neutrality, and placed in a muffle furnace for pyrolysis to obtain acid-modified biochar (HBC); the acid-modified biochar was ultrasonically mixed with MgCO3 and Fe3O4, and a modified lignin-silk peptide complex was added. The mixture was transferred to a high-pressure reactor for high-pressure reaction, and the product was washed with anhydrous ethanol and deionized water and then dried to obtain magnetic magnesium-iron co-modified biochar (MBC).

2. The magnetic magnesium-iron co-modified biochar according to claim 1, characterized in that: The preparation of the modified lignin-silk fibroin peptide complex comprises the following steps: Bombyx mori silk fibroin was dissolved in LiBr solution, and trypsin was added to hydrolyze and retain components with a molecular weight of 500-1000Da. The silk fibroin peptide fragments were separated and collected, and freeze-dried for later use. Ethyl gallate and laccase were added to sodium lignin sulfonate borate buffer to react and generate a quinone-type structure graft body. ZnCl2 solution was added dropwise to form a blue metal complex precipitate. The resulting product was mixed with deionized water, ultrasonically treated at 4°C, and quickly freeze-dried to obtain a powdered modified lignin-silk fibroin peptide complex.

3. The magnetic magnesium-iron co-modified biochar according to claim 2, characterized in that: The citric acid concentration is 0.8-1.5 mol / L.

4. The magnetic magnesium-iron co-modified biochar according to claim 3, characterized in that: The citric acid soaking time is 12-36 hours.

5. The magnetic magnesium-iron co-modified biochar according to claim 4, characterized in that: The muffle furnace pyrolysis heating rate is 8-15°C / min.

6. The magnetic magnesium-iron co-modified biochar according to claim 5, characterized in that: The mass ratio of the acid-modified biochar to MgCO3 and Fe3O4 is (3-5): (3-5):

1.

7. The magnetic magnesium-iron co-modified biochar according to claim 6, characterized in that: The mass ratio of trypsin to substrate is 1:(45-55).

8. The magnetic magnesium-iron co-modified biochar according to claim 7, characterized in that: The molar ratio of ZnCl2 to gallic acid is 1:

2.

9. The magnetic magnesium-iron co-modified biochar according to claim 8, characterized in that: The mass ratio of the silk fibroin peptide to the blue metal complex precipitate is 1:

3.

10. Use of any one of the magnetic magnesium-iron co-modified biochars according to claims 1-9 in lead ion adsorption, characterized in that: Magnetic magnesium-iron co-modified biochar was added into a lead ion aqueous solution, and the mass ratio of biochar to lead ion aqueous solution was 1:1000.

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