A soil amendment containing biomass char and a method of making the same

Abstract

The application provides a preparation method of a soil remediation agent containing biomass charcoal, and belongs to the technical field of soil conditioning materials; the preparation method comprises the following steps: preparing complexing agent microcapsules, preparing composite charcoal, preparing hollow porous silicon dioxide, and loading; the method for preparing the complexing agent microcapsules is as follows: adding arabic gum, sodium alginate and Tween 80 into deionized water, uniformly stirring, then adding a mixed solution of glutamic acid N,N-diacetic acid and citric acid, stirring at 7000-9000 r / min for 4-6 min, obtaining an emulsion, and spraying and drying the emulsion to obtain the complexing agent microcapsules; the soil remediation agent can reduce the soil bulk density from 2.18 g / cm3 to 1.57-1.64 g / cm3, increase the water-stable aggregate greater than 0.25 mm from 34% to 55-58%, and has the absorption rates of 82-86%, 87-90%, 90-95% and 85-88% for heavy metals cadmium, lead and copper and organic pollutants, respectively; after simulation aging, the heavy metal ion precipitation rates of cadmium, lead and copper are 4.2-4.8%, 5.1-5.7% and 3.1-3.6%, respectively.

Description

Technical Field

[0001] This invention belongs to the field of soil conditioning materials technology, specifically relating to a method for preparing a soil remediation agent containing biochar. Background Technology

[0003] Soil remediation agents are a means of improving soil problems. Currently, the mainstream soil remediation agents are biochar-based soil remediation agents. Biochar has the characteristics of being porous, having a large specific surface area, and being rich in hydrophilic oxygen-containing functional groups. It has a significant impact on the main physicochemical properties of soil, and can improve soil bulk density and porosity, water retention capacity, pH value, and cation exchange capacity. The pores of biochar provide habitats for microorganisms, improve soil aeration, and enhance microbial activity. Biochar can also adsorb heavy metals and organic pollutants in the soil, such as pesticides and fertilizers, through adsorption and complexation.

[0004] However, biochar-based soil remediation agents also pose some potential risks. For example, organic and inorganic pollutants, such as heavy metals and polycyclic aromatic hydrocarbons, adsorbed from the soil environment by biochar may still be toxic. They are only adsorbed and fixed by biochar and are still bioavailable. When the properties of biochar change (such as biochar aging and cracking) and are no longer sufficient to adsorb and fix these pollutants, they will migrate and transform from biochar into the soil, causing harm to the soil ecology and plants and animals.

[0005] The method of applying biochar in combination with complexing agents and microbial agents can effectively complex heavy metal ions and decompose organic pollutants. However, complexing agents, such as EDTA, can form extremely stable complexes with most heavy metal ions (such as Pb, Cd, Cu, and Zn), reducing the toxicity of heavy metal ions. But EDTA itself is not easily degraded and may cause secondary pollution if it remains in the soil for a long time. On the other hand, although citric acid, malic acid, and oxalic acid are natural / environmentally friendly complexing agents, when they are combined with biochar and microbial agents and applied to the soil, the process of biochar adsorbing heavy metal ions takes time. During this time, the microorganisms have already decomposed the complexing agents, resulting in a significant decrease in the complexing effect on heavy metal ions. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a soil remediation agent containing biochar and its preparation method, achieving the following objectives: improving soil, reducing soil bulk density, increasing the total percentage content of water-stable aggregates greater than 0.25 mm, effectively adsorbing heavy metal ions and organic pollutants in the soil, and preventing the secondary precipitation of heavy metal ions after biochar aging.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a soil remediation agent containing biochar includes the following steps: 1. Preparation of complexing agent microcapsules Gum arabic, sodium alginate, Tween 80, and deionized water were added and stirred at 2000-3000 r / min and 50-60℃ for 25-35 min. Then, a mixed solution of N,N-diacetic acid and citric acid was added and stirred at 7000-9000 r / min for 4-6 min to obtain an emulsion. The emulsion was then spray-dried to obtain complexing agent microcapsules. The mass ratio of the mixed solution of gum arabic, sodium alginate, Tween 80, deionized water, N,N-diacetic glutamic acid, and citric acid is 2.5–3.5: 0.8–1.2: 0.1–0.3: 7–9: 3.4–3.8. In the mixed solution of N,N-diacetic glutamic acid and citric acid, the mass ratio of N,N-diacetic glutamic acid, citric acid, and deionized water is 1.0–1.2:0.3–0.5:2.0–2.2. The spray drying process is carried out at an air velocity of 20–24 m / s. 3 / h, peristaltic pump speed 11~13r / min, inlet air temperature 170~190℃.

[0008] 2. Preparation of composite biochar Wheat straw was washed clean, crushed, and passed through a 100-140 mesh sieve. It was then added to pure water and, under sealed conditions, heated to 260-300°C at a rate of 3-6°C / min, and held at this temperature for 5-8 hours, maintaining a stable internal pressure of 2-5 MPa. After the reaction was complete and cooled to room temperature, the filtered solid was dried at 95-105°C for 20-24 hours. Subsequently, it was placed in a tube furnace and activated at 700-800°C for 0.8-1.2 hours under an argon atmosphere by heating at 8-10°C / min. After cooling, it was treated with HCl. The solution and deionized water were alternately washed until neutral, and dried at 70-80℃ to constant weight to obtain biochar. The nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution and biochar were mixed evenly and cultured at 25-35℃ and 150-200 r / min for 12-48 h. Then, the mixture was centrifuged at 7500-8500 r / min for 5-10 min, and the lower solid layer was collected and dried at 25-30℃ for 30-50 min to obtain composite biochar. The mass ratio of wheat straw to pure water is 0.9–1.1:8–12; The HCl solution has a mass fraction of 10-20%; The mass ratio of the nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar is 1.5–2.5: 2.8–3.2: 6–8: 3.5–4.5: 3–5: 0.8–1.2. The viable count of the nitrogen-fixing bacteria solution was 1.1–1.3 × 10⁻⁶. 8 CFU / ml; The Bacillus megaterium culture solution has a concentration of 2.1–2.5 × 10⁻⁶. 7 CFU / ml; The Bacillus subtilis bacterial solution has a concentration of 5–6 × 10⁻⁶. 8 CFU / ml; The yeast culture solution has a concentration of 4.5–4.9 × 10⁻⁶. 7 CFU / ml; The lactic acid bacteria culture solution has a concentration of 9.0–9.6 × 10⁻⁶. 6 CFU / ml.

[0009] 3. Preparation of hollow porous silica Polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, and ammonia were added to deionized water and stirred thoroughly. After reacting for 8–12 hours, the mixture was filtered, washed 2–4 times with ethanol solution, dried at 50–60°C for 30–50 minutes, and calcined at 550–650°C for 3–5 hours to remove the polyacrylamide gel, yielding hollow porous silica. The mass ratio of the polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, ammonia, and deionized water is 0.2–0.4: 2.5–2.9: 25–35: 0.8–1.2: 1.4–1.6. The mass fraction of the ammonia solution is 20-30%. The ethanol solution has a mass fraction of 5-15%; The preparation method of the polyacrylamide gel is as follows: under nitrogen atmosphere, the surfactant Span60 is added to cyclohexane and stirred until a homogeneous and transparent solution is formed for later use. Acrylamide, N,N-methylenebisacrylamide, and ammonium persulfate were dissolved in deionized water and then slowly added dropwise to the above homogeneous and transparent solution. After the addition was complete, the mixture was reacted at 55-65°C for 3-5 hours. After filtration, the solid product was washed clean and then soaked in deionized water for 15-30 minutes. Finally, it was freeze-dried at -40--50°C to obtain polyacrylamide gel. The mass ratio of the surfactant Span60 to cyclohexane is 0.8–1.2:90–110; The mass ratio of acrylamide, N,N-methylenebisacrylamide, ammonium persulfate, and deionized water is 1.5–2.5: 0.05–0.15: 0.11–0.13: 8–12. The droplet acceleration rate is 1–3 ml / min.

[0010] 4. Load Hollow porous silica, complexing agent microcapsules, and composite biochar are mixed evenly and stirred and shaken continuously for 1 to 2 hours to obtain a soil remediation agent. The mass ratio of the hollow porous silica, complexing agent microcapsules, and composite biochar is 5-7:2.5-3.5:1.8-2.2.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The composite biochar prepared by this invention contains a variety of microbial agents, which can effectively decompose organic pollutants. At the same time, the negatively charged functional groups (such as carboxyl groups and phosphate groups) on the surface of the microbial cell wall can adsorb heavy metal cations in the solution like a magnet. Some microorganisms can also actively transport heavy metal ions into the cell and reduce their biotoxicity by binding with specific proteins (such as metallothionein). In addition, the metabolites of some microorganisms (such as sulfide ions and carbonate ions) can form insoluble or very low-solubility compounds with heavy metal ions.

[0012] 2. The complexing agent microcapsules prepared in this invention are obtained by encapsulating the complexing agent N,N-diacetic acid glutamic acid with citric acid. This effectively prevents microorganisms from decomposing the complexing agent while decomposing organic pollutants. When the biochar adsorption gradually reaches saturation, the capsule wall of the complexing agent microcapsule is gradually decomposed by microorganisms, and the released complexing agent directly complexes with the heavy metal ions inside the biochar, thus avoiding the waste of the complexing agent in the early stage of adsorption.

[0013] 3. The hollow porous silica prepared by this invention loads composite biochar and complexing agent microcapsules. The hollow porous silica has good loading, adsorption, pressure resistance and aging resistance. When the composite biochar ages, even if heavy metal ions are released a second time, they can remain inside the hollow porous silica to prevent secondary pollution.

[0014] 4. The biochar-containing soil remediation agent of the present invention can significantly reduce soil bulk density, specifically from 2.18 g / cm³ to 1.57–1.64 g / cm³; it can effectively increase the total percentage content of water-stable aggregates larger than 0.25 mm, specifically from 34% to 55–58%; it can effectively adsorb heavy metal ions and organic pollutants, with absorption rates of 82–86% for heavy metals cadmium, lead, and copper, and 85–88% for organic pollutants; after simulated aging, the release rate of heavy metal ions is low, with 4.2–4.8% for cadmium, 5.1–5.7% for lead, and 3.1–3.6% for copper. Detailed Implementation

[0015] Example 1 1. Preparation of complexing agent microcapsules Gum arabic, sodium alginate, Tween 80, and deionized water were added and stirred at 2500 r / min and 55℃ for 30 min. Then, a mixed solution of N,N-diacetic acid and citric acid was added and stirred at 8000 r / min for 5 min to obtain an emulsion. The emulsion was then spray-dried to obtain complexing agent microcapsules. The mass ratio of the mixed solution of gum arabic, sodium alginate, Tween 80, deionized water, N,N-diacetic glutamic acid and citric acid is 3:1:0.2:8:3.6. In the mixed solution of N,N-diacetic glutamic acid and citric acid, the mass ratio of N,N-diacetic glutamic acid, citric acid, and deionized water is 1.1:0.4:2.1. The spray drying process is carried out at a wind speed of 22 m / s. 3 / h, peristaltic pump speed 12r / min, inlet air temperature 180℃.

[0016] 2. Preparation of composite biochar Wheat straw was cleaned, crushed, and passed through a 120-mesh sieve. It was then added to pure water and heated to 280°C at a rate of 5°C / min in a sealed environment. The temperature was maintained for 6 hours while keeping the internal pressure stable at 4 MPa. After the reaction was completed and cooled to room temperature, the filtered solid was dried at 100°C for 22 hours. It was then placed in a tube furnace and activated at 750°C for 1 hour under an argon atmosphere by heating at 9°C / min. After cooling, it was washed alternately with HCl solution and deionized water until neutral and dried at 75°C to constant weight to obtain biochar. Nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar were mixed evenly and cultured at 30°C and 180 r / min for 30 hours. Then, it was centrifuged at 8000 r / min for 8 minutes, and the lower solid layer was taken out and dried at 28°C for 40 minutes to obtain composite biochar. The mass ratio of wheat straw to pure water is 1:10; The HCl solution has a mass fraction of 15%. The mass ratio of the nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar is 2:3:7:4:4:1. The viable count of the nitrogen-fixing bacteria solution was 1.2 × 10⁻⁶. 8 CFU / ml; The Bacillus megaterium culture solution was 2.3 × 10⁻⁶. 7 CFU / ml; The Bacillus subtilis bacterial culture was 5.5 × 10⁻⁶. 8 CFU / ml; The yeast culture solution has a concentration of 4.7 × 10⁻⁶. 7 CFU / ml; The lactic acid bacteria culture solution has a concentration of 9.3 × 10⁻⁶. 6 CFU / ml.

[0017] 3. Preparation of hollow porous silica Polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, and ammonia were added to deionized water and stirred thoroughly. After reacting for 10 hours, the mixture was filtered, washed three times with ethanol solution, dried at 55°C for 40 minutes, and calcined at 600°C for 4 hours to remove the polyacrylamide gel, thus obtaining hollow porous silica. The mass ratio of the polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, ammonia, and deionized water is 0.3:2.7:30:1:1.5. The mass fraction of the ammonia solution is 25%. The ethanol solution has a mass fraction of 10%. The preparation method of the polyacrylamide gel is as follows: under nitrogen atmosphere, the surfactant Span60 is added to cyclohexane and stirred until a homogeneous and transparent solution is formed for later use. Acrylamide, N,N-methylenebisacrylamide, and ammonium persulfate were dissolved in deionized water and then slowly added dropwise to the above homogeneous and transparent solution. After the addition was complete, the mixture was reacted at 60°C for 4 hours, filtered, and the solid product was washed clean. The product was then soaked in deionized water for 22 minutes and freeze-dried at -45°C to obtain polyacrylamide gel. The mass ratio of the surfactant Span60 to cyclohexane is 1:100; The mass ratio of acrylamide, N,N-methylenebisacrylamide, ammonium persulfate, and deionized water is 2:0.1:0.12:10. The droplet acceleration rate is 2 ml / min.

[0018] 4. Load Hollow porous silica, complexing agent microcapsules, and composite biochar are mixed evenly and stirred and shaken continuously for 1.5 hours to obtain a soil remediation agent. The mass ratio of the hollow porous silica, complexing agent microcapsules, and composite biochar is 6:3:2.

[0019] Example 2 1. Preparation of complexing agent microcapsules Gum arabic, sodium alginate, Tween 80, and deionized water were added and stirred at 3000 r / min and 60℃ for 35 min. Then, a mixed solution of N,N-diacetic acid and citric acid was added and stirred at 9000 r / min for 6 min to obtain an emulsion. The emulsion was then spray-dried to obtain complexing agent microcapsules. The mass ratio of the mixed solution of gum arabic, sodium alginate, Tween 80, deionized water, N,N-diacetic glutamic acid and citric acid is 3.5:1.2:0.3:9:3.8. In the mixed solution of N,N-diacetic glutamic acid and citric acid, the mass ratio of N,N-diacetic glutamic acid, citric acid, and deionized water is 1.2:0.5:2.2. The spray drying process is carried out at a wind speed of 24 m / s. 3 / h, peristaltic pump speed 13r / min, inlet air temperature 190℃.

[0020] 2. Preparation of composite biochar Wheat straw was cleaned, crushed, and passed through a 140-mesh sieve. It was then added to pure water and heated to 300°C at a rate of 6°C / min in a sealed environment. The temperature was maintained for 8 hours, during which the internal pressure was kept stable at 5 MPa. After the reaction was completed and cooled to room temperature, the filtered solid was dried at 105°C for 24 hours. It was then placed in a tube furnace and activated at 800°C for 1.2 hours under an argon atmosphere by heating at 10°C / min. After cooling, it was washed alternately with HCl solution and deionized water until neutral and dried at 80°C to constant weight to obtain biochar. Nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar were mixed evenly and cultured at 35°C and 200 r / min for 48 hours. Then, it was centrifuged at 8500 r / min for 10 minutes, and the lower solid layer was taken out and dried at 30°C for 50 minutes to obtain composite biochar. The mass ratio of wheat straw to pure water is 1.1:12; The HCl solution has a mass fraction of 20%. The mass ratio of the nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar is 2.5:3.2:8:4.5:5:1.2. The viable count of the nitrogen-fixing bacteria solution was 1.3 × 10⁻⁶. 8 CFU / ml; The Bacillus megaterium culture solution was 2.5 × 10⁻⁶. 7 CFU / ml; The Bacillus subtilis bacterial solution was 6 × 10⁻⁶. 8 CFU / ml; The yeast culture solution had a concentration of 4.9 × 10⁻⁶. 7 CFU / ml; The lactic acid bacteria culture solution has a concentration of 9.6 × 10⁻⁶. 6 CFU / ml.

[0021] 3. Preparation of hollow porous silica Polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, and ammonia were added to deionized water and stirred thoroughly. After reacting for 12 hours, the mixture was filtered, washed four times with ethanol solution, dried at 60°C for 50 minutes, and calcined at 650°C for 5 hours to remove the polyacrylamide gel, thus obtaining hollow porous silica. The mass ratio of the polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, ammonia, and deionized water is 0.4:2.9:35:1.2:1.6. The mass fraction of the ammonia solution is 30%. The ethanol solution has a mass fraction of 15%. The preparation method of the polyacrylamide gel is as follows: under nitrogen atmosphere, the surfactant Span60 is added to cyclohexane and stirred until a homogeneous and transparent solution is formed for later use. Acrylamide, N,N-methylenebisacrylamide, and ammonium persulfate were dissolved in deionized water and then slowly added dropwise to the above homogeneous and transparent solution. After the addition was complete, the mixture was reacted at 65°C for 5 hours, filtered, and the solid product was washed clean. The product was then soaked in deionized water for 30 minutes and freeze-dried at -50°C to obtain polyacrylamide gel. The mass ratio of the surfactant Span60 to cyclohexane is 1.2:110; The mass ratio of acrylamide, N,N-methylenebisacrylamide, ammonium persulfate, and deionized water is 2.5:0.15:0.13:12. The droplet acceleration rate is 3 ml / min.

[0022] 4. Load Hollow porous silica, complexing agent microcapsules, and composite biochar are mixed evenly and stirred and shaken continuously for 2 hours to obtain a soil remediation agent. The mass ratio of the hollow porous silica, complexing agent microcapsules, and composite biochar is 7:3.5:2.2.

[0023] Example 3 1. Preparation of complexing agent microcapsules Gum arabic, sodium alginate, Tween 80 were added to deionized water and stirred at 2000 r / min and 50℃ for 25 min. Then, a mixed solution of N,N-diacetic acid and citric acid was added and stirred at 7000 r / min for 4 min to obtain an emulsion. The emulsion was then spray-dried to obtain complexing agent microcapsules. The mass ratio of the mixed solution of gum arabic, sodium alginate, Tween 80, deionized water, N,N-diacetic glutamic acid and citric acid is 2.5:0.8:0.1:7:3.4. In the mixed solution of N,N-diacetic glutamic acid and citric acid, the mass ratio of N,N-diacetic glutamic acid, citric acid, and deionized water is 1.0:0.3:2.0. The spray drying process is carried out at a wind speed of 20 m / s. 3 / h, peristaltic pump speed 11r / min, inlet air temperature 170℃.

[0024] 2. Preparation of composite biochar Wheat straw was cleaned, crushed, and passed through a 100-mesh sieve. It was then added to pure water and heated to 260°C at a rate of 3°C / min in a sealed environment. The temperature was maintained for 5 hours, during which the internal pressure was kept stable at 2 MPa. After the reaction was completed and cooled to room temperature, the filtered solid was dried at 95°C for 20 hours. It was then placed in a tube furnace and activated at 700°C for 0.8 hours under an argon atmosphere by heating at 8°C / min. After cooling, it was washed alternately with HCl solution and deionized water until neutral and dried at 70°C to constant weight to obtain biochar. Nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar were mixed evenly and cultured at 25°C and 150 r / min for 12 hours. Then, it was centrifuged at 7500 r / min for 5 minutes, and the lower solid layer was taken out and dried at 25°C for 30 minutes to obtain composite biochar. The mass ratio of wheat straw to pure water is 0.9:8; The HCl solution has a mass fraction of 10%. The mass ratio of the nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar is 1.5:2.8:6:3.5:3:0.8. The viable count of the nitrogen-fixing bacteria solution was 1.1 × 10⁻⁶. 8 CFU / ml; The Bacillus megaterium culture solution was 2.1 × 10⁻⁶. 7 CFU / ml; The Bacillus subtilis bacterial solution was 5 × 10⁻⁶. 8 CFU / ml; The yeast culture solution has a concentration of 4.5 × 10⁻⁶. 7 CFU / ml; The lactic acid bacteria culture solution has a concentration of 9.0 × 10⁻⁶. 6 CFU / ml.

[0025] 3. Preparation of hollow porous silica Polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, and ammonia were added to deionized water and stirred thoroughly. After reacting for 8 hours, the mixture was filtered, washed twice with ethanol solution, dried at 50°C for 30 minutes, and calcined at 550°C for 3 hours to remove the polyacrylamide gel, thus obtaining hollow porous silica. The mass ratio of the polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, ammonia, and deionized water is 0.2:2.5:25:0.8:1.4. The mass fraction of the ammonia solution is 20%. The ethanol solution has a mass fraction of 5%; The preparation method of the polyacrylamide gel is as follows: under nitrogen atmosphere, the surfactant Span60 is added to cyclohexane and stirred until a homogeneous and transparent solution is formed for later use. Acrylamide, N,N-methylenebisacrylamide, and ammonium persulfate were dissolved in deionized water and then slowly added dropwise to the above homogeneous and transparent solution. After the addition was complete, the mixture was reacted at 55°C for 3 hours, filtered, and the solid product was washed clean. The product was then soaked in deionized water for 15 minutes and freeze-dried at -40°C to obtain polyacrylamide gel. The mass ratio of the surfactant Span60 to cyclohexane is 0.8:90; The mass ratio of acrylamide, N,N-methylenebisacrylamide, ammonium persulfate, and deionized water is 1.5:0.05:0.11:8. The droplet acceleration rate is 1 ml / min.

[0026] 4. Load Hollow porous silica, complexing agent microcapsules, and composite biochar are mixed evenly and stirred and shaken continuously for 1 hour to obtain a soil remediation agent. The mass ratio of the hollow porous silica, complexing agent microcapsules, and composite biochar is 5:2.5:1.8.

[0027] Comparative Example 1 Based on Example 1, the step of preparing the complexing agent microcapsules was omitted and replaced with an equal mass mixture of N,N-diacetic glutamate and citric acid, specifically: 1. Preparation of composite biochar Wheat straw was cleaned, crushed, and passed through a 120-mesh sieve. It was then added to pure water and heated to 280°C at a rate of 5°C / min in a sealed environment. The temperature was maintained for 6 hours while keeping the internal pressure stable at 4 MPa. After the reaction was completed and cooled to room temperature, the filtered solid was dried at 100°C for 22 hours. It was then placed in a tube furnace and activated at 750°C for 1 hour under an argon atmosphere by heating at 9°C / min. After cooling, it was washed alternately with HCl solution and deionized water until neutral and dried at 75°C to constant weight to obtain biochar. Nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar were mixed evenly and cultured at 30°C and 180 r / min for 30 hours. Then, it was centrifuged at 8000 r / min for 8 minutes, and the lower solid layer was taken out and dried at 28°C for 40 minutes to obtain composite biochar. The mass ratio of wheat straw to pure water is 1:10; The HCl solution has a mass fraction of 15%. The mass ratio of the nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar is 2:3:7:4:4:1. The viable count of the nitrogen-fixing bacteria solution was 1.2 × 10⁻⁶. 8 CFU / ml; The Bacillus megaterium culture solution was 2.3 × 10⁻⁶. 7 CFU / ml; The Bacillus subtilis bacterial culture was 5.5 × 10⁻⁶. 8 CFU / ml; The yeast culture solution has a concentration of 4.7 × 10⁻⁶. 7 CFU / ml; The lactic acid bacteria culture solution has a concentration of 9.3 × 10⁻⁶. 6 CFU / ml.

[0028] 2. Preparation of hollow porous silica Polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, and ammonia were added to deionized water and stirred thoroughly. After reacting for 10 hours, the mixture was filtered, washed three times with ethanol solution, dried at 55°C for 40 minutes, and calcined at 600°C for 4 hours to remove the polyacrylamide gel, thus obtaining hollow porous silica. The mass ratio of the polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, ammonia, and deionized water is 0.3:2.7:30:1:1.5. The mass fraction of the ammonia solution is 25%. The ethanol solution has a mass fraction of 10%. The preparation method of the polyacrylamide gel is as follows: under nitrogen atmosphere, the surfactant Span60 is added to cyclohexane and stirred until a homogeneous and transparent solution is formed for later use. Acrylamide, N,N-methylenebisacrylamide, and ammonium persulfate were dissolved in deionized water and then slowly added dropwise to the above homogeneous and transparent solution. After the addition was complete, the mixture was reacted at 60°C for 4 hours, filtered, and the solid product was washed clean. The product was then soaked in deionized water for 22 minutes and freeze-dried at -45°C to obtain polyacrylamide gel. The mass ratio of the surfactant Span60 to cyclohexane is 1:100; The mass ratio of acrylamide, N,N-methylenebisacrylamide, ammonium persulfate, and deionized water is 2:0.1:0.12:10. The droplet acceleration rate is 2 ml / min.

[0029] 3. Load Hollow porous silica, N,N-diacetic acid, citric acid, and composite biochar were mixed evenly and stirred and shaken continuously for 1.5 hours to obtain a soil remediation agent. The mass ratio of the hollow porous silica, N,N-diacetic acid, citric acid, and composite biochar is 6:2.2:0.8:2.

[0030] Comparative Example 2 Based on Example 1, the step of preparing hollow porous silica is omitted, and instead: 1. Preparation of complexing agent microcapsules Gum arabic, sodium alginate, Tween 80, and deionized water were added and stirred at 2500 r / min and 55℃ for 30 min. Then, a mixed solution of N,N-diacetic acid and citric acid was added and stirred at 8000 r / min for 5 min to obtain an emulsion. The emulsion was then spray-dried to obtain complexing agent microcapsules. The mass ratio of the mixed solution of gum arabic, sodium alginate, Tween 80, deionized water, N,N-diacetic glutamic acid and citric acid is 3:1:0.2:8:3.6. In the mixed solution of N,N-diacetic glutamic acid and citric acid, the mass ratio of N,N-diacetic glutamic acid, citric acid, and deionized water is 1.1:0.4:2.1. The spray drying process is carried out at a wind speed of 22 m / s. 3 / h, peristaltic pump speed 12r / min, inlet air temperature 180℃.

[0031] 2. Preparation of composite biochar Wheat straw was cleaned, crushed, and passed through a 120-mesh sieve. It was then added to pure water and heated to 280°C at a rate of 5°C / min in a sealed environment. The temperature was maintained for 6 hours while keeping the internal pressure stable at 4 MPa. After the reaction was completed and cooled to room temperature, the filtered solid was dried at 100°C for 22 hours. It was then placed in a tube furnace and activated at 750°C for 1 hour under an argon atmosphere by heating at 9°C / min. After cooling, it was washed alternately with HCl solution and deionized water until neutral and dried at 75°C to constant weight to obtain biochar. Nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar were mixed evenly and cultured at 30°C and 180 r / min for 30 hours. Then, it was centrifuged at 8000 r / min for 8 minutes, and the lower solid layer was taken out and dried at 28°C for 40 minutes to obtain composite biochar. The mass ratio of wheat straw to pure water is 1:10; The HCl solution has a mass fraction of 15%. The mass ratio of the nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar is 2:3:7:4:4:1. The viable count of the nitrogen-fixing bacteria solution was 1.2 × 10⁻⁶. 8 CFU / ml; The Bacillus megaterium culture solution was 2.3 × 10⁻⁶. 7 CFU / ml; The Bacillus subtilis bacterial culture was 5.5 × 10⁻⁶. 8 CFU / ml; The yeast culture solution has a concentration of 4.7 × 10⁻⁶. 7 CFU / ml; The lactic acid bacteria culture solution has a concentration of 9.3 × 10⁻⁶. 6 CFU / ml.

[0032] 3. Load The complexing agent microcapsules and composite biochar were mixed evenly and stirred and shaken continuously for 1.5 hours to obtain the soil remediation agent. The mass ratio of the complexing agent microcapsules to the composite biochar is 3:2.

[0033] Experimental Example 1 The soil remediation agents prepared in Examples 1-3 and Comparative Examples 1-2 were applied to the corresponding experimental fields. After 30 days, the soil bulk density and the total percentage of water-stable aggregates larger than 0.25 mm were tested. The test results are shown in Table 1. Table 1

[0034] The soil bulk density of the experimental field was tested using the ring sampler method after 30 days, and the calculation formula is as follows: ρb=m / V In the formula: ρb is the soil bulk density, g / cm³; m is the mass of the soil sample after drying, g; V is the volume of the soil sample before drying, cm³.

[0035] The initial soil bulk density of the experimental field was 2.18 g / cm³.

[0036] The total percentage of water-stable aggregates larger than 0.25 mm in the experimental field was tested using a wet sieving method after 30 days. The calculation formula is as follows: X=m / W In the formula: m is the dried weight of water-stable agglomerates after wet sieving (greater than 0.25 mm), in g; W is the dried weight of the soil sample taken during dry sieving, in g.

[0037] The total percentage of water-stable aggregates larger than 0.25 mm in the initial experimental field was 34%.

[0038] Experimental Example 2 1. Prepare soil samples containing 100 mg / kg of cadmium ions, 100 mg / kg of lead ions, 100 mg / kg of copper ions, and 10 mg / kg of organic pollutant (pesticide acetamiprid). Add the soil remediation agents prepared in Examples 1-3 and Comparative Examples 1-2, respectively. After 30 days, detect the concentrations of cadmium, lead, copper ions, and organic pollutant (pesticide acetamiprid) in the soil, and then calculate the absorption rate of heavy metal ions and organic pollutants. The results are shown in Table 2. Table 2

[0039] 2. The above-mentioned soil remediation agent was recovered and placed in an environment with 70% humidity for 12 hours, then dried in an oven at 60℃ for 12 hours. This cycle was repeated for 30 days to obtain a soil remediation agent that simulates natural drying, wetting, cooling, and heating cycles. The aged soil remediation agent was then placed in soil with 50% humidity. After 30 days, the content of heavy metal ions in the soil was measured, and the heavy metal ion release rate was calculated. The results are shown in Table 3. Table 3

[0040] The results above show that the complexing agent in Comparative Example 1 lacks microcapsule protection, which leads to premature decomposition by microorganisms, resulting in a decrease in the complexing effect on heavy metal ions, a decrease in absorption rate, and an increase in precipitation rate. In Comparative Example 2, the lack of hollow porous silica barrier resulted in an increased rate of heavy metal ion release after aging of the composite biochar.

Claims

1. A method for preparing a soil remediation agent containing biochar, characterized in that: The preparation method includes preparing complexing agent microcapsules, preparing composite biochar, preparing hollow porous silica, and loading. The method for preparing complexing agent microcapsules is as follows: gum arabic, sodium alginate, Tween 80 are added to deionized water and stirred at 2000-3000 r / min and 50-60℃ for 25-35 min. Then, a mixed solution of N,N-diacetic acid and citric acid is added and stirred at 7000-9000 r / min for 4-6 min to obtain an emulsion. The emulsion is then spray-dried to obtain complexing agent microcapsules. The method for preparing hollow porous silica is as follows: polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, and ammonia are added to deionized water, stirred thoroughly, and reacted for 8-12 hours. After filtration, the mixture is washed 2-4 times with ethanol solution, dried at 50-60°C for 30-50 minutes, and then calcined at 550-650°C for 3-5 hours to remove the polyacrylamide gel, thereby obtaining hollow porous silica.

2. The method for preparing a biochar-containing soil remediation agent according to claim 1, characterized in that: In the method for preparing complexing agent microcapsules, the mass ratio of the mixed solution of gum arabic, sodium alginate, Tween 80, deionized water, N,N-diacetic glutamate, and citric acid is 2.5–3.5: 0.8–1.2: 0.1–0.3: 7–9: 3.4–3.

8. In a mixed solution of N,N-diacetic glutamic acid and citric acid, the mass ratio of N,N-diacetic glutamic acid, citric acid, and deionized water is 1.0–1.2:0.3–0.5:2.0–2.

2. Spray drying, wind speed 20-24m 3 / h, peristaltic pump speed 11~13r / min, inlet air temperature 170~190℃.

3. The method for preparing a biochar-containing soil remediation agent according to claim 1, characterized in that: In the method for preparing hollow porous silica, the mass ratio of polyacrylamide gel, tetraethyl orthosilicate, anhydrous ethanol, ammonia, and deionized water is 0.2–0.4: 2.5–2.9: 25–35: 0.8–1.2: 1.4–1.

6. The mass fraction of ammonia in the solution is 20-30%. The ethanol solution has a mass fraction of 5-15%.

4. The method for preparing a biochar-containing soil remediation agent according to claim 1, characterized in that: In the method for preparing hollow porous silica, the polyacrylamide gel is prepared by adding the surfactant Span60 to cyclohexane under nitrogen atmosphere and stirring until a homogeneous and transparent solution is formed for later use. Acrylamide, N,N-methylenebisacrylamide, and ammonium persulfate were dissolved in deionized water and then slowly added dropwise to the homogeneous and transparent solution. After the addition was complete, the mixture was reacted at 55–65°C for 3–5 hours. The mixture was then filtered, and the solid product was washed clean. It was then soaked in deionized water for 15–30 minutes and freeze-dried at -40–-50°C to obtain polyacrylamide gel.

5. The method for preparing a biochar-containing soil remediation agent according to claim 4, characterized in that: In the preparation method of the polyacrylamide gel, the mass ratio of surfactant Span60 to cyclohexane is 0.8-1.2:90-110; The mass ratio of acrylamide, N,N-methylenebisacrylamide, ammonium persulfate, and deionized water is 1.5–2.5: 0.05–0.15: 0.11–0.13: 8–12. The drip rate is 1–3 ml / min.

6. The method for preparing a biochar-containing soil remediation agent according to claim 1, characterized in that: The method for preparing composite biochar is as follows: Wheat straw is washed, crushed, sieved, and added to pure water. Under a sealed environment, the temperature is raised to 260-300℃ at a rate of 3-6℃ / min, and held for 5-8 hours, during which the internal pressure is maintained at 2-5 MPa. After cooling and filtration, it is placed in a tube furnace and activated at 700-800℃ for 0.8-1.2 hours under an argon atmosphere by raising the temperature at 8-10℃ / min. After cooling, washing, and drying, biochar is obtained. Nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar are mixed evenly and cultured at 25-35℃ and 150-200 r / min for 12-48 hours. Then, it is centrifuged at 7500-8500 r / min for 5-10 minutes, and the lower solid layer is taken out and dried at 25-30℃ for 30-50 minutes to obtain composite biochar.

7. The method for preparing a biochar-containing soil remediation agent according to claim 6, characterized in that: In the method for preparing composite biochar, the mass ratio of wheat straw to pure water is 0.9–1.1:8–12; The mass fraction of the HCl solution is 10-20%. The mass ratio of nitrogen-fixing bacteria solution, Bacillus megaterium solution, Bacillus subtilis solution, yeast solution, lactic acid bacteria solution, and biochar is 1.5–2.5: 2.8–3.2: 6–8: 3.5–4.5: 3–5: 0.8–1.

2. The viable count of nitrogen-fixing bacteria in the bacterial suspension was 1.1–1.3 × 10⁻⁶. 8 CFU / ml; The bacterial culture of Bacillus megaterium was 2.1–2.5 × 10⁻⁶. 7 CFU / ml; Bacillus subtilis bacterial culture concentration: 5–6 × 10⁻⁶ 8 CFU / ml; The yeast culture medium was 4.5–4.9 × 10⁻⁶. 7 CFU / ml; The lactic acid bacteria culture concentration was 9.0–9.6 × 10⁻⁶. 6 CFU / ml.

8. The method for preparing a biochar-containing soil remediation agent according to claim 1, characterized in that: The loading method involves mixing hollow porous silica, complexing agent microcapsules, and composite biochar evenly, and then continuously stirring and shaking for 1-2 hours to obtain the soil remediation agent.

9. A method for preparing a biochar-containing soil remediation agent according to claim 8, characterized in that: In the loading method, the mass ratio of hollow porous silica, complexing agent microcapsules, and composite biochar is 5-7:2.5-3.5:1.8-2.

2.

10. A soil remediation agent prepared by the preparation method according to any one of claims 1-9.

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