A composition for remediation of heavy metal contaminated soil, and a preparation method and application thereof

Abstract

The present application relates to the technical field of contaminated soil remediation, in particular to a heavy metal contaminated soil remediation composition, a preparation method and application thereof.The heavy metal contaminated soil remediation composition is composed of a microbial agent for heavy metal treatment and Fe3O4@TiO2@C material, and the microbial agent for heavy metal treatment is loaded on the Fe3O4@TiO2@C material.The composition can simultaneously perform physical remediation, chemical remediation and biological remediation, Fe3O4 and C are used to produce physical adsorption of heavy metal ions, so that the heavy metal ions are enriched on the composition, Fe3O4@TiO2@C is used to perform chemical photocatalytic degradation of the heavy metal ions, and then the heavy metal ions are converted by microorganisms, so that the composition can realize efficient treatment of the heavy metal ions in the soil.

Description

Technical Field

[0001] This invention relates to the field of contaminated soil remediation technology, specifically to a composition for the remediation of heavy metal contaminated soil, its preparation method, and its application. Background Technology

[0002] Heavy metals refer to substances with a density greater than 4.5 g / cm³. 3 Heavy metals, as referred to in environmental pollution, mainly include mercury, arsenic, lead, chromium, and cadmium. Soil pollution has become one of the most important global environmental problems. Due to mining, metal smelting, and the agricultural application of industrial wastewater and sludge, large amounts of toxic and harmful heavy metals enter the soil system. These elements remain in the soil for a long time and are characterized by their reluctance to degrade, their insidious nature, and their irreversibility. This not only leads to soil degradation and reduced crop yields and quality but may also affect human health through the food chain.

[0003] Currently, methods for remediating heavy metal pollution include physical remediation, chemical remediation, and bioremediation. Bioremediation utilizes the unique ability of organisms to decompose toxic and harmful substances, thereby removing pollutants from the soil. Its advantages include minimal disruption to soil organic matter and structure, and low cost. However, it has a long remediation cycle and is generally unsuitable for highly contaminated soils. Physical remediation involves removing or separating pollutants from the soil through various physical processes. Its advantages include high efficiency and speed, but it is often more expensive. Chemical remediation involves adding chemicals to the soil, which remove pollutants or reduce their bioavailability or toxicity through oxidation-reduction, chelation, or precipitation reactions of heavy metals and organic matter. Its advantages include relatively high efficiency and speed, but it can damage soil structure and cause secondary pollution due to the addition of chemicals. Therefore, each of the physical, chemical, and biological remediation methods has its own advantages and disadvantages.

[0004] Existing technologies often consider physical remediation, chemical remediation, or biological remediation to treat heavy metal soil pollution, and the functions of the materials disclosed in existing technologies are relatively limited. These factors all contribute to the poor remediation capacity of heavy metal contaminated soil. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a composition for remediating heavy metal contaminated soil, its preparation method, and its application. The composition for remediating heavy metal contaminated soil of this invention can simultaneously perform physical, chemical, and bioremediation. It utilizes Fe3O4 and C to physically adsorb heavy metal ions, enriching them on the composition. Fe3O4@TiO2@C is then used for photocatalytic degradation of the heavy metal ions, followed by microbial transformation. This composition achieves highly efficient treatment of heavy metal ions in the soil.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A composition for remediating heavy metal contaminated soil comprises a microbial agent for heavy metal treatment and a Fe3O4@TiO2@C material. The microbial agent for heavy metal treatment is loaded onto the Fe3O4@TiO2@C material, which has a large specific surface area, allowing the microbial agent to be stably loaded onto the surface and pores of the Fe3O4@TiO2@C material.

[0008] The Fe3O4@TiO2@C material is prepared by blending polyacrylonitrile, organic porogen, nano-TiO2 and nano-Fe3O4, followed by electrospinning and high-temperature calcination.

[0009] Preferably, the Fe3O4@TiO2@C material is prepared according to the following steps:

[0010] Polyacrylonitrile and an organic porogen were co-dispersed in N,N-dimethylformamide to obtain a precursor. Polyacrylonitrile was used as the carbon feedstock, and it is currently the most widely used material for preparing carbon fibers. The organic porogen volatilized during the carbonization process of polyacrylonitrile, causing the obtained carbon material to form an internal porous structure. After calcination of polyacrylonitrile, porous carbon material was obtained. The porous structure of the porous carbon material facilitates the loading of microbial agents. The mass ratio of polyacrylonitrile to N,N'-dimethylformamide was 10-15:100, and the mass ratio of methyl methacrylate to polyacrylonitrile was 40-80:100.

[0011] Nano-TiO2 and nano-Fe3O4 are co-mixed in a precursor to obtain a spinning solution. Nano-TiO2 is an important inorganic semiconductor material with non-toxicity and good photochemical stability, therefore it is used in this application for photocatalytic degradation. However, TiO2 has a large band gap (E = 3.2 eV), which cannot effectively utilize solar energy, resulting in low photocatalytic efficiency and difficulties in recycling, easily causing secondary pollution. Based on this, this invention co-mixes nano-TiO2 and nano-Fe3O4 in the precursor. In this case, nano-Fe3O4 facilitates the adsorption of heavy metal ions in the soil and the recycling of the entire composition. Furthermore, after nano-TiO2 and nano-Fe3O4 are co-composite in porous carbon materials, trace amounts of Fe... 3+ It can reduce the band gap of TiO2, thereby expanding the absorption wavelength range and improving photocatalytic performance.

[0012] Electrospinning of the spinning solution yields spun fibers, which are then crushed and calcined to obtain Fe3O4@TiO2@C material. The purpose of electrospinning is to fix nano-TiO2 and nano-Fe3O4 in the precursor, and then crush it to obtain small-sized material. At this time, nano-TiO2 and nano-Fe3O4 are stably combined with porous carbon material.

[0013] The electrospinning conditions are as follows: an electrospinning needle with an inner diameter of 0.27-1.15 mm is used, and the needle is advanced at a voltage of 13-22 kV and a receiving distance of 13-22 cm. The advancement speed of the electrospinning needle is 0.5-2 mL / h.

[0014] Microbial agents for heavy metal treatment are loaded onto Fe3O4@TiO2@C materials to obtain a composition for remediating heavy metal contaminated soil. The porous structure of Fe3O4@TiO2@C materials is suitable for the attachment of microbial agents. At this time, the composition for remediating heavy metal contaminated soil is used to treat heavy metals in the soil.

[0015] Preferably, the microbial agent is composed of bacterial powder and bioactive substances. The bioactive substances are composed of sugar and amino acids, and the mass ratio of bacterial powder, sugar and amino acids is 60-80:20-40:20-30. The sugar is a carbon source, selected from glucose, fructose, lactose or maltose, and the amino acids are a nitrogen source. The bioactive substances provide the nutrients required for the growth of the bacterial powder.

[0016] Preferably, the bacterial powder is composed of Pseudomonas sp., Acidithiobacillus sp., and Geobacter metallireducens. The bacterial powder transforms heavy metals, enhances treatment capacity, and improves soil structure. The mass ratio of the three is 1-3:2-3:2-4. Of course, any bacterial agent that can be applied to the remediation of heavy metal contaminated soil can be used in this application, and is not limited to the few disclosed in this application.

[0017] Preferably, the loading method is as follows: Fe3O4@TiO2@C material is added to the immobilization culture medium, then sterilized, and then 5-10% by mass of microbial agent is added, and fixed at room temperature for 12-24 hours;

[0018] The mass ratio of Fe3O4@TiO2@C material to immobilization culture medium is 1-1.5:100.

[0019] Preferably, the mass ratio of nano-TiO2, nano-Fe3O4 to polyacrylonitrile is 0.8-1.2:1:100.

[0020] Preferably, the organic pore-forming agent is selected from methyl methacrylate. The added methyl methacrylate volatilizes during the carbonization process, causing the carbon material to form an internal porous structure.

[0021] Preferably, the calcination conditions are as follows: under an inert atmosphere, the temperature is first raised to 180-250℃ and held for 1-3 hours, and then calcined at 500-800℃ for 1-4 hours. During the calcination process, the polyacrylonitrile is decomposed to obtain carbon material.

[0022] The present invention also protects the composition for remediation of heavy metal contaminated soil prepared by the above preparation method. In the composition for remediation of heavy metal contaminated soil, porous carbon material is used as a carrier, and nano Fe3O4 and nano TiO2 are stably attached to the porous carbon material, and then microorganisms are adsorbed on the surface of the porous carbon material.

[0023] This invention also protects the application of the composition for remediation of heavy metal contaminated soil in the preparation of remediation materials for heavy metal contaminated soil, wherein the heavy metal ion in the heavy metal contaminated soil is Cd. 2+ Cr 4+ As 3+ Pb 4+ Hg 2+ or Zn 2+ .

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention provides a composition for the remediation of heavy metal contaminated soil. The composition consists of a microbial agent for heavy metal treatment and a Fe3O4@TiO2@C material. The Fe3O4@TiO2@C material uses carbon as a carrier, and carbon achieves stable adhesion of Fe3O4 and TiO2. Due to its strong electron storage capacity and the characteristics of the metal conduction band, carbon materials can accept photogenerated electrons. After the carbon nanomaterials coat TiO2, the Fermi level difference between carbon and TiO2 leads to the enrichment of electrons towards the carbon nanomaterials, thus promoting the separation of photogenerated holes and electrons, thereby improving the photocatalytic efficiency of TiO2. In addition, the trace amounts of Fe in Fe3O4... 3+ It can reduce the band gap of TiO2, thereby expanding the absorption wavelength range and improving photocatalytic performance.

[0026] 2. The toxic effects of heavy metals on humans are often closely related to their state of existence. Generally speaking, the toxic effects of metals vary depending on their form of existence. Microorganisms cannot degrade or destroy heavy metals, but they can fix, move, or transform heavy metals in the soil, altering their environmental chemical formation in the soil, promoting the detoxification or reducing the toxicity of harmful substances, thereby achieving the purpose of bioremediation. Therefore, in this invention, Pseudomonas sp., Acidithiobacillus sp., and Geobacter metallireducens were loaded onto Fe3O4@TiO2@C materials.

[0027] Pseudomonas sp. and Geobacter metallireducens bind to surrounding heavy metal ions through microbial cells to form precipitates, thereby reducing the concentration of free heavy metal ions in the soil. At the same time, they transform heavy metal ions through oxidation / reduction reactions, converting them into non-toxic or low-toxic forms to complete the remediation process.

[0028] Acidithiobacillus sp. can adsorb trivalent arsenic in the soil onto the surface of iron oxides. Tetravalent chromium is reduced to trivalent and adsorbed onto the surface of iron oxides. Tetravalent molybdenum, tetravalent and hexavalent selenium, and hexavalent uranium undergo redox reactions with iron compounds. Soil organic matter stimulates the acidithiobacillus to decompose sulfates. The products react with heavy metals in the soil to form sulfides. The sulfides are adsorbed onto the surface of iron oxides, increasing their stability. Mercury ions undergo a series of reactions to form sulfide precipitates, which are adsorbed onto the surface of iron oxides, increasing their stability. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of the Fe3O4@TiO2@C material from Example 1;

[0030] Figure 2 The image shows the UV-Vis absorption spectrum of the Fe3O4@TiO2@C material in Example 1. Detailed Implementation

[0031] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0032] Nano-TiO2 is an important inorganic semiconductor material, widely used in photocatalysis, dye-sensitized photovoltaic cells, and photocatalytic water splitting for hydrogen production due to its non-toxicity and good photochemical stability. Two-dimensional nano-TiO2 exhibits high light utilization and surface activity, making it an ideal photocatalytic material. However, its photocatalytic application still faces challenges such as low photocatalytic efficiency and difficult recovery. This invention addresses these issues by combining Fe3O4 and TiO2 with carbon materials. Fe3O4 adsorbs heavy metals, is easily recovered, and enhances the photocatalytic performance of nano-TiO2, thus overcoming the existing technical shortcomings of nano-TiO2.

[0033] The Pseudomonas sp. strain used in this application was purchased from Shanghai Lianmai Biotechnology Co., Ltd., the Acidithiobacillus sp. strain was purchased from Shanghai Guyan Industrial Co., Ltd., and the Geobacter metallireducens strain was purchased from Ningbo Mingzhou Biotechnology Co., Ltd.

[0034] The immobilization culture medium in this invention consists of 10g sucrose, 6g beef extract, and 1000mL distilled water, with the pH adjusted to 7.0-7.5.

[0035] The technical solution of the present invention will be further explained and illustrated below with reference to embodiments, as detailed below:

[0036] Example 1

[0037] A method for preparing a composition for remediating heavy metal contaminated soil includes the following steps:

[0038] S1. Polyacrylonitrile and organic porogen methyl methacrylate are co-dispersed in N,N-dimethylformamide to obtain the precursor;

[0039] The mass ratio of polyacrylonitrile to N,N'-dimethylformamide is 13:100; the mass ratio of methyl methacrylate to polyacrylonitrile is 60:100.

[0040] S2. Nano TiO2 and nano Fe3O4 are mixed together in the precursor to obtain a spinning solution;

[0041] The mass ratio of nano-TiO2, nano-Fe3O4 and polyacrylonitrile is 1:1:100;

[0042] S3. Electrospinning the spinning solution yields spun fibers, which are then dried, cut into millimeter lengths, and calcined to obtain Fe3O4@TiO2@C material.

[0043] The electrospinning conditions were as follows: an electrospinning needle with an inner diameter of 1.0 mm was used, and the needle was advanced at a voltage of 20 kV and a receiving distance of 20 cm. The advancement speed of the electrospinning needle was 1.5 mL / h.

[0044] The calcination conditions are as follows: under an inert atmosphere, first heat to 200℃ and hold for 2 hours, then calcine at 600℃ for 3 hours;

[0045] S4. The microbial agent for heavy metal treatment is loaded onto Fe3O4@TiO2@C material to obtain a composition for remediation of heavy metal contaminated soil;

[0046] The microbial inoculant consists of bacterial powder and bioactive substances. The bioactive substances are composed of sugars and amino acids, and the mass ratio of bacterial powder, sugar, and amino acids is 70:30:25. The bacterial powder is composed of Pseudomonas sp., Acidithiobacillus sp., and Geobacter metallireducens, and the mass ratio of the three is 2:2.5:3.

[0047] The load method is as follows:

[0048] Fe3O4@TiO2@C material was added to the immobilization culture medium, then sterilized, and then 8% by weight of microbial agent was added. The mixture was then fixed at room temperature for 18 hours.

[0049] The mass ratio of Fe3O4@TiO2@C material to immobilization culture medium was 1.2:100.

[0050] Example 2

[0051] A method for preparing a composition for remediating heavy metal contaminated soil includes the following steps:

[0052] S1. Polyacrylonitrile and organic porogen methyl methacrylate are co-dispersed in N,N-dimethylformamide to obtain the precursor;

[0053] The mass ratio of polyacrylonitrile to N,N'-dimethylformamide is 10:100; the mass ratio of methyl methacrylate to polyacrylonitrile is 40:100.

[0054] S2. Nano TiO2 and nano Fe3O4 are mixed together in the precursor to obtain a spinning solution;

[0055] The mass ratio of nano-TiO2, nano-Fe3O4 to polyacrylonitrile is 0.8:1:100;

[0056] S3. Electrospinning the spinning solution yields spun fibers, which are then dried, cut into millimeter lengths, and calcined to obtain Fe3O4@TiO2@C material.

[0057] The electrospinning conditions were as follows: an electrospinning needle with an inner diameter of 0.27 mm was used, and the needle was advanced at a voltage of 22 kV and a receiving distance of 13 cm. The advancement speed of the electrospinning needle was 0.5 mL / h.

[0058] The calcination conditions are as follows: under an inert atmosphere, first heat to 250℃ and hold for 1 hour, then calcine at 500℃ for 4 hours;

[0059] S4. The microbial agent for heavy metal treatment is loaded onto Fe3O4@TiO2@C material to obtain a composition for remediation of heavy metal contaminated soil;

[0060] The microbial inoculant consists of bacterial powder and bioactive substances. The bioactive substances are composed of sugars and amino acids, and the mass ratio of bacterial powder, sugar, and amino acids is 60:20:20. The bacterial powder is composed of Pseudomonas sp., Acidithiobacillus sp., and Geobacter metallireducens, and the mass ratio of the three is 1:2:4.

[0061] The loading method is as follows: Fe3O4@TiO2@C material is added to the immobilization culture medium, then sterilized, and then 5% by mass of microbial agent is added, and fixed at room temperature for 12 hours;

[0062] The mass ratio of Fe3O4@TiO2@C material to immobilization culture medium was 1:100.

[0063] Example 3

[0064] A method for preparing a composition for remediating heavy metal contaminated soil includes the following steps:

[0065] S1. Polyacrylonitrile and organic porogen methyl methacrylate are co-dispersed in N,N-dimethylformamide to obtain the precursor;

[0066] The mass ratio of polyacrylonitrile to N,N'-dimethylformamide is 15:100; the mass ratio of methyl methacrylate to polyacrylonitrile is 70:100.

[0067] S2. Nano TiO2 and nano Fe3O4 are mixed together in the precursor to obtain a spinning solution;

[0068] The mass ratio of nano-TiO2, nano-Fe3O4 to polyacrylonitrile is 1.1:1:100;

[0069] S3. Electrospinning the spinning solution yields spun fibers, which are then dried, cut into millimeter lengths, and calcined to obtain Fe3O4@TiO2@C material.

[0070] The electrospinning conditions were as follows: an electrospinning needle with an inner diameter of 1.0 mm was used, and the needle was advanced at a voltage of 13 kV and a receiving distance of 22 cm. The advancement speed of the electrospinning needle was 1.5 mL / h.

[0071] The calcination conditions are as follows: under an inert atmosphere, first heat to 180℃ and hold for 2 hours, then calcine at 800℃ for 1 hour;

[0072] S4. The microbial agent for heavy metal treatment is loaded onto Fe3O4@TiO2@C material to obtain a composition for remediation of heavy metal contaminated soil;

[0073] The microbial inoculant consists of bacterial powder and bioactive substances. The bioactive substances are composed of sugars and amino acids, with a mass ratio of bacterial powder, sugar, and amino acids of 70:40:25. The bacterial powder is composed of Pseudomonas sp., Acidithiobacillus sp., and Geobacter metallireducens, with a mass ratio of 2:3:4.

[0074] The loading method is as follows: Fe3O4@TiO2@C material is added to the immobilization culture medium, then sterilized, and then 8% by mass of microbial agent is added, and fixed at room temperature for 18 hours;

[0075] The mass ratio of Fe3O4@TiO2@C material to immobilization culture medium was 1.5:100.

[0076] Example 4

[0077] A method for preparing a composition for remediating heavy metal contaminated soil includes the following steps:

[0078] S1. Polyacrylonitrile and organic porogen methyl methacrylate are co-dispersed in N,N-dimethylformamide to obtain the precursor;

[0079] The mass ratio of polyacrylonitrile to N,N'-dimethylformamide is 13:100; the mass ratio of methyl methacrylate to polyacrylonitrile is 80:100.

[0080] S2. Nano TiO2 and nano Fe3O4 are mixed together in the precursor to obtain a spinning solution;

[0081] The mass ratio of nano-TiO2, nano-Fe3O4 to polyacrylonitrile is 1.2:1:100;

[0082] S3. Electrospinning the spinning solution yields spun fibers, which are then dried, cut into millimeter lengths, and calcined to obtain Fe3O4@TiO2@C material.

[0083] The electrospinning conditions were as follows: an electrospinning needle with an inner diameter of 1.15 mm was used, and the needle was advanced at a voltage of 18 kV and a receiving distance of 20 cm. The advancement speed of the electrospinning needle was 2 mL / h.

[0084] The calcination conditions are as follows: under an inert atmosphere, first heat to 160℃ and hold for 3 hours, then calcine at 700℃ for 2.5 hours;

[0085] S4. The microbial agent for heavy metal treatment is loaded onto Fe3O4@TiO2@C material to obtain a composition for remediation of heavy metal contaminated soil;

[0086] The microbial inoculant consists of bacterial powder and bioactive substances. The bioactive substances are composed of sugars and amino acids, with a mass ratio of bacterial powder, sugar, and amino acids of 80:40:30. The bacterial powder is composed of Pseudomonas sp., Acidithiobacillus sp., and Geobacter metallireducens, with a mass ratio of 3:3:4.

[0087] The loading method is as follows: Fe3O4@TiO2@C material is added to the immobilization culture medium, then sterilized, and then 10% by mass of microbial agent is added, and fixed at room temperature for 24 hours;

[0088] The mass ratio of Fe3O4@TiO2@C material to immobilization culture medium was 1.5:100.

[0089] Examples 1-4 of this invention all yielded compositions for the remediation of heavy metal contaminated soil using heavy metal ion treatment. The composition for heavy metal contaminated soil remediation prepared in Example 1 is used as an example for further research. Specific research methods and results are shown below:

[0090] (1) Structural confirmation of Fe3O4@TiO2@C material:

[0091] Figure 1 The image shows a scanning electron microscope (SEM) image of the Fe3O4@TiO2@C material from Example 1. The results indicate that the Fe3O4@TiO2@C material has a good morphology and a porous structure, which facilitates the attachment of microorganisms.

[0092] Figure 2 The image shows the UV-Vis absorption spectrum of the Fe3O4@TiO2@C material in Example 1. The results show that pure TiO2 has strong light absorption only in the ultraviolet region, while the Fe3O4@TiO2@C material exhibits strong light absorption in the visible light range. Therefore, compared with TiO2, the Fe3O4@TiO2@C material enhances light absorption and photocatalytic activity.

[0093] (2) Remediation of heavy metal soil pollution:

[0094] The composition of Example 1 of this invention was used to remediate heavy metal contaminated soil. The soil to be remediated was arsenic contaminated soil. The specific operations carried out during the remediation process are as follows:

[0095] Biomass determination method: Well-grown *Gnaphalium affine* from the tailings area was selected as the experimental subject. The plants were dug up along with their roots and soil, and 10 plants of similar height were selected as parallel samples. The *Gnaphalium affine* was separated from its rhizosphere soil. The soil sample was then air-dried in a cool, dry place, stones were removed, and the soil was ground through a 0.2mm sieve and dried for later use. After washing and drying, the height and fresh weight of the *Gnaphalium affine* were measured. It was then dried at 60℃ to constant weight, and the dry weight of the roots and aboveground parts was measured. The roots and aboveground parts of the plant were then pulverized separately, and the pulverized samples were stored separately.

[0096] Arsenic concentration determination method: Soil samples and *Gnaphalium affine* were added separately to polytetrafluoroethylene digestion tubes, moistened with water, and then 16 mL of nitric acid and 4 mL of perchloric acid were added. The tubes were capped and shaken well. After standing for 24 hours, the tubes were placed in a digester and heated for 1 hour. The caps were removed and heating continued at a temperature below 200℃ until a grayish-white residue remained in the tubes. The tubes were then removed and cooled. The residue was dissolved in 50% nitric acid solution and transferred to a 50 mL colorimetric tube. The tubes were washed with ultrapure water and then diluted to volume with ultrapure water. The arsenic concentration in the soil samples and *Gnaphalium affine* was determined using an atomic fluorescence spectrophotometer. All detection processes were performed in triplicate, and the average value of the results was taken.

[0097] Method for remediating arsenic-contaminated soil using a composition: Add 1.5 kg of uncontaminated soil to a flowerpot, then add 1 mg / mL of the mixture to the soil. -1 An arsenic standard solution was prepared to achieve an arsenic concentration of 5 mg / kg in the potting soil. -1 Ten selected *Gnaphalium affine* plants were planted, and 50 mg of the composition from Example 1 was sown on the soil surface. The *Gnaphalium affine* seedlings were allowed to recover for 7 days, then watered every two days, maintaining a water content of 60%. Nutrient solution was added once after 10 days. After 60 days, the entire *Gnaphalium affine* plant was removed, washed, and then treated with 5 mmol·L⁻¹ nutrient solution. -1 After soaking the roots in calcium nitrate solution for 15 minutes, they were washed with deionized water, blanched and dried. The biomass, plant height and arsenic concentration of the windmill grass were measured, and the arsenic concentration in the soil was also measured. Ten windmill grass plants without the added composition were used as a control. The plant height of the control group was similar to that of the experimental group, and this group was denoted as CK.

[0098] Table 1. Biomass results before and after the experiment.

[0099]

[0100] The biomass of *Gnaphalium affine* before and after the experiment is shown in Table 1. After the soil was treated with the composition, the plant height and fresh weight of *Gnaphalium affine* both increased, proving that the composition can effectively promote the growth of *Gnaphalium affine* after treating arsenic-contaminated soil. This is because the metabolic activities of microorganisms and the arsenic treatment improved the physical and chemical properties of the soil to a certain extent, thus promoting plant growth.

[0101] Table 2. Arsenic concentration results in *Gnaphalium affine* and soil.

[0102]

[0103]

[0104] The results of the arsenic concentration determination in the windmill grass and soil are shown in Table 2. As can be seen from Table 2, after the composition was sown on the soil and the windmill grass was cultivated for a period of time, the arsenic concentration in both the windmill grass and the soil was greatly improved. This is because the composition improved the physical and chemical properties of the soil to a certain extent, promoted the absorption and accumulation of heavy metals in the soil and windmill grass, and achieved the purpose of rapidly remediating arsenic-contaminated soil.

[0105] The following study investigates the growth-promoting effects on maize:

[0106] The experimental site was located in Halahai Town, Nong'an County, which is 60 km from Changchun City. It lies on the western edge of the northeastern uplift zone of the Songliao Plain depression. The county is generally flat, with arable land mainly composed of black calcareous soil. The experiment consisted of two treatments with three replicates, and each plot was 10 m². 2Treatment 1 was a conventional fertilizer treatment; Treatment 2 was a combination of conventional fertilizer and fertilizer; the corn variety was Xianyu 335, and the density was 60,000 / hm². 2 The typical total fertilizer application rate is 270-90-90 kg / hm² (N-P₂O₅-K₂O). 2 The base fertilizer N-P2O5-K2O content is 90-90-90 kg / hm. 2 Both treatments were top-fertilized at the jointing stage. The yield data analysis is shown in Table 3.

[0107] Table 3. Corn Yield Measurement Data for the Communities

[0108]

[0109] A significant difference in maize yield was observed between the combined fertilizer treatment and the conventional fertilizer treatment. The yield of the plot treated with the combined fertilizer treatment was 9.74 kg / 5m². 2 The yield per hectare, calculated by area, was 19481.74 kg / hectare; the yield of conventional fertilizer-treated plots was 6.18 kg / 5m². 2 The yield is 12355.36 kg / hectare based on area.

[0110] Table 4. Effects of different annual fertilizer combinations and conventional fertilizer treatments on maize yield composition and yield.

[0111]

[0112] Table 5. The impact of conventional fertilizer treatments on maize yield composition and yield in different years.

[0113]

[0114] As can be seen from Table 4-5, which shows the composition of corn yield in 2022-2023, the yield of corn using a combination fertilizer plus conventional fertilizer in 2022 was 799.93 kg / 667 m². 2 The yield with conventional fertilizer treatment is 772.35 kg / 667m². 2 The combination of the fertilizer and conventional fertilizer treatment increased yield by 3.5% compared to the conventional fertilizer treatment; in 2023, the corn yield of the combination of the fertilizer and conventional fertilizer treatment was 826.42 kg / 667m². 2 Conventional fertilizer treatment: 781.9 kg / 667 m³ 2 The combination of the compound and conventional fertilizer treatment increased yield by 5.6% compared to the conventional fertilizer treatment.

[0115] In 2022-2023, the average yield of the combination fertilizer plus conventional fertilizer treatment was 813.18 kg / mu, with a yield increase rate of 3.3%. In contrast, the average yield of conventional fertilizer treatment alone was 777.17 kg / mu over the two years, with a yield increase rate of 1.2%. Since the combination fertilizer plus conventional fertilizer is relatively stable and has good repeatability, there was no difference between the two years of the same treatment.

[0116] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A composition for remediation of heavy metal contaminated soil, characterized by, The microbial agent for heavy metal treatment and Fe3O4@TiO2@C material are used for heavy metal treatment, and the microbial agent for heavy metal treatment is loaded on the Fe3O4@TiO2@C material. The Fe3O4@TiO2@C material is prepared according to the following steps: Polyacrylonitrile and an organic pore-forming agent are dispersed in N, N-dimethylformamide to obtain a precursor; Nano-TiO2 and nano-Fe3O4 are mixed in the precursor to obtain a spinning solution; After electrospinning of the spinning solution, the Fe3O4@TiO2@C material is obtained by crushing and calcination; The mass ratio of nano-TiO2, nano-Fe3O4 and polyacrylonitrile is 0.8-1.2:1:

100. The microbial agent is composed of bacterial powder and bioactive substances, and the bacterial powder is composed of Pseudomonas sp, Acidithiobacillus sp and Geobacter metallireducens.

2. The composition for remediation of heavy metal contaminated soil according to claim 1, wherein The organic pore-forming agent is selected from methyl methacrylate.

3. The composition for remediation of heavy metal contaminated soil according to claim 1, wherein The calcination conditions are as follows: first, heat to 180-250 DEG C under an inert atmosphere, then keep the temperature for 1-3 h, and then calcine at 500-800 DEG C for 1-4 h.

4. The composition for remediation of heavy metal contaminated soil according to claim 1, wherein The bioactive substances are composed of sugar and amino acids, and the mass ratio of the bacterial powder, sugar and amino acids is 60-80:20-40:20-30.

5. A method for preparing the composition for remediation of heavy metal contaminated soil according to claim 1, characterized by, The method comprises the following steps: The Fe3O4@TiO2@C material is added to the immobilized culture medium, then sterilized, and then 5-10% of the microbial agent is added, and the immobilization is carried out at room temperature for 12-24 h. The mass ratio of the Fe3O4@TiO2@C material to the immobilized culture medium is 1-1.5:

100.

6. The use of the composition for heavy metal contaminated soil remediation according to claim 1 in the preparation of As3+ heavy metal contaminated soil remediation material.

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