A method for combined remediation of mine heavy metal contaminated soil by biochar and plants

Abstract

The application discloses a kind of mine heavy metal contaminated soil's biochar-plant combined repair method, it is related to modified biochar and repair accelerator, the preparation method of the modified biochar includes: peanut shell high-temperature carbonization is then added to ferric solution and NaOH solution, ultrasonic treatment is carried out, and biochar is obtained;Biomass raw material is broken and treated, composted, and pretreated biomass is obtained, then heated and reacted with ferric solution, the reaction product is mixed with the biochar and continues to be carbonized, i.e. obtained.The repair accelerator includes grass charcoal, phosphor lime powder, mannitol, plant growth regulator, microbial inoculant, chelating agent.The repair method of the application combines modified biochar, repair accelerator and the planting of enrichment plant, forms a synergistic repair mechanism, the three synergistic effects significantly improve the removal efficiency of heavy metal, improve the biomass and survival rate of enrichment plant, realize the efficient and accurate repair of mine heavy metal contaminated soil.

Description

Technical Field

[0001] This invention relates to the field of heavy metal contaminated soil remediation technology, and in particular to a biochar-phytoremediation method for heavy metal contaminated soil in mines. Background Technology

[0002] Mine soil pollution prevention and control refers to technical measures to control or mitigate soil environmental pollution caused by mining operations. Pollutants generated during mining operations enter the soil and accumulate continuously through processes such as physical and mechanical absorption, retention, colloidal physicochemical adsorption, chemical precipitation, and biological absorption. When these pollutants reach a certain level, they cause deterioration of the soil's composition, structure, properties, and functions. Heavy metals are difficult to degrade in soil and exhibit strong cumulative and biological toxicity.

[0003] Currently, the main technologies for remediating heavy metal contaminated soil in mines include physical remediation, chemical remediation, and bioremediation. Phytoremediation, a type of bioremediation, is widely used due to its advantages such as not damaging soil structure, not causing secondary pollution, low remediation cost, and vegetation restoration capabilities. However, in practical applications, plants planted in contaminated soil are easily toxicized by pollutants, resulting in slow growth and low survival rates for some plants, thus compromising the effectiveness of soil treatment. Furthermore, phytoremediation alone cannot completely and effectively remove pollutants from the soil, leading to poor remediation results. Biochar, a novel environmental functional material, is a class of insoluble, stable, highly aromatic, carbon-rich solid substances produced by the high-temperature pyrolysis of biological residues under anaerobic conditions. It possesses a well-developed porous structure, large specific surface area, and a large number of functional groups and negative charges on its surface, exhibiting strong adsorption of heavy metal ions. As a good adsorbent material, it shows potential in soil pollution remediation.

[0004] Therefore, it is necessary to explore a biochar-phytoremediation co-remediation method to further improve existing phytoremediation methods. Summary of the Invention

[0005] To address the above shortcomings, this invention provides a biochar-phytoremediation method for heavy metal contaminated soil in mines. The addition of modified biochar and remediation promoters, combined with the planting of enriching plants, forms a synergistic remediation mechanism, significantly improving the removal efficiency of heavy metals and increasing the biomass and survival rate of enriching plants. The specific technical solution is as follows:

[0006] A biochar-phytoremediation method for heavy metal contaminated soil in mines includes the following steps:

[0007] S1. Detect the types of heavy metals contained in the contaminated soil and determine the species and planting methods of enriching plants;

[0008] S2. Use a tiller to turn over the contaminated soil, then irrigate the contaminated soil. After 5-10 days, spread the modified biochar evenly on the surface of the contaminated soil and turn it over to mix the modified biochar evenly with the contaminated soil.

[0009] S3. Plant enrichment plants in contaminated soil, apply alkaline clay 1-2 weeks after planting, apply remediation promoter once a month, and harvest the enrichment plants when they mature and carry out centralized harmless treatment.

[0010] S4. Take samples of the contaminated soil for testing. If the contamination content is greater than the national standard, repeat steps S2 and S3 until the soil test results meet the national standards, and the remediation can be completed.

[0011] The method for preparing the modified biochar includes:

[0012] Peanut shells are dried, crushed, and sieved, then carbonized at high temperature to obtain raw biochar. The raw biochar is added to a ferric solution, NaOH solution is added, and the mixture is ultrasonically treated. Then it is heated and stirred, dried, and washed with distilled water until pH=7 to obtain biochar. Biomass raw materials are crushed, and orange or grapefruit peels are added to remove odors. The humidity is controlled at 40-50% and composted in a composting tank. The humidity is then controlled at 60-70% and composting continues to obtain pretreated biomass. The pretreated biomass is mixed with a ferric solution and heated to react. The reaction product is mixed with the biochar to obtain a carbon mixture. NaOH solution is added to the carbon mixture to prepare an alkaline suspension. The suspension is continuously shaken at room temperature and then carbonized at high temperature again to obtain modified biochar.

[0013] The repair promoter comprises, by weight, the following:

[0014] The ingredients are: 10-20 parts peat moss, 5-10 parts phosphate lime powder, 3-8 parts mannitol, 1-3 parts plant growth regulator, 0.1-0.3 parts microbial inoculant, and 0.2-1 parts chelating agent; the chelating agent is ethylenediaminetetraacetic acid.

[0015] Preferably, the enriching plants include one of the following: black nightshade, fleabane, sepia, sepia, vetiver, scabra, Indian mustard, sunflower, camel thorn, and white thorn.

[0016] Preferably, the preparation method of the biochar specifically includes the following steps: Peanut shells are dried, crushed, and sieved, then carbonized at 700-800℃, naturally cooled to room temperature, and removed to obtain raw biochar. The raw biochar is added to a ferric solution, followed by 0.1-0.2 mol / L NaOH solution, and ultrasonically treated. Then, it is heated and stirred at 80-90℃ for 2-4 hours, dried at 80-100℃, and washed with distilled water until pH=7 to obtain biochar. The biomass raw material is crushed, and orange or grapefruit peel is added to remove odor. The humidity is controlled at 40-50%, and the material is composted in a composting tank for 10-20 days. Then, the compost is turned, and the humidity is controlled at 60-70% for another 10-20 days, with turning every 1-2 days to obtain pretreated biomass. The pretreated biomass is mixed with a ferric solution and reacted at 50-70℃ for 2-5 hours. The reaction product is mixed with the biochar to obtain a char mixture. 1-2 mol / L NaOH solution is added to the char mixture. An alkaline suspension is prepared by using mol / L NaOH solution, and the suspension is continuously shaken at room temperature for 8-15 hours. Then, it is carbonized at a high temperature of 400-600℃ to obtain modified biochar.

[0017] Preferably, the biomass raw materials include one or more of the following: straw, agricultural and forestry waste, poultry and livestock manure, fruit and vegetable residues, and kitchen waste.

[0018] Preferably, the preparation method of the alkaline clay includes: adding 20-30 parts of starch to 80-100 parts of water, heating to 88-95℃, and gelatinizing for 60-90 minutes to obtain gelatinized starch; adding 10-20 parts of sodium alginate, 20-30 parts of bentonite, 10-15 parts of sodium bicarbonate, and 4-6 parts of alkyl glycoside to the gelatinized starch, heating to 50-60℃, stirring at 600-800 r / min for 5-10 minutes, then adding 0.3-1 parts of crosslinking agent, heating to 60-70℃, and stirring at 200-300 r / min for 30-40 minutes to obtain the final product.

[0019] Preferably, the crosslinking agent is N,N-methylenebisacrylamide.

[0020] Preferably, the concentration of ferric ions in the ferric solution is 0.1-1 mol / L, and the concentration of biochar in the ferric solution is 80-100 g / L.

[0021] Preferably, the solid-liquid ratio of the biochar to the NaOH solution is 1-3g:150-200ml; the solid-liquid ratio of the char mixture to the NaOH solution is 1-3g:100-120ml.

[0022] Preferably, the microbial agent comprises, by weight: 1.0-2.0 × 10 8CFU / g Azotoxin spirochetes 2-7 portions, 1.0-2.0 × 10⁻⁶ 8 cfu / g Azotobacter chrysophagus 5-15 samples, 2.0-3.0×10 8 Two to three portions of EM bacteria at cfu / g; the plant growth regulators include one or more of auxin, gibberellin, cytokinin, abscisic acid, and brassinolide.

[0023] Preferably, the modified biochar is applied at a rate of 10-20 kg / mu, the remediation agent is applied at a rate of 5-15 kg / mu, and the alkaline clay is applied at a rate of 20-30 kg / mu.

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

[0025] 1. This invention provides a biochar-phytoremediation method for heavy metal contaminated soil in mines. The addition of modified biochar and remediation promoters, combined with the planting of enriching plants, forms a synergistic remediation mechanism. This method can improve soil structure, increase soil porosity and water retention, and provide favorable conditions for plant growth. At the same time, it can also adsorb heavy metals and reduce their bioavailability. The enriching plants absorb and enrich heavy metals in the soil through their roots, and the remediation promoters further enhance the overall adsorption stability and adsorption capacity. The synergistic effect of the three significantly improves the removal efficiency of heavy metals, increases the biomass and survival rate of enriching plants, and achieves efficient and precise remediation of heavy metal contaminated soil in mines.

[0026] 2. In the modified biochar of the present invention, peanut shell biochar is loaded with humus and then carbonized again at high temperature, which enriches the microstructure of the modified biochar, further enhances the adsorption and conversion of heavy metal ions by the biochar, improves soil physicochemical indicators, steadily increases the total organic carbon content of the soil, and improves the availability of nutrients in the soil, thereby providing sufficient nutrient supply for the growth of enriching plants, increasing the biomass of enriching plants, and making full use of waste.

[0027] 3. The peat moss in the remediation accelerator improves soil structure and increases soil fertility; phosphate lime powder helps regulate soil pH and improves plant tolerance to heavy metals; mannitol acts as a nutrient supplement for plant growth, promoting plant growth; plant growth regulators regulate plant growth and development processes, enhancing plants' ability to absorb heavy metals; the addition of microbial agents improves the soil microbial community structure, promotes plant root growth, promotes the restoration of the soil ecosystem, and enhances the soil's self-repair capacity; the chelating agent ethylenediaminetetraacetic acid (EDTA) forms stable complexes with heavy metal ions, reducing their migration and biotoxicity in the soil. These components work synergistically to promote the remediation process from multiple aspects, making the remediation effect more stable and reliable.

[0028] 4. This invention uses starch, sodium alginate, bentonite, sodium bicarbonate, and alkyl glycosides as raw materials to prepare alkaline clay that can balance the pH of mine-polluted soils. It also possesses certain water retention properties, balancing the moisture content of polluted soils and reducing soil erosion and nutrient loss, thus creating a suitable environment for plant growth. The cross-linking agent increases the stability of the alkaline clay. Furthermore, the alkaline clay has a synergistic effect on remediation promoters, improving their permeability in the soil and increasing the absorption rate of fertilizers by plants. Simultaneously, the adsorption effect of the clay particles helps to fix heavy metals in the soil, reducing their migration and diffusion, further stabilizing the remediation effect. Detailed Implementation

[0029] 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. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0030] Example 1

[0031] Preparation of modified biochar:

[0032] Peanut shells were dried, crushed, and sieved, then carbonized at 700℃. After naturally cooling to room temperature, the shells were removed to obtain biochar. The biochar was then added to a ferric sulfate solution with a ferric ion concentration of 0.2 mol / L and a biochar concentration of 80 g / L. Then, 0.1 mol / L of [a specific chemical solution] was added. The biochar was prepared by ultrasonic treatment with NaOH solution and a solid-liquid ratio of 1g:150ml. It was then heated and stirred at 80℃ for 3 hours, dried at 80℃, and washed with distilled water until pH=7 to obtain biochar. Kitchen waste was crushed and mixed with 4% (by weight) orange or grapefruit peel to remove odors. The composting was carried out in a composting trough with humidity controlled at 40% for 10 days. The compost was then turned over and composted for another 10 days with humidity controlled at 60%, turning every day to obtain pretreated biomass. The pretreated biomass was mixed with ferric sulfate solution and reacted at 50℃ for 5 hours. The reaction product was mixed with biochar to obtain a char mixture. A 1mol / L NaOH solution was added again to prepare an alkaline suspension. The solid-liquid ratio of the char mixture to the NaOH solution was 1g:100ml. The mixture was continuously shaken at room temperature for 8 hours and then carbonized at 500℃ to obtain modified biochar.

[0033] Preparation of repair promoters:

[0034] Mix the following raw materials evenly in parts by weight: 10 parts peat moss, 5 parts phosphate lime powder, 3 parts mannitol, 1 part plant growth regulator, 0.1 part microbial inoculant, and 0.2 parts EDTA. The microbial inoculant comprises, by weight: 1.0 × 10⁻⁶ parts per ... 8 Two samples of CFU / g Azotospira, 1.0 × 10⁻⁶ 8 Five samples of *Azotocinus chrysophagus* (cfu / g) at a concentration of 2.0 × 10⁻⁶ were collected. 8 Two portions of EM bacteria (cfu / g); the plant growth regulators include gibberellin, cytokinin, and brassinolide in a mass ratio of 1:1:0.3.

[0035] Preparation of alkaline clay:

[0036] Add 20 parts of starch to 80 parts of water, heat to 88℃, and gelatinize for 60 minutes to obtain gelatinized starch; add 10 parts of sodium alginate, 20 parts of bentonite, 10 parts of sodium bicarbonate, and 4 parts of alkyl glycoside to the gelatinized starch, heat to 50℃, stir at 600 r / min for 5 minutes, then add 0.3 parts of N,N-methylenebisacrylamide, heat to 60℃, and stir at 200 r / min for 30 minutes to obtain the final product.

[0037] Example 2

[0038] Preparation of modified biochar:

[0039] Peanut shells were dried, crushed, and sieved, then carbonized at 750℃. After naturally cooling to room temperature, the shells were removed to obtain biochar. The biochar was then added to a ferric sulfate solution with a ferric ion concentration of 0.5 mol / L and a biochar concentration of 90 g / L. Then, 0.1 mol / L of [unspecified substance] was added. The biochar was prepared by ultrasonic treatment with NaOH solution and a solid-liquid ratio of 2g:180ml. It was then heated and stirred at 85℃ for 3 hours, dried at 90℃, and washed with distilled water until pH=7 to obtain biochar. Kitchen waste was crushed and mixed with 4% (by weight) of orange or grapefruit peel to remove odors. The composting was carried out in a composting tank with humidity controlled at 45% for 15 days. The compost was then turned over and composted for another 15 days with humidity controlled at 65%, turning every day to obtain pretreated biomass. The pretreated biomass was mixed with ferric solution and reacted at 60℃ for 4 hours. The reaction product was mixed with biochar to obtain a char mixture. A 1.5mol / L NaOH solution was added again to prepare an alkaline suspension. The solid-liquid ratio of the char mixture to the NaOH solution was 2g:110ml. The mixture was continuously shaken at room temperature for 12 hours and then carbonized at 500℃ to obtain modified biochar.

[0040] Preparation of repair promoters:

[0041] Mix the following raw materials evenly in parts by weight: 15 parts peat moss, 8 parts phosphate lime powder, 5 parts mannitol, 2 parts plant growth regulator, 0.2 parts microbial inoculant, and 0.2-1 parts EDTA. The microbial inoculant comprises, by weight: 1.5 × 10⁻⁶ parts. 8 Five samples of CFU / g Azotoxin spirochetes, 1.5 × 10⁻⁶ 8 10 samples of *Azotocinus chrysophagus* (cfu / g) at 2.5 × 10⁻⁶ ppm. 8 2.5 portions of EM bacteria with cfu / g; the plant growth regulators include gibberellin, cytokinin, abscisic acid and brassinolide in a mass ratio of 1:1:1.5:0.3.

[0042] Preparation of alkaline clay:

[0043] Add 25 parts of starch to 90 parts of water, heat to 90℃, and gelatinize for 80 minutes to obtain gelatinized starch; add 15 parts of sodium alginate, 25 parts of bentonite, 12 parts of sodium bicarbonate, and 5 parts of alkyl glycoside to the gelatinized starch, heat to 55℃, stir at 700 r / min for 8 minutes, then add 0.5 parts of N,N-methylenebisacrylamide, heat to 65℃, and stir at 200 r / min for 35 minutes to obtain the final product.

[0044] Example 3

[0045] The biochar-phytoremediation method for heavy metal contaminated soil in mines in this embodiment includes the following steps:

[0046] S1. Detect the types of heavy metals contained in the contaminated soil and determine the species and planting methods of enriching plants;

[0047] S2. Use a tiller to turn over the contaminated soil, then irrigate the contaminated soil. After 7 days, spread the modified biochar evenly on the surface of the contaminated soil and turn it over to mix the modified biochar evenly with the contaminated soil. The application rate of modified biochar is 10 kg / mu.

[0048] S3. Plant enrichment plants in contaminated soil. Apply alkaline clay one week after planting at a rate of 20 kg / mu. Apply a remediation promoter once a month at a rate of 12 kg / mu. When the enrichment plants mature, harvest them and carry out centralized harmless treatment, including incineration and compressing followed by harmless landfill.

[0049] S4. Take samples of the contaminated soil for testing. If the contamination content is greater than the national standard, repeat steps S2 and S3 until the soil test results meet the national standards, and the remediation can be completed.

[0050] The repair agents used in this embodiment are the modified biochar, repair promoter, and alkaline clay prepared in Example 2.

[0051] Example 4

[0052] The biochar-phytoremediation method for heavy metal contaminated soil in mines in this embodiment includes the following steps:

[0053] S1. Detect the types of heavy metals contained in the contaminated soil and determine the species and planting methods of enriching plants;

[0054] S2. Use a tiller to turn over the contaminated soil, then irrigate the contaminated soil. After 7 days, spread the modified biochar evenly on the surface of the contaminated soil and turn it over to mix the modified biochar evenly with the contaminated soil. The application rate of modified biochar is 15 kg / mu.

[0055] S3. Plant enrichment plants in contaminated soil. Apply alkaline clay one week after planting at a rate of 25 kg / mu. Apply a remediation accelerator once a month at a rate of 10 kg / mu. When the enrichment plants mature, harvest them and carry out centralized harmless treatment, including incineration and compressing followed by harmless landfill.

[0056] S4. Take samples of the contaminated soil for testing. If the contamination content is greater than the national standard, repeat steps S2 and S3 until the soil test results meet the national standards, and the remediation can be completed.

[0057] The repair agents used in this embodiment are the modified biochar, repair promoter, and alkaline clay prepared in Example 2.

[0058] Comparative Example 1

[0059] The method for preparing the modified biochar in this comparative example is as follows:

[0060] Peanut shells were dried, crushed, and sieved. They were then carbonized at 750℃ and allowed to cool naturally to room temperature to obtain biochar. The biochar was added to a 0.1 mol / L NaOH solution at a solid-liquid ratio of 2 g:180 ml and subjected to ultrasonic treatment. The mixture was then heated and stirred at 85℃ for 3 hours, dried at 90℃, and washed with distilled water until the pH reached 7 to obtain biochar.

[0061] The remaining methods are the same as in Example 4.

[0062] Comparative Example 2

[0063] The preparation method of the repair promoter in this comparative example is as follows:

[0064] Mix the following raw materials evenly in parts by weight: 15 parts peat moss, 2 parts plant growth regulator, and 0.2 parts microbial inoculant. The microbial inoculant comprises, by weight: 1.5 × 10⁻⁶ parts. 8Five samples of CFU / g Azotoxin spirochetes, 1.5 × 10⁻⁶ 8 10 samples of *Azotocinus chrysophagus* (cfu / g) at 2.5 × 10⁻⁶ ppm. 8 2.5 portions of EM bacteria with cfu / g; the plant growth regulators include gibberellin, cytokinin, abscisic acid and brassinolide in a mass ratio of 1:1:1.5:0.3.

[0065] The remaining methods are the same as in Example 4.

[0066] Comparative Example 3

[0067] This comparative example does not contain alkaline clay.

[0068] The remaining methods are the same as in Example 4.

[0069] Comparative Example 4

[0070] The preparation method of the alkaline clay in this comparative example is as follows:

[0071] Add 25 parts starch to 90 parts water and stir until smooth. Then add 25 parts bentonite and 12 parts sodium bicarbonate. Heat to 55°C and stir at 700 r / min for 8 minutes to obtain the final product.

[0072] The remaining methods are the same as in Example 4.

[0073] The repair methods of Examples 3-4 and Comparative Examples 1-4 of this invention were tested. The applicant conducted the tests in the mining area of ​​Matou Town, Pingguo City, Guangxi Province. The tests were divided into 6 groups, with each group having a test area of ​​50m. 2 Each group had three replicates. The soil pH in the experimental area was 4-4.5. The cadmium content in the contaminated soil was 6.23 mg / kg, lead content was 73.21 mg / kg, and arsenic content was 30.98 mg / kg, all exceeding the standards. Indian mustard was used as the enrichment plant in the experiment, with a row spacing of 50 cm and a plant spacing of 30 cm. Fertilization and watering were carried out according to conventional Indian mustard management methods, including regular weeding, soil loosening, and pest and disease control. The removal rates of cadmium, lead, and arsenic in the soil were measured after the first and second rounds of Indian mustard planting matured. Biomass and survival rates were also determined. The results are shown in Tables 1 and 2.

[0074] Table 1. Biomass of mature Indian mustard after the first round of planting, as well as the removal rate and survival rate of heavy metals in the soil.

[0075]

[0076] Table 2. Biomass of mature Indian mustard after the second round of planting, as well as the removal rate and survival rate of heavy metals in the soil.

[0077]

[0078] The modified biochar prepared by the methods of Example 1, Example 2, and Comparative Example 1 were tested. 0.2g of modified biochar sample was taken from each sample and mixed with 3ml of solution containing 50mg / L cadmium and 20mg / L rhodamine B dye. The mixture was shaken intermittently at room temperature, with an interval of 6 hours between each shake and a shaking time of 1min. The removal effect after 96h is shown in Table 3 below.

[0079] Table 3

[0080]

[0081] As shown in Table 3 above, compared with the modified biochar of Comparative Example 1, the embodiments of the present invention can still achieve good adsorption effect under the interference of organic matter, and also have a certain removal rate of organic matter.

[0082] The alkaline clays prepared by the methods of Example 1, Example 2, and Comparative Example 4 were tested. 8g of alkaline clay samples were piled on one side of a beaker, and 5ml of a solution containing 50mg / L cadmium and 20mg / L rhodamine B dye was added to the beaker. The removal effect after standing for 5 days is shown in Table 4 below.

[0083] Table 4

[0084]

[0085] As shown in Table 4 above, the embodiments of the present invention, compared with the alkaline clay of Comparative Example 4, can help fix heavy metals and reduce their migration and diffusion in the soil.

[0086] In summary, this invention provides a biochar-phytoremediation method for heavy metal contaminated soil in mines. The addition of modified biochar remediation promoters combined with the planting of enriching plants forms a synergistic remediation mechanism. Biochar improves soil structure, increases soil porosity and water retention, providing favorable conditions for plant growth. It also adsorbs heavy metals, reducing their bioavailability. Enriching plants absorb and accumulate heavy metals in the soil through their roots. The remediation promoter further enhances the overall adsorption stability and capacity. The synergistic effect of these three factors significantly improves the removal efficiency of heavy metals, increases the biomass and survival rate of enriching plants, and achieves efficient and precise remediation of heavy metal contaminated soil in mines. In the modified biochar of this invention, peanut shell biochar is loaded with humus and then subjected to high-temperature carbonization, enriching the microstructure of the modified biochar and further enhancing its adsorption and conversion of heavy metal ions. This improves soil physicochemical indicators, steadily increases the total organic carbon content of the soil, and enhances the availability of nutrients in the soil, thereby providing sufficient nutrient supply for the growth of enriching plants, increasing their biomass, and ensuring full utilization of waste materials. The peat moss in the remediation accelerator improves soil structure and increases soil fertility; phosphate lime powder helps regulate soil pH and improves plant tolerance to heavy metals; mannitol acts as a nutrient supplement for plant growth, promoting plant growth; plant growth regulators regulate plant growth and development processes, enhancing plants' ability to absorb heavy metals; the addition of microbial agents improves the soil microbial community structure, promotes plant root growth, promotes the restoration of the soil ecosystem, and enhances the soil's self-repair capacity; the chelating agent ethylenediaminetetraacetic acid (EDTA) forms stable complexes with heavy metal ions, reducing their migration and biotoxicity in the soil. These components work synergistically to promote the remediation process from multiple aspects, making the remediation effect more stable and reliable. The alkaline clay prepared by this invention using starch, sodium alginate, bentonite, sodium bicarbonate, and alkyl glycosides as raw materials can balance the pH of mine-polluted soil and has a certain water retention capacity, which can balance the humidity of polluted soil, reduce soil erosion and nutrient loss, and create a suitable environment for plant growth. The cross-linking agent increases the stability of the alkaline clay. The alkaline clay also has a synergistic effect on remediation promoters, which can improve the permeability of remediation promoters in the soil and increase the absorption rate of fertilizers by plants. At the same time, the adsorption effect of clay particles also helps to fix heavy metals in the soil, reduce their migration and diffusion in the soil, and further stabilize the remediation effect.

[0087] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A biochar-phytoremediation method for heavy metal contaminated soil in mines, characterized in that, Includes the following steps: S1. Detect the types of heavy metals contained in the contaminated soil and determine the species and planting methods of enriching plants; S2. Use a tiller to turn over the contaminated soil, then irrigate the contaminated soil. After 5-10 days, spread the modified biochar evenly on the surface of the contaminated soil and turn it over to mix the modified biochar evenly with the contaminated soil. S3. Plant enrichment plants in contaminated soil, apply alkaline clay 1-2 weeks after planting, apply remediation promoter once a month, and harvest the enrichment plants when they mature and carry out centralized harmless treatment. S4. Take samples of the contaminated soil for testing. If the pollutant content is greater than the national standard, repeat steps S2 and S3 until the soil test results meet the national regulations, and the remediation can be completed. The method for preparing the modified biochar includes: Peanut shells are dried, crushed, and sieved, then carbonized at high temperature to obtain biochar. The biochar is added to a ferric solution, NaOH solution is added, and the mixture is ultrasonically treated. Then it is heated and stirred, dried, and washed with distilled water until pH=7 to obtain biochar. Biomass raw materials are crushed, and orange or grapefruit peels are added to remove odors. The mixture is composted in a composting tank with humidity controlled at 40-50%, and then composted again with humidity controlled at 60-70% to obtain pretreated biomass. The pretreated biomass is mixed with a ferric solution and heated to react. The reaction product is mixed with the biochar to obtain a carbon mixture. NaOH solution is added to the carbon mixture to prepare an alkaline suspension. The suspension is continuously shaken at room temperature and then carbonized at high temperature again to obtain modified biochar. The repair promoter comprises, by weight, the following: The ingredients are: 10-20 parts peat moss, 5-10 parts phosphate lime powder, 3-8 parts mannitol, 1-3 parts plant growth regulator, 0.1-0.3 parts microbial inoculant, and 0.2-1 parts chelating agent; wherein the chelating agent is ethylenediaminetetraacetic acid. The preparation method of the alkaline clay includes: adding 20-30 parts of starch to 80-100 parts of water, heating to 88-95℃, and gelatinizing for 60-90 minutes to obtain gelatinized starch; adding 10-20 parts of sodium alginate, 20-30 parts of bentonite, 10-15 parts of sodium bicarbonate, and 4-6 parts of alkyl glycoside to the gelatinized starch, heating to 50-60℃, stirring at 600-800 r / min for 5-10 minutes, then adding 0.3-1 parts of crosslinking agent, heating to 60-70℃, and stirring at 200-300 r / min for 30-40 minutes to obtain the desired product; The microbial inoculant comprises, by weight: 1.0-2.0 × 10 8 CFU / g Azotoxin spirochetes 2-7 portions, 1.0-2.0 × 10⁻⁶ 8 cfu / g Azotobacter chrysophagus 5-15 samples, 2.0-3.0×10 8 Two to three portions of EM bacteria with cfu / g; the plant growth regulators include one or more of auxin, gibberellin, cytokinin, abscisic acid, and brassinolide. The modified biochar is applied at a rate of 10-20 kg / mu, the remediation promoter is applied at a rate of 5-15 kg / mu, and the alkaline clay is applied at a rate of 20-30 kg / mu.

2. The biochar-phytoremediation method for heavy metal contaminated soil in mines according to claim 1, characterized in that, The enriching plants include one of the following: black nightshade, fleabane, sepia, sepia, vetiver, scabra, Indian mustard, sunflower, camel thorn, and white thorn.

3. The biochar-phytoremediation method for heavy metal contaminated soil in mines according to claim 1, characterized in that, The preparation method of the modified biochar specifically includes the following steps: Peanut shells are dried, crushed, and sieved, then carbonized at 700-800℃. After natural cooling to room temperature, the raw biochar is obtained. The raw biochar is added to a ferric solution, followed by 0.1-0.2 mol / L NaOH solution. The mixture is then ultrasonically treated, heated and stirred at 80-90℃, dried at 80-100℃, and washed with distilled water until pH=7 to obtain biochar. Biomass raw materials are crushed, and orange or grapefruit peels are added to remove odors. The humidity is controlled at 40-50%, and the mixture is composted in a composting tank for 10-20 days. The compost is then turned, and the humidity is controlled at 60-70% for another 10-20 days, with turning every 1-2 days to obtain pretreated biomass. The pretreated biomass is mixed with a ferric solution and reacted at 50-70℃ for 2-5 hours. The reaction product is mixed with the biochar to obtain a char mixture. 1-2 mol / L NaOH solution is added to the char mixture. An alkaline suspension is prepared using NaOH solution, continuously shaken at room temperature for 8-15 hours, and then carbonized at a high temperature of 400-600℃ to obtain modified biochar.

4. The biochar-phytoremediation method for heavy metal contaminated soil in mines according to claim 1, characterized in that, The biomass raw materials include one or more of the following: straw, agricultural and forestry waste, poultry and livestock manure, fruit and vegetable residues, and kitchen waste.

5. The biochar-phytoremediation method for heavy metal contaminated soil in mines according to claim 1, characterized in that, The crosslinking agent is N,N-methylenebisacrylamide.

6. The biochar-phytoremediation method for heavy metal contaminated soil in mines according to claim 1, characterized in that, The concentration of ferric ions in the ferric solution is 0.1-1 mol / L, and the concentration of biochar in the ferric solution is 80-100 g / L.

7. The biochar-phytoremediation method for heavy metal contaminated soil in mines according to claim 1, characterized in that, The solid-liquid ratio of the biochar to the NaOH solution is 1-3g:150-200ml; the solid-liquid ratio of the char mixture to the NaOH solution is 1-3g:100-120ml.

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