Preparation method and application of heavy metal contaminated soil remediation agent

Abstract

The present application belongs to the technical field of heavy metal pollution treatment, and relates to a preparation method and application of a heavy metal contaminated soil remediation agent. The heavy metal contaminated soil remediation agent mainly comprises the following components in parts by weight: alkali modified cotton stalk biochar 20-30 parts, sepiolite 5-10 parts, humic acid 15-20 parts, and calcium silicate 5-10 parts. The heavy metal contaminated soil remediation agent can effectively remove mercury, arsenic, cadmium and / or lead pollution in heavy metal contaminated soil, and improve the heavy metal contaminated soil environment. After the soil remediation agent is used to treat heavy metal cadmium contaminated soil, the soil pH value can be improved, and the absorption and enrichment of crops to cadmium and lead can be reduced, so that a new type of biological remediation method with low cost, high efficiency, simplicity and environmental friendliness is provided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heavy metal pollution treatment, and relates to a preparation method and application of a heavy metal contaminated soil remediation agent. BACKGROUND

[0002] With the rapid development of modern agriculture, industry and transportation, various heavy metals have accumulated in the ecological environment, leading to the destruction of soil biodiversity, aggravating the destruction of resources, and threatening the safety and health of organisms, which is an urgent problem to be dealt with. The pollution of heavy metals such as nickel (Ni), lead (Pb), cobalt (Co), cadmium (Cd), manganese (Mn), chromium (Cr) and zinc (Zn) is becoming more and more serious. Soil heavy metal pollution is hidden, cumulative, lagging and irreversible. Too high concentration of heavy metals will not only affect crop growth, but also will eventually endanger human health through food chain enrichment.

[0003] Common soil heavy metal pollution remediation methods include physical remediation, chemical remediation, biological remediation and combined remediation. The physical remediation engineering measure has high cost, the plant remediation period is too long, the microbial remediation technology is not mature, and the most practical method at present is chemical passivation remediation technology. The chemical passivation remediation technology is to apply a passivation agent to the soil to reduce the biological availability and mobility of heavy metals in the soil through adsorption, precipitation, complexation, ion exchange and oxidation-reduction processes.

[0004] Domestic and foreign scholars mainly carry out remediation research on contaminated soil through physical, chemical and biological methods. Due to the differences in the physical and chemical properties of soil, the types of heavy metal pollution and the degree of pollution, the remediation effect is not ideal, and further comprehensive research methods are needed to reduce the residual heavy metals, reduce the toxicity of heavy metals, improve the ecological restoration efficiency, beautify the living environment and eliminate the adverse effects of pollution. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a preparation method and application of a heavy metal contaminated soil remediation agent, which can effectively remove mercury, arsenic, cadmium and / or lead pollution in heavy metal contaminated soil and effectively improve the heavy metal contaminated soil environment.

[0006] To achieve the above purpose, the following technical solutions are adopted in the present application:

[0007] In a first aspect, the present application provides a heavy metal contaminated soil remediation agent, which mainly comprises the following components in parts by weight: alkali modified cotton stalk biochar 20-30 parts, sepiolite 5-10 parts, humic acid 15-20 parts and calcium silicate 5-10 parts.

[0008] Further, the heavy metal contaminated soil remediation agent mainly comprises the following components in parts by weight: alkali modified cotton stalk biochar 25 parts, sepiolite 8 parts, humic acid 10 parts and calcium silicate 7 parts.

[0009] In a second aspect, the present application provides a preparation method of the heavy metal contaminated soil remediation agent, which is:

[0010] (1) Preparation of alkali modified cotton stalk biochar: the cotton stalk is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60℃; the cotton stalk is mixed with MgCl2 and stirred vigorously for 6h, and then dried in an oven at 60℃ for more than 10h to reach a constant weight; then it is heated to 700℃ at a heating rate of 10℃ / min in a tube furnace, and calcined at high temperature under nitrogen for 1-1.5h to obtain the alkali modified cotton stalk biochar.

[0011] (2) The biochar, sepiolite, humic acid and calcium silicate are mixed and ground to obtain the heavy metal contaminated soil remediation agent.

[0012] Further, the concentration of MgCl2 in step (1) is 0.5 mol / L.

[0013] Further, the mass-volume ratio of cotton stalk to MgCl2 in step (1) is 1g:(10mL-20mL).

[0014] Further, the mass-volume ratio of cotton stalk to MgCl2 in step (1) is 1g:15mL.

[0015] Further, the high-temperature calcination under nitrogen in step (1) is performed for 1h.

[0016] In a third aspect, the present application provides the application of the heavy metal contaminated soil remediation agent prepared by the above preparation method in the in-situ remediation of heavy metal contaminated soil.

[0017] In a fourth aspect, the present application provides a use method of the heavy metal contaminated soil remediation agent, which is: applying the heavy metal contaminated soil remediation agent to the heavy metal contaminated soil and ploughing.

[0018] Further, when the application environment is potting, the application amount of the heavy metal contaminated soil remediation agent is 2%-5% of the weight of the potting soil; when the application environment is a field, the application amount of the heavy metal contaminated soil remediation agent is 140-220kg / acre.

[0019] Further, the heavy metal contamination is mercury, arsenic, cadmium and / or lead contamination.

[0020] Biochar is a kind of solid material with high aromaticity and rich carbon element, which is prepared by thermo-chemical conversion or pyrolysis of solid waste such as agricultural waste, animal biomass or sludge under anaerobic conditions. Biochar is generally alkaline, has large porosity and specific surface area, and also contains a large amount of phenolic hydroxyl, carboxyl and other oxygen-containing functional groups. Biochar can improve the adsorption and transformation capacity of soil to heavy metals, reduce the availability of heavy metals, and promote the remediation of heavy metal contaminated soil, but the remediation effect is closely related to the preparation material, pyrolysis temperature, addition ratio and the like. Modified biochar is prepared by modification of metal salt or metal oxide, acid, alkali and organic compound. The modification treatment can change the specific surface area, redox activity, functional group abundance and other properties of biochar, and has great application potential in fixing heavy metals in soil. Sepiolite is a silicate mineral belonging to the mineral group of antigorite peridotite, which has good adsorption and ion exchange properties due to its large porosity and specific surface area, and can be effectively used to control heavy metal pollution in water body. Humic acid is a kind of colloid with negative charge and weak acidity, but the edge of humic acid is positively charged, and the surface of clay crystal in soil has negative charge, so soil can adsorb humic acid colloid. Since most metal ions have positive charge, the combination of humic acid and soil colloid can enhance the adsorption of heavy metals in soil. Calcium silicate is a porous material, and its pore structure can provide a large amount of adsorption surface area, which is beneficial to adsorb heavy metal ions. In addition, calcium silicate also has high chemical reactivity, which can react with heavy metal ions to form stable adsorption products. The adsorption mechanism of calcium silicate to heavy metal ions mainly includes surface adsorption and ion exchange. In surface adsorption, heavy metal ions and active calcium silicate surface adsorption sites produce physical adsorption. The four components are combined in the present application, which shows significant synergistic effect in heavy metal contaminated soil, and the removal of mercury, arsenic, cadmium and / or lead pollution effect is remarkable.

[0021] The present application has the following beneficial effects:

[0022] After the soil remediation agent of the present application is treated, the available mercury and arsenic contents in the soil are significantly reduced.

[0023] After the soil remediation agent of the present application is treated for heavy metal cadmium contaminated soil, the soil pH value can be increased, the availability of heavy metals cadmium and lead in the soil can be significantly reduced, and the absorption and enrichment of cadmium and lead by crops can be reduced, which is a new type of biological remediation method with low cost, high efficiency, simplicity and environmental friendliness. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the present application or prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments.

[0025] Figure 1Passivation rate of heavy metal contaminated soil remediation agent of the present application to mercury pollution

[0026] Compared with the CK group, * P<0.05, ** P<0.01; compared with the A group, # P<0.05, ## P<0.01.

[0027] Figure 2 Passivation rate of heavy metal contaminated soil remediation agent of the present application to arsenic pollution

[0028] Compared with the CK group, * P<0.05, ** P<0.01; compared with the A group, # P<0.05, ## P<0.01.

[0029] Figure 3 Effect of heavy metal contaminated soil remediation agent of the present application on soil pH value

[0030] Compared with the CK group, * P<0.05.

[0031] Figure 4 Effect of heavy metal contaminated soil remediation agent of the present application on cadmium accumulation in the roots of San Ye Qing

[0032] Compared with the CK group, * P<0.05, ** P<0.01; compared with the A group, # P<0.05, ## P<0.01.

[0033] Figure 5 Effect of heavy metal contaminated soil remediation agent of the present application on lead accumulation in the roots of San Ye Qing

[0034] Compared with the CK group, * P<0.05, ** P<0.01; compared with the A group, # P<0.05, ## P<0.01. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below in combination with specific examples. In the following examples, the test reagents used are conventional biochemical reagents unless otherwise specified; and the experimental methods are conventional methods unless otherwise specified.

[0036] Example 1 Heavy metal contaminated soil remediation agent and its preparation method

[0037] The heavy metal contaminated soil remediation agent mainly comprises the following components in parts by weight: alkali modified cotton stalk biochar 25 parts, sepiolite 8 parts, humic acid 10 parts and calcium silicate 7 parts.

[0038] The preparation method is as follows: (1) preparation of alkali modified cotton stalk biochar: the cotton stalk is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60 DEG C; the cotton stalk is mixed with 0.5 mol / L MgCl2 at a mass-volume ratio of 1 g:15 mL, and stirred vigorously for 6 h, and then dried in an oven at 60 DEG C for more than 10 h to reach a constant weight, and then heated to 700 DEG C at a heating rate of 10 DEG C / min in a tube furnace, and calcined at high temperature under nitrogen for 1-1.5 h to obtain the alkali modified cotton stalk biochar; (2) the biochar, sepiolite, humic acid and calcium silicate are mixed and ground to obtain the heavy metal contaminated soil remediation agent.

[0039] Example 2 heavy metal contaminated soil remediation agent and preparation method thereof

[0040] The heavy metal contaminated soil remediation agent mainly comprises the following components in parts by weight: alkali modified cotton stalk biochar 30 parts, sepiolite 10 parts, humic acid 15 parts and calcium silicate 10 parts.

[0041] The preparation method is as follows: (1) preparation of alkali modified cotton stalk biochar: the cotton stalk is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60 DEG C; the cotton stalk is mixed with 0.5 mol / L MgCl2 at a mass-volume ratio of 1 g:20 mL, and stirred vigorously for 6 h, and then dried in an oven at 60 DEG C for more than 10 h to reach a constant weight, and then heated to 700 DEG C at a heating rate of 10 DEG C / min in a tube furnace, and calcined at high temperature under nitrogen for 1.5 h to obtain the alkali modified cotton stalk biochar; (2) the biochar, sepiolite, humic acid and calcium silicate are mixed and ground to obtain the heavy metal contaminated soil remediation agent.

[0042] Example 3 heavy metal contaminated soil remediation agent and preparation method thereof

[0043] The heavy metal contaminated soil remediation agent mainly comprises the following components in parts by weight: alkali modified cotton stalk biochar 25 parts, sepiolite 10 parts, humic acid 15 parts and calcium silicate 8 parts.

[0044] The preparation method is: (1) preparation of alkali modified cotton stalk biochar: the cotton stalk is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60°C; the cotton stalk is mixed with 0.5 mol / L MgCl2 at a mass-volume ratio of 1 g:10 mL, and stirred vigorously for 6 h, then dried in an oven at 60°C for more than 10 h to reach a constant weight, and then heated to 700°C at a heating rate of 10°C / min in a tube furnace, and calcined at high temperature under nitrogen for 1.5 h to obtain the alkali modified cotton stalk biochar; (2) the biochar, sepiolite, humic acid and calcium silicate are mixed and ground to obtain the heavy metal contaminated soil remediation agent.

[0045] Example 4 heavy metal contaminated soil remediation agent and its preparation method

[0046] The heavy metal contaminated soil remediation agent mainly includes the following components by weight: alkali modified cotton stalk biochar 30 parts, sepiolite 5 parts, humic acid 20 parts and calcium silicate 5 parts.

[0047] The preparation method is: (1) preparation of alkali modified cotton stalk biochar: the cotton stalk is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60°C; the cotton stalk is mixed with 0.5 mol / L MgCl2 at a mass-volume ratio of 1 g:15 mL, and stirred vigorously for 6 h, then dried in an oven at 60°C for more than 10 h to reach a constant weight, and then heated to 700°C at a heating rate of 10°C / min in a tube furnace, and calcined at high temperature under nitrogen for 1 h to obtain the alkali modified cotton stalk biochar; (2) the biochar, sepiolite, humic acid and calcium silicate are mixed and ground to obtain the heavy metal contaminated soil remediation agent.

[0048] Example 5 heavy metal contaminated soil remediation agent and its preparation method

[0049] The heavy metal contaminated soil remediation agent mainly includes the following components by weight: alkali modified cotton stalk biochar 20 parts, sepiolite 10 parts, humic acid 15 parts and calcium silicate 10 parts.

[0050] The preparation method is: (1) preparation of alkali modified cotton stalk biochar: the cotton stalk is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60°C; the cotton stalk is mixed with 0.5 mol / L MgCl2 at a mass-volume ratio of 1 g:15 mL, and stirred vigorously for 6 h, then dried in an oven at 60°C for more than 10 h to reach a constant weight, and then heated to 700°C at a heating rate of 10°C / min in a tube furnace, and calcined at high temperature under nitrogen for 1 h to obtain the alkali modified cotton stalk biochar; (2) the biochar, sepiolite, humic acid and calcium silicate are mixed and ground to obtain the heavy metal contaminated soil remediation agent.

[0051] Heavy metal contaminated soil remediation agent and preparation method thereof

[0052] The heavy metal contaminated soil remediation agent mainly comprises the following components in parts by weight: 25 parts of cotton stalk biochar, 8 parts of sepiolite, 10 parts of humic acid and 7 parts of calcium silicate.

[0053] The preparation method is as follows: (1) preparation of cotton stalk biochar: the cotton stalk is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60°C; the cotton stalk is heated to 700°C at a heating rate of 10°C / min in a tube furnace, and calcined at high temperature under nitrogen for 1-1.5 h to obtain the cotton stalk biochar; (2) mixing, grinding and obtaining the heavy metal contaminated soil remediation agent.

[0054] Heavy metal contaminated soil remediation agent and preparation method thereof

[0055] The heavy metal contaminated soil remediation agent mainly comprises the following components in parts by weight: 25 parts of alkali-modified peanut shell biochar, 8 parts of sepiolite, 10 parts of humic acid and 7 parts of calcium silicate.

[0056] The preparation method is as follows: (1) preparation of alkali-modified peanut shell biochar: the peanut shell is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60°C; the peanut shell is mixed with 0.5 mol / L MgCl2 at a mass-volume ratio of 1 g:15 mL, and stirred vigorously for 6 h, and then dried in an oven at 60°C for more than 10 h to reach a constant weight; the peanut shell is heated to 700°C at a heating rate of 10°C / min in a tube furnace, and calcined at high temperature under nitrogen for 1-1.5 h to obtain the alkali-modified peanut shell biochar; (2) mixing, grinding and obtaining the heavy metal contaminated soil remediation agent.

[0057] Heavy metal contaminated soil remediation agent and preparation method thereof

[0058] The heavy metal contaminated soil remediation agent mainly comprises the following components in parts by weight: 25 parts of alkali-modified peanut shell biochar, 8 parts of sepiolite, 10 parts of humic acid and 7 parts of calcium silicate.

[0059] The preparation method is: (1) preparation of alkali modified cotton stalk biochar: the cotton stalk is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60°C; the cotton stalk is mixed with 0.5 mol / L MgCl2 at a mass-volume ratio of 1 g:15 mL, and stirred vigorously for 6 h, then dried in an oven at 60°C for more than 10 h to reach a constant weight, then heated to 700°C at a heating rate of 10°C / min in a tube furnace, and calcined at high temperature under nitrogen for 1-1.5 h to obtain the alkali modified cotton stalk biochar; (2) mixing the biochar, red mud, humic acid and calcium silicate, and grinding to obtain the heavy metal contaminated soil remediation agent.

[0060] Heavy metal contaminated soil remediation agent and preparation method thereof

[0061] The heavy metal contaminated soil remediation agent mainly comprises the following components by weight: 15 parts of alkali modified cotton stalk biochar, 15 parts of sepiolite, 10 parts of humic acid and 15 parts of calcium silicate.

[0062] The preparation method is: (1) preparation of alkali modified cotton stalk biochar: the cotton stalk is naturally air-dried, crushed and sieved through a 20-mesh sieve, and then dried in an oven at 60°C; the cotton stalk is mixed with 0.5 mol / L MgCl2 at a mass-volume ratio of 1 g:15 mL, and stirred vigorously for 6 h, then dried in an oven at 60°C for more than 10 h to reach a constant weight, then heated to 700°C at a heating rate of 10°C / min in a tube furnace, and calcined at high temperature under nitrogen for 1-1.5 h to obtain the alkali modified cotton stalk biochar; (2) mixing the biochar, sepiolite, humic acid and calcium silicate, and grinding to obtain the heavy metal contaminated soil remediation agent.

[0063] Test example 1 remediation effect of the remediation agent of the application on mercury and arsenic contaminated soil

[0064] 1. Experimental method

[0065] The test soil is mercury and arsenic contaminated soil, taken from a certain abandoned chemical plant area, with a water content of 21.5% and a pH of 7.5. The soil available content of mercury and arsenic is extracted by EDTA one-step extraction method. The available content of mercury in the soil is 12.37 mg / kg, and the available content of arsenic is 63.54 mg / kg.

[0066] The collected soil sample is air-dried, crushed and sieved through a 20-mesh sieve. An indoor soil culture method is used to set up 7 treatments: a control group (CK group), an example 1 group (A group), an example 2 group (B group), a comparative example 1 group (C group), a comparative example 2 group (D group), a comparative example 3 group (E group) and a comparative example 4 group (F group). Each treatment is set up in triplicate, and passivated for 21 d.

[0067] Using the soil sample without remediation agent as the control group, the AF group used the remediation agent prepared by Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 at a mass fraction of 2.5%. The soil moisture was maintained at about 55% water content. The culture vessels were covered with plastic wrap, placed in the dark, and left to stand for 24 hours in the dark.

[0068] 2. Determination of available mercury and arsenic content in soil

[0069] Soil samples were collected after remediation, and the passivation rate was measured. The passivation rate was then used to analyze the remediation effect on heavy metals.

[0070] Passivation rate = (Content of effective heavy metals before repair - Content of effective heavy metals after repair) / Content of effective heavy metals before repair.

[0071] 3. Data Processing

[0072] All data are the mean ± standard deviation of three replicates. Statistical analysis was performed using SPSS 19.0 software, and significance analysis was performed using Duncan's method. Graphpad Prism 7.0 software was used for plotting.

[0073] 4. Results of determination of available mercury and arsenic content in soil

[0074] like Figure 1 , 2 As shown, after remediation, compared with the control group (CK) without remediation, groups A and B, treated with remediation agents, significantly reduced the content of available mercury and arsenic in the soil. The passivation efficiencies of group A for available mercury and arsenic were 79.2% and 85.1%, respectively, while those of group B were 74.5% and 83.8%, respectively. The effects of groups A and B in reducing the content of available mercury and arsenic in the soil were significantly better than those of groups C, D, E, and F.

[0075] Experimental Example 2: The Remediation Effect of the Soil Remediation Agent of the Present Invention on Complexly Contaminated Soil

[0076] 1. Experimental Methods

[0077] The soil samples were taken from the topsoil of a farmland contaminated with heavy metals. The soil pH was 6.48 and the organic matter content was 24.76 g / kg.

[0078] The total cadmium content and total lead content in the soil sample were determined according to the Graphite Furnace Atomic Absorption Spectrophotometry in the Soil Quality Lead and Cadmium Determination (GB / T 17141-1997), and the effective state cadmium and lead in the soil were determined according to the Soil Quality Effective State Lead and Cadmium Determination (GB / T 23739-2009) by using an atomic absorption spectrophotometer. The total cadmium content in the soil was 2.17 mg / kg, the effective state cadmium was 1.05 mg / kg, the total lead content was 139.54 mg / kg, and the effective state lead was 62.05 mg / kg.

[0079] The collected soil sample was air-dried, crushed and sieved through a 20-mesh sieve. Five treatments were set: a control group (CK group), an example 1 group (A group), a comparative example 1 group (B group), a comparative example 2 group (C group) and a comparative example 3 group (D group). Each treatment was set in triplicate, totaling 15 pots. The test soil sample without the remediation agent was used as the control group, and the remediation agents prepared from example 1, comparative example 1, comparative example 2 and comparative example 3 with a mass fraction of 2.5% were used in groups A-D.

[0080] After the remediation agents were uniformly mixed with the soil, they were transferred to the pots, each containing 3 kg of soil. The Radix Stephaniae Tetrandrae seeds were planted in the soil. After 10 days, 3 uniform seedlings were retained in each pot, and regular watering was performed to maintain the soil water holding capacity at about 55%. The plants were grown in a greenhouse at 25-30°C for 25 days, and the soil samples were collected and the Radix Stephaniae Tetrandrae plants were harvested.

[0081] 2. Determination of soil pH value and heavy metal content of Radix Stephaniae Tetrandrae

[0082] 2.1 The soil pH value was determined by the electrode method.

[0083] 2.2 Determination of heavy metal content in Radix Stephaniae Tetrandrae tuber: The Radix Stephaniae Tetrandrae was harvested at 25 days, the root mud and sand were washed and dried, and then sliced. The slices were dried at 60°C to a constant weight, crushed and sieved through a 0.15 mm aperture nylon screen to obtain a sample powder. The lead and cadmium contents in the Radix Stephaniae Tetrandrae tuber were determined by microwave digestion and inductively coupled plasma emission spectrometry.

[0084] 3. Data processing

[0085] The data results were the average values ± standard deviations of three replicates, and the statistical analysis was performed by using SPSS 19.0 software, the significant difference analysis was performed by using the Duncan method, and the drawing was performed by using Graphpad Prism 7.0 software.

[0086] 4. Results

[0087] 4.1 Determination of soil pH value

[0088] Compared with CK without applying the repairing agent, the soil pH value of group A can be improved. Figure 3

[0089] 4.2 Heavy metal content determination of radix tetrastigmae

[0090] Compared with CK without applying the repairing agent, the cadmium content of radix tetrastigmae of group A can be significantly reduced. Figure 4

[0091] Compared with CK without applying the repairing agent, the lead content of radix tetrastigmae of group A can be significantly reduced. Figure 5

[0092] After the soil repairing agent of the present application is applied to the heavy metal cadmium contaminated soil, the soil pH value can be improved, the availability of heavy metals cadmium and lead in the soil can be significantly reduced, and the absorption and enrichment of crops to cadmium and lead can be reduced, so that the present application is a new type of biological remediation method with low cost, high efficiency, simplicity and environmental friendliness.

[0093] From the above results, it can be known that the remediation effect of heavy metal contaminated soil will be obviously reduced after the components of the heavy metal contaminated soil repairing agent of the present application or the ratio of each component is changed, and the components of the soil repairing agent of the present application complement each other to realize the synergistic effect among the components.

[0094] The present application is intended to cover all such alternatives, modifications, and variations that fall within the broad scope of the appended claims. Accordingly, any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.​​​

Claims

1. A soil remediation agent for heavy metal contaminated soil, characterized in that, The heavy metal contaminated soil remediation agent comprises the following components by weight: 20-30 parts alkali-modified cotton straw biochar, 5-10 parts sepiolite, 15-20 parts humic acid, and 5-10 parts calcium silicate. The preparation method of the heavy metal contaminated soil remediation agent is as follows: (1) Preparation of alkali-modified cotton straw biochar: the cotton straw is naturally air-dried, crushed and passed through a 20-mesh sieve, and the sieved cotton straw is dried in an oven at 60°C; the cotton straw is mixed with MgCl2 and stirred vigorously for 6 hours, filtered and dried in an oven at 60°C for more than 10 hours to reach constant weight, and then placed in a tube furnace and heated to 700°C at a heating rate of 10°C / min, and calcined at high temperature for 1-1.5 hours under nitrogen to obtain alkali-modified cotton straw biochar; (2) the biochar, sepiolite, humic acid and calcium silicate are mixed and ground to obtain the heavy metal contaminated soil remediation agent; In step (1), the concentration of MgCl2 is 0.5 mol / L; In step (1), the mass-to-volume ratio of cotton stalks to MgCl2 is 1g:(10mL-20mL).

2. The heavy metal contaminated soil remediation agent according to claim 1, characterized in that, The heavy metal contaminated soil remediation agent mainly comprises the following components by weight: 25 parts alkali-modified cotton straw biochar, 8 parts sepiolite, 10 parts humic acid, and 7 parts calcium silicate.

3. The heavy metal contaminated soil remediation agent according to claim 1, characterized in that, In step (1), the mass-to-volume ratio of cotton stalks to MgCl2 is 1g:15mL.

4. The heavy metal contaminated soil remediation agent according to claim 1, characterized in that, In step (1), the sample is calcined at high temperature under nitrogen for 1 hour.

5. The application of the heavy metal contaminated soil remediation agent according to claim 1 in in-situ remediation of heavy metal contaminated soil.

6. The application according to claim 5, characterized in that, The heavy metal pollution mentioned refers to mercury, arsenic, cadmium, and / or lead pollution.

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