Heavy metal contaminated soil remediation material

Abstract

The invention provides a heavy metal contaminated soil remediation material, and belongs to the technical field of soil remediation. According to the method, the silicon-magnesium modified sunflower straw biochar and the organic fertilizer (chicken manure) are used for synergistically repairing the chromium and lead heavy metal contaminated soil, the adsorption performance of the modified biochar and the biological absorption effect of the organic fertilizer are used for jointly reducing the absorption of spinach to the heavy metal chromium and lead, meanwhile, the physical and chemical properties of the soil are improved, and the nutrient activity of the soil is remarkably improved. Results show that the effective cation exchange capacity, organic matters and available phosphorus of the soil are improved by synergistic remediation of the modified biochar and the organic fertilizer, the pH value of the soil is reduced (averagely reduced by 0.48), the combined application effect of the modified biochar and the organic fertilizer is more obvious, and the absorption of chromium and lead by the spinach is averagely reduced by 26.04% and 18.22% respectively. The invention provides an effective and practical way for reducing the composite toxicity of plants to various metals such as chromium, lead and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and particularly to a soil remediation material for heavy metal contaminated soil. Background Art

[0002] With the acceleration of the global industrialization and modernization processes, agricultural production has achieved rapid development, and the problem of heavy metal pollution in soil has followed, posing a serious threat to soil quality, crop yields, and human health. Heavy metal pollutants mainly refer to heavy metals such as cadmium, lead, copper, zinc, mercury, chromium, nickel, and arsenic and other pollutants harmful to the ecological environment. Heavy metal pollution will have an adverse impact on the quality of the soil environment, and in severe cases, it will even cause the deterioration of the soil ecological environment. Different from organic pollutants that can be degraded and removed, heavy metals have the characteristics of concealment, difficulty in treatment, irreversibility, and long-term nature. Once heavy metals enter the soil, it is difficult to eliminate and degrade them, and their toxicity will accumulate over time. When the concentration exceeds the permitted range, heavy metals will first affect microorganisms, causing soil enzymes to become inactivated and the respiration intensity to decrease, resulting in changes in ecological characteristics such as microbial biomass, microbial community structure, and diversity. In severe cases, it will damage the structure and function of microbial cells, leading to a sharp reduction in the number of original dominant microorganisms and even extinction. Therefore, it is urgent to develop targeted, scientific, and comprehensive soil remediation and treatment technologies, and in principle of not over-remediating, combined with regional characteristics, to improve the soil ecological environment.

[0003] Large-scale tailings accumulation occupies a large amount of land resources, causing vegetation damage in local areas and seriously damaging the surrounding ecological environment. The discharge of mining wastewater and ore dressing waste liquid, as well as the stacking and leaching of solid wastes such as waste rocks and tailings, cause a large amount of heavy metals to accumulate in the soil around the tailings pond. Heavy metals can migrate from the soil to ecological systems such as groundwater and crops, and endanger human health through the food chain. Many malignant tumors and birth defects are related to the toxicity of heavy metals, seriously affecting human health and sustainable development. Some laboratory test data show that the contents of heavy metals lead and chromium in a farmland soil in Longnan are significantly higher than other heavy metals. Therefore, it is particularly important to strengthen the treatment of heavy metal contaminated soil in Longnan.

[0004] Biochar has a large specific surface area and porosity, contains abundant surface functional groups, as well as rich nutrients and minerals. Therefore, it is widely used as an adsorbent, catalyst, and can also be used to synthesize many other functional materials. In addition, it is widely applied in fields such as soil remediation, carbon sequestration, and wastewater treatment. Biochar has received extensive attention as a very promising soil remediation material. It can increase the water-holding capacity of the soil, improve soil fertility and crop yields, adsorb organic pollutants, and immobilize heavy metals. To further improve the bioremediation effect, biochar is often modified to improve its disadvantages and enhance the adsorption effect. Common modification methods include acid-base modification, metal salt / oxide modification, and microbial modification. Straw, as a biomass raw material, is often used to prepare biochar. However, biochar prepared from straw-based agricultural waste generally has problems such as low carbon content and lack of nutrient elements after being applied to the soil, and it needs to be used in combination with organic fertilizers, etc. to improve the soil and increase the fertility of sandy soil. Thus, it is very important to prepare a straw biochar rich in nutrients for the improvement of infertile soil.

[0005] Organic fertilizers play an important role in providing nutrients and promoting crop growth in agricultural production. In the remediation of heavy metal contaminated soil, organic fertilizers can achieve the purpose of soil remediation by changing the physical and chemical properties of the soil, promoting plant growth, and changing the forms and distributions of heavy metals in the soil. Organic fertilizers also have rich organic matter and microorganisms, which can improve the soil structure and increase soil fertility. In the remediation of heavy metal contaminated soil, organic fertilizers can reduce the bioavailability of heavy metals through adsorption, complexation, etc., thereby reducing their harm to crops and the environment. Therefore, by selecting appropriate types of organic fertilizers and application strategies, combined with other remediation technologies, the heavy metal content in the soil can be effectively reduced, and the soil ecological environment can be improved. Summary of the Invention

[0006] The purpose of the present invention is to provide a heavy metal contaminated soil remediation material to solve the technical problems in the prior art of lacking targeted, scientific, and comprehensive heavy metal contaminated soil remediation technologies and green and efficient soil remediation materials.

[0007] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0008] The present invention provides a heavy metal contaminated soil remediation material, which is composed of components including modified biochar and organic fertilizer:

[0009] The addition amount of the modified biochar is 0 - 2 wt% of the soil mass, and the addition amount of the organic fertilizer is 0 - 10 wt% of the soil mass, wherein the addition amount of the modified biochar is not 0;

[0010] The preparation method of the modified biochar is as follows: mix straw powder and sodium silicate solution, conduct hydrothermal reaction, and then successively add magnesium chloride solution for impregnation and heat treatment.

[0011] Further, the straw powder includes sunflower straw powder, and the particle size of the straw powder is 0.1 - 0.3 mm.

[0012] Further, the concentration of the sodium silicate solution is 0.03 - 0.1 M, and the dosage ratio of the straw powder to the sodium silicate solution is 5 - 15 g:50 - 150 mL.

[0013] Further, after mixing the straw powder and the sodium silicate solution, adjust the pH of the obtained material to 4 - 6.

[0014] Further, the temperature of the hydrothermal reaction is 150 - 220 °C, and the time of the hydrothermal reaction is 3 - 6 h.

[0015] Further, the concentration of the magnesium chloride solution is 0.8 - 1.5 M.

[0016] Further, the temperature of the heat treatment is 400 - 600 °C, and the time of the heat treatment is 3 - 6 h.

[0017] Further, the pH of the modified biochar is 6 - 7.5.

[0018] Further, the organic fertilizer includes chicken manure.

[0019] The beneficial effects of the present invention:

[0020] The present invention aims to construct a new type of modified biochar combined with organic fertilizer for the green and efficient remediation of lead- and chromium-heavy metal contaminated soil, and to explore the changes in soil physical and chemical properties caused by the combined application of modified biochar and organic fertilizer. The present invention selects sunflower straw biomass materials to synthesize biochar materials at different temperatures by co-pyrolysis, and uses silicon and magnesium to modify it to prepare an enhanced modified biochar material. Finally, it combines with chicken manure to repair lead- and chromium-heavy metal contaminated soil, and investigates the reduction of chromium and lead absorption by spinach when the modified biochar and chicken manure are applied together. The advantages of the present invention are that, on the one hand, agricultural straw as a remediation material is a new way for waste reduction, harmless treatment and resource utilization; on the other hand, these wastes are pyrolyzed and then applied to contaminated soil as remediation materials, which can not only improve soil properties and reduce soil pollution to a certain extent, but also reduce waste treatment costs and costs, and at the same time realize the resource utilization of waste liquid, sludge and agricultural and forestry waste, which is of great significance to environmental protection and resource conservation. The present invention has important significance for innovating heavy metal contaminated soil remediation technologies, and also provides theoretical reference and technical support for realizing green and efficient heavy metal contaminated soil remediation. Description of the Drawings

[0021] Figure 1 BET diagram of the modified biochar obtained in Example 1;

[0022] Figure 2 BET diagram of the modified biochar obtained in Example 2;

[0023] Figure 3 BET diagram of the modified biochar obtained in Example 3;

[0024] Figure 4 Infrared spectra of the modified biochars obtained in Examples 1 to 3 respectively. Detailed implementation mode

[0025] The present invention provides a heavy metal contaminated soil remediation material, which consists of components including modified biochar and organic fertilizer:

[0026] The addition amount of the modified biochar is 0 to 2 wt% of the soil mass, and the addition amount of the organic fertilizer is 0 to 10 wt% of the soil mass, wherein the addition amount of the modified biochar is not 0;

[0027] The preparation method of the modified biochar is as follows: mix straw powder and sodium silicate solution and then carry out hydrothermal reaction, and then sequentially add magnesium chloride solution for impregnation and heat treatment.

[0028] In the present invention, the addition amount of the modified biochar is preferably 0.5 to 1.5 wt% of the soil mass, and more preferably 1 wt%.

[0029] In the present invention, the addition amount of the organic fertilizer is preferably 2 to 8 wt% of the soil mass, and more preferably 5 wt%.

[0030] In the present invention, the straw powder is preferably sunflower straw powder, and the particle size of the straw powder is 0.1 to 0.3 mm, preferably 0.2 mm.

[0031] In the present invention, the preparation method of the straw powder is to wash the straw with deionized water, air-dry it, and then grind and sieve it with a pulverizer.

[0032] In the present invention, the concentration of the sodium silicate solution is 0.03 to 0.1 M, preferably 0.05 to 0.08 M, and more preferably 0.06 M; the dosage ratio of the straw powder to the sodium silicate solution is 5 to 15 g: 50 to 150 mL, preferably 8 to 12 g: 80 to 120 mL, and more preferably 10 g: 100 mL.

[0033] In the present invention, after the straw powder and the sodium silicate solution are mixed, the pH of the obtained material is adjusted to 4 to 6, preferably 5.

[0034] In the present invention, calcium sulfate is preferably used to adjust the pH of the obtained material.

[0035] In the present invention, the reaction temperature of the hydrothermal reaction is 150 - 220 °C, preferably 180 - 200 °C, and more preferably 190 °C; the time of the hydrothermal reaction is 3 - 6 h, preferably 5 h.

[0036] In the present invention, the concentration of the magnesium chloride solution is 0.8 - 1.5 M, preferably 1 M.

[0037] In the present invention, the amount of the magnesium chloride solution used is preferably such that the magnesium chloride solution completely impregnates the material.

[0038] In the present invention, the impregnation time is preferably 40 min.

[0039] In the present invention, the temperature of the heat treatment is 400 - 600 °C, preferably 450 - 550 °C, and more preferably 500 °C; the time of the heat treatment is 3 - 6 h, preferably 5 h.

[0040] In the present invention, the heat treatment is carried out in a tubular furnace, preferably under anaerobic conditions.

[0041] In the present invention, the pH of the modified biochar is 6 - 7.5, and more preferably 7.

[0042] In the present invention, the organic fertilizer is preferably chicken manure.

[0043] In the present invention, the sunflower straw is purchased from Kaibian Town, Zhenyuan County, Qingyang City, Gansu Province.

[0044] In the present invention, the experimental soil is from a certain county in Longnan City, Gansu Province, with geographical coordinates of 106.1629′N, 33.8750′E.

[0045] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0046] Example 1

[0047] The sunflower straw was rinsed with deionized water, air-dried, ground with a pulverizer and sieved through a 0.15 mm sieve to obtain straw powder. 10 g of the straw powder was mixed with 100 mL of a sodium silicate solution with a concentration of 0.05 M, and the pH was adjusted to 5. The obtained mixture was subjected to a hydrothermal reaction at 180 °C for 4 h. After removing the moisture, the mixture was impregnated in a 1 M magnesium chloride solution for 40 min, and then heat-treated under anaerobic conditions at a temperature of 400 °C for 4 h. After cooling, the material was rinsed with deionized water until the pH value reached neutrality, and the modified biochar, denoted as BC400, was obtained.

[0048] Example 2

[0049] Different from Example 1, in this example, the heat treatment temperature is 500 °C, and the obtained modified biochar is denoted as BC500.

[0050] Example 3

[0051] Different from Example 1, in this example, the heat treatment temperature is 600 °C, and the obtained modified biochar is denoted as BC600.

[0052] Table 1 shows the physical and chemical properties of the experimental soil.

[0053] Table 1 Physical and Chemical Properties of the Experimental Soil

[0054]

[0055] 2) Experimental setup:

[0056] A greenhouse pot experiment was conducted in the School of Materials Science and Engineering, Lanzhou University of Technology. This experiment adopted a completely randomized design. The modified biochar was put into three soil samples at four levels of 0%, 0.5%, 1%, and 2% and stirred evenly to obtain the modified biochar and soil mixed samples, which were respectively labeled as BCY1-0, BCY1-0.5, BCY1-1, BCY1-2, BCY2-0, BCY2-0.5, BCY2-1, BCY2-2, BCY3-0, BCY3-0.5, BCY3-1, BCY3-2. Organic fertilizer treatments of 0, 1, 3, and 5 mg / L were set, namely O0, O1, O3, and O5, and were respectively added to the above mixed samples, with a total of 48 treatments. The samples were kept stable within 60 days, and appropriate amounts of samples were taken to measure their physical and chemical properties. Additionally, 48 flowerpots were taken, each flowerpot was 15 cm high and 21.9 cm in diameter, and contained soil (2 kg). Each flowerpot was added with inorganic fertilizers, namely urea, potassium dihydrogen phosphate, and potassium chloride (all analytical grade), and the dosages were: (N) = 60 mg / kg, (P2O5) = 36 mg / kg, (K2O) = 78 mg / kg. These fertilizers were fully mixed with the soil. After about 30 days of cultivating spinach germination, the spinach seedlings were evenly transplanted into the mixed soil applied with modified biochar and organic fertilizer. Subsequently, the treatment methods and conditions of each flowerpot were the same, and after 60 days, the growth status of spinach was observed.

[0057] 3) Preparation of simulated heavy metal chromium and lead contaminated soil

[0058] As can be seen from Table 1, the average contents of chromium and lead in the original soil are 19.37 mg / kg and 51.48 mg / kg respectively, which are within the range of the soil environmental quality standard. Therefore, the method of artificially simulating chromium and lead contaminated soil is adopted. A chromium concentration of 100 mg / kg represents mild to moderate chromium pollution, and a lead concentration of 400 mg / kg represents relatively severe lead pollution. These concentration selections are helpful for studying the adsorption effect of biochar and the soil remediation potential under different pollution degrees. Therefore, heavy metal solutions with concentrations of 100 mg / kg and 400 mg / kg are prepared with potassium dichromate (K2CrO4) and lead nitrate (Pb(NO3)2) respectively. The heavy metal solutions are evenly sprayed onto the soil samples, and at the same time, continuous stirring is carried out to fully mix the two. Then, it is placed in a lightless environment for passivation. Ensure its field water holding capacity of 60% to promote the interaction between heavy metals and the soil and reach equilibrium. After one month, the soil is ground again, passed through a 2 mm sieve and stored for subsequent experiments.

[0059] 4) Test methods

[0060] Dissolved organic carbon (DOC) in the soil is extracted from the supernatant of a 1:15 (w / v) suspension with ultrapure water for subsequent analysis. The determination of heavy metals in potting soil (1.000 g) is carried out by microwave digestion with a mixed acid (HNO3:HCl:HF = 6:2:2). If there is residue in the soil sample after microwave digestion, sulfuric acid H2SO4 (1 mL) and HF (1 mL) are added. Select tender spinach leaves, wash and dry them with distilled water, and then quickly freeze the leaves in liquid nitrogen for subsequent biochemical analysis.

[0061] 5) Test results

[0062] The elemental compositions of unmodified biochar and silica-magnesium modified biochar prepared from sunflower straw at different temperatures are shown in Table 2. Among them, compared with the modified biochar, the preparation method of the unmodified biochar does not include the modification process in sodium silicate solution and magnesium chloride solution.

[0063] Table 2 Percentage of biochar element content

[0064]

[0065] As can be seen from the table, the elemental content of biochar changes with the increase in temperature. Since sunflower straw belongs to lignocellulosic materials, the biochar produced from this raw material contains a large amount of carbon element, making it less likely to degrade and more stable during the thermal conversion process compared to other biochars with lower carbon content. It can also be seen from the table that the carbon element content and sulfur element content increase with the increase in temperature, while the oxygen element content decreases with the increase in temperature. This is because the increase in preparation temperature leads to a large consumption of oxygen in the biochar, and at the same time, substances rich in carbon and sulfur elements are produced.

[0066] The measured data of the pH, electrical conductivity, and ash content of the modified biochars and unmodified biochars prepared at three different temperatures of 400 °C, 500 °C, and 600 °C in Examples 1 to 3 are shown in Table 3. Among them, compared with the modified biochars, the preparation method of the unmodified biochars does not include the modification process in sodium silicate solution and magnesium chloride solution.

[0067] Table 3 Biochar pH, Electrical Conductivity, Ash Content

[0068]

[0069] As can be seen from Table 3, with the continuous increase in temperature, the pH, electrical conductivity, and ash content of the biochar all show an increasing trend. The main reasons for these increases are mainly related to the chemical and physical changes of the biochar during pyrolysis. The pH values of the biochars are all between 7 and 11, showing alkaline characteristics, which are mainly caused by the volatilization of acidic substances and the formation of alkaline substances. During the pyrolysis of the biochar, with the increase in temperature, elements such as C, O, and H in the biochar are lost more, and at the same time, the acidic substances formed will gradually volatilize. The reduction of these acidic substances leads to a decrease in the acidity of the biochar, thus increasing the pH value. On the other hand, inorganic elements such as Ca, Mg, Na, and Si in the biochar will sinter and fuse to form inorganic minerals at high temperatures. The formation of these inorganic minerals increases the ash content of the biochar, and these ash substances are often alkaline, further increasing the pH value of the biochar; the main reason for the increase in electrical conductivity is the change in the carbon structure. High-temperature carbonization usually produces a relatively dense carbon structure, and this structural change helps to improve the electrical conductivity of the biochar. Because the dense carbon structure helps the conduction of electrons, thus increasing the electrical conductivity of the biochar; the reason for the increase in ash content is the enrichment of inorganic elements. At high temperatures, inorganic elements in the biochar will undergo reactions such as sintering and fusion to form a more stable inorganic mineral structure. The formation and enrichment of these inorganic minerals are important reasons for the increase in the ash content of the biochar.

[0070] Application Example 1

[0071] Taking the modified biochar prepared in Example 3 as an example, the effects of applying modified biochar alone, applying organic fertilizer alone, and applying the combination of modified biochar and organic fertilizer on soil pH, cation exchange capacity, organic matter, and available phosphorus were investigated respectively. Table 4 shows the effects of the combined application of the modified biochar and organic fertilizer obtained in Example 3 on soil physical and chemical properties.

[0072] Table 4 Effects of the combined application of the modified biochar and organic fertilizer obtained in Example 3 on soil physical and chemical properties

[0073]

[0074]

[0075] It can be seen from Table 4 that compared with the soil without applying modified biochar, organic fertilizer, and the complex of modified biochar and organic fertilizer, with the increase in the addition amounts of modified biochar, organic fertilizer, and the complex of modified biochar and organic fertilizer, the soil pH decreased, while the cation exchange capacity, organic matter, and available phosphorus increased. The reason for the decrease in soil pH value after applying modified biochar, organic fertilizer, and the complex of modified biochar and organic fertilizer may be related to the acidic characteristics of modified biochar and the buffering effect of organic fertilizer; while the reason for the increase in cation exchange capacity may be related to the adsorption of modified biochar, the nutrient release of organic fertilizer, the improvement of soil structure, and the increase in cation exchange sites. These changes jointly promoted the improvement of soil fertility and the optimization of crop growth environment.

[0076] The application of modified biochar, the application of organic fertilizer, and the application of the complex of modified biochar and organic fertilizer also significantly improved the soil organic matter status. This is because modified biochar usually has specific acid-base properties, which helps to regulate soil pH value. In alkaline soil, by adding acidic modified biochar, the soil pH value can be reduced, thereby indirectly affecting the balance of soil carbonates. The porous structure and surface functional groups of modified biochar endow it with strong adsorption ability, which can adsorb nutrient elements in the soil, including elements related to carbonates (calcium, magnesium, etc.), thereby indirectly affecting the content and form of soil carbonates. On the other hand, organic fertilizer is rich in organic matter, and these organic matters can produce humus after decomposition in the soil, which helps to improve soil structure and fertility. The organic acids produced during the decomposition of organic matter can affect the dissolution and transformation of soil carbonates, thereby reducing the soil carbonate content. Another important reason may be that the combined application of modified biochar and organic fertilizer can synergistically improve soil structure, make the soil more loose, promote the recycling of soil nutrients, and thus accelerate the cycle and transformation of soil carbonates.

[0077] The experiment also studied the adsorption properties of modified biochar, organic fertilizer, and the combined complex of modified biochar and organic fertilizer for lead and chromium in soil. It can also be seen from Table 4 that the combined application of modified biochar and organic fertilizer has a good adsorption effect on lead and chromium in soil. This is mainly because the surface of modified biochar is rich in functional groups such as hydroxyl groups and carboxyl groups. The combined application of modified biochar and organic fertilizer can form a synergistic effect. The organic matter and nutrients in the organic fertilizer can promote the complexation reaction between the functional groups on the surface of biochar and heavy metal ions such as lead and chromium in the soil, forming stable complexes, thereby fixing them in the soil. It is also possible that the addition of modified biochar changes the morphological distribution of heavy metals in the soil, converting them from bioavailable forms to residual forms with lower activity, thereby reducing their environmental risks and biological toxicity.

[0078] The application of modified biochar alone can reduce the uptake of Cr and Pb by spinach. Under the treatment of 0.5% modified biochar, the uptake of Pb and Cr by spinach decreased by 10.96% and 7.74% respectively. Under the treatment of 1% modified biochar, the uptake of Pb by spinach decreased by 17.85%, and the uptake of Cr decreased by 10.45%. Under the treatment of 2% modified biochar, the uptake of Pb and Cr by spinach decreased by 16.96% and 10.74% respectively. However, the combined application of modified biochar and organic fertilizer greatly reduced the uptake of Pb and Cr by spinach. Under the treatment of 0.5% modified biochar + 10% organic fertilizer, the uptake of Pb and Cr by spinach decreased by 15.75% and 17.86% respectively. Under the treatment of 1% modified biochar + 3% organic fertilizer, the uptake of Pb and Cr by spinach decreased by 29.86% and 32.52% respectively. Under the treatment of 2% modified biochar + 3% organic fertilizer, the uptake of Pb and Cr by spinach decreased by 33.62% and 39.86% respectively. The combined application of modified biochar and organic fertilizer can reduce the uptake of heavy metals lead and chromium by spinach. The main reasons can be analyzed from the following aspects: On the one hand, due to the rich pore structure and functional groups of modified biochar, these characteristics enable it to effectively adsorb heavy metal ions such as lead and chromium in the soil. Through the adsorption effect, modified biochar can fix heavy metal ions on its surface or pores, thereby reducing their concentration in the soil and further reducing the uptake of heavy metals by spinach. Organic fertilizer contains organic matter and various nutrient elements, which can promote the activities and metabolism of soil microorganisms, thus improving the soil structure and providing a better environment for the growth of spinach. On the other hand, modified biochar and organic fertilizer have a complementary effect in reducing the uptake of heavy metals by spinach. Modified biochar mainly reduces the concentration of heavy metals in the soil through adsorption and fixation, while organic fertilizer reduces the bioavailability of heavy metals by providing organic matter and nutrients and competing for adsorption sites. Through the combined application, modified biochar and organic fertilizer can jointly improve the soil environment, increase the fertility and quality of the soil, and provide better conditions for the growth of spinach. This improvement helps the healthy growth and development of spinach while reducing its uptake of heavy metals. In summary, the combined application of modified biochar and organic fertilizer can act together through multiple mechanisms to reduce the uptake of heavy metals lead and chromium by spinach.

[0079] As can be seen from the above embodiments, the present invention provides a heavy metal contaminated soil remediation material. Through the electron microscopy scanning of the modified biochar obtained in Examples 1 to 3, it can be seen that the biochar has a rough surface and a rich porous structure, with three-dimensional interconnectivity. And as the temperature increases, the surface of the biochar becomes rougher and even ruptures, and the pore structure also becomes disordered. This is because during the carbonization process of sunflower straw, due to the heat effect, a huge amount of heat will be rapidly generated inside, which is sufficient to break through the internal structure of the straw to form pores. As the pyrolysis temperature gradually increases, its pore structure will show a more complex and disordered state, the number of pores increases significantly, and the pore structure becomes more complex. This change leads to an increase in the surface roughness of the biochar, and thus its specific surface area increases significantly.

[0080] Figures 1 to 3 They are the BET diagrams of the modified biochar obtained in Examples 1 to 3 respectively. The pore size and pore structure have an important impact on the adsorption performance of biochar. The specific surface area test method (BET) analysis confirmed its pore size and pore structure. From Figures 1 to 3 it can be seen that especially in the rapid N2 adsorption stage under the relative pressure (P / P 0 0 to 0.08), it shows typical type I isotherm characteristics, indicating the existence of a large number of micropores. The specific surface area of the biochar material is 948.28 m 2 ·g -1 , the total pore volume is 0.45 cm 3 / g, and the average pore diameter is 2.38 nm. It is worth mentioning that the excellent pore structure is an important reason for the biochar to adsorb heavy metals.

[0081] Figure 4 They are the infrared spectra of the modified biochar obtained in Examples 1 to 3 respectively. FTIR spectroscopy characterization can further understand the surface bonding state and chemical environment of the biochar material. From Figure 4 it can be seen that the characteristic peaks at 1610 cm -1 , 1384 cm -1 and 1067 cm -1 correspond to aromatic C—C stretching (C—O stretching), alkane C—H bending and alkoxy C—O stretching vibrations respectively. A significant result shows that most of the carbon in the biochar substance is aromatic carbon. In addition, during the carbonization process, carbon is converted from alkyl carbon and carbonyl carbon to aromatic carbon, thus greatly enhancing the sp 2 structure of carbon atoms. This ensures that the biochar has stable properties and functional applications in soil remediation and carbon sequestration.

[0082] The present invention synthesizes biochar with a large specific surface area and good pore structure by using sunflower straw biomass raw materials, modifies it with silicon and magnesium to obtain a modified biochar material with strong adsorption performance, and finally successfully applies it in combination with organic fertilizer (chicken manure) to the remediation of lead- and chromium-contaminated soil. The experimental results show that the combined application of the modified biochar and the organic fertilizer can significantly improve the physical and chemical properties of the soil, has a good remediation effect on lead- and chromium-contaminated soil, the composite of the modified biochar and the organic fertilizer exhibits certain adsorption and fixation capabilities for heavy metals lead and chromium in the soil, can effectively reduce the content and availability of heavy metals in the soil, and the combined application of the modified biochar and the organic fertilizer can significantly reduce the absorption of lead and chromium by spinach. This composite is expected to be applied to the remediation of other heavy metal-contaminated soils.

[0083] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A heavy metal contaminated soil remediation material, characterized in that: Composed of components including modified biochar and organic fertilizer: The amount of modified biochar added is 0-2wt% of the soil mass, and the amount of organic fertilizer added is 0-10wt% of the soil mass, wherein the amount of modified biochar added is not 0; The modified biochar preparation method comprises: mixing straw powder and sodium silicate solution, performing hydrothermal reaction, and then sequentially adding magnesium chloride solution for impregnation and heat treatment.

2. A heavy metal contaminated soil remediation material according to claim 1, characterized in that: The straw powder includes sunflower straw powder, and the particle size of the straw powder is 0.1-0.3 mm.

3. A heavy metal contaminated soil remediation material according to claim 1 or 2, characterized in that: The concentration of the sodium silicate solution is 0.03-0.1M, and the dosage ratio of the straw powder to the sodium silicate solution is 5-15g:50-150mL.

4. The heavy metal contaminated soil remediation material according to claim 1, characterized in that: After the straw powder and the sodium silicate solution are mixed, the pH of the obtained material is adjusted to 4-6.

5. A heavy metal contaminated soil remediation material according to claim 1 or 4, characterized in that: The temperature of the hydrothermal reaction is 150-220° C., and the time of the hydrothermal reaction is 3-6 hours.

6. A heavy metal contaminated soil remediation material according to claim 5, characterized in that: The concentration of the magnesium chloride solution is 0.8-1.5M.

7. A heavy metal contaminated soil remediation material according to claim 1, 4 or 6, characterized in that: The heat treatment temperature is 400-600° C., and the heat treatment time is 3-6 hours.

8. The heavy metal contaminated soil remediation material according to claim 1, characterized in that: The pH of the modified biochar is 6 to 7.

5.

9. The heavy metal contaminated soil remediation material according to claim 1, characterized in that: The organic fertilizer includes chicken manure.

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