Composite soil remediation agent, preparation method and application thereof

Abstract

The application relates to the technical field of soil remediation, and particularly discloses a composite soil remediation agent, a preparation method and application thereof.A composite soil remediation agent comprises modified calcined oyster shell, plant biomass carbon, bone charcoal, compost, microbial preparation and ferrous sulfide; the preparation of the modified calcined oyster shell comprises the following steps: crushing, calcining oyster shell, and then adding a modified solution prepared from urea, rhamnolipid, iminodisuccinic acid tetrasodium and sodium dodecylbenzenesulfonate to modify the calcined oyster shell, so that the modified calcined oyster shell is obtained.The composite soil remediation agent can effectively adsorb and fix heavy metals in slightly heavy metal contaminated soil, reduce the mobility and bioavailability of the heavy metals, and thus reduce the harm of the heavy metals to soil and crops.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and in particular to a composite soil remediation agent, its preparation method, and its application. Background Technology

[0002] In recent years, with rapid economic and social development, many heavy metal pollutants have been generated. These pollutants accumulate in the soil through rainwater runoff, sewage irrigation, or atmospheric deposition, causing heavy metal pollution in the soil. Surveys show that soil heavy metal pollution is mainly composed of complex heavy metals, including lead, cadmium, mercury, arsenic, chromium, and nickel. Heavy metal pollution in soil, especially in arable land, not only affects crop growth but also poses a serious threat to human health through the food chain. Therefore, heavy metal contaminated soil remediation technology has become a key means to solve this problem.

[0003] Existing technologies for remediating heavy metal-contaminated soil can be broadly categorized into two types. One type involves separating the soil from the heavy metals, reducing their concentration. This approach includes methods such as phytoremediation, soil replacement, and electrodynamic remediation. However, these methods suffer from drawbacks such as high cost, low efficiency, long processing times, and potential secondary environmental pollution. The other type of heavy metal-contaminated soil remediation technology primarily aims to reduce the risk of heavy metal pollution by transforming the forms of heavy metals in the soil, thereby reducing their mobility and bioavailability. This approach can be further divided into agronomic regulation and passivation remediation. Agronomic regulation relies on precise field management, requiring specific planting techniques and potentially impacting crop yields. Passivation remediation, on the other hand, involves adding passivating agents to the soil, which adsorb, fix, and transform the heavy metals. Compared to other heavy metal-contaminated soil remediation technologies, passivation remediation offers advantages such as high efficiency, low risk, and ease of operation, making it a significant development direction in current heavy metal-contaminated soil remediation technologies.

[0004] However, passivation remediation methods place high demands on the stability of the soil remediation agents used. Some soil remediation agents, susceptible to chemical and biological influences, may exhibit poor stability, making it difficult to achieve stable binding with heavy metals. This results in weak passivation stability, leading to the reactivation or release of heavy metals, causing a re-increase in the bioavailability of heavy metals in the soil, and ultimately resulting in poor soil remediation outcomes. Therefore, developing a soil remediation agent with high stability and good passivation effect is of significant practical importance. Summary of the Invention

[0005] To improve the stability and passivation effect of soil remediation agents, this application provides a composite soil remediation agent, its preparation method, and its application. The composite soil remediation agent of this application, through modification of calcined oyster shells, specifically through a mixture of calcined oyster shells, urea, rhamnolipid, tetrasodium iminodisuccinate, and sodium dodecylbenzenesulfonate, can effectively adsorb and immobilize heavy metals in lightly contaminated soils, reducing their mobility and bioavailability, thereby mitigating the harm of heavy metals to soil and crops.

[0006] Firstly, the composite soil remediation agent provided in this application adopts the following technical solution:

[0007] A composite soil remediation agent comprises the following components in parts by weight: 30-50 parts modified calcined oyster shell, 10-20 parts plant biochar, 10-20 parts bone char, 10-20 parts compost, 5-10 parts microbial preparation, and 1-3 parts ferrous sulfide.

[0008] The preparation method of the modified calcined oyster shell includes the following steps:

[0009] s1: Clean, dry, and pulverize oyster shells into 0.2-0.5mm oyster shell powder;

[0010] s2: Calcine oyster shell powder at 500-700℃ for 2-4 hours to obtain calcined oyster shells;

[0011] s3: The calcined oyster shells and the modified solution were mixed at a mass ratio of 1:(8-12), stirred at 20-28℃ for 8-12 hours, and then centrifuged, washed and dried to obtain the modified calcined oyster shells.

[0012] The modified solution comprises the following components by weight percentage: 1%-3% urea, 0.5%-1% rhamnolipid, 0.05%-0.1% tetrasodium iminodisuccinate, 0.01%-0.05% sodium dodecylbenzenesulfonate, with the balance being water.

[0013] In the above technical solution, this application achieves efficient adsorption and fixation of heavy metals in the soil by modifying and calcining oyster shells, plant biochar, bone char, compost, microbial agents, and ferrous sulfide through the interaction of these raw materials, thereby improving soil fertility. By crushing and calcining oyster shells, the specific surface area is increased, the pore structure is enriched, and more adsorption sites are provided, thereby enhancing the adsorption capacity for heavy metals. Through the modification of calcined oyster shells, by blending calcined oyster shells, urea, rhamnolipids, tetrasodium iminodisuccinate, and sodium dodecylbenzenesulfonate, it not only helps to increase the soil pH value, thereby reducing the dissolution and migration of heavy metals, but also promotes the combination of composite soil remediation agents with heavy metals such as lead and cadmium to form stable complexes, reducing their toxicity and migration. At the same time, the blending of the five raw materials can also promote the growth of beneficial microorganisms and plants in the soil, thereby promoting plant growth and improving the soil environment.

[0014] Preferably, the microbial preparation is a mixture of Bacillus polymyxa and Bacillus fusiformis, wherein the mass ratio of Bacillus polymyxa to Bacillus fusiformis is 1:(1-2).

[0015] In the above technical solution, this application specifies that the microbial agents are Bacillus polymyxa and Bacillus fusiformis. Bacillus polymyxa and Bacillus fusiformis work synergistically to further stabilize soil pH, increase soil soluble carbonate content, further promote the co-precipitation and speciation of heavy metals and soluble carbonates, further stabilize heavy metals in the soil, and further reduce the absorption and accumulation of heavy metals by planted plants.

[0016] Preferably, the plant biochar is obtained by high-temperature pyrolysis of corn stalks, wheat stalks, rice straw, or sawdust.

[0017] Preferably, the method for preparing the plant biochar includes: first, cleaning and drying the plant raw materials, and then pyrolyzing them under anaerobic conditions at a temperature of 400-500℃ for 3-5 hours to obtain plant biochar.

[0018] In the aforementioned technical solution, this application uses corn stalks, wheat stalks, rice straw, or sawdust as raw materials and processes them through high-temperature pyrolysis to produce plant biochar. This plant biochar possesses a high specific surface area and abundant pore structure, providing more adsorption sites and thus enhancing its adsorption capacity for heavy metals. Furthermore, the addition of plant biochar helps improve the physical structure of the soil, increases soil aeration and water retention, and provides a favorable soil environment for plant growth.

[0019] Preferably, the method for preparing the bone char includes: first, cleaning and drying the pig bones, and then pyrolyzing them under anaerobic conditions at a temperature of 500-600℃ for 2-4 hours to obtain bone char.

[0020] In the above technical solution, this application uses pig bones as raw materials and prepares bone char through a specific pyrolysis process. The bone char can not only effectively adsorb heavy metals in the soil to form stable complexes, but also contains abundant organic minerals such as phosphorus and calcium. It can further precipitate or stabilize heavy metals in the soil through co-precipitation, thereby improving soil quality and promoting healthy plant growth.

[0021] Preferably, the method for preparing the compost includes: crushing agricultural waste into residue, fermenting it under aerobic conditions at a temperature of 30-50°C for 15-30 days to obtain compost.

[0022] In the above technical solution, this application uses agricultural waste such as straw, livestock and poultry manure, and green manure as raw materials to prepare compost through aerobic fermentation. The compost is rich in organic matter and microorganisms, which can improve the physical and chemical properties of the soil, increase soil fertility, and promote plant growth. At the same time, the microorganisms in the compost can participate in the decomposition of organic matter in the soil, further promoting the effective adsorption and fixation of heavy metals in the soil by the composite soil remediation agent, reducing its bioavailability and mobility, and further stabilizing the heavy metals in the soil.

[0023] Secondly, the preparation method of the composite soil remediation agent provided in this application adopts the following technical solution:

[0024] A method for preparing a composite soil remediation agent includes the following steps:

[0025] Step 1: Mix plant biochar, bone char and ferrous sulfide and ball mill them. Add modified calcined oyster shells during the ball milling process to obtain a mixture.

[0026] Step 2: Mix the mixture with compost and microbial agents evenly to obtain a composite soil remediation agent.

[0027] In the above technical solution, this application further improves the uniformity and activity of the composite soil remediation agent by mixing and ball milling plant biochar, bone char, ferrous sulfide and modified calcined oyster shells, and further increases the surface area of ​​the composite soil remediation agent, thereby increasing the contact area between the composite soil remediation agent and heavy metals in the soil, and improving the adsorption and fixation capacity of the remediation agent. This application can further improve the soil structure, promote the decomposition and transformation of organic matter in the soil, increase soil fertility and improve soil biological activity by further mixing compost and microbial agents.

[0028] Thirdly, the application of the composite soil remediation agent provided in this application adopts the following technical solution:

[0029] The application of a composite soil remediation agent involves adding the composite soil remediation agent to soil contaminated with heavy metals.

[0030] Preferably, the composite soil remediation agent is added to the heavy metal contaminated soil at a mass ratio of 1%-5%, and the moisture content of the heavy metal contaminated soil is controlled at 30%-60%.

[0031] In the above-mentioned technical solution, this application, by adding a composite soil remediation agent to lightly heavy metal-contaminated soil, can significantly improve the soil environment, enhance soil fertility, promote plant growth, and reduce the impact of heavy metals on human health through the food chain. This application further limits the addition ratio of the composite soil remediation agent to 1%-5% by mass, while controlling the soil moisture content between 30%-60%, which helps to ensure the uniform distribution of the remediation agent and achieve better remediation results.

[0032] In practical applications, the composite soil remediation agent of this application can be effectively applied to various types of soil with mild heavy metal contamination, such as farmland, industrial land, and areas surrounding mines. It can significantly reduce the concentration of heavy metals in the soil, reduce the impact of heavy metals on crop growth, and improve the physical and chemical properties of the soil, thereby increasing soil fertility and productivity. Furthermore, the composite soil remediation agent of this application also has the advantages of being easy to operate and environmentally friendly, and has broad application prospects and promotional value.

[0033] In summary, this application includes at least one of the following beneficial technical effects:

[0034] 1. This application improves soil pH by blending calcined oyster shells, urea, rhamnolipin, tetrasodium iminodisuccinate and sodium dodecylbenzenesulfonate, effectively promoting the adsorption and conversion of heavy metals by the composite soil remediation agent, and promoting plant growth and improving the soil environment.

[0035] 2. This application prepares a composite soil remediation agent by selecting specific raw materials. By mixing and ball milling modified calcined oyster shells, plant biochar, bone char, and ferrous sulfide, the adsorption capacity of the composite soil remediation agent for heavy metals is further enhanced. At the same time, the modification effect during the ball milling process improves the complexation and fixation efficiency of the remediation agent for heavy metals.

[0036] 3. This application further optimizes the soil microbial environment by adding compost and microbial agents, especially by adding Bacillus polymyxa and Bacillus fusiformis, promoting the growth and reproduction of beneficial microorganisms in the soil, stabilizing soil pH, increasing soil soluble carbonate content, further promoting the co-precipitation and speciation of heavy metals and soluble carbonates, further stabilizing heavy metals in the soil, and enhancing the soil's self-repair ability. Detailed Implementation

[0037] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0038] Example 1

[0039] A composite soil remediation agent comprises 30g modified calcined oyster shell, 20g plant biochar, 10g bone char, 10g compost, 5g microbial preparation, and 3g ferrous sulfide.

[0040] The method for preparing modified calcined oyster shells includes the following steps:

[0041] s1: Clean, dry, and crush the collected oyster shells, and sieve them to obtain oyster shell powder with a particle size between 0.2-0.5mm.

[0042] s2: Calcine oyster shell powder at 700℃ for 1 hour, and then calcine it at 600℃ for 1 hour to obtain calcined oyster shells.

[0043] s3: The calcined oyster shells and the modified solution were mixed at a mass ratio of 1:8, stirred at 20°C for 12 hours, and then centrifuged, washed, and dried to obtain the modified calcined oyster shells.

[0044] The modified solution was prepared by mixing and stirring 978.9g of water, 10g of urea, 10g of rhamnolipid, 1g of tetrasodium iminodisuccinate and 0.1g of sodium dodecylbenzenesulfonate.

[0045] The urea was purchased from Guangzhou Linlong Chemical Technology Co., Ltd.

[0046] Among them, rhamnolipin was purchased from Hubei Xinjiecheng Chemical Technology Co., Ltd.

[0047] Tetrasodium iminodisuccinate was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0048] Sodium dodecylbenzenesulfonate was purchased from Foshan Zhaojing Environmental Protection Technology Co., Ltd.

[0049] The method for preparing plant biochar includes: cleaning and drying collected corn stalks, and then pyrolyzing them under anaerobic conditions. The pyrolysis is first carried out at 500℃ for 2 hours, followed by pyrolysis at 450℃ for 1 hour to obtain plant biochar.

[0050] The method for preparing bone char includes: cleaning and drying pig bones, and then pyrolyzing them under anaerobic conditions. The bones are first pyrolyzed at 600℃ for 1 hour, and then at 550℃ for 1 hour to obtain bone char.

[0051] The compost preparation method includes: crushing the collected corn stalks into residue, allowing them to ferment naturally under aerobic conditions at a temperature of 50°C for 15 days, turning them over every 2 days during fermentation, and obtaining compost after fermentation.

[0052] The microbial preparation is made by mixing Bacillus polymyxa and Bacillus fusiformis in a mass ratio of 1:2.

[0053] Among them, Bacillus polymyxa is CGMCC1.15984, which is from the China General Microbiological Culture Collection Center.

[0054] Among them, Bacillus fusiformis is CGMCC1.10306, a strain of Bacillus fusiformis from the China General Microbiological Culture Collection Center.

[0055] The preparation method of the composite soil remediation agent includes the following steps:

[0056] Step 1: Mix plant biochar, bone char and ferrous sulfide and ball mill. During the ball milling process, gradually add modified calcined oyster shells. After adding all the shells, continue ball milling until the fineness is below 100 mesh to obtain a mixture.

[0057] Step 2: Mix the mixture with compost and microbial agents evenly to obtain a composite soil remediation agent.

[0058] Ferrous sulfide was purchased from Guangdong Fangxin Biotechnology Co., Ltd.

[0059] Example 2

[0060] A composite soil remediation agent, which differs from Example 1, includes 40g of modified calcined oyster shells, 15g of plant biochar, 15g of bone char, 15g of compost, 7g of microbial preparation, and 2g of ferrous sulfide.

[0061] The method for preparing modified calcined oyster shells includes the following steps:

[0062] s1: Clean, dry, and crush the collected oyster shells, and sieve them to obtain oyster shell powder with a particle size between 0.2-0.5mm.

[0063] s2: Oyster shell powder is calcined at 650℃ for 1.5h, and then calcined at 550℃ for 1.5h to obtain calcined oyster shells.

[0064] s3: The calcined oyster shells and the modification solution were mixed at a mass ratio of 1:10, stirred at 26℃ for 10 h, and then centrifuged, washed and dried to obtain the modified calcined oyster shells.

[0065] The modified solution was prepared by mixing and stirring 970.8g of water, 20g of urea, 8g of rhamnolipid, 0.8g of tetrasodium iminodisuccinate and 0.4g of sodium dodecylbenzenesulfonate.

[0066] The method for preparing plant biochar includes: cleaning and drying collected corn stalks, and then pyrolyzing them under anaerobic conditions. The pyrolysis is first carried out at 500℃ for 2 hours, followed by pyrolysis at 400℃ for 1 hour to obtain plant biochar.

[0067] The method for preparing bone char includes: cleaning and drying pig bones, and then pyrolyzing them under anaerobic conditions. The bones are first pyrolyzed at 550℃ for 2 hours, and then at 500℃ for 1 hour to obtain bone char.

[0068] The compost preparation method includes: crushing the collected corn stalks into residue, allowing them to ferment naturally under aerobic conditions at a temperature of 40°C for 20 days, turning them over every 3 days during fermentation, and obtaining compost after fermentation.

[0069] The microbial preparation is made by mixing Bacillus polymyxa and Bacillus fusiformis in a 1:1 mass ratio.

[0070] The preparation method of the composite soil remediation agent includes the following steps:

[0071] Step 1: Mix plant biochar, bone char and ferrous sulfide and ball mill. During the ball milling process, gradually add modified calcined oyster shells. After adding all the shells, continue ball milling until the fineness is below 100 mesh to obtain a mixture.

[0072] Step 2: Mix the mixture with compost and microbial agents evenly to obtain a composite soil remediation agent.

[0073] Example 3

[0074] A composite soil remediation agent, which differs from Example 1, comprises 50g of modified calcined oyster shell, 10g of plant biochar, 20g of bone char, 20g of compost, 10g of microbial preparation, and 1g of ferrous sulfide.

[0075] The method for preparing modified calcined oyster shells includes the following steps:

[0076] s1: Clean, dry, and crush the collected oyster shells, and sieve them to obtain oyster shell powder with a particle size between 0.2-0.5mm.

[0077] s2: Oyster shell powder is calcined at 600℃ for 2 hours, and then calcined at 500℃ for 2 hours to obtain calcined oyster shells.

[0078] s3: The calcined oyster shells and the modified solution were mixed at a mass ratio of 1:12, stirred at 28°C for 8 hours, and then centrifuged, washed, and dried to obtain the modified calcined oyster shells.

[0079] The modified solution is prepared by mixing and stirring 964g of water, 30g of urea, 5g of rhamnolipid, 0.5g of tetrasodium iminodisuccinate and 0.5g of sodium dodecylbenzenesulfonate.

[0080] The method for preparing plant biochar includes: cleaning and drying collected corn stalks, and then pyrolyzing them under anaerobic conditions. The pyrolysis is first carried out at 450℃ for 3 hours, followed by pyrolysis at 400℃ for 2 hours to obtain plant biochar.

[0081] The method for preparing bone char includes: cleaning and drying pig bones, and then pyrolyzing them under anaerobic conditions. First, pyrolyze at 550℃ for 2 hours, then at 500℃ for 2 hours to obtain bone char.

[0082] The compost preparation method includes: crushing the collected corn stalks into residue, allowing them to ferment naturally under aerobic conditions at a temperature of 30°C for 30 days, turning them over every 4 days during fermentation, and obtaining compost after fermentation.

[0083] The microbial preparation is made by mixing Bacillus polymyxa and Bacillus fusiformis in a 1:1 mass ratio.

[0084] The preparation method of the composite soil remediation agent includes the following steps:

[0085] Step 1: Mix plant biochar, bone char and ferrous sulfide and ball mill. During the ball milling process, gradually add modified calcined oyster shells. After adding all the shells, continue ball milling until the fineness is below 100 mesh to obtain a mixture.

[0086] Step 2: Mix the mixture with compost and microbial agents evenly to obtain a composite soil remediation agent.

[0087] Example 4

[0088] A composite soil remediation agent differs from Example 1 in that the preparation method of the composite soil remediation agent differs in step 1.

[0089] Step 1 in the preparation method of the composite soil remediation agent is as follows:

[0090] Plant biochar, bone char, and ferrous sulfide are mixed and ball-milled until the fineness is below 100 mesh. Modified calcined oyster shells are then added and stirred evenly to obtain a mixture.

[0091] Example 5

[0092] A composite soil remediation agent, which differs from Example 1 in that Bacillus polymyxa is replaced with an equal amount of Bacillus licheniformis.

[0093] Among them, Bacillus licheniformis is CGMCC1.10314 Bacillus licheniformis from the China General Microbiological Culture Collection Center.

[0094] Example 6

[0095] A composite soil remediation agent, which differs from Example 1 in that Bacillus fusiformis is replaced in equal amounts with Bacillus subtilis.

[0096] Among them, Bacillus subtilis is CGMCC1.8801 Bacillus subtilis from the China General Microbiological Culture Collection Center.

[0097] Comparative Example 1

[0098] A composite soil remediation agent, which differs from Example 1 in that ferrous sulfide is replaced by an equal amount of calcium hydroxide.

[0099] Comparative Example 2

[0100] A composite soil remediation agent, which differs from Example 1 in that bone char is replaced with an equal amount of plant biochar.

[0101] Comparative Example 3

[0102] A composite soil remediation agent, which differs from Example 1 in that plant biochar is replaced with an equal amount of bone char.

[0103] Comparative Example 4

[0104] A composite soil remediation agent, which differs from Example 1 in that the urea used in the preparation of modified calcined oyster shells is replaced with an equal amount of ammonium nitrate.

[0105] Comparative Example 5

[0106] A composite soil remediation agent, which differs from Example 1 in that the rhamnolipid used in the preparation of the modified calcined oyster shell is replaced with an equal amount of sodium gluconate.

[0107] Comparative Example 6

[0108] A composite soil remediation agent, which differs from Example 1 in that the tetrasodium iminodisuccinate used in the preparation of modified calcined oyster shells is replaced with an equal amount of sodium citrate.

[0109] Comparative Example 7

[0110] A composite soil remediation agent, which differs from Example 1 in that sodium dodecylbenzenesulfonate used in the preparation of modified calcined oyster shells is replaced with an equal amount of sodium dodecyl sulfate.

[0111] Performance testing

[0112] Test samples: Composite soil remediation agents of the above-described embodiments and comparative examples.

[0113] Test soil: Topsoil of farmland in a certain area, with a pH of 7.3. After testing, the total lead content was found to be 510.61 mg / kg, the available lead content was 264.57 mg / kg, the total cadmium content was 4.2 mg / kg, and the available cadmium content was 1.73 mg / kg. The test sample was evenly spread on the surface of the corresponding test soil at a 5% addition ratio. The soil was then gently turned over to ensure thorough mixing. No test sample was applied to the blank control group. Finally, water was added until the soil moisture content reached 45%-50%.

[0114] The experimental plant was ryegrass. Before the experiment, ryegrass seeds were evenly sown in uncontaminated soil, with a sowing amount of 10g per pot. After sowing, the soil was thoroughly watered and kept moist. The potted plants were then cultivated in a well-lit and well-ventilated environment at room temperature. When the ryegrass reached four weeks of growth, it was transplanted into experimental soils containing different experimental samples.

[0115] Experimental method: After applying the remediation agent, continue to cultivate ryegrass under the above conditions, water regularly, and maintain the soil moisture content at 45%-50%.

[0116] Test 1: When the ryegrass grows to 12 weeks, the above-ground parts of the ryegrass are collected, dried to constant weight, ground into powder, digested by HNO3-HClO4 method, and then the cadmium and lead content of the plants is determined by ICP-MS inductively coupled plasma mass spectrometry.

[0117] Test 2: Soil samples were taken at 8 and 12 weeks of ryegrass growth, respectively. The soil pH was measured, and the samples were dried to constant weight. The soil was digested using the HCl-HNO3-HClO4-HF method, and the cadmium and lead content in the soil was determined by ICP-MS inductively coupled plasma mass spectrometry. The cadmium and lead removal rates (%) were calculated as follows: Removal rate (%) = [(Blank control group detection value - Experimental group detection value) / Blank control group detection value] * 100%.

[0118] The test results are shown in Table 1.

[0119]

[0120] Specifically, based on the heavy metal content analysis of ryegrass in Examples 1-6 and Comparative Examples 1-7, no cadmium was detected in the ryegrass plants of Examples 1-6 after 12 weeks of growth, and no lead was detected in the ryegrass plants of Examples 1-3 after 12 weeks of growth. This indicates that the composite soil remediation agent of this application can effectively prevent the accumulation of heavy metals in plants. Further analysis of soil pH shows that the soil pH of Examples 1-4 showed a stable upward trend, indicating that the composite soil remediation agent of this application has a regulatory effect on soil pH, which helps to improve the soil's self-repair capacity. Further analysis of cadmium and lead removal rates in the soil shows that the composite soil remediation agent of this application exhibits a significant effect in improving the removal efficiency of heavy metals in the soil.

[0121] Specifically, based on the analysis of Example 1 and Comparative Examples 1-3, the difference between Comparative Examples 1-3 and Example 1 lies in the replacement of ferrous sulfide, plant biochar, and bone char, respectively. Example 1 has a good effect on removing cadmium and lead. It can be seen that adding ferrous sulfide, plant biochar, and bone char to the composite soil remediation agent has a significant impact on improving the performance of the composite soil remediation agent. Only when these factors work together can the remediation effect of the composite soil remediation agent on heavy metal contaminated soil be further improved.

[0122] Specifically, combining the analysis of Example 1 and Comparative Examples 4-7, the difference between Comparative Examples 4-7 and Example 1 lies in the replacement of urea, rhamnolipin, tetrasodium iminodisuccinate, and sodium dodecylbenzenesulfonate, respectively. Example 1 demonstrates good removal effects of cadmium and lead. It is evident that adding calcined oyster shells modified with urea, rhamnolipin, tetrasodium iminodisuccinate, and sodium dodecylbenzenesulfonate to the composite soil remediation agent plays an important role. Only by adding modified calcined oyster shells modified with urea, rhamnolipin, tetrasodium iminodisuccinate, and sodium dodecylbenzenesulfonate to the composite soil remediation agent can the accumulation of heavy metals in plants be effectively prevented, the soil pH value be adjusted, the soil self-repair capacity be improved, and the removal efficiency of heavy metals in the soil be significantly improved.

[0123] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A composite soil remediation agent, characterized by, Comprise the following components by weight: 30-50 parts of modified calcined oyster shell, 10-20 parts of plant biomass charcoal, 10-20 parts of bone charcoal, 10-20 parts of compost, 5-10 parts of microbial preparation, 1-3 parts of ferrous sulfide; The preparation method of the modified calcined oyster shell comprises the following steps: s1: clean, dry and crush the oyster shell to 0.2-0.5mm oyster shell powder; s2: calcine the oyster shell powder at a temperature of 500-700℃ for 2-4h to obtain calcined oyster shell; s3: mix the calcined oyster shell with a modified solution at a mass ratio of 1:(8-12), stir at 20-28℃ for 8-12h, centrifuge, wash and dry to obtain the modified calcined oyster shell; The modified solution comprises the following components by weight percentage: 1%-3% urea, 0.5%-1% rhamnolipid, 0.05%-0.1% tetrasodium iminodisuccinate, 0.01%-0.05% sodium dodecyl benzene sulfonate, and the balance is water; The plant biomass charcoal is corn straw, wheat straw, rice straw or sawdust prepared by high-temperature pyrolysis; The preparation method of the plant biomass charcoal comprises: first cleaning and drying the plant raw material, and then pyrolyzing under anaerobic conditions, with a pyrolysis temperature of 400-500℃ and a pyrolysis time of 3-5h to obtain the plant biomass charcoal; The preparation method of the bone charcoal comprises: first cleaning and drying the pig bone, and then pyrolyzing under anaerobic conditions, with a pyrolysis temperature of 500-600℃ and a pyrolysis time of 2-4h to obtain the bone charcoal; The microbial preparation is a mixture of Paenibacillus polymyxa and Lysinibacillus fusiformis, and the mass ratio of Paenibacillus polymyxa to Lysinibacillus fusiformis is 1:(1-2).

2. The composite soil amendment of claim 1, wherein, The preparation method of the compost comprises: crushing the agricultural waste into dregs, and fermenting under aerobic conditions, with a fermentation temperature of 30-50℃ and a fermentation time of 15-30d to obtain the compost.

3. A method of preparing the composite soil amendment of any one of claims 1-2, wherein, Comprise the following steps: Step 1: mix and ball mill the plant biomass charcoal, bone charcoal and ferrous sulfide, and add the modified calcined oyster shell during the ball milling process to obtain a mixture; Step 2: mix the mixture with the compost and microbial preparation uniformly to obtain the composite soil remediation agent.

4. Use of a composite soil conditioner as claimed in any one of claims 1 to 2, characterised in that, Add the composite soil remediation agent to the heavy metal contaminated soil.

5. Use of a composite soil conditioner according to claim 4, characterized in that, The addition mass ratio of the composite soil remediation agent in the heavy metal contaminated soil is 1%-5%, and the water content of the heavy metal contaminated soil is controlled at 30%-60%.

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