Contaminated soil remediation agent, preparation method thereof and soil remediation method

Abstract

The invention relates to the field of contaminated soil remediation, in particular to a contaminated soil remediation agent, a preparation method thereof and a soil remediation method. The contaminated soil remediation agent comprises a micro-nano iron-based material, an auxiliary material and an oxidizing agent, the micro-nano iron-based material is prepared through heteroatomization modification, carbon doping modification and antioxidant modification. The auxiliary materials comprise a liquid-phase reducing agent, an iron-cycle-based strengthening auxiliary material and a solubilizing and desorbing surfactant. According to the remediation agent disclosed by the invention, through mutual cooperation of the micro-nano iron-based material, the auxiliary material and the oxidizing agent, the capability of decomposing organic pollutants is improved, and the remediation effect on contaminated soil in the ferrous metallurgy industry is improved.

Description

Technical Field

[0001] The present application relates to the field of contaminated soil remediation, and in particular to a contaminated soil remediation agent, a preparation method thereof, and a soil remediation method. Background Art

[0002] The organic solid pollutants generated by the steel and metallurgical industry during the long-term production process are mainly PAHs, including benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluoranthene, indeno(1,2,3-cd)pyrene and dibenzo(a,h)anthracene. The highest excess of the standard is more than 200 times. The industry has many types, long storage time and high pollution level.

[0003] The contaminated sites caused by the steel and metallurgical industry are characterized by high concentrations and complex types of pollutants. Biological remediation technology and physical thermal desorption technology are difficult to cope with, and chemical degradation technology has become the preferred alternative technology.

[0004] The mainstream technology for chemical oxidation remediation is advanced oxidation technology (ADT). This utilizes a series of physical and chemical interactions to generate highly active free radicals within the system, oxidizing and decomposing recalcitrant organic pollutants into small molecules. Reduction-catalytic functional materials are at the core of chemical redox technology. Iron-based materials, such as zero-valent iron and ferrous minerals, are key persulfate activation technologies. These materials are environmentally friendly, inexpensive, highly oxidative, and have a wide range of applications. They have already been used in industrial water treatment and groundwater remediation.

[0005] Due to its strong reducing properties, zero-valent iron (ZVI) is the most widely used remediation material in chemical redox remediation technology. Early large-particle ZVI was primarily used to construct permeable reaction walls through a dig-and-fill method, passively reducing the groundwater contamination plume flowing through the permeable reaction walls. Reducing the ZVI particle size to the nanoscale theoretically not only increases its reactivity but also allows it to flow through the pores of aqueous media, actively attacking pollutants. However, nano-ZVI tends to aggregate and grow, reducing its activity and mobility. Furthermore, during the catalytic process, its surface undergoes passivation, reducing the reaction rate. Furthermore, it undergoes intense side reactions with water molecules, significantly limiting its application in soil pollution control.

[0006] In order to solve the above problems, technicians have adopted methods such as fixing nano-zero-valent iron on a carrier with a large specific surface area, strong mechanical properties, adsorption properties and thermal stability to make loaded nano-zero-valent iron or adding surfactants.

[0007] Regarding the above-mentioned related technologies, the applicant found that soil particles have a strong binding ability for organic pollutants. Due to the adsorption effect of soil particles, highly hydrophobic organic pollutants such as PAHs are difficult to effectively contact oxidants and catalysts at the microscopic level, resulting in low reaction activity and thus a low pollutant degradation rate. Summary of the Invention

[0008] In order to improve the remediation effect of contaminated soil in the steel and metallurgical industry, the present application provides a contaminated soil remediation agent, a preparation method thereof, and a soil remediation method.

[0009] In a first aspect, the present application provides a contaminated soil remediation agent, which adopts the following technical solution.

[0010] A contaminated soil remediation agent, comprising a micro-nano iron-based material, an auxiliary material and an oxidant; The micro-nano iron-based material is prepared by heteroatom modification, carbon doping modification and anti-oxidation modification; The auxiliary materials are a liquid phase reducing agent, an iron cycle-based strengthening auxiliary material, and a solubilizing and desorption surfactant.

[0011] Through the above technical solution, the micro-nano iron-based materials prepared through heteroatomization, carbon doping, and antioxidant modification have unique microstructures and physical and chemical properties. The introduction of heteroatoms can change the material's electron cloud distribution, enhance its ability to activate oxidants, and produce more highly oxidizing free radicals, such as sulfate and hydroxyl radicals, which can rapidly oxidize and decompose organic pollutants in the soil. Carbon doping can improve the material's conductivity and stability, promote electron transfer, and accelerate the redox reaction rate. Antioxidant modification prevents the micro-nano iron-based materials from rapid oxidation and deactivation in the soil environment, ensuring their continued catalytic activity.

[0012] Liquid-phase reducing agents can provide electrons to iron-based materials, promoting the circulation of iron ions and maintaining a high level of activity. Iron-cycle-based reinforcing auxiliary materials can replenish iron sources, stabilize the presence of iron ions, and maintain the efficient operation of the iron cycle. Solubilizing and desorption surfactants can reduce the surface tension between soil particles and organic pollutants, making it easier for organic pollutants to desorb from the soil particle surface into the liquid phase. This increases the contact between organic pollutants and micro-nano iron-based materials and oxidants, thereby improving remediation efficiency.

[0013] In the advanced oxidation technology of organically contaminated soil, the use of oxidants and catalysts is one of the key factors restricting the application of this technology. The development of amphiphilic high-mass-transfer micro-nano agents and the research and development of auxiliary enhanced PAHs desorption technology and iron cycle regulation technology have overcome this bottleneck problem. At the same time, it has solved problems such as the difficulty of oxidants being activated during the remediation process, the inability of oxidants to accurately reach the target depth and distance, the limited diffusion area of the agents, uneven soil mixing, large amounts of oxidants used, and long reaction times.

[0014] Furthermore, the preparation method of the micro-nano iron-based material is: 1) Ball milling pretreatment Industrial zero-valent iron powder, heteroatom source, and carbon source are mixed and ground to a particle size of 150-200 nm. 2) High temperature carbonization and heteroatom doping The ground material obtained in 1) is heated to 550-650°C and kept at this temperature for 2 hours; then the temperature is further raised to 750-850°C and kept at this temperature for 1 hour to obtain a carbonized material; 3) Antioxidant surface modification The carbonized material was immersed in a polyvinyl pyrrolidone solution, ultrasonically treated for 30 minutes, and then dried to obtain a micro-nano iron-based material.

[0015] Furthermore, the heteroatom source is a mixture of thiourea and sodium phosphate in a weight ratio of 3:1; and the carbon source is glucose.

[0016] By employing this technical solution, thiourea molecules contain sulfur and nitrogen atoms, which can be incorporated into the iron-based material's crystal lattice as heteroatoms. Based on the principle of elemental doping, the introduction of sulfur alters the electron cloud distribution of the iron-based material. From a crystal structure perspective, the radius of sulfur atoms differs from that of iron atoms. Doping causes lattice distortion and creates lattice defects, which serve as active sites for the adsorption and activation of oxidant molecules. Sodium phosphate provides phosphorus, which can also integrate into the iron-based material's crystal lattice. Phosphorus doping further modifies the material's electronic structure and enhances its stability. Phosphorus atoms form chemical bonds with iron atoms, improving the material's thermal and chemical stability and mitigating deactivation of the micro-nano iron-based material in soil environments due to oxidation and hydrolysis. Furthermore, the presence of phosphorus optimizes the charge distribution on the material's surface, enhancing its adsorption of oppositely charged pollutants in the soil. For example, negatively charged organic pollutants are more likely to accumulate on the material's surface through electrostatic interactions, increasing the probability of reaction and thus improving remediation efficiency.

[0017] Under the ratio of this application, the two heteroatoms of sulfur and phosphorus achieve a good synergistic doping effect in the lattice of the iron-based material. The sulfur atoms introduce more active sites, while the phosphorus atoms ensure the stability of the material. The two cooperate with each other to ensure that the material has high activity to efficiently degrade pollutants, and maintain the stability of the material in complex soil environments, so that it can continue to play a repair role.

[0018] Furthermore, the weight ratio of the heteroatom source to the industrial zero-valent iron powder is 1:(8-15), and the weight ratio of the carbon source to the industrial zero-valent iron powder is 1:(8-12).

[0019] Furthermore, the liquid-phase reducing agent is a mixture of ascorbic acid, sodium sulfite and oxalic acid in a weight ratio of 1:(2-3):(1-2).

[0020] By employing this technical solution, ascorbic acid exhibits strong reducing properties. In soil remediation systems, it can rapidly reduce high-valent iron ions generated by oxidation on the surface of iron-based materials to ferrous ions. Ferrous ions are the key active species that activate oxidants in iron-based materials. Ascorbic acid continuously supplies ferrous ions, maintaining the high activity of iron-based materials and promoting the production of more highly oxidizing free radicals and hydroxyl radicals by oxidants, effectively degrading organic pollutants in the soil.

[0021] Sodium sulfite can not only reduce iron ions, but also react with oxides on the surface of iron-based materials, remove the surface oxide layer, and expose the active sites inside the iron-based materials. The presence of sodium sulfite helps to stabilize the ferrous ions on the surface of iron-based materials, reduce the possibility of their re-oxidation, extend the service life of iron-based materials, and enhance their stability during soil remediation.

[0022] Oxalic acid forms a stable complex with iron ions. This complexation alters the iron ions' form, increasing their solubility in soil solutions and enhancing their mobility. This facilitates their contact with pollutants and promotes redox reactions. Furthermore, this complexation modulates the iron ions' redox potential, making them more readily involved in the iron cycle and further enhancing the activity of iron-based materials. When treating soils contaminated with both heavy metals and PAHs, oxalic acid not only enhances the PAH degradation efficiency of iron-based materials but also promotes the activation and removal of heavy metals through complexation.

[0023] Within the ratio range specified in this application, ascorbic acid provides rapid initial reducing ability, sodium sulfite continuously and stably reduces the surface of iron-based materials and enhances their stability, and oxalic acid regulates the form and redox potential of iron ions through complexation. The three work together to give full play to their respective advantages, maximize the activity and stability of iron-based materials, and ensure that the soil remediation process is efficient and continuous.

[0024] Furthermore, the iron cycle-based strengthening auxiliary material is a mixture of iron-containing minerals and iron chelating agents in a weight ratio of 1:(3-5).

[0025] By adopting the above technical solution, iron-containing minerals are important participants in the iron cycle. During the soil remediation process, the ferrous ions inside them can be oxidized under certain conditions, continuously replenishing ferrous ions for iron-based materials and the entire remediation system. From the perspective of chemical reactions, pyrite will undergo oxidation reactions under the action of dissolved oxygen and microorganisms in the soil, releasing ferrous ions. These ferrous ions are the key to activating oxidants in iron-based materials to produce strong oxidizing free radicals, thereby maintaining the ability to continuously oxidize and degrade organic pollutants PAHs in the soil.

[0026] Iron chelators form stable chelates with iron ions. In the soil environment, they regulate the activity and form of iron ions, preventing them from precipitating or becoming fixed in the soil. They also enhance their mobility and make them more readily involved in the iron cycle. Iron chelators also control the release rate of iron ions, preventing the rapid oxidation or loss of ferrous ions and ensuring the stability of the iron cycle.

[0027] Within the specified ratios in this application, iron minerals provide an ample source of iron, while iron chelators effectively stabilize iron ions and promote their migration and circulation. Iron chelators can effectively encapsulate ferrous ions released by iron-containing minerals, preventing them from excessive oxidation and precipitation, ensuring the effective concentration of iron ions in the soil and more precisely regulating the activity and distribution of iron ions. This synergistic effect ensures the efficient and stable circulation of iron, continuously providing power for soil remediation.

[0028] Furthermore, the weight ratio of the liquid-phase reducing agent, the iron cycle-based strengthening auxiliary material and the solubilizing and desorption surfactant is 2: (2-4): (4-6), and the weight ratio of the micro-nano iron-based material, the auxiliary material and the oxidant is 2: 3: 5.

[0029] In a second aspect, the present application provides a method for preparing a contaminated soil remediation agent, which adopts the following technical solution.

[0030] A method for preparing a contaminated soil remediation agent comprises the following steps: The micro-nano iron-based material, auxiliary materials and oxidant are mixed to obtain a contaminated soil remediation agent.

[0031] In a third aspect, the present application provides a method for remediating contaminated soil, which adopts the following technical solution.

[0032] A contaminated soil remediation method uses any of the above-mentioned contaminated soil remediation agents to remediate soil at PAHs-contaminated sites in the steel and metallurgical industry.

[0033] In summary, this application has the following beneficial effects: This application adopts micro-nano iron-based materials, auxiliary materials and oxidants as contaminated soil remediation agents. The micro-nano iron-based materials are modified by heteroatomization, carbon doping and antioxidant modification. The introduction of heteroatoms can change the electron cloud distribution of the material, enhance its activation ability to oxidants, and produce more free radicals with strong oxidizing properties, such as sulfate radicals and hydroxyl radicals. These free radicals can quickly oxidize and decompose organic pollutants in the soil. Carbon doping can improve the conductivity and stability of the material, promote electron transfer, and accelerate the redox reaction rate. Antioxidant modification prevents the micro-nano iron-based materials from being rapidly oxidized and inactivated in the soil environment, ensuring their continued catalytic activity. The auxiliary materials provide electrons, supplement iron sources, solubilize, etc. through iron-based materials, further stimulating the decomposition of organic matter by micro-nano iron-based materials and improving the remediation efficiency. DETAILED DESCRIPTION

[0034] The present application is further described in detail below with reference to the embodiments.

[0035] Preparation examples of raw materials and intermediates raw material The raw materials in the examples of this application can be obtained commercially: oxidizing agents, persulfates; Industrial zero-valent iron powder, particle size 40-50μm, iron content ≥80%; Thiourea, chemically pure ≥99%; Sodium phosphate, analytical grade ≥98%; Glucose, food grade; polyvinylpyrrolidone solution, 5 wt%; Ascorbic acid, analytical grade ≥98%; Sodium sulfite, analytical grade ≥98%; Oxalic acid, analytical grade ≥98%; iron-bearing mineral, pyrite; iron chelator, EDTA; Chemical surfactant, nonionic surfactant Triton X-100; biosurfactant, rhamnolipid; Micro-nano biochar, corn straw biochar, the average particle size of the nano-scale part is about 80nm, the average particle size of the micron-scale part is about 2.5μm, and the specific surface area is 500m² / g.

[0036] Preparation Example Preparation Example 1 A micro-nano iron-based material, the preparation method of which is as follows: 1) Ball milling pretreatment Industrial zero-valent iron powder, a heteroatom source, and a carbon source were mixed and ground using a planetary ball mill (zirconia balls, a ball-to-material ratio of 10:1) at 400 rpm for 24 hours, resulting in a particle size of 150-200 nm. The industrial zero-valent iron powder was 100 kg, the weight ratio of the heteroatom source to the industrial zero-valent iron powder was 1:12, and the weight ratio of the carbon source to the industrial zero-valent iron powder was 1:10. The heteroatom source was a mixture of thiourea and sodium phosphate in a weight ratio of 3:1. The carbon source was glucose. 2) High-temperature carbonization and heteroatom doping In a tube furnace, under nitrogen protection, the ground material obtained in 1) was heated to 600°C at a heating rate of 5°C / min and kept at this temperature for 2 hours; then the temperature was further raised to 800°C and kept at this temperature for 1 hour to obtain a carbonized material; ‌3) Antioxidant surface modification‌ The carbonized material was completely immersed in a polyvinyl pyrrolidone solution, ultrasonically treated for 30 minutes, and then vacuum dried at 60°C for 12 hours to obtain a micro-nano iron-based material.

[0037] Preparation Example 2 Different from Preparation Example 1, in Preparation Example 2, the weight ratio of the heteroatom source to the industrial zero-valent iron powder is 1:15, and the weight ratio of the carbon source to the industrial zero-valent iron powder is 1:8.

[0038] Preparation Example 3 Different from Preparation Example 1, in Preparation Example 3, the weight ratio of the heteroatom source to the industrial zero-valent iron powder is 1:8, and the weight ratio of the carbon source to the industrial zero-valent iron powder is 1:12.

[0039] Preparation Example 4 Different from Preparation Example 1, the heteroatom source in Preparation Example 4 is a mixture of thiourea and sodium phosphate in a weight ratio of 1:3.

[0040] Preparation Example 5 Different from Preparation Example 1, the heteroatom source in Preparation Example 5 is thiourea.

[0041] Preparation Example 6 Different from Preparation Example 1, the heteroatom source in Preparation Example 6 is sodium phosphate.

[0042] Example Example 1

[0043] A contaminated soil remediation agent, the preparation method of which is as follows: 200 kg of micro-nano iron-based materials, 300 kg of auxiliary materials and 500 kg of oxidants were mixed to obtain a contaminated soil remediation agent.

[0044] The micro-nano iron-based material comes from Preparation Example 1; the auxiliary materials include a liquid-phase reducing agent with a weight ratio of 2:3:5, an enhanced auxiliary material based on iron circulation, and a solubilizing and desorption surfactant; the liquid-phase reducing agent is a mixture of ascorbic acid, sodium sulfite and oxalic acid with a weight ratio of 1:2:2, a mixture of iron-containing minerals and iron chelating agents with a weight ratio of 1:4 based on the enhanced auxiliary material of iron circulation, and the solubilizing and desorption surfactant is a mixture of chemical surfactants, biological surfactants and micro-nano biochar with a weight ratio of 2:3:4; the oxidant is persulfate.

[0045] Examples 2-6 Different from Example 1, the micro-nano iron-based materials in Examples 2-6 come from Preparation Examples 2-6 respectively.

[0046] Example 7 Different from Example 1, the auxiliary materials in Example 7 include a liquid-phase reducing agent, an iron cycle-based reinforcing auxiliary material, and a solubilizing and desorption surfactant in a weight ratio of 2:4:4.

[0047] Example 8 Different from Example 1, the auxiliary materials in Example 8 include a liquid-phase reducing agent, an iron cycle-based reinforcing auxiliary material, and a solubilizing and desorption surfactant in a weight ratio of 5:3:2.

[0048] Example 9 Different from Example 1, the liquid-phase reducing agent in Example 9 is a mixture of ascorbic acid and oxalic acid in a weight ratio of 1:2.

[0049] Example 10 Different from Example 1, the liquid phase reducing agent in Example 10 is ascorbic acid.

[0050] Example 11 Different from Example 1, the strengthening auxiliary material based on the iron cycle in Example 11 is a mixture of iron-containing minerals and iron chelating agents at a ratio of 1:5.

[0051] Example 12 Different from Example 1, the strengthening auxiliary material based on the iron cycle in Example 12 is a mixture of iron-containing minerals and iron chelating agents at a ratio of 4:1.

[0052] Example 13 Different from Example 1, the solubilizing and desorption surfactant in Example 13 is a mixture of a chemical surfactant and micro-nano biochar in a weight ratio of 2:3.

[0053] Example 14 Different from Example 1, the solubilizing and desorption surfactant in Example 14 is a mixture of a chemical surfactant and a biological surfactant in a weight ratio of 2:3:4.

[0054] Comparative Example Comparative Example 1 The difference from Example 1 is that in Comparative Example 1, the auxiliary material is replaced by an equal amount of micro-nano iron-based material.

[0055] Comparative Example 2 Different from Example 1, the auxiliary material in Comparative Example 2 is a liquid-phase reducing agent.

[0056] Comparative Example 3 Different from Example 1, the auxiliary material in Comparative Example 3 is a strengthening auxiliary material based on iron circulation.

[0057] Comparative Example 4 Different from Example 1, the auxiliary material in Comparative Example 4 is a solubilizing and desorption surfactant.

[0058] Comparative Example 5 Different from Example 1, the auxiliary material in Comparative Example 5 includes a liquid-phase reducing agent and an iron cycle-based strengthening auxiliary material in a weight ratio of 2:3.

[0059] Comparative Example 6 Different from Example 1, the auxiliary materials in Comparative Example 6 include a liquid-phase reducing agent and a solubilizing and desorption surfactant in a weight ratio of 2:5.

[0060] Application Examples Application Example 1 A method for remediating contaminated soil comprises the following steps: The contaminated soil remediation agent obtained in Example 1 was injected into the contaminated soil by high-pressure injection. The amount of the remediation agent added was 0.1-0.6 mol / m³ of soil. The contaminated soil was a contaminated plot of land of a steel company. Samples were taken for testing 5 months after remediation.

[0061] Application Example 2-14 Different from Application Example 1, the contaminated soil remediation agents in Application Examples 2-14 are respectively derived from Examples 2-14.

[0062] Comparative Application Examples Comparative Application Examples 1-6 Different from Application Example 1, the contaminated soil remediation agents in Comparative Application Examples 1-6 are respectively derived from Comparative Examples 1-6.

[0063] Performance testing With reference to the "Determination of Semivolatile Organic Compounds in Soil and Sediment by Gas Chromatography-Mass Spectrometry" HJ 834-2017, the soil before and after remediation was sampled and tested using a gas chromatography-mass spectrometry (single quadrupole). The pollutant contents in the soil before remediation were 30.8 mg / kg for benzo(a)anthracene, 28.3 mg / kg for benzo(b)fluoranthene, 19.8 mg / kg for benzo(a)pyrene, 28.6 mg / kg for indeno(1,2,3-cd)pyrene, and 60.6 mg / kg for dibenzo(a,h)anthracene. The results of the pollutant content test in the soil after remediation are shown in Table 1.

[0064] Table 1 Performance test results ; ;

[0065] Combining Application Examples 1-14 with Comparative Application Examples 1-6 and Table 1, it can be seen that the pollutant content of the contaminated soil after repair in Application Examples 1-14 is lower and the repair effect is better. This shows that the soil remediation agent and remediation method obtained in this application have a better remediation effect on contaminated soil in the steel and metallurgical industry and are suitable for industrial development.

[0066] In conjunction with application example 1 and comparative example application example 1, and in conjunction with table 1 it can be seen that the pollutant content in the soil after repairing in application example 1 is lower than comparative application example 1, this illustrates that micro-nano iron-based materials, auxiliary materials and oxidant compound can effectively improve contaminated soil remediation effect, this may be because micro-nano iron-based materials mainly play the effect of decomposing organic matter, and in auxiliary materials, liquid phase reductant can provide electrons for iron-based materials, promotes the circulation of iron ion, makes iron-based materials always keep higher active state. Based on the strengthening auxiliary material of iron circulation, iron source can be supplemented, the existence form of stabilizing iron ion, maintains the efficient carrying out of iron circulation. Solubilizing desorption surfactant can reduce the surface tension between soil particles and organic pollutants, makes organic pollutants more easily desorbed from soil particle surface and enter liquid phase, increases the contact chance of organic pollutants and micro-nano iron-based materials and oxidant, thus improves remediation efficiency.

[0067] Combining Application Example 1 with Comparative Example Application Examples 2-6, and combining with Table 1, it can be seen that the liquid phase reducing agent, the iron cycle-based strengthening auxiliary material, and the solubilizing and desorption surfactant can assist the micro-nano iron-based material to a greater extent in exerting its role in decomposing organic pollutants.

[0068] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A contaminated soil remediation agent, characterized in that: Including micro-nano iron-based materials, auxiliary materials and oxidants; The micro-nano iron-based material is prepared by heteroatom modification, carbon doping modification and anti-oxidation modification; The auxiliary materials are a liquid phase reducing agent, an iron cycle-based strengthening auxiliary material, and a solubilizing and desorption surfactant; The preparation method of the micro-nano iron-based material is: ‌1) Ball milling pretreatment‌ Industrial zero-valent iron powder, heteroatom source, and carbon source are mixed and ground to a particle size of 150-200 nm. 2) High-temperature carbonization and heteroatom doping The ground material obtained in 1) is heated to 550-650°C and kept at this temperature for 2 hours; then the temperature is further raised to 750-850°C and kept at this temperature for 1 hour to obtain a carbonized material; ‌3) Antioxidant surface modification‌ The carbonized material was immersed in a polyvinyl pyrrolidone solution, ultrasonically treated for 30 minutes, and then dried to obtain a micro-nano iron-based material.

2. A contaminated soil remediation agent according to claim 1, characterized in that: The heteroatom source is a mixture of thiourea and sodium phosphate in a weight ratio of 3:1; and the carbon source is glucose.

3. A contaminated soil remediation agent according to claim 2, characterized in that: The weight ratio of the heteroatom source to the industrial zero-valent iron powder is 1:(8-15), and the weight ratio of the carbon source to the industrial zero-valent iron powder is 1:(8-12).

4. A contaminated soil remediation agent according to claim 1, characterized in that: The liquid-phase reducing agent is a mixture of ascorbic acid, sodium sulfite and oxalic acid in a weight ratio of 1:(2-3):(1-2).

5. The contaminated soil remediation agent according to claim 1, characterized in that: The iron cycle-based strengthening auxiliary material is a mixture of iron-containing minerals and iron chelating agents in a weight ratio of 1:(3-5).

6. The contaminated soil remediation agent according to claim 1, characterized in that: The solubilizing and desorption surfactant is a mixture of a chemical surfactant, a biological surfactant and micro-nano biochar in a weight ratio of (2-3): (2-3): (4-5).

7. The contaminated soil remediation agent according to claim 1, characterized in that: The weight ratio of the liquid-phase reducing agent, the iron cycle-based strengthening auxiliary material and the solubilizing and desorption surfactant is 2:(2-4):(4-6), and the weight ratio of the micro-nano iron-based material, the auxiliary material and the oxidant is 2:3:

5.

8. A method for preparing the contaminated soil remediation agent according to any one of claims 1 to 7, characterized in that: The following steps are involved: The micro-nano iron-based material, auxiliary materials and oxidant are mixed to obtain a contaminated soil remediation agent.

9. A method for remediating contaminated soil, characterized in that: The contaminated soil remediation agent according to any one of claims 1 to 7 is used to remediate soil contaminated by PAHs in steel and metallurgical industries.

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