Heavy metal soil passivation remediation method for environmental protection

Abstract

The invention discloses a heavy metal soil passivation remediation method for environmental protection, and belongs to the technical field of soil remediation. Aiming at the technical defects that the existing biochar is insufficient in adsorption capacity and zero-valent iron is easy to oxidize and agglomerate, a multi-mechanism synergistic remediation scheme taking the FeNi-coated TA-AC composite material as a core is provided. The surface of the zero-valent iron is coated with the porous activated carbon to form a core-shell structure, a carbon layer serves as a physical barrier to isolate oxygen and moisture and prevent the zero-valent iron from being oxidized, and the high specific surface area of the activated carbon and the high adsorbability of the zero-valent iron synergistically remove heavy metal; the surface of biochar is modified through tannic acid, tannic acid anchors activated carbon through polyphenol hydroxyl, and quinonyl of tannic acid serves as an electron mediator to accelerate heavy metal reduction; fe-Ni bimetal reduces surface energy through lattice distortion, and electron transfer is promoted through potential difference. The prepared composite material has obvious passivation efficiency on Pb, Cd and As, can be recycled after being recycled through a magnetic separation method, improves the material utilization rate, and has the advantages of being green and environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil passivation and remediation, and particularly relates to a heavy metal soil passivation and remediation method for environmental protection. Background Art

[0002] With the rapid development of industry and agriculture, the problem of soil heavy metal pollution has evolved into a global environmental challenge. After heavy metals such as lead, cadmium, chromium, and arsenic invade the soil ecosystem through multiple pathways, they not only cause the imbalance of microbial communities and the blockage of nutrient cycles, but also threaten human health through the biological magnification effect of the food chain. Although the current mainstream remediation technologies have their own advantages, there are technical bottlenecks that are difficult to break through.

[0003] For the adsorption and fixation technology, biochar is widely used due to its porous structure. However, conventional biochar (such as rice husk char) only contains a small amount of hydroxyl / carboxyl functional groups on its surface, and its reduction and transformation ability for variable valence heavy metals such as As(III) and Cr(VI) is insufficient. More critically, its adsorption sites are easily occupied by soil organic matter competition, and even heavy metal desorption will occur under acidic conditions (pH < 5), resulting in irreversible degradation of the remediation effect.

[0004] To enhance the reduction ability, the academic community has turned to zero-valent iron (ZVI) technology. Zero-valent iron can reduce high-valent heavy metals to low-toxic forms by releasing electrons. However, bare zero-valent iron nanoparticles still face difficulties in the soil environment: on the one hand, their high surface energy leads to serious aggregation phenomena and a sharp drop in specific surface area; on the other hand, zero-valent iron rapidly oxidizes to form an iron oxide shell in a humid environment, which not only blocks electron transfer, but also the dissolution of Fe 2+ will cause secondary pollution.

[0005] Therefore, a single material is difficult to simultaneously meet the multiple requirements of heavy metal adsorption-reduction-stabilization, and a simple combination cannot achieve the synergistic effect of functional components. Therefore, developing a composite material with high stability and multi-mechanism synergy has become the key to breaking through the technical dilemma of heavy metal soil remediation. Summary of the Invention

[0006] In view of the above situation, to overcome the defects of the prior art, the present invention improves the preparation method of biomass activated carbon and develops an efficient, stable and environmentally friendly heavy metal soil passivation and remediation method.

[0007] To achieve the above object, the following technical solutions are adopted: The present invention provides a heavy metal soil passivation and remediation method for environmental protection, including the following steps:

[0008] Preparation of S1. FeNi@TA-AC composite material: Dispersed the bio-based activated carbon in deionized water according to the mass fraction of 1-3% to obtain an activated carbon dispersion liquid, and dispersed oleylamine in absolute ethanol according to the mass fraction of 2-5% to obtain an oleylamine dispersion liquid;

[0009] Dropped 1mol / L Tris buffer solution into the activated carbon dispersion liquid to adjust the pH to 8, then added tannic acid, stirred at 25-30°C for 6-12h, then added the oleylamine dispersion liquid, heated to 60°C and reacted for 12-24h. After the reaction ended, filtered out the solid, washed it three times with absolute ethanol and deionized water, and obtained the modified biochar after vacuum drying;

[0010] Added ferric nitrate nonahydrate and nickel chloride hexahydrate to deionized water according to the liquid-solid mass ratio of 5:1-10:1, stirred evenly, then added the modified activated carbon, oscillated in a vortex mixer for 2h, then filtered out the activated carbon, dried it in a vacuum oven at 60°C for 2h, and then heated the dried activated carbon in a tubular furnace to 650°C at a heating rate of 15°C / min, maintained it at 650°C for 2h. After the tubular furnace cooled to room temperature, the FeNi@TA-AC composite material was obtained;

[0011] S2. Soil pretreatment: Collected the surface soil of 0-20cm in the area to be repaired, first picked out sundries such as stones and residues, then passed through a 2mm sieve. When the soil water content was too high, it was ventilated and dried and turned over. When the water content was low, deionized water was sprayed to adjust the soil water content to 10%-15%;

[0012] S3. Soil remediation: According to the mass ratio of composite material to soil = 1:5, mixed FeNi@TA-AC with the pretreated soil, adjusted the soil water content to 20-30%, stirred evenly and then left it standing for 24h, then added calcium carbonate and humic acid to adjust the pH of the soil mixture to 6.0-7.5, controlled the temperature at 25-40°C, ploughed the soil every week, sampled the soil and calculated the passivation efficiency. When the cadmium content in the soil ≤ 0.4mg / kg, mercury content ≤ 1.3mg / kg, arsenic content ≤ 25mg / kg, lead content ≤ 90mg / kg, the remediation was terminated.

[0013] Furthermore, the bio-based activated carbon is activated carbon made from one or more of rice husk, corn straw, wheat straw, peanut shell and coconut shell.

[0014] Furthermore, in the step S1, the mass ratio of the bio-based activated carbon to tannic acid is 1:0.5-0.7, and the mass ratio of oleylamine to the bio-based activated carbon is 1:20-1:30.

[0015] Further, in the step S1, the molar ratio of iron nitrate nonahydrate to nickel chloride hexahydrate is Fe:Ni = 4:1 - 6:1, and the mass ratio of the total iron and nickel metals to the modified biochar is 1:4 - 1:6.

[0016] Further, in the step S1, a H2 / Ar mixed gas is introduced during the heating stage of the tubular furnace, and the volume percentage of H2 is 3 - 8%.

[0017] Further, in the step S3, the pH of the soil mixture is adjusted by compounding calcium carbonate and humic acid according to a mass ratio of 1:0.4 - 0.6.

[0018] Further, in the step S3, the plowing frequency per week is dynamically adjusted according to the initial concentration of heavy metals in the soil:

[0019] When the total amount of heavy metals > 500 mg / kg, plow twice a week;

[0020] When the total amount of heavy metals ≤ 500 mg / kg, plow once a week.

[0021] Further, after the step S3 terminates the remediation, the ZVI@TA-AC composite material is recovered by magnetic separation, and the recovered material is washed with 0.1 mol / L HCl and then recycled.

[0022] Further, in the mixing process of the step S3, a double-shaft mixer is used, the rotation speed is 80 - 100 rpm, the mixing time is 40 - 60 min, and the particle size of the soil aggregates after mixing is ≤ 5 mm.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) In the present invention, porous activated carbon is coated on the surface of zero-valent iron to form a core-shell structure. The carbon layer serves as a physical barrier to isolate oxygen and moisture, preventing the oxidation of zero-valent iron. At the same time, the high specific surface area of activated carbon and the high adsorption capacity of zero-valent iron synergistically remove heavy metals;

[0025] (2) The present invention also modifies the surface of activated carbon with tannic acid. Tannic acid can form strong hydrogen bonds with activated carbon through polyphenolic hydroxyl groups. At the same time, its quinone groups act as electron mediators to accelerate the electron transfer from zero-valent iron to heavy metals. The hydrophobic long chains of oleylamine inhibit the aggregation of zero-valent iron through steric hindrance effects. Tannic acid is rich in functional groups such as amino, hydroxyl, and quinone groups, which can bind to the surface of activated carbon through hydrogen bonds, π-π interactions, or covalent bonds, and at the same time provide abundant anchoring sites for subsequent loading of zero-valent iron. Moreover, the polar functional groups of tannic acid can prevent the aggregation of zero-valent iron during the loading process through electrostatic repulsion or steric hindrance effects, thereby improving the dispersion uniformity of ZVI on activated carbon. The catechol and amino groups in tannic acid can specifically complex with As(III) and Pb 2+, combined with the reduction of zero-valent iron, As(III) is oxidized to less toxic As(V), and the weak acidic functional groups in tannic acid also have pH buffering ability to reduce the soil pH value;

[0026] (3) In the process of preparing zero-valent iron in the present invention, the second metal Ni is introduced to form bimetallic particles Fe-Ni, which enhances the reduction and adsorption ability of heavy metals through catalytic or electron transfer effects, reduces the agglomeration of zero-valent iron, and increases the specific surface area. The doping of Ni causes lattice distortion of zero-valent iron and reduces the surface energy. At the same time, the potential difference between metals promotes electron transfer. Ni can also catalyze the generation of H radicals and enhance the oxidation and fixation ability of As(III);

[0027] (4) The composite material prepared in the present invention can be recycled after magnetic separation, improving the material utilization rate and having the advantages of environmental protection. Description of the Drawings

[0028] Figure 1 It is the reduction rate of available cadmium in the soil after passivation and remediation of each example and comparative example of the present invention;

[0029] Figure 2 It is the reduction rate of available arsenic in the soil after passivation and remediation of each example and comparative example of the present invention;

[0030] Figure 3 It is the reduction rate of available lead in the soil after passivation and remediation of each example and comparative example of the present invention;

[0031] Figure 4 It is the pH value of the soil after passivation and remediation of each example and comparative example of the present invention;

[0032] Figure 5 It is the organic matter content of the soil after passivation and remediation of each example and comparative example of the present invention.

[0033] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. Detailed Embodiments

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0035] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the present invention. The preferred methods and materials described herein are for illustrative purposes only and do not limit the content of this application.

[0036] The experimental methods in the following examples are all conventional methods unless otherwise specified. The test materials used in the following examples are all obtained from commercial channels unless otherwise specified.

[0037] Example 1

[0038] Preparation of FeNi@TA-AC composite

[0039] The rice husk activated carbon was dispersed in deionized water at a mass fraction of 1% to obtain an activated carbon dispersion. The oleylamine was dispersed in absolute ethanol at a mass fraction of 2% to obtain an oleylamine dispersion.

[0040] 1 mol / L Tris buffer solution was added dropwise to the activated carbon dispersion to adjust the pH to 8, and then tannic acid was added (the mass ratio of bio-based activated carbon to tannic acid was 1:0.5). The mixture was stirred at 25 °C for 6 h, and then the oleylamine dispersion was added (the mass ratio of oleylamine to bio-based activated carbon was 1:30). The temperature was raised to 60 °C and the reaction was carried out for 12 h. After the reaction was completed, the solid was filtered out, washed three times with absolute ethanol and deionized water, and dried in vacuum to obtain modified biochar.

[0041] Ferric nitrate nonahydrate and nickel chloride hexahydrate were added to deionized water at a liquid-solid mass ratio of 5:1 (the molar ratio of ferric nitrate nonahydrate to nickel chloride hexahydrate was Fe:Ni = 4:1). The mixture was stirred evenly, and then the modified activated carbon was added (the mass ratio of the total iron and nickel metals to the modified biochar was 1:6). The mixture was shaken in a vortex mixer for 2 h, and then the activated carbon was filtered out and dried in a vacuum oven at 60 °C for 2 h. Then, the dried activated carbon was heated to 650 °C in a tube furnace at a heating rate of 15 °C / min and maintained at 650 °C for 2 h. After the tube furnace cooled to room temperature, the FeNi@TA-AC composite was obtained.

[0042] Example 2

[0043] Preparation of FeNi@TA-AC composite

[0044] The coconut shell activated carbon was dispersed in deionized water at a mass fraction of 3% to obtain an activated carbon dispersion. The oleylamine was dispersed in absolute ethanol at a mass fraction of 5% to obtain an oleylamine dispersion.

[0045] Add 1 mol / L Tris buffer dropwise to the activated carbon dispersion to adjust the pH to 8, then add tannic acid (the mass ratio of bio-based activated carbon to tannic acid is 1:0.7), stir at 30 °C for 12 h, then add oleylamine dispersion (the mass ratio of oleylamine to bio-based activated carbon is 1:20), heat to 60 °C and react for 24 h. After the reaction, filter out the solid, wash it three times with absolute ethanol and deionized water, and obtain the modified biochar after vacuum drying;

[0046] Add ferric nitrate nonahydrate and nickel chloride hexahydrate to deionized water according to the liquid-solid mass ratio of 10:1 (the molar ratio of ferric nitrate nonahydrate to nickel chloride hexahydrate is Fe:Ni = 6:1), stir evenly, then add the modified activated carbon (the total mass ratio of iron and nickel metals to the modified biochar is 1:4), shake in a vortex mixer for 2 h, then filter out the activated carbon, dry it in a vacuum oven at 60 °C for 2 h, then heat the dried activated carbon in a tubular furnace to 650 °C at a heating rate of 15 °C / min, hold at 650 °C for 2 h, and obtain the FeNi@TA-AC composite material after the tubular furnace cools to room temperature.

[0047] Example 3

[0048] Preparation of FeNi@TA-AC Composite Material

[0049] Disperse bio-based activated carbon in deionized water at a mass fraction of 2% to obtain an activated carbon dispersion, and disperse oleylamine in absolute ethanol at a mass fraction of 3.5% to obtain an oleylamine dispersion;

[0050] Add 1 mol / L Tris buffer dropwise to the activated carbon dispersion to adjust the pH to 8, then add tannic acid (the mass ratio of bio-based activated carbon to tannic acid is 1:0.6), stir at 27 °C for 9 h, then add oleylamine dispersion (the mass ratio of oleylamine to bio-based activated carbon is 1:25), heat to 60 °C and react for 18 h. After the reaction, filter out the solid, wash it three times with absolute ethanol and deionized water, and obtain the modified biochar after vacuum drying;

[0051] Add ferric nitrate nonahydrate and nickel chloride hexahydrate to deionized water according to the liquid-solid mass ratio of 7.5:1 (the molar ratio of ferric nitrate nonahydrate to nickel chloride hexahydrate is Fe:Ni = 5:1), stir evenly, then add the modified activated carbon (the total mass ratio of iron and nickel metals to the modified biochar is 1:5), shake in a vortex mixer for 2 h, then filter out the activated carbon, dry it in a vacuum oven at 60 °C for 2 h, then heat the dried activated carbon in a tubular furnace to 650 °C at a heating rate of 15 °C / min, hold at 650 °C for 2 h, and obtain the FeNi@TA-AC composite material after the tubular furnace cools to room temperature.

[0052] The bio-based activated carbon is the activated carbon made from corn straw and wheat straw mixed in equal mass ratio.

[0053] Comparative Example 1

[0054] In this comparative example, the same biomass activated carbon as that in Example 3 was used to replace the FeNi@TA-AC composite material.

[0055] Comparative Example 2

[0056] The composite material prepared in this comparative example is a single-metal Fe@TA-AC composite material, that is, ferric nitrate nonahydrate in equal amount was used to replace nickel chloride hexahydrate during the preparation of the composite material, and the rest were the same as the steps in Example 3.

[0057] Comparative Example 3

[0058] This comparative example omitted the step of modifying with tannic acid, that is, the same biomass activated carbon as that in Example 3 was used to replace the modified activated carbon, and the rest were the same as the steps in Example 3.

[0059] Result Analysis

[0060] Collect the dry cropland surface soil contaminated by heavy metals at 0 - 20 cm. The pH of the collected soil is 8.2, the total cadmium content is 2.15 mg / kg, the total arsenic content is 225.4 mg / kg, the total lead content is 205.9 mg / kg, and the soil organic matter content is 2.5%;

[0061] First, pick out the sundries such as stones and residues in the surface soil, and then pass through a 2 mm sieve. When the soil water content is too high, ventilate and air-dry and turn it over. When the water content is low, spray deionized water to adjust the soil water content to 10% - 15%;

[0062] According to the mass ratio of composite material to soil = 1:5, mix the FeNi@TA-AC prepared in each example and comparative example with the pretreated soil, adjust the soil water content to 20 - 30%, mix with a double-shaft mixer at a rotation speed of 100 rpm and a mixing time of 50 min. After mixing, the soil aggregate particle size ≤ 5 mm. After mixing evenly, let it stand for 24 h, and then add calcium carbonate and humic acid to adjust the pH of the soil mixture to 6.0 - 7.5 (calcium carbonate and humic acid are compounded according to the mass ratio of 1:0.5), control the temperature at 25 - 40 °C, and plow the soil every week;

[0063] After 20 days, use the DTPA extraction method to measure the available cadmium in the soil, use the silver diethyldithiocarbamate colorimetric method to measure the available arsenic in the soil, use the DTPA extraction method to measure the available lead in the soil, calculate the reduction rates of available cadmium, available arsenic and available lead, and at the same time measure the pH value and organic matter content of the soil. The above test results are shown in Figures 1-5 .

[0064] From Figures 1-3 It can be seen that: the reduction rates of available cadmium, available arsenic and available lead in Examples 1-3 are significantly higher than those in the comparative examples. This indicates that the FeNi@TA-AC composite material prepared by the present invention has a remarkable passivation effect on heavy metals in soil. In the examples, through the modification of biomass activated carbon, the introduction of the second metal Ni to form bimetallic particles Fe-Ni, and the modification effect of tannic acid and other multiple mechanisms working together, the adsorption, reduction and fixation abilities of heavy metals are enhanced, thereby effectively reducing the content of available heavy metals in soil.

[0065] Comparative Example 1 uses unmodified biomass activated carbon, and its heavy metal removal effect is much lower than that in the examples, indicating that pure biomass activated carbon has limitations in heavy metal remediation, while the modification method of the present invention can significantly improve the performance of the material.

[0066] The heavy metal reduction rate of the single-metal composite material prepared in Comparative Example 2 is lower than that in the examples, indicating that the introduction of the second metal Ni to form bimetallic particles Fe-Ni enhances the reduction and adsorption abilities of heavy metals through catalytic or electron transfer effects, etc., and has a better remediation effect than single metals.

[0067] After omitting the tannic acid modification step in Comparative Example 3, its heavy metal reduction rate is also inferior to that in the examples, which reflects the important role of tannic acid in the present invention. Tannic acid can not only form strong hydrogen bonds with activated carbon, but also act as an electron mediator to accelerate electron transfer, and at the same time provide an anchoring site for loading zero-valent iron to prevent zero-valent iron aggregation, and its functional groups can specifically complex certain heavy metals, further improving the heavy metal removal ability.

[0068] From Figure 4 It can be seen that the soil pH in the examples is stable at 5.2-5.6, which is attributed to: the precise regulation of the acidic environment by the compounding of humic acid and calcium carbonate to avoid the dissolution of Fe 2+ dissolution or the precipitation of heavy metal hydroxides caused by the over-oxidation of zero-valent iron, and the weak acidic functional groups of tannic acid in the composite material contribute to the pH buffering ability.

[0069] From Figure 5 It can be seen that the organic matter content in the examples increases to 4.2-4.6%, indicating that the degradation products of tannic acid and humic acid jointly supplement soil organic matter, promote microbial activity, assist in heavy metal stabilization, and the modified activated carbon itself, as an organic carbon source, can long-term improve soil structure and increase the organic matter content.

[0070] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

[0071] The above description of the present invention and its embodiments is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual application is not limited thereto. In general, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design in a non-creative way similar ways and embodiments to this technical solution, they should all fall within the protection scope of the present invention.

Claims

1. A heavy metal soil passivation and remediation method for environmental protection, characterized in that: It includes the following steps: Preparation of FeNi@TA-AC composite material: Dispersing bio-based activated carbon in deionized water according to a mass fraction of 1-3% to obtain an activated carbon dispersion, and dispersing oleylamine in absolute ethanol according to a mass fraction of 2-5% to obtain an oleylamine dispersion; Dropping 1 mol / L Tris buffer solution into the activated carbon dispersion to adjust the pH to 8, then adding tannic acid, stirring at 25-30 °C for 6-12 h, then adding the oleylamine dispersion, heating to 60 °C and reacting for 12-24 h. After the reaction ends, filtering out the solid, washing it three times with absolute ethanol and deionized water, and drying it in vacuum to obtain modified biochar; Adding ferric nitrate nonahydrate and nickel chloride hexahydrate to deionized water according to a liquid-solid mass ratio of 5:1-10:1, stirring evenly, then adding the modified activated carbon, shaking it in a vortex mixer for 2 h, then filtering out the activated carbon, drying it in a vacuum oven at 60 °C for 2 h, and then heating the dried activated carbon in a tubular furnace to 650 °C at a heating rate of 15 °C / min, maintaining it at 650 °C for 2 h. After the tubular furnace cools down to room temperature, the FeNi@TA-AC composite material is obtained; S2. Soil pretreatment: Collecting the surface soil of 0-20 cm in the area to be repaired, first picking out sundries such as stones and residues, then passing it through a 2 mm sieve. When the soil water content is too high, ventilating and drying it while turning it over, and when the water content is low, spraying deionized water to adjust the soil water content to 10%-15%; S3. Soil remediation: Mixing FeNi@TA-AC with the pretreated soil according to a mass ratio of composite material to soil = 1:5, adjusting the soil water content to 20-30%, mixing evenly and then standing for 24 h, then adding calcium carbonate and humic acid to adjust the pH of the soil mixture to 6.0-7.5, controlling the temperature at 25-40 °C, plowing the soil once a week, sampling the soil and calculating the passivation efficiency. When the cadmium content in the soil ≤ 0.4 mg / kg, the mercury content ≤ 1.3 mg / kg, the arsenic content ≤ 25 mg / kg, and the lead content ≤ 90 mg / kg, the remediation is terminated.

2. The heavy metal soil passivation and remediation method for environmental protection according to claim 1, characterized in that: The bio-based activated carbon is activated carbon made from one or more of rice husk, corn straw, wheat straw, peanut shell, and coconut shell.

3. The heavy metal soil passivation and remediation method for environmental protection according to claim 2, characterized in that: In step S1, the mass ratio of the bio-based activated carbon to tannic acid is 1:0.5-0.7, and the mass ratio of oleylamine to the bio-based activated carbon is 1:20-1:

30.

4. The heavy metal soil passivation and remediation method for environmental protection according to claim 3, characterized in that: In step S1, the molar ratio of ferric nitrate nonahydrate to nickel chloride hexahydrate is Fe:Ni = 4:1-6:1, and the mass ratio of the total iron and nickel metals to the modified biochar is 1:4-1:

6.

5. The heavy metal soil passivation and remediation method for environmental protection according to claim 4, characterized in that: In the heating stage of the tubular furnace in step S1, a H2 / Ar mixed gas is introduced, and the volume fraction of H2 is 3-8%.

6. The heavy metal soil passivation and remediation method for environmental protection according to claim 5, characterized in that: In step S3, the pH of the soil mixture is adjusted by compounding calcium carbonate and humic acid according to a mass ratio of 1:0.4-0.

6.

7. The heavy metal soil passivation and remediation method for environmental protection according to claim 6, characterized in that: In step S3, the plowing frequency per week is dynamically adjusted according to the initial concentration of heavy metals in the soil: When the total amount of heavy metals > 500 mg / kg, plow twice a week; When the total amount of heavy metals ≤ 500 mg / kg, plow once a week.

8. The heavy metal soil passivation and remediation method for environmental protection according to claim 7, characterized in that: After the repair in step S3 is terminated, the ZVI@TA-AC composite material is recovered by magnetic separation, and the recovered material is washed with 0.1 mol / L HCl and then recycled.

9. The heavy metal soil passivation and remediation method for environmental protection according to claim 8, characterized in that: In the mixing process of step S3, a double-shaft mixer is used, with a rotation speed of 80 - 100 rpm, a mixing time of 40 - 60 min, and the particle size of the soil aggregates after mixing ≤ 5 mm.

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