Method for remediation of zinc-cadmium contaminated soil

Abstract

The present application relates to a method for remediation of zinc-cadmium contaminated soil, and belongs to the technical field of soil pollution control. The present application provides a method for remediation of zinc-cadmium contaminated soil. First, the contaminated soil is mixed with a composite leaching agent aqueous solution at a ratio of 1g:10-15mL, the pH is adjusted to 5.0-5.5, and the mixture is oscillated at 180-200rpm for 2-3h. The leaching agent contains 10g / L sodium lignosulfonate and 2g / L polyaspartic acid. After leaching, the leached soil is obtained by solid-liquid separation, and a composite passivation agent accounting for 0.5-1.5% of the dry weight of the soil is applied. The passivation agent is composed of nano ferrous sulfide and phosphoric acid activated biochar at a mass ratio of 1:2-3. Finally, the water content of the soil is adjusted to 20-30%, and after 15-20 days of curing, the soil is seeded with Sedum plumbizincicola. This method can efficiently remove zinc and cadmium heavy metals from the soil, enhance the stability of passivation, and achieve vegetation reconstruction of the contaminated soil. It is suitable for remediation of farmland and industrial contaminated sites.

Description

Technical Field

[0001] This invention relates to the field of contaminated soil remediation technology. More specifically, this invention relates to a method for remediating zinc-cadmium contaminated soil. Background Technology

[0002] Soil is a vital material foundation for human survival and development. Currently, remediation methods for heavy metal-contaminated soil mainly include physical remediation, chemical remediation, and bioremediation. Soil leaching, as the most effective and practical chemical remediation method for thoroughly removing heavy metals, can be applied alone to the treatment of small areas of highly contaminated soil, and can also serve as a pretreatment technology for other contaminated soil remediation methods, making it an effective and feasible remediation technology. However, existing technologies using single leaching agents have low removal rates for zinc and cadmium, affecting the remediation effect on contaminated soil. Summary of the Invention

[0003] Another objective of this invention is to provide a method for remediating zinc-cadmium contaminated soil, as traditional leaching has low efficiency in the simultaneous desorption of zinc and cadmium.

[0004] This addresses the risks of secondary pollution from leachate and the low efficiency of heavy metal recovery. Traditional leachate treatment uses chemical precipitation, which generates large amounts of sludge containing heavy metals, increasing disposal costs.

[0005] This addresses the issue of performance degradation caused by non-specific adsorption of compound leaching agents in soil. Sodium lignosulfonate and polyaspartic acid are easily adsorbed by soil colloids, shortening the effective action time and reducing their sustained desorption-chelation capacity for zinc and cadmium.

[0006] This addresses the issue of uneven component dispersion during the formulation of composite leaching agents. Direct mixing at high temperatures can easily cause sodium lignosulfonate to clump and polyaspartic acid to degrade, resulting in uneven distribution of the active ingredients in the leaching agent and affecting leaching stability.

[0007] This addresses the issues of easy pore blockage and insufficient specific surface area in biochar passivating agents.

[0008] This addresses the challenge of maintaining the activity of passivating agents in soil environments. Nano-ferrous sulfide is prone to oxidation and degradation upon exposure to air, and the contact between the passivating agent and the insoluble phosphate-encapsulated heavy metals is insufficient.

[0009] To achieve these objectives and other advantages according to the present invention, a method for remediating zinc-cadmium contaminated soil is provided, comprising the following steps: Step 1: Mix zinc-cadmium contaminated soil with a composite leaching agent aqueous solution at a mass ratio of 1g: 10-15mL, adjust the pH of the system to 5.0-5.5, and shake the mixture at 180-200 rpm for 2-3 hours on a horizontal shaker. The composite leaching agent aqueous solution includes: sodium lignosulfonate, polyaspartic acid, and the remainder water. The mass concentration of sodium lignosulfonate in the composite leaching agent aqueous solution is 10g / L, and the mass concentration of polyaspartic acid is 2g / L. Step 2: After leaching, the leached soil is obtained through solid-liquid separation. A composite passivating agent is added to the leached soil and mixed to obtain treated soil. The amount of composite passivating agent added is 0.5-1.5% of the dry weight of the zinc-cadmium contaminated soil. The composite passivating agent includes nano-ferrous sulfide and phosphoric acid activated biochar in a mass ratio of 1:2-3. Step 3: Spray water into the treated soil to adjust the moisture content to 20-30%. Then, cure the treated soil mound for 15-20 days. After the curing is completed, sow Sedum sarmentosum in the treated soil to rebuild vegetation.

[0010] Preferably, in step two, the eluent obtained by separating the solid and liquid after rinsing is processed by adding mercapto-modified magnetic zeolite to the eluent, wherein 20-40g of mercapto-modified magnetic zeolite is added to each liter of eluent.

[0011] Preferably, the preparation method of the thiol-modified magnetic zeolite includes the following steps: Zeolite powder with a particle size of 75~150 μm was dispersed in water, and a mixture of FeCl3·6H2O and FeSO4·7H2O, with a total mass of 10~30% of the zeolite powder, was added. The molar ratio of FeCl3·6H2O to FeSO4·7H2O in the mixture was 2:1. Under nitrogen protection, a 6 M sodium hydroxide solution was added dropwise until the pH of the system was 10.0±0.5. The mixture was reacted at 60℃ for 2 h, and the first product was obtained by magnetic separation. The first product was dispersed in an aqueous solution with a volume ratio of 4:1 (ethanol and water), and 3-mercaptopropyltrimethoxysilane was added. The mixture was refluxed at 70°C for 6 hours, and then subjected to magnetic separation, washing with ethanol, and vacuum drying at 60°C to obtain mercapto-modified magnetic zeolite. The amount of 3-mercaptopropyltrimethoxysilane used was 5-8% of the mass of the zeolite powder.

[0012] Preferably, the composite rinsing agent aqueous solution further includes ammonium glycyrrhizate, and the mass concentration of ammonium glycyrrhizate in the composite rinsing agent aqueous solution is 1 g / L.

[0013] Preferably, the preparation method of the composite rinsing agent aqueous solution includes the following steps: Heat the water to 38-40℃, add sodium lignosulfonate to the water while stirring at 300 rpm, and continue stirring for 25-30 minutes. Add polyaspartic acid to the system while stirring at 300 rpm, and continue stirring for 20-25 minutes. Ammonium glycyrrhizate was added to the system while stirring at 200 rpm, and the mixture was stirred for 15-20 minutes. The mixture was then cooled to room temperature to obtain the aqueous solution of the composite rinsing agent.

[0014] Preferably, the method for preparing phosphoric acid activated biochar in step two includes the following steps: Rice husk biomass pulverized to 80-100 mesh was immersed in a 40 wt% phosphoric acid solution with a ratio of rice husk biomass to phosphoric acid solution of 1 g: 4 mL, and ultrasonically treated for 30 minutes. After separation, the impregnated biomass is first pre-carbonized at 150℃ for 30 minutes by heating at 5℃ / min, and then pyrolyzed at 550℃ for 1 hour by heating at 10℃ / min, with a nitrogen flow rate of 0.5 L / min. After cooling, the pyrolysis products were washed successively with 0.1 mol / L nitric acid solution and deionized water until the conductivity of the filtrate was <50 μS / cm, and then dried under vacuum at 105℃ to obtain phosphoric acid activated biochar.

[0015] Preferably, in step one, during the shaking reaction, ozone gas is introduced into the system every 30 minutes, with an ozone introduction rate of 0.1~0.2L per liter of reaction system and an ozone gas concentration of 80~100mg / L.

[0016] Preferably, the maintenance method in step three is as follows: A1. Compact the treated soil pile and cover the surface with a sealing film. Vacuum the soil to -0.05~-0.08 MPa and maintain the ambient temperature at 30-35℃ for 5~7 days. After maintenance, turn the soil pile over. A2. After the turning operation is completed, cover with a sealing film, and make multiple micropores in the sealing film with a pore diameter of 0.5~1mm and a pore density of 40~60 pores / m³. 2 Maintain for 10-13 days, then spray a citric acid-ascorbic acid composite activating solution onto the surface of the soil mound through micropores, with a spraying rate of 50-100 mL / m². 2 The citric acid-ascorbic acid composite activating solution contains 1 g / L of citric acid and 0.7 g / L of ascorbic acid.

[0017] Preferably, the citric acid-ascorbic acid composite activating solution is applied in two batches: The first spray should consist of 40% of the total mass of the citric acid-ascorbic acid composite activating solution, sprayed after the micropores are opened; The remaining citric acid-ascorbic acid compound activating solution was sprayed a second time, 24 hours after the first spray.

[0018] Preferably, in step three, three days before sowing Sedum sarmentosum, 0.3% to 0.5% of well-rotted organic fertilizer by weight of the soil is applied to the treated soil. The well-rotted organic fertilizer has an organic matter content of ≥45% and a total nitrogen, phosphorus and potassium content of ≥5%. The soil is then tilled after application.

[0019] The present invention has at least the following beneficial effects: First, this invention effectively improves the removal efficiency of zinc and cadmium by adding sodium lignosulfonate and polyaspartic acid. The effect is even more significant when both are used together. When sodium lignosulfonate and polyaspartic acid are used in combination, sodium lignosulfonate first releases bound zinc and cadmium from the soil into the solution through surface activity and desorption. Subsequently, polyaspartic acid immediately chelates with the desorbed zinc and cadmium ions, forming stable and water-soluble chelates that prevent their re-adsorption by the soil. This synergistic "desorption-chelation" process solves the problem of insufficient chelating capacity of sodium lignosulfonate alone and compensates for the low desorption efficiency of polyaspartic acid alone, thereby significantly improving the overall removal efficiency of zinc and cadmium.

[0020] Secondly, by adding ammonium glycyrrhizate, the uronic acid groups in the ammonium glycyrrhizate molecule form a synergistic dispersion system with sodium lignosulfonate and polyaspartic acid, which inhibits the non-specific adsorption of the two on the surface of soil particles, prolongs their retention time in soil pores, and enhances the water solubility of the complex, thereby improving the desorption-leaching efficiency of zinc and cadmium, and has no heavy metal complexing activity itself.

[0021] Third, this invention effectively improves the curing rate of zinc and cadmium and the germination rate of seeds in the remediated soil by covering with a sealing film, evacuating to -0.05 to -0.08 MPa, and spraying a citric acid-ascorbic acid composite activating solution. This is because the chelating effect of citric acid dissolves insoluble phosphates or releases encapsulated heavy metals, increasing their contact opportunities with the passivating agent. Citric acid also forms soluble complexes with heavy metal ions (such as Cd²⁺ and Zn²⁺), increasing their mobility in the soil solution and making it easier for them to diffuse to the surface of the passivating agent (especially nano-FeS) particles to react (forming more stable CdS / ZnS precipitates). At the same time, ascorbic acid maintains the activity of the nano-ferrous sulfide surface, prolonging its ability to fix heavy metals, thereby achieving a higher curing rate of zinc and cadmium and reducing the impact of zinc and cadmium on seeds.

[0022] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0024] <Example 1> The remediation method for zinc-cadmium contaminated soil includes the following steps: Step 1: Mix zinc-cadmium contaminated soil with a composite leaching agent aqueous solution at a mass ratio of 1g:12mL, adjust the pH of the system to 5.0~5.5, and shake the mixture at 200 rpm for 3 hours on a horizontal shaker. The composite leaching agent aqueous solution includes: sodium lignosulfonate, polyaspartic acid, and the remainder water. The mass concentration of sodium lignosulfonate in the composite leaching agent aqueous solution is 10 g / L, and the mass concentration of polyaspartic acid is 2 g / L. Step 2: After leaching, the leached soil is obtained through solid-liquid separation. A composite passivating agent is added to the leached soil and mixed to obtain treated soil. The amount of composite passivating agent added is 1.2% of the dry weight of the zinc-cadmium contaminated soil. The composite passivating agent includes nano-ferrous sulfide and phosphoric acid activated biochar in a mass ratio of 1:2. Step 3: Spray water into the treated soil to adjust the moisture content to 25%, then cure the treated soil mound for 18 days. After the curing period, sow Sedum sarmentosum in the treated soil to rebuild vegetation.

[0025] <Example 2> Soil remediation was carried out using the method of Example 1, except that in step two of this example, the leachate obtained after solid-liquid separation was treated by adding mercapto-modified magnetic zeolite to the leachate, wherein 30g of mercapto-modified magnetic zeolite was added per liter of leachate.

[0026] The preparation method of the thiol-modified magnetic zeolite includes the following steps: Zeolite powder with a particle size of 80~100 μm was dispersed in water, and a mixture of FeCl3·6H2O and FeSO4·7H2O, accounting for 20% of the total mass of the zeolite powder, was added. The molar ratio of FeCl3·6H2O to FeSO4·7H2O in the mixture was 2:1. Under nitrogen protection, a 6 M sodium hydroxide solution was added dropwise until the pH of the system was 10.0±0.5. The mixture was then reacted at 60℃ for 2 h, and the first product was obtained by magnetic separation. The first product was dispersed in an aqueous solution with a volume ratio of 4:1 (ethanol and water), and 3-mercaptopropyltrimethoxysilane was added. The mixture was refluxed at 70°C for 6 hours, and then subjected to magnetic separation, washing with ethanol, and vacuum drying at 60°C to obtain mercapto-modified magnetic zeolite. The amount of 3-mercaptopropyltrimethoxysilane used was 6% of the mass of the zeolite powder.

[0027] <Example 3> The remediation method for zinc-cadmium contaminated soil includes the following steps: Step 1: Mix zinc-cadmium contaminated soil with a composite leaching agent aqueous solution at a mass ratio of 1g:12mL, adjust the pH of the system to 5.0~5.5, and shake the mixture at 200 rpm for 3 hours on a horizontal shaker. The composite leaching agent aqueous solution includes: sodium lignosulfonate, polyaspartic acid, and the remainder water. The mass concentration of sodium lignosulfonate in the composite leaching agent aqueous solution is 10 g / L, and the mass concentration of polyaspartic acid is 2 g / L. Step 2: After leaching, the leached soil is obtained through solid-liquid separation. A composite passivating agent is added to the leached soil and mixed to obtain treated soil. The amount of composite passivating agent added is 1.2% of the dry weight of the zinc-cadmium contaminated soil. The composite passivating agent includes nano-ferrous sulfide and phosphoric acid activated biochar in a mass ratio of 1:2. Step 3: Spray water into the treated soil to adjust the moisture content to 25%, then cure the treated soil mound for 18 days. After the curing period, sow Sedum sarmentosum in the treated soil to rebuild vegetation.

[0028] In step two, the eluent obtained by separating the solid and liquid after rinsing is processed by adding mercapto-modified magnetic zeolite to the eluent, wherein 30g of mercapto-modified magnetic zeolite is added to each liter of eluent.

[0029] The preparation method of the thiol-modified magnetic zeolite includes the following steps: Zeolite powder with a particle size of 80-100 μm was dispersed in water, and a mixture of FeCl3·6H2O and FeSO4·7H2O, accounting for 20% of the total mass of the zeolite powder, was added. The molar ratio of FeCl3·6H2O to FeSO4·7H2O in the mixture was 2:1. Under nitrogen protection, a 6 M sodium hydroxide solution was added dropwise until the pH of the system reached 10.0±0.5. The mixture was then reacted at 60℃ for 2 h, and the first product (Fe3O4@Zeolite) was obtained by magnetic separation. The first product was dispersed in an aqueous solution with a volume ratio of 4:1 (ethanol and water), and 3-mercaptopropyltrimethoxysilane was added. The mixture was refluxed at 70°C for 6 hours, and then subjected to magnetic separation, washing with ethanol, and vacuum drying at 60°C to obtain mercapto-modified magnetic zeolite. The amount of 3-mercaptopropyltrimethoxysilane used was 6% of the mass of the zeolite powder.

[0030] The composite rinsing agent aqueous solution also includes ammonium glycyrrhizate, and the mass concentration of ammonium glycyrrhizate in the composite rinsing agent aqueous solution is 1 g / L.

[0031] The preparation method of the composite rinsing agent aqueous solution includes the following steps: Heat the water to 38-40℃, add sodium lignosulfonate to the water while stirring at 300 rpm, and continue stirring for 25-30 minutes. Add polyaspartic acid to the system while stirring at 300 rpm, and continue stirring for 20-25 minutes. Ammonium glycyrrhizate was added to the system while stirring at 200 rpm, and the mixture was stirred for 15-20 minutes. The mixture was then cooled to room temperature to obtain the aqueous solution of the composite rinsing agent.

[0032] The preparation method of phosphoric acid activated biochar in step two includes the following steps: Rice husk biomass pulverized to 80-100 mesh was immersed in a 40 wt% phosphoric acid solution with a ratio of rice husk biomass to phosphoric acid solution of 1 g: 4 mL, and ultrasonically treated for 30 minutes. After separation, the impregnated biomass is first pre-carbonized at 150℃ for 30 minutes by heating at 5℃ / min, and then pyrolyzed at 550℃ for 1 hour by heating at 10℃ / min, with a nitrogen flow rate of 0.5 L / min. After cooling, the pyrolysis products were first washed with 0.1 mol / L nitric acid solution (3 times), then washed with deionized water until the conductivity of the filtrate was <50 μS / cm, and then dried under vacuum at 105℃ to obtain phosphoric acid activated biochar.

[0033] In step one, during the shaking reaction, ozone gas is introduced into the system every 30 minutes at a rate of 0.1 L per liter of reaction system and an ozone gas concentration of 80 mg / L.

[0034] The maintenance method in step three is as follows: A1. Compact the treated soil pile and cover the surface with a sealing film. Vacuum the soil to -0.05~-0.08 MPa and maintain the ambient temperature at 30-35℃ for 6 days. After maintenance, turn the soil pile over. A2. After the turning operation is completed, cover with a sealing film, and make multiple micropores in the sealing film with a pore diameter of 0.5~1mm and a pore density of 50 pores / m³. 2 For 12 days, a citric acid-ascorbic acid composite activating solution is sprayed onto the surface of the soil mound through micropores (using a pressurized spraying device at 0.2~0.5MPa), with a spraying volume of 70mL / m². 2 The citric acid-ascorbic acid composite activating solution contains 1 g / L of citric acid and 0.7 g / L of ascorbic acid.

[0035] The citric acid-ascorbic acid composite activating solution was applied in two batches: The first spray should consist of 40% of the total mass of the citric acid-ascorbic acid composite activating solution, sprayed after the micropores are opened; The remaining citric acid-ascorbic acid compound activating solution was sprayed a second time, 24 hours after the first spray.

[0036] Step 3: Three days before sowing Sedum sarmentosum, apply 0.4% of the mass of well-rotted organic fertilizer to the treated soil. The well-rotted organic fertilizer has an organic matter content of ≥45% and a total nitrogen, phosphorus and potassium content of ≥5%. After application, till the soil.

[0037] <Example 4> Soil remediation was carried out using the method of Example 3, except that the composite leaching agent aqueous solution in this example does not include ammonium glycyrrhizate.

[0038] <Example 5> Soil remediation was carried out using the method of Example 3, except that ozone was not introduced during the oscillation reaction process in this example.

[0039] <Example 6> Soil remediation was carried out using the method of Example 3, except that the maintenance method in step three of this example was as follows: the treated soil pile was compacted and maintained for 6 days. After the maintenance period, the soil pile was turned over and maintained for another 12 days.

[0040] <Example 7> Soil remediation was carried out using the method of Example 3, except that no well-rotted organic fertilizer was applied in step three of this example.

[0041] <Comparative Example 1> Soil remediation was carried out using the method of Example 1, except that the composite leaching agent aqueous solution in step one of this example includes sodium lignosulfonate with a mass concentration of 12% and the remainder water.

[0042] <Comparative Example 2> Soil remediation was carried out using the method of Example 1, except that the composite leaching agent aqueous solution in step one of this example includes 12% polyaspartic acid by mass and the remainder water.

[0043] In the above embodiments, the acid-base regulator is an inorganic acid solution or an inorganic alkali solution, selected from at least one of hydrochloric acid (HCl), sulfuric acid (H2SO4), sodium hydroxide (NaOH), and sodium bicarbonate (NaHCO3); the ratio of zeolite powder to water is 1 g: 5 mL.

[0044] <Comparative Example 3> Soil remediation was carried out using the method of Example 3, except that in step three of this example, only a citric acid aqueous solution with a mass concentration of 1.7 g / L was sprayed during the maintenance process at a rate of 70 mL / m³. 2 .

[0045] <Comparative Example 4> Soil remediation was carried out using the method of Example 3, except that in step three of this example, only an ascorbic acid aqueous solution with a mass concentration of 1.7 g / L was sprayed at a rate of 70 mL / m³ during the maintenance process. 2 .

[0046] <Comparative Example 5> Soil remediation was carried out using the method of Example 2, except that zeolite powder was added to the leaching solution instead of mercapto-modified magnetic zeolite.

[0047] <Experimental Characterization> 1. Zinc and cadmium removal efficiency Example 1: Soil remediation was carried out using the methods of Examples 3-5. The removal efficiency of zinc and cadmium in the remediated soil was tested 120 days after the planting of Sedum aizoon in each group of experiments. The results are shown in Table 1. Table 1 shows the zinc and cadmium removal efficiency. Example 1 74.8% 80.2% Example 3 87.5% 93.7% Example 4 83.1% 87.3% Example 5 81.6% 90.5% Comparative Example 1 63.1% 65.4% Comparative Example 2 62.4% 67.5% Compare and analyze the data in Table 1: In Example 1, the addition of sodium lignosulfonate and polyaspartic acid effectively improved the removal efficiency of zinc and cadmium. The effect was even more significant when both were used together. This is because when sodium lignosulfonate and polyaspartic acid are used in combination, sodium lignosulfonate first releases bound zinc and cadmium from the soil into the solution through surface activity and desorption. Subsequently, polyaspartic acid immediately chelates with the desorbed zinc and cadmium ions, forming stable and water-soluble chelates that prevent their re-adsorption by the soil. This synergistic "desorption-chelation" process solves the problem of insufficient chelating capacity of sodium lignosulfonate alone and compensates for the low desorption efficiency of polyaspartic acid alone, thus significantly improving the overall removal efficiency of zinc and cadmium. Furthermore, data from Comparative Examples 1 and 2 demonstrate that the combined effect is superior to that of sodium lignosulfonate or polyaspartic acid alone. Comparing the data from Examples 3 and 4, it can be seen that adding ammonium glycyrrhizate can effectively improve the removal efficiency of zinc and cadmium. This indicates that by adding ammonium glycyrrhizate, the uronic acid group in the ammonium glycyrrhizate molecule forms a synergistic dispersion system with sodium lignosulfonate and polyaspartic acid, inhibiting the non-specific adsorption of the two on the surface of soil particles, prolonging their retention time in soil pores, and enhancing the water solubility of the complex, thereby improving the desorption-leaching efficiency of zinc and cadmium, and having no heavy metal complexing activity itself. Comparing the data from Example 3 and Example 5, it can be seen that the present invention can effectively improve the dissolution of cadmium and zinc in the aqueous solution of the composite leaching agent by introducing ozone during the shaking reaction, thereby improving the zinc and cadmium removal efficiency. 2. Rapeseed germination rate Rapeseed was planted in the remediated soil of Examples 3, 6, 3, and 4. The germination rate of rapeseed in each group of experiments was counted, and the results are shown in Table 2. Table 2 Rapeseed Germination Rate Example 3 91% Example 6 74% Comparative Example 3 72% Comparative Example 4 77% Comparing the data from Examples 3 and 6, and Comparative Examples 3 and 4, it can be seen that the present invention, by covering with a sealing film and evacuating to -0.05 to -0.08 MPa, and spraying with a citric acid-ascorbic acid composite activating solution, can effectively improve the curing rate of zinc and cadmium and increase the germination rate of seeds in the remediated soil. This is because the chelating effect of citric acid dissolves insoluble phosphates or releases encapsulated heavy metals, increasing their contact opportunities with the passivating agent. Furthermore, citric acid forms soluble complexes with heavy metal ions (such as Cd²⁺ and Zn²⁺), increasing their mobility in the soil solution and making it easier for them to diffuse to the surface of the passivating agent (especially nano-FeS) particles for reaction (forming more stable CdS / ZnS precipitates). At the same time, ascorbic acid is used to maintain the activity of the nano-ferrous sulfide surface, prolonging its ability to fix heavy metals, thereby achieving a higher curing rate of zinc and cadmium and reducing the impact of zinc and cadmium on seeds.

[0048] 3. Recycling rate The contents of zinc and cadmium in the treated leaching solutions of Example 2 and Comparative Example 5 were detected, and the results are shown in Table 3. Table 3 Zinc and Cadmium Content in Leachate Example 2 8 0.2 Comparative Example 5 21 7 Comparative analysis of the data from Example 2 and Comparative Example 5 shows that the thiol-modified magnetic zeolite prepared in this application has a better treatment effect on the eluent. This is because its performance is upgraded through two-step modification: First, the zeolite is given magnetism by loading Fe3O4 (generated by the reaction of FeCl3・6H2O and FeSO4・7H2O), which enables it to be quickly recovered through magnetic separation and avoids zeolite powder residue; Second, the 3-mercaptopropyltrimethoxysilane modification increases the number of strong adsorption groups such as thiol (-SH), which can form stable chelates with zinc and cadmium ions in the eluent, significantly improving the adsorption capacity and selectivity.

[0049] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention, and those skilled in the art can easily implement other modifications. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to specific applications. The specific details and embodiments shown and described herein.

Claims

1. A method for remediating zinc-cadmium contaminated soil, characterized in that, Includes the following steps: Step 1: Mix zinc-cadmium contaminated soil with a composite leaching agent aqueous solution at a mass-volume ratio of 1g: 10-15mL, adjust the pH of the system to 5.0-5.5, and shake the mixture at 180-200 rpm for 2-3 hours on a horizontal shaker. The composite leaching agent aqueous solution includes: sodium lignosulfonate, polyaspartic acid, and the remainder water. The mass concentration of sodium lignosulfonate in the composite leaching agent aqueous solution is 10 g / L, and the mass concentration of polyaspartic acid is 2 g / L. Step 2: After leaching, the leached soil obtained through solid-liquid separation is mixed with a composite passivating agent to obtain treated soil. The amount of composite passivating agent added is 0.5~1.5% of the dry weight of the zinc-cadmium contaminated soil. The composite passivating agent includes nano-ferrous sulfide and phosphoric acid activated biochar in a mass ratio of 1:(2~3). Step 3: Spray water into the treated soil to adjust the moisture content to 20-30%. Then, cure the treated soil mound for 15-20 days. After the curing is completed, sow Sedum sarmentosum in the treated soil to rebuild vegetation. In step two, the eluent obtained by separating the solid and liquid after rinsing is processed by adding mercapto-modified magnetic zeolite to the eluent, wherein 20-40g of mercapto-modified magnetic zeolite is added to each liter of eluent. The preparation method of the thiol-modified magnetic zeolite includes the following steps: Zeolite powder with a particle size of 75-150 μm was dispersed in water, and a mixture of FeCl3·6H2O and FeSO4·7H2O, with a total mass of 10-30% of the zeolite powder, was added. The molar ratio of FeCl3·6H2O to FeSO4·7H2O in the mixture was 2:

1. Under nitrogen protection, a 6 M sodium hydroxide solution was added dropwise until the pH of the system was 10.0±0.

5. The mixture was reacted at 60℃ for 2 h, and the first product was obtained by magnetic separation. The first product was dispersed in an aqueous solution of ethanol at a volume ratio of 4:1, and 3-mercaptopropyltrimethoxysilane was added. The mixture was refluxed at 70°C for 6 hours, and then subjected to magnetic separation, washing with ethanol, and vacuum drying at 60°C to obtain mercapto-modified magnetic zeolite. The amount of 3-mercaptopropyltrimethoxysilane used was 5-8% of the mass of the zeolite powder. The composite rinsing agent aqueous solution also includes ammonium glycyrrhizate, and the mass concentration of ammonium glycyrrhizate in the composite rinsing agent aqueous solution is 1 g / L; The preparation method of the composite rinsing agent aqueous solution includes the following steps: Heat the water to 38-40℃, add sodium lignosulfonate to the water while stirring at 300 rpm, and continue stirring for 25-30 minutes. Add polyaspartic acid to the system while stirring at 300 rpm, and continue stirring for 20-25 minutes. Ammonium glycyrrhizate was added to the system while stirring at 200 rpm, and the mixture was stirred for 15-20 minutes. The mixture was then cooled to room temperature to obtain the aqueous solution of the composite rinsing agent.

2. The method for remediating zinc-cadmium contaminated soil as described in claim 1, characterized in that, The preparation method of phosphoric acid activated biochar in step two includes the following steps: Rice husk biomass pulverized to 80-100 mesh was immersed in a 40 wt% phosphoric acid solution with a ratio of rice husk biomass to phosphoric acid solution of 1 g: 4 mL, and ultrasonically treated for 30 minutes. After separation, the impregnated biomass is first pre-carbonized at 150℃ for 30 minutes by heating at 5℃ / min, and then pyrolyzed at 550℃ for 1 hour by heating at 10℃ / min, with a nitrogen flow rate of 0.5 L / min. After cooling, the pyrolysis products were washed successively with 0.1 mol / L nitric acid solution and deionized water until the conductivity of the filtrate was <50 μS / cm, and then dried under vacuum at 105℃ to obtain phosphoric acid activated biochar.

3. The method for remediating zinc-cadmium contaminated soil as described in claim 1, characterized in that, In step one, during the shaking reaction, ozone gas is introduced into the system every 30 minutes. The ozone introduction rate is 0.1~0.2L per liter of reaction system, and the ozone gas concentration is 80~100mg / L.

4. The method for remediating zinc-cadmium contaminated soil as described in claim 1, characterized in that, The maintenance method in step three is as follows: A1. Compact the treated soil pile and cover the surface with a sealing film. Vacuum the soil to -0.05~-0.08 MPa and maintain the ambient temperature at 30-35℃ for 5~7 days. After maintenance, turn the soil pile over. A2. After the turning operation is completed, cover with a sealing film, and make multiple micropores in the sealing film with a pore diameter of 0.5~1mm and a pore density of 40~60 pores / m³. 2 Maintain for 10-13 days, then spray a citric acid-ascorbic acid composite activating solution onto the surface of the soil mound through micropores, with a spraying rate of 50-100 mL / m². 2 The citric acid-ascorbic acid composite activating solution contains 1 g / L of citric acid and 0.7 g / L of ascorbic acid.

5. The method for remediating zinc-cadmium contaminated soil as described in claim 4, characterized in that, The citric acid-ascorbic acid composite activating solution was applied in two batches: The first spray should consist of 40% of the total mass of the citric acid-ascorbic acid composite activating solution, sprayed after the micropores are opened; The remaining citric acid-ascorbic acid composite activating solution was sprayed a second time, 24 hours after the first spray.

6. The method for remediating zinc-cadmium contaminated soil as described in claim 1, characterized in that, Step 3: Three days before sowing Sedum sarmentosum, apply 0.3% to 0.5% of well-rotted organic fertilizer by weight of the soil to the treated soil. The well-rotted organic fertilizer shall have an organic matter content of ≥45% and a total nitrogen, phosphorus and potassium content of ≥5%. After application, till the soil.