A pH value responsive soil heavy metal passivator and a preparation method thereof

Abstract

This invention discloses a pH-responsive soil heavy metal passivating agent and its preparation method. The passivating agent is a carbon nanowire / iron nanoparticle composite material, prepared by polyamide coating of an iron-based material followed by solution spinning and microwave carbonization. The composite material has a one-dimensional nanowire structure and its surface is grafted with acid-base functional groups. The passivating agent can dynamically respond to changes in soil pH and is compatible with both anionic and cationic heavy metal ions. Through adsorption and co-precipitation with metals, it converts active heavy metals into stable states and remains dormant when the heavy metals are in a stable state. The passivating agent of this invention can dynamically respond to soil pH and is compatible with cationic heavy metals in acidic soils and anionic heavy metals in alkaline soils, solving the problems of narrow adaptability and poor passivation specificity of traditional passivating agents. It has excellent passivation effects on various heavy metals such as mercury and cadmium.

Description

Technical Field

[0001] This invention relates to a pH-responsive soil heavy metal passivating agent and its preparation method, belonging to the field of soil heavy metal treatment technology. Background Technology

[0002] Remediation of soil heavy metal pollution has become a pressing technical challenge. Among these technologies, heavy metal passivation has become one of the most widely used due to its advantages such as ease of operation, short remediation cycle, and controllable cost. This technology involves applying heavy metal passivating agents to contaminated soil. The passivating agents then adsorb, complex, and precipitate heavy metal ions in the soil, reducing the bioavailability and mobility of heavy metals. This reduces the absorption of heavy metals by crops, thus achieving in-situ remediation of soil pollution.

[0003] However, existing technologies have significant drawbacks: the occurrence forms (stable / active) of heavy metals in soil are significantly affected by soil pH, and they usually only transform from a stable state to a bioavailable active state (cationic or anionic state) within a specific pH range; traditional heavy metal passivating agents do not have environmental responsiveness, and in order to ensure effective passivation when heavy metals are in an active state, excessive application is required in practical applications, which not only wastes passivating agent resources and increases remediation costs, but may also cause secondary ecological risks due to the accumulation of excessive agents interfering with the original physicochemical properties of the soil.

[0004] To address these issues, pH-responsive soil heavy metal passivators have gradually become a research hotspot. However, existing pH-responsive passivators still suffer from insufficient functional synergy, low response sensitivity, and complex preparation processes, which limit their large-scale application. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a pH-responsive soil heavy metal passivating agent and its preparation method, which is simple in process, low in cost, accurate in response, and has high passivation efficiency.

[0006] To achieve the above objectives, the present invention employs a pH-responsive soil heavy metal passivating agent, wherein the passivating agent is prepared by polyamide coating of iron-based materials and then by solution spinning, microwave carbonization, acidification modification, and amination modification. The passivating agent has a one-dimensional nanowire structure and acid and base functional groups grafted onto its surface.

[0007] The polyamide-coated iron-based material is obtained by mixing the iron-based material with polyamide in an organic solvent;

[0008] The acidification modification is performed by standing in a mixed acid solution;

[0009] The amination modification was performed by standing in an amine solution;

[0010] The passivating agent can dynamically respond to changes in soil pH and is compatible with anionic or cationic heavy metal ions. Through adsorption and co-precipitation with metals, it converts active heavy metals into stable states and remains dormant when the heavy metals are in a stable state. The dormant state means that the acid-base functional groups on the surface of the passivating agent no longer react with ions in the soil environment.

[0011] A second aspect of the present invention also provides a method for preparing the pH-responsive soil heavy metal passivating agent, comprising the following steps:

[0012] (1) Take iron-based materials and polyamide, add them to an organic solvent, disperse and dissolve them at room temperature and stir evenly to obtain a mixed system;

[0013] (2) The mixture obtained in step (1) is solution spun to obtain iron-based material / polyamide composite nanowires;

[0014] (3) The iron-based material / polyamide composite nanowires obtained in step (2) are placed in a microwave oven and carbonized and fixed by microwave heating to obtain carbon nanowire / iron nanoparticle composite material.

[0015] (4) The carbon nanowire / iron nanoparticle composite material obtained in step (3) is placed in a mixed acid solution for acidification treatment to obtain an acidified modified composite material.

[0016] (5) The acidified modified composite material obtained in step (4) is placed in an amine solution for amination treatment to obtain the pH-responsive soil heavy metal passivating agent.

[0017] As an improvement, in step (1), the mass ratio of iron-based material to polyamide is (1-5):(1-50).

[0018] The iron-based material is at least one of iron powder, iron oxide, iron sulfate, iron chloride, and iron acetate; the polyamide is at least one of polycaprolactam, polyhexamethylene adipamide, poly(m-phenylene isophthalamide), and poly(m-phenylene adipamide).

[0019] As an improvement, in step (1), the mass-to-volume ratio of the iron-based material to the organic solvent is (1-5) g: (50-200) ml; the organic solvent is at least one of ethanol, ethylene glycol, dimethylformamide, and toluene.

[0020] As an improvement, in step (2), the heating temperature of solution spinning is 50-200℃ and the spinning speed is 1-10 m / min; in step (3), the power of microwave heating is 300-1000w and the heating time is 10-90s.

[0021] As an improvement, in step (4), the mass-to-volume ratio of the carbon nanowire / iron nanoparticle composite material to the mixed acid solution is (1-10) g: (10-100) ml, the molar concentration of the mixed acid solution is 0.1-2 mol / L, and the mixed acid solution is at least two of hydrochloric acid, sulfuric acid, acetic acid, nitric acid, oxalic acid, and citric acid.

[0022] As an improvement, in step (5), the mass-to-volume ratio of the acidified modified composite material to the amine solution is (1-20) g: (5-200) ml, the molar concentration of the amine solution is 0.05-3 mol / L, and the amine solution is at least one of ammonia, ethylenediamine, and aniline.

[0023] A third aspect of the present invention also provides the application of the pH-responsive soil heavy metal passivating agent or the pH-responsive soil heavy metal passivating agent prepared by the preparation method in in-situ remediation of heavy metal contaminated soil.

[0024] As an improvement, the heavy metal includes at least one of arsenic, lead, chromium, nickel, and cadmium.

[0025] As an improvement, the contaminated soil is farmland soil, and the passivating agent is applied by broadcasting, trenching, or mixing with the soil.

[0026] Mechanism of the invention:

[0027] One-dimensional nanowire structures prepared by solution spinning possess ultra-large specific surface area and abundant pore structure (specific surface area ranges from 168 to 236 m²). 2 / g; pore volume 0.35-0.69cm 3 On the one hand, the carbon nanowires provide ample physical adsorption sites for heavy metal ions, enabling rapid physical adsorption through van der Waals forces and hydrophobic interactions. On the other hand, the high stability of the carbon nanowires serves as a support framework, uniformly fixing iron nanoparticles on the surface and within the pores, preventing aggregation and ensuring full exposure of their reactive sites. After microwave carbonization, the iron-based material is transformed into highly active iron nanoparticles. The carbon layer formed by polyamide carbonization further prevents rapid oxidation and deactivation of the iron nanoparticles while ensuring effective contact with heavy metal ions, providing a stable chemical basis for subsequent co-precipitation reactions.

[0028] The acid-base functional groups (acidic groups such as carboxyl and sulfonic acid groups; basic groups such as amino and imine groups) grafted onto the surface of the passivating agent through acidification-amine modification are the core of achieving pH response, and their adaptation logic is as follows:

[0029] Acidic soil environment (low pH): At this time, heavy metals in the soil mostly exist in cationic form. The basic functional groups (amine groups) on the surface of the passivating agent undergo a protonation reaction. The positively charged groups precisely capture cationic heavy metal ions in the soil through electrostatic adsorption and complexation, forming stable complexes.

[0030] Alkaline soil environment (high pH): At this time, heavy metals in the soil mostly exist in anionic state. The acidic functional groups (carboxyl groups) on the surface of the passivating agent undergo a dissociation reaction. The negatively charged groups specifically bind to anionic heavy metal ions through electrostatic adsorption and ion exchange, thus completing targeted capture.

[0031] Dormant mechanism: When all heavy metal ions in the soil have been converted into a stable state (without active heavy metals), the acid and base functional groups on the surface of the passivating agent no longer react with ions in the soil environment and are in a "dormant" state. This avoids ineffective consumption caused by combining with other harmless ions in the soil, and achieves on-demand activation, solving the drawbacks of excessive application of traditional passivating agents.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] (1) The passivating agent is a carbon nanowire / iron nanoparticle composite structure. The ultra-large specific surface area of ​​the one-dimensional nanowires provides sufficient adsorption sites, which can rapidly enrich active heavy metals in the soil. The iron nanoparticles undergo redox and co-precipitation reactions with the heavy metals, transforming them into stable precipitates with low bioavailability. The porous structure of the carbon nanowires physically encapsulates the precipitates, preventing them from dissociating again and achieving long-term passivation. At the same time, the acid-base functional groups grafted on the surface of the passivating agent can dynamically respond to the soil pH, accurately adapting to cationic heavy metals in acidic soils and anionic heavy metals in alkaline soils. This solves the problem of the narrow adaptability range and poor passivation specificity of traditional passivating agents to soil pH. It has excellent passivation effects on various heavy metals such as mercury, cadmium, lead, manganese, chromium, and arsenic.

[0034] (2) The passivating agent of the present invention does not need to rely on morphological transformation or component release to achieve response. When the heavy metals in the soil have been transformed into a stable state, the acid and base functional groups on its surface will enter a dormant state and no longer react ineffectively with harmless ions in the soil. This fundamentally avoids the drawback of traditional passivating agents that need to be applied in excess due to lack of responsiveness, greatly reduces the amount of passivating agent applied, reduces the raw materials and application costs of soil remediation, and avoids the waste of resources caused by excessive agent accumulation.

[0035] (3) During the preparation process, the iron-based material is coated with polyamide, which not only achieves uniform dispersion of the iron-based material, but also uses polyamide as a carbon source and structure guide to build a stable carbon-iron composite system. The subsequent microwave carbonization process realizes the nano-fixation of the iron-based material, avoids the aggregation of iron nanoparticles from the root, ensures that the adsorption sites of carbon nanowires and the reaction sites of iron nanoparticles are fully exposed, and enhances the synergistic passivation efficiency of "adsorption-co-precipitation". Compared with the carbon-iron composite passivating agent prepared by conventional encapsulation method, the material structure stability is greatly improved, the functional components are less lost during use, and the passivation activity can be maintained for a long time, improving the repair effect of unit agent.

[0036] (4) The passivating agent of the present invention achieves pH response and binding with heavy metals only through the charge change of surface functional groups. There is no release of additional components throughout the process. It will not introduce toxic and harmful impurities into the soil, nor will it interfere with the original acidity, alkalinity and physicochemical properties of the soil. It solves the problem that traditional pH-responsive passivating agents are prone to damage to the soil ecology due to morphological changes and component release. At the same time, the carbon-iron composite substrate of the passivating agent has good environmental compatibility and will not damage soil microorganisms or soil aggregate structure. While achieving heavy metal passivation, it ensures the integrity and stability of the soil ecosystem and is suitable for farmland soil and other scenarios with high requirements for ecological safety.

[0037] (5) The passivating agent preparation process of the present invention is raw material compounding, solution spinning, microwave carbonization, acid modification, and amination modification. The process parameters of each step are clear and the operation is simple. There is no need for complicated production equipment. The microwave carbonization process heats quickly and evenly, which greatly shortens the preparation cycle. The iron-based materials, polyamides, organic solvents, acid / amine solutions and other materials used in the preparation are all common chemical raw materials. They are widely available and inexpensive. Moreover, the ratio of each raw material and the process parameters can be flexibly adjusted according to the actual repair needs, which makes it easy to achieve large-scale and industrialized production.

[0038] (6) The passivating agent of the present invention can be applied to contaminated soil by conventional methods such as broadcasting, trenching, or mixing with soil, without the need for special application equipment. It is compatible with existing farmland and site soil remediation procedures, has a low operating threshold, and is easy for grassroots agricultural technicians and construction workers to master. Moreover, the passivating agent has shown excellent passivation effects in various contaminated soils such as coal gangue artificial soil, and has a wide range of applicable scenarios. It has strong practical application value in the in-situ remediation of heavy metal contaminated soil. The passivating agent of the present invention is designed for farmland soil pollution remediation. After being applied to contaminated farmland, it can effectively reduce the bioavailability of heavy metals in the soil, reduce the absorption of heavy metals by crops, and ensure the quality and safety of agricultural products. At the same time, because there is no secondary pollution and no damage to the physical and chemical properties of the soil, the remediated soil can continue to be used for agricultural production, realizing the synergy between soil heavy metal passivation remediation and normal use of arable land, which meets the needs of sustainable agricultural development. Attached Figure Description

[0039] Figure 1 This is a SEM image of the carbon nanowire / iron nanoparticle composite material of Example 1 of the present invention;

[0040] Figure 2 The image shows a comparison of the removal effects of the passivating agent (addition amount 0.5%, passivation time 30 days) of Example 1 of this invention on heavy metal ions (arsenic, lead, chromium, nickel, cadmium) at different pH values.

[0041] Figure 3 The image shows a comparison of the removal effects of the passivating agent (pH 7, passivation time 30 days) of Example 1 of this invention on heavy metal ions (arsenic, lead, chromium, nickel, cadmium) at different addition amounts.

[0042] Figure 4 This is a comparison chart showing the removal effect of the passivating agent (pH 7, passivating agent addition amount 0.5%) of Example 1 of the present invention on heavy metal ions (arsenic, lead, chromium, nickel, cadmium) at different passivation times. Detailed Implementation

[0043] The following embodiments are further illustrations of the present invention and serve as explanations of the technical content of the present invention. However, the essence of the present invention is not limited to the embodiments described below. Those skilled in the art can and should know that any simple changes or substitutions based on the spirit of the present invention should fall within the protection scope claimed by the present invention. Example

[0044] A method for preparing a pH-responsive soil heavy metal passivating agent includes the following steps:

[0045] (1) Weigh 1g of iron oxide and 10g of polyhexamethylene adipamide, and add them together to a three-necked flask containing 100mL of anhydrous ethanol. Stir continuously for 10 minutes at room temperature and a stirring rate of 300r / min to ensure that the iron oxide and polyhexamethylene adipamide are completely dispersed and dissolved to obtain a uniform and stable mixed system.

[0046] (2) The mixture obtained in step (1) is transferred to the feed tank of the solution spinning equipment. The spinning heating temperature is set to 50°C and the spinning speed is 1m / min. After spinning and drawing, the initial product is collected. The initial product is placed in a forced-air drying oven and dried at 50°C and normal pressure for 8 hours to remove residual solvent and obtain iron-based material / polyamide composite nanowires with uniform morphology.

[0047] (3) Take 5g of the iron-based material / polyamide composite nanowires obtained in step (2), spread them evenly on the bottom of the ceramic crucible, put the crucible into an industrial microwave oven; set the microwave power to 800w and the microwave heating time to 60s, and complete the carbonization and iron-based nano-fixation in the air atmosphere. After naturally cooling to room temperature, collect the carbon nanowire / iron nanoparticle composite material.

[0048] (4) Weigh 2g of the carbon nanowire / iron nanoparticle composite material obtained in step (3), place it in a sealed container containing 100mL of mixed acid solution, wherein the mixed acid solution is a mixture of hydrochloric acid and acetic acid in a volume ratio of 1:1 and a molar concentration of 1mol / L, let it stand at room temperature (25℃) for 15 minutes, filter and collect the solid product, wash with deionized water until the pH of the filtrate is neutral, and vacuum dry to obtain the acid-modified composite material;

[0049] (5) Place 2g of the acidified modified composite material obtained in step (4) into a sealed container containing 100mL of ammonia solution with a concentration of 1mol / L, and let it stand at room temperature for 10 minutes to obtain the target product pH-responsive soil heavy metal passivating agent.

[0050] SEM image of the carbon nanowire / iron nanoparticle composite material prepared in Example 1, as shown below. Figure 1 As shown in the analysis, the material exhibits a regular one-dimensional nanowire morphology, with iron nanoparticles uniformly dispersed on the surface and in the pores of the carbon nanowires, without obvious agglomeration. The overall structure is rich in pores, forming a carbon nanowire framework with an ultra-large specific surface area. This structure can fully expose the physical adsorption sites and the chemical reaction sites of the iron nanoparticles, laying a good structural foundation for the efficient performance of the synergistic effect of adsorption-coprecipitation during the subsequent passivation process.

[0051] The passivating agent prepared in Example 1 was subjected to performance testing, and the results are as follows: Figures 2-4 As shown in the analysis, we can conclude that:

[0052] Soil with a pH value < 7 is acidic, and soil with a pH value > 7 is alkaline. Figure 2 It is evident that the available content of various heavy metal ions in the soil is highest when the soil pH is 7 (neutral). However, when the soil pH deviates from neutral (<7 or >7), the pH-responsive function of the passivating agent is activated. Through the adsorption-coprecipitation synergistic effect of the acid-base functional groups grafted on the surface, the passivation effect is significantly better than that under neutral conditions. The available content of various heavy metal ions in the soil is lower than that at pH=7, which confirms the dynamic adaptability of the passivating agent to soils with different pH levels.

[0053] from Figure 3 It can be seen that the amount of passivating agent added is positively correlated with the passivation effect of heavy metals: when the amount added is less than 0.5% of the soil mass, there are insufficient effective action sites for the passivating agent, and the passivation rate of heavy metals is at a low level; when the amount added exceeds 0.5%, the rate of increase in passivation rate slows down significantly, and further increasing the amount can no longer achieve a synchronous improvement in the passivation effect. Considering both the sufficiency of the passivation effect and the economy of practical application, the optimal amount of passivating agent added is determined to be 0.5% of the soil mass.

[0054] from Figure 4 It can be seen that the passivation effect gradually increases with the extension of passivation time: when the treatment time is less than 30 days, the active heavy metals in the soil have not been fully converted, and the passivation rate is low; when the treatment time reaches 30 days, the rate of increase in passivation slows down significantly, indicating that most of the active heavy metals in the soil have been converted into a stable state, and the passivating agent gradually enters a dormant state due to the lack of excess active heavy metals to act on. Considering both passivation efficiency and practical application requirements, 30 days is determined to be the optimal treatment cycle for this passivating agent to remediate heavy metal contaminated soil. Example

[0055] A method for preparing a pH-responsive soil heavy metal passivating agent includes the following steps:

[0056] (1) Weigh 1g of ferric chloride and 5g of polycaprolactam, and add them together to a three-necked flask containing 50mL of ethylene glycol; under the conditions of room temperature and stirring speed of 250r / min, continue stirring for 8 minutes to ensure that ferric chloride and polycaprolactam are completely dispersed and dissolved to obtain a uniform and stable mixed system.

[0057] (2) The mixture obtained in step (1) is transferred to the feed tank of the solution spinning equipment. The spinning heating temperature is set to 80℃ and the spinning speed is 3m / min. After spinning and drawing, the initial product is collected. The initial product is placed in a forced-air drying oven and dried at 60℃ and normal pressure for 6 hours to remove residual solvent and obtain iron-based material / polyamide composite nanowires with uniform morphology.

[0058] (3) Take 3g of the iron-based material / polyamide composite nanowires obtained in step (2), spread them evenly on the bottom of the ceramic crucible, put the crucible into an industrial microwave oven; set the microwave power to 500w and the microwave heating time to 30s, complete the carbonization and iron-based nano-fixation in the air atmosphere, and collect the carbon nanowire / iron nanoparticle composite material after naturally cooling to room temperature.

[0059] (4) Weigh 1g of the carbon nanowire / iron nanoparticle composite material obtained in step (3) and place it in a sealed container containing 50mL of mixed acid solution. The mixed acid solution is a mixture of sulfuric acid and citric acid in a volume ratio of 2:1 with a molar concentration of 0.5mol / L. Let it stand at room temperature (25℃) for 10 minutes, filter and collect the solid product, wash it with deionized water until the pH of the filtrate is neutral, and vacuum dry it to obtain the acid-modified composite material.

[0060] (5) Place 1g of the acidified modified composite material obtained in step (4) into a sealed container containing 50mL of 0.5mol / L ethylenediamine solution (amine solution) and let it stand at room temperature for 8 minutes to obtain the target product pH-responsive soil heavy metal passivating agent. Example

[0061] A method for preparing a pH-responsive soil heavy metal passivating agent includes the following steps:

[0062] (1) Weigh 4g of ferric sulfate and 40g of poly(m-phenylene isophthalamide), and add them together to a three-necked flask containing 180mL of dimethylformamide. Stir continuously for 15 minutes at room temperature and a stirring rate of 350r / min to ensure that ferric sulfate and poly(m-phenylene isophthalamide) are completely dispersed and dissolved to obtain a uniform and stable mixed system.

[0063] (2) The mixture obtained in step (1) is transferred to the feed tank of the solution spinning equipment. The spinning heating temperature is set to 180℃ and the spinning speed is 8m / min. After spinning and drawing, the initial product is collected. The initial product is placed in a forced-air drying oven and dried at 70℃ and normal pressure for 10 hours to remove residual solvent and obtain iron-based material / polyamide composite nanowires with uniform morphology.

[0064] (3) Take 8g of the iron-based material / polyamide composite nanowires obtained in step (2), spread them evenly on the bottom of the ceramic crucible, put the crucible into an industrial microwave oven; set the microwave power to 900w and the microwave heating time to 80s, and complete the carbonization and iron-based nano-fixation in the air atmosphere. After naturally cooling to room temperature, collect the carbon nanowire / iron nanoparticle composite material.

[0065] (4) Weigh 8g of the carbon nanowire / iron nanoparticle composite material obtained in step (3) and place it in a sealed container containing 90mL of mixed acid solution. The mixed acid solution is a mixture of nitric acid and oxalic acid in a volume ratio of 1:2 and a molar concentration of 1.8mol / L. Let it stand at room temperature (25℃) for 20 minutes, filter and collect the solid product, wash it with deionized water until the pH of the filtrate is neutral, and vacuum dry it to obtain the acid-modified composite material.

[0066] (5) Place 15g of the acidified modified composite material obtained in step (4) into a sealed container containing 180mL of 2.5mol / L aniline solution (amine solution) and let it stand at room temperature for 15 minutes to obtain the target product pH-responsive soil heavy metal passivating agent.

[0067] Application examples

[0068] Artificial heavy metal contaminated soil was prepared from coal gangue (initial available arsenic content 60 mg / kg, available cadmium content 80 mg / kg, soil pH=7); pH-responsive soil heavy metal passivating agent prepared in Example 1 was weighed at 0.5% of soil mass, and thoroughly mixed with the soil before incubation for 30 days.

[0069] Testing revealed that the available arsenic content in the treated soil decreased to 32 mg / kg, and the available cadmium content decreased to 41 mg / kg, demonstrating a significant passivation effect and verifying the practical application value of this passivating agent in in-situ remediation of heavy metal contaminated soil.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pH-responsive soil heavy metal passivating agent, characterized in that, The passivating agent is prepared by polyamide coating of iron-based material and then solution spinning, microwave carbonization, acidification modification and amination modification. The passivating agent has a one-dimensional nanowire structure and acid and base functional groups grafted on its surface. The polyamide-coated iron-based material is obtained by mixing the iron-based material with polyamide in an organic solvent; The acidification modification is performed by standing in a mixed acid solution; The amination modification was performed by standing in an amine solution; The passivating agent can dynamically respond to changes in soil pH and is compatible with anionic or cationic heavy metal ions. Through adsorption and co-precipitation with metals, it converts active heavy metals into stable states and remains dormant when the heavy metals are in a stable state. The dormant state means that the acid-base functional groups on the surface of the passivating agent no longer react with ions in the soil environment.

2. A method for preparing a pH-responsive soil heavy metal passivating agent as described in claim 1, characterized in that, Includes the following steps: (1) Take iron-based materials and polyamide, add them to an organic solvent, disperse and dissolve them at room temperature and stir evenly to obtain a mixed system; (2) The mixture obtained in step (1) is solution spun to obtain iron-based material / polyamide composite nanowires; (3) The iron-based material / polyamide composite nanowires obtained in step (2) are placed in a microwave oven and carbonized and fixed by microwave heating to obtain carbon nanowire / iron nanoparticle composite material. (4) The carbon nanowire / iron nanoparticle composite material obtained in step (3) is placed in a mixed acid solution for acidification treatment to obtain an acidified modified composite material. (5) The acidified modified composite material obtained in step (4) is placed in an amine solution for amination treatment to obtain the pH-responsive soil heavy metal passivating agent.

3. The preparation method of a pH-responsive soil heavy metal passivating agent as described in claim 2, characterized in that, In step (1), the mass ratio of iron-based material to polyamide is (1-5):(1-50); the iron-based material is at least one of iron powder, iron oxide, iron sulfate, iron chloride, and iron acetate; the polyamide is at least one of polycaprolactam, polyhexamethylene adipamide, polyisophthalamide, and polyisophthalamide.

4. The preparation method of a pH-responsive soil heavy metal passivating agent as described in claim 2, characterized in that, In step (1), the mass-to-volume ratio of the iron-based material to the organic solvent is (1-5) g: (50-200) ml; the organic solvent is at least one of ethanol, ethylene glycol, dimethylformamide, and toluene.

5. The preparation method of a pH-responsive soil heavy metal passivating agent as described in claim 2, characterized in that, In step (2), the heating temperature of solution spinning is 50-200℃ and the spinning speed is 1-10 m / min; in step (3), the power of microwave heating is 300-1000w and the heating time is 10-90s.

6. The method for preparing a pH-responsive soil heavy metal passivating agent as described in claim 2, characterized in that, In step (4), the mass-to-volume ratio of the carbon nanowire / iron nanoparticle composite material to the mixed acid solution is (1-10) g: (10-100) ml; The molar concentration of the mixed acid solution is 0.1-2 mol / L, and the mixed acid solution is at least two of hydrochloric acid, sulfuric acid, acetic acid, nitric acid, oxalic acid, and citric acid.

7. The preparation method of a pH-responsive soil heavy metal passivating agent as described in claim 2, characterized in that, In step (5), the mass-to-volume ratio of the acidified modified composite material to the amine solution is (1-20) g: (5-200) ml; the molar concentration of the amine solution is 0.05-3 mol / L, and the amine solution is at least one of ammonia, ethylenediamine, and aniline.

8. The application of a pH-responsive soil heavy metal passivating agent as described in claim 1 or a pH-responsive soil heavy metal passivating agent prepared by any one of claims 2-7 in the in-situ remediation of heavy metal contaminated soil.

9. The application as described in claim 8, characterized in that, The heavy metals include at least one of arsenic, lead, chromium, nickel, and cadmium.

10. The application as described in claim 8, characterized in that, The contaminated soil is farmland soil, and the passivating agent is applied by broadcasting, trenching, or mixing with the soil.

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