In-situ electrokinetic clogging-stabilization remediation method for heavy metal contaminated soil

Abstract

The present application belongs to the field of electrokinetic remediation of heavy metal contaminated soil, and particularly relates to a method for in-situ electrokinetic remediation of heavy metal contaminated soil. Specifically, a hollow functional material with an inner cavity is pre-embedded in the middle transition zone of the contaminated soil area to be treated; a direct current electric field is applied to both ends of the contaminated soil area to be treated, which drives the migration of heavy metal ions in the initial anode region to the middle transition zone, promotes the aggregation of colloids in the zone, compresses the soil pores, and forms an ion bypass channel with the inner cavity of the hollow functional material; when the physicochemical characteristics of the middle transition zone reach the threshold condition, the polarity of the electrodes at both ends of the contaminated soil area to be treated is switched; the reverse electric field promotes the migration of heavy metal ions in the initial cathode direction to the bypass channel formed above, and in-situ enrichment and stable remediation are realized with the counter-migrating stabilized ions in the bypass channel. The method breaks through the mass transfer limitation of traditional electrokinetic remediation, and realizes efficient spatial enrichment and synchronous stabilization of heavy metals.

Description

Technical Field

[0001] This invention belongs to the field of electrodynamic remediation of heavy metal contaminated soil, and specifically relates to an in-situ electrodynamic locking-stabilization remediation method for heavy metal contaminated soil (based on electric field regulation to block the diffusion of heavy metals in contaminated soil by colloidal blockage of contaminated soil to achieve directional enrichment remediation). Background Technology

[0002] Heavy metal pollution is one of the main types of soil pollution and a key focus of soil environmental remediation. Electrokinetic remediation technology has received continuous attention due to its convenience of in-situ application and high efficiency of mass transfer reactions. Under electrokinetic effects, heavy metals are mainly removed from contaminated soil in the form of migratable ions (water-soluble and acid-soluble). However, existing electrokinetic remediation technologies suffer from a focusing effect: that is, the H+ generated at the anode... + Acidified soils release heavy metal ions, but these ions readily react with OH groups in the cathode region during migration. - The formation of hydroxide precipitates results in approximately one-third of the soil area between the anode and cathode being difficult to remove heavy metals (Sun et al., 2019), creating a remediation blind zone. Traditional unidirectional electric field treatment requires a long acidification process (usually exceeding 30 days) to migrate heavy metals to the near-cathode area, resulting in high energy consumption. Furthermore, heavy metals that have migrated to the cathode area can still be released again as mobile ions due to soil particle disintegration, fragmentation, or acid rain erosion. Due to their unstable form, they pose a significant environmental risk.

[0003] To address these issues, existing technologies have proposed several improvement schemes. For example, the electrode approximation method involves repeatedly moving the electrode to track and collect the sedimentation zone, which is complex and difficult to scale up. Adding chelating agents (such as EDTA) can form stable complexes with heavy metals to promote migration, but the chelating agents themselves may cause secondary pollution and are costly. The electro-permeable reactive barrier (PRB) combined technology sets up a reaction medium along the pollutant migration path, but the PRB is only for passive capture, and the reaction medium has the problem of saturation and failure, requiring replacement.

[0004] It is worth noting that most existing technological improvements focus on how to "guide out" or "adsorb and capture" heavy metals, with the core objective remaining the "removal" or "transfer" of pollutants. This approach inevitably requires continuous energy and material input to sustain the migration process. Therefore, there is a need to develop a novel electrokinetic remediation technology capable of efficiently concentrating heavy metal-rich areas and ensuring the durability of stabilization effects. This invention is proposed based on this technological requirement.

[0005] Currently, some studies have proposed methods for heavy metal enrichment by periodically switching electrode polarity. This method repeatedly changes the electric field direction, causing the precipitation zone to dissolve and reprecipitate repeatedly. While this can expand the acidification area to some extent, it leads to pollutants repeatedly "swaying" in the soil, failing to achieve effective targeted enrichment and concentration, and the energy consumption problem remains unresolved. Other studies have used electrode switching in electrokinetic remediation to repair soil, but this only targets organic pollutants. The purpose of switching electrodes is to maintain neutral pH conditions in the soil, which is beneficial to microbial activity.

[0006] Unlike the aforementioned approaches of "guiding out," this invention takes a different approach, proposing a strategy of "guiding in and locking in." We have observed that under the influence of an electric field, natural colloids in the soil can aggregate and block soil pores under certain conditions, affecting the migration pathways of ions. Inspired by this, this invention aims to actively utilize and enhance this "colloidal blockage" phenomenon, constructing a low-permeability "heavy metal locking zone" in a specific area. This zone directs and enriches heavy metal ions, and then uses a cavity material to create flow channels, maintaining the current transmission pathway for conductive ions. Simultaneously, a stabilizer transforms the heavy metals into a long-term stable form, thereby achieving a technological paradigm shift from "removal" to "in-situ fixed-point blocking and stabilization."

[0007] References [1] Sun Z , Wu B , Guo P ,et al.Enhanced electrokinetic remediationand simulation of cadmium-contaminated soil by superimposed electric field[J].Chemosphere: Environmental toxicology and risk assessment, 2019.DOI:10.1016 / j.chemosphere.2019.05.233. Summary of the Invention

[0008] The purpose of this invention is to provide a method for the targeted enrichment and remediation of heavy metal contaminated soil based on electric field-controlled colloidal blockage.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: An in-situ electrically locked-stabilization remediation method for heavy metal contaminated soil: (1) A hollow functional material with an inner cavity is pre-buried in the intermediate transition zone of the area of ​​the contaminated soil to be treated; (2) Apply a DC electric field to both ends of the contaminated soil area to drive the heavy metal ions in the initial anode area to migrate to the intermediate transition zone, while promoting the colloidal aggregation in this zone and compressing the soil pores, and forming an ion flow channel by means of the inner cavity of the hollow functional material. (3) When the physicochemical characteristics of the intermediate transition zone reach the threshold condition, switch the electrode polarity at both ends of the contaminated soil area to be treated; (4) The reverse electric field promotes the migration of heavy metals in the initial cathode direction to the flow channel formed in step (2), and the stabilized ions that migrate in the opposite direction achieve in-situ enrichment and stable repair in the flow channel.

[0010] The intermediate transition zone described above is located at the center between the anode and cathode, extending laterally to both sides of the electrode. The total length of the extension is 1 / 10 to 1 / 7 of the length of the contaminated soil area to be treated. The area enclosed by this zone is the intermediate transition zone. When the pH near the anode is 2, the pH of this zone is between 4 and 6.

[0011] The hollow functional material with an inner cavity is carbonized straw, hollow glass microspheres, or hollow ceramic particles.

[0012] In step (1), a hollow functional material with an inner cavity is pre-embedded in the intermediate transition zone of the contaminated soil area to be treated. The hollow functional material is added to the contaminated soil in strips along the direction of the electric field, with an implantation density of 0.1-0.2 g / cm³. 3 .

[0013] In step (2), a DC electric field is applied to both ends of the contaminated soil area to be treated. The electrolyte used at the positive electrode is an aqueous solution containing 0.05~0.15 mol / L calcium ions, and the electrolyte used at the negative electrode is an aqueous solution containing 0.1~0.3 mol / L sodium or potassium ions. Under the drive of the electric field, the difference between the actual transport rate of hydrogen ions and the migration rate of heavy metal ions is used to make the heavy metal ions in the initial anode area migrate to the intermediate transition area, while promoting the colloidal aggregation and locking in this area, and forming an ion flow channel by means of the hollow material's internal cavity structure.

[0014] Under the influence of the electric field, colloidal particles in the soil agglomerate and deposit due to changes in ionic strength (aggregation of high-valence cations in the soil, which can be calcium, iron, and aluminum ions) and pH (increase in hydrogen ion content). This reduces the porosity of the soil in the intermediate transition zone, forming non-uniform pores. The hollow material maintains a large, interconnected pore channel. Hydrogen ions migrate towards the cathode through the large pores and flow channels. As a result, the average particle size of the aggregated particles is 15-35 μm. The accumulated heavy metals inside are difficult to contact and decompose with hydrogen ions, forming physical blockages.

[0015] The electric field strength is 1~2.5 V / cm, and the soil bulk density is 1.5~1.7 g / cm³.3 .

[0016] In step (3), the physicochemical characteristics of a certain region must meet at least two of the following conditions (1)-(4) to reach the threshold condition. (1) The proportion of the intermediate transition region in the total voltage division is reduced by 50-70%; (2) The heavy metal content in the intermediate transition zone is 2 to 3 times that of the initial contaminated soil, and the heavy metal content in the initial anode area is reduced to less than 5% of that in the initial contaminated soil. (3) The soil pH in the intermediate transition zone is in the range of 40 to 6.0; (4) The electrodialysis flow towards the cathode gradually stops or forms a reverse (towards) electrodialysis flow towards the anode.

[0017] In step (4), the electrode direction is switched. The electrolyte used at the cathode is a salt solution with pH 2-3 containing stable heavy metal ions to be treated, and the electrolyte used at the positive electrode is an aqueous solution containing 0.1-0.3 mol / L sodium or potassium ions. The direction of the electric field is used to migrate the heavy metals remaining in the area near the original cathode to the central part for enrichment through the electrodynamic effect. At the same time, the anions in the cathode electrolyte migrate towards the anode and enter the soil. They react with the heavy metals that have migrated to the central part in the flow channel to form a stable precipitate, thereby achieving in-situ enrichment and stable remediation.

[0018] In step (4), the electric field strength is 0.5-1.5V / cm.

[0019] In the above-described treatment method, electrodes are inserted on both sides of the contaminated soil area to be treated. The areas where the electrodes are inserted serve as electrolytic cells, and the space between the two electrolytic cells forms the soil chamber of the contaminated soil area to be treated. At the other end of each of the two electrolytic cells, a receiving area is provided to collect the overflowing electrodialysis solution via pipelines. The receiving area can be a trench dug on both sides of the remediation area, or it can be a container.

[0020] Furthermore, a horizontal electric field is applied to both sides of the contaminated soil area to be treated. The areas where electrodes are inserted serve as electrolytic cells, and the area between the two electrolytic cells is a soil chamber for the contaminated soil area to be treated. The soil chamber can be sequentially divided into an initial anode area (S1 area), a near-electrode area (S2 area), an intermediate transition area (S3 area), a near-electrode area (S4 area), and an initial cathode area (S5 area). At the other end of the two electrolytic cells, a receiving area is set up to receive the overflowing electrodialysis liquid through a pipeline. The receiving area can be a trench opened on both sides of the remediation area or a container.

[0021] The intermediate transition zone described above is located at the center between the anode and cathode, extending laterally to both sides of the electrode. The total length of the extension is 1 / 10 to 1 / 7 of the length of the contaminated soil area to be treated. The area enclosed by this extension zone is the intermediate transition zone. When the initial pH of the anode zone is 2, the pH of this zone is between 4 and 6.

[0022] The width of the two electrolytic cell regions is the same as the width of the soil region to be treated, which is 1 / 5 to 1 / 3 of the length of the contaminated soil region to be treated.

[0023] The heavy metals include one or more of Cd, Pb, Cu, and Zn.

[0024] The advantages and beneficial effects of this invention are: When traditional unidirectional electric fields promote the enrichment of heavy metals, they often rely on the precipitation of heavy metals in alkaline regions. Even when switching electric fields is used, the enrichment of heavy metals is achieved through repeated switching, which is a long process.

[0025] This invention utilizes a triple synergy of "physical bypass-chemical interception-electrode switching" and leverages the coupling of colloids with an electric field to enable the migration and regulation of heavy metals, achieving the precise remediation goal of "high concentration enrichment-blocking-stabilization". This provides a new technological paradigm for the remediation of heavy metal contaminated soil that is efficient, stable and energy-saving. This invention utilizes the time difference between colloidal sedimentation in the intermediate transition zone and heavy metal desorption and migration in the anolyte zone to purposefully desorb and migrate heavy metals from the anolyte area to the intermediate transition zone. A high-valence cationic electrolyte is used to simultaneously control the sedimentation of soil colloids in the intermediate transition zone, encapsulating the heavy metals. Subsequently, a single electrode switch achieves the enrichment of heavy metals on both the initial anode and cathode sides. The enriched area accounts for less than 20% of the soil to be remediated. Experiments show that the heavy metal content in zones S1, S2, S4, and S5 can be reduced to below 5% of the initial concentration, while the enriched concentration in zone S3 can reach 4-5 times the initial value. Furthermore, through simultaneous stabilization treatment, the enriched heavy metals can be converted to a low-leaching state, reducing toxicity and ecological risks. By optimizing the electrolyte combination and electric field switching strategy, the remediation cycle is shortened (experiments show significant effects within 12 days), energy consumption is reduced, and remediation efficiency is improved. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the electric remediation device provided in an embodiment of the present invention; wherein, A is a schematic diagram of the device, B is a cross-sectional schematic diagram of the device and a schematic diagram of soil sample partitioning; in the figure, 1 is electrolytic cell No. 1, 2 is electrolytic cell No. 2, 3 is the soil chamber, 4 is a switchable DC power supply, 5 is the electrode in electrolytic cell No. 1, 6 is the electrode in electrolytic cell No. 2, 7 is the receiving and measuring bottle for the overflowing electrodialysis liquid from electrolytic cell No. 1, 8 is the receiving and measuring bottle for the overflowing electrodialysis liquid from electrolytic cell No. 2, and 9 is the distributed strip-shaped hollow material. Figure 2 The influence of different electrolytes on electrodialysis flow provided in the embodiments of the present invention Figure 3The variations in voltage percentage and soil pH over time in different soil zones under different electrolyte conditions are provided in this embodiment of the invention. Figure 4 Distribution characteristics of soil Cd under different electrolyte conditions provided in embodiments of the present invention Figure 5 The enrichment effect of switching electric fields on Cd by different treatments provided in embodiments of the present invention Figure 6 The TCLP leaching concentration of Cd after switching electric field treatment and unidirectional electric field treatment provided in the embodiments of the present invention Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] This invention utilizes electric field modulation to construct colloidal blocking zones and stabilization reaction channels in specific regions, achieving a method for the directional enrichment and simultaneous stabilization of heavy metals. Specifically, it employs a triple synergy of "physical bypassing, chemical interception, and electrode switching." This involves: (1) pre-burying cavity materials in the target area to maintain soil pore structure; (2) applying a gradient electric field to induce local colloidal aggregation; and (3) utilizing the blocking effect to intercept and in-situ stabilize heavy metals. Physical bypassing occurs because colloidal aggregation blocks and forms large pore channels. Chemical interception occurs after electrolytic switching when stabilizing ions are added, resulting in a chemical reaction. Physical bypassing simply refers to a change in the migration path without a chemical reaction. Furthermore, colloidal aggregation first encapsulates and settles the heavy metals migrating to the intermediate transition zone, simultaneously forming bypass channels. The blockage actually occurs through the channels where the encapsulated heavy metals react with hydrogen ions. Stabilization is achieved by adding chemical ions, causing the heavy metals blocked in the region by physical action to react with stabilizing ions, thus completely fixing them through chemical action.

[0029] Example 1: In-situ electrically interlocked-stabilized remediation experiment of cadmium-contaminated soil like Figure 1 and 2 A horizontal electric field is applied to both sides of the contaminated soil area to be treated. The areas where electrodes are inserted are used as electrolytic cells. The soil chamber between the two electrolytic cells is the soil chamber of the contaminated soil area to be treated. The soil chamber is divided into 5 areas on average (i.e., S1-S5 from left to right). The two electrolytic cells are connected to the receiving and measuring bottle of the overflowing electrodialysis liquid through pipelines.

[0030] In this embodiment, the contaminated soil area to be treated is a region of 15 cm x 5 cm, with electrolytic cells of 3 x 5 cm on both sides.

[0031] Artificially prepared Cd-contaminated soil with a Cd content of 36 mg / kg was used. 300 g of the contaminated soil was placed in… Figure 1In the soil chamber shown, the soil moisture content was set to 30%; activated carbon columnar electrodes were inserted, and the experiment was then set up... (1) Hollow functional materials with internal cavities are pre-embedded in the intermediate transition zone of the contaminated soil area to be treated. The hollow functional materials are laid horizontally in strips and layers in the contaminated soil, with an implantation density of 0.1 g / cm³. 3 .

[0032] (2) Apply a DC electric field to both ends of the contaminated soil area to be treated as the first remediation cycle. The electrolyte used for the positive electrode is shown in Table 1, and the electrolyte used for the negative electrode is shown in Table 1. Under the drive of the electric field, the difference between the actual transport rate of hydrogen ions and the migration rate of heavy metal ions is used to make the heavy metal ions in the initial anode area (S1, S2) migrate to the intermediate transition area. At the same time, it promotes the colloidal aggregation in this area to form a lock for heavy metal ions and forms a flow channel by means of the hollow material cavity.

[0033] Under the influence of an electric field, colloidal particles in the soil agglomerate and deposit due to changes in ionic strength and pH, resulting in reduced porosity in the intermediate transition zone and the formation of non-uniform pores. The hollow material maintains a large, interconnected pore channel. Hydrogen ions migrate towards the cathode through the large pores and flow channels, causing the accumulated heavy metals, with an average particle size of 30-35 μm, to become difficult to contact and decompose with hydrogen ions, resulting in physical blockage.

[0034] (3) When the physicochemical characteristics of the intermediate transition zone reach the threshold condition, switch the electrode polarity at both ends of the contaminated soil area to be treated; (4) Switching the electrode direction as the second remediation cycle, the electrolyte used for the cathode is shown in Table 1, and the electrolyte used for the anode is shown in Table 1. The electric field direction is used to migrate the heavy metals remaining in the area near the original cathode (S4, S5) to the intermediate transition zone (S3) for enrichment through electrokinetic effect. At the same time, the anions of the stabilizer in the cathode electrolyte migrate to the anode direction after switching, enter the soil, and react with the heavy metals that have migrated to the intermediate transition zone in the flow channel formed in the cavity to form a stable precipitate, thereby achieving in-situ enrichment and stable remediation.

[0035] In this embodiment, the hollow functional material with an inner cavity is carbonized straw with a particle size of 1-2 mm, containing micron-sized cavities of 0-100 µm and nano-sized pores of 2-50 nm. The preparation process involves anaerobic carbonization of dried straw segments (1-2 cm) in a tube furnace at a heating rate of 10 °C / min, raising the temperature from room temperature to 400 °C and holding for 30 minutes, then raising the temperature to 500 °C at 5 °C / min and holding for 30 minutes, cooling to room temperature under a nitrogen atmosphere, crushing and sieving to retain 1-2 mm particles.

[0036] The switching conditions are that the electrodialysis flow reverses, the heavy metal content in the intermediate transition zone reaches 2.2 times that of the initial contaminated soil, and the heavy metal content in the initial anode zone drops to 1% of the initial concentration of the contaminated soil.

[0037] Meanwhile, a control group was set up with unidirectional electrode experiments and reverse electrode experiments where no stabilizing electrolyte was added to the cathode. Notably, no hollow functional material was pre-embedded in the unidirectional electrode experiments.

[0038] That is, T1 and T2 are unidirectional experimental groups with different electrolytes added; T3 and T5 are bidirectional experimental groups with hollow functional materials with cavities added in S3 and different electrolytes added; and T4 is a bidirectional experimental group with hollow functional materials with cavities not added in S3.

[0039] Following the experimental treatments shown in Table 1, an electrolyte solution was added to bring the soil moisture content to 30%. Activated carbon columnar electrodes were inserted into electrolytic cells 1 and 2, and a DC voltage was applied across the electrodes (in this embodiment, the left side was the anode when the electrodes were first inserted), forming a voltage gradient of 1 V / cm. Electrode polarity was switched after day 6 during the electric field switching treatment. At this time, the electrodialysis flow reversed, and the heavy metal content in the intermediate transition zone reached 2.2 times that of the initially contaminated soil. Furthermore, the heavy metal content in the initial anode zone decreased to 1% of the initial concentration of the contaminated soil. The accumulated volume of electrodialysis liquid in both electrolytic cells was collected and recorded during the experiment. Soil samples were divided into several equal parts at days 6 and 12, and their soil pH and Cd content were measured. The TCLP leaching concentration of Cd in the soil was measured after the experiment to characterize the soil Cd stabilization effect. For the T5 treatment group, carbonized hollow straw material was pre-buried in area S3 before the experiment, with two layers from top to bottom, three strips per layer, each strip 0.2 cm wide.

[0040] Table 1 Experimental Setup

[0041] In the unidirectional electric field treatment groups T1 and T2, the electrodialysis solution initially flowed from electrolytic cell 1 (anode) to electrolytic cell 2 (cathode). After 6 days of electrodynamic treatment, the electrodialysis flow gradually stopped and reversed direction. Especially when the electrolyte was 0.05M Ca(NO3)2 (T2 group), the total electrodialysis flow decreased significantly. After 6 days of electrodynamic treatment, Cd at S1 and S2 decreased to below 5% of the original contaminated soil concentration; Cd mainly accumulated in the S3 region. However, with prolonged treatment time, in the treatment group using potassium nitrate as the electrolyte (T1 group), cadmium continued to migrate towards the cathode, but the Cd concentration in the intermediate transition zone remained higher than the initial value after 12 days. In contrast, in the treatment group using calcium nitrate as the electrolyte (T2), the cadmium accumulation in the intermediate transition zone gradually increased, but no migration towards the cathode occurred.

[0042] It is evident that high-valence calcium ions exert a significant compressive effect on the soil colloidal double layer, causing soil colloids to aggregate and weakening the electroosmotic flow, especially in region S3. Due to the reverse flow of the electroosmotic flow, the pore fluid in this region moves to both sides, resulting in a state of repeated wetting and drying. When soil water is drained due to electroosmosis, the pore water pressure decreases, leading to a sudden increase in the effective stress acting on the soil particle skeleton. Under the increased effective stress, particles are prone to slippage, rotation, and rearrangement. Fine particles are squeezed into macropores, resulting in a reduction in the total pore volume and a significant decrease or even disappearance of macropores. The soil becomes dense and compacted. Furthermore, due to the aggregation of soil colloids, the probability of Cd contacting hydrogen ions in the pore fluid is reduced, forming a distinct weak migration zone.

[0043] For the electric field switching treatment groups, before the electrode switching, the soil in region S3 of treatment groups T3, T4, and T5 was enriched with cadmium. After the electric field switching, the enrichment of cadmium in region S3 continued to increase, especially in treatment group T5 (which implemented electrode switching and added stabilizing electrolyte, and pre-embedded hollow material), where the enrichment was significantly higher than in treatment groups T3 (only electrode switching was implemented, without adding stabilizing electrolyte) and T4 (electrode switching was implemented, and stabilizing electrolyte was added, but hollow material was not pre-embedded). The cadmium content in regions S4 and S5 dropped to below 5% of the initial concentration. However, because no stabilizing electrolyte was added in T3, some cadmium migrated through the intermediate transition zone to the initial anode regions S1 and S2. Further analysis of the TCLP leaching concentration of Cd in the soil revealed that the leaching concentration of Cd in each region of the T5 treatment group was significantly lower than that of the T1-T4 treatment groups. The content of migratable Cd in regions S1-S2 and S4-S5 was less than 0.3 mg / kg. Compared with the T3 treatment group (where only electrode switching was implemented), the migratable Cd concentration in region S3 of the T5 treatment group decreased by 75%. This demonstrates that electrode switching control, combined with the synergistic transport process of the stabilizing electrolyte, can significantly promote the enrichment, migration, and stabilization of Cd in the soil towards colloidal aggregation zones.

[0044] Based on the coupling mechanism between colloidal aggregation behavior and heavy metal migration during electrokinetic remediation, the novel electrokinetic treatment strategy of directional closure-stabilization proposed in this invention has the advantages of high efficiency and stability. It breaks through the extensive mode of "full-area acidification" in traditional electrokinetic remediation and achieves for the first time the precise regulation of "high concentration enrichment-physical blocking-chemical stabilization" of heavy metals, providing a new paradigm for electrokinetic remediation of contaminated soil.

Claims

1. A method for in-situ electrically interlocked stabilization remediation of heavy metal contaminated soil, characterized in that: (1) A hollow functional material with an inner cavity is pre-buried in the intermediate transition zone of the area of ​​the contaminated soil to be treated; (2) Apply a DC electric field to both ends of the contaminated soil area to drive the heavy metal ions in the initial anode area to migrate to the intermediate transition zone, while promoting the colloidal aggregation in this zone and compressing the soil pores, and forming an ion flow channel by means of the inner cavity of the hollow functional material. (3) When the physicochemical characteristics of the intermediate transition zone reach the threshold condition, switch the electrode polarity at both ends of the contaminated soil area to be treated; (4) The reverse electric field promotes the migration of heavy metals in the initial cathode direction to the flow channel formed in step (2), and the stabilized ions that migrate in the opposite direction achieve in-situ enrichment and stabilization repair in the flow channel. The hollow functional material with an inner cavity is carbonized straw, hollow glass microspheres, or hollow ceramic particles; In step (2), a DC electric field is applied to both ends of the contaminated soil area to be treated. The electrolyte used at the positive electrode is an aqueous solution containing 0.05~0.15 mol / L calcium ions, and the electrolyte used at the negative electrode is an aqueous solution containing 0.1~0.3 mol / L sodium or potassium ions. Under the drive of the electric field, the difference between the actual transport rate of hydrogen ions and the migration rate of heavy metal ions is used to make the heavy metal ions in the initial anode area migrate to the intermediate transition area, while promoting the colloidal aggregation and closure in this area, and forming an ion flow channel by means of the hollow material's internal cavity structure. In step (3), the physicochemical characteristics must meet at least two of the following conditions ①-④ to reach the threshold. ① The proportion of the intermediate transition region in the total voltage division is reduced by 50-70%; ②The heavy metal content in the intermediate transition zone is 2 to 3 times that of the initially contaminated soil, and the heavy metal content in the initial anode area drops to less than 5% of that in the initial contaminated soil; ③ The soil pH in the intermediate transition zone is in the range of 4.0 to 6.0; ④ The electrodialysis flow flowing towards the cathode gradually stops or forms a reverse electrodialysis flow towards the anode; After switching the electrode direction in step (4), the electrolyte used at the cathode is a salt solution with pH 2-3 containing stable heavy metal ions to be treated, and the electrolyte used at the anode is an aqueous solution containing 0.1-0.3 mol / L sodium or potassium ions. By utilizing the electric field direction and the electrodynamic effect, the heavy metals remaining in the area near the original cathode are migrated to the intermediate transition zone for enrichment. At the same time, the anions in the cathode electrolyte migrate towards the anode direction and enter the soil, reacting with the heavy metals that have migrated to the intermediate transition zone in the flow channel to form a stable precipitate, thereby achieving in-situ enrichment and stabilization remediation.

2. The in-situ electrically interlocked-stabilized remediation method for heavy metal contaminated soil according to claim 1, characterized in that: In step (1), hollow functional material with an inner cavity is pre-embedded in strips along the direction of the electric field in the intermediate transition zone of the contaminated soil area to be treated, with an implantation density of 0.1-0.2 g / cm³. 3 .

3. The in-situ electrically interlocked-stabilized remediation method for heavy metal contaminated soil according to claim 1, characterized in that: Under the drive of the electric field, colloidal particles in the soil agglomerate and deposit due to changes in ionic strength and pH, which reduces the porosity of the soil in the intermediate transition zone and forms non-uniform pores. The inner cavity of the hollow material maintains a large, interconnected pore channel. Hydrogen ions migrate towards the cathode through the large pores and flow channels, causing the agglomerated particles with an average particle size of 15-35 μm to encapsulate the enriched heavy metals and form physical blockages.

4. The in-situ electrically interlocked-stabilization remediation method for heavy metal contaminated soil according to claim 1, characterized in that: The electric field strength is 1~2.5 V / cm, and the soil bulk density is 1.5~1.7 g / cm³. 3 .

5. The in-situ electrically interlocked stabilization remediation method for heavy metal contaminated soil according to claim 1, characterized in that: The electric field strength in step (4) is 0.5-1.5V / cm.

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