An electric combined EICP in-situ remediation system and process for heavy metal pollution in low permeability sites

Abstract

The application discloses a kind of electric combined EICP in-situ remediation low-permeability site heavy metal pollution system and process, system includes electric field driving, chelating agent injection, electrode liquid circulation and intelligent control etc. unit, the present scheme is aimed at the inert state heavy metal pollutants not easy to dissolve in soil, by chelating agent it is converted into water-soluble chelate, make it migrate to cathode under the action of electric field, again by urea-urease reaction produced carbonate, it reacts with heavy metal pollution ion to generate intrinsic carbonate, realize main body precipitation solidification;Calcium source is injected near cathode simultaneously, generate calcium carbonate precipitation, play the role of densification and reinforcement, by calcium carbonate and intrinsic carbonate co-precipitation effect to effectively improve long-term stability;The present scheme combines electric migration with EICP biochemical solidification organically, forms chelation solubilization-electric migration-biological fixation synergistic mechanism, significantly improve soil pollution remediation efficiency and sustainability, applicable to low-permeability site inert state heavy metal contaminated soil in-situ management.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and mentions an in-situ remediation system for inert heavy metal pollution in low-permeability sites based on the coupling of electrokinetic remediation and enzyme-induced carbonate precipitation (EICP), and particularly relates to an electrokinetic combined with EICP in-situ remediation system and process for heavy metal pollution in low-permeability sites. Background Technology

[0002] Low-permeability soft soil areas, long affected by industrial wastewater, metallurgical and electroplating emissions, and solid waste accumulation, are characterized by low permeability coefficients, high water content, fine particles, and abundant clay components. In such environments, cationic heavy metals such as Pb, Cd, Zn, and Cu mainly exist in surface adsorption, weakly crystalline solid phases, or co-precipitation states on clay particles and organic matter carriers. Poor pore connectivity and low diffusion coefficients restrict convective transport, making it difficult for traditional extraction and infiltration methods to achieve effective coverage. While large-scale excavation and off-site disposal can reduce environmental risks, they involve high engineering disturbances and life-cycle costs, and are not conducive to the stabilization of pollutants under in-situ conditions. Although single chemical solidification / stabilization can reduce the leaching toxicity of heavy metals to some extent, it is often accompanied by problems such as changes in seepage paths and limited space for secondary treatment. In summary, existing traditional remediation methods are often ineffective in treating heavy metal pollution in low-permeability soft soils and cannot meet the current urgent need for green, low-carbon, and efficient remediation.

[0003] Electrokinetic remediation (EMR) technology effectively drives the migration of dissolved or free heavy metal ions in groundwater by applying a direct current electric field, thereby remediating heavy metal pollutants. It is particularly suitable for remediating low-permeability soils because the electrokinetic flow is minimally affected by soil particle size. However, this technology has limited effectiveness for the migration of heavy metal pollutants in inert forms such as those bound to iron and manganese oxides or organic matter. To overcome this bottleneck, chelating agents can be introduced. Chelating agents can form stable water-soluble charged complexes with inert heavy metal ions through multiple coordinating atoms (such as nitrogen, oxygen, and sulfur), thus achieving efficient migration under the influence of an electric field. However, traditional EMR technology has significant drawbacks: the electrode solution rich in heavy metals requires external collection and secondary treatment, which not only increases operational complexity and cost but also poses a risk of secondary pollution.

[0004] Enzyme-induced carbonate precipitation (EICP) is an emerging biomineralization technology that utilizes urease to catalyze the hydrolysis of urea, producing carbonate ions, which then react with metal ions to form stable carbonate precipitates, thereby converting heavy metals from a soluble state to a stable solid state. EICP technology offers advantages such as environmental friendliness, high remediation efficiency, and operational flexibility; however, its application is limited by factors such as enzyme activity stability, remediation depth, and reaction conditions (e.g., pH, temperature).

[0005] Therefore, coupling electrokinetic remediation with EICP technology holds promise for creating a complementary and innovative solution: electrokinetic remediation efficiently activates and drives the migration of deep heavy metals, while EICP technology immobilizes the migrating heavy metal ions into stable carbonate minerals in situ within a designated area (such as near the cathode). However, how to organically integrate these two technologies to construct a synergistic, efficient, and process-controllable integrated remediation system, especially for the treatment of inert heavy metals in low-permeability soft soils, remains a pressing challenge. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose an electrodynamic combined EICP in-situ remediation system and process for heavy metal pollution in low-permeability sites, which is used to solve the problems of uneven current field distribution, low migration efficiency, heavy metal redeposition and unstable chemical fixation in traditional electrodynamic remediation processes, so as to achieve efficient, low-energy consumption and sustainable in-situ remediation of heavy metal contaminated soil.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by this invention is as follows: An electric combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites includes: an electric field driving unit, a chemical reagent injection unit, an electrode liquid circulation unit, and an intelligent control unit. The electric field driving unit includes an anode layer, a cathode layer, and a power source. The cathode layer is electrically connected to the negative terminal of the power source and is disposed on the upper layer of the heavy metal contaminated soil. An injection hole is vertically inserted into the heavy metal contaminated soil. The anode layer is injected and formed at the lower end of the injection hole through the injection hole, and the anode layer is electrically connected to the positive terminal of the power source. An electric field is formed between the anode layer and the cathode layer from bottom to top. The chemical reagent injection unit includes an anolyte injection device, a cathode injection device, a urea and urease injection device, a chelating agent injection device, and a calcium source injection device. The anolyte injection device, cathode injection device, chelating agent injection device, urea and urease injection device, and calcium source injection device all use pumps and valve groups to inject liquid into the heavy metal contaminated soil between the cathode layer and the anolyte layer in a zoned, quantitative, and / or programmed manner. The electrode liquid circulation unit is located in the area where the cathode layer is located, and is used to collect the electrode liquid in the area where the cathode layer is located, and to purify and recycle it. The intelligent control unit is connected to the electric field driving unit, the chemical reagent injection unit, and the electrode liquid circulation unit, and controls their operation.

[0008] As one possible implementation, the intelligent control unit of this solution further includes a sensing and detection module, a control execution module, a power management module, and a data communication module. The sensing and detection module includes a sensor group, which is deployed in the heavy metal contaminated soil between the cathode layer and the anode layer. The sensor group is used to monitor the voltage, current, pH, conductivity, and / or liquid level of the soil.

[0009] As one possible implementation, the chelating agent injection device of this solution further includes a chelating agent storage device and multiple injection sleeves. The multiple injection sleeves are vertically inserted into the heavy metal contaminated soil between the cathode layer and the anode layer, with their upper ends serving as input ends. The output end of the chelating agent storage device is connected to the upper ends of the multiple injection sleeves through a pipeline. A pump is deployed on the main pipeline connected to the output end of the chelating agent storage device, and valves are deployed on both the main pipeline and its branches. The intelligent control unit is electrically connected to the pump and valves on the pipeline connected to the chelating agent storage device and controls their operation.

[0010] As one possible implementation, further, the injection cannula of this solution includes an inner cannula and an outer cannula. The outer diameter of the inner cannula is adapted to the inner diameter of the outer cannula. The outer cannula is slidably connected to the outside of the inner cannula. The inner cannula has a plurality of first through holes along its length. The outer cannula has a corresponding second through hole for each of the plurality of first through holes. A traction device is also inserted and connected to the upper end of the outer cannula. The traction end of the traction device is connected to the outer cannula, and the traction device pulls the outer cannula up and down to realize the relative movement between the outer cannula and the inner cannula. When the inner cannula is inside the outer cannula, the plurality of first through holes and the plurality of second through holes have one of the following engagement states: (1) The second through hole located on the upper part of the outer sleeve is opposite to the first through hole on the inner sleeve and the two are connected, allowing the chelating agent to flow laterally into the heavy metal contaminated soil; (2) The second through hole located in the middle of the outer sleeve is opposite to the first through hole on the inner sleeve and the two are connected, allowing the chelating agent to flow laterally into the heavy metal contaminated soil; (3) The second through hole located at the lower part of the outer sleeve is opposite to the first through hole on the inner sleeve and the two are connected, allowing the chelating agent to flow laterally into the heavy metal contaminated soil; (4) The second through hole on the outer sleeve and the first through hole on the inner sleeve are misaligned, thus blocking the side channel for the chelating agent to flow into the heavy metal contaminated soil.

[0011] As a preferred implementation method, the cathode layer in this scheme is preferably a stainless steel mesh belt, and two layers of sand and gravel pads are laid between the upper layer of the heavy metal contaminated soil and the cathode layer; the anode layer is graphene material injected and filled into the lower end of the injection hole through the injection hole, and the anode layer is electrically connected to the positive electrode of the power supply through a metal transition piece or conductive clamp.

[0012] As a preferred embodiment, the urea and urease injection device of this solution preferably includes a urease storage device, a urea storage device, and a urea and urease injection pipeline. The urea and urease injection pipeline is deployed between two layers of sand and gravel cushion layers and is connected to the output ends of the urease storage device and the urea storage device respectively through pipelines. The pipeline is equipped with valves electrically connected to the intelligent control unit. The output ends of the urease storage device and the urea storage device are each equipped with pumps electrically connected to the intelligent control unit.

[0013] As a preferred embodiment, the anolyte buffer injection device of this solution preferably includes: an anolyte buffer storage device, the output end of which is connected to the region where the anode layer is located via a pipeline and is used to input the anolyte buffer into the region where the anode layer is located. A pump and a valve electrically connected to the intelligent control unit are deployed on the pipeline connected to the output end of the anolyte buffer storage device.

[0014] As a preferred embodiment, the cathode buffer injection device of this solution preferably includes: a cathode buffer storage device, the output end of which is connected to the region where the cathode layer is located via a pipeline and is used to input the cathode buffer into the region where the cathode layer is located. A pump and a valve electrically connected to the intelligent control unit are deployed on the pipeline connected to the output end of the cathode buffer storage device.

[0015] As a preferred embodiment, the electrode liquid circulation unit of this solution preferably includes: a collection tank, a cathode buffer recovery tank, a water pump, and a cathode liquid purification device; The collection tank is located on a sand and gravel pad in the area where the cathode layer is located, forming a collection channel for collecting electrode liquid. The cathode buffer recovery tank is connected to one end of the collection tank and is used to collect the electrode liquid collected in the collection tank. The input end of the cathode liquid purification device is connected to the cathode buffer recovery tank through a pipeline, and the water pump is installed on the pipeline to pump the electrode liquid in the cathode buffer recovery tank to the cathode liquid purification device. The output end of the cathode liquid purification device is connected to the input end of the anode buffer injection device.

[0016] As a preferred embodiment, the calcium source injection device of this solution preferably includes: a calcium source storage device and a calcium source injection pipeline. The calcium source injection pipeline is deployed between the sand and gravel cushion layer and the heavy metal contaminated soil below the urea and urease injection pipeline. It is connected to the output end of the calcium source storage device through a pipeline, and the pipeline is equipped with a valve and a pump that are electrically connected to the intelligent control unit.

[0017] As a preferred implementation method, the power source in this solution is preferably a solar panel assembly.

[0018] As a preferred implementation method, the urea and urease injection pipeline and the calcium source injection pipeline described in this solution are both deployed in the form of a pipeline network, and the pipelines on the network are provided with multiple liquid outlet holes on their sides.

[0019] Based on the above, this solution also proposes an electric combined EICP in-situ remediation process for heavy metal contamination in low-permeability sites, which is applied to the aforementioned electric combined EICP in-situ remediation system for heavy metal contamination in low-permeability sites, and includes: (I) Drill injection holes extending to the lower part of the soil in the area of ​​heavy metal contaminated soil, and then inject graphene material through the injection holes to form a graphite filling layer at the lower end of the injection holes as an anode layer. Lay a cathode stainless steel mesh belt on the upper part of the contaminated layer by excavation and burial to form a cathode layer. Then deploy a power supply, an electrode liquid circulation unit, a chemical reagent injection unit and an intelligent control unit, and connect the cathode layer to the negative electrode of the power supply and the anode layer to the positive electrode of the power supply. (II) Anode buffer is slowly injected into the anode neighborhood or the high side of the electric field through the anode buffer injection device of the chemical reagent injection unit to stabilize the anode microenvironment and establish an electric field from bottom to top; cathode buffer is injected into the area where the cathode layer is located through the cathode buffer injection device of the chemical reagent injection unit. (III) A chelating agent is injected into the heavy metal contaminated soil between the cathode layer and the anode layer through the chelating agent injection device of the chemical reagent injection unit, so that the adsorbed / solid phase heavy metals are converted into a migratable ion complex. (IV) Under the action of an electric field, heavy metals in a mobile form are directionally migrated and accumulated towards the cathode region along the field direction; (V) Urea, urease and calcium source are injected into the cathode neighborhood in a programmed sequence through the urea and urease injection device and the calcium source injection device of the chemical reagent injection unit. Heavy metal carbonate precipitates are preferentially formed and the main fixation is achieved. At the same time, the generated calcium carbonate serves as a pore framework and undergoes co-precipitation or embedding in a secondary manner. (VI) The electrode liquid in the area where the cathode layer is located is collected by the electrode liquid circulation unit, and it is purified and recycled. The recovered cathode electrode liquid is processed and then circulated to the anode buffer injection device for use. The intelligent control unit adjusts the electric field and the injection liquid in conjunction with the monitoring signal to complete the closed-loop control of the repair process.

[0020] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This scheme achieves a unified coupling of electrokinetic migration and EICP reaction at the mechanistic level. Traditional electrokinetic remediation often suffers from low migration efficiency, ion retention, or redeposition. This scheme, however, activates contaminant ions by introducing a biodegradable chelating agent in the anodic region and simultaneously triggers the EICP reaction in the cathode region. This immediately co-precipitates and fixes the heavy metal ions migrating to the cathode, forming a continuous "migration-reaction-fixation" reaction chain, achieving efficient migration and stabilization of contaminant ions. This design significantly improves migration efficiency and reaction utilization, shortening the remediation cycle.

[0021] 2. This solution employs a biodegradable complexing system, exhibiting excellent environmental compatibility and sustainability. The biodegradable chelating agent used in this solution enhances metal activation and migration capabilities while avoiding the introduction of persistent pollution. The organic residues generated in the system can be naturally degraded by microorganisms, effectively replacing traditional EDTA and NTA chelating agents, reducing secondary environmental risks, and aligning with the sustainable concept of green remediation.

[0022] 3. This scheme achieves efficient reaction in low-permeability soil through a multi-layer structure. The graphite filling layer on the anode side significantly reduces electrode contact resistance and enhances the uniformity of current distribution; the high-permeability sand and gravel cushion layer on the cathode side improves solution diffusion and gas release conditions, making the reaction space uniformly distributed and ensuring that the remediation system can still maintain efficient operation in low-permeability cohesive soils or clay-containing strata.

[0023] 4. This solution establishes a closed-loop electrode liquid circulation system and a solar power module to achieve resource recovery and energy conservation. Through the collection, purification, and reuse of the electrode liquid, not only is the amount of waste liquid discharged during operation reduced, but dependence on external water sources is also lowered. Simultaneously, energy consumption and material costs are saved, significantly improving the system's economic efficiency and sustainability. The accompanying solar panel modules serve as the power module, providing the system with long-term, stable, clean energy, enabling low-carbon operation and unattended operation. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a simplified implementation diagram of the system in this solution; Figure 2 This is a schematic diagram of the unit module connections of this system. Figure 3 This is one of the simplified implementation layout diagrams of the chelating agent injection pipeline (injection sleeve) in the solution system; Figure 4 This is a schematic diagram of the electric field formed between the anode layer and the cathode layer in this scheme, extending from bottom to top. Figure 5 This is a simplified schematic diagram of the chelating agent injection pipeline (injection sleeve) in this scheme. a is the inner sleeve, b is the outer sleeve, and c is a schematic diagram of the mating cross section of the injection sleeve. Figure 6 This is a top-view diagram and corresponding diagram of the inner and outer sleeves of the chelating agent injection pipeline in this scheme. Figure 5 A schematic diagram of the cross-section; Figure 7 This is a schematic diagram of the deployment of the urease injection pipeline or calcium source injection pipeline in the form of a pipeline network in this solution system. Figure 8 This is a side view of the urease injection pipeline or calcium source injection pipeline of this system when deployed in the form of a pipeline network. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the invention. Similarly, the following embodiments are only some, not all, embodiments of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] like Figures 1 to 8 As shown in one embodiment, this embodiment provides an electric combined EICP in-situ remediation system for heavy metal contamination in low-permeability sites, which includes: an electric field driving unit A, a chemical reagent injection unit B, an electrode liquid circulation unit C, and an intelligent control unit D.

[0028] This proposal presents a synergistic remediation system combining electrokinetic and enzyme-induced carbonate precipitation (EICP) technologies, primarily applicable to in-situ remediation of low-permeability sites contaminated with heavy metals, especially soils contaminated with heavy metals such as Pb, Zn, and Cd. The system achieves in-situ migration, in-situ fixation, and structural densification of pollutants through an integrated pathway of "electrokinetic migration (EK) + biodegradable chelating agent + enzyme-induced carbonate precipitation (EICP)".

[0029] The electric field driving unit A includes an anode layer 18, a cathode layer 13, and a power supply 9. The cathode layer 13 is electrically connected to the negative terminal of the power supply 9 and is disposed on the upper layer of the heavy metal contaminated soil. An injection hole 20 is vertically inserted into the heavy metal contaminated soil, with its upper end extending above the ground and its lower end extending to the lower part of the heavy metal contaminated soil. The anode layer 18 is injected and formed at the lower end of the injection hole 20 through the injection hole 20, and the anode layer 18 is electrically connected to the positive terminal of the power supply 9. Together with the cathode layer 13, they form an electric field extending from bottom to top (see reference). Figure 4 ).

[0030] In this embodiment, the anode layer 18 is a conductive layer formed by injecting and filling graphene material into the lower end of the injection hole 20. The anode layer 18 is electrically connected to the positive electrode of the power supply 9 through a metal transition piece or conductive clamp. As an example, in this embodiment, the graphite anode injection holes can be arranged by drilling. High-purity graphite slurry is injected into the holes by high-pressure rotary jet injection. After settling and light vibration compaction, a continuous conductive filling layer is formed to obtain low contact resistance and uniform current density distribution.

[0031] On the cathode side, the cathode layer 13 of this scheme is a stainless steel mesh belt, which is laid on the upper layer of the heavy metal contaminated soil (such as at the ground surface). Two layers of sand and gravel cushion layer 14 are laid between the upper layer of the heavy metal contaminated soil and the cathode layer 13. The sand and gravel cushion layer 14 is a high-permeability sand and gravel cushion layer.

[0032] In this scheme, the stainless steel mesh belt is laid on the cathode side by surface excavation and burial. That is, a working pit or shallow trench of a certain depth is excavated on the ground at the designed location, the stainless steel mesh belt is laid on the high-permeability sand and gravel cushion layer, and then backfilled and compacted with soil, so that the mesh belt and the sand and gravel cushion layer form a stable, uniform and drainable reaction-collection interface.

[0033] Preferably, the power source 9 in this solution can be a solar panel assembly. The power source 9 can lead out a circuit bus 19, whose positive and negative terminals are electrically connected to the anode layer 18 and the cathode layer 13, respectively. In this solution, the cathode layer 13 and the anode layer 18 are arranged opposite each other in the area where the heavy metal contaminated soil is located. The two are connected to the bus 19 through a cable to realize the connection of the power source 9 to form a stable electric field, so as to drive the directional migration of positively charged heavy metal ions in the contaminated soil.

[0034] The chemical reagent injection unit B includes an anolyte buffer injection device B1, a cathode buffer injection device B2, a urea and urease injection device B3, a chelating agent injection device B4, and a calcium source injection device B5. The anolyte buffer injection device B1, the cathode buffer injection device B2, the chelating agent injection device B4, the urea and urease injection device B3, and the calcium source injection device B5 all inject liquid into the heavy metal contaminated soil between the cathode layer 13 and the anode layer 18 in a zoned, quantitative, and / or programmed manner through a pump 5 and a valve group (including multiple valves 8).

[0035] In this scheme, along with the cathode layer 13, injection pipelines related to EICP are also buried, including: injection pipe 15 corresponding to the urea and urease injection device B3, and injection pipe 16 corresponding to the calcium source injection device B5. These are all buried in the soil after surface excavation and connected to valve 8 and pump 5 (high-pressure injection pump). After backfilling, the surface is leveled to ensure concealment and disturbance resistance during operation. The above-mentioned buried arrangement takes into account hydraulic safety, construction efficiency, and accessibility for later maintenance.

[0036] In this scheme, the anolyte buffer solution output from anolyte buffer injection device B1 is used to maintain pH stability in the anolyte area and prevent electrode polarization and gas evolution effects; the chelating agent output from chelating agent injection device B4 converts adsorbed or precipitated heavy metals in the soil into migratory ionic complexes, enhancing their mobility; the urea output from urea and urease injection device B3 and the calcium source output from calcium source injection device B5 employ staggered peak control; urease catalyzes the hydrolysis of urea to release carbonate ions and raise the local pH; and calcium source injection device B5 provides Ca²⁺. + CaCO3 crystals are generated, in which heavy metal ions react with carbonate ions to form their intrinsic carbonate (MCO3) as the main fixed form. CaCO3 mainly serves as the pore framework and undergoes co-precipitation or embedding in a secondary manner to enhance stability.

[0037] The electrode liquid circulation unit C is located in the area where the cathode layer 13 is located, and is used to collect the electrode liquid in the area where the cathode layer 13 is located, and to purify and recycle it.

[0038] In this scheme, the electrode liquid circulation unit C includes: a collection tank 11, a cathode buffer recovery tank 28, a water pump 12, and a cathode liquid purification device 29.

[0039] The collection tank 11 is disposed on the sand and gravel pad 14 in the area where the cathode layer 13 is located, and forms a collection channel for collecting electrode liquid. The cathode buffer recovery tank 28 is connected to one end of the collection tank 11 and is used to collect the electrode liquid collected in the collection tank 11. The input end of the cathode liquid purification device 29 is connected to the cathode buffer recovery tank 28 through a pipeline, and the water pump 12 is disposed on the pipeline and is used to pump the electrode liquid in the cathode buffer recovery tank 28 to the cathode liquid purification device 29. The output end of the cathode liquid purification device 29 is connected to the input end of the anode buffer injection device B1.

[0040] In this scheme, the sand and gravel cushion layer 14 is a high-permeability sand and gravel cushion layer, which is laid below the cathode area of ​​the cathode layer 13. It is used to enhance the liquid seepage and diffusion capacity and ensure the uniformity of the cathode area reaction. The liquid collection tank 11 is connected to the cathode buffer recovery tank 28 and is used to collect the cathode effluent and transport it to the downstream purification unit (cathode liquid purification device 29) for secondary treatment. The treated liquid is returned to the anode buffer storage tank 1 of the anode buffer injection device B1 to realize the recycling of electrode liquid and prevent secondary pollution.

[0041] The intelligent control unit D is connected to the electric field driving unit, the chemical reagent injection unit, and the electrode liquid circulation unit, and controls their operation.

[0042] Each unit in this scheme is connected to the monitoring line through a corrosion-resistant pipeline network and cables, and is uniformly dispatched by the command and control system to achieve coordinated control and safety boundary management of multiple physical fields including electric field, hydraulic field, chemical field and biochemical field.

[0043] As one possible implementation, the intelligent control unit of this solution further includes a sensing and detection module, a control execution module, a power management module, and a data communication module. The sensing and detection module includes a sensor group, which is deployed in the heavy metal contaminated soil between the cathode layer and the anode layer. The sensor group is used to monitor the voltage, current, pH, conductivity, and / or liquid level of the soil.

[0044] In this solution, the sensing and detection module is used to monitor key operating parameters such as voltage, current, pH, conductivity, and flow rate in real time; the control and execution module automatically adjusts the electric field output and solution injection cycle based on real-time data; the power management module can be connected to the solar panel assembly that serves as the power source to achieve independent power supply; and the data communication module transmits the system operation data to the host computer or remote monitoring platform to achieve remote visual management and intelligent control.

[0045] exist Figure 1 Based on this, focus on reference Figure 3 , Figure 5 , Figure 6 As one possible implementation, the chelating agent injection device B4 of this solution further includes a chelating agent storage device 4 and multiple injection sleeves 17. The multiple injection sleeves 17 are vertically inserted into the heavy metal contaminated soil between the cathode layer 13 and the anode layer 18, with their upper ends serving as input ends. The output end of the chelating agent storage device 4 is connected to the upper ends of the multiple injection sleeves 17 via a pipeline. A pump 5 is deployed on the main pipeline connected to the output end of the chelating agent storage device 4, and valves 8 are deployed on both the main pipeline and its branches. The intelligent control unit is electrically connected to the pump 5 and valves 8 on the pipeline connected to the chelating agent storage device 4 and controls their operation. In this solution, the chelating agent output by the chelating agent injection device B4 is injected into the heavy metal contaminated soil between the cathode layer 13 and the anode layer 18 in a periodic manner.

[0046] As one possible implementation, the injection sleeve 17 of this solution further includes an inner sleeve 23 and an outer sleeve 24. The outer diameter of the inner sleeve 23 is adapted to the inner diameter of the outer sleeve 24. The outer sleeve 23 is slidably connected to the outside of the inner sleeve 24. The inner sleeve 23 is provided with a plurality of first through holes 21 along its length. The outer sleeve 24 is provided with second through holes 22 corresponding to the plurality of first through holes 21. A traction device 10 is also connected to the upper end of the outer sleeve 24. The traction end of the traction device 10 is connected to the outer sleeve 24. The traction device 10 pulls the outer sleeve 23 up and down to realize the relative movement of the outer sleeve 24 and the inner sleeve 23. When the inner sleeve 23 is inside the outer sleeve 24, the plurality of first through holes 21 and the plurality of second through holes 22 have one of the following matching states: (1) The second through hole 22 located on the upper part of the outer sleeve 24 is opposite to the first through hole 21 on the inner sleeve 23 and the two are connected, allowing the chelating agent to flow laterally into the heavy metal contaminated soil. (2) The second through hole 22 located in the middle of the outer sleeve 24 is opposite to the first through hole 21 on the inner sleeve 23 and the two are connected, allowing the chelating agent to flow laterally into the heavy metal contaminated soil. (3) The second through hole 22 located at the lower part of the outer sleeve 24 is opposite to the first through hole 21 on the inner sleeve 23 and the two are connected, allowing the chelating agent to flow sideways into the heavy metal contaminated soil; (4) The second through hole 22 on the outer sleeve 24 and the first through hole 21 on the inner sleeve 23 are both misaligned, thus blocking the side channel for the chelating agent to flow into the heavy metal contaminated soil.

[0047] As a preferred embodiment, the anolyte buffer injection device B1 of this solution preferably includes: an anolyte buffer storage device 1, the output end of which is connected to the region where the anode layer 18 is located via a pipeline, and is used to input the anolyte buffer into the region where the anode layer 18 is located. A pump 5 and a valve 8 electrically connected to the intelligent control unit D are deployed on the pipeline connected to the output end of the anolyte buffer storage device 1. In this solution, the anolyte buffer output by the anolyte buffer injection device 1 is supplied in a slow injection manner to maintain the electrochemical stability of the anode.

[0048] As a preferred embodiment, the cathode buffer injection device B2 of this solution preferably includes: a cathode buffer storage device 7, the output end of which is connected to the region where the cathode layer 13 is located via a pipeline, and is used to input cathode buffer into the region where the cathode layer 13 is located. A pump 5 and a valve electrically connected to the intelligent control unit D are deployed on the pipeline connected to the output end of the cathode buffer storage device 7.

[0049] As a preferred embodiment, the urea and urease injection device B3 of this solution preferably includes a urease storage device 2, a urea storage device 3, and a urea and urease injection pipeline 15. The urea and urease injection pipeline 15 is deployed between two layers of sand and gravel cushion 14 and is connected to the output ends of the urease storage device 2 and the urea storage device 3 respectively through pipelines. The pipeline is equipped with a valve 8 electrically connected to the intelligent control unit D. The output ends of the urease storage device 2 and the urea storage device 3 are each equipped with a pump 5 electrically connected to the intelligent control unit D.

[0050] As a preferred embodiment, the calcium source injection device B5 of this solution preferably includes: a calcium source storage device 6 and a calcium source injection pipe 16. The calcium source injection pipe 16 is deployed between the sand and gravel cushion layer 14 and the heavy metal contaminated soil below the urea and urease injection pipe 15. It is connected to the output end of the calcium source storage device 6 through a pipeline, and the pipeline is equipped with a valve 8 and a pump 5 that are electrically connected to the intelligent control unit D.

[0051] Key reference Figure 6 As shown, in terms of pipeline implementation, as a preferred option, the urea and urease injection pipeline 15 and the calcium source injection pipeline 16 are both deployed in a pipeline network, and multiple outlet holes 26 are provided on the side of the pipelines in the pipeline network. When deployed in a pipeline network, the urea and urease injection pipeline 15 and the calcium source injection pipeline 16 can be connected to the pipeline by setting an injection port 25 in the middle area, so as to realize the connection of the calcium source storage device 6, the urease storage device 2, and the urea storage device 3.

[0052] In some embodiments, the stainless steel mesh belt of the cathode layer 13 is buried at a depth of 2.0–3.0 m, and the sand and gravel pad 14 below the mesh belt is 0.2–0.4 m thick with a particle size distribution of 2–20 mm, to improve the lateral flow capacity of the electrode liquid and suppress local "short-circuit seepage". The stainless steel mesh belt of the cathode layer 13 is connected to the busbar 19 of the power supply 9 using waterproof sealed terminals. Conductive reinforcing plates are provided at the ends and corners of the mesh belt to reduce the risk of local resistance and electrochemical corrosion. To ensure the spatial uniformity of the EICP reaction, urea and urease injection pipes are buried 0.3–0.5 m above the mesh belt, and calcium source injection pipes are located 0.3–0.5 m below or to the side of it, forming a staggered supply pattern of "upper enzyme—upper urea—lower calcium source". The three overlap with the cathode reaction zone in space to obtain stable conditions for calcium carbonate nucleation and growth.

[0053] In this scheme, the urea and urease output from the urea and urease injection device B3 and the calcium source output from the calcium source injection device B5 are operated in a staggered order to match the carbonate and calcium content. 2+ The formation rate is high, resulting in a uniform and stable precipitate layer. The system operation stages include an electromigration stage and an EICP fixation stage. The former drives the migration of heavy metals to the cathode region, while the latter uses the EICP reaction to form and fix the metals in situ with MCO3-based precipitates. CaCO3 provides dense structure and secondary co-precipitation support.

[0054] Based on the above, this solution also proposes an electric combined EICP in-situ remediation process for heavy metal contamination in low-permeability sites, which is applied to the aforementioned electric combined EICP in-situ remediation system for heavy metal contamination in low-permeability sites, and includes: (I) Drill injection holes 20 extending to the lower part of the soil in the area of ​​heavy metal contaminated soil, and then inject graphene material through the injection holes to form a graphite filling layer at the lower end of the injection holes 20 as an anode layer 18. Lay a cathode stainless steel mesh belt on the upper part of the contaminated layer by excavation and burial to form a cathode layer 13. Then deploy a power supply 9, an electrode liquid circulation unit C, a chemical reagent injection unit B and an intelligent control unit D, so that the cathode layer 13 is electrically connected to the negative electrode of the power supply 9 and the anode layer 18 is electrically connected to the positive electrode of the power supply 9. (II) Anode buffer is slowly injected into the anode neighborhood or the high side of the electric field through the anode buffer injection device of the chemical reagent injection unit C to stabilize the anode microenvironment and establish an electric field from bottom to top; cathode buffer is injected into the region where the cathode layer 13 is located through the cathode buffer injection device B2 of the chemical reagent injection unit C. (III) A chelating agent is injected into the heavy metal contaminated soil between the cathode layer 13 and the anode layer 18 through the chelating agent injection device B4 of the chemical reagent injection unit C, so that the adsorbed / solid phase heavy metals are converted into a migratable ion complex. (IV) Under the action of an electric field, heavy metals in a mobile form are directionally migrated and accumulated towards the cathode region along the field direction; (V) Urea, urease and calcium source are injected into the cathode neighborhood in a programmed sequence through the urea and urease injection device B3 and the calcium source injection device B5 of the chemical reagent injection unit C. Heavy metal carbonate precipitates are preferentially formed and the main fixation is achieved. At the same time, the generated calcium carbonate serves as a pore framework and undergoes co-precipitation or embedding in a secondary manner. (VI) The electrode liquid in the area where the cathode layer 13 is located is collected by the electrode liquid circulation unit C, and it is purified and recycled. The recovered cathode electrode liquid is processed and then circulated to the anode buffer injection device B1 for use. The intelligent control unit D adjusts the electric field and the injection liquid in conjunction with the monitoring signal to complete the closed-loop control of the repair process.

[0055] The technical solution of this embodiment is aimed at the remediation and long-term stabilization of in-situ inert heavy metal pollution. Through electrochemical-biological multi-field coupling and engineering layout, a continuous process closed loop of migration-fixation-densification-maintenance is realized. It has clear professional integrity and engineering feasibility and can be used in riverbed sediment, nearshore pollution zone and other inert heavy metal contaminated soil environments that require in-situ remediation.

[0056] Based on the above, as an example of this solution, it includes the following: Combination Figures 1 to 8 As shown in one embodiment, during system operation control, the electric field constructed between the cathode layer 13 and the anode layer 18 can be powered by a programmable DC regulated power supply. A low-voltage preheating mode is used initially to reduce polarization accumulation, and the field strength is gradually increased to the target strength after the current-voltage curve stabilizes. The anode region is continuously injected with a small flow rate of anode buffer solution through the anode buffer injection device B1 to stabilize the pH of the anode microenvironment, effectively suppress oxygen evolution and polarization effects, and ensure the conductivity and reversibility of the electrochemical reaction at the anode interface.

[0057] Key points combined Figure 5 , Figure 6 As shown, after the system enters the stable power-on phase, the chelating agent injection device B4 begins to operate. This device adopts a double-layered tubing structure, consisting of an inner tubing 23 and an outer tubing 24 coaxially nested. The inner tubing 23 serves as the main infusion channel, and its wall is provided with several micropores (pore diameter d). i The outer sleeve 24 is a liftable control layer, and its outer wall has large holes (diameter d) that are staggered with the inner hole. i+1 d i ≠ d i+1 The two are staggered in axial position, forming a staggered spray section structure.

[0058] In this solution, the traction component 10 drives the outer sleeve 24 of the injection sleeve 17 to slide relative to the inner sleeve 23, which is a reuse of existing technology. The details will not be elaborated here. This solution ingeniously introduces this structural solution to realize the positional changes of the first through hole 21 and the second through hole 22.

[0059] As an example, in this scheme, the outer sleeve 24 of the chelating agent injection device B4 is divided into four independent modules, each corresponding to an electric lifting assembly (traction assembly 10). Through independent lifting control of the electric lifting assembly, precise displacement of the outer sleeve relative to the inner sleeve can be achieved, thereby controlling the alignment of the injection holes at different heights. When the outer sleeve hole coincides with the inner sleeve hole, the chelating agent is directionally injected; when they are misaligned, the corresponding hole segment is closed.

[0060] In this scheme, during the injection process, only 1-2 cross-sectional injection outlets are opened for pulsed injection each time to ensure stable liquid flow rate and range. The chelating agent storage device employs a "few-hole, high-pressure" segmented control mode, which effectively increases the single-hole liquid output rate under a fixed injection pressure, enhances injection penetration, and significantly expands the penetration radius of the chelating agent (from the conventional 0.3 m to over 0.6 m). By programming the opening and closing rhythm and layer sequence of the injection holes, several controllable reaction activation zones can be formed at different depths for storage, achieving precise activation and uniform diffusion in the central area of ​​the contaminated zone.

[0061] Key points combined Figure 1 , Figure 7 , Figure 8 As shown, in this embodiment, the EICP reaction is carried out using a buried supply mode of "enzyme and urea in the upper layer, calcium in the lower layer": firstly, urea and urease solutions are slowly injected into the upper soil of the reaction zone of the cathode layer through a buried pipeline via a urea and urease injection device, allowing the enzymes to be fully distributed in the sand and gravel cushion layer and the pores around the stainless steel mesh belt serving as the cathode layer; after a certain interval, CaCl2 solution is slowly injected into the lower reaction zone through a calcium source injection device. Urease catalyzes the hydrolysis of urea to produce CO3²⁻. - , with Ca² + The reaction produces CaCO3 crystals. The crystal nuclei preferentially reside in microregions near the cathode with low potential, convergent flow lines, and better pore connectivity. These nuclei then grow and connect along the potential and flow directions, gradually forming a dense, continuous calcium carbonate mineralization zone. Heavy metal ions migrating to the cathode region preferentially react with carbonate ions in the carbonate system formed by the EICP reaction to produce intrinsic carbonate precipitates, constituting the primary fixed morphology. Simultaneously, the generated calcium carbonate crystals, during precipitation, exhibit lattice embedding, surface coordination adsorption, and co-precipitation effects on some metal ions, forming a secondary embedded and solidified structure.

[0062] In some embodiments, to avoid pore blockage caused by early local oversaturation, the high-pressure injection pump and valves operate according to a "low flow, intermittent injection, zone rotation" strategy: the enzyme / urea-calcium supply injection cycles in the same zone are staggered, adjacent zones are staggered by a phase difference of 10-30 minutes, and the single injection volume is adaptively fine-tuned by online feedback from the flow meter and conductivity to ensure that Ca²⁺ + With CO3² - The diffusion-migration-reaction rate matching.

[0063] Please see Figure 1 As shown, in this embodiment, a liquid collection tank 11 is set in the area where the cathode layer 13 is located, forming an efficient electrode liquid collection channel with the sand and gravel pad layer 14. The electrode liquid enters the porous liquid collection tank (arranged in the horizontal direction) in the pores by gravity and electric drive and flows into the cathode buffer recovery tank 28. It is then pumped to the surface purification unit by the water pump 12 (which can use reverse osmosis, ion exchange or electrolytic precipitation, etc.). After purification, it flows back to the anode buffer storage tank 1, forming a closed loop.

[0064] In some embodiments, the recycling rate of the above-mentioned closed loop can reach more than 90%. When the concentration of metal ions in the collection tank 11 is abnormally increased and the pH does not reach the alkaline window, the system automatically delays the injection of calcium source and supplements enzyme / urea first to avoid inefficient precipitation caused by "calcium first and enzyme later". When the flow rate of electrode liquid is decreased and the pore pressure is increased, the system triggers a combination program of short-term reverse electric field and low-pressure backwashing with clean water to quickly restore channel connectivity and prevent irreversible blockage.

[0065] In this embodiment, the system is powered by solar panels as power source 9, which, together with the energy storage and voltage stabilization module, provide stable power to the electrode circuit, pump valve circuit, and sensing-communication unit. The host computer uses six parameters—voltage, current, pH, conductivity, flow rate, and micro-pressure—as core data to construct a two-layer control logic based on threshold and trend: when the anode potential rises to the threshold or the cathode pH deviates from the upper limit, the field strength is automatically reduced and the cycle time of the anode buffer / enzyme-urea-calcium source three paths is adjusted; when the slope of the decrease in metal ion concentration in the sampling hole slows down, the system automatically switches to the maintenance curve to reduce energy consumption; when polarization signs or abnormal gas evolution are detected, the polarity is briefly switched or peak clipping is performed to maintain operation within the safety window. This control system ensures the consistency and spatial coupling of the cycle time of EK migration, complexation activation, and EICP mineralization, enabling the system to maintain reproducible remediation effects and deterministic safety boundaries under different soil conditions and hydrological boundaries.

[0066] In some embodiments, for low-permeability silty clay or high CEC (cation exchange capacity) soils, the sand and gravel cushion layer 14 can be thickened on the cathode side or a thin layer of quartz sand can be laid at the bottom of the anode hole to improve initial hydraulic connectivity; for high-salt or polyvalent anion (such as SO4²⁻) soils, the sand and gravel cushion layer 14 can be thickened on the cathode side or a thin layer of quartz sand can be laid at the bottom of the anode hole to improve initial hydraulic connectivity; -In areas prone to interference, pre-rinsing reduces competing ions and optimizes the ionic strength of the anolyte buffer. These engineering details further demonstrate the professional completeness and feasibility of this invention in complex scenarios.

[0067] In this embodiment, the cathode is a stainless steel mesh belt buried after surface excavation, serving as the cathode layer 13, arranged above the pollution zone and laid on a high-permeability sand and gravel cushion layer 14; the anode is a graphite-filled layer formed by high-pressure jet grouting and compaction, serving as the anode layer 18, located below the pollution zone. This constitutes a vertical field layout of upper cathode and lower anode, allowing cationic heavy metals to migrate directionally from bottom to top under the influence of the applied potential gradient and accumulate in the vicinity of the cathode. The planar and vertical spacing between the cathode and anode are determined comprehensively based on site dimensions, soil resistivity and water content, target field strength, and construction accessibility, and the final arrangement is determined through on-site electrical tests or numerical comparisons.

[0068] In this design, the stainless steel mesh belt on the cathode side is crimped to the busbar 19 via waterproof sealing terminals and led to the power control cabinet by an insulated cable. The sand and gravel pad 14 serves both as an electrode liquid confluence and support structure, facilitating liquid supply and drainage during the subsequent EICP stage. After the graphite electrode on the anode side completes high-pressure rotary spraying, it is connected to the busbar using a metal transition piece: a tin-plated copper connector is pre-embedded or embedded at the graphite end (forming a surface contact with the graphite / silver powder conductive epoxy), and then the busbar 19 is exothermically fused or silver brazed to the copper connector to obtain a current input terminal with low contact resistance and resistance to electrochemical corrosion. To reduce the impact of environmental and mechanical stress, the anode connector and the outer layer of the downlead cable are encapsulated with a double layer of epoxy + elastic sealing, and stress relief clamps are provided.

[0069] The power supply uses a programmable DC regulated power supply; alternatively, solar panels can be configured as a power source and energy storage voltage regulator module to achieve a low-voltage preheating—smooth rise to the target field strength operating curve, ensuring stable electrochemical interface activity, uniform electric field distribution, and controllable migration flux. The above-mentioned upper cathode—lower anode arrangement and connection process ensures stable and maintainable long-term power-on operation of the system under in-situ conditions.

[0070] Before system startup, anolyte buffer is slowly injected into the anode hole (injection hole) by the anolyte buffer storage device 1 to form a stable conductive liquid environment and avoid anolyte polarization. After the conductivity of the pore water increases, the power is turned on to establish a stable electric field between the anode and cathode. The current is distributed to the underground medium through the graphite-filled anode layer 18, forming a uniform potential gradient within the contaminated zone.

[0071] In some embodiments, the electric field strength is maintained at approximately 35 V / m during the energizing phase, and the duration is determined based on the contamination depth and site conditions. After the electric field is established, the chelating agent storage device injects chelating agent (concentration determined by design) into the central region or anode-central transition zone, causing heavy metal ions in the contaminated soil to form complex ions with the chelating agent, increasing their mobility. This phase involves slow injection, which, combined with electric field drive, allows heavy metals to migrate towards the cathode.

[0072] Then it proceeds to the EICP phase.

[0073] In this embodiment, the system operates in the following order: "first power on, then enzyme urine, then calcium source": ② Maintain an electric field to keep the ion migration channels open; ② Inject urea solution and urease solution into the upper soil of the cathode area through urea and urease injection device B3; ③ After the urease is evenly distributed in the pores, inject CaCl2 solution through the calcium source injection device B5.

[0074] Urease catalyzes the hydrolysis of urea to produce CO3² - , with Ca² + The calcium carbonate ions combine to form CaCO3 precipitate. Due to the presence of the electric field, carbonate ions migrate towards the cathode along the potential gradient, and calcium ions are injected from the cathode side to form a concentration superposition zone, thus causing calcium carbonate precipitation near the cathode reaction zone.

[0075] In this embodiment, the cathode region is equipped with a collection tank 11, a cathode buffer recovery device 28, a water pump 12, and a cathode buffer purification device 29. Pore water in the high-permeability sand and gravel cushion layer 14 is collected in the collection tank by gravity and electric force, and then discharged or recycled by the collection tank 11, cathode buffer recovery device 28, water pump 12, and cathode buffer purification device 29. This design maintains a stable liquid level in the cathode region, prevents excessive water accumulation, and recovers ion-rich solutions for subsequent reuse or treatment.

[0076] During operation in the electric field, the system control unit can automatically adjust the electric field strength according to changes in current and voltage to maintain a stable output. If necessary, a short-term polarity reversal can be performed to mitigate polarization. The replenishment of the anolyte buffer maintains the anolyte pH within a suitable range, ensuring long-term conductivity.

[0077] In some embodiments, to avoid excessively high pH in the cathode area leading to urease inactivation, a staggered injection strategy is adopted for the urease and urea injection stages. Each zone is injected with a certain interval before an adjacent zone is injected, maintaining enzyme activity and reaction continuity. The calcium source injection volume is controlled in stages via valve 8 to prevent excessively rapid local precipitation from causing pore blockage.

[0078] The entire system is powered by solar panels 9, which are then output to the main control cabinet via a voltage regulator module. The anode and cathode are connected via bus 19, forming an independent closed circuit. This power supply method simplifies on-site power layout and is suitable for long-term operation in riverside or outdoor environments.

[0079] In this embodiment, the arrangement of electrodes, pumps, valves, and the injection system is modular, allowing for expansion based on different site areas and depths. If the contaminated zone is wide, auxiliary anodes or cathodes can be added in the middle to achieve multi-electrode electric field coupling; if the soil permeability is low, the thickness of the sand and gravel cushion layer can be appropriately increased to improve seepage conditions. The entire system maintains structural symmetry, facilitating later maintenance.

[0080] In some embodiments, after the system stops operating, the residual solution can be drained by pump 12 and valve 8 can be closed. After the cathode and anode wiring is removed, the buried components are retained as long-term monitoring nodes to facilitate subsequent testing of soil strength and heavy metal stability.

[0081] Since the cathode is completely buried below the surface, vegetation can be restored or lightweight slope protection can be laid on the ground, which maintains the ecological landscape and facilitates the restart of the system.

[0082] By employing the above structure and process, this invention can achieve electrokinetic migration and in-situ solidification of heavy metals without disturbing contaminated sediment. An electric field provides directional driving force, chelating agents enhance migration, and enzyme-induced carbonate precipitation achieves stabilization and consolidation. The entire process is continuous, controllable, and without external discharge. The device has a compact structure, and its buried installation improves safety and durability, demonstrating strong engineering feasibility.

[0083] In this embodiment, after long-term operation, the cathode neighborhood undergoes EICP reaction to form an in-situ precipitation zone within the pores, primarily composed of intrinsic heavy metal carbonates, accompanied by a mineralized matrix of calcium carbonate as its structural framework (minor co-precipitation / lattice embedding and surface coordination adsorption occur). This composite mineralized layer of "intrinsic heavy metal carbonate-calcium carbonate" forms a stable interface with the soil particle surface, enhancing pore density and structural integrity through crystal filling and bridging effects. This, in turn, inhibits heavy metal re-migration over the long term and endows the soil with continuously enhanced resistance to disturbance and impermeability.

[0084] In some embodiments, the high-permeability sand and gravel cushion layer 14 on the cathode side continues to serve as a passive drainage and pressure equalization layer after power is cut off; the collection tank 11, cathode buffer recovery device 28, water pump (12), and cathode buffer purification device 29 arranged in conjunction with it can resume circulation when needed to maintain the hydraulic balance of the reaction zone. After the anode graphite filling layer 18 and the underground cable-busbar 19 remain intact, the system can be "started and stopped twice" in situ without repeated drilling and large-scale excavation, reflecting the renewability and economic efficiency of operation and maintenance.

[0085] Key references Figures 1-4 , Figure 7 , Figure 8 In this embodiment, the urea and urease injection pipeline 15, the calcium source injection pipeline 16, and the stainless steel cathode mesh belt 13 are all buried after being excavated to form shallow trenches / working pits on the surface, and then backfilled and compacted. The advantages of the above-mentioned shallow buried arrangement are: first, the construction process causes little disturbance to the original strata, avoiding the structural risks caused by deep hole construction; second, the pipelines, valves 8, and high-pressure injection pump 5 can be centrally managed in the surface inspection well, which is convenient for operation and maintenance; third, the geometric relationship with the sand and gravel cushion layer 14 can be optimized as needed to form a staggered reaction pattern of "enzyme / urea supply above, calcium supply below", ensuring the spatial uniformity of EICP nucleation and growth.

[0086] In some embodiments, a low-load electric field and low-frequency chemical replenishment are used during the long-term maintenance phase to maintain the integrity of the mineralized layer and achieve "post-solidification" of residual migration. Once the monitored operating indicators (such as the stable range of voltage / current, and the functional relationship between local liquid level and valve cycle time) reach a set threshold, the process can transition to a shutdown-weak electric field termination curve. If a restart requirement arises in the future, only the electric field and zonal injection need to be restored to achieve secondary mineralization reinforcement on the original structure. The above strategy revolves around the engineering logic of "controllable—stoppable—restartable," ensuring operational safety and cost control throughout the entire lifespan.

[0087] From the perspective of material and environmental safety, the anolyte, chelating agent, urea, urease and CaCl2 used in this embodiment are all conventional materials with clear engineering sources and easy management. The injection process controls the reaction front through valve grouping and low-flow intermittent strategy, and reduces the process risks of local oversaturation blockage and interface polarization by combining short-term polarity switching and peak shaving when necessary. The circulating water operates in a closed loop of collection-purification-recirculation, which reduces the uncertainty of discharge and facilitates process monitoring.

[0088] In some embodiments, surface vegetation can be restored or a lightweight protective layer can be laid above the system without altering the existing electrode-injection-mineralization system underground. If long-term sampling or maintenance points are required, removable components can be installed in the maintenance well without damaging the shallow overburden bearing capacity, ensuring subsequent inspections and necessary reinforcement operations. Compared to the traditional large-scale excavation-transportation-off-site disposal route, this embodiment follows a "in-situ-minimally disturbed-closed-loop" technical path, reducing secondary risks and overall costs associated with transportation and disposal.

[0089] In summary, this scheme proposes a synergistic mechanism and device deployment method for electrokinetic migration (EK) + chelating agent + enzyme-induced carbonate precipitation (EICP) in low-permeability sites with inert heavy metal pollutants: an electric field provides directional drive to achieve controllable migration; the chelating agent weakens particle-ion binding and enhances migration; EICP generates calcium carbonate in situ in the reaction zone, which forms stable solidification with the migrating metal ions through surface adsorption, lattice substitution, and (Ca,M)CO3. The device adopts a combined structure of surface excavation and burial injection pipes, cathode mesh belts, anode injection holes + graphite filling layers, and other engineering elements such as sand and gravel cushion layers, liquid collection-return closed loops, and solar power supply to form a feasible, maintainable, and scalable complete system.

[0090] The above description is only a part of the embodiments of the present invention and does not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made based on the content of the present invention specification and drawings, or direct or indirect application in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An electric combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites, characterized in that, It includes: an electric field driving unit, a chemical reagent injection unit, an electrode liquid circulation unit, and an intelligent control unit; The electric field driving unit includes an anode layer, a cathode layer, and a power source. The cathode layer is electrically connected to the negative terminal of the power source and is disposed on the upper layer of the heavy metal contaminated soil. An injection hole is vertically inserted into the heavy metal contaminated soil. The anode layer is injected and formed at the lower end of the injection hole through the injection hole, and the anode layer is electrically connected to the positive terminal of the power source. An electric field is formed between the anode layer and the cathode layer from bottom to top. The chemical reagent injection unit includes an anolyte injection device, a cathode injection device, a urea and urease injection device, a chelating agent injection device, and a calcium source injection device. The anolyte injection device, cathode injection device, chelating agent injection device, urea and urease injection device, and calcium source injection device all use pumps and valve groups to inject liquid into the heavy metal contaminated soil between the cathode layer and the anolyte layer in a zoned, quantitative, and / or programmed manner. The electrode liquid circulation unit is located in the area where the cathode layer is located, and is used to collect the electrode liquid in the area where the cathode layer is located, and to purify and recycle it. The intelligent control unit is connected to the electric field driving unit, the chemical reagent injection unit, and the electrode liquid circulation unit, and controls their operation. The chelating agent injection device includes multiple injection sleeves, which are vertically inserted into the heavy metal contaminated soil between the cathode layer and the anode layer. The cathode layer is a stainless steel mesh belt, and two layers of sand and gravel are laid between the upper layer of the heavy metal contaminated soil and the cathode layer; the anode layer is a graphite filling layer. The urea and urease injection device includes urea and urease injection pipes, which are laterally deployed between two layers of sand and gravel cushion. The calcium source injection device includes a calcium source injection pipe, which is laterally deployed between the sand and gravel cushion layer and the heavy metal contaminated soil below the urea and urease injection pipe.

2. The electric combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites as described in claim 1, characterized in that, The intelligent control unit includes a sensing and detection module, a control execution module, a power management module, and a data communication module. The sensing and detection module includes a sensor group deployed in the heavy metal contaminated soil between the cathode layer and the anode layer. The sensor group is used to monitor the voltage, current, pH, conductivity, and / or liquid level of the soil.

3. The electric combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites as described in claim 1, characterized in that, The chelating agent injection device also includes a chelating agent storage device. The output end of the chelating agent storage device is connected to the upper end of multiple injection sleeves through a pipeline. A pump is deployed on the main pipeline connected to the output end of the chelating agent storage device, and valves are deployed on both the main pipeline and the branch pipeline. The intelligent control unit is electrically connected to the pump and valves on the pipeline connected to the chelating agent storage device and controls their operation. The injection cannula includes an inner cannula and an outer cannula. The outer diameter of the inner cannula is adapted to the inner diameter of the outer cannula. The outer cannula is slidably connected to the outside of the inner cannula. The inner cannula has a plurality of first through holes along its length. The outer cannula has a corresponding second through hole for each of the plurality of first through holes. A traction device is also inserted and connected to the upper end of the outer cannula. The traction end of the traction device is connected to the outer cannula, and the traction device pulls the outer cannula up and down to realize the relative movement between the outer cannula and the inner cannula. When the inner cannula is inside the outer cannula, the plurality of first through holes and the plurality of second through holes have one of the following engagement states: (1) The second through hole located on the upper part of the outer sleeve is opposite to the first through hole on the inner sleeve and the two are connected, allowing the chelating agent to flow laterally into the heavy metal contaminated soil; (2) The second through hole located in the middle of the outer sleeve is opposite to the first through hole on the inner sleeve and the two are connected, allowing the chelating agent to flow laterally into the heavy metal contaminated soil; (3) The second through hole located at the lower part of the outer sleeve is opposite to the first through hole on the inner sleeve and the two are connected, allowing the chelating agent to flow laterally into the heavy metal contaminated soil; (4) The second through hole on the outer sleeve and the first through hole on the inner sleeve are misaligned, thus blocking the side channel for the chelating agent to flow into the heavy metal contaminated soil.

4. The electrically powered combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites as described in any one of claims 1 to 3, characterized in that, The anode layer is electrically connected to the positive terminal of the power source via a metal transition piece or conductive clamp.

5. The electric combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites as described in claim 4, characterized in that, The urea and urease injection device includes a urease storage device and a urea storage device. The urea and urease injection pipeline is connected to the output ends of the urease storage device and the urea storage device respectively through pipelines, and the pipeline is equipped with a valve electrically connected to the intelligent control unit. The output ends of the urease storage device and the urea storage device are each equipped with a pump electrically connected to the intelligent control unit.

6. The electrically powered combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites as described in claim 4, characterized in that, The anolyte buffer injection device includes: an anolyte buffer storage device, the output end of which is connected to the region where the anode layer is located via a pipeline and is used to input the anolyte buffer into the region where the anode layer is located; a pump and a valve electrically connected to the intelligent control unit are deployed on the pipeline connected to the output end of the anolyte buffer storage device. The cathode buffer injection device includes a cathode buffer storage device, the output end of which is connected to the region where the cathode layer is located via a pipeline and is used to input cathode buffer into the region where the cathode layer is located. A pump and a valve electrically connected to the intelligent control unit are deployed on the pipeline connected to the output end of the cathode buffer storage device.

7. The electrically powered combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites as described in claim 6, characterized in that, The electrode liquid circulation unit includes: a collection tank, a cathode buffer recovery tank, a water pump, and a cathode liquid purification device; The collection tank is located on a sand and gravel pad in the area where the cathode layer is located, forming a collection channel for collecting electrode liquid. The cathode buffer recovery tank is connected to one end of the collection tank and is used to collect the electrode liquid collected in the collection tank. The input end of the cathode liquid purification device is connected to the cathode buffer recovery tank through a pipeline, and the water pump is installed on the pipeline to pump the electrode liquid in the cathode buffer recovery tank to the cathode liquid purification device. The output end of the cathode liquid purification device is connected to the input end of the anode buffer injection device.

8. The electric combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites as described in claim 5, characterized in that, The calcium source injection device includes a calcium source storage device, and the calcium source injection pipeline is connected to the output end of the calcium source storage device through a pipeline, and the pipeline is equipped with a valve and a pump that are electrically connected to the intelligent control unit.

9. The electrically powered combined EICP in-situ remediation system for heavy metal contamination of low-permeability sites as described in claim 8, characterized in that, The power source is a solar panel assembly; The urea and urease injection pipelines and the calcium source injection pipelines are all deployed in a pipeline network, and multiple liquid outlet holes are provided on the side of the pipelines on the pipeline network.

10. A method for in-situ remediation of heavy metal contamination in low-permeability sites using an electric combined EICP system, applied to the electric combined EICP system for in-situ remediation of heavy metal contamination in low-permeability sites as described in any one of claims 1 to 9, characterized in that... It includes: (I) Drill injection holes extending to the lower part of the soil in the area of ​​heavy metal contaminated soil, and then inject graphite material through the injection holes to form a graphite filling layer at the lower end of the injection holes as an anode layer. Lay a cathode stainless steel mesh belt on the upper part of the contaminated layer by excavation and burial to form a cathode layer. Then deploy a power supply, an electrode liquid circulation unit, a chemical reagent injection unit and an intelligent control unit, and connect the cathode layer to the negative electrode of the power supply and the anode layer to the positive electrode of the power supply. (II) Anode buffer is slowly injected into the anode neighborhood or the high side of the electric field through the anode buffer injection device of the chemical reagent injection unit to stabilize the anode microenvironment and establish an electric field from bottom to top; cathode buffer is injected into the area where the cathode layer is located through the cathode buffer injection device of the chemical reagent injection unit. (III) A chelating agent is injected into the heavy metal contaminated soil between the cathode layer and the anode layer through the chelating agent injection device of the chemical reagent injection unit, so that the adsorbed / solid phase heavy metals are converted into a migratable ion complex. (IV) Under the action of an electric field, heavy metals in a mobile form are directionally migrated and accumulated towards the cathode region along the field direction; (V) Urea, urease and calcium source are injected into the cathode neighborhood in a programmed sequence through the urea and urease injection device and the calcium source injection device of the chemical reagent injection unit. Heavy metal carbonate precipitates are preferentially formed and the main fixation is achieved. At the same time, the generated calcium carbonate serves as a pore framework and undergoes co-precipitation or embedding in a secondary manner. (VI) The electrode liquid in the area where the cathode layer is located is collected by the electrode liquid circulation unit, and it is purified and recycled. The recovered cathode electrode liquid is processed and then circulated to the anode buffer injection device for use. The intelligent control unit adjusts the electric field and the injection liquid in conjunction with the monitoring signal to complete the closed-loop control of the repair process.

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