A method and apparatus for treating heavy metal contaminants in soil using electroosmosis

Abstract

The application discloses a method and device for treating heavy metal pollutants in soil by using an electroosmosis technology, and relates to the technical field of soil pollution treatment and remediation. The method comprises the following steps: constructing an electroosmosis system, a liquid injection system and a liquid pumping system; injecting and pumping liquid, injecting an electroosmosis enhancer liquid into the soil, simultaneously pumping liquid, until the concentration of the electroosmosis enhancer in the pumped liquid reaches a preset requirement; soaking and electroosmosis; sampling and detecting, sampling the soil in the region to be treated by pumping liquid, until the residual concentration of the pollutants meets the preset requirement; injecting and pumping liquid, injecting clean water into the soil, simultaneously pumping liquid, until the concentration of the electroosmosis enhancer in the pumped liquid is less than or equal to a preset concentration limit value, and the soil treatment is completed. The application can efficiently and reliably reduce heavy metals in the soil by injecting appropriate electroosmosis enhancer liquid, freeing the heavy metal pollutants by electroosmosis and pumping the heavy metal pollutants into a hazardous waste pool.

Description

Technical Field

[0001] This invention relates to the field of soil pollution control and remediation technology, specifically to a method and apparatus for treating heavy metal pollutants in soil using electroosmosis technology. Background Technology

[0002] Early electroosmosis applications used metal electrodes, which were very expensive; moreover, metal electrodes were prone to corrosion, making it difficult to meet the electroosmosis duration requirements of engineering applications. Therefore, early electroosmosis technology was difficult to widely promote and apply.

[0003] To address the issue of electrode corrosion, existing technologies have developed "electro-osmotic drainage boards" and "electro-osmotic electrode tubes" using EKG (electro-geosynthetic material), and established an electro-osmotic drainage consolidation method. The EKG electrode tube core has axially grooved outer walls, drainage holes are drilled in the tube wall, and copper wires are embedded axially within the tube wall. The EKG electro-osmotic drainage board has copper wires running through it, and the core is wrapped with a conductive geotextile filter membrane. This EKG electro-osmotic technology has been widely applied in the treatment of industrial sludge, riverbed sediment, dredged fill, and mine tailings.

[0004] Engineering practice shows that while the above-mentioned electroosmosis technology can achieve drainage consolidation, its effect on removing heavy metals is not ideal, especially when the heavy metal content in the soil is high. In such cases, this method struggles to meet relevant regulatory requirements. The main reason for these difficulties is that some heavy metals in the soil are adsorbed on the surface of soil particles, and their adsorption force is relatively strong. Electroosmosis alone is insufficient to release them, and therefore, electroosmosis alone cannot effectively remove heavy metal pollutants from the soil to compliant levels.

[0005] Therefore, there is a need to develop a new electroosmosis technology method and device that is easy to construct and operate, combines electrode plates (electroosmotic drainage plates) and electrode tubes, and can quickly and effectively remove pollutants (such as heavy metal cations or anionic groups containing heavy metals) from the soil. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a new method and device for electroosmosis technology that is convenient to construct, simple to operate, and combines electrode plates and electrode tubes to quickly and effectively remove heavy metal pollutants from soil.

[0007] The technical solution of this invention is: a method for treating heavy metal pollutants in soil using electroosmosis technology, comprising the following steps:

[0008] Construction of electroosmosis system, injection system and pumping system;

[0009] The process of injection and drainage includes: injecting electroosmotic enhancer solution into the soil of the area to be treated through the injection system, and simultaneously draining the liquid from the soil through the drainage system. When the injection volume of the electroosmotic enhancer solution is close to the preset volume, the concentration of the electroosmotic enhancer in the drained liquid is detected and it is determined whether the preset requirements are met. If so, the next step of soaking and electroosmosis is carried out. If not, the injection and drainage are continued until the preset requirements are met.

[0010] Soaking and electroosmosis are carried out, specifically including: soaking the soil in an electroosmosis enhancer solution, and after soaking, turning on the power to supply electricity to the electroosmosis system to carry out electroosmosis treatment;

[0011] Sampling and testing are carried out, including: taking liquid samples from the soil in the area to be treated, testing the residual concentration of pollutants and determining whether it meets the preset requirements. If it does, proceed to the next step of water injection and drainage; otherwise, repeat the soaking and electroosmosis steps until the residual concentration of pollutants meets the preset requirements.

[0012] The process of water injection and drainage includes: injecting clean water into the soil of the area to be treated through the injection system, and simultaneously draining the liquid through the drainage system until the concentration of the electroosmotic enhancer in the drained liquid is less than or equal to the preset concentration limit, at which point the soil treatment is completed.

[0013] A preferred method for treating heavy metal pollutants in soil using electroosmosis technology, wherein the electroosmosis system includes multiple rows of electrode plates and multiple rows of electrode tubes arranged alternately and inserted into the soil layer of the area to be treated, and a dedicated power supply device for electroosmosis, wherein the electrode plates and electrode tubes are electrically connected to the two poles of the dedicated power supply device for electroosmosis.

[0014] A further method for treating heavy metal pollutants in soil using electroosmosis technology involves connecting the electrode plate and electrode tube to the negative and positive electrodes of a dedicated electroosmosis power supply device, respectively, when the soil pollutant is a heavy metal cation; and connecting the electrode plate and electrode tube to the positive and negative electrodes of the dedicated electroosmosis power supply device, respectively, when the soil pollutant is a heavy metal anion group.

[0015] A preferred method for treating heavy metal pollutants in soil using electroosmosis technology, wherein the injection system includes an electroosmosis enhancement liquid tank and an injection pump located on one side of the area to be treated, and a delivery pipe with its inlet connected to the electroosmosis enhancement liquid tank, wherein the delivery pipe is connected to the top of the electrode tube on the surface of the area to be treated for injecting liquid into the soil layer.

[0016] A further method for treating heavy metal pollutants in soil using electroosmosis technology, wherein the pumping system includes a hazardous waste liquid pool and a pump located on the other side of the treatment area, and a drainage pipe with an outlet connected to the hazardous waste liquid pool. The drainage pipe is connected to the top of the electrode plate on the surface of the treatment area, and a woven geotextile and a sealing membrane are laid sequentially on the surface of the treatment area.

[0017] A further method for treating heavy metal pollutants in soil using electroosmosis technology, wherein in the injection and drainage steps, an electroosmosis enhancer solution with an initial concentration of C0 is injected into the soil of the area to be treated via an injection system, and at the same time, the liquid in the soil is drained via a drainage system. The preset requirement is that the concentration of the electroosmosis enhancer C1 in the drained liquid is ≥60%C0.

[0018] A further method for treating heavy metal pollutants in soil using electroosmosis technology, wherein in the injection and drainage steps, when the injection volume of the electroosmosis enhancer solution is close to the preset volume V0, the concentration of the electroosmosis enhancer in the drainage solution is detected, where V0 is 1.2 to 1.5 times the total pore volume of the soil to be repaired in the treatment area.

[0019] A preferred method for treating heavy metal pollutants in soil using electroosmosis technology, wherein in the soaking and electroosmosis steps, the potential difference between the positive and negative electrodes of the electroosmosis treatment is 20~60V, the initial soaking time is a preset time T0, T0 is 7~10 days, and the initial electroosmosis time is a preset time T1, T1 is 3~5 days.

[0020] When repeated soaking and electroosmosis are required in the sampling and testing steps, the soaking time for each subsequent soaking is T0 / 3~T0, and the electroosmosis time for each subsequent electroosmosis is T1 / 3~T1.

[0021] A further method for treating heavy metal pollutants in soil using electroosmosis technology, wherein the preset concentration limit in the water injection and pumping steps is 5%CO~10%CO.

[0022] The present invention also provides an apparatus for use in any of the methods for treating heavy metal pollutants in soil using electroosmosis technology, comprising:

[0023] An electroosmosis system, comprising electrode plates and electrode tubes inserted into the soil layer of the area to be treated, and a dedicated power supply for electroosmosis, wherein multiple electrode plates and multiple electrode tubes are arranged in rows at intervals, and the multiple rows of electrode plates and multiple rows of electrode tubes are arranged alternately at intervals, and the electrode plates and electrode tubes are electrically connected to the two poles of the dedicated power supply for electroosmosis respectively.

[0024] The liquid injection system includes an electroosmotic enhancement liquid tank and a liquid injection pump located on one side of the area to be treated, and a liquid delivery pipe with an inlet connected to the electroosmotic enhancement liquid tank. The liquid delivery pipe is connected to the top of the electrode tube on the surface of the area to be treated for injecting liquid into the soil layer.

[0025] The system includes a hazardous waste liquid pool and a pump located on the other side of the treatment area, as well as a drainage pipe with an outlet connected to the hazardous waste liquid pool. The drainage pipe is connected to the top of the electrode plate on the surface of the treatment area. A woven geotextile and a sealing membrane are laid sequentially on the surface of the treatment area above the infusion pipe and the drainage pipe.

[0026] The preferred method for treating heavy metal pollutants in soil using electroosmosis technology uses an apparatus in which multiple electrode plates are arranged in rows along the longitudinal direction of the area to be treated at intervals d, and multiple electrode tubes are arranged in rows along the longitudinal direction of the area to be treated at intervals d, with the width of each electrode plate arranged along the longitudinal direction of the area to be treated.

[0027] Multiple rows of electrode plates and multiple rows of electrode tubes are arranged laterally along the area to be treated at intervals d and alternately. The corresponding electrode plates and electrode tubes in adjacent rows are arranged laterally aligned or staggered.

[0028] The electrode tube has a water outlet hole, and the electrode tube is surrounded by a first filter cloth. The bottom is fitted with a foot sleeve with an opening at the top, and the foot sleeve wraps the lower end of the filter cloth inside. The upper end of each electrode tube is connected to a first vertical tube by a clamp, and the upper end of the first vertical tube is provided with a T-connector to communicate with the infusion pipeline.

[0029] A more preferred method for treating heavy metal pollutants in soil using electroosmosis technology uses an apparatus in which the three-way connector has a T-shaped structure, with the lower port connected to the first vertical pipe and the upper two ports connected to the infusion pipeline.

[0030] The preferred apparatus for treating heavy metal pollutants in soil using electroosmosis technology includes a delivery pipeline comprising a pre-pump delivery pipe connected to the inlet of an injection pump and a post-pump delivery pipe connected to the outlet of the injection pump, wherein the post-pump delivery pipe is connected to the top of an electrode tube on the surface of the area to be treated.

[0031] The preferred method for treating heavy metal pollutants in soil using electroosmosis technology includes an apparatus in which the drainage pipe comprises a pre-pump drainage pipe connected to the inlet of a pump and a post-pump drainage pipe connected to the outlet of the pump, and the top of the electrode plate is wrapped and tied to the pre-pump drainage pipe on the surface of the area to be treated.

[0032] The preferred method for treating heavy metal pollutants in soil using electroosmosis technology uses an apparatus in which the infusion pipeline is a waterproof PVC steel wire hose and the drainage pipeline is a waterproof PVC steel wire hose with a second filter cloth wrapped around its surface.

[0033] The preferred method for treating heavy metal pollutants in soil using electroosmosis technology uses an apparatus in which the sealing membrane has an outlet, and the infusion pipe and drainage pipe pass through the sealing membrane via the outlet.

[0034] The preferred method for treating heavy metal pollutants in soil using electroosmosis technology involves an apparatus in which a pressure trench is formed around the area to be treated, and the sealing membrane is surrounded by soil filled and compacted within the pressure trench.

[0035] The beneficial effects of this invention are:

[0036] (1) The treatment method of the present invention can quickly and effectively remove pollutants from soil, such as heavy metal cations (e.g., Cd).2+ Pb 2+ Zn 2+ Cu 2+ Ni 2+ (etc.), and heavy metal anionic groups (such as heavy metal anions chromate CrO4). 2- This method achieves soil purification in a relatively short time. Based on the pollutants in the soil, an electroosmotic enhancer is selected to efficiently separate these pollutants, thereby removing them. The method of this invention can treat contaminated soil layers of varying thicknesses, effectively treating thicknesses up to 30m or even thicker.

[0037] (2) In the treatment method of the present invention, a hollow electrode tube is placed in the soil during the construction of the injection system, and the electroosmotic enhancer solution is injected into the deep soil area through the electrode tube; the electroosmotic enhancer solution interacts with the heavy metal pollutants, reducing their adsorption force with soil particles; through the electric field formed by the electrode tube and electrode plate, heavy metal ions are ionized and condensed around the electrode plate; the hazardous waste liquid containing pollutants is discharged to an external hazardous waste pool by a pump. This method of injecting appropriate electroosmotic enhancer solution, ionizing pollutants through electroosmosis, and pumping them to a hazardous waste pool can reliably and efficiently remove heavy metal pollutants from the soil.

[0038] (3) The soaking and electroosmosis steps of the treatment method of the present invention employ a process of soaking the soil in a static solution of the enhancing agent. This allows the pollutants to react fully with the electroosmotic enhancing agent, and eliminates the need for a large amount of enhancing agent solution, significantly reducing removal costs. A suitable electroosmotic enhancing agent is selected based on the pollutants in the soil: for example, if the main pollutant is Pb... 2+ Cu 2+ Furthermore, if the soil is acidic, sodium hydroxide or sodium carbonate can be selected as an electroosmotic enhancement agent; if the main pollutant is Cd... 2+ Pb 2+ Zn 2+ For heavy metals and alkaline soil, hydrochloric acid or nitric acid can be used as electroosmotic enhancement agents; if the main pollutant is Cd... 2+ Ni 2+ For heavy metals, sodium chloride or ammonium chloride can be selected as electroosmotic enhancement agents.

[0039] (4) The water injection and drainage steps of the treatment method of the present invention involve injecting clean water to replace and drain the reinforcing agent solution (hazardous waste liquid) containing heavy metals. Therefore, the reinforcing agent solution originally injected into the soil is also removed, thereby achieving a very ideal soil purification effect.

[0040] (5) In the treatment method of this invention, since the electroosmotic enhancer solution is ultimately replaced and discharged by clean water, there is no need to worry about the enhancer solution remaining in the soil causing soil acidification, excessive soil salinity, or groundwater pollution due to its difficulty in degradation. This also increases the range of agent types that can be selected. For example, for Cd in the soil... 2+ Pb 2+ Zn 2+ For heavy metals, inorganic acids with extremely low cost and good desorption effect can be selected as electroosmotic enhancement agents for treatment. There is no need to worry about their impact on soil acidification. While achieving good heavy metal removal effect, the project cost is also greatly reduced.

[0041] (6) In the device of the present invention, the alternating arrangement of each row of electrode plates and each row of electrode tubes in the electroosmosis system can make the positive and negative electrodes correspond one-to-one, maintain the electric field effect, and gather pollutant ions near the electrode plates; the electrode plates and electrode tubes in adjacent rows are arranged horizontally aligned or staggered. When staggered, the adjacent electrode plates have less obstruction to the liquid injection of the electrode tube, and the liquid injection efficiency of the electrode tube in the soil layer is higher.

[0042] (7) The electrode tube of the electroosmosis system of the present invention is a hollow tube made of EKG material with water outlet holes around it and wrapped with filter cloth. The length of the electrode tube is determined according to the thickness of the soil layer to be treated, and can reach 30m or longer, so that it can be used in areas to be treated at various depths. A first vertical pipe (PVC pipe) is set at the upper end of the electrode tube to quickly connect to the infusion pipeline.

[0043] (8) The electroosmotic enhancement liquid pool of the injection system of the present invention can be excavated on-site as needed and sealed with a polyethylene film to facilitate the storage and use of sufficient electroosmotic enhancement liquid. The injection pump can be a reciprocating pump to provide sufficient injection pressure, and the delivery pipe can be a PVC steel wire hose, which has high strength and is easy to adapt to deformation according to ground settlement.

[0044] (9) The pumping system of the present invention is provided with a woven geotextile and a sealing membrane above the ground surface. The purpose of setting the woven geotextile is to protect the sealing membrane from being punctured by debris such as board ends and wire ends. The sealing membrane covers the entire treatment area and is pressed into the membrane trench around the area to ensure that the vacuum pressure under the membrane reaches the required level during the pumping process.

[0045] This invention utilizes a combination of an injection system, an electroosmosis system, and a pumping system to quickly and effectively remove heavy metal pollutants from soil, thereby achieving soil purification in a relatively short time. Attached Figure Description

[0046] Figure 1 This is a flowchart of the method of the present invention.

[0047] Figure 2 This is a schematic diagram (vertical) of the overall device of this application.

[0048] Figure 3 This is a schematic diagram showing the liquid flow direction during operation of the device in this application.

[0049] Figure 4 Electrode tube structure diagram

[0050] Figure 5 A schematic diagram of the planar arrangement of the electrode plates and electrode tubes (aligned arrangement).

[0051] Figure 6 A schematic diagram of the planar arrangement of electrode plates and electrode tubes (staggered arrangement).

[0052] Wherein: 1-Area to be treated; 2-Electrode plate; 3-Electrode tube (31-Water outlet; 32-First filter cloth; 33-Foot cover); 4-Hazardous waste liquid pool; 5-Injection pump; 6-Pre-pump infusion pipe; 7-Post-pump infusion pipe; 8-Film pressing trench; 9-Pre-pump drainage pipe; 10-Post-pump drainage pipe; 11-Woven geotextile; 12-Sealing membrane; 13-First conductor; 14-Second conductor; 15-Drainage pump; 16-Electroosmosis dedicated power supply equipment; 17-Electroosmosis enhanced liquid pool; 18-Clamping hoop; 19-First vertical pipe; 20-T-connector. Detailed Implementation

[0053] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0054] The following specific embodiments will provide a more detailed description of the present invention.

[0055] like Figure 2-6 As shown, this invention provides an apparatus for treating heavy metal pollutants in soil using electroosmosis technology, comprising an electroosmosis system, an injection system, and a pumping system. Through the coordinated operation of the injection system, electroosmosis system, and pumping system, heavy metal pollutants in contaminated soil can be removed quickly and effectively, thereby achieving soil purification in a relatively short time.

[0056] The electroosmosis system includes electrode plates 2 and electrode tubes 3 inserted into the soil layer of the area to be treated 1. Multiple electrode plates 2 and electrode tubes 3 are arranged in rows with intervals between them. The electroosmosis system also includes a dedicated electroosmosis power supply 16. All electrode plates 2 are electrically connected to one of the positive and negative electrodes of the dedicated electroosmosis power supply 16 via a first wire 13, and all electrode tubes 3 are electrically connected to the other of the positive and negative electrodes of the dedicated electroosmosis power supply 16 via a second wire 14. The connection of the electrode plates 2 and electrode tubes 3 to the positive and negative electrodes is determined by the substance to be removed: to remove heavy metal ions (such as Cd). 2+ Pb 2+ Zn 2+ Cu 2+ Ni 2+ When (etc.), electrode tube 3 is connected to the positive electrode of electroosmosis power supply 16, and electrode plate 2 is connected to the negative electrode of electroosmosis power supply 16; to remove heavy metal anionic groups (such as heavy metal anion chromate CrO4), 2- When the electrode tube 3 is connected to the negative terminal of the electroosmosis power supply device 16, the electrode plate 2 is connected to the positive terminal of the electroosmosis power supply device 16, and the voltage range of the electroosmosis power supply device 16 is 20V~60V.

[0057] In a preferred embodiment, if one of the horizontal directions of the area to be processed is taken as the longitudinal direction, then the other horizontal direction perpendicular to the longitudinal direction is taken as the transverse direction. The specific arrangement of the electrode tubes 3 and the electrode plates 2 is as follows: multiple electrode plates 2 are arranged in rows along the longitudinal direction of the area to be processed at intervals d, and multiple electrode tubes 3 are arranged in rows along the longitudinal direction of the area to be processed at intervals d. The width of all electrode plates 2 is arranged along the longitudinal direction of the area to be processed. At this time, the length direction of each electrode plate 2 is along the vertical direction, the thickness direction is along the transverse direction of the area to be processed, and the width direction is along the longitudinal direction of the area to be processed.

[0058] In a preferred embodiment, multiple rows of electrode plates 2 and multiple rows of electrode tubes 3 are arranged laterally along the area to be treated at intervals d, alternating in this manner. Adjacent rows of electrode plates 2 and electrode tubes 3 are arranged laterally aligned or staggered, with the interval d ranging from 0.8 to 1.5 m. In another preferred embodiment, the number of electrode plates 2 and electrode tubes 3 in each row are the same, the number of rows of electrode plates 2 is the same as the number of rows of electrode tubes 3, and all rows of electrode plates 2 and electrode tubes 3 are arranged laterally aligned.

[0059] In a preferred embodiment, the area to be processed is square, with the width direction as the vertical axis, such as... Figure 5-6 Up and down; with length as the horizontal direction, such as... Figure 5-6 The arrangement is oriented left-right. Six electrode plates 2 are arranged longitudinally at intervals d, and six electrode tubes 3 are also arranged longitudinally at intervals d. The three rows of electrode plates 2 and three rows of electrode tubes 3 are arranged laterally at intervals d, alternating between each other. Adjacent rows of corresponding electrode plates 2 and electrode tubes 3 can be laterally aligned, such as... Figure 5As shown; adjacent rows of corresponding electrode plates 2 and electrode tubes 3 can also be arranged laterally staggered, such as... Figure 6 As shown, the staggered spacing is d / 2, that is, the longitudinal spacing between the electrode plate 2 and the electrode tube 3 corresponding to the adjacent rows is d / 2. At this time, there is no electrode plate 2 blocking the transverse sides of each electrode tube 3. Therefore, when the staggered arrangement is used, the adjacent electrode plate 2 has less obstruction to the liquid injection of the electrode tube 3, and the liquid injection efficiency of the electrode tube in the soil layer is higher.

[0060] The electrode tube 3 has an outlet hole 31. A first filter cloth 32 surrounds the electrode tube 3, and a foot sleeve 33 with an open top is fitted at the bottom, enclosing the lower end of the first filter cloth 32. Each electrode tube 3 is connected to a first vertical tube 19 via a clamp 18. A T-connector 20 is installed at the upper end of the first vertical tube 19, connecting it to the infusion pipeline. The T-connector 20 has a T-shaped structure, with its lower end connected to the first vertical tube 19 and its two upper ends connected to the infusion pipeline. The electrode tube 3 is a hollow tube made of EKG material. The outlet holes 31 are circumferentially spaced on the tube wall and spaced along the tube's length. In a preferred embodiment, the electrode tube 3 generally has an outer diameter of 30mm, and the outer wall has grooves along the tube's length, with multiple grooves spaced circumferentially. The outlet holes 31 are located within these grooves. The length of the electrode tube 3 is determined by the thickness of the soil layer to be treated. The first vertical tube 19 is preferably a DN40 PVC pipe with an outer diameter of 40mm.

[0061] The injection system includes an electroosmotic enhancement solution tank 17 and an injection pump 5 located on one side of the treatment area 1 outside the site, as well as a delivery pipe with its inlet connected to the electroosmotic enhancement solution tank 17. The electroosmotic enhancement solution tank 17 is excavated on-site as needed and sealed with a polyethylene film at the bottom. The delivery pipe connects to the top of the electrode tube 3 on the surface of the treatment area 1 for injecting solution into the soil layer. In a preferred embodiment, the injection pump 5 can be a reciprocating pump with a rated pressure of 2.0~3.0 MPa. The delivery pipe includes a pre-pump delivery pipe 6 connected to the inlet of the injection pump 5 and a post-pump delivery pipe 7 connected to the outlet of the injection pump 5. The post-pump delivery pipe 7 connects to the top of the electrode tube 3 on the surface of the treatment area 1 via a tee connector 20 and a first vertical pipe 19. The post-pump delivery pipe 7 is a waterproof PVC steel wire hose, preferably a DN25 PVC steel wire hose with an outer diameter of 25 mm.

[0062] The drainage system includes a hazardous waste liquid tank 4 located on the other side of the treatment area 1, a drainage pump 15, and a drainage pipe with its outlet connected to the hazardous waste liquid tank 4. The hazardous waste liquid tank 4 is excavated on-site as needed and sealed with a polyethylene membrane at the bottom. The drainage pipe connects to the top of the electrode plate 2 on the surface of the treatment area 1. A woven geotextile 11 and a sealing membrane 12 are sequentially laid upwards on the surface of the treatment area 1 above the infusion and drainage pipes. In a preferred embodiment, the drainage pump 15 is preferably a water-air separator pump, and the number of pumps can be set according to their own power and the area of ​​the treatment area. The drainage pipe includes a pre-pump drainage pipe 9 connected to the inlet of the drainage pump 15 and a post-pump drainage pipe 10 connected to the outlet of the drainage pump 15. The top of the electrode plate 2 is wrapped and tied to the pre-pump drainage pipe 9 on the surface of the treatment area 1. The pre-pump drainage pipe 9 is a water-permeable PVC steel wire hose with a second filter cloth wrapped around its surface.

[0063] The sealing membrane 12 has an outlet (not shown in the figure). The infusion pipe 7 after the pump of the infusion pipeline and the drainage pipe 9 before the pump of the drainage pipeline both pass through the sealing membrane 12 through the outlet. A membrane pressure trench 8 is opened around the treatment area 1. Soil is filled and compacted around the sealing membrane 12 to ensure that the vacuum pressure under the membrane reaches the required level during the pumping process. For cases where only heavy metal pollutants need to be removed, the vacuum pressure under the membrane ranges from 20 to 50 kPa. For cases where the mechanical properties of the soil need to be improved while removing heavy metal pollutants, the vacuum pressure under the membrane ranges from 60 to 80 kPa. The sealing membrane 12 can be made of polyethylene film with a thickness of 0.12 to 0.16 mm.

[0064] In a preferred embodiment, to prevent the spread of the chemical solution, the area to be treated 1 can be separated from the surrounding area by an isolation wall or isolation sheet piles.

[0065] Example 2

[0066] like Figure 1 As shown, the method for treating heavy metal pollutants in soil using electroosmosis technology according to the present invention is carried out according to the following steps. Before on-site construction, preparatory work must be completed:

[0067] ① Select an appropriate electroosmotic enhancer based on the specific heavy metal content of the soil. For example, the main heavy metal in the soil is Cd. 2+ Ni 2+ Ammonium chloride can be selected as an electroosmosis enhancing agent;

[0068] ②The initial concentration C0 and the intended soaking time T0 of the electroosmotic enhancer solution were determined through batch testing;

[0069] ③ Calculate the total amount of electroosmotic enhancer solution required, V0. V0 is 1.2 to 1.5 times the total pore volume of the soil to be repaired in the treatment area 1.

[0070] S1. Construct the electroosmosis system, injection system, and pumping system according to the device structure of Example 1.

[0071] 1) Construction of electrode plate 2: According to the design requirements, the electrode plates 2 are arranged in a plane (multiple rows of electrode plates 2 and multiple rows of electrode tubes 3 are arranged alternately). The electrode plates 2 are installed by using a plate inserter. The depth of the electrode plates 2 in the soil is 8~12m.

[0072] 2) Installation of Electrode Tube 3: Following the design plan (multiple rows of electrode plates 2 and multiple rows of electrode tubes 3 arranged alternately), the electrode tube 3 is inserted using a tube insertion machine to the same depth as the lower end of the electrode plate 2. Before insertion, the electrode tube 3 is wrapped with the first filter cloth 32, fitted with a foot sleeve 33 at the bottom, and connected to the upper first vertical pipe 19, with the wire extended. After insertion, the wire is led to the ground, and the opening is backfilled and compacted with soil to ensure the electrode tube 3 remains secure.

[0073] 3) Excavate an electroosmosis enhancement liquid pool 17 on one side of the area to be treated and install an injection pump 5. Excavate a hazardous waste liquid pool 4 on the other side of the area to be treated and install a pumping pump 15. Install a dedicated electroosmosis power supply device 16 outside the area to be treated.

[0074] 4) Connection of the injection system: Lay the pump delivery pipe 7 on the ground of the area to be treated 1. One end is connected to the electrode pipe 3, and the other end is connected to the outlet of the injection pump 5 through the membrane outlet and the sealing membrane 12. The inlet of the injection pump 5 is connected to the outlet of the pump delivery pipe 6. The inlet of the pump delivery pipe 6 is connected to the electroosmotic enhancement liquid pool 17.

[0075] 5) Connection of the electroosmosis system: The first wire 13 connects all electrode plates 2, and the second wire 14 connects all electrode tubes 3. Both the first wire 13 and the second wire 14 are led out of the site through the bottom of the pressure trench 8 and connected to the electroosmosis power supply equipment 16. The first wire 13 is connected to the negative electrode, and the second wire 14 is connected to the positive electrode.

[0076] 6) Connection of the pumping system: Lay the pump inlet drain pipe 9 on the ground of the area to be treated 1. The top of the electrode plate 2 is connected to the pump inlet drain pipe 9 by winding. The pump inlet drain pipe 9 passes through the membrane outlet and the sealing membrane 12 to the inlet of the pumping pump 15. The outlet of the pumping pump 15 is connected to the inlet of the pump outlet drain pipe 10. The outlet of the pump outlet drain pipe 10 is connected to the hazardous waste liquid tank 4.

[0077] 7) Laying the sealing membrane 12: The membrane trench 8 has been dug around the area to be treated 1. First, a layer of woven geotextile 11 is laid on the ground, then the sealing membrane 12 is laid, and the edge of the sealing membrane 12 is stepped into the membrane trench 8 and backfilled and compacted.

[0078] S2, Perform injection and drainage.

[0079] Start the injection pump 5 to inject an electroosmotic enhancer solution (ammonium chloride solution) with an initial concentration of C0 (C0=0.1~0.3mol / L) into the soil of the area to be treated 1 through the electrode tube 3 at an injection pressure of 20~50kPa. At the same time, start the pump 15 to pump out the original pore fluid in the soil at a vacuum pressure of 20~50kPa under the membrane. When the amount of the enhanced agent solution injected is close to the preset total amount V0, check the concentration of the electroosmotic enhancer C1 in the pumped solution. When the concentration of the electroosmotic enhancer meets the preset requirement C1≥60%·C0, stop the injection pump 5 and the pump 15. If C1<60%·C0, continue the injection and pumping until the preset requirement is met.

[0080] S3. Perform soaking and electroosmosis.

[0081] When the pump is stopped, the soil is left to soak in the electroosmotic enhancer solution. The initial soaking time is the preset time T0 (T0=7~10 days). After soaking, the electroosmotic power supply device 16 is turned on to supply power to the electrode plate 2 and electrode tube 3 for electroosmosis treatment. The potential difference is 20~60V. The initial power supply time is the preset time T1 (T1=3~5 days). The electroosmosis is stopped when the power is turned off.

[0082] S4. Perform sampling and testing.

[0083] Start pump 15 to extract and sample soil from the area to be treated, test the residual concentration of pollutants in the extracted liquid, and determine whether it meets the preset requirements (the preset requirements can refer to relevant industry regulations or be set according to needs, such as Cd). 2+ If the concentration is ≤1.5mg / kg, proceed to the next step; otherwise, repeat the previous soaking and electroosmosis steps, continuing the soaking time T0 / 3 and electroosmosis time T1 until the residual concentration of pollutants meets the preset requirements.

[0084] S5. Perform water injection and drainage.

[0085] Start the injection pump 5 to inject clean water into the soil of the area to be treated (injection pressure 20~50kPa), and at the same time start the pump 15 (vacuum pressure 20~50kPa). Detect the concentration of the electroosmotic enhancer in the pumped liquid until the concentration of the electroosmotic enhancer is ≤ the preset concentration limit. The preset concentration limit ranges from 5%·C0 to 10%·C0. In this embodiment, it is 5%·C0. That is, when the concentration of the electroosmotic enhancer in the pumped liquid is ≤5%·C0, stop water injection and pumping, and the soil treatment is completed.

Claims

1. A method for treating heavy metal pollutants in soil using electroosmosis technology, characterized in that, Includes the following steps: Construction of electroosmosis system, injection system and pumping system; The process of injection and drainage includes: injecting electroosmotic enhancer solution into the soil of the area to be treated through the injection system, and simultaneously draining the liquid from the soil through the drainage system. When the injection volume of the electroosmotic enhancer solution is close to the preset volume, the concentration of the electroosmotic enhancer in the drained liquid is detected and it is determined whether the preset requirements are met. If so, the next step of soaking and electroosmosis is carried out. If not, the injection and drainage are continued until the preset requirements are met. Soaking and electroosmosis are carried out, specifically including: soaking the soil in an electroosmosis enhancer solution, and after soaking, turning on the power to supply electricity to the electroosmosis system to carry out electroosmosis treatment; Sampling and testing are carried out, including: taking liquid samples from the soil in the area to be treated, testing the residual concentration of pollutants and determining whether it meets the preset requirements. If it does, proceed to the next step of water injection and drainage; otherwise, repeat the soaking and electroosmosis steps until the residual concentration of pollutants meets the preset requirements. The process of water injection and drainage includes: injecting clean water into the soil of the area to be treated through the injection system, and simultaneously draining the liquid through the drainage system until the concentration of the electroosmotic enhancer in the drained liquid is less than or equal to the preset concentration limit, at which point the soil treatment is completed.

2. The method for treating heavy metal pollutants in soil using electroosmosis technology as described in claim 1, characterized in that, The electroosmosis system includes multiple rows of electrode plates (2) and multiple rows of electrode tubes (3) inserted into the soil layer of the area to be treated (1) and arranged alternately, as well as a dedicated power supply device (16) for electroosmosis. The electrode plates (2) and electrode tubes (3) are electrically connected to the two poles of the dedicated power supply device (16) for electroosmosis.

3. The method for treating heavy metal pollutants in soil using electroosmosis technology as described in claim 2, characterized in that, The injection system includes an electroosmotic enhancement liquid tank (17) and an injection pump (5) located on the side outside the treatment area (1), and a delivery pipe with an inlet connected to the electroosmotic enhancement liquid tank (17). The delivery pipe is connected to the top of the electrode tube (3) on the surface of the treatment area (1) for injecting liquid into the soil layer.

4. The method for treating heavy metal pollutants in soil using electroosmosis technology as described in claim 3, characterized in that, The drainage system includes a hazardous waste liquid pool (4) and a drainage pump (15) located on the other side of the treatment area (1), and a drainage pipe with an outlet connected to the hazardous waste liquid pool (4). The drainage pipe is connected to the top of the electrode plate (2) on the surface of the treatment area (1). The surface of the treatment area (1) is covered with woven geotextile (11) and sealing membrane (12) in sequence.

5. The method for treating heavy metal pollutants in soil using electroosmosis technology as described in claim 1, characterized in that, In the injection and drainage steps, an electroosmotic enhancer solution with an original concentration of C0 is injected into the soil of the area to be treated through the injection system, and at the same time, the liquid in the soil is drained through the drainage system. The preset requirement is that the concentration of electroosmotic enhancer C1 in the drained liquid is ≥60%C0.

6. The method for treating heavy metal pollutants in soil using electroosmosis technology as described in claim 1, characterized in that, In the soaking and electroosmosis steps, the potential difference between the positive and negative electrodes of the electroosmosis treatment is 20~60V. The first soaking time is a preset time T0, which is 7~10 days. The first electroosmosis time is a preset time T1, which is 3~5 days.

7. The method for treating heavy metal pollutants in soil using electroosmosis as described in claim 6, characterized in that, When repeated soaking and electroosmosis are required in the sampling and testing process, the soaking time for each subsequent soaking should be T0 / 3~T0, and the electroosmosis time should be T1 / 3~T1.

8. The method for treating heavy metal pollutants in soil using electroosmosis as described in claim 5, characterized in that, In the water injection and drainage steps, the preset concentration limit is set at 5%CO~10%CO.

9. An apparatus used in the method for treating heavy metal pollutants in soil using electroosmosis as described in any one of claims 1 to 8, characterized in that, include: An electroosmosis system, comprising an electrode plate (2) and an electrode tube (3) inserted into the soil layer of the area to be treated (1), and an electroosmosis power supply device (16). Multiple electrode plates (2) and multiple electrode tubes (3) are arranged in rows at intervals, and the multiple rows of electrode plates (2) and multiple rows of electrode tubes (3) are arranged alternately at intervals. The electrode plates (2) and electrode tubes (3) are electrically connected to the two poles of the electroosmosis power supply device (16). The injection system includes an electroosmotic enhancement liquid tank (17) and an injection pump (5) located on the side outside the treatment area (1), and a delivery pipe with an inlet connected to the electroosmotic enhancement liquid tank (17). The delivery pipe is connected to the top of the electrode tube (3) on the surface of the treatment area (1) for injecting liquid into the soil layer. The system includes a hazardous waste liquid tank (4) and a pump (15) located on the other side of the treatment area (1), and a drainage pipe with an outlet connected to the hazardous waste liquid tank (4). The drainage pipe is connected to the top of the electrode plate (2) on the surface of the treatment area (1). The surface of the treatment area (1) is covered with a woven geotextile (11) and a sealing membrane (12) in sequence above the infusion pipe and the drainage pipe.

10. The apparatus used in the method for treating heavy metal pollutants in soil using electroosmosis as described in claim 9, characterized in that, Multiple electrode plates (2) are arranged in rows along the longitudinal direction of the area to be treated at a distance d, and multiple electrode tubes (3) are arranged in rows along the longitudinal direction of the area to be treated at a distance d. The width of each electrode plate (2) is arranged along the longitudinal direction of the area to be treated. The multiple rows of electrode plates (2) and multiple rows of electrode tubes (3) are arranged horizontally along the area to be treated at intervals d and alternately. The electrode plates (2) and electrode tubes (3) of adjacent rows are arranged horizontally aligned or staggered.

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