A method for solar-coupled electrochemically enhanced mineral remediation of chromium-contaminated soil and / or groundwater

Abstract

The present invention discloses a method for solar-coupled electrochemically enhanced mineral remediation of chromium-contaminated soil and / or groundwater, comprising: constructing at least two electrode units and placing them in chromium-contaminated soil and / or groundwater, filling the outside and bottom of the electrode units with a mineral material having hexavalent chromium reduction and fixation capabilities and / or attaching it to the electrodes as an electrode coating; utilizing a solar power source to power an online monitoring and control system, monitoring the temperature, humidity, pH, redox potential, and current and voltage changes of the electrode unit's surrounding environment through the online monitoring and control system, and regulating the current and voltage between the electrodes based on real-time monitoring data, achieving chromium reduction and fixation by electrically driving the migration of chromium-containing pollutants and the migration of reducing ions released by the mineral material, and repairing chromium-contaminated soil and / or groundwater. The present invention provides a simple, green, safe, and highly efficient and synergistic method for effectively treating chromium-contaminated soil and groundwater.

Description

Technical Field

[0001] The present invention relates to the technical field of soil and groundwater remediation, and is applicable to in-situ or ex-situ remediation of chromium-contaminated soil and / or groundwater, and in particular to a method for remediating chromium-contaminated soil and / or groundwater by using solar-coupled electrochemically enhanced minerals. Background Art

[0002] The remediation technologies for chromium-contaminated soil and groundwater mainly include physical remediation, chemical remediation, and biological remediation. Physical remediation mainly includes soil replacement, topsoil removal, and isolation. Due to its huge engineering workload, it is only suitable for treating small-scale soils with severe chromium contamination. Chemical remediation mainly uses some reducing agents such as calcium polysulfide, sodium dithionite, and sodium sulfide to convert highly toxic hexavalent chromium into low-toxic trivalent chromium. Chemical remediation is fast-acting but is prone to secondary pollution and is not suitable for soils with low permeability. Biological remediation mainly reduces or fixes hexavalent chromium through the activities of plants and microorganisms. It is eco-friendly and cost-effective, but the remediation efficiency is not high and it is not suitable for sites with high chromium pollution concentrations.

[0003] Electric remediation and electrochemical remediation are chromium remediation technologies that have emerged in recent years. They have attracted widespread attention because they do not require additional electron sources, are not prone to secondary pollution, and are suitable for low-permeability soils that are difficult to treat with other remediation methods. Electric remediation mainly applies a DC electric field to contaminated soil or water, and uses electromigration, electrodialysis, and electrophoresis to migrate pollutants to specific locations for removal. Electrochemical remediation mainly removes hexavalent chromium through the reduction effect of electrodes or the reduction effect of coupled microorganisms. However, electric remediation technology currently faces problems such as high energy consumption costs, frequent replacement of electrode materials, obvious focusing effects, and soil degradation. Although electrochemical remediation technology has relatively low energy consumption, it also has problems such as high electrode costs, frequent replacement of electrodes, and insufficient chromium stabilization.

[0004] In recent years, mineral remediation has also been used to treat chromium-contaminated soil or water. Compared to chemical agents, mineral materials offer certain advantages in chromium remediation, capable of reducing and immobilizing hexavalent chromium, reducing the risk of chromium reoxidation. However, similar to chemical remediation, mineral remediation imposes certain requirements on the water content and permeability of the contaminated medium, and the engineering effort required for in-situ remediation is substantial. These limitations limit its application in treating chromium contamination in situ. Summary of the Invention

[0005] To overcome the deficiencies of the aforementioned prior art, the present invention aims to provide a solar-coupled electrochemically enhanced mineral in-situ remediation method for chromium-contaminated soil and / or groundwater. By constructing an electrode unit and applying a low-voltage electric field to the contaminated medium, the electron transfer between organic matter and indigenous microorganisms is enhanced, and most importantly, the reduction and fixation of chromium by mineral materials is strengthened. This avoids the problems of large-scale soil tillage, frequent electrode replacement, and secondary treatment of chromium contaminants in conventional electrical and mineral remediation technologies. While reducing costs and operational difficulty, it achieves efficient chromium removal and reduces the risk of chromium "reversion" to yellowing.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for solar-coupled electrochemically enhanced mineral remediation of chromium-contaminated soil and / or groundwater, comprising:

[0008] 1) constructing at least two electrode units and placing them in chromium-contaminated soil and / or groundwater, wherein at least one of the two electrode units serves as an anode and the other as a cathode; the electrode units comprise an electrode, a support, and an electrode sleeve, wherein the electrode is disposed on the support, which is located within the electrode sleeve; and filling the exterior of the electrode unit, the bottom of the support, and / or attaching a mineral material having hexavalent chromium reduction and fixation capabilities to the electrode unit, the support, and / or attaching the material to the electrode as an electrode coating.

[0009] 2) connecting the electrode unit to an online monitoring and control system, which includes an adjustable DC regulated power supply module, a sensor, and a data acquisition module. The electrodes in the electrode unit are connected to the positive or negative pole of the adjustable DC regulated power supply module. The sensor is used to monitor changes in temperature, humidity, pH, redox potential, and current and voltage of the environment surrounding the electrode unit, and transmit the monitoring data to the data acquisition module.

[0010] 3) Using solar power to power an online monitoring and control system, the online monitoring and control system regulates the magnitude and direction of the current and voltage between electrodes based on real-time monitoring data, thereby electrically driving the migration of chromium-containing pollutants and the migration of reducing ions released by mineral materials, thereby achieving chromium reduction and fixation, and repairing chromium-contaminated soil and / or groundwater.

[0011] The mineral material used in the present invention has the ability to reduce and fix hexavalent chromium, and can be selected from pyrrhotite, magnetite, pyrite, pyrite and their naturally occurring or associated minerals. Preferably, the mineral material is crushed, ground and sieved to a particle size of 20-200 mesh; then the powdered mineral material is filled on the outside of the electrode unit and / or the bottom of the carrier, wherein a porous packaging bag made of polylactic acid, chitosan, starch-based material or other biodegradable material can be used to subpackage the powdered mineral material and then fill it on the outside of the electrode unit and / or the bottom of the carrier, and the pore size on the porous packaging bag is preferably smaller than the particle size of the mineral material. A conductive adhesive can also be used to bond the powdered mineral material to the electrode and air-dry it at room temperature as an electrode coating.

[0012] The electrodes in the electrode unit can be electrode strips or electrode ropes made of graphite, titanium alloy, mixed metal oxides or other conductive materials with good corrosion resistance.

[0013] Preferably, the carrier is made of PVC, PPR, PE or any other insulating tubing with a certain strength, and the electrode tape or electrode rope is wound on the carrier in a spiral or other irregular manner. Preferably, the carrier has pores with a diameter of 0.4 to 1 cm evenly distributed.

[0014] The electrode sleeve is an insulating tubing made of a material such as PVC, PPR, or PE, with a larger diameter than the carrier and possessing a certain strength and water permeability. The electrode sleeve is evenly distributed with small holes, preferably with a diameter of 0.1 to 3 mm. Preferably, space is left between the electrode sleeve and the carrier for a sampling tube.

[0015] Step 1) Two or more electrode units are set in the chromium-contaminated soil and / or groundwater. The spatial arrangement of the electrode units can be a linear arrangement, or can refer to Figure 2 , arranged in the form of polygonal vertices such as triangles and quadrilaterals, polygonal vertices such as triangles and quadrilaterals and their centers, or arranged in space in other ways.

[0016] The online monitoring and control system in step 2) includes multiple sensors, which are arranged at monitoring sites in chromium-contaminated soil and / or groundwater, preferably inside a tubular carrier. The sensors transmit monitoring data to a data acquisition module via wired or wireless transmission.

[0017] Furthermore, the online monitoring and control system is also equipped with an Internet of Things module, which is connected to the data acquisition module to upload real-time monitoring data to the cloud. In addition, the online monitoring and control system can also be equipped with a camera for real-time observation of the on-site conditions of the contaminated site.

[0018] The solar power source in step 3) includes a solar panel and its bracket, a controller, an inverter and a battery, wherein the solar panel is mounted on the bracket, the solar panel, the inverter and the battery are respectively connected to the controller, the solar panel converts light energy into electrical energy, the battery stores the converted electrical energy, the controller regulates the charge and discharge power of the solar panel, and the inverter converts direct current into alternating current to supply the online monitoring and control system.

[0019] In step 3), the online monitoring and control system adjusts the voltage and current between the electrodes through the adjustable DC regulated power supply module according to the real-time monitoring data, so that the electric field strength is 0.02-1 V / cm and the current strength is 0.2-2 A.

[0020] In step 3), samples are collected from the chromium-contaminated soil and / or groundwater via a sampling tube to monitor the progress of remediation. Once remediation is complete, the electrodes can be directly removed and recycled for multiple uses, and the mineral material can be recovered magnetically.

[0021] The solar-coupled electrochemically enhanced mineral remediation method of chromium-contaminated soil and / or groundwater of the present invention can be implemented in chromium-contaminated sites by the following operating steps:

[0022] Step 1: Determine the layout of the electrode units, including their horizontal locations and depths, based on the spatial distribution of chromium pollution concentration, electrical conductivity, and moisture content of the site. Prepare electrodes, carriers, and electrode sleeves of appropriate lengths. The carriers are tubular and smaller in diameter than the electrode sleeves, with permeable holes distributed on the carriers and electrode sleeves.

[0023] Step 2: Select a suitable solar power source based on the operating power of each component. The daily power generation of the solar power source should be 1 to 1.5 times the daily operating power of the entire device.

[0024] Step 3: Based on the electrode unit layout plan determined in Step 1, a well is constructed at the corresponding location and an electrode sleeve is placed. During the well construction process, the packaged mineral materials and quartz sand particles are evenly filled into the outer periphery of the electrode sleeve in a layered and alternating manner;

[0025] Step 4: Install the solar power source identified in step 2 at the chromium-contaminated site;

[0026] Step 5: Fix the electrode to the carrier, place the sensor inside the carrier, and vertically insert it into the electrode sleeve;

[0027] Step 6: Place the sampling tube into the electrode sleeve;

[0028] Step 7: Connect the electrode to the adjustable DC regulated power supply in the online monitoring and control system to start the repair;

[0029] Step 8: During the repair process, monitor the change of hexavalent chromium concentration through a sampling tube. When the hexavalent chromium concentration does not change for more than a specified time (such as 15 days), introduce mineral material powder into the bottom of the carrier through a capillary tube as needed; at the same time, monitor the changes of temperature, humidity, redox potential, pH and conductivity of the electrode unit. Maintain the moisture content above 10% by adding water, reduce the voltage between electrodes or temporarily exchange the anode and cathode to reduce the pH fluctuation to less than 30%, and maintain the cathode redox potential below -100mV by adjusting the voltage between electrodes. When the conductivity decays by more than 20% compared to the initial value, add mineral material to the bottom of the carrier;

[0030] Step 9: After the repair is completed, the electrode unit can be directly pulled out and recycled for repeated use. The mineral material can be recovered magnetically.

[0031] Preferably, in the first step above, the electrode unit spacing is adjusted according to the moisture content as follows:

[0032] 1) The moisture content of the site is above 30%, and the spacing between electrode units is about 10m;

[0033] 2) The moisture content of the site is between 20% and 30%, and the spacing between electrode units is 8-10m;

[0034] 3) The moisture content of the site is between 10% and 20%, and the spacing between electrode units should be 6-8m;

[0035] 4) If the moisture content of the site is below 10%, add water to above 10% and the spacing between electrode units should be 4-6m.

[0036] The beneficial effects of the present invention are:

[0037] 1. The present invention uses electrochemical technology to simultaneously provide an acidic environment that is conducive to chromium reduction and an alkaline environment that is conducive to chromium precipitation stabilization.

[0038] 2. The present invention stimulates the activity of indigenous microorganisms on the site through the action of the electric field, strengthens the electron transfer between organic matter and pollutants, and improves the reduction efficiency of chromium.

[0039] 3. The mineral material of the present invention can not only reduce hexavalent chromium, but also fix chromium into the crystal lattice or form other stable products, thereby reducing the risk of chromium "reverting to yellow".

[0040] 4. The reducing ions released by the mineral material of the present invention can migrate to the contaminated soil or groundwater outside the electrode unit area under the action of the electric field and reduce chromium, avoiding the problem of large amounts of reagents added in mineral remediation or chemical remediation.

[0041] 5. The mineral material of the present invention can enhance the conductivity of contaminated soil or groundwater and accelerate the transfer efficiency between electron donors and hexavalent chromium.

[0042] 6. The mineral material of the present invention can reduce the pH change of the cathode, thereby reducing the focusing effect in traditional electric repair.

[0043] 7. The replacement frequency of the electrode material in the present invention is low, which avoids the frequent replacement of electrodes or composite electrodes in traditional electric repair or electrochemical repair technology.

[0044] 8. The electrodes of the present invention are wound on the carrier in a spiral or other irregular manner, and the non-uniform electric field formed reduces the consumption of electric energy on the electrode surface.

[0045] 9. In the present invention, the electric field intensity between the electrode units is low, the required energy consumption is small, the cost of mineral materials is controllable, and at the same time, the power supply fully utilizes solar energy, providing a green and low-carbon repair device and model. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the device for electrochemically enhanced mineral remediation of chromium-contaminated soil and / or groundwater used in an embodiment of the present invention.

[0047] Figure 2 Schematic diagram of the spatial distribution of electrode units arranged in four ways: center-triangle, triangle, center-quadrilateral, and quadrilateral.

[0048] Figure 3 Schematic diagram of the combination of mineral material electrode coating and electrode.

[0049] The main symbols in the figure are as follows:

[0050] 1 is contaminated soil or groundwater, 2 is solar power supply, 3 is online monitoring and control system, 4 is electrode unit, 5 is mineral material, 6 is quartz sand filter material, 7 is electrode, 8 is carrier, 9 is electrode sleeve, 10 is sensor, 11 is solar panel, 12 is controller, 13 is battery, 14 is inverter, 15 is sampling tube, 16 is camera, 17 is Internet of Things module, 18 is data acquisition module, and 19 is adjustable DC regulated power supply. DETAILED DESCRIPTION

[0051] The following further describes the device structure adopted by the present invention, its practical application scenarios and technical effects through embodiments in conjunction with the accompanying drawings.

[0052] The solar-coupled electrochemically enhanced mineral remediation devices for chromium-contaminated soil and / or groundwater used in the following examples are similar, and the basic composition is as follows: Figure 1 As shown, it includes a solar power source 2, an online monitoring and control system 3, an electrode unit 4 and a mineral material 5, wherein:

[0053] The electrode unit 4 is composed of an electrode 7, a carrier 8 and an electrode sleeve 9. The electrode 7 is wound on the tubular carrier 8, and the carrier 8 is placed in the electrode sleeve 9. The mineral material 5 is filled on the outside of the electrode unit 4, the bottom of the carrier 8 and / or as a coating on the electrode 7 (see Figure 3 ); A space is reserved between the electrode sleeve 9 and the carrier 8 to place the sampling tube 15;

[0054] The online monitoring and control system 3 includes a sensor 10, an adjustable DC regulated power supply module 19, a data acquisition module 18, an Internet of Things module 17, and a camera 16. The sensor 10 is used to monitor data such as temperature, humidity, pH, redox potential, and conductivity. The sensor 10 is disposed in the carrier 8 of the electrode unit 4, and a signal connection is provided between the sensor 10 and the data acquisition module 18. The adjustable DC regulated power supply module 19 is electrically connected to each electrode 7 and is used to adjust the voltage and current between the electrodes 7. The data acquisition module 18 is used to record the measured data of each sensor 10 and upload the measured data to the cloud through the Internet of Things module 17. The camera 16 is used to observe the on-site conditions of the contaminated site in real time.

[0055] The solar power source 2 is connected to the online monitoring and control system 3 to provide energy for the operation of the electrode unit 4 and the online monitoring and control system 3; the solar power source 2 includes a solar panel 11 and its mounting bracket, a controller 12, an inverter 14 and a battery 13, wherein the controller 12 is connected to the solar panel 11, the inverter 14 and the battery 13 respectively. The solar panel 11 converts light energy into electrical energy, and the controller 12 regulates the charging and discharging power of the solar panel 11; the battery 13 stores the converted electrical energy, and the inverter 14 converts direct current into alternating current to supply the online monitoring and control system 3.

[0056] Example 1

[0057] This embodiment is a laboratory test for electrochemically enhanced mineral in-situ remediation of chromium-contaminated soil and groundwater. The main body is a rectangular reaction vessel, which is designed as follows: 300 mm in length, 100 mm in width, and 100 mm in height, with water inlets and outlets set at the bottom of both ends of the reaction vessel. The contaminated medium in the reaction vessel is composed of 2.5 kg of quartz sand and 800 mL of potassium dichromate solution with a concentration of 1 g / L. The water inlet and outlet of the reaction vessel are connected by a hose and the chromium-contaminated water body is circulated under the action of a peristaltic pump to simulate groundwater flow. The solar panel 11 in the solar power supply 2 has a power of 20 W and is matched with a corresponding controller 12 and a battery 13. The electrode unit 4 adopts a straight line layout with one cathode and one anode alternating between them. The distance between adjacent electrode units 4 is 200 mm, and a group is arranged in the center of the reaction vessel. Electrode 7 is made of graphite rope, wrapped around carrier 8. Carrier 8 is made of PE tubing with an outer diameter of 20 mm. Electrode sleeve 9 is made of PE tubing with an outer diameter of 32 mm. 1 mm pores are evenly distributed across the surface of electrode sleeve 9. A potential difference of 5 V is maintained between the cathode and anode of electrode unit 4. Mineral material 5, with a particle size of 200 mesh, is introduced through a flexible hose to the outer surface of electrode sleeve 9. The amount of mineral material 5 added is 5% of the initial total chromium content. After 30 days of repair, samples were taken through sampling tube 15, and the hexavalent chromium removal rate in the contaminated medium was found to be 99.7%.

[0058] Example 2

[0059] The storage of chromium slag at a chemical plant caused soil pollution. The device of the present invention was used to conduct an in-situ pilot test, and the soil remediation area was 100m 2 The total power of the solar panels 11 in the solar power source 2 is 1440W, and is matched with the corresponding controller 12, inverter 14 and battery 13. The electrode unit 4 adopts a triangular space layout (see Figure 2 ), the distance between the electrode units 4 is 2m, and two groups are arranged. The electrode 7 is made of an electrode strip with a titanium base and a mixed metal oxide coating, and a mineral material coating is bonded to the electrode strip (see Figure 3), the electrode belt is wrapped around the carrier 8, the carrier 8 is made of PVC pipe with an outer diameter of 50mm, the electrode sleeve 9 is made of PVC pipe with an outer diameter of 100mm, the surface of the carrier 8 is evenly distributed with small holes of 4mm in diameter, and the surface of the electrode sleeve 9 is evenly distributed with small holes of 3mm in diameter. The potential difference between the cathode and anode of the electrode unit 4 is 10V, and the current intensity is 1A. The particle size of the mineral material 5 is 100-200 mesh, and it is packaged in sub-packaging bags and evenly filled on the outside of the electrode sleeve 9. The amount of mineral material added is 10% of the total estimated chromium content of the site. Sensors 10 for temperature, humidity, pH and conductivity are arranged at the center of the electrode unit group and the center and four sides of the site, with a depth of 1m, and the data are uploaded to the cloud in real time through the data acquisition module 18 and the Internet of Things module 17. After 30 days of repair, sampling was carried out through the sampling tube 15 to detect the concentration of hexavalent chromium in the soil at fixed points, and the removal rate reached 98.6%.

[0060] Example 3

[0061] The storage of chromium slag at a chemical plant caused large-scale soil and groundwater pollution. The device of the present invention was used for in-situ remediation, and the remediation area was 4000m 2 The total power of the solar panels 11 in the solar power source 2 is 7200W, and is matched with the corresponding controller 12, inverter 14 and battery 13. The electrode unit 4 adopts a center-quadrilateral space layout (see Figure 2 ), the distance between the central electrode unit and the four-side electrode units is 6m, and a total of five groups are arranged to cover the upper and lower edges of the contaminated area and the severely polluted area in the middle of the contaminated area. Electrode 7 uses an electrode strip with a titanium base and a mixed metal oxide coating, and a mineral material coating is bonded to the electrode strip (see Figure 3 ), the electrode tape is wrapped around carrier 8, which is made of PVC tubing with an outer diameter of 50 mm. The electrode sleeve 9 is made of PVC tubing with an outer diameter of 100 mm. Small holes with a diameter of 4 mm are evenly distributed on the surface of carrier 8, and small holes with a diameter of 3 mm are evenly distributed on the surface of electrode sleeve 9. The potential difference between the cathode and anode of electrode unit 4 is 20 V, and the current intensity is 1.5 A. The mineral material 5 has a particle size of 100-200 mesh and is packaged in subpackages with a volume of 30×30×30 mm. 3 quartz sand filter media 6 is evenly layered and filled onto the outside of the electrode sleeve 9. The amount of mineral material added is 5% of the estimated total chromium content of the site. pH, conductivity, and redox potential sensors 10 are installed within each electrode unit at a depth of 5-12 meters. Data is uploaded to the cloud in real time via a data acquisition module 18 and an IoT module 17. Sixty days after remediation, sampling via sampling tubes 15 revealed an average hexavalent chromium removal rate of 92.7% at each monitoring point.

[0062] Finally, it should be noted that the above embodiments are intended only to facilitate a further understanding of the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments.

Claims

1. A method for solar-coupled electrochemically enhanced mineral remediation of chromium-contaminated soil and / or groundwater, comprising: 1) construct at least two electrode units and place them in chromium-contaminated soil and / or groundwater, with at least one of them serving as an anode and the other as a cathode; The electrode unit is composed of an electrode, a carrier and an electrode sleeve, the electrode is arranged on the carrier, and the carrier is located in the electrode sleeve; a mineral material with hexavalent chromium reduction and fixing ability is filled on the outside of the electrode unit, the bottom of the carrier and / or attached to the electrode as an electrode coating; wherein the mineral material is selected from pyrrhotite, magnetite, pyrite, pyrite and their natural symbiotic or associated minerals; the mineral material is crushed, ground and sieved to make its particle size of 20-200 mesh, and then the powdered mineral material is filled on the outside of the electrode unit and / or the bottom of the carrier, and / or, the powdered mineral material is bonded and fixed to the electrode using a conductive adhesive, and air-dried at room temperature to form an electrode coating; the spacing between the electrode units is adjusted as follows according to the moisture content of the site: a) When the moisture content of the site is above 30%, the spacing between the electrode units is 10 m; b) When the moisture content of the site is between 20%-30%, the spacing between the electrode units is 8-10 m; c) When the moisture content of the site is between 10%-20%, the spacing between the electrode units is 6-8 m; d) The moisture content of the site is below 10%, and the water is replenished to above 10%. The electrode units are arranged at a spacing of 4-6 m; 2) The electrode units are connected to an online monitoring and control system, which includes an adjustable DC voltage-regulated power supply module, a sensor and a data acquisition module. The electrodes in the electrode units are connected to the positive or negative pole of the adjustable DC voltage-regulated power supply module. The sensor is used to monitor the changes in temperature, humidity, pH, redox potential, and current and voltage of the environment surrounding the electrode units, and transmit the monitoring data to the data acquisition module; 3) A solar power source is used to power the online monitoring and control system. The online monitoring and control system regulates the current and voltage between the electrodes according to real-time monitoring data, and realizes the reduction and fixation of chromium by electrically driving the migration of chromium-containing pollutants and the migration of reducing ions released by mineral materials, thereby repairing chromium-contaminated soil and / or groundwater.

2. The method according to claim 1, wherein The powdered mineral material is subpackaged using a porous packaging bag made of biodegradable material, and then the subpackage is filled outside the electrode unit and / or at the bottom of the carrier, wherein the pore size of the porous packaging bag is smaller than the particle size of the mineral material.

3. The method according to claim 1, wherein The carrier and the electrode sleeve are both insulating tubes, wherein the diameter of the electrode sleeve is larger than the diameter of the carrier; the electrode is an electrode belt or electrode rope made of conductive material, which is wound on the carrier; small holes are evenly distributed on the carrier and the electrode sleeve.

4. The method according to claim 1, wherein Step 1) two or more electrode units are set in the chromium-contaminated soil and / or groundwater. The electrode units are spatially arranged in a straight line, or in a manner of triangular vertices, triangular vertices and center, quadrilateral vertices, quadrilateral vertices and center.

5. The method according to claim 1, wherein The online monitoring and control system is further provided with an Internet of Things module, which is connected to the data acquisition module; sensors installed in the chromium-contaminated soil and / or groundwater transmit monitoring data to the data acquisition module via wired or wireless transmission, and the real-time monitoring data is uploaded to the cloud via the Internet of Things module; and / or the online monitoring and control system is further provided with a camera for real-time observation of the on-site conditions of the contaminated site.

6. The method according to claim 1, wherein The solar power supply includes a solar panel and its bracket, a controller, an inverter and a battery, wherein the solar panel is installed on the bracket, and the solar panel, inverter and battery are respectively connected to the controller. The solar panel converts light energy into electrical energy, and the battery stores the converted electrical energy. The controller regulates the charging and discharging power of the solar panel, and the inverter converts direct current into alternating current to supply the online monitoring and control system.

7. The method according to claim 1, wherein In step 3), the online monitoring and control system adjusts the voltage and current between the electrodes through an adjustable DC regulated power supply module based on real-time monitoring data, so that the electric field strength is 0.02~1 V / cm and the current strength is 0.2~2 A; and samples are taken from the chromium-contaminated soil and / or groundwater through a sampling tube to monitor the remediation progress.

8. The method according to claim 1, wherein The method is implemented in chromium-contaminated sites through the following operating steps: Step 1: Determine the layout plan of the electrode units, including the horizontal distribution position and corresponding depth, based on the spatial distribution of the chromium pollution concentration, electrical conductivity and moisture content of the site, and prepare electrodes, carriers and electrode sleeves of corresponding lengths, wherein the carrier is tubular and its diameter is smaller than that of the electrode sleeve, and small water-permeable holes are distributed on the carrier and electrode sleeve; Step 2: Select a suitable solar power source based on the operating power of each component, and the daily power generation power of the solar power source is 1 to 1.5 times the daily operating power of the entire device; Step 3: Based on the electrode unit layout plan determined in Step 1, a well is constructed at the corresponding location and an electrode sleeve is placed. During the well construction process, mineral material and quartz sand particles are evenly filled into the periphery of the electrode sleeve in a layered and alternating manner. The mineral material is in powder form and is packaged in porous packaging bags made of biodegradable materials. Step 4: Install the solar power source selected in step 2 at the chromium contaminated site; Step 5: Fix the electrode to the carrier, place the sensor in the carrier, and insert it vertically into the electrode sleeve; Step 6: Place the sampling tube in the electrode sleeve; Step 7: Connect the electrode to the adjustable DC regulated power supply in the online monitoring and control system to start the repair; Step 8: During the repair process, monitor the change of hexavalent chromium concentration through the sampling tube. When the hexavalent chromium concentration does not change for more than the specified time, introduce the mineral material powder into the bottom of the carrier through a thin tube as needed; At the same time, monitor the changes in temperature and humidity, redox potential, pH and conductivity of the electrode unit, and keep the moisture content above 10% by replenishing water. By reducing the voltage between the electrodes or briefly exchanging the anode and cathode, the pH fluctuation range is less than 30%. By adjusting the voltage between the electrodes, the cathode redox potential is kept below -100 mV. When the conductivity decays by more than 20% compared with the initial value, add mineral material to the bottom of the carrier; Step 9: After the repair is completed, the electrode unit is directly pulled out and recycled, and the mineral material is recovered magnetically.

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