Electrokinetic remediation system, method and application of chromium-contaminated soil

Abstract

The present application relates to the technical field of soil pollution remediation, and particularly relates to a chromium-polluted soil electrodynamic remediation system based on synergistic effect of graphite three-dimensional electrode and chitosan, aiming at the problems of low chromium migration efficiency, poor remediation effect stability and limited reaction interface in the existing electrodynamic remediation technology.In the three-dimensional electrode system, a chitosan adsorption layer is arranged in the anode region, and conductive graphite particle materials are introduced into the soil to construct a three-dimensional electrode structure.Under the action of an external electric field, Cr(VI) migrates to the anode region in the form of anions, is effectively adsorbed and fixed by chitosan, and is reduced and converted under the action of electrochemistry, thereby inhibiting chromium back migration and improving removal efficiency.The method can significantly improve the remediation effect of chromium-polluted soil and reduce energy consumption, and is suitable for in-situ or ex-situ remediation of chromium-polluted soil.

Description

Technical Field

[0001] This application relates to the field of soil pollution remediation technology, and in particular to an electric remediation system, method and application for chromium-contaminated soil. Background Technology

[0002] In recent years, with the acceleration of industrialization, soil chromium pollution has become a global environmental concern due to its high toxicity and widespread distribution. Chromium exists in the environment mainly as Cr(III) and the highly toxic Cr(VI). Cr(VI) can enter soil and water bodies through various pathways and harm human health through the food chain or contact, leading to serious problems such as digestive system damage and liver and kidney failure.

[0003] Currently, soil chromium pollution remediation mainly relies on physical, biological, and chemical methods. Physical methods involve large engineering projects and are only suitable for small, shallow contaminated sites. Microbial and phytoremediation are time-consuming, slow, and susceptible to external factors. Their effects are limited to the root zone and generate large amounts of chromium-containing biomass that require treatment, making them unsuitable for large-scale remediation. Although chemical reduction methods are commonly used, they require high soil permeability, and there is a risk that the reducing agent may have difficulty contacting encapsulated pollutants. Furthermore, reduced Cr(III) may be re-oxidized to Cr(VI) by manganese oxides in the soil, affecting the long-term stability of the remediation effect.

[0004] Electroremediation technology utilizes an electric field to drive the directional migration and accumulation of chromium ions in the soil within the electrode region. Combined with mechanisms such as electrodialysis, electrochemical reduction, and precipitation, it achieves highly efficient removal of pollutants, providing a new approach for contaminated soil remediation. Compared to traditional physical soil replacement methods that damage soil structure, the long cycle of bioremediation, and the risk of secondary pollution from chemical leaching, this technology offers advantages such as non-destructiveness, applicability to low-permeability soils, short treatment cycles, and the ability to simultaneously control pollutant speciation, such as reducing highly toxic Cr(VI) to less toxic Cr(III). It is particularly suitable for remediating complex geological conditions or mixed contaminated sites. However, traditional two-dimensional electroremediation systems suffer from high energy consumption and limited reaction areas.

[0005] Three-dimensional electrode systems overcome the limitations of enclosed reaction zones by filling the space between the anode and cathode with conductive particles or fragmented materials, polarizing the particles into charged particles, thus allowing the reaction zone to be expanded to the entire reactor. Furthermore, the rough surface, porous structure, and large area-to-volume ratio of the particle electrodes can improve the current efficiency per unit spacetime, thereby enhancing electrochemical efficiency. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low chromium migration efficiency, limited reaction interface, insufficient remediation efficiency and stability, and strong pH dependence in existing electrokinetic remediation technologies. It provides an electrokinetic remediation system for chromium-contaminated soil based on a three-dimensional electrode and chitosan adsorption, to achieve directional migration, effective fixation, and efficient removal of chromium. Based on this remediation system, this invention also discloses an electrokinetic remediation method for chromium-contaminated soil using the aforementioned electrokinetic remediation system.

[0007] This invention is achieved through the following technical solution: An electrodynamic remediation system for chromium-contaminated soil includes: an anode plate, a cathode plate, a chitosan adsorption layer disposed on the anode plate, a soil chamber disposed on the cathode plate, and filter paper disposed between the soil chamber and the chitosan adsorption layer; the soil chamber is filled with a three-dimensional electrode and chromium-contaminated soil; a DC power supply is electrically connected to the anode plate and the cathode plate to form an electric field in the soil chamber, causing chromium to migrate directionally to the anode plate or the cathode plate.

[0008] Furthermore, the anode plate and the cathode plate are graphite plates, the distance between the anode plate and the cathode plate is 1.5 cm, the chitosan thickness is 0.5 cm, and the soil chamber thickness is 1 cm.

[0009] Furthermore, the anode plate is located below the cathode plate.

[0010] Furthermore, the voltage gradient in the soil region is 3 V / cm.

[0011] Furthermore, the three-dimensional electrode is a cylindrical graphite particle with a purity of 99.9%.

[0012] Furthermore, in the soil chamber, the amount of the three-dimensional electrode added is 5% of the soil mass.

[0013] Furthermore, the chitosan adsorption layer contains a 0.1 mol / L sodium chloride solution.

[0014] Furthermore, the chitosan adsorption layer has a water content of 100%.

[0015] An electrokinetic remediation method for chromium-contaminated soil includes: Prepare an electro-electric remediation system for chromium-contaminated soil as described in any of the above-mentioned embodiments; After drying the chromium-contaminated soil and removing large areas of impurities by sieving, the soil was mixed with a 5% three-dimensional electrode for soil treatment, and deionized water was added until the moisture content of the chromium-contaminated soil reached 50%. Prepare a 0.1 mol / L sodium chloride solution, wet the chitosan until the water content is 100%, and place the chitosan on the anode plate to form a chitosan adsorption layer; The anode plate, chitosan adsorption layer, filter paper, soil chamber, and cathode plate are arranged sequentially from bottom to top, wherein the soil chamber is filled with a three-dimensional electrode and chromium-contaminated soil. A DC power supply supplies power to the anode plate and the cathode plate, making the voltage gradient in the soil chamber region 3 V / cm.

[0016] The present invention also provides the application of the electro-remediation system or method for chromium-contaminated soil in the field of ecological pollution control.

[0017] The beneficial effects of this invention are as follows: (1) By introducing a three-dimensional electrode, the electrochemical reaction area is extended from the electrode surface to the entire soil remediation area, which greatly increases the reaction area and promotes the migration and transformation of Cr(VI) and Cr(III). (2) During the remediation process, even if the concentration of ions in the pore water fluctuates due to electrolysis or metal precipitation, the micro electric field network formed by the three-dimensional electrode can still maintain a relatively stable current transmission channel, thereby significantly improving the stability of the overall soil conductivity, preventing the interruption of electroosmosis, and ensuring the continuous and efficient progress of the remediation process. (3) The chitosan adsorption layer acts as a terminal trap, which efficiently adsorbs and reduces the migrating Cr(VI) in the anode region, thereby enhancing the targeted removal and fixation of highly toxic Cr(VI) and preventing its secondary release. (4) The introduction of three-dimensional electrodes improves the overall conductivity and current efficiency of the system, reduces the energy consumption for removing chromium per unit mass, reduces damage to soil structure, is suitable for in-situ remediation of soil in actual sites with different pollution levels, and has a simple system structure, is easy to implement, and has good engineering application prospects. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the electro-hydraulic remediation system for chromium-contaminated soil disclosed in this invention; Figure 2 The difference in remediation efficiency of different remediation systems compared to the electrodynamic remediation system for chromium-contaminated soil is the difference in Cr(VI) remediation efficiency. Figure 3 The difference in total chromium remediation efficiency between different remediation systems and the electrostatic remediation system for the chromium-contaminated soil is as follows: Figure 4 This is a comparison chart of current changes in different repair systems; Figure 5 This is a comparison chart of the energy consumption of different repair systems.

[0020] in: 1. DC power supply; 2. Electrode plate (anode plate or cathode plate); 3. Chitosan adsorption layer; 4. Filter paper; 5. Soil chamber; 6. Three-dimensional electrode. Detailed Implementation

[0021] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0022] Please refer to Figure 1 The present invention discloses an electro-hydraulic remediation system for chromium-contaminated soil, comprising: DC power supply 1, which supplies power to the electric repair system; Anode plate 2, which is connected to the positive terminal of the DC power supply 1; Cathode plate 2, which is connected to the negative terminal of the DC power supply 1; Chitosan adsorption layer 3 is attached to the anode plate 2 and located between the anode plate 2 and the cathode plate 2. Filter paper 4 covers the chitosan adsorption layer 3; Soil chamber 5 is installed below the cathode plate 2, located between the filter paper 4 and the cathode plate 2.

[0023] The soil chamber 5 is filled with a three-dimensional electrode 6 and chromium-contaminated soil; the DC power supply 1 is electrically connected to the anode plate 2 and the cathode plate 2, forming an electric field in the soil chamber 5, causing chromium to migrate directionally to the anode plate 2 or the cathode plate 2.

[0024] The anode plate 2 and the cathode plate 2 are graphite plates, and the distance between the anode plate 2 and the cathode plate 2 is 1 cm.

[0025] In the electrokinetic remediation system for chromium-contaminated soil, the anode plate 2, chitosan adsorption layer 3, filter paper 4, soil chamber 5, and cathode plate 2 are arranged sequentially from bottom to top. The filter paper 4 prevents solid particles (soil and graphite particles) in the soil chamber 5 from mixing with the chitosan adsorption layer 3, avoiding cross-contamination, while simultaneously allowing ions in the solution to pass freely under the influence of the electric field. Therefore, Cr(VI) anions (CrO4) 2- Cr2O7 2-It can successfully migrate from the soil chamber to the chitosan adsorption layer while the soil structure remains intact.

[0026] The three-dimensional electrode 6 within the soil chamber 5 is composed of cylindrical graphite particles with a purity of 99.9%. The amount of the three-dimensional electrode 6 added is 5% of the soil mass. The graphite particle electrode functions throughout the reactor, promoting migration, mitigating aggregation, reducing energy consumption, and providing reduction points for Cr(VI) throughout the soil by increasing conductivity and creating a micro-electric field.

[0027] The chitosan adsorption layer 3 is used to capture, enrich, and promote the reduction and fixation of Cr(VI) that eventually migrates to the anode. Chitosan provides limited reducing power at the anode, mainly for the adsorption and fixation of Cr(VI).

[0028] To increase the conductivity of the chitosan adsorption layer 3, a 0.1 mol / L sodium chloride solution is contained in the chitosan adsorption layer 3, so that the water content of the chitosan adsorption layer 3 is 100%.

[0029] Spraying a 0.1 mol / L sodium chloride solution onto the chitosan adsorption layer 3 is because the Cl in NaCl... － A higher transference number in Na helps stabilize the current. ＋ NaCl does not readily complex or precipitate with chitosan, and it is inexpensive, readily available, and has minimal impact on the soil environment. Too low an electrolyte content offers limited improvement in conductivity, while excessively high concentrations can cause electrode side reactions such as Cl2 precipitation, damaging the chitosan adsorption layer, reducing current efficiency, increasing energy consumption, and potentially leading to equipment corrosion and secondary pollution risks. Therefore, the concentration of sodium chloride solution used is 0.1 mol / L.

[0030] Example 1 Pretreatment was performed on 99.9% pure, cylindrical graphite particles with a size of 3 mmΦ×3 mm: the graphite particles were soaked in concentrated hydrochloric acid for 12 h to remove impurities, and then repeatedly ultrasonically cleaned with deionized water until the pH of the graphite particle leachate was 7. Finally, the particles were dried in an oven at 60 ℃ for later use.

[0031] Filter paper 4 is made of MCE mixed cellulose and has a size of 50 mm × 0.22 μg.

[0032] The cathode plate 2 and the anode plate 2 are made of graphite electrodes with dimensions of 70×70×4 mm.

[0033] The soil was contaminated with chromium, with a chromium content of approximately 10,468 mg / kg.

[0034] Example 2 Based on the material content and electrokinetic remediation system for chromium-contaminated soil in Example 1, this invention discloses an electrokinetic remediation method for chromium-contaminated soil, comprising the following steps: S1. After drying the chromium-contaminated soil at a constant temperature of 60 ℃ for 24 hours, grind it and pass it through a 100-mesh sieve to remove large areas of impurities. Store it in a cool, dry place in a sealed container for experimental use.

[0035] S2, mix 10 g of the chromium-contaminated soil prepared in step S1 with 0.5 g of graphite particles evenly, and add deionized water until the soil moisture content is 50%.

[0036] S3, place the chromium-contaminated soil containing the three-dimensional electrode 6 from step S2 into the soil chamber 5, compact and level it, and cover it with filter paper 4.

[0037] S4. Prepare a 0.1 mol / L NaCl solution using deionized water. Take chitosan and moisten it with the prepared NaCl solution. Then place the moistened chitosan between the anode plate 2 and the soil chamber 5 as an adsorption layer. Separate the adsorption layer from the soil with filter paper 4 to avoid cross-contamination. Control the distance between the anode plate 2 and the cathode plate 2 to be about 1.5 cm. The soil chamber 5 is 1 cm thick and the chitosan adsorption layer 3 is 0.5 cm thick.

[0038] S5, arrange the anode plate 2, chitosan adsorption layer 3, filter paper 4, soil chamber 5, and cathode plate 2 in sequence from bottom to top.

[0039] S6, the positive terminal of the DC power supply 1 is electrically connected to the anode plate 2 and the negative terminal is electrically connected to the cathode plate 2, and the output is in a constant voltage mode. The output voltage of the DC power supply 1 is 0 to 30 V and the output current is 0 to 3 A. During the repair process, a constant voltage of 3 V / cm is used.

[0040] S7. Current data was collected by an electrochemical workstation. After 2 hours of reaction, samples were taken and the Cr(VI) and total chromium concentrations of the samples were determined by UV spectrophotometer and ICP-OES, respectively.

[0041] S8, set up control groups, where each control group is configured as follows: 5% GP-0V is the removal rate of Cr(VI) in soil with graphite electrodes added but without electricity applied; 0% GP-3V is the removal rate of Cr(VI) in soil without the addition of graphite electrodes, as in step S6 after 2 hours of energization. 5% GP-3V is the removal rate of Cr(VI) in soil after adding graphite electrodes, such as in step S6, and energizing for 2 hours. CS-5% GP-3V is the removal rate of Cr(VI) after adding graphite electrodes to the soil, such as adding a chitosan adsorption layer 3 on the anode plate 2 in step S4, and energizing for 2 hours in step S6. Please refer to Figure 2 and Figure 3 After 2 hours of static remediation (5% GP-0V), two-dimensional electrode remediation (0% GP-3V), and three-dimensional electrode remediation (5% GP-3V) on actual chromium-containing soil, the distribution and removal rate of hexavalent chromium and total chromium in the soil are as follows: Figure 2 and Figure 3 As shown. Compared with 5% GP-0V and 5% GP-3V, the applied electric field increased the Cr(VI) repair efficiency by 37.83% and the total chromium repair efficiency by 9.59%. Compared with 0% GP-3V and 5% GP-3V, the addition of a particulate electrode increased the Cr(VI) repair efficiency by 8.49% and the total chromium repair efficiency by 26.43%. Compared with 5% GP-3V and CS-5% GP-3V, the addition of chitosan increased the Cr(VI) repair efficiency by 7.27% and the total chromium repair efficiency by 20.34%.

[0042] As can be seen from the above, the external electric field, the three-dimensional electrode 6, and the addition of chitosan to the anode can all improve the remediation efficiency of Cr(VI) to a certain extent, and can also significantly improve the remediation efficiency of total chromium. This indicates that the introduction of the three-dimensional electrode 6 and chitosan can reduce the accumulation of Cr pollution in the soil by improving the directional movement ability of Cr.

[0043] Please refer to Figure 4 Comparative analysis of current changes during the remediation of contaminated soil under different systems. Figure 4 The current exhibits a pattern of first decreasing, then increasing, and finally decreasing again. Notably, in the two-dimensional electrode (0% GP-3V) system, the current recovery process even lasted up to 120 minutes. This prolonged recovery period can be attributed to the high metal ion content in the actual soil, and also indicates that the metal ion release efficiency of the two-dimensional electrode (0% GP-3V) system is lower than that of the three-dimensional electrode 6 (5% GP-3V) system.

[0044] Figure 5 The energy consumption for chromium remediation in soil under different systems was demonstrated. The two-dimensional electrode (0% GP-3V) system maintained the highest energy consumption (0.0220 kWh / g). Adding a graphite particle electrode (5% GP-3V) significantly reduced energy consumption to 0.0069 kWh / g. When chitosan (CS-5% GP-3V) was added, energy consumption further decreased to 0.0041 kWh / g.

[0045] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An electro-hydraulic remediation system for chromium-contaminated soil, characterized in that, include: An anode plate, a cathode plate, a chitosan adsorption layer disposed on the anode plate, a soil chamber disposed on the cathode plate, and filter paper disposed between the soil chamber and the chitosan adsorption layer; the soil chamber is filled with a three-dimensional electrode and chromium-contaminated soil; a DC power supply is electrically connected to the anode plate and the cathode plate to form an electric field in the soil chamber, causing chromium to migrate directionally to the anode plate or the cathode plate.

2. The electrodynamic remediation system for chromium-contaminated soil according to claim 1, characterized in that, The anode plate and the cathode plate are graphite plates, the distance between the anode plate and the cathode plate is 1.5 cm, the chitosan thickness is 0.5 cm, and the soil chamber thickness is 1 cm.

3. The electrodynamic remediation system for chromium-contaminated soil according to claim 1, characterized in that, The anode plate is located below the cathode plate.

4. The electrodynamic remediation system for chromium-contaminated soil according to claim 1, characterized in that, The voltage gradient in the soil region is 3 V / cm.

5. The electro-hydraulic remediation system for chromium-contaminated soil according to claim 1, characterized in that, The three-dimensional electrode is a cylindrical graphite particle with a purity of 99.9%.

6. The electrodynamic remediation system for chromium-contaminated soil according to claim 1 or 5, characterized in that, In the soil chamber, the amount of the three-dimensional electrode added is 5% of the soil mass.

7. The electro-hydraulic remediation system for chromium-contaminated soil according to claim 1, characterized in that, The chitosan adsorption layer contains a 0.1 mol / L sodium chloride solution.

8. The electro-hydraulic remediation system for chromium-contaminated soil according to claim 7, characterized in that, The chitosan adsorption layer has a water content of 100%.

9. An electrokinetic remediation method for chromium-contaminated soil, characterized in that, include: Prepare an electro-hydraulic remediation system for chromium-contaminated soil as described in any one of claims 1 to 8; After drying the chromium-contaminated soil and removing large areas of impurities by sieving, the soil was mixed with a 5% three-dimensional electrode for soil treatment, and deionized water was added until the moisture content of the chromium-contaminated soil reached 50%. Prepare a 0.1 mol / L sodium chloride solution, wet the chitosan until the water content is 100%, and place the chitosan on the anode plate to form a chitosan adsorption layer; The anode plate, chitosan adsorption layer, filter paper, soil chamber, and cathode plate are arranged sequentially from bottom to top, wherein the soil chamber is filled with a three-dimensional electrode and chromium-contaminated soil. A DC power supply supplies power to the anode plate and the cathode plate, making the voltage gradient in the soil chamber region 3 V / cm.

10. The application of the electro-remediation system for chromium-contaminated soil according to any one of claims 1 to 8 or the electro-remediation method for chromium-contaminated soil according to claim 9 in the field of ecological pollution control.

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