A heavy metal contaminated soil electrokinetic-permeable reaction wall coupling remediation method

Abstract

The application discloses a heavy metal contaminated soil electrokinetic-permeable reaction wall coupling remediation method, which comprises the following steps: step one, PRB arrangement, a total of three groups of electrodes are arranged, R1 and R3 electrodes are arranged in electrolyte on both sides of the remediation soil respectively, the PRB is arranged between the anode and the cathode and close to the cathode 2 / 5 position, and a piece of net-shaped conductive material is inserted on the PRB material side close to the R1 electrode as the third group of electrodes R2; step two, soil remediation operation, in the first stage of remediation, R1 and R3 are connected to the positive and negative poles of the power supply respectively, a direct current electric field is applied for remediation, after a certain time of remediation, the second stage of remediation is carried out, the electrodes and the polarity are switched, namely R3 and R2 are connected to the positive and negative poles of the power supply respectively, a direct current electric field is applied for remediation, after a certain time of remediation, the remediation is ended. The beneficial effect is that no additional auxiliary reagents such as organic acid are needed, heavy metals are enriched in the filling area of the permeable reaction wall, efficient remediation is realized, and the power consumption is reduced.

Description

Technical Field

[0001] This invention relates to the field of heavy metal contaminated soil remediation technology, and in particular to an electro-permeable reactive barrier coupled remediation method for heavy metal contaminated soil. Background Technology

[0003] Electroremediation combined with permeable reactive barrier (EK-PRB) utilizes a direct current electric field to drive the directional migration of heavy metals. The permeable reactive barrier acts as a pre-defined reaction zone, filled with heavy metal adsorbent material, which adsorbs or precipitates the migrated heavy metals, preventing their diffusion and achieving removal. This technology has attracted widespread attention due to its unique advantages in treating low-permeability clay soils. However, this technology still faces significant challenges in practical applications. The strong alkalization of the soil caused by the cathodic electrolysis reaction (pH can rise to 12) can trigger heavy metal precipitation, forming a "focusing effect" that hinders migration. Simultaneously, the high energy consumption of this technology limits its large-scale engineering application. Many studies have used chemical reagents such as citric acid to adjust soil pH to mitigate the focusing effect, but this increases remediation costs and may cause secondary soil pollution.

[0004] In view of the above, it is necessary to improve existing soil remediation methods to adapt them to the current needs of soil use. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for the coupled remediation of heavy metal contaminated soil using an electrodynamic-permeable reactive barrier, comprising the following steps: Step 1: Electrode and PRB placement. A total of 3 sets of electrodes are placed. The R1 and R3 electrodes are placed in the electrolyte on both sides of the soil to be repaired. The PRB is placed between the anode and the cathode, about 2 / 5 of the way from the cathode. At the same time, a mesh conductive material is inserted into the PRB material near the R1 electrode as the third set of electrodes R2. Step 2: Soil remediation operation. In the first stage of remediation, R1 and R3 are connected to the positive and negative terminals of the power supply, respectively, and a DC electric field is applied for remediation. After a certain period of remediation, the second stage of remediation is carried out by switching the electrodes and polarity, i.e., R3 and R2 are connected to the positive and negative terminals of the power supply, respectively, and a DC electric field is applied for remediation. After a certain period of remediation, the remediation is completed.

[0006] As a further supplement to this technical solution, the electrolyte in step one is selected from low-concentration sulfate or nitrate solutions.

[0007] As a further supplement to this technical solution, the PRB filling material is a material that can adsorb heavy metals.

[0008] As a further supplement to this technical solution, the energizing time of the first stage of remediation in step two is determined based on the concentration of heavy metals in the soil near electrode R1 of PRB. The first stage of remediation is stopped when the removal of heavy metals in the soil reaches more than 85%.

[0009] As a further supplement to this technical solution, the energizing time for the second stage of remediation in step two is determined based on the concentration of heavy metals in the soil near electrode R3 of PRB. The second stage of remediation is stopped when the removal of heavy metals in the soil reaches more than 85%.

[0010] A remediation device employing an electrodynamic-permeable reactive wall coupled remediation method for heavy metal contaminated soil includes a permeable reactive wall region. A mesh-like charged material is inserted as electrode R2 near electrode R1 on the PRB material side. The permeable reactive wall divides the contaminated soil into two parts. Electrolyte tanks are located on both sides of the contaminated soil, each filled with electrolyte. Electrodes R1 and R3 are inserted in these tanks. This invention uses two DC power supplies connected to the electrodes by wires. The positive terminal of the first power supply is connected to electrode R1, and its negative terminal is connected to electrode R3. The positive terminal of the second power supply is connected to electrode R3, and its negative terminal is connected to electrode R2.

[0011] Its beneficial effect is that it can enrich heavy metals in the area filled by the permeable reactive wall without the need to add additional organic acids or other auxiliary reagents, thereby achieving efficient remediation and reducing power consumption. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the electrode arrangement of the present invention; Figure 2 This is a diagram illustrating the electric field application method of the present invention. Detailed Implementation

[0013] To facilitate a clearer understanding of this technical solution for those skilled in the art, the following will be described in conjunction with the appendix. Figure 1-2 The technical solution of the present invention is described in detail below: like Figure 1 and Figure 2 As shown, the EK-PRB coupled remediation device includes a permeable reactive wall area. A mesh-like conductive material is inserted into the PRB material near electrode R1 as electrode R2. The permeable reactive wall divides the contaminated soil into two parts. Electrolyte tanks are located on both sides of the contaminated soil, each filled with electrolyte, and electrodes R1 and R3 are inserted therein. This invention uses two DC power supplies connected to the electrodes by wires. The positive terminal of power supply 1 is connected to electrode R1, and the negative terminal is connected to electrode R3. The positive terminal of power supply 2 is connected to electrode R3, and the negative terminal is connected to electrode R2.

[0014] In the first stage of repair, power supply 1 is turned on and power supply 2 is turned off. Electrodes R1 and R3 are energized, with R1 being the positive terminal and R3 being the negative terminal.

[0015] The energizing time is determined based on the concentration of heavy metals in the soil near electrode R1 of the PRB. When the removal of heavy metals in the soil reaches more than 85%, the first stage of remediation is stopped, and the running time is T1.

[0016] In the second stage of repair, power supply 1 is turned off and power supply 2 is turned on. Electrode R3 and electrode R2 are energized, with R3 being the positive terminal and R2 being the negative terminal.

[0017] The energizing time is determined based on the concentration of heavy metals in the soil near electrode R3 of the PRB. When the removal of heavy metals in the soil reaches more than 85%, the first stage of remediation is stopped, and the running time is T2.

[0018] Therefore, by switching between electrodes R1-R3 and R3-R2 and switching their polarity, the efficient removal of heavy metals from soil can be achieved.

[0019] Example 1 The contaminated soil remediated in this embodiment was self-prepared cadmium-contaminated soil. The clean soil was collected from the top 0-20cm layer of soil in Songshan Lake, Dongguan City, Guangdong Province. After natural air drying in the laboratory, stones and plant roots were removed, the soil was ground and passed through a 20-mesh sieve, and cadmium chloride was artificially added, resulting in a final cadmium concentration of approximately 10 mg / kg. Soil remediation employed… Figure 1 The apparatus shown is 27 cm long, 4 cm wide, and 6 cm high. The apparatus consists of two sections: an electrolyte tank, each 4 cm long, filled with 0.1M sodium sulfate solution, and two vertically inserted sheet graphite electrodes, R1 and R3, measuring 6 cm × 4 cm × 0.5 cm. A soil tank, 19 cm long, is located in the middle of the soil tank, 6-10 cm from the electrolyte tank containing electrode R3. This area is filled with iron-manganese oxide-modified biochar material, level with the soil. A stainless steel mesh, serving as electrode R2, is inserted into the permeable reactive wall near electrode R1. The soil tank is filled with 400 g of contaminated soil, approximately 4 cm high.

[0020] The experiment uses two DC power supplies: power supply 1 has a voltage of 18V and power supply 2 has a voltage of 6V. The power supplies are connected to the electrodes by wires. The positive terminal of power supply 1 is connected to electrode R1 and the negative terminal is connected to electrode R3. The positive terminal of power supply 2 is connected to electrode R3 and the negative terminal is connected to electrode R2.

[0021] Remediation Phase 1: Power supply 1 is turned on, power supply 2 is turned off, and electrodes R1 and R3 are energized, with R1 being the positive electrode and R3 the negative electrode. Based on the migration rate of cadmium ions in the soil under different pH conditions and the migration rate of hydrogen ions towards the cathode under an electric field, it is calculated that the time required for cadmium removal in the soil near electrode R1 to reach more than 85% is 15 days, i.e., the remediation phase 1 time T1 = 15 days.

[0022] Remediation Phase 2: Power supply 1 is turned off, power supply 2 is turned on, and electrodes R3 and R2 are energized, with R3 as the positive electrode and R2 as the negative electrode. By measuring soil pH and the rate of hydrogen ion migration, it is calculated that the time required for cadmium removal in the soil near electrode R3 to reach more than 85% is 10 days, i.e., the remediation phase 1 time T2 = 10 days.

[0023] Thus, after two phases of remediation totaling 25 days, the removal rate of total cadmium in the soil was 91.4%.

[0024] Example 2 The difference from Example 1 is that the contaminated soil used in this experiment was a self-prepared composite contaminated soil containing cadmium and lead. Cadmium chloride and lead chloride were artificially added, resulting in a composite contaminated soil with final concentrations of approximately 10 mg / kg for cadmium and 500 mg / kg for lead. The total treatment time was 25 days, with the first remediation stage lasting 15 days and the second remediation stage lasting 10 days. After 25 days of treatment, the removal rate of total cadmium in the soil was 90.1%, and the removal rate of total lead was 86.3%.

[0025] The above technical solutions only embody the preferred technical solutions of the present invention. Any modifications that may be made by those skilled in the art to certain parts thereof embody the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A method for remediating heavy metal contaminated soil using an electrodynamic-permeable reactive barrier coupling, characterized in that, Includes the following steps: Step 1: Electrode and PRB placement. A total of 3 sets of electrodes are placed. The R1 and R3 electrodes are placed in the electrolyte on both sides of the soil to be repaired. The PRB is placed between the anode and the cathode, about 2 / 5 of the way from the cathode. At the same time, a mesh conductive material is inserted into the PRB material near the R1 electrode as the third set of electrodes R2. Step 2: Soil remediation operation. In the first stage of remediation, R1 and R3 are connected to the positive and negative terminals of the power supply, respectively, and a DC electric field is applied for remediation. After a certain period of remediation, the second stage of remediation is carried out by switching the electrodes and polarity, i.e., R3 and R2 are connected to the positive and negative terminals of the power supply, respectively, and a DC electric field is applied for remediation. After a certain period of remediation, the remediation is completed.

2. The method for coupled remediation of heavy metal contaminated soil using an electrodynamic-permeable reactive barrier according to claim 1, characterized in that, In the aforementioned step, a low-concentration sulfate or nitrate electrolyte is selected.

3. The method for coupled remediation of heavy metal contaminated soil using an electrodynamic-permeable reactive barrier according to claim 2, characterized in that, The PRB filling material is a material that can adsorb heavy metals.

4. The method for coupled remediation of heavy metal contaminated soil using an electrodynamic-permeable reactive barrier according to claim 3, characterized in that, In step two, the energizing time for the first stage of remediation is determined based on the concentration of heavy metals in the soil near electrode R1 of the PRB. The first stage of remediation is stopped when the removal of heavy metals in the soil reaches more than 85%.

5. The method for remediation of heavy metal contaminated soil using an electrodynamic-permeable reactive barrier according to claim 1, characterized in that, In step two, the energizing time for the second stage of remediation is determined based on the concentration of heavy metals in the soil near electrode R3 of the PRB. The second stage of remediation is stopped when the removal of heavy metals in the soil reaches more than 85%.

6. A remediation device employing the electrodynamic-permeable reactive barrier coupled remediation method for heavy metal contaminated soil as described in any one of claims 1-5, characterized in that, The invention includes a permeable reactive barrier area, with a mesh-like charged material inserted into the PRB material as electrode R2. The permeable reactive barrier divides the contaminated soil into two parts, with electrolyte tanks on both sides of the contaminated soil, each filled with electrolyte. Electrodes R1 and R3 are also inserted in these tanks. The invention uses two DC power supplies, which are connected to the electrodes by wires. The positive terminal of the first power supply is connected to electrode R1, and its negative terminal is connected to electrode R3. The positive terminal of the second power supply is connected to electrode R3, and its negative terminal is connected to electrode R2.

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