In-situ electric reinforced persulfate remediation method and device for heavy metal-organic matter combined contaminated soil

Abstract

The invention belongs to the technical field of in-situ remediation of contaminated soil, and relates to an in-situ electric reinforced persulfate remediation method and device for heavy metal-organic matter combined contaminated soil. In the method, heavy metals in a soil medium are migrated out of a soil environment under the action of an electric field while the migration of persulfate is promoted by an electric technology, and the soil temperature is continuously increased by electric field heat along with the proceeding of an electric experiment, so that the activation of the persulfate is realized, and the degradation of pollutants is promoted; under the combined action of the electric field force and active substances generated by the persulfate, remediation of the heavy metal-organic matter combined contaminated soil is achieved. The problems that at the present stage, persulfate is short in migration distance in a soil medium and low in activation efficiency, and the remediation effect of heavy metal-organic matter combined contaminated soil is poor are solved, heavy metal-organic matter synchronous removal is achieved, meanwhile, electric field heat is utilized to the maximum extent, the defect of energy waste of an electric technology is overcome, and the application prospect is wide. And the removal efficiency of pollutants is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of in-situ remediation of contaminated soil, and particularly relates to an in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic compound contaminated soil. Background Art

[0002] Polycyclic aromatic hydrocarbons (PAHs) are persistent hydrophobic compounds that are ubiquitous in nature and have been found in various environmental media. PAHs usually coexist with heavy metals (HMs), and these pollutants pose a serious threat to human health and the environment. The pollution of PAHs and HMs mostly occurs in industrial areas, mainly generated by chemical fuel combustion and waste incineration, etc. The coexistence of PAHs and HMs is widespread in various environmental media. Soil is the main repository of PAHs and HMs. Since soil can receive pollutants from various sources, these pollutants can be directly generated and enter the soil through ways such as fuel combustion and industrial production in coking plants. In soil, both of these pollutants will adhere to organic particles or mineral particles, and they have strong persistence. Compared with single pollution, the retention of these two pollutants in soil is more harmful to the ecological environment and human health. Therefore, it is very necessary to develop effective and sustainable methods to eliminate these pollutants.

[0003] Currently, there are various treatment methods available for treating HMs and PAHs. Among them, the EK-AOP water treatment technology has advantages such as high treatment efficiency, thorough treatment, and simple operation. It is considered an effective measure for remediating organic matter in soil and groundwater and has been widely applied. The most commonly used oxidants in the field of soil remediation include ozone, Fenton, permanganate, and persulfate (PS). Among them, PS not only has the advantages of high solubility, a wide range of pollutants that can be treated, and a moderate reaction rate, but also has a stable structure. In recent years, it has been widely used in the removal of organic matter in the subsurface environment. In addition, PS can be activated by heat, transition metals, and ultraviolet light, etc., to generate sulfate radicals (E 0 = 2.5 - 3.1V) and hydroxyl radicals (E 0 = 2.74V), which are strong and non-selective oxidizing substances. Research shows that compared with Fenton's reagent, the impact of thermally activated PS on soil microorganisms is much smaller. However, there are also some disadvantages after the advanced oxidation technology is applied to the HM and PAHs composite contaminated site. For example, the advanced oxidation technology has an unsatisfactory removal effect on heavy metals; the migration of PS in low-permeability formations remains an urgent problem to be solved.

[0004] EK technology has good removal effects on low-permeability media and heavy metals. It applies low-voltage direct current to electrodes inserted into the soil, and relies on the effects of electromigration (EM), electroosmosis (EOF), or electrophoresis to complete the removal of heavy metals and the uniform distribution of electrolyte in low-permeability media. Using electrokinetically enhanced persulfate can, on the one hand, promote the migration of persulfate in the soil medium and expand the influence range of persulfate; on the other hand, the Joule heat can effectively activate persulfate to achieve the removal of organic matter, and heavy metals also migrate towards the cathode under the action of the electric field, completing the synchronous removal of heavy metals and organic matter.

[0005] Based on this, it is very necessary to develop an in-situ electrokinetically enhanced persulfate remediation method for heavy metal-organic contaminated soil. It uses electrokinetically enhanced persulfate to remediate heavy metal-organic contaminated soil, which can not only solve the problems of short migration distance of persulfate in the soil medium, low activation efficiency, and poor remediation effect of heavy metal-organic contaminated soil at the present stage, but also achieve the efficient synchronous removal of heavy metals and organic matter. Summary of the Invention

[0006] The object of the present invention is to provide an in-situ remediation method for heavy metal-organic contaminated soil with high removal efficiency and no secondary pollution to the soil, and also provide a device used in the above method. It uses electrokinetically enhanced persulfate to remediate heavy metal-organic contaminated soil to solve the problems of short migration distance of persulfate in the soil medium, low activation efficiency, and poor remediation effect of heavy metal-organic contaminated soil.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] An in-situ electrokinetically enhanced persulfate remediation method for heavy metal-organic contaminated soil includes the following steps:

[0009] A. Activate persulfate using Joule heat:

[0010] A1. Uniformly fill the soil into the soil pool, and place a filter paper between the soil and the electrolysis chamber.

[0011] A2. In the electrolysis chamber, use NaNO3 solution to hydrate the soil to make the soil completely saturated; then suck out the NaNO3 solution in the electrolysis chamber and pump the electrolyte solution into the electrolysis chamber.

[0012] A3. Use the electric field to complete the transportation of persulfate: Use PS solution as the anolyte and NaNO3 solution as the catholyte, and use Joule heat to activate persulfate. Under the combined action of the electric field force and the active substances generated by persulfate, remediate heavy metal-organic contaminated soil.

[0013] B. Analytical detection:

[0014] B1. Determination of phenanthrene concentration: After one working cycle, the soil sample in the soil pool is divided into five equal parts from the cathode to the anode (S1 - S5); the soil sample is freeze-dried under vacuum and screened through a 1 mm sieve, and the residual phenanthrene in the dried sample is extracted by Soxhlet extraction;

[0015] B2. Determination of persulfate concentration:

[0016] The content of PS during the electrokinetic process is measured by ultraviolet spectrophotometry; the NaHCO3 solution and KI solution are mixed with the PS solution and allowed to develop color for 15 min; subsequently, the absorbance of the sample is measured using a UV-visible spectrophotometer at a wavelength of 352 nm, and its concentration is determined;

[0017] C. Analysis of remediation effect

[0018] According to the measurement results obtained in step B, calculate the migration distance of soil persulfate, the removal efficiency of heavy metals copper and lead in the soil, and the removal efficiency of organic matter phenanthrene in the soil.

[0019] Furthermore, in step A1, the soil is 1.5 kg of dry soil.

[0020] Furthermore, in step A2, the soil is hydrated with 0.01 M NaNO3 solution for 24 h.

[0021] Furthermore, in step A2, the electrolyte solution is pumped into the electrolysis chamber through a peristaltic pump at a flow rate of approximately 35 mL / min, and the electrolyte solution is a PS solution with a concentration of 3% - 10%.

[0022] Furthermore, in step A3, the environmental temperature is 30°C - 45°C, and the electric field strength is 0.5 - 1 V / cm.

[0023] Furthermore, in step B, the extraction includes the following steps:

[0024] a. Weigh 3 g of the sample into a Soxhlet extraction thimble, and add 100 ml of a mixed solvent of acetone and n-hexane at a ratio of 1:1 to the Soxhlet flask;

[0025] b. Extract for 24 h at 4 - 6 cycles per hour, and then cool;

[0026] c. Concentrate the extract and reserve it for later use. Subsequently, the concentration of phenanthrene in the extract is detected by gas chromatography (Agilent 1260 infinity Ⅱ).

[0027] Even further, the working cycle is set to 7 d.

[0028] Furthermore, by mass, 1 mL of a 0.005 g / mL NaHCO3 solution and 1 mL of a 0.1 g / mL KI solution were mixed with 300 μL of a PS solution.

[0029] An experimental device used in an in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic contaminated soil consists of 1 soil cell, 2 electrode chambers, 2 electrolyte storage tanks, 1 DC power supply, 1 peristaltic pump, and 2 graphite electrode plates.

[0030] Among them, the soil cell is located at the center of the device and directly accommodates the contaminated soil to be treated.

[0031] The 2 electrode chambers include an anode chamber and a cathode chamber, which are respectively adjacent to the left and right sides of the soil cell, allowing ion migration but blocking soil particles, providing an electrolysis reaction site. An oxidation reaction occurs in the anode chamber, and a reduction reaction occurs in the cathode chamber to maintain the stability of the electrolyte.

[0032] The 2 graphite electrode plates are respectively located at the connections between the cathode and anode chambers and the soil cell, serving as inert electrodes to conduct current. An acidic environment is generated at the anode, and a basic environment is generated at the cathode to drive the migration of pollutants in the soil.

[0033] The 2 electrolyte storage tanks, including an anolyte tank and a catholyte tank, are located behind or below the electrode chambers and are connected to the electrode chambers through pipelines.

[0034] The electrolyte storage tanks are used to store and buffer the electrolyte to maintain the ion concentration in the electrode chambers and prevent electrode corrosion.

[0035] The peristaltic pump is usually close to the storage tank and forms a circulation loop with the storage tank and the electrode chambers through a hose to circulate the electrolyte, avoid excessive / high or low local concentration in the electrode chambers, and carry away the reaction products.

[0036] The DC power supply is placed independently outside the device and is connected to the graphite electrode plates on both sides of the electrode chambers through wires, used to provide a stable voltage / current, establish an electric field gradient in the soil cell, and drive the processes of electrodialysis and electro-migration.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] The present invention realizes the remediation of heavy metal-organic contaminated soil through electrokinetic enhanced persulfate. While the electrokinetic technology promotes the migration of persulfate, heavy metals in the soil medium also migrate out of the soil environment under the action of the electric field. As the electrokinetic experiment progresses, the electric field heat continuously increases the soil temperature, realizing the activation of persulfate and promoting the degradation of pollutants. This method achieves multiple purposes such as the migration and activation of persulfate, the reuse of electric field heat, and the synchronous removal of heavy metals and organic matters. At the same time, it also has the significant advantages of high removal efficiency and no secondary pollution. Brief Description of the Drawings

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0040] Figure 1 Schematic structural diagram of the experimental device for the in-situ electrokinetic enhanced persulfate remediation method of heavy metal-organic contaminated soil;

[0041] Figure 2 Schematic diagram of the migration distance of soil persulfate;

[0042] Figure 3 Schematic diagram of the removal efficiency of heavy metals in soil;

[0043] Figure 4 Schematic diagram of the removal efficiency of organic matter in soil. Detailed Description of the Embodiments

[0044] The present invention will be further described below in conjunction with the embodiments:

[0045] The present invention will be further described in detail below in conjunction with the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. In addition, it should be noted that for the convenience of description, only parts related to the present invention rather than all structures are shown in the drawings.

[0046] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of the present invention, terms such as "first", "second", etc. are only used for distinguishing descriptions, and cannot be understood as indicating or implying relative importance.

[0047] The in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic contaminated soil of the present invention includes the following steps:

[0048] 1. Use electric field to thermally activate persulfate:

[0049] 11. Uniformly load 1.5 kg of dry soil into the soil pool, and place a filter paper between the soil and the electrolysis chamber to prevent soil from entering the electrolysis chamber. All experiments are carried out under open flow boundaries, allowing water to freely flow through the boundary between the soil and the electrolyte.

[0050] 12. In the electrolysis chamber, the soil is hydrated with a 0.01 M NaNO3 solution for 24 h to fully saturate the soil. Then, the NaNO3 solution in the electrolysis chamber is suctioned out, and the electrolyte solution is pumped into the electrolysis chamber through a peristaltic pump at a flow rate of approximately 35 mL / min. The electrolyte solution is a PS solution with a concentration of 3% - 10%.

[0051] The PS solution is prepared using sodium persulfate (Na2S2O8). The preparation method of the 3% concentration PS solution is as follows: Weigh 30 g of PS powder, dissolve it in 970 mL of ultrapure water, and heat and stir at 40 - 50 °C until completely dissolved. Similarly, the preparation method of the 5% concentration PS solution is: Weigh 50 g of PS powder, dissolve it in 950 mL of ultrapure water, and heat and stir until completely dissolved.

[0052] 13. Use an electric field to complete the transport of persulfate: Using the PS solution as the anolyte and the NaNO3 solution as the catholyte, at an ambient temperature of 30 °C - 45 °C, apply an electric field with an intensity of 0.5 - 1 V / cm to activate the persulfate using electrothermal heating. Under the combined action of the electric field force and the active substances generated by the persulfate, the remediation of heavy metal - organic contaminated soil is achieved.

[0053] 2. Analysis and detection:

[0054] 21. Determination of phenanthrene concentration: After one action cycle, the soil samples in the soil pool are divided into five equal parts from the cathode to the anode (S1 - S5). The soil samples are vacuum freeze - dried and screened through a 1 mm sieve. The residual phenanthrene in the dried samples is extracted by the Soxhlet extraction method. The specific method is as follows:

[0055] (a) Weigh 3 g of the sample into a Soxhlet extraction thimble, and add 100 ml of a 1:1 mixed solvent of acetone and n - hexane to the Soxhlet flask;

[0056] (b) Extract for 24 h at 4 - 6 cycles per hour, and then cool;

[0057] (c) Concentrate the extract and reserve it for later use. Subsequently, the concentration of phenanthrene in the extract is detected using gas chromatography (Agilent 1260 infinity Ⅱ).

[0058] In the present invention, according to the migration and transformation law of pollutants in the electric field and the migration distance of persulfate under the action of the electric field, the action cycle is set to 7 d.

[0059] 22. Determination of persulfate concentration:

[0060] The content of PS during the electrokinetic process was measured by ultraviolet spectrophotometry. 1 mL of NaHCO3 solution (0.005 g / mL by mass) and 1 mL of KI solution (0.1 g / mL by mass) were mixed with 300 μL of PS solution and allowed to develop color for 15 min. Subsequently, the absorbance of the sample was measured at a wavelength of 352 nm using a UV-visible spectrophotometer (Thermo Fisher Scientiffc, Shanghai), and its concentration was determined.

[0061] 3. Analysis of the repair effect

[0062] According to the measurement results obtained in step 2, calculate the migration distance of soil persulfate, the removal efficiency of heavy metals (copper, lead) in the soil, and the removal efficiency of organic matter (phenanthrene) in the soil.

[0063] The calculation method of the migration distance of soil persulfate is as follows:

[0064] During the repair process, soil samples were collected layer by layer at time intervals (such as sampling every 5 cm in depth). The migration distance (L) is the soil layer position where the concentration of S2O8 2- reaches 10% - 20% of the initial concentration. The formula is: L = √2Deff+(vet) 2 . Where Deff is the effective diffusion coefficient, ve is the electro-migration velocity, ve = μeE, μe is the ion mobility, E is the electric field strength, and t is the repair time. The removal efficiencies of heavy metals copper, lead, and organic matter phenanthrene are calculated by the total amount method. The formula is: η = (1 - C t / C0)×100%, where C0 is the total amount of heavy metals in the soil before repair (mg / kg), and C t is the total amount of remaining heavy metals in the soil after repair (mg / kg).

[0065] As Figure 1 shown, the experimental device used in the in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic contaminated soil of the present invention consists of 1 soil tank, 2 electrode chambers, 2 electrolyte storage tanks, 1 DC power supply, 1 peristaltic pump, and 2 graphite electrode plates. The whole device can be divided into a core treatment area and an auxiliary system area. The positions, connection relationships, and functions of each component are as follows.

[0066] Core treatment area:

[0067] Soil tank: Located in the center of the device, directly accommodating the contaminated soil to be treated.

[0068] Electrode chambers (anode chamber and cathode chamber): Respectively adjacent to the left and right sides of the soil tank, allowing ion migration but blocking soil particles. Providing an electrolysis reaction site, an oxidation reaction occurs in the anode chamber, and a reduction reaction occurs in the cathode chamber to maintain the stability of the electrolyte.

[0069] Graphite electrode plates: Two electrode plates are respectively located at the joints of the cathode and anode chambers and the soil pool. As inert electrodes, they conduct current. An acidic environment is generated at the anode, and a basic environment is generated at the cathode to drive the migration of pollutants in the soil.

[0070] Auxiliary system area: Electrolyte storage tanks (anode liquid tank, cathode liquid tank): Located behind or below the electrode chamber and connected to the electrode chamber through pipelines.

[0071] Electrolyte storage tank: Stores and buffers electrolytes (such as NaCl, H2SO4, etc.), maintains the ion concentration in the electrode chamber, and prevents electrode corrosion. Peristaltic pump: Usually close to the storage tank, forms a circulation loop with the storage tank and the electrode chamber through a hose. Circulates the electrolyte to avoid too high or too low local concentration in the electrode chamber and takes away reaction products (such as gases, precipitates).

[0072] DC power supply: Independently placed outside the device and connected to the graphite electrode plates on both sides of the electrode chamber through wires. Provides a stable voltage / current, establishes an electric field gradient in the soil pool, and drives processes such as electrodialysis and electromigration.

[0073] Example 1

[0074] As Figure 1 shown, the experimental device for the in-situ electrokinetic enhanced persulfate remediation method of heavy metal-organic contaminated soil includes a 5*25*4 plexiglass tank with a thickness of 0.5 cm. One soil pool and two electrode chambers are installed in the plexiglass tank. It also includes two electrolyte storage tanks, one DC power supply, one peristaltic pump, and two graphite electrode plates.

[0075] At the beginning of each experiment, about 1.5 kg of dry soil is evenly filled into the soil unit. A filter paper is placed between the soil and the electrolysis chamber to prevent soil from entering the electrolysis chamber. However, all experiments are carried out under an open flow boundary, allowing water to freely flow through the boundary between the soil and the electrolyte. Before the start of each experiment, the soil is hydrated with 0.01M NaNO3 solution for 24 h to completely saturate the soil. After completing the above steps, the NaNO3 solution in the electrolysis chamber is sucked out, and the electrolyte required during the experiment is added.

[0076] The PS concentration used in this example is 10%. A certain amount of electrolyte solution is prepared in the anode storage bottle and pumped into the electrolysis chamber through a peristaltic pump at a flow rate of about 35 mL / min. The experiment lasts for 7 days. During the experiment, the current change during the electrokinetic process is recorded at regular intervals, and the conductivity and pH changes are regularly sampled and detected. The specific experimental process is shown in Table 2.1.

[0077] Table 2.1

[0078]

[0079] 2.2 Analytical and detection methods

[0080] (1) Determination of phenanthrene concentration: After the experiment, the soil samples in the soil unit were divided into five equal parts from the cathode to the anode (S1 - S5). The soil samples were freeze-dried under vacuum and sieved through a 1 mm sieve. The residual phenanthrene in the dried samples was extracted by Soxhlet extraction. The specific method is as follows: (a) Weigh 3 g of the sample into a Soxhlet extraction thimble, and add 100 ml of a mixed solvent of acetone and n-hexane at a ratio of 1:1 to the Soxhlet flask; (b) Extract for 24 h at 4 - 6 cycles per hour, and then cool; (c) Concentrate the extract and reserve it for later use. Subsequently, the concentration of phenanthrene in the extract was detected by gas chromatography (Agilent 1260 infinity Ⅱ).

[0081] (2) Determination of persulfate concentration: The content of PS during the electrokinetic process was measured by ultraviolet spectrophotometry. 1 ml of NaHCO3 solution (0.005 g / mL by mass) and 1 mL of KI solution (0.1 g / mL by mass) were mixed with 300 μL of PS solution and allowed to develop color for 15 min. Subsequently, the absorbance of the sample was measured at a wavelength of 352 nm using a UV-visible spectrophotometer (Thermo Fisher Scientiffc, Shanghai), and its concentration was determined.

[0082] 2.3 Promotion of persulfate migration by electrokinetic technology

[0083] During the electrokinetic-persulfate treatment process, the distribution of persulfate in the soil medium is as Figure 2 shown. The figure shows that when persulfate is injected from the anode, the concentration of persulfate increases from the anode to the cathode. Without applying an electric field, after 48 h, persulfate is transported to the S2 section. Since the transferability of persulfate in the soil medium is poor, persulfate cannot be detected in the cathode chamber at the end of the experiment. In this process, the migration of PS mainly relies on the action of water flow. At a voltage intensity of 0.5 V / cm, as Figure 2 shown in b, persulfate was detected in the S2 section after 24 h, with a concentration of 0.003 mol / L. After 84 h, the persulfate peak in the S2 section increased to 0.062 mol / L, and persulfate was detected near the cathode chamber. As the voltage intensity increases, the migration ability of persulfate gradually increases. As Figure 2 shown in c, a small amount of persulfate was detected in the cathode chamber after 12 h and accumulated over time. This phenomenon is consistent with the expected situation. Under the action of the electric field, PS promotes the migration of PS in the soil medium with the joint participation of electroosmotic flow and electromigration.

[0084] 2.4 Removal efficiency of copper and lead

[0085] Figure 3 The removal efficiencies of Cu and Pb after electrokinetic treatment are shown. The lowest removal efficiency of Cu in EK1 - EK5 is 1.48%, and the highest is 84.11%; the lowest removal efficiency of Pb is 3%, and the highest is 82.51%. The results indicate that the removal efficiency of heavy metals can be effectively improved under the action of an electric field, and the higher the electric field strength, the higher the removal efficiency of heavy metals; the elution efficiency of heavy metals can be significantly improved with the participation of surfactants. The surfactant forms a complex with heavy metals, enhancing the removal efficiency of heavy metals through electromigration and electroosmosis.

[0086] As Figure 3 shown, the removal efficiency of Cu is higher than that of Pb in the electrokinetic experiment. This is mainly because the contact intensity between Cu and soil organic matter in the soil environment is small, making it easy to be eluted. In the electrokinetic experiment, the removal efficiency of heavy metals is higher in the area near the anode. After the intersection of acid - base peaks, the removal efficiency begins to decline. The main reason for this phenomenon is that the OH - formed at the cathode precipitates with heavy metal ions, hindering the migration of heavy metal ions. Therefore, the removal efficiency decreases.

[0087] 2.4 Removal efficiency of phenanthrene

[0088] Figure 4 The removal efficiencies of phenanthrene after different treatments are shown. Among them, the removal efficiencies of EK1 and EK2 are the worst, only between 20% - 30%. In EK1, the removal efficiency in the S1 area is as high as 51.41%, much higher than other areas in the same group of experiments. This is mainly because PS migrates under the action of water flow and can come into full contact with phenanthrene in the S1 area. However, the migration distance of PS under the action of water flow alone is very limited. Therefore, the phenomenon that the removal efficiency of phenanthrene is very high only in the S1 area occurs. EK3 and EK4 compare the removal efficiencies of phenanthrene under different voltage intensities. The results show that a higher voltage intensity promotes the migration of PS in the soil, resulting in a higher removal efficiency.

[0089] In the present invention, persulfate is used as the anolyte and transported to the soil environment under the action of electricity to study the activation efficiency of persulfate by electrothermal effect, as well as the removal efficiency and migration and transformation laws of heavy metals and organic matters in the soil during this process. In the present invention, different voltage intensities are used to deliver and activate persulfate to the soil medium. Different voltages have different delivery and activation efficiencies for persulfate, and the influence ranges of the electrothermal effect are also different. By using different voltages, the delivery and activation methods of persulfate under different conditions can be compared. In the present invention, persulfate is activated by electrothermal effect. A persulfate solution is added to the anode chamber. Persulfate is activated under the action of electrothermal effect to generate oxidation active substances, achieving the removal of organic matters. At the same time, heavy metals migrate out of the soil medium under the action of the electric field. By using the electrokinetic enhanced persulfate technology to act on heavy metal-organic matter contaminated soil, the present invention realizes the migration of persulfate in the soil medium, the activation of persulfate by electrothermal effect, and the synchronous removal of heavy metal-organic matter contamination, and the removal efficiency increases with the increase of the voltage intensity.

[0090] Note that the above are only the preferred embodiments of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein. Various obvious changes, re-adjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments only. Without departing from the concept of the present invention, more other equivalent embodiments can be included, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. An in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic compound contaminated soil, characterized in that, It includes the following steps: A. Using electric field to thermally activate persulfate: A1. Uniformly load the soil into the soil pool and place a filter paper between the soil and the electrolysis chamber. A2. In the electrolysis chamber, use the NaNO3 solution to hydrate the soil to make the soil fully saturated; then suck out the NaNO3 solution in the electrolysis chamber and pump the electrolyte solution into the electrolysis chamber. A3. Use the electric field to complete the transportation of persulfate: Use the PS solution as the anolyte and the NaNO3 solution as the catholyte, and utilize the electric field heat to activate the persulfate. Under the combined action of the electric field force and the active substances generated by the persulfate, realize the remediation of heavy metal-organic contaminated soil. B. Analysis and detection: B1. Determination of phenanthrene concentration: After one action cycle, divide the soil samples in the soil pool into five equal parts from the cathode to the anode, i.e., S1 - S5. The soil samples are freeze-dried under vacuum and screened through a 1 mm sieve, and the residual phenanthrene in the dried samples is extracted by Soxhlet extraction. B2. Determination of persulfate concentration: Measure the content of PS during the electrokinetic process by ultraviolet spectrophotometry; mix the NaHCO3 solution and the KI solution with the PS solution and color for 15 min; then, use a UV-visible spectrophotometer to measure the absorbance of the sample at a wavelength of 352 nm and determine its concentration. C. Analysis of remediation effect According to the measurement results obtained in step B, calculate the migration distance of persulfate in the soil, the removal efficiency of heavy metals copper and lead in the soil, and the removal efficiency of the organic matter phenanthrene in the soil.

2. The in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic composite contaminated soil according to claim 1, characterized in that: In step A1, the soil is 1.5 kg of dry soil.

3. An in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic composite contaminated soil according to claim 1, characterized in that: In step A2, use 0.01 M NaNO3 solution to hydrate the soil for 24 h.

4. An in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic contaminated soil according to claim 1, characterized in that: In step A2, pump the electrolyte solution into the electrolysis chamber through a peristaltic pump at a flow rate of about 35 mL / min, and the electrolyte solution is a PS solution with a concentration of 3% - 10%.

5. An in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic composite contaminated soil according to claim 1, characterized in that: In step A3, the environmental temperature is 30°C - 45°C, and the electric field strength is 0.5 - 1 V / cm.

6. The in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic composite contaminated soil according to claim 1, characterized in that, In step B, the extraction includes the following steps: a. Weigh 3 g of the sample into a Soxhlet extraction thimble and add 100 ml of a 1:1 mixed solvent of acetone and n-hexane to the Soxhlet flask. b. Extract for 24 h at 4 - 6 cycles per hour, and then cool. c. Concentrate the extract and reserve it for later use. Subsequently, detect the concentration of phenanthrene in the extract by gas chromatography.

7. An in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic composite contaminated soil according to claim 6, characterized in that: The action cycle is set to 7 d.

8. An in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic compound contaminated soil according to claim 6, characterized in that: By mass, use 1 ml of 0.005 g / mL NaHCO3 solution and 1 mL of 0.1 g / mL KI solution and mix with 300 μL of PS solution.

9. The experimental device used in the in-situ electrokinetic enhanced persulfate remediation method for heavy metal-organic composite contaminated soil according to claim 1, characterized in that: It consists of 1 soil pool, 2 electrode chambers, 2 electrolyte storage tanks, 1 DC power supply, 1 peristaltic pump, and 2 graphite electrode plates. Among them, the soil pool is located in the center of the device and directly accommodates the contaminated soil to be treated. The 2 electrode chambers include an anode chamber and a cathode chamber, which are respectively adjacent to the left and right sides of the soil pool, allow ion migration but block soil particles, provide an electrolysis reaction site, the anode chamber undergoes an oxidation reaction, and the cathode chamber undergoes a reduction reaction to maintain the stability of the electrolyte. The two graphite electrode plates are respectively located at the joints of the cathode and anode chambers and the soil pool, serving as inert electrodes to conduct current. An acidic environment is generated at the anode and a basic environment is generated at the cathode to drive the migration of pollutants in the soil. The two electrolyte storage tanks, including the anolyte tank and the catholyte tank, are located behind or below the electrode chamber and are connected to the electrode chamber through pipelines. The electrolyte storage tank is used to store and buffer the electrolyte to maintain the ion concentration in the electrode chamber and prevent electrode corrosion. The peristaltic pump, usually close to the storage tank, forms a circulation loop with the storage tank and the electrode chamber through a hose to circulate the electrolyte, avoid too high or too low local concentration in the electrode chamber, and carry away the reaction products. The DC power supply is independently placed outside the device and is connected to the graphite electrode plates in both electrode chambers through wires, used to provide a stable voltage / current, establish an electric field gradient in the soil pool, and drive the processes of electrodialysis and electro-migration.

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