In-situ electrokinetic remediation device for heavy metal contaminated soil in sand layer and remediation method thereof

Abstract

The application provides a sand layer heavy metal contaminated soil in-situ electric dynamic remediation device and a remediation method thereof, and relates to the technical field of environmental protection engineering construction. The sand layer heavy metal contaminated soil in-situ electric dynamic remediation device comprises two electrode chambers, at least two liquid control chambers are installed on each electrode chamber, at least two remediation pipes are fixedly installed on the bottom of the at least two liquid control chambers in correspondence, soft clay is filled into the at least two remediation pipes, and the at least two remediation pipes are communicated with the liquid control chambers and the electrode chambers through the soft clay. Based on the low permeability of the contaminated soft clay, the remediation pipe is used, the pipe opening avoids the sand layer, the electrolyte above the ground and the electrode are used, and the contaminated soil is remediated by applying a direct current electric field.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental protection engineering construction, and particularly relates to a device for in-situ electrokinetic remediation of heavy metal contaminated soil with sand intercalation and a remediation method thereof. BACKGROUND

[0002] Electrokinetic remediation is a kind of in-situ remediation technology for heavy metal contaminated soil with good application prospect. In-situ remediation of contaminated soil does not need to build expensive ground environmental engineering infrastructure and long-distance transportation, and is easy to operate and maintain, and can also reduce secondary pollution. The existing electrokinetic remediation technology usually injects electrolyte into the position where the electrode is located after the electrode pipe is punched into the soil body, which leads to the penetration of electrolyte into the surrounding soil body. If sand layer is encountered, the leakage amount of electrolyte will be larger, which not only increases the use amount and engineering cost of electrolyte, but also causes pollution to the soil body or possible underground water. SUMMARY

[0003] In order to solve the above-mentioned technical problems or part of them, the purpose of the present application is to provide a device for in-situ electrokinetic remediation of heavy metal contaminated soil with sand intercalation and a remediation method thereof, based on the low permeability of contaminated soft clay, a remediation pipe which penetrates into contaminated soil at different depths and has a pipe opening avoiding sand layer, and electrolyte and electrodes above the ground are used, and heavy metals in contaminated soil are migrated to electrolyte by applying a direct current field, so as to realize in-situ electrokinetic remediation of heavy metal contaminated soil with sand intercalation.

[0004] In the first aspect of the present application, a device for in-situ electrokinetic remediation of heavy metal contaminated soil with sand intercalation is provided, comprising: two electrode chambers, at least two liquid control chambers are installed on each electrode chamber; at least two remediation pipes are fixedly installed on the bottom of at least two liquid control chambers correspondingly; soft clay is filled into the at least two remediation pipes, and the at least two remediation pipes are in communication with the liquid control chambers and the electrode chambers through the soft clay.

[0005] Further, each electrode chamber has at least two screw holes, which are arranged on the bottom of each electrode chamber; the upper end and the lower end of each liquid control chamber are provided with threaded interfaces, the threaded interface of the upper end of the liquid control chamber penetrates through the screw hole and is threadedly connected therewith, and the threaded interface of the lower end of the liquid control chamber is threadedly connected with the remediation pipe.

[0006] Further, at least a part of each liquid control chamber is located in the electrode chamber; the top of the threaded interface of the upper end of the liquid control chamber is connected with a threaded cover, and the threaded cover is configured to have different hole rates.

[0007] Further, a sheet electrode is vertically placed in each electrode chamber; each electrode chamber is in the shape of a transparent cylinder, and the outer side of the electrode chamber is provided with water level graduation lines.

[0008] Further, the water content of the soft clay is 50%-60%; the sheet electrode is made of non-corrosive electrodynamic geosynthetic material; and the sheet electrode is connected with an integral connecting terminal at the center thereof.

[0009] Further, a tip protection boot is arranged on the bottom end of each repair pipe and surrounds the pipe wall thereof; and the at least two screw holes include a plurality of screw holes, and the screw holes not connected with the repair pipe are sealed by a cover.

[0010] Further, each of the at least two repair pipes is assembled by at least one repair pipe segment, each of the at least one repair pipe segment has a predetermined length; the pipe diameter of each repair pipe segment is 10-20 cm, and the pipe opening of each repair pipe segment is provided with internal threads or external threads, so that two adjacent repair pipe segments are fixedly connected by screwing.

[0011] Further, the length of the at least two repair pipes is determined according to the soil layer distribution of the contaminated site, so that the bottom opening of the at least two repair pipes is not located in the sand layer; the electrode chamber further comprises electrolyte injected therein, and the sheet electrodes in the two electrode chambers are respectively connected with the positive and negative poles of a direct current power supply through wires, for in-situ electrodynamic remediation of the heavy metal contaminated soil in the sand layer.

[0012] In the second aspect of the present application, the in-situ electrodynamic remediation method for the heavy metal contaminated soil in the sand layer is applicable to the in-situ electrodynamic remediation device for the heavy metal contaminated soil in the sand layer, and the in-situ electrodynamic remediation method for the heavy metal contaminated soil in the sand layer comprises the following steps:

[0013] S1, drilling a soil sample in-situ at a contaminated site, obtaining the physical property indexes of the soil layer distribution and the water content of each soil layer of the contaminated site through a geotechnical test, and testing the types and concentrations of heavy metal pollutants contained in each soil layer, to determine the arrangement interval of the electrode chamber, the type of electrolyte, the number of repair pipes and the depth of the repair pipe into the soil;

[0014] S2, for the heavy metal contaminated soil site in the sand layer, the soil body water content of the remediation soil layer is controlled to be not less than 30% by means of spraying, drilling, high-pressure splitting and liquid injection;

[0015] S3, according to the thickness of the soil layer to be repaired, assembling the first repair pipe segment at each repair point, pressing the assembled first repair pipe segment into the soil layer at the repair point, installing the second repair pipe segment at the top end of the first repair pipe segment, continuing to press into the soil layer, and sequentially installing and pressing into a predetermined number of repair pipe segments until the designed repair depth is reached.

[0016] S4, a multi-shaft stirring machine is used to sequentially insert each stirring shaft into each repair pipe section, while stirring and injecting water, the mud and gravel in the repair pipe section is pumped out of the ground;

[0017] S5, soft clay with a water content of 50%-60% is injected into each repair pipe section;

[0018] S6, the electrode chamber, the liquid control chamber, the threaded cover, and each repair pipe section are sequentially connected, electrolyte is injected into the electrode chamber, the sheet-shaped electrode is vertically placed in the electrolyte, the sheet-shaped electrode is connected to the positive and negative poles of the direct current power supply through the wire, the electrolyte is collected and updated at regular intervals during the electric repair process, and the repair is completed.

[0019] Further, in the step S2, the liquid sprayed and injected into the soil is a low-concentration organic acid, and the low-concentration organic acid is citric acid with a concentration of 0.2 mol / L; in the step S3, the distance from the pipe opening at the bottom of the repair pipe section closest to the surface and the bottom surface of the sand layer to the sand layer is not less than 0.5 m; in the repair soil layer except the sand layer, a repair pipe section is arranged every 1-2 m in thickness range, and the bottom pipe opening of the repair pipe is located in the range; in the step S3, the soil layer is repaired layer by layer in a layered manner, and the thickness of the soil layer is 1-2 m.

[0020] The sand layer-enclosed heavy metal contaminated soil in-situ electric repair device and the repair method thereof provided by the embodiment of the present application have at least one of the following advantages or at least part of one advantage:

[0021] (1) The sand layer-enclosed heavy metal contaminated soil in-situ electric repair device and the repair method thereof provided by the embodiment of the present application use the repair pipe with the pipe opening avoiding the sand layer and inserted into the contaminated soil at different depths, and the electrolyte and the electrode above the ground, to form the electric repair circuit along the depth direction of the contaminated soil by applying the direct current electric field, and each circuit moves the heavy metal in the depth range to the electrolyte, thereby realizing the in-situ electric repair of the sand layer-enclosed heavy metal contaminated soil;

[0022] (2) The sand layer-enclosed heavy metal contaminated soil in-situ electric repair device and the repair method thereof provided by the embodiment of the present application can avoid the problems such as excessive penetration or leakage of the electrolyte under the action of gravity, based on the low permeability of the soft clay filled in the repair pipe and the setting of the pipe opening of each repair pipe avoiding the sand layer, and under the action of the electric field, the hydrated cations in the anode electrolyte migrate to the soft clay filled in each repair pipe connected below the anode electrode chamber, so that part or all of the heavy metals in the contaminated soil at different depths are converted into free state and moved to the cathode electrolyte. Thus, the present application can reduce the amount of electrolyte, reduce the engineering cost, and avoid the pollution of groundwater.

[0023] (3) The in-situ electrokinetic remediation device for heavy metal contaminated soil in sand intercalation layer provided by the embodiment of the present application is provided with a liquid control chamber, the upper port of the liquid control chamber is connected with screw caps with different porosities to control the migration rate of ions, if the electrokinetic remediation efficiency of a certain depth of remediation circuit is tested, the upper port of the liquid control chamber is sealed by selecting a screw cap with a porosity of 0; if the migration rate of ions is slowed down to make them fully chelate and analyze the heavy metals in the contaminated soil, a screw cap with a certain porosity is selected to reduce the charge conduction area of the electrode and the liquid control chamber.

[0024] (4) In the in-situ electrokinetic remediation device for heavy metal contaminated soil in sand intercalation layer and the remediation method thereof provided by the embodiment of the present application, the electrokinetic remediation device is simple in structure, convenient to operate and maintain, energy-saving and environment-friendly, does not need to build expensive ground environmental engineering infrastructure and transport remotely, and can efficiently realize in-situ electrokinetic remediation of heavy metal contaminated soil in sand intercalation layer. BRIEF DESCRIPTION OF DRAWINGS

[0025] These and / or other aspects and advantages of the present application will become apparent and be more readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0026] Figure 1 Fig. 1 is a structural schematic diagram of the in-situ electrokinetic remediation device for heavy metal contaminated soil in sand intercalation layer according to an embodiment of the present application in a working state;

[0027] Figure 2 Fig. 2 is a structural schematic diagram of one electrode chamber, liquid control chamber and remediation pipe shown in Fig. 1; Figure 1

[0028] Figure 3 Fig. 3 is a structural schematic diagram of one electrode chamber and liquid control chamber shown in Fig. 1; Figure 1

[0029] Figure 4 Fig. 4 is a working principle diagram of the in-situ electrokinetic remediation device for heavy metal contaminated soil in sand intercalation layer shown in Fig. 1; Figure 1

[0030] Fig. 5 is an implementation working schematic diagram of the in-situ electrokinetic remediation method for heavy metal contaminated soil in sand intercalation layer provided according to another embodiment of the present application. Figure 5 Legend of reference numerals: electrode chamber 110, liquid control chamber 120, screw cap 121, upper end threaded interface 122, lower end threaded interface 123, remediation pipe 130, protection shoe 140, electrolyte 150, electrode 160, direct current power supply 170, wire 180, shallow layer contaminated soil 200, sand layer 300, deep layer contaminated soil 400, soft clay 500, electric field line 600.

[0031] DETAILED DESCRIPTION

[0032] ​​​The features of the present application will be further illustrated by specific examples. The following description of the embodiments of the present application with reference to the accompanying drawings is intended to explain the general principles of the present application and should not be understood as a limitation of the present application.

[0033] Referring to Figures 1-3 Fig. 1 shows a structural schematic diagram of a sand layer heavy metal contaminated soil in-situ electrokinetic remediation device and components thereof according to an embodiment of the present application.

[0034] The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device comprises two electrode chambers 110, at least two liquid control chambers 120 are installed on each electrode chamber 110; at least two remediation pipes 130 are fixedly installed on the bottom of the at least two liquid control chambers 120 correspondingly; and soft clay is filled in the remediation pipes 130.

[0035] Further, the electrode chamber 110 comprises electrolyte 150 injected therein and a sheet-shaped electrode 160 made of non-corrosive electrokinetic geosynthetic material vertically arranged therein, the sheet-shaped electrode 160 is connected at the center with a wire connector of the same material, the wire connector is integrally connected with the sheet-shaped electrode 160, and is used to connect the sheet-shaped electrode 160 with the wire 180 outside the electrolyte 150. The arrangement of the sheet-shaped electrode is conducive to increasing the conduction area of the electric charge, thereby increasing the current, improving the ion migration rate, improving the electrokinetic remediation efficiency, and using the integrally connected wire 180 to simplify the connection mode and increase the firmness.

[0036] In addition, the sheet-shaped electrodes 160 in the two electrode chambers 110 are respectively connected with the positive and negative poles of the direct current power supply 170 through the wires 180. The electrode chamber connected with the positive pole of the direct current power supply 170 is the anode electrode chamber, and the electrode chamber connected with the negative pole of the direct current power supply 170 is the cathode electrode chamber.

[0037] Specifically, during the electrokinetic remediation, the hydrated cations in the electrolyte in the anode electrode chamber and the pore water of the contaminated soil migrate to the cathode, resulting in continuous reduction of the electrolyte in the anode electrode chamber and continuous increase of the electrolyte in the cathode electrode chamber. The volume changes of the electrolyte in the anode and cathode electrode chambers are obtained through the water level scale on the outer side of the electrode chamber, and the difference between the volume changes of the two is the drainage amount of the contaminated soil. When the current size appears obvious fluctuation and shows multiple continuous decrease phenomenon, even if the voltage is increased, the current is still not obviously increased, and at the same time the drainage amount of the contaminated soil tends to be flat, indicating that the contaminated soil remediation is completed.

[0038] In some embodiments, at least a portion of each liquid control chamber 120 is located in the electrode chamber 110. That is, the liquid control chamber 120 can be arranged to be completely located in the electrode chamber 110, or alternatively, a portion of the liquid control chamber 120 is located in the electrode chamber 110 and another portion is located outside the electrode chamber 110.

[0039] In some embodiments, the bottom of each electrode chamber 110 has at least two threaded holes; the upper end and the lower end of each liquid control chamber 120 is provided with a threaded interface 122, 123, the threaded interface 122 of the upper end of the liquid control chamber 120 passes through the threaded hole and is threadedly connected therewith, and the threaded interface 123 of the lower end of at least a portion of the liquid control chambers 120 is threadedly connected with the repair pipe 130.

[0040] In some embodiments, the top of the threaded interface of the upper end of the liquid control chamber 120 is connected with a threaded cover 121, and the threaded cover 121 is configured to have different porosities. The threaded cover 121 with different porosities at the top of the liquid control chamber 120 can be used to seal the liquid control chamber 120 or control the migration rate of ions.

[0041] If the electrokinetic repair efficiency of a certain depth repair circuit needs to be tested, the repair circuit of other depths needs to be suspended, and the threaded cover 121 with a porosity of 0 is selected to seal the upper end of the liquid control chamber 120. If it is necessary to slow down the migration rate of ions so as to fully chelate and resolve the heavy metals in the contaminated soil, the threaded cover 121 with a smaller porosity is selected to reduce the charge conduction area of the electrode and the liquid control chamber 120.

[0042] It should be noted that the number of the at least two threaded holes provided on the bottom of the electrode chamber 110 can be multiple, desirably, they are uniformly distributed on the bottom of the electrode chamber 110, of course, a person skilled in the art can also arrange them to be non-uniform or other design patterns according to needs. If the number of the repair pipes 130 to be connected is less than the number of the liquid control chambers 120, the upper end of the unused liquid control chamber 120 will be sealed with the threaded cover 121 without holes when the repair device is in use.

[0043] In the embodiments of the present application, the threaded holes on the bottom of each electrode chamber 110 are exemplarily provided as three, and the liquid control chambers 120 are also designed as three, and the repair pipes 130 are also designed as three repair pipes 131-133 with different lengths.

[0044] In some embodiments, the repair pipe 130 is assembled by at least one repair pipe section, and each repair pipe section of the at least one repair pipe section has a predetermined length. The length of each repair pipe section is 1-2 m, and the pipe diameter is 10-20 cm. The pipe opening of each repair pipe section is provided with internal threads or external threads, so that two adjacent repair pipe sections are fixedly connected together by screwing. The three repair pipes 131-133 are assembled by repair pipe sections with different numbers of pitches.

[0045] In a further embodiment, the in-situ electric remediation device for heavy metal contaminated soil in sandy layers may also include a protective boot 140 with a pointed tip, which is set at the bottom end of the last section of each remediation pipe 130 and sleeved around the pipe wall of the remediation pipe section to protect the opening of the remediation pipe section, but does not close the remediation pipe section.

[0046] In some embodiments, the length of the at least one remediation pipe 130 is determined according to the soil layer distribution of the contaminated site, such that the bottom opening of the at least one remediation pipe 130 is not located in the sand layer 300. Specifically, the number of remediation pipe segments assembled is determined by the thickness and distribution of the soil layers in the contaminated site, and the bottom openings of one or more remediation pipe segments driven into the soil layers should avoid the sand layer 300 and be evenly distributed in other contaminated soil layers.

[0047] In some embodiments, the bottom opening of the repair pipe 130 closest to the upper and lower surfaces of the sand layer 300 should be at least 0.5m away from the sand layer. In the repair soil layers other than the sand layer 300, there should be a repair pipe 130 with its bottom opening at every 1-2m thickness range.

[0048] like Figure 1 As shown, the present invention exemplarily illustrates the structural schematic diagram of the in-situ electric remediation device for heavy metal contaminated soil in sandy layers in its working state. The bottom opening of the remediation pipe 131 is located in the shallow contaminated soil 200 above the sand layer 300. The remediation pipes 132 and 133 have different lengths, and their bottom openings are both located in the deep contaminated soil 300 below the sand layer 300.

[0049] In some embodiments, the electrode chamber 110 is a transparent cylindrical shape, and a water level scale is provided on the outer surface of the electrode chamber 110. The water level scale is used to measure the volume change of the electrolyte 150 in the electrode chamber 110, thereby determining the consumption of the electrolyte 150.

[0050] This invention provides a method for utilizing... Figure 1 The in-situ electrokinetic remediation method for heavy metal contaminated soil in sandy layers using the illustrated electrokinetic remediation device 100 includes the following steps:

[0051] S1. Drill soil samples in situ at the contaminated site, obtain the soil layer distribution and physical property indicators such as water content of each soil layer through geotechnical tests, and use appropriate related instruments known in the art to test the types and concentrations of heavy metal pollutants contained in each soil layer (thereby determining the in-situ electroremediation design scheme), and determine the arrangement spacing of the two electrode chambers 110, the type of electrolyte, the number of remediation tubes 130 and the soil penetration depth of the remediation tubes 130.

[0052] S2, for the heavy metal contaminated soil site in the sand layer, by spraying, drilling, high pressure splitting, injection of liquid and other ways to control the repair of soil moisture content is not less than 30%, spraying and injection of liquid soil for low concentration of organic acid, the low concentration of organic acid section is, for example, the concentration of 0.2 mol / L of citric acid.

[0053] S3, according to the thickness of the soil layer to be repaired, assemble the first section of the repair pipe segment at each repair point, press the assembled first section of the repair pipe segment into the soil layer at the repair point, install the second section of the repair pipe segment at the top end of the first section of the repair pipe segment, and continue to press into the soil; a predetermined number of repair pipe segments are installed and pressed in turn until the designed repair depth is reached.

[0054] S4, using multi-shaft stirring machinery to extend each stirring shaft into each repair pipe segment, while stirring and injecting water, the mud, sand and other materials in the repair pipe segment are extracted to the ground surface;

[0055] S5, fill each repair pipe segment with soft clay with a water content of 50%-60%500;

[0056] S6, connect the electrode chamber 110, the liquid control chamber 120, the screw cover 121 and each repair pipe segment in turn, inject electrolyte into the electrode chamber 110, vertically place the sheet electrode 160 into the electrolyte, connect the sheet electrode 160 with the positive and negative electrodes of the direct current power supply 170 through the wire 180, and update the collected electrolyte at regular intervals during the electric repair process until the repair is completed.

[0057] The electrolyte has a very important influence on the electric repair effect of the contaminated soil, and the amount of electrolyte depends on two aspects: one is the penetration / leakage of the electrolyte in the soil under the action of gravity, and the other is the migration of ions in the electrolyte in the soil under the action of the electric field, so that part of the heavy metals in the soil are resolved or migrated to the cathode chamber by chelation. Because the permeability coefficient of the contaminated soft clay is very small, 10 -6 -10 -9 cm / s, taking the contaminated soft clay with a permeability coefficient of 5 x 10 -7 cm / s as an example, it takes 2314.8 days, about 6.3 years, for the electrolyte to penetrate 1 m vertically in the soil.

[0058] During the repair process, if the electric repair efficiency of the repair circuit at a certain depth is tested, the upper port of the corresponding liquid control chamber 120 is sealed with a screw cover 121 with a hole rate of 0. If it is necessary to slow down the migration rate of ions to make them fully chelate and resolve the heavy metals in the contaminated soil, a screw cover 121 with a small hole rate is selected to reduce the charge conduction area between the electrode and the liquid control chamber 120.

[0059] Referring to Figure 4, shows the working principle of the in-situ electrokinetic remediation method of sand layer heavy metal contaminated soil according to an embodiment of the application. The in-situ electrokinetic remediation device for sand layer heavy metal contaminated soil is used. The electrodes placed in the electrolyte above the ground are connected with the direct current power supply. The electrode connected with the positive pole of the direct current power supply is the anode, and the electrode connected with the negative pole of the direct current power supply is the cathode. Under the action of the electric field applied by the direct current power supply, an electric field is formed in the depth range of about 1-2 m between the pipe orifices of the remediation pipes with the same depth of soil penetration connected below the two adjacent electrode chambers. At this time, the cations in the anode electrolyte, such as hydrogen ions, migrate to the contaminated soil at different depths through the soft clay filled in each remediation pipe connected below the anode electrode chamber, resolve the heavy metal pollutants adsorbed on the soil particles, and convert part or all of the heavy metals in the contaminated soil at different depths into free state, and then migrate to the cathode electrolyte together, so as to realize the in-situ electrokinetic remediation of the sand layer heavy metal contaminated soil.

[0060] The electric field in the schematic diagram illustrates the thickness range of each remediation pipe when the in-situ electrokinetic remediation device and the remediation method of the application are used for layered synchronous remediation or layer-by-layer remediation of the contaminated soil layer with large thickness.

[0061] If the thickness of the remediation soil layer except the sand layer 300 is thick, the number of remediation pipes required according to the thickness reaches 5 or more. At this time, the number of remediation pipes does not need to be increased, and the layered layer-by-layer remediation method is adopted. The layered thickness is 1-2 m, that is, after the remediation of the soil body of one layered thickness is completed by the remediation pipe segment, a section of remediation pipe is installed at the top end of the remediation pipe segment, and is pressed to the middle position of the next layered thickness to remediate the soil body of the layered thickness. In this way, the remediation of the whole soil layer is completed. The electrolyte 150 in the electrode chamber 110 can be updated in real time by using a peristaltic pump, or can be replaced completely after the electrolyte 150 works for a certain period of time.

[0062] Referring to Figure 5 , shows the implementation working schematic diagram of the in-situ electrokinetic remediation method of sand layer heavy metal contaminated soil according to another embodiment of the application. The in-situ electrokinetic remediation device for sand layer heavy metal contaminated soil and the remediation method thereof provided in the embodiment of the application are verified for feasibility in the indoor electrokinetic remediation model test of the sand layer heavy metal contaminated soil. The size of the model box is 30 x 15 x 30 cm 3 (length x width x height). The voltage applied by the direct current power supply starts from 20 V, increases by 10 V each time, and reaches 60 V. The working time of each voltage level is 60 h. The anode and cathode electrolytes are replaced every 10 h, and the initial volume is 220 mL.

[0063] Taking heavy metal copper and zinc contaminated soft clay as the research object, after about 260 h of electrokinetic remediation, the average removal rates of heavy metals copper and zinc reach more than 85%. The specific experimental data are shown in Tables 1-3:

[0064] Table 1 Heavy metal copper and zinc contaminated soil layer distribution and soil test parameters in indoor model test

[0065]

[0066]

[0067] Table 2 Design conditions of indoor model test

[0068]

[0069] Table 3 Average removal rate of heavy metals in contaminated soil layer

[0070]

[0071] According to the sand layer heavy metal contaminated soil in-situ electrokinetic remediation device and the remediation method thereof, at least one of the following advantages or at least part of one advantage is provided:

[0072] (1) The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device and the remediation method thereof provided by the embodiment of the present application, the repair pipe penetrating into the contaminated soil at different depths and the pipe opening avoiding the sand layer are adopted, and the electrolyte and the electrode above the ground are adopted. An electrokinetic remediation circuit equivalent to the number of repair pipes is formed along the depth direction of the contaminated soil by applying a direct current electric field. Each circuit moves the heavy metals in the depth range to the electrolyte, thereby realizing in-situ electrokinetic remediation of the sand layer heavy metal contaminated soil.

[0073] (2) The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device and the remediation method thereof provided by the embodiment of the present application can avoid problems such as excessive penetration or leakage of the electrolyte under the action of gravity, based on the low permeability of the soft clay filled in the repair pipe and the setting of the pipe opening of each repair pipe avoiding the sand layer. At the same time, under the action of the electric field, the hydrated cations in the anode electrolyte migrate to different depths of the contaminated soil through the soft clay filled in each repair pipe connected to the anode electrode chamber, so that part or all of the heavy metals in the contaminated soil at different depths are converted into free state and migrate to the cathode electrolyte together. Thus, the present application can reduce the amount of electrolyte, reduce the engineering cost, and avoid pollution of groundwater.

[0074] (3) The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device provided by the embodiment of the present application is provided with a liquid control chamber. The upper port of the liquid control chamber is connected with a screw cover with different porosities to control the migration rate of ions. If the electrokinetic remediation efficiency of the repair circuit at a certain depth is tested, the repair circuit at other depths needs to be suspended, and a screw cover with a porosity of 0 is selected to seal the upper port of the liquid control chamber. If the migration rate of ions is slowed down to allow sufficient chelation and analysis of heavy metals in the contaminated soil, a screw cover with a certain porosity is selected to reduce the charge conduction area of the electrode and the liquid control chamber.

[0075] (4) In the sand layer heavy metal contaminated soil in-situ electrodynamic remediation device and the remediation method thereof provided by the embodiment of the present application, the electrodynamic remediation device is simple in structure, convenient to operate and maintain, energy-saving and environment-friendly, does not need to construct expensive ground environmental engineering infrastructure and long-distance transportation, and can efficiently realize in-situ electrodynamic remediation of the sand layer heavy metal contaminated soil.

[0076] The above only describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. It should be understood by those skilled in the art that the embodiments can be changed without departing from the principles and spirits of the general concept of the present application, and these changes should also be considered to fall within the protection scope of the present application. The scope of the present application is defined by the claims and their equivalents.

Claims

1. An in-situ electrokinetic remediation device for heavy metal contaminated soil with sandy layers, characterized in that, The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device comprises: two electrode chambers, each of which is provided with at least two liquid control chambers; at least two remediation pipes, which are fixedly installed on the bottom of the at least two liquid control chambers correspondingly; soft clay filled into the at least two remediation pipes; each of the at least two remediation pipes is assembled by at least one remediation pipe segment, each of the at least one remediation pipe segment has a predetermined length; the length of the at least two remediation pipes is determined according to the soil layer distribution of the contaminated site, so that the bottom pipe opening of the at least two remediation pipes is not located in the sand layer.

2. The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device according to claim 1, wherein each electrode chamber is provided with at least two screw holes, which are arranged on the bottom of each electrode chamber; the upper end and the lower end of each liquid control chamber are provided with threaded interfaces, the threaded interface of the upper end of the liquid control chamber passes through the screw hole and is threadedly connected therewith, and the threaded interface of at least part of the lower end of the liquid control chamber is threadedly connected with the remediation pipe.

3. The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device according to claim 2, wherein at least a part of each liquid control chamber is located in the electrode chamber; the top of the threaded interface of the upper end of the liquid control chamber is connected with a threaded cap, and the threaded cap is configured to have different hole rates.

4. The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device according to claim 3, wherein each electrode chamber is provided with a sheet-shaped electrode vertically placed therein; each electrode chamber is in a transparent cylindrical shape, and the outer side of the electrode chamber is provided with water level graduation lines.

5. The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device according to claim 4, wherein the water content of the soft clay is 50%-60%; the sheet-shaped electrode is made of electrokinetic geosynthetic material which is not easy to corrode; the center of the sheet-shaped electrode is connected with an integral terminal.

6. The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device according to claim 5, wherein the bottom end of each remediation pipe is provided with a layer of tip protection boots around the pipe wall thereof; the at least two screw holes include a plurality of screw holes, and the screw holes not connected with the remediation pipe are closed by a cover.

7. The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device according to claim 6, wherein the pipe diameter of each remediation pipe segment is 10-20 cm, the pipe opening of each remediation pipe segment is provided with internal threads or external threads, so that two adjacent remediation pipe segments are fixedly connected together by screwing.

8. The sand layer heavy metal contaminated soil in-situ electrokinetic remediation device according to claim 7, wherein the electrode chamber further comprises electrolyte injected therein, and the sheet-shaped electrodes in the two electrode chambers are respectively connected with the positive and negative poles of a direct current power supply through wires, for in-situ electrokinetic remediation of the sand layer heavy metal contaminated soil.

9. A method for in-situ electrokinetic remediation of heavy metal contaminated soil with sand layer, characterized in that, The in-situ electrokinetic remediation method for sand intercalated heavy metal contaminated soil is applicable to the in-situ electrokinetic remediation device for sand intercalated heavy metal contaminated soil according to any one of claims 1-8, The in-situ electrokinetic remediation method for sand intercalated heavy metal contaminated soil comprises the following steps: S1, drilling holes in the contaminated site to obtain soil samples, obtaining the physical property indexes of the soil layer distribution and the water content of each soil layer of the contaminated site through soil test, and testing the types and concentrations of heavy metal pollutants contained in each soil layer to determine the arrangement interval of the electrode chamber, the type of electrolyte, the number of remediation pipes, and the depth of the remediation pipe into the soil; S2, for the heavy metal contaminated soil site in the sand intercalated layer, the soil layer soil moisture content is controlled to be not less than 30% by spraying, drilling, high pressure splitting, and liquid injection; S3, according to the thickness of the soil layer to be repaired, assembling the first section of the remediation pipe segment at each remediation point, pressing the assembled first section of the remediation pipe segment into the soil layer at the remediation point, installing the second section of the remediation pipe segment at the top end of the first section of the remediation pipe segment, continuing to press into the soil layer, and sequentially installing and pressing into a predetermined number of remediation pipe segments until the designed remediation depth is reached; S4, using multi-shaft stirring machinery to sequentially extend each stirring shaft into each remediation pipe segment, while stirring and injecting water, and pumping the mud and gravel in the remediation pipe segment out of the ground; S5, filling each remediation pipe segment with soft clay with a water content of 50%-60%; S6, sequentially connecting the electrode chamber, the liquid control chamber, the screw cover, and each remediation pipe segment, injecting electrolyte into the electrode chamber, vertically placing the sheet electrode into the electrolyte, connecting the sheet electrode to the positive and negative electrodes of the direct current power supply through the wire, and regularly updating and collecting the electrolyte during the electrokinetic remediation process until the remediation is completed.

10. The in-situ electrokinetic remediation method for sand intercalated heavy metal contaminated soil according to claim 9, wherein, In the step S2, the liquid sprayed and injected into the soil is a low-concentration organic acid, and the low-concentration organic acid is citric acid with a concentration of 0.2 mol / L; In the step S3, the distance from the pipe opening at the bottom of the remediation pipe segment closest to the surface and the bottom surface of the sand layer to the sand layer is not less than 0.5 m; In the remediation soil layer other than the sand layer, one remediation pipe segment is arranged every 1-2 m in thickness, and the bottom pipe opening of the remediation pipe is located therein; In the step S3, the soil layer is repaired layer by layer, and the soil layer layering thickness is 1-2 m.

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