A technical method for controlling electroosmotic flow in electrokinetic remediation

Abstract

The present invention relates to the technical field of soil remediation, in particular to a technical method for controlling electroosmotic flow in electrokinetic remediation. The steps are as follows: (1) Test the zeta potential of the target soil under the original pH condition and judge the direction of electroosmotic flow; (2) Install an electrokinetic remediation device and cathode and anode liquid circulation pumps; (3) Adjust the flow rates of the cathode and anode circulation pumps according to the positive and negative values of the soil zeta potential. The present invention solves the technical problem that it is difficult to control the direction and magnitude of electroosmotic flow during electrokinetic remediation, thereby improving the electrokinetic remediation efficiency of heavy metal contaminated soil.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and specifically to a technical method for controlling electroosmotic flow in electrokinetic remediation. Background Art

[0002] The remediation of contaminated soil is a technology that urgently needs to be developed at present, because soil pollution can cause very serious environmental problems, affecting human health and social development. Compared with organic pollutants, heavy metal pollutants are prone to migrate in soil and water bodies and cannot be degraded by remediation technologies, so their remediation is more difficult.

[0003] As a new remediation method, electrokinetic remediation has developed rapidly in recent years and has also been applied in engineering. The basic principle of this technology is to apply a DC voltage across the contaminated soil, and the pollutants in the soil are migrated out of the soil under the action of the electric field. It has the characteristics of fast treatment, low cost, deep treatment depth, and wide applicability, and has been applied in developed countries such as the Netherlands, the United States, Germany, and South Korea.

[0004] In electrokinetic remediation, electromigration and electroosmotic flow are two main migration mechanisms of soil pollutants. Electromigration mainly refers to the process in which charged ions migrate to electrodes with opposite polarities, that is, cations migrate to the cathode and anions migrate to the anode. Electroosmotic flow is that a thin layer of charged solution formed by the double electric layer on the surface of soil particles will migrate under the action of the electric field. When the soil zeta potential is negative, this thin layer of charged solution is positively charged and will move towards the cathode under the action of the electric field, while when the soil zeta potential is positive, the thin layer of charged solution moves towards the anode. When the directions of electromigration and electroosmotic flow of pollutants are the same under the action of the electric field, the migration of pollutants is accelerated, while when the two directions are opposite, the migration of pollutants is hindered. For the electrokinetic remediation of heavy metal contaminated soil, since most heavy metals in the soil exist in insoluble and immobile forms such as iron and manganese oxide-bound states and organic-bound states, chemical reagents such as complexing agents are usually added to the soil to improve the solubility of heavy metals, thereby enhancing the migration of heavy metals in the soil under the action of the electric field. Generally speaking, heavy metal complexes carry negative charges, and their electromigration direction is from the cathode to the anode; when the soil zeta potential is negative, the electroosmotic flow direction is from the anode to the cathode, which is opposite to the direction of electromigration, thus seriously hindering the migration of heavy metal complexes and further reducing the electrokinetic removal efficiency of heavy metals. When oxidant persulfate is added to the cathode during electrokinetic enhanced-chemical oxidation remediation of organic contaminated soil, the persulfate anion will move towards the anode through electromigration, but it will also be hindered by the electroosmotic flow moving from the anode to the cathode (when the soil zeta potential is negative), thus affecting the migration of the oxidant towards the anode and reducing the pollutant removal efficiency.

[0005] Traditionally, the main method of controlling electroosmotic flow is to regulate the absolute value and sign of the zeta potential by adjusting the pH and ionic strength of the system. Generally, reducing the soil pH can reduce the electroosmotic flow. When the pH is low, the zeta potential can change from negative to positive, thus changing the direction of the electroosmotic flow. Increasing the ionic strength can compress the electric double layer and reduce the electroosmotic flow rate, but it cannot change the direction of the electroosmotic flow. The above methods are all chemical methods. During the adjustment process, a large amount of chemical reagents need to be added to the soil, interfering with the electrokinetic remediation process and seriously affecting the soil properties, which is not conducive to the reuse of the soil after remediation. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a technical method for controlling electroosmotic flow in electrokinetic remediation.

[0007] To achieve the above purpose, the present invention provides the following technical solution: A technical method for controlling electroosmotic flow in electrokinetic remediation, the steps of which are as follows:

[0008] (1) Measure the electrokinetic potential of the target soil under the original pH condition and judge the direction of the electroosmotic flow;

[0009] (2) Install an electrokinetic remediation device and cathode and anode liquid circulation pumps;

[0010] (3) Adjust the flow rates of the cathode and anode circulation pumps according to the positive and negative values of the soil electrokinetic potential.

[0011] In some embodiments, according to step (1), the specific method is: use electrophoresis to measure the electrokinetic potential of the soil under the original pH condition and clarify the direction of the electroosmotic flow in electrokinetic remediation.

[0012] In some embodiments, according to step (2), the specific method is: install an electrokinetic remediation device, and use independent electrolyte circulation pumps for the cathode and anode solutions to adjust the flow rates separately.

[0013] In some embodiments, according to step (3), the specific method is: when the soil electrokinetic potential value is negative, adjust the flow rate of the cathode pump to be greater than that of the anode pump; when the soil electrokinetic potential value is positive, adjust the flow rate of the anode pump to be greater than that of the cathode pump.

[0014] In some embodiments, the flow rate ratio of the cathode circulation pump to the anode circulation pump is 1.2:1 to 4:1.

[0015] In some of these embodiments, the electric remediation device includes a soil chamber, an anode chamber, a cathode chamber, an anode, a cathode, and a DC power supply. The DC power supply is connected to the anode and the cathode through wires. The anode chamber and the cathode chamber are respectively located on both sides of the soil chamber. The anode is located inside the anode chamber, and the cathode is located inside the cathode chamber. An anode circulation pump is connected to the anode chamber, and the anode solution is pumped into the anode chamber through the anode circulation pump. A cathode circulation pump is connected to the cathode chamber, and the cathode solution is pumped into the cathode chamber through the cathode circulation pump.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] ① The magnitude of the electroosmotic flow is adjusted by the relative flow rate of the electrolyte circulation pump, and the operation is simple and convenient;

[0018] ② No external chemical reagents need to be added during the regulation process, which does not affect the soil properties and is conducive to the reuse of the soil after remediation;

[0019] ③ By regulating the electroosmotic flow and weakening its negative impact on the migration of heavy metals, the electrokinetic removal efficiency of heavy metals in the soil can be significantly improved.

[0020] The details of one or more embodiments of the present application are set forth in the following drawings and description, so that the other features, objects, and advantages of the present application will become more concise and understandable. The present application will be described in detail and understood through the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the electric remediation device;

[0022] Figure 2 It is a graph showing the influence of different ratios of the flow rates of the cathode and anode circulation pumps on the electroosmotic flow rate;

[0023] Figure 3 It is a graph showing the changes in current (a) and electroosmotic flow (b);

[0024] Figure 4 It is a graph showing the changes in soil pH (a) and EC (b) after remediation

[0025] Figure 5 It is a graph showing the changes in the copper content of each cross-section of the soil after remediation. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0027] The present invention provides a technical solution: a technical method for controlling electroosmotic flow in electrokinetic remediation, which uses the Figure 1 shown electrokinetic remediation device to conduct experiments. The main structure of this device includes a soil chamber 1, an anode chamber 2, a cathode chamber 3, an anode 4, a cathode 5. The DC power supply 6 is connected to the anode 4 and the cathode 5 through wires. The anode chamber 2 and the cathode chamber 3 can respectively provide different solution circulation speeds according to needs through an anode solution pump 7 and a cathode solution pump 8. The test soil is taken from a certain site in Zhejiang. The soil is air-dried, ground fine, and passed through a 10-mesh sieve. 700 g of soil is loaded into the soil chamber 1. Connect each part of the device according to Figure 1 shown, and conduct electrokinetic remediation experiments.

[0028] Before the experiment, the zeta potential of the test soil was measured. The specific method is as follows: Weigh 0.100 g of soil, add 200 ml of water, shake well, disperse it ultrasonically for 2 h at 25 °C, and let it stand at room temperature for 3 - 5 days (shake and disperse it 3 times a day during this period), then take the suspension and measure it on the machine. The test instrument uses the Shanghai Zhongchen JS94 microelectrophoresis instrument. It is measured that the zeta potential of this soil is negative, so the direction of electroosmotic flow is from the anode to the cathode.

[0029] Since the zeta potential of the soil is negative, according to the present invention, the method of making the flow rate of the cathode pump higher than that of the anode pump is used to weaken the electroosmotic flow rate, and experiments are carried out with 3 different flow rate ratios. Treatment 1 is the control, where the flow rates of the cathode pump and the anode pump are the same, both 10 ml / min, and the cathode-anode flow rate ratio is 1:1; for Treatment 2, the designed flow rate of the cathode pump (12 ml / min) is slightly greater than that of the anode (10 ml / min), and the cathode-anode flow rate ratio is 1.2:1; for Treatment 3, the designed flow rate of the cathode pump (24 ml / min) is significantly greater than that of the anode pump (10 ml / min), and the cathode-anode flow rate ratio is 2.4:1. The test time is 10 days, and the DC voltage is 20 V. The change in the electroosmotic flow is calculated by regularly measuring the change in the volume of the anode cell solution, as shown in Figure 2 . From Figure 2 it can be seen that as time goes by, the electroosmotic flow of each treatment gradually increases, and all can be represented by a linear equation (see Table 1), and the correlation coefficients are all above 0.98; from different treatments, when the cathode-anode flow rate ratio is 1:1, the electroosmotic flow rate is the highest, 395.1 ml. When the cathode-anode flow rate ratio is 1.2:1, the electroosmotic flow rate slightly decreases, to 389.4 ml. When the cathode-anode flow rate ratio increases to 2.4:1, the electroosmotic flow rate decreases significantly, only 228.6 ml. The results show that through the present invention, the electroosmotic flow rate can be significantly reduced, playing a very good role in balancing the electroosmotic flow.

[0030] Table 1. Fitting equations of electroosmotic flow rates under different cathode and anode circulation pump flow rate ratios

[0031]

[0032] Example 1:

[0033] Use the Figure 1 shown electrokinetic remediation device to conduct the experiment. The contaminated soil was collected from a contaminated site in Zhejiang. The soil zeta potential was similar to that in Example 1 and was also negative. Other physical and chemical properties of this soil were: pH was 8.23, conductivity was 0.216 ms / cm, and the total copper content in the soil was 514 mg / kg. The soil loading amount for this experiment was 700 g. Connect each part of the electrokinetic remediation device according to Figure 1 shown. The anode solution component was 0.01 mol / L NaCl solution, and the cathode solution component was 0.5 mol / L GLDA (tetrasodium glutamate diacetate) + 0.01 mol / L NaCl solution. GLDA is a chelating agent that can improve the solubility and mobility of heavy metals in the soil. The chelate formed by it and heavy metals is negatively charged. In the soil of this example, the GLDA chelate of heavy metals will move towards the anode by electromigration. However, at the same time, because the zeta of the soil is negative, the electroosmotic flow moves towards the cathode, and the opposite moving directions of the two hinder the movement of the GLDA chelate towards the anode, thus affecting the removal efficiency of heavy metals. Therefore, according to the present invention, the electroosmotic flow is controlled by increasing the flow rate of the cathode circulation pump to reduce its hindrance to the migration of heavy metals.

[0034] A total of 2 treatments were set up in the experiment. Treatment 1 had a cathode-to-anode circulation pump flow rate ratio of 1.2:1, and Treatment 2 had a ratio of 2.4:1. The test time was 10 days, and the DC voltage was 20 V. After the test ended, the soil column was evenly divided into 3 parts, which were sequentially recorded as S1, S2, and S3 from the anode to the cathode. All the soil samples in each part were taken out from the soil column, air-dried, ground, and passed through 10-mesh and 100-mesh sieves to measure the soil pH, EC, and the content of heavy metal copper.

[0035] Figure 3 shows the changes in current and electroosmotic flow in different cathode-to-anode circulation pump flow rate ratios during the electrokinetic treatment process. It can be seen from the figure that the current at the high flow rate ratio (2.4:1) is significantly higher than that at the low flow rate ratio (1.2:1), and at the same time, its electroosmotic flow rate is less than that at the low flow rate ratio (1.2:1). These results indicate that by increasing the flow rate of the cathode solution circulation pump, the current during the electrokinetic remediation process can be increased, which is beneficial to the migration of heavy metal pollutants; at the same time, the electroosmotic flow rate in the high flow rate treatment is smaller, and its hindrance to the migration of heavy metal chelates also becomes smaller, so it is also beneficial to the migration of heavy metal pollutants.

[0036] Figure 4are the changes in soil pH and EC after electrokinetic treatment. After electrokinetic treatment, the soil pH near the anode decreases, and the decrease is more significant under the high flow rate ratio (2.4:1) treatment. While the soil pH near the cathode increases, and the increase is more significant under the high flow rate ratio (2.4:1) treatment. This is because the increase and decrease of soil pH are related to the hydrolysis reactions at the anode and cathode. The higher the current, the more intense the hydrolysis reactions, and the more hydrogen ions and hydroxide ions are generated, resulting in a greater amplitude of soil pH decrease and increase. The change in soil conductivity is also closely related to the current. The higher the current, the more ions are input into the soil, thus increasing the soil conductivity. The current in the high flow rate ratio (2.4:1) treatment is higher than that in the low flow rate ratio (1.2:1) treatment. Therefore, the changes in soil pH and EC are stronger than those in the low flow rate ratio (1.2:1) treatment. Generally speaking, the method provided by the present invention has a relatively small impact on soil pH and EC, much smaller than that of the traditional method of adding chemical agents on soil pH and EC.

[0037] Figure 5 are the changes in copper content in each cross-section of the soil after electrokinetic treatment. As can be seen from the figure, for the treatment with a low flow rate ratio (1.2:1), the copper content in the soil of cross-section S1 near the anode is the lowest, the copper content in the soil of cross-section S2 is the highest, which is higher than the initial value, while the copper content in the soil of cross-section S3 near the cathode is slightly lower than the initial value. One of the reasons for the accumulation of copper in cross-section S2 is that the heavy metal chelate is affected by both electro-migration and electro-osmotic flow in the electric field, and the directions of the two are opposite, resulting in part of the copper accumulating in the soil column and being difficult to move out, generating an "accumulation effect". In the treatment with a high flow rate ratio (2.4:1), due to the technical method provided by the present invention effectively suppressing the hindering effect of electro-osmotic flow on the migration of heavy metal chelates, there is no phenomenon of copper accumulation in the soil column, and the copper content in each cross-section is lower than the initial value and the copper content in the low flow rate treatment. By calculating the removal rate of copper in the soil, the removal rate in the high flow rate treatment is 33.4%, which is significantly higher than 9.89% in the low flow rate treatment. This result shows that the application of the present invention can significantly inhibit the negative impact of electro-osmotic flow on the movement of heavy metals and effectively improve the removal rate of soil heavy metals.

[0038] Through the present technical solution, the liquid levels of the cathode and anode electrolytic cells are finely adjusted by adjusting the flow rates of the cathode and anode circulating liquids, so as to balance the electro-osmotic flow generated during the electrokinetic process.

[0039] The above embodiments only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

[0040] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling electroosmotic flow in electrokinetic remediation, characterized in that: The steps are as follows: (1) Measure the zeta potential of the target soil under the original pH condition and determine the direction of electroosmotic flow; (2) Install the electrokinetic remediation device, the cathode solution circulation pump and the anode solution circulation pump; (3) Adjust the flow rates of the cathode solution circulation pump and the anode solution circulation pump according to the positive or negative value of the soil zeta potential; According to step (3), the specific method is as follows: when the soil zeta potential value is negative, adjust the flow rate of the cathode solution circulation pump to be greater than that of the anode solution circulation pump; when the soil zeta potential value is positive, adjust the flow rate of the anode solution circulation pump to be greater than that of the cathode solution circulation pump; The flow rate ratio of the cathode solution circulation pump to the anode solution circulation pump is 1.2:1 to 4:

1.

2. A method for controlling electroosmotic flow in electrokinetic remediation according to claim 1, characterized in that: According to step (1), the specific method is as follows: measure the zeta potential under the original pH condition of the soil by electrophoresis method to clarify the direction of electroosmotic flow in electrokinetic remediation.

3. A method for controlling electroosmotic flow in electrokinetic remediation according to claim 2, characterized in that: According to step (2), the specific method is as follows: install the electrokinetic remediation device, the cathode solution is circulated through the cathode solution circulation pump, the anode solution is circulated through the anode solution circulation pump, and the flow rates of the cathode solution circulation pump and the anode solution circulation pump are adjusted separately.

4. A method for controlling electroosmotic flow in electrokinetic remediation according to claim 1, characterized in that: The electrokinetic remediation device described above includes a soil chamber, an anode chamber, a cathode chamber, an anode, a cathode and a DC power supply. The DC power supply is connected to the anode and the cathode through wires. The anode chamber and the cathode chamber are respectively located on both sides of the soil chamber. The anode is located in the anode chamber, the cathode is located in the cathode chamber. The anode solution circulation pump is connected to the anode chamber, and the anode solution is pumped into the anode chamber through the anode solution circulation pump. The cathode solution circulation pump is connected to the cathode chamber, and the cathode solution is pumped into the cathode chamber through the cathode solution circulation pump.

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