A method for remediating arsenic-contaminated soil

Abstract

The application relates to a method for repairing arsenic contaminated soil, which comprises the following steps: S1, inserting a first positive electrode and a first negative electrode outside a soil area to be repaired; applying an electrolyte to a soil area around the negative electrode; the first positive electrode and the first negative electrode are in communication with a power supply; resting for 10-14 hours after power-on for 10-14 hours; S2, exchanging the electrodes; continuing to power-on for 10-14 hours and resting for 10-14 hours; S3, detecting the content of pentavalent arsenic in the soil, if the content is less than 85%, repeating steps S1 and S2; if the content is greater than 85%, removing the first positive electrode and the first negative electrode and inserting a second positive electrode and a second negative electrode at the positions of the original electrodes. The application injects an oxidizing agent into the soil through electro-osmosis, oxidizes trivalent arsenic in the soil into pentavalent arsenic which is easy to be stabilized, introduces ferrous ions into the soil by using a sacrificial anode, and makes the ferrous ions to have adsorption-precipitation reaction with arsenite and arsenate, so that the purpose of stabilizing the arsenic contaminated soil is achieved.

Description

Technical Field

[0001] This invention relates to arsenic-contaminated soil remediation technology, and particularly to a method for remediating arsenic-contaminated soil. Background Technology

[0002] Arsenic is a highly toxic metalloid. Arsenic pollution in soil can cause the pollutant to accumulate in plants and, through the food chain, enter the bodies of humans and animals, harming human health and causing cancer and other diseases. Remediation technologies for arsenic-contaminated soil include chemical, physical, and biological methods. Stabilization technology involves adding exogenous agents to arsenic-contaminated soil. The arsenic in the soil undergoes a complex chemical reaction with the agent to form a stabilized body with low toxicity, mobility, and solubility. One of the key factors for effective stabilization is the uniform mixing of the agent with the soil. For highly clayey soils, achieving uniform mixing requires a significant amount of time and energy.

[0003] Prior art CN 107457266 B discloses a heavy metal contaminated soil remediation system including a plant layer, a power supply, a horizontal anode, a horizontal cathode, and an electrolyte circulation device. The plant layer is placed on the upper surface of the soil to be remediated and is made of local soil and manure mixed in a 1:1 volume ratio. The power supply is a DC power supply; the horizontal anode is made of graphite or metal and is cylindrical or cuboid in shape; the horizontal cathode is also made of graphite or metal and is cylindrical or cuboid in shape; the horizontal cathode is placed horizontally and is parallel to the horizontal anode in space; several horizontal cathodes are arranged parallel to each other in space. The electrolyte circulation device includes an electrolyte percolator, an electrolyte collector, an electrolyte pre-pump, an electrolyte ion exchange filter tower, an electrolyte storage tank, and an electrolyte post-pump. However, this patent achieves the removal of heavy metal ions from the soil through plant enrichment and electrolyte migration. Plant growth is affected by factors such as temperature, humidity, and pH, making it difficult to control. Furthermore, the patent involves subsequent treatment of the plants and electrolytes enriched with heavy metals, which is a cumbersome process.

[0004] Existing technology CN 109926447 A discloses a multi-contaminated soil advanced oxidation synergistic electrodynamic in-situ remediation system, including a DC regulated power supply and a soil remediation device. The soil remediation device includes a housing and an advanced oxidant dosing device. The housing is equipped with a left and right partition, which divide the interior of the housing from left to right into an anode chamber, a soil chamber, and a cathode chamber. Both the left and right partitions have several through holes. A left and right drain valve are located at the lower front of the housing. The DC regulated power supply is connected to the upper ends of two columnar graphite electrodes via wires. However, this patent involves the treatment of soil and electrolytes enriched with heavy metals, which is cumbersome to operate. Furthermore, for heavy metal ions with relatively poor mobility, the power consumption is high, resulting in high electrodynamic remediation costs.

[0005] Therefore, it is essential to develop technologies for remediating clayey arsenic-contaminated soil. Summary of the Invention

[0006] The purpose of this invention is to provide a method for remediating arsenic-contaminated soil.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] A method for remediating arsenic-contaminated soil includes the following steps:

[0009] S1. Insert a positive electrode and a negative electrode outside the soil area to be repaired; apply electrolyte to the soil area around the negative electrode; connect the positive electrode and the negative electrode to the power source; let stand for 10-14 hours after energizing;

[0010] S2, exchange electrodes; continue energizing for 10-14 hours, then let stand for 10-14 hours;

[0011] S3. Detect the content of pentavalent arsenic in the soil. If it is less than 85% of the total arsenic, repeat steps S1 and S2. If it is greater than 85%, remove the first positive electrode and the first negative electrode, and insert the second positive electrode and the second negative electrode in the original electrode position. Stop adding electrolyte.

[0012] S4. After powering on for 10-14 hours, let it stand for 10-14 hours.

[0013] S5, exchange electrodes; continue energizing for 10-14 hours, then let stand for 10-14 hours;

[0014] S6. Detect the concentration of arsenic in the soil. If the remediation requirements are met, remove the electrode to complete the remediation. If not, repeat steps S4 and S5 until the concentration of arsenic in the soil meets the remediation requirements.

[0015] Both the first positive electrode and the first negative electrode are made of inert materials;

[0016] The second positive electrode is an iron-containing material, and the electrolyte contains permanganate.

[0017] Remediation requirements vary depending on the soil use pathway.

[0018] Both the first positive electrode and the first negative electrode are made of inert materials. If other metal electrodes, such as iron-containing electrodes, are used, the Fe produced will be... 2+ It will react with permanganate, leading to the loss of permanganate and affecting the repair effect.

[0019] If the energizing time in step S1 is too short, it will not be enough for the electrolyte to migrate and distribute throughout the entire soil remediation area through electrodynamic action, thus affecting the remediation effect. If the energizing time is too long, it will cause increased energy consumption, electrode corrosion, and damage to the soil structure.

[0020] If the energizing time in step S4 is too short, it will not be sufficient for Fe to... 2+ The electrical current is distributed throughout the entire remediation soil area through electrodynamic action, thus affecting the remediation effect. If the energizing time is too long, it will cause increased energy consumption, electrode corrosion and damage to the soil structure.

[0021] In one preferred embodiment, step S1 further includes determining the total amount of arsenic in the soil to be remediated before inserting the electrode.

[0022] In one preferred embodiment, the second negative electrode material is an inert material.

[0023] In one preferred embodiment, the inert material is one or more of graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon-based materials, titanium-based materials, and tin-based materials.

[0024] In one preferred embodiment, the second cathode material is any one of high-silicon cast iron anode, steel anode, iron-nickel anode, Fe co-deposited γ-MnO2 anode, and iron-based superionic conductor anode.

[0025] In one preferred embodiment, the concentration of permanganate in the electrolyte is 3% to 5%.

[0026] Potassium permanganate solutions with excessively high concentrations may damage soil structure due to their strong oxidizing properties; while solutions with excessively low concentrations require a larger amount of potassium permanganate solution per unit volume of soil, resulting in higher transportation and spraying costs.

[0027] In one preferred embodiment, the amount of electrolyte added is 600-800 mg / kg soil.

[0028] In one preferred embodiment, the voltage gradient between the positive electrode and the negative electrode is 1V / cm to 2V / cm.

[0029] If the voltage gradient is too low, the repair time will be prolonged and the energy consumption will increase; if the voltage gradient is too high, it may damage the soil structure, aggravate electrode corrosion, and increase the repair energy consumption.

[0030] In one preferred embodiment, the voltage gradient between the second positive electrode and the second negative electrode is 1V / cm to 2V / cm.

[0031] If the voltage gradient is too low, the repair time will be prolonged and the energy consumption will increase; if the voltage gradient is too high, it may damage the soil structure, aggravate electrode corrosion, and increase the repair energy consumption.

[0032] Both electrochemical methods and permanganates possess certain reactivity. Permanganates are strong oxidants, and in electrochemical systems, electrochemical methods can alter the reaction environment on the electrode surface. For example, they can generate highly oxidizing active substances such as hydroxyl radicals on the electrode surface. These active substances synergistically enhance the oxidation effect of permanganates on recalcitrant pollutants in soil or water.

[0033] Electrochemical methods exhibit good selectivity. By adjusting conditions such as electrode potential, the selective direction of the oxidation reaction can be controlled. When combined with permanganate, the advantages of electrochemical regulation can be utilized to directionally oxidize arsenic with permanganate, reducing adverse effects on other substances in the environment.

[0034] In electrochemical remediation, electric current promotes the reaction between electrons and pollutants, while permanganate provides additional oxidizing power. For some pollutants that are difficult to treat by a single method, combining the two can improve remediation efficiency. For example, for some high-concentration organic pollutants, electrochemical methods can initially decompose some of the pollutants, and then permanganate can further oxidize and decompose the remaining intermediate products.

[0035] However, if operating conditions are not controlled, combining the two methods may trigger side reactions. For example, in soil remediation, it may produce some difficult-to-degrade oxidative products or alter the structure and chemical properties of the soil. Combining the two methods requires precise control of reaction conditions, such as electrode potential, permanganate concentration, and reaction time. Improper operation may affect the remediation effect or even produce negative effects.

[0036] This invention achieves stabilization of arsenic-contaminated soil by periodically exchanging electrodes during the remediation process, with the iron anode being sacrificed during the exchange. Oxidant is injected into highly viscous soil via electroosmosis, oxidizing trivalent arsenic in the soil into easily stabilized pentavalent arsenic. Ferrous ions are introduced into the highly viscous soil using the sacrificial iron anode. These ferrous ions bind to arsenic and undergo adsorption-precipitation reactions with arsenite and arsenate ions, thereby achieving the goal of stabilizing arsenic-contaminated soil.

[0037] Simultaneously, highly oxidizing active substances such as hydroxyl radicals are generated on the electrode surface. These active substances synergistically enhance the oxidation effect of permanganate, thereby strengthening the oxidation of arsenic in the soil. Utilizing the advantages of electrochemistry, permanganate is used to directionally oxidize arsenic in the soil, reducing its adverse impact on other substances in the environment. During the electrochemical remediation process, the current promotes the reaction between ferrous ions and pollutants, while permanganate provides additional oxidizing capacity; the two work synergistically to improve the stabilization effect on arsenic.

[0038] Electrode swapping involves interchangeing the positive and negative electrodes of a battery or power source. For example, in a battery-powered device, where the positive electrode was originally connected to one part of the circuit and the negative electrode to another, the connection is now reversed.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1) This invention is applicable to the stabilization and remediation of highly viscous arsenic-contaminated soils. Compared with ordinary chemical mixing stabilization technology, it has energy-saving and economic advantages.

[0041] 2) This invention causes minimal soil disturbance, and the pH value of the remediated arsenic-contaminated soil is between 6.5 and 8.2, with minimal impact on soil function.

[0042] 3) This invention will not cause secondary pollution to the soil and has the advantages of green and environmentally friendly remediation.

[0043] 4) This invention is simple to operate, low in cost, fast in processing time, flexible in processing method, can be moved at any time, has the feasibility of large-scale engineering implementation, and has a wide range of applications. Attached Figure Description

[0044] Figure 1 This is a schematic flowchart of the repair method of the present invention. Detailed Implementation

[0045] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0046] Example 1

[0047] In a certain arsenic-contaminated soil area, the pH value of the arsenic-contaminated soil was 7.5, the total arsenic concentration in the soil was 195.6 mg / kg, and the leached arsenic content was 51.13 mg / kg.

[0048] like Figure 1 As described in the process, this embodiment uses the following technical solution for repair:

[0049] 1) Soil pretreatment. Remove gravel and level the soil surface;

[0050] 2) After draining as much water as possible from the soil in the remediation area, insert two graphite electrodes into the soil. Connect the two graphite electrodes to the positive and negative terminals of a DC regulated power supply, respectively, as the positive and negative electrodes. The voltage gradient between the two electrodes is 1V / cm. Add 4% KMnO4 as an electrolyte to the soil at the cathode electrode, at a dosage of 650mg / kg of soil. Connect the power supply.

[0051] 3) Apply electricity for 12 hours, then let stand for 12 hours; exchange the anode and cathode electrodes to neutralize the H+ produced by hydrolysis. + / OH- The process involved uniformly introducing KMnO4 into the soil via electroosmosis. This process was repeated for 144 hours. With the addition of the KMnO4 electrolyte, pentavalent arsenic accounted for 92% of the total arsenic in the soil, and the soil moisture content was approximately 35%.

[0052] 4) Remove the two graphite electrodes, stop adding electrolyte, and insert a high-silicon cast iron electrode and a graphite electrode into the original soil electrode positions, connecting them to the positive and negative terminals of a DC regulated power supply, respectively. The high-silicon cast iron electrode serves as the anode, and the graphite electrode as the negative electrode. The voltage gradient between the two electrodes is 1V / cm. Turn on the power supply.

[0053] 5) Power on for 12 hours, then let stand for 12 hours;

[0054] 6) Exchange the anode and cathode electrodes; after energizing for 12 hours, the iron anode is electrolyzed into Fe. 2+ The arsenic then seeped into the soil under the influence of an electric field. After a cumulative run of steps 5)-6) for 168 hours, analysis of the sample results showed that the soil pH was 6.9 and the content of leached arsenic decreased to 14.50 mg / kg, a reduction of 71.64% compared to before remediation.

[0055] Example 2

[0056] Based on Example 1, the concentration of KMnO4 in step 2) was adjusted to 3%, and the rest was the same as in Example 1.

[0057] As a result, the analysis of the sample results showed that the soil pH was 6.8 and the content of leached arsenic decreased to 15.53 mg / kg, a decrease of 69.63% compared with before remediation.

[0058] Example 3

[0059] Based on Example 1, the two electrodes in step 2) are both made of titanium-based material, and the rest is the same as in Example 1.

[0060] As a result, the analysis of the sample results showed that the soil pH was 6.9 and the content of leached arsenic decreased to 15.41 mg / kg, a decrease of 69.86% compared with before remediation.

[0061] Example 4

[0062] Based on Example 1, the voltage gradient in step 2) is adjusted to 2V / cm, and the rest is the same as in Example 1.

[0063] As a result, the analysis of the sample results showed that the soil pH was 6.7 and the content of leached arsenic decreased to 13.76 mg / kg, a decrease of 73.09% compared with before remediation.

[0064] Example 5

[0065] Based on Example 1, the power-on time in step 5) is adjusted to 14 hours, and the rest is the same as in Example 1.

[0066] As a result, the analysis of the sample results showed that the soil pH was 6.9 and the content of leached arsenic decreased to 14.22 mg / kg, a decrease of 72.19% compared with before remediation.

[0067] Comparative Example 1

[0068] Based on Example 1, the electrodes in step 2) are adjusted as follows: the positive electrode is a high-silicon cast iron electrode, the negative electrode is a graphite electrode, and the rest is the same as in Example 1.

[0069] As a result, the analysis of the sample results showed that the soil pH was 6.9 and the content of leached arsenic decreased to 38.34 mg / kg, a decrease of 25.01% compared with before remediation.

[0070] Comparative Example 2

[0071] Based on Example 1, step 4) is adjusted to use two graphite electrodes, while the rest is the same as in Example 1.

[0072] As a result, the analysis of the sample results showed that the soil pH was 6.9 and the content of leached arsenic decreased to 48.54 mg / kg, a decrease of 5.07% compared with before remediation.

[0073] Comparative Example 3

[0074] Based on Example 1, steps 4)-6) are removed, and everything else is the same as in Example 1.

[0075] As a result, the analysis of the sample results showed that the soil pH was 6.9 and the content of leached arsenic decreased to 48.23 mg / kg, a decrease of 5.67% compared with before remediation.

[0076] Comparative Example 4

[0077] Based on Example 1, the electrodes in step 2) are directly adjusted to be: the positive electrode is a high-silicon cast iron electrode and the negative electrode is a graphite electrode, and steps 4)-6) are removed, while the rest is the same as in Example 1.

[0078] As a result, the analysis of the sample results showed that the soil pH was 6.9 and the content of leached arsenic decreased to 49.60 mg / kg, a decrease of 2.99% compared with before remediation.

[0079] Comparative Example 5

[0080] Based on Example 1, the voltage gradient in step 2) is directly adjusted to 0.5V / cm, and the rest is the same as in Example 1.

[0081] As a result, the analysis of the sample results showed that the soil pH was 6.8 and the content of leached arsenic decreased to 34.77 mg / kg, a decrease of 32.00% compared with before remediation.

[0082] Comparative Example 6

[0083] Based on Example 1, the concentration of potassium permanganate in step 2) is directly adjusted to 1% or 10%, and the rest is the same as in Example 1.

[0084] As a result, the analysis of the sample test results showed that when the concentration of potassium permanganate was 1%, the soil pH was 6.9 and the content of leached arsenic decreased to 36.9 mg / kg, which was 27.83% lower than before the remediation.

[0085] When the concentration of potassium permanganate is 10%, the resulting soil pH is 4.0. Its strong oxidizing properties damage the soil structure and have an adverse effect on subsequent soil use.

[0086] Comparative Example 7

[0087] Based on Example 1, directly adjust the power-on time and resting time in step 3): power on for 12 hours, rest for 12 hours, and run for 72 hours according to this pattern. Other steps are the same as in Example 1.

[0088] As a result, the analysis of the sample results showed that the soil pH was 6.9 and the content of leached arsenic decreased to 34.29 mg / kg, a decrease of 32.94% compared with before remediation.

[0089] Comparative Example 8

[0090] Based on Example 1, directly adjust the power-on time and resting time in step 5): power on for 12 hours, rest for 12 hours, and run for 72 hours according to this pattern. Other steps are the same as in Example 1.

[0091] As a result, the analysis of the sample results showed that the soil pH was 6.9 and the content of leached arsenic decreased to 29.60 mg / kg, a decrease of 42.11% compared with before remediation.

[0092] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for remediating arsenic-contaminated soil, characterized in that, Includes the following steps: S1. After the soil in the area to be repaired is drained of water, insert a positive electrode and a negative electrode into the soil; apply electrolyte to the soil area around the negative electrode; connect the positive electrode and the negative electrode to the power source; let it stand for 10-14 hours after being powered on. S2, exchange electrodes; continue energizing for 10-14 hours, then let stand for 10-14 hours; S3. Detect the content of pentavalent arsenic in the soil as a percentage of total arsenic. If it is less than 85%, repeat steps S1 and S2. If it is greater than 85%, remove the first positive electrode and the first negative electrode, and insert the second positive electrode and the second negative electrode in the original electrode positions. Stop adding electrolyte. S4. After powering on for 10-14 hours, let it stand for 10-14 hours. S5, exchange electrodes; continue energizing for 10-14 hours, then let stand for 10-14 hours; S6. Detect the concentration of arsenic in the soil. If the remediation requirements are met, remove the electrode to complete the remediation. If not, repeat steps S4 and S5 until the concentration of arsenic in the soil meets the remediation requirements. Both the first positive electrode and the first negative electrode are made of inert materials; The second positive electrode is an iron-containing material, and the electrolyte contains permanganate. The concentration of permanganate in the electrolyte is 3% to 5%; The voltage gradient between the positive and negative terminals is 1V / cm to 2V / cm. The voltage gradient between the second positive terminal and the second negative terminal is 1V / cm~2V / cm; The second negative electrode material is an inert material; The electrolyte dosage is 600-800 mg / kg soil.

2. The method for remediating arsenic-contaminated soil according to claim 1, characterized in that, The inert material is one or more of the following: graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon-based materials, titanium-based materials, and tin-based materials.

3. The method for remediating arsenic-contaminated soil according to claim 1, characterized in that, The second cathode material can be any one of the following: high-silicon cast iron anode, steel anode, iron-nickel anode, Fe co-deposited γ-MnO2 anode, or iron-based superionic conductor anode.

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