Method for repairing arsenic-polluted soil

Abstract

The invention relates to a method for repairing arsenic-polluted soil. The method comprises the following steps that S1, a first positive electrode and a first negative electrode are inserted outside a to-be-repaired soil area; an electrolyte is applied to the soil area around the negative electrode; the first positive electrode and the first negative electrode are communicated with a power supply; after electrifying for 10 to 14 hours, standing for 10 to 14 hours; s2, exchanging electrodes; continuously electrifying for 10 to 14 hours, and standing for 10 to 14 hours; s3, detecting the content of pentavalent arsenic in the soil, and if the content is less than 85%, repeating the steps S1 and S2; and if the concentration is greater than 85%, removing the No.1 positive electrode and the No.1 negative electrode, and inserting the No.2 positive electrode and the No.2 negative electrode at the original electrode position. According to the method, the oxidizing agent is injected into the soil through electroosmosis, and trivalent arsenic in the soil is oxidized into pentavalent arsenic easy to stabilize; ferrous ions are introduced into the soil by utilizing the sacrificial positive iron electrode and are subjected to adsorption-precipitation reaction with arsenite and arsenate, so that the aim of stabilizing the arsenic-polluted soil is fulfilled.

Description

Technical Field

[0001] The present invention relates to a technology for repairing arsenic-contaminated soil, and particularly to a method for repairing arsenic-contaminated soil. Background Art

[0002] Arsenic is a highly toxic metalloid. Arsenic contamination in soil can cause pollutants to accumulate in plants and be enriched in the human body and animals through the food chain, endangering human health and causing cancers and other diseases. For the technology of repairing arsenic-contaminated soil, available methods include chemical, physical, and biological methods. The stabilization technology is to add exogenous agents to arsenic-contaminated soil, and the arsenic in the soil undergoes complex chemical reactions with the agents to form a stabilized body with very low toxicity, mobility, and solubility. One of the key factors for the stabilization effect is the uniform mixing of the agent and the soil. For soils with high viscosity, if uniform mixing is to be achieved, the mixing process requires a large amount of time and energy consumption.

[0003] The prior art CN 107457266 B discloses a heavy metal contaminated soil remediation system, including a plant planting layer, a power supply, a flat anode, a flat cathode, and an electrolyte circulation device. The plant planting layer is arranged on the upper surface of the soil plot to be repaired, and the plant planting layer is made of local soil and feces mixed in a volume ratio of 1:1. The power supply is a DC power supply; the flat anode is made of graphite or metal material, and the shape of the flat anode is cylindrical or cuboid; the flat cathode is made of graphite or metal material, and the shape of the flat cathode is cylindrical or cuboid; the flat cathode is horizontally placed during operation and is parallel to the flat anode in space; there are several flat cathodes, which are 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 removes heavy metal ions from the soil through plant enrichment and electrolyte migration, and the growth of plants is affected by factors such as temperature, humidity, and pH, with low controllability. Moreover, this patent subsequently involves the treatment of plants and electrolytes enriched with heavy metals, and the post-treatment operation is cumbersome.

[0004] The prior art CN 109926447 A discloses a multi-polluted soil advanced oxidation collaborative electrokinetic in-situ remediation system, including a DC regulated power supply and a soil remediation device. The soil remediation device includes a box body and an advanced oxidant dosing device. Inside the box body, a left partition and a right partition are arranged, and the left partition and the right partition divide the inside of the box body into an anode chamber, a soil chamber, and a cathode chamber from left to right in sequence. A plurality of through holes are opened on both the left partition and the right partition. A left drain valve and a right drain valve are arranged at the lower part of the front side of the box body. The DC regulated power supply is connected to the upper ends of two columnar graphite electrodes through wires respectively. However, this patent subsequently involves the treatment of soil and electrolytes enriched with heavy metals, with cumbersome operations. Moreover, for heavy metal ions with relatively poor mobility, the power consumption is large and the electrokinetic remediation cost is high.

[0005] Therefore, it is very necessary to develop a technology for repairing sticky arsenic-contaminated soil. Summary of the Invention

[0006] The object of the present invention is to provide a method for repairing arsenic-contaminated soil.

[0007] In order to achieve the above object, the solution of the present invention is as follows:

[0008] A method for repairing arsenic-contaminated soil, comprising the following steps:

[0009] S1. Insert a first positive electrode and a first negative electrode outside the soil area to be repaired; apply an electrolyte to the soil area around the negative electrode; the first positive electrode and the first negative electrode are connected to a power supply; after power-on for 10-14 h, let it stand for 10-14 h;

[0010] S2. Exchange the electrodes; continue to power on for 10-14 h and then let it stand for 10-14 h;

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

[0012] S4. Power on for 10-14 h and then let it stand for 10-14 h;

[0013] S5. Exchange the electrodes; continue to power on for 10-14 h and then let it stand for 10-14 h;

[0014] S6. Detect the concentration of arsenic in the soil. If the repair requirement is met, remove the electrodes to complete the repair; if not, repeat steps S4 and S5 until the concentration of arsenic in the soil meets the repair requirement;

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

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

[0017] The repair requirements vary according to 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 generated Fe 2+ will react with the permanganate, resulting in the loss of permanganate and affecting the repair effect.

[0019] If the energization time in step S1 is too short, it is not sufficient to allow the electrolyte to migrate and distribute throughout the soil remediation area through electrokinetic action, thereby affecting the remediation effect. If the energization time is too long, it will cause increased energy consumption, electrode corrosion, and soil structure damage.

[0020] If the energization time in step S4 is too short, it is not sufficient to allow Fe 2+ to migrate and distribute throughout the soil remediation area through electrokinetic action, thereby affecting the remediation effect. If the energization time is too long, it will cause increased energy consumption, electrode corrosion, and soil structure damage.

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

[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 several of graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon-based materials, titanium-based materials, and tin-based materials.

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

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

[0026] A potassium permanganate solution with too high a concentration may damage the soil structure due to its strong oxidizing property; if the concentration is too low, more potassium permanganate solution is required per unit volume of soil, resulting in high transportation and spraying costs.

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

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

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

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

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

[0032] Both electrochemical methods and permanganates have certain reaction activities. Permanganates are strong oxidants. In an electrochemical system, electrochemical methods can change the reaction environment on the electrode surface. For example, strongly oxidizing active substances such as hydroxyl radicals are generated on the electrode surface. The oxidation effects of these active substances and permanganates are synergistic, which can enhance the oxidation effect on refractory pollutants in soil or water bodies.

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

[0034] During the electrochemical remediation process, the current promotes the reaction of electrons with pollutants, while permanganates provide additional oxidation ability. For some pollutants that are difficult to treat by a single method, the combination of the two can improve the remediation efficiency. For example, for some high-concentration organic pollutants, electrochemical methods can preliminarily decompose some pollutants, and then permanganates further oxidize and decompose the remaining intermediate products.

[0035] However, if the operating conditions are not controlled, side reactions may occur when the two are combined. For example, in soil remediation, some refractory oxidation products may be generated or the structure and chemical properties of the soil may be changed. The combination of the two methods requires precise control of reaction conditions such as the electrode potential, the concentration of permanganates, and the reaction time. Improper operation may affect the remediation effect and even produce negative effects.

[0036] In the present invention, the electrodes are regularly exchanged during the remediation process, and the sacrificial iron anode is used during the electrode exchange process. The oxidant is injected into the highly viscous soil through electroosmosis to oxidize trivalent arsenic in the soil into pentavalent arsenic that is easily stabilized; the sacrificial iron anode is used to introduce ferrous ions into the highly viscous soil, and the ferrous ions combine with arsenic to undergo an adsorption-precipitation reaction with arsenite and arsenate, thereby achieving the purpose of stabilizing arsenic-contaminated soil.

[0037] Meanwhile, strongly oxidizing active substances such as hydroxyl radicals are generated on the electrode surface. The oxidation effects of these active substances and permanganates are synergistic, strengthening the oxidation effect on soil arsenic. Utilizing the advantages of electrochemistry, permanganates are enabled to oxidize arsenic in the soil directionally, reducing the adverse effects on other substances in the environment. During the electrochemical remediation process, the current promotes the reaction of ferrous ions with pollutants, while permanganates provide additional oxidation ability, and the two act synergistically to improve the stabilization effect on arsenic.

[0038] Exchanging electrodes means reversing the connection of the positive and negative electrodes of a battery or power supply. For example, in a device powered by a battery, originally the positive electrode is connected to a certain part of the circuit and the negative electrode is connected to another part, and now the connection relationship between the two is reversed.

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

[0040] 1) The present invention is applicable to the stabilization and remediation of highly viscous arsenic-contaminated soil. Compared with ordinary reagent mixing and stabilization technologies, it has energy-saving and economic advantages.

[0041] 2) The present invention causes little disturbance to the soil. The pH value of the arsenic-contaminated soil after remediation ranges between 6.5 and 8.2, and has little impact on soil functions.

[0042] 3) The present invention will not cause secondary pollution to the soil and has the advantage of green environmental protection remediation.

[0043] 4) The present invention is simple to operate, has a low cost, a relatively fast treatment time, a flexible treatment method, can be moved at any time, has the feasibility of large-scale engineering implementation, and has a wide application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic flow chart of the remediation method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The following will describe the implementation scheme of the present invention in detail in conjunction with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase.

[0046] Example 1

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

[0048] As Figure 1 described in the process of

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

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

[0051] 3) Electrify for 12 h and let it stand for 12 h; Exchange the positive and negative electrodes to neutralize the H + / OH- and make KMnO4 uniformly enter the soil through electroosmosis. Operate for 144 h according to the above rules. Through the addition of the KMnO4 electrolyte solution, the pentavalent arsenic in the soil accounts for 92% of the total arsenic, and the soil water content is about 35%.

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

[0053] 5) Electrify for 12 h and let it stand for 12 h;

[0054] 6) Exchange the anode and cathode electrodes; electrify for 12 h, and the iron anode is electrolyzed into Fe 2+ and infiltrate into the soil under the action of the electric field. After steps 5)-6) are cumulatively operated for 168 h, through the analysis of the sample measurement results, the soil pH is 6.9, and the content of leachable arsenic is reduced to 14.50 mg / kg, which is a 71.64% decrease compared with that before remediation.

[0055] Example 2

[0056] On the basis of Example 1, adjust the concentration of KMnO4 in step 2) to 3%, and the others are the same as in Example 1.

[0057] As a result, through the analysis of the sample measurement results, the soil pH is 6.8, and the content of leachable arsenic is reduced to 15.53 mg / kg, which is a 69.63% decrease compared with that before remediation.

[0058] Example 3

[0059] On the basis of Example 1, adjust both electrodes in step 2) to be made of titanium-based materials, and the others are the same as in Example 1.

[0060] As a result, through the analysis of the sample measurement results, the soil pH is 6.9, and the content of leachable arsenic is reduced to 15.41 mg / kg, which is a 69.86% decrease compared with that before remediation.

[0061] Example 4

[0062] On the basis of Example 1, adjust the voltage gradient in step 2) to 2 V / cm, and the others are the same as in Example 1.

[0063] As a result, through the analysis of the sample measurement results, the soil pH is 6.7, and the content of leachable arsenic is reduced to 13.76 mg / kg, which is a 73.09% decrease compared with that before remediation.

[0064] Example 5

[0065] On the basis of Example 1, adjust the energization time in step 5) to 14 h, and the others are the same as in Example 1.

[0066] As a result, through the analysis of the sample measurement results, the soil pH is 6.9, and the content of leachable arsenic is reduced to 14.22 mg / kg, a decrease of 72.19% compared with that before remediation.

[0067] Comparative Example 1

[0068] On the basis of Example 1, adjust the electrodes in step 2) as follows: the positive electrode is a high-silicon cast iron electrode, and the negative electrode is a graphite electrode, and the others are the same as in Example 1.

[0069] As a result, through the analysis of the sample measurement results, the soil pH is 6.9, and the content of leachable arsenic is reduced to 38.34 mg / kg, a decrease of 25.01% compared with that before remediation.

[0070] Comparative Example 2

[0071] On the basis of Example 1, adjust the electrodes in step 4) to two graphite electrodes, and the others are the same as in Example 1.

[0072] As a result, through the analysis of the sample measurement results, the soil pH is 6.9, and the content of leachable arsenic is reduced to 48.54 mg / kg, a decrease of 5.07% compared with that before remediation.

[0073] Comparative Example 3

[0074] On the basis of Example 1, remove steps 4)-6), and the others are the same as in Example 1.

[0075] As a result, through the analysis of the sample measurement results, the soil pH is 6.9, and the content of leachable arsenic is reduced to 48.23 mg / kg, a decrease of 5.67% compared with that before remediation.

[0076] Comparative Example 4

[0077] On the basis of Example 1, directly adjust the electrodes in step 2) as follows: the positive electrode is a high-silicon cast iron electrode, and the negative electrode is a graphite electrode, and remove steps 4)-6), and the others are the same as in Example 1.

[0078] As a result, through the analysis of the sample measurement results, the soil pH is 6.9, and the content of leachable arsenic is reduced to 49.60 mg / kg, a decrease of 2.99% compared with that before remediation.

[0079] Comparative Example 5

[0080] On the basis of Example 1, directly adjust the voltage gradient in step 2) to 0.5 V / cm, and the others are the same as in Example 1.

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

[0082] Comparative Example 6

[0083] On the basis of Example 1, directly adjust the concentration of potassium permanganate in step 2) to 1% or 10%, and the others are the same as in Example 1.

[0084] As a result, through the analysis of the test sample results, when the concentration of potassium permanganate was 1%, the obtained soil pH was 6.9, and the content of leachable arsenic decreased to 36.9 mg / kg, a decrease of 27.83% compared with that before remediation.

[0085] When the concentration of potassium permanganate was 10%, the obtained soil pH was 4.0, and its strong oxidizing property damaged the soil structure, which had an adverse effect on the subsequent soil utilization.

[0086] Comparative Example 7

[0087] On the basis of Example 1, directly adjust the energization time and standing time in step 3), energize for 12 h and stand for 12 h, and operate according to this rule for 72 h, and the others are the same as in Example 1.

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

[0089] Comparative Example 8

[0090] On the basis of Example 1, directly adjust the energization time and standing time in step 5), energize for 12 h and stand for 12 h, and operate according to this rule for 72 h, and the others are the same as in Example 1.

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

[0092] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for remediating arsenic-contaminated soil, characterized in that: The following steps are involved: 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 a power source; and leave the soil to stand for 10-14 hours after powering on for 10-14 hours; S2, exchange electrodes; continue to energize for 10-14 hours and then let stand for 10-14 hours; S3, detecting the content of pentavalent arsenic in the soil, if less than 85%, repeating steps S1 and S2; if greater than 85%, removing the first positive electrode and the first negative electrode, inserting the second positive electrode and the second negative electrode at the original electrode position; stopping the addition of electrolyte; S4, power on for 10-14 hours and then let stand for 10-14 hours; S5. Exchange electrodes; continue to energize for 10-14 hours and then let stand for 10-14 hours; S6. Detect the arsenic concentration in the soil. If it meets the remediation requirements, remove the electrodes and complete the remediation. If it does not meet the requirements, repeat steps S4 and S5 until the arsenic concentration in the soil meets the remediation requirements. The first positive electrode and the first negative electrode are both inert materials; The second positive electrode is made of iron-containing material, and the electrolyte contains permanganate.

2. The method for remediating arsenic-contaminated soil according to claim 1, characterized in that: The No. 2 negative electrode material is an inert material.

3. The method for remediating arsenic-contaminated soil according to claim 2, characterized in that: 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.

4. The method for remediating arsenic-contaminated soil according to claim 1, characterized in that: The No. 2 positive electrode material is any one of a high-silicon cast iron anode, a steel anode, an iron-containing nickel anode, a Fe co-deposited γ-MnO2 anode, and an iron-based superionic conductor anode.

5. The method for remediating arsenic-contaminated soil according to claim 1, characterized in that: The concentration of permanganate in the electrolyte is 3% to 5%.

6. The method for remediating arsenic-contaminated soil according to claim 1, characterized in that: The dosage of electrolyte is 600-800 mg / kg soil.

7. The method for remediating arsenic-contaminated soil according to claim 1, characterized in that: The voltage gradient between the first positive electrode and the first negative electrode is 1V / cm to 2V / cm.

8. The method for remediating arsenic-contaminated soil according to any one of claims 1 to 7, characterized in that: The voltage gradient of the second positive electrode and the second negative electrode is 1V / cm to 2V / cm.

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