Method for restoring arsenic and halogenated hydrocarbon combined polluted soil through oxidation enhanced leaching and leaching agent

Abstract

The invention discloses a method for restoring arsenic and halogenated hydrocarbon combined contaminated soil through oxidation enhanced leaching and a leaching agent. The leaching agent is composed of a first-stage leaching solution and a second-stage leaching solution. The first-stage leacheate eluting agent is composed of persulfate and strong base; the second-stage leacheate eluting agent is composed of organic acid and alcohol. According to the method, a two-stage leaching mode is adopted for the arsenic and halogenated hydrocarbon combined contaminated soil, synchronous removal of arsenic and halogenated hydrocarbon in the contaminated soil can be achieved through the oxidation strengthening synergistic interaction effect of the leaching agent, the toxicity of arsenic can be reduced, potential safety hazards in the subsequent waste liquid treatment process can be reduced, and the method is mild in condition and easy to implement. The method has the advantages of high removal rate, low cost and the like.

Description

Technical Field

[0001] The invention relates to a method for repairing soil contaminated by arsenic and halogenated hydrocarbons and a leaching agent, and in particular to a method for repairing soil contaminated by arsenic and halogenated hydrocarbons by oxidation-enhanced leaching and a leaching agent, belonging to the technical field of soil treatment. Background Art

[0002] Arsenic is carcinogenic, teratogenic and mutagenic. Arsenic and organic compound pollution is a common environmental pollution problem, which is common in soil and groundwater. For example, arsenic and halogenated hydrocarbons are often detected at the same time in chemical sites and coking sites.

[0003] At present, the main treatment technologies for heavy metal and organic composite contaminated soil in my country include industrial kiln coordinated disposal, oxidation-elution remediation, thermal desorption-stabilization remediation, and bioremediation. For example, the Chinese patent (publication number CN114535279A) discloses a contaminated soil remediation and treatment system and treatment method using cement kilns for coordinated disposal. The method achieves the remediation of contaminated soil by establishing a set of cement kiln coordinated disposal system. For example, the Chinese patent (publication number CN106964642A) discloses an ultrasonic enhanced oxidation-elution combined remediation method for chromium contaminated sites. This method uses ultrasonic enhanced H2O2 oxidation to improve the oxidation efficiency while avoiding the use of excessive H2O2 to affect the subsequent elution effect, and also reduces the impact on the soil texture structure; then water is used for elution, which is safe and pollution-free, reduces the interference of chemical reagents to the soil environment, and has high remediation efficiency. For example, the Chinese patent (publication number CN110076185B) discloses a method for repairing soil contaminated by heavy metals and polycyclic aromatic hydrocarbons. This method first uses high-temperature thermal desorption to remove polycyclic aromatic hydrocarbon organic pollutants in the soil contaminated by heavy metals and polycyclic aromatic hydrocarbons, and then stabilizes the heavy metals through a stabilizing agent. For example, a Chinese patent (publication number CN105013815B) discloses a bioremediation method for polycyclic aromatic hydrocarbon-heavy metal contaminated soil, specifically, rice straw, white rot fungus spore suspension, and trace element liquid are mixed and solid-state fermented to obtain a fermented rice straw mixture; the fermented rice straw mixture, surfactant, deionized water, and polycyclic aromatic hydrocarbon-heavy metal contaminated soil are mixed and solid-state fermented to obtain a fermented composite contaminated soil mixture; the fermented composite contaminated soil mixture is mixed with deionized water, and ultrasonic and oscillation treatments are performed to complete the remediation of the composite contaminated soil.

[0004] The existing disclosed methods for remediating soils contaminated with arsenic and organic matter have advantages and disadvantages: the industrial kiln co-treatment technology can remediate soils contaminated with arsenic and organic matter more thoroughly, but it has high energy consumption and will damage the original soil microbial environment, affecting the secondary utilization of the soil; the oxidation-elution remediation technology requires oxidation first and then elution, and the remediation and disposal are carried out in two steps. The operation is complicated, and it is mainly used for remediation of heavy metal contaminated soil. The oxidant and the elution liquid fail to effectively form a synergistic effect to remove heavy metal ions and organic matter at the same time; the thermal desorption-stabilization remediation also requires thermal desorption to remove organic matter first, and then stabilization treatment of heavy metals. The operation is complicated, the energy consumption is high, the remediation cost is high, and it is difficult to achieve the remediation goal without removing heavy metals; biological remediation is suitable for the remediation of low-concentration arsenic and organic compound contaminated soil. High-concentration arsenic and organic matter (especially halogenated hydrocarbons) will inhibit the ability of organisms to adsorb and degrade pollutants. It is difficult to ensure the remediation effect during the actual construction process, and the remediation period is long, and the remediation effect is greatly affected by the environment. Summary of the invention

[0005] In view of the defects of the elution agents for soil contaminated by arsenic and halogenated hydrocarbons in the prior art, the first object of the present invention is to provide a elution agent for soil contaminated by arsenic and halogenated hydrocarbons, which has obvious oxidation-enhanced synergistic effect, can achieve the simultaneous removal of arsenic and halogenated hydrocarbons in the contaminated soil, and can reduce the toxicity of arsenic, thereby reducing the safety hazards in the subsequent waste liquid treatment process.

[0006] The second object of the present invention is to provide a method for oxidative enhanced leaching to repair soil contaminated with arsenic and halogenated hydrocarbons. The method has mild conditions and reduces the toxicity of arsenic while effectively oxidizing organic pollutants in the contaminated soil through the combination of oxidative enhanced leaching and acid leaching. It has the advantages of high removal rate and low cost.

[0007] In order to achieve the above technical objectives, the present invention provides a elution agent for soil contaminated with arsenic and halogenated hydrocarbons, which is composed of a first-stage eluent and a second-stage eluent; the first-stage eluent eluent is composed of persulfate and strong alkali; the second-stage eluent eluent is composed of organic acids and alcohols.

[0008] The present invention adopts oxidation enhanced leaching technology to achieve the simultaneous removal of arsenic and halogenated hydrocarbons in contaminated soil. The leaching principle is as follows: a two-stage leaching method is adopted, and the first-stage leaching liquid is composed of persulfate and strong alkali, wherein persulfate is a strong oxidant, and mainly oxidizes organic matter by forming sulfate free radicals. Sulfate free radicals are a strong oxidant, and the process of oxidizing organic matter is a free radical chain reaction, which is mainly divided into three stages: initiation, propagation, and termination. After the persulfate of the present invention is activated by a strong alkali, the -OO- bond in the molecular structure is broken to generate sulfate free radicals SO4 －•, the oxidation of halogenated hydrocarbons is completed through three methods: hydrogen atom extraction, free radical addition, and electron transfer. For arsenic, trivalent arsenic loses electrons and oxidizes to become pentavalent arsenic. The toxicity of pentavalent arsenic is less than that of trivalent arsenic, and the adsorption of oxidized arsenic on soil particles will be weakened. It will enter the eluent after elution and be discharged with the waste liquid. For halogenated hydrocarbons, the strong oxidizing sulfate radicals attack the carbon-halogen bonds in the halogenated hydrocarbon molecules, causing them to break and decompose the halogenated hydrocarbons into small molecules, thereby reducing the adsorption of halogenated hydrocarbons in the soil and making them easier to be eluted. The strong alkali in the first-stage eluent can enhance the migration ability of arsenic in the soil under high pH conditions, dissolve the mineral components in the contaminated soil, desorb through ion exchange, and deeply leach out the arsenic in the soil. In the presence of strong alkali, the leaching of arsenic in the soil is further promoted by catalytic oxidation heat release, thereby improving the elution efficiency. Then, the soil is placed in an acidic environment through the second-stage organic acid and alcohol leaching solution, which reduces the soil pH and promotes the desorption of arsenic. The purpose of deep removal of arsenic is achieved through the complexation of organic acids. At the same time, organic acids can not only promote the leaching of arsenic, but also neutralize the alkali remaining in the soil during the first-stage leaching process, which is convenient for the subsequent resource utilization of the soil. Moreover, the halogenated hydrocarbons in the soil are more easily dissolved in alcohols after being oxidized and decomposed by persulfate in the first-stage leaching solution. As they are removed by solid-liquid separation, the repair and removal rate of halogenated hydrocarbons is further improved.

[0009] Therefore, by selecting a suitable eluent and controlling the parameters of the eluent process, the present invention can not only effectively oxidize the halogenated hydrocarbon pollutants in the contaminated soil and remove the heavy metal arsenic in the soil by eluent, but also reduce the toxicity of arsenic and reduce the safety hazards in the subsequent waste liquid treatment process. After the two-stage elution mud is solid-liquid separated and filtered and dehydrated, the next step of repair is carried out.

[0010] In addition, the inventors found that in the present invention, persulfate and strong base need to be added simultaneously in the first eluent. This is because in order to improve the oxidation efficiency, persulfate needs to be activated by strong base to break the -OO- bond in the molecular structure and generate sulfate radical SO4. － •, complete the oxidation of halogenated hydrocarbons. Therefore, persulfate and strong alkali need to be added simultaneously or mixed in proportion before adding. If persulfate is added first and then strong alkali, the oxidizing properties of persulfate will be consumed by the original reducing substances in the soil without being effectively stimulated. Only part of the persulfate will be activated by the subsequent addition of strong alkali, which greatly reduces the oxidizing performance; and if strong alkali is added first and then persulfate, the strong alkali will be consumed by the original acidic substances in the soil, or consumed by other metal mineral ion exchange in the soil, and the persulfate cannot be effectively activated, resulting in reduced oxidation efficiency.

[0011] As a preferred solution, the persulfate includes at least one of sodium persulfate, potassium persulfate and ammonium persulfate; more preferably, sodium persulfate.

[0012] As a preferred solution, the strong base includes at least one of sodium hydroxide, calcium hydroxide and potassium hydroxide, and is more preferably sodium hydroxide.

[0013] As a preferred solution, the organic acid includes at least one of oxalic acid, citric acid and humic acid, and more preferably oxalic acid.

[0014] As a preferred solution, the alcohol includes at least one of ethylene glycol and propylene glycol, and more preferably ethylene glycol.

[0015] As a preferred solution, the mass concentration of the eluent in the first-stage eluent is 1.5-3%. When the mass concentration of the first-stage eluent is too low, it is not enough to completely desorb the pollutants in the soil, resulting in low elution efficiency; when the mass concentration is too high, although the elution efficiency may be improved, it may also increase the amount and cost of the eluent used, and may also damage the soil structure. In the present invention, the solvents in the first-stage eluent and the second-stage eluent are both water.

[0016] As a preferred solution, the mass ratio of persulfate to strong alkali in the first-stage eluent is (2-4): 1. The mass ratio of persulfate to strong alkali in the first eluent has a direct impact on the elution effect. When the mass ratio of strong alkali is too low, the pH of the solution is too low, and the persulfate cannot be effectively activated, resulting in reduced oxidation performance; and when the mass ratio of strong alkali is too high, the pH of the solution is too high, which is easy to cause corrosion to the equipment.

[0017] As a preferred solution, the mass concentration of the eluent in the second-stage eluent is 10-20%, and the mass ratio of the organic acid to the alcohol is (1-3):1. The organic acid selected in the present invention has certain acidity and complexing ability, and can further adjust the pH of the soil through acidic action, changing the adsorption-desorption equilibrium between soil particles and pollutants. Organic acids can also form complexes with arsenic, making it easier for arsenic to transfer from the surface of soil particles to the eluent. When the mass concentration of organic acid is too low, arsenic cannot be desorbed, resulting in a decrease in the arsenic removal rate. Through the principle of like dissolves like, the remaining halogenated hydrocarbons in the soil can be leached into the alcohols and removed with the solid-liquid separation, further improving the repair and removal rate of the halogenated hydrocarbons.

[0018] The present invention also provides a method for oxidative enhanced leaching to repair soil contaminated by arsenic and halogenated hydrocarbons. The method comprises the steps of crushing and sieving the soil contaminated by arsenic and halogenated hydrocarbons to obtain composite contaminated soil particles; adding a first-stage elution liquid to the composite contaminated soil particles for shock elution, and adding a second-stage elution liquid to the solid matter again for shock elution after solid-liquid separation.

[0019] The preparation method of the present invention combines oxidation-enhanced elution with acid elution to reduce the toxicity of arsenic while effectively oxidizing halogenated hydrocarbon pollutants in contaminated soil, and has the advantages of high removal rate, low cost, and the like.

[0020] As a preferred solution, during the elution process of the first-stage eluent, the liquid-to-solid ratio is (3-5):1, the oscillation frequency is 100-180 r / min, and the elution time is 0.5-1 h.

[0021] As a preferred solution, during the elution process of the second-stage elution liquid, the liquid-to-solid ratio is (5-10):1, and the elution time is 0.5-1h. Under the conditions of the first-stage elution and the second-stage elution selected by the present invention, the present invention has the best elution effect of removing arsenic and halogenated hydrocarbons.

[0022] As a preferred solution, the halogenated hydrocarbon includes dichloromethane and / or trichloroethylene.

[0023] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0024] 1) The present invention adopts oxidation enhanced chemical leaching technology, which has obvious synergistic effect and can simultaneously remove arsenic and halogenated hydrocarbon pollutants in the soil. The treated soil meets the screening value standards of arsenic and halogenated hydrocarbon pollutants in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standards (Trial)" (GB36600-2018). The repaired qualified soil can be utilized as a resource.

[0025] 2) The oxidation efficiency of persulfate is improved after being catalyzed by strong base. It can not only catalyze the oxidation of halogenated hydrocarbon pollutants, but also oxidize trivalent arsenic to pentavalent arsenic, reducing the toxicity of arsenic and reducing the safety hazards in the subsequent leaching wastewater treatment process. Moreover, the catalytic oxidation of halogenated hydrocarbon pollutants by persulfate is an exothermic reaction. The increase in the temperature of the leaching solution can increase the solubility of arsenic and halogenated hydrocarbons, which is beneficial to the removal of heavy metal arsenic and halogenated hydrocarbons.

[0026] 3) The strong alkali in the first-stage eluent can not only catalyze the rapid oxidation of halogenated hydrocarbon pollutants by persulfate, thereby achieving rapid removal of halogenated hydrocarbon pollutants; but also the strong alkali can enhance the migration ability of arsenic in the soil under high pH conditions, dissolve the mineral components in the contaminated soil, desorb through ion exchange, and leach out the arsenic in the soil.

[0027] 4) The organic acid in the second-stage elution solution can make the soil in an acidic environment, lower the soil pH and promote the desorption of arsenic, and achieve the purpose of removing arsenic through its own complexation; and the organic acid can neutralize the alkali remaining in the soil during the first-stage elution process, which is convenient for the subsequent resource utilization of the soil. According to the principle of like dissolves like, the remaining halogenated hydrocarbons in the soil can be leached into alcohols and removed with solid-liquid separation, further improving the remediation and removal rate of halogenated hydrocarbons.

[0028] 5) The present invention adds oxidants and eluents to the soil contaminated by arsenic and halogenated hydrocarbons to perform oxidation-enhanced chemical leaching remediation, thereby ensuring the oxidation remediation of the soil contaminated by halogenated hydrocarbons and ensuring that the soluble arsenic in the soil is transferred to the liquid phase, and then the liquid phase wastewater is comprehensively treated. The oxidation-enhanced chemical leaching technology can achieve rapid and effective remediation of the soil contaminated by arsenic and halogenated hydrocarbons, and has the advantages of simple method and low treatment cost. DETAILED DESCRIPTION

[0029] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed manner in conjunction with preferred embodiments below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0031] Unless otherwise specified, all reagents and raw materials used in the present invention are commercially available products or products that can be prepared by known methods.

[0032] Example 1

[0033] First, the arsenic and halogenated hydrocarbon contaminated soil was naturally air-dried, ground and crushed with an agate mortar, and passed through a 10-mesh sieve for later use. Take 5g of the sieved air-dried soil sample in a 150mL conical flask, add a 2% NaS2O8 and NaOH mixed solution (the mass ratio of NaS2O8 and NaOH is 3:1) at a liquid-solid ratio of 5:1, oscillate and leach at 150r / min for 30min at room temperature, let it stand, and after solid-liquid separation, add a 15% oxalic acid and ethylene glycol mixed solution (the mass ratio of oxalic acid and ethylene glycol is 2:1) at a liquid-solid ratio of 10:1, oscillate and leach for 1h, let it stand, solid-liquid separation, and take the leached soil sample to the testing company to determine the content of heavy metal arsenic and halogenated hydrocarbon pollutants. After remediation, the total amount of arsenic in the soil dropped from 100.00 mg / kg to 11.01 mg / kg, the total amount of dichloromethane dropped from 188.40 mg / kg to 55.43 mg / kg, and the total amount of trichloroethylene dropped from 3.13 mg / kg to 0.30 mg / kg, meeting the screening value standards of arsenic, dichloromethane, and trichloroethylene in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018) (22 mg / kg, 94 mg / kg, and 0.7 mg / kg). The remediated soil can be utilized as a resource.

[0034] Example 2

[0035] First, the arsenic and halogenated hydrocarbon contaminated soil was naturally air-dried, ground and crushed with an agate mortar, and passed through a 10-mesh sieve for later use. Take 5g of the sieved air-dried soil sample in a 150mL conical flask, add a 3% NaS2O8 and NaOH mixed solution (the mass ratio of NaS2O8 and NaOH is 2:1) at a liquid-solid ratio of 3:1, oscillate and leach at 150r / min for 30min at room temperature, let it stand, and after solid-liquid separation, add a 20% oxalic acid and ethylene glycol mixed solution (the mass ratio of oxalic acid and ethylene glycol is 3:1) at a liquid-solid ratio of 5:1, oscillate and leach for 1h, let it stand, solid-liquid separation, and take the leached soil sample to the testing company to determine the content of heavy metal arsenic and halogenated hydrocarbon pollutants.

[0036] After remediation, the total amount of arsenic in the soil dropped from 100.00 mg / kg to 13.95 mg / kg, the total amount of dichloromethane dropped from 188.40 mg / kg to 63.11 mg / kg, and the total amount of trichloroethylene dropped from 3.13 mg / kg to 0.35 mg / kg, meeting the screening value standards of arsenic, dichloromethane, and trichloroethylene in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018) (22 mg / kg, 94 mg / kg, and 0.7 mg / kg). The remediated soil can be utilized as a resource.

[0037] Example 3

[0038] First, the arsenic and halogenated hydrocarbon contaminated soil was naturally air-dried, ground and crushed with an agate mortar, and passed through a 10-mesh sieve for later use. Take 5g of the sieved air-dried soil sample in a 150mL conical flask, add a 1.5% NaS2O8 and NaOH mixed solution at a liquid-solid ratio of 4:1 (the mass ratio of NaS2O8 and NaOH is 4:1), oscillate and leach at 180r / min at room temperature for 60min, then let it stand, after solid-liquid separation, add a 10% oxalic acid and ethylene glycol mixed solution at a liquid-solid ratio of 10:1 (the mass ratio of oxalic acid and ethylene glycol is 1:1), oscillate and leach for 0.5h, let it stand, solid-liquid separation, and take the leached soil sample to the testing company to determine the content of heavy metal arsenic and halogenated hydrocarbon pollutants.

[0039] After remediation, the total amount of arsenic in the soil dropped from 100.00 mg / kg to 17.05 mg / kg, the total amount of dichloromethane dropped from 188.40 mg / kg to 78.23 mg / kg, and the total amount of trichloroethylene dropped from 3.13 mg / kg to 0.58 mg / kg, meeting the screening value standards of arsenic, dichloromethane, and trichloroethylene in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018) (22 mg / kg, 94 mg / kg, and 0.7 mg / kg). The remediated soil can be utilized as a resource.

[0040] Comparative Example 1

[0041] The difference between this comparative example and Example 1 is that the mass concentration of the mixed solution of NaS2O8 and NaOH in the first-stage eluent is changed to 0.5%, and the other steps and conditions are the same.

[0042] The soil samples after leaching were sent to the testing company to determine the content of heavy metal arsenic and organic pollutants. After restoration, the total amount of arsenic in the soil dropped from 100.00 mg / kg to 38.18 mg / kg, the total amount of dichloromethane dropped from 188.40 mg / kg to 149.40 mg / kg, and the total amount of trichloroethylene dropped from 3.13 mg / kg to 2.34 mg / kg, which did not meet the screening value standards of arsenic, dichloromethane, and trichloroethylene in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018) (22 mg / kg, 94 mg / kg, 0.7 mg / kg).

[0043] Comparative Example 2

[0044] The difference between this comparative example and Example 1 is that the mass concentration of the mixed solution of oxalic acid and ethylene glycol in the second-stage eluent is changed to 5%, and the other steps and conditions are the same.

[0045] The soil samples after leaching were sent to the testing company to determine the content of heavy metal arsenic and organic pollutants. After the restoration, the total amount of arsenic in the soil dropped from 100.00 mg / kg to 36.50 mg / kg, the total amount of dichloromethane dropped from 188.40 mg / kg to 58.75 mg / kg, and the total amount of trichloroethylene dropped from 3.13 mg / kg to 0.37 mg / kg. Arsenic did not reach the screening value standard (22 mg / kg) in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018).

[0046] Comparative Example 3

[0047] The difference between this comparative example and Example 1 is that only NaS2O8 is added to the first-stage eluent without adding NaOH, and the other steps and conditions are the same.

[0048] The soil samples after leaching were sent to the testing company to determine the content of heavy metal arsenic and organic pollutants. After restoration, the total amount of arsenic in the soil dropped from 100.00 mg / kg to 59.53 mg / kg, the total amount of dichloromethane dropped from 188.40 mg / kg to 148.24 mg / kg, and the total amount of trichloroethylene dropped from 3.13 mg / kg to 2.35 mg / kg, which did not meet the screening value standards of arsenic, dichloromethane, and trichloroethylene in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018) (22 mg / kg, 94 mg / kg, 0.7 mg / kg).

[0049] Comparative Example 4

[0050] The difference between this comparative example and Example 1 is that NaS2O8 is added first and NaOH is added later in the first-stage eluent, and the other steps and conditions are the same.

[0051] The soil samples after leaching were sent to the testing company to determine the content of heavy metal arsenic and organic pollutants. After the restoration, the total amount of arsenic in the soil dropped from 100.00 mg / kg to 12.18 mg / kg, the total amount of dichloromethane dropped from 188.40 mg / kg to 100.11 mg / kg, and the total amount of trichloroethylene dropped from 3.13 mg / kg to 1.69 mg / kg, which did not meet the screening value standards of dichloromethane and trichloroethylene in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018) (94 mg / kg, 0.7 mg / kg).

[0052] Comparative Example 5

[0053] The only difference between this comparative example and Example 1 is that NaOH is added first and NaS2O8 is added later in the first-stage eluent, and the other steps and conditions are the same.

[0054] The soil samples after leaching were sent to the testing company to determine the content of heavy metal arsenic and organic pollutants. After the restoration, the total amount of arsenic in the soil dropped from 100.00 mg / kg to 12.35 mg / kg, the total amount of dichloromethane dropped from 188.40 mg / kg to 75.43 mg / kg, and the total amount of trichloroethylene dropped from 3.13 mg / kg to 1.05 mg / kg, which did not meet the screening value standard (0.7 mg / kg) of trichloroethylene in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018).

[0055] Comparative Example 6

[0056] The difference between this comparative example and Example 1 is that the mixed solution of oxalic acid and ethylene glycol for elution in the second step is not added, and the other steps and conditions are the same.

[0057] The soil samples after leaching were sent to the testing company to determine the content of heavy metal arsenic and organic pollutants. After the restoration, the total amount of arsenic in the soil dropped from 100.00 mg / kg to 49.15 mg / kg, the total amount of dichloromethane dropped from 188.40 mg / kg to 60.40 mg / kg, and the total amount of trichloroethylene dropped from 3.13 mg / kg to 0.42 mg / kg, which did not meet the screening value standard (22 mg / kg) of arsenic in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)" (GB36600-2018).

Claims

1. A leaching agent for soil contaminated by arsenic and halogenated hydrocarbons, characterized in that: It is composed of a first-stage eluent and a second-stage eluent; The first-stage eluent eluent is composed of persulfate and strong alkali; The second-stage eluent is composed of organic acid and alcohol.

2. The elution agent for soil contaminated by arsenic and halogenated hydrocarbons according to claim 1, characterized in that: The persulfate includes at least one of sodium persulfate, potassium persulfate and ammonium persulfate; The strong base includes at least one of sodium hydroxide, calcium hydroxide and potassium hydroxide; The organic acid comprises at least one of oxalic acid, citric acid and humic acid; The alcohol includes at least one of ethylene glycol and glycerol.

3. The elution agent for soil contaminated by arsenic and halogenated hydrocarbons according to claim 1 or 2, characterized in that: The mass concentration of the eluent in the first-stage eluent is 1.5-3%.

4. The elution agent for soil contaminated by arsenic and halogenated hydrocarbons according to claim 3, characterized in that: The mass ratio of persulfate to strong alkali in the first-stage eluent is (2-4):

1.

5. The elution agent for soil contaminated by arsenic and halogenated hydrocarbons according to claim 1, characterized in that: The mass concentration of the eluent in the second-stage eluent is 10-20%, and the mass ratio of the organic acid to the alcohol is (1-3):

1.

6. A method for remediating soil contaminated by arsenic and halogenated hydrocarbons using the elution agent according to any one of claims 1 to 5, characterized in that: The composite contaminated soil of arsenic and halogenated hydrocarbons is crushed and sieved to obtain composite contaminated soil particles; the composite contaminated soil particles are added with a first-stage eluent for shaking and eluting, and after solid-liquid separation, a second-stage eluent is added to the solid matter for shaking and eluting again.

7. The method for remediating soil contaminated by arsenic and halogenated hydrocarbons using the elution agent according to claim 6, characterized in that: During the elution process of the first-stage eluent, the liquid-to-solid ratio is (3-5):1, the oscillation frequency is 100-180 r / min, and the elution time is 0.5-1 h.

8. The method for remediating soil contaminated by arsenic and halogenated hydrocarbons using the elution agent according to claim 7, characterized in that: During the elution process of the second-stage eluent, the liquid-to-solid ratio is (5-10):1, and the elution time is 0.5-1h.

9. The method for remediating soil contaminated by arsenic and halogenated hydrocarbons using the elution agent according to claim 7 or 8, characterized in that: The halogenated hydrocarbons include dichloromethane and / or trichloroethylene.