Method for repairing chlorohydrocarbon polluted site by in-situ chemical oxidation
Technical Field
The invention relates to a method for restoring a site polluted by chlorohydrocarbon by in-situ chemical oxidation, belonging to the field of in-situ chemical oxidation methods of soil.
Background
Chlorinated hydrocarbon solvents are used as important chemical raw materials and organic solvents and widely applied to the chemical industry. Due to the reasons of inappropriate mass production, use and storage of chlorinated hydrocarbons, chlorinated hydrocarbons enter soil and underground water and become common pollutants in the environment, particularly trichloromethane, trichloroethane, trichloroethylene, tetrachloroethylene and the like. The chlorinated hydrocarbon generally has carcinogenicity, teratogenicity and mutagenicity, and the carbon-hydrogen bond energy of the chlorinated hydrocarbon is higher, so that the chlorinated hydrocarbon can exist in the environment for a long time, and the toxic effect on the human health and the ecological environment is increased. Chlorinated hydrocarbons are mostly heavy non-aqueous phase liquids, have the characteristics of low solubility and high density, and pollute soil and underground water by taking gravity infiltration as a main power when the chlorinated hydrocarbons are leaked or discharged to the surface and underground. When the gas-coated zone soil layer enters the underground water layer and meets the 'barrier layer' with smaller permeability coefficient, the gas-coated zone soil layer is easy to stay at the top of the barrier layer and transversely diffuses along with the flow of the underground water, and further the safe utilization of the underground water in a larger range is threatened.
In-situ chemical oxidation (ISCO) is a remediation technique that introduces a chemical oxidant into an underground water environment to undergo a redox reaction with a pollutant, so that the pollutant is degraded or converted into a low-toxicity and low-mobility product, and common oxidants include permanganate, hydrogen peroxide, fenton's reagent, persulfate, ozone, and the like. However, due to the complexity of the soil structure and chemical components, humic acid, reducing metals and other substances present in the soil consume a large amount of oxidizing agents. In addition, the chemical oxidizing agent is injected into the soil in an area with non-directional migration direction and range and poor soil layer permeability, so that the transmission rate of the chemical oxidizing agent is low, and the oxidation efficiency is affected.
Based on the problems in the prior art, the invention provides a method for repairing a typical chlorinated hydrocarbon polluted site in soil by in-situ chemical oxidation.
Disclosure of Invention
The invention provides a method for repairing a chlorinated hydrocarbon polluted site by in-situ chemical oxidation aiming at the defects in the prior art, and aims to solve the problems in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for restoring a site polluted by chlorohydrocarbon by in-situ chemical oxidation comprises the following steps:
(1) firstly, spraying a fine sand powder spraying pile foundation into a specific soil depth to improve a soil mechanism and improve the water permeability of soil;
(2) uniformly mixing calcium peroxide, persulfate, ferrous sulfate and cement, spraying the mixture into the ground through a powder spraying pile machine, solidifying and wrapping the mixture into clusters by using the cement to form a coating-like effect, and prolonging the oxidation effect of an oxidant;
(3) spraying fine sand into soil of a polluted site by a dry method by using a powder spraying pile machine; then separately and uniformly mixing the ferrous sulfate catalyst and the cement, and spraying the mixture into the soil of the polluted site by a dry method through a powder spraying pile machine;
(4) after cement in the soil is solidified, hydrogen peroxide liquid oxidant is injected into the upstream area of underground water in the soil of the polluted site through an injection well and diffuses towards the downstream of underground water migration under the natural migration effect of the underground water.
(5) A plurality of injection wells are deployed in the field, and the ends of the injection wells do not penetrate the water barrier.
Furthermore, the adding amount of the fine sand in the step (1) is 50 kg-180 kg/m of each pile3。
Further, the molar ratio of the addition amount of the calcium oxide to the addition amount of the ferrous sulfate in the step (2) is 10-20: 1, and the molar ratio of the addition amount of the persulfate to the addition amount of the ferrous sulfate is 2-10: 1.
Further, the molar ratio of the total addition of the calcium peroxide and the persulfate in the step (2) to the content of the chlorinated hydrocarbon in the polluted soil is 8-10: 1; the mass ratio of the calcium peroxide to the persulfate is 1: 2-4.
Further, the adding amount of the cement in the step (2) is 60-150 kg/m of each pile3。
Further, the molar ratio of the adding amount of the ferrous sulfate in the step (3) to the adding amount of the hydrogen peroxide in the step (4) is 5-20: 1.
Further, the hydrogen peroxide in the step (4) is hydrogen peroxide liquid with the mass fraction of 20-30%; the molar ratio of the addition amount of the hydrogen peroxide to the content of the chlorinated hydrocarbon in the polluted soil is 5-10: 1.
Further, the adding amount of the fine sand in the step (3) is 50 kg-180 kg/m of each pile3。
Further, the adding amount of the cement in the step (3) is 60-150 kg/m of each pile3。
Further, the ferrous sulfate in the steps (2) and (3) has a particle size of 6-20 meshes.
The in-situ chemical oxidation repair technology adopts a mode of combining a solid chemical oxidant and a liquid chemical oxidant, uses calcium peroxide, persulfate and hydrogen peroxide as an oxidant group, and uses ferrous sulfate as a catalyst. The calcium peroxide and the persulfate are solid or powder particle reagents, the hydrogen peroxide is a liquid reagent with the concentration of 20-30%, and the ferrous sulfate is a solid particle reagent.
After being uniformly mixed with cement, the solid or powder particle oxidant and the solid particle catalyst are injected into soil in a spraying mode of a powder-spraying pile machine, and the cement achieves the effect similar to 'coating' after being solidified; the liquid reagent is injected into the underground through an injection well, and is mixed with soil and underground water to generate chemical oxidation reaction by utilizing the natural migration characteristic of the underground water.
According to the field pollution condition, a plurality of solid oxidant injection point positions can be distributed according to a grid method or a plum blossom method and the like, fine sand is injected underground in a preferential injection mode, and then the solid oxidant, the catalyst and the cement are mixed and injected underground. And (3) arranging an injection well according to the flow direction of underground water in the polluted site, and arranging a ferrous sulfate catalyst at the downstream position of the underground water of the injection well to form a finished product character.
The liquid reagent is injected underground through an injection well, the depth of the injection well does not penetrate through a water-resisting layer, and the situation that pollutants move downwards along with the injection well due to the fact that the injection well penetrates through the water-resisting layer is prevented, and the pollution depth and the pollution range are further expanded.
The liquid oxidant meets the slowly-released catalyst in the process of moving downstream under the action of groundwater dynamic force, so that a large number of hydroxyl free radicals can be released, the reaction rate of the oxidant is improved, and the reaction time of the oxidant and pollutants is prolonged. In addition, the slowly released catalyst encounters the released solid oxidant to carry out catalytic reaction again in the process of underground water migration, so that the oxidation efficiency of the solid oxidant is improved.
Compared with the prior art, the invention has the following beneficial effects because the technology is adopted:
1. according to the invention, the content of sand grains in the soil is increased through the injection of the fine sand, the soil structure is improved, and the water permeability of the soil is enhanced. The cement is solidified to form a solidified substance which can effectively wrap solid or powder chemical agents, the dissolution and release of the chemical agents are delayed, and the solidified substance can react with a hydrogen peroxide liquid oxidant injected into an injection well by matching with a good permeable structure formed by fine sand, so that the oxidation efficiency of a chemical oxidant group is further improved.
2. The catalyzed solid oxidant and the catalyzed liquid oxidant can obtain higher oxidation potential, calcium peroxide and hydrogen peroxide can release a large amount of hydroxyl free radicals to degrade chlorinated hydrocarbon pollutants, and the oxidation capacity of the hydrogen peroxide and persulfate is greatly improved under the catalytic action of ferrous sulfate.
3. The cement, the fine sand and the solid reagent injected by powder spraying are mixed with the natural soil body, the reference of the cement and the fine sand is controlled, the solidified structure can be formed but has lower strength, and the solid oxidant and the catalyst ferrous sulfate which are wrapped by the solidified cement can be slowly released after being eroded by underground water.
Drawings
Fig. 1 is a schematic view of the layout of a contaminated site.
Detailed Description
The invention is further elucidated with reference to the drawings and the detailed description.
Example 1:
a method for restoring a site polluted by chlorohydrocarbon by in-situ chemical oxidation comprises the following steps:
1. according to the situation of a polluted site, solid oxidant points and liquid oxidant injection wells are arranged at equal intervals according to a grid method.
2. The molar ratio of the total addition amount of the solid oxidant to the concentration of the chlorinated hydrocarbon site pollutants is 8:1, and the mass ratio of the calcium peroxide to the persulfate oxidant is 1: 2.
3. Before the solid oxidant is sprayed into the ground, the fine sand is firstly injected into the ground by using a powder-jet pile driver, and the injection quantity is 80kg/m per pile3。
4. The dosage of the catalyst ferrous sulfate injected underground along with the solid oxidant adopts: the molar ratio of the added calcium peroxide to the added ferrous sulfate is 20:1, and the molar ratio of the added persulfate to the added ferrous sulfate is 10: 1.
5. the dosage of the underground cement injected together with the solid oxidant is 90kg/m per pile3。
6. Before the ferrous sulfate catalyst is sprayed into the ground, the fine sand is injected into the ground by means of powder-spraying pile driver, and the injection quantity is 100kg/m per pile3。
7. The injection amount of the separately sprayed catalyst ferrous sulfate was: the molar ratio of the amount of the ferrous sulfate catalyst to the amount of the hydrogen peroxide liquid oxidant is 5: 1.
8. The dosage of the underground cement injected together with the solid catalyst is 60kg/m per pile3。
9. After cement is solidified, the total amount of the injected hydrogen peroxide liquid oxidant with the mass fraction of 28 percent is diluted into diluent with the volume fraction of 5 percent according to the mol ratio of 5:1 to the chlorinated hydrocarbon pollutant in the polluted soil, the diluent is injected into the upstream area of the underground water in the soil of the polluted site in 8 times of equal amount, the injection time interval is 7d, and the depth of an injection well does not penetrate through a water-resisting layer.
The liquid oxidant meets the slowly released catalyst in the process of moving downstream under the action of groundwater dynamic force, and the slowly released catalyst meets the released solid oxidant in the process of moving the groundwater to perform catalytic reaction again.
In this embodiment, the ferrous sulfate has a particle size of 6-20 mesh.
Example 2:
a method for restoring a site polluted by chlorohydrocarbon by in-situ chemical oxidation comprises the following steps:
1. according to the situation of a polluted site, solid oxidant points and liquid oxidant injection wells are arranged at equal intervals according to a plum blossom method.
2. The molar ratio of the total addition amount of the solid oxidant to the concentration of the chlorinated hydrocarbon site pollutant is 10:1, and the mass ratio of the calcium peroxide to the persulfate oxidant is 1: 4.
3. Before the solid oxidant is sprayed into the ground, the fine sand is firstly injected into the ground by using a powder-jet pile driver, and the injection quantity is 160kg/m per pile3。
4. The dosage of the catalyst ferrous sulfate injected underground along with the solid oxidant adopts: the molar ratio of the added calcium peroxide to the added ferrous sulfate is 10:1, and the molar ratio of the added persulfate to the added ferrous sulfate is 2: 1.
5. the dosage of the underground cement injected together with the solid oxidant is 100kg/m per pile3。
6. Before the ferrous sulfate catalyst is sprayed into the ground, the fine sand is injected into the ground by using a powder-spraying pile machine, and the injection amount is 120kg/m per pile3。
7. The injection amount of the separately sprayed catalyst ferrous sulfate was: the molar ratio of the amount of ferrous sulfate catalyst to the amount of liquid hydrogen peroxide oxidant added is 20: 1.
8. The dosage of the underground cement injected together with the solid catalyst is 80kg/m per pile3。
9. After cement is solidified, the total amount of injected hydrogen peroxide liquid oxidant with the mass fraction of 20 percent is diluted into diluent with the volume fraction of 4 percent according to the mol ratio of 10:1 to chlorinated hydrocarbon pollutant in the polluted soil, the diluent is injected into the upstream area of underground water in the soil of a polluted site in 10 times and equal amount, the injection time interval is 10d, and the depth of an injection well does not penetrate through a water-resisting layer.
The liquid oxidant meets the slowly released catalyst in the process of moving downstream under the action of groundwater dynamic force, and the slowly released catalyst meets the released solid oxidant in the process of moving the groundwater to perform catalytic reaction again.
In this embodiment, the ferrous sulfate has a particle size of 6-20 mesh.
The liquid oxidant meets the slowly released catalyst in the process of moving downstream under the action of groundwater dynamic force, and the slowly released catalyst and the solid oxidant released downstream of groundwater movement are subjected to catalytic reaction again.
TABLE 1 monitoring results of the concentration of pollutants in the soil for chemical oxidation remediation of chlorinated hydrocarbons in a chemical field
Note: the restoration target value is a screening value of a second-class land according to soil pollution risk management and control standard (trial) of soil environment quality construction land (GB 36600-2018).
The above-mentioned embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the present invention, and the scope of the present invention should be defined by the claims, and equivalents including technical features of the claims, i.e., equivalent modifications within the scope of the present invention.