Vertical barrier material for high-concentration and high-risk organic pollution source as well as preparation method and application of vertical barrier material

Abstract

The invention discloses a vertical barrier material for a high-concentration and high-risk organic pollution source as well as a preparation method and application of the vertical barrier material. The pollution source barrier material mainly comprises organic pollution in-situ soil and commercial sodium modified calcium bentonite, a bentonite organic modifier is a hydrogenated styrene-butadiene-styrene block copolymer or a styrene-butadiene-styrene block copolymer, a bentonite viscosity reducer is sodium tripolyphosphate, and a bentonite viscosity reducer is sodium hydroxide. The mass ratio of the sodium pyrophosphate to the sodium hexaphosphate is controlled to be 100: (8-12): (1-3): (0.1-0.25). The barrier material can directly utilize an organic pollution source to pollute soil, can still meet the anti-seepage blocking performance requirement under the stress of high-risk high-concentration organic pollutants, and is good in construction workability. In addition, the preparation method of the barrier material is simple and convenient, and facilitates popularization and field use.

Description

Technical Field

[0001] The invention relates to a vertical barrier material for high-concentration and high-risk organic pollution sources and a preparation method thereof, belonging to the technical field of geotechnical engineering materials and environmental engineering. Background Art

[0002] The organic chemical industry has many underground pipelines, densely packed ground production facilities, a large number of organic and synthetic organic raw materials, and many sensitive receptors near water sources and residential areas. It is easy for organic compounds involved in production to enter the soil and groundwater through pipeline leakage, transportation process, and equipment leakage in the form of "leakage", forming a high-concentration, high-risk organic pollution source, which seriously endangers the surrounding environment and human health and safety. According to reports, common pollutants in organic pollution sites include: petroleum hydrocarbons, polycyclic aromatic hydrocarbons, benzene series, chlorinated hydrocarbons, pesticides, etc.

[0003] In order to prevent such high-concentration organic pollution sources from further polluting the surrounding soil and groundwater, it is urgent to implement risk control measures based on barrier technology for this pollution source. Traditional vertical barrier technology is mainly based on cement-based materials. Cement cannot be hydrated under the action of high-concentration organic matter. This is the current industry consensus. It has been reported that when using three-axis mixing pile technology with cement slurry as slurry to cross high-concentration organic pollution sources, the barrier barrier has problems such as extremely low strength, no wall, slurry foam, and anti-seepage failure. In addition, the commonly used vertical barrier technology internationally is based on bentonite-based materials, that is, soil-bentonite materials. However, under the action of high-concentration organic matter (the dielectric constant is much lower than that of water), combined with the Gouy-Chapman double layer theory, the lower the dielectric constant of the pore solution, the worse the development of the double layer, so the anti-seepage performance of the soil-bentonite material will be greatly weakened and cannot meet the anti-seepage requirements. In short, the existing barrier materials commonly used at home and abroad cannot solve the anti-seepage problem of high-concentration organic pollution sources.

[0004] In addition, in the existing risk control technology field, the isolation of organic pollutants mainly revolves around dissolved organic pollutants. The concentration of dissolved organic matter is extremely low, far from reaching the concentration level of the real pollution source mentioned above. The real organic pollution source is mainly non-aqueous organic matter (NAPL). Dissolved organic matter is only the pollution diffusion problem caused by NAPL contacting water, which can also be described as a pollution plume. That is, the modified material technology in the existing research mainly revolves around the isolation and control of the pollution plume, and cannot solve the problem of high-concentration organic pollution sources. In addition, the existing modified materials all require high-temperature pressurization and grinding treatment, which is extremely complex and costly, making it difficult to implement.

[0005] For example, application number CN202010228748.2 discloses a double-modified bentonite and a preparation method thereof, which requires high temperature pressurization and grinding treatment. The double-modified organic bentonite can be used in vertical barrier technology, but it mainly targets the problem of dissolved organic pollutants and inorganic salts, that is, the pollution plume problem. Application number 202111352751.6 discloses an in-situ chemical barrier material for contaminated soil and its preparation and application. The research and development of this material is to block the existing heavy metal, organic and composite pollution problems in the soil. However, the organic concentration of concern is extremely low, only 2.87 mg / kg, which is far from the current pollution level. The permeability coefficients of concern are all permeability coefficients under the stress of dissolved organic solution. Application number 202010124087.9 discloses an insulating and crack-resistant vertical barrier material and preparation method for composite pollutants, which also only focuses on the problem of dissolved organic pollutants.

[0006] In summary, traditional vertical barrier technology fails to prevent seepage under the threat of high-concentration and high-risk organic pollution sources. The modified material technology in existing research mainly focuses on the isolation and control of pollution plumes and cannot solve the problem of high-concentration organic pollution sources. There is an urgent need to study vertical barrier materials for high-concentration and high-risk organic pollution sources. Summary of the invention

[0007] Purpose of the invention: The purpose of the present invention is to provide a vertical barrier material for high-concentration and high-risk organic pollution sources and a preparation method thereof. Specifically, the anti-seepage performance of the vertical barrier material under the stress of high-concentration and high-risk organic pollution sources meets the requirement that the organic permeability coefficient is less than 10 -7 cm / s anti-seepage requirement (Technical Specifications for Vertical Barriers for Industrial Polluted Sites (HG / T 20715-2020)); secondly, the material has good construction and workability and can be constructed through trenchless construction methods, thereby avoiding the volatile organic compounds generated during the construction process that endanger human health and environmental safety; thirdly, the preparation process of the vertical barrier material only requires simple mixing, and does not require high temperature, high pressure and grinding treatment.

[0008] Technical solution: To achieve the above purpose, the present invention adopts the following technical solution: A vertical barrier material for high-concentration and high-risk organic pollution sources, mainly including organic pollution in-situ soil, commercial sodium-modified calcium-based bentonite, bentonite organic modifier (hydrogenated styrene-butadiene-styrene block copolymer or styrene-butadiene-styrene block copolymer), bentonite viscosity reducer (sodium tripolyphosphate, sodium pyrophosphate and sodium hexaphosphate). The mass ratio is controlled to be 100:8~12:1~3:0.1~0.25.

[0009] Based on the previous tests, the most preferred bentonite organic modifier is hydrogenated styrene-butadiene-styrene block copolymer, and the bentonite viscosity reducer is sodium tripolyphosphate.

[0010] Among them, the in-situ soil of the organic pollution source belongs to the in-situ soil at the organic pollution source in the actual on-site risk control project. The material proposed in this technical solution is a barrier material based on the in-situ non-excavation method, so the main body of the barrier material is still the in-situ soil.

[0011] Since my country lacks high-quality natural sodium-based bentonite, calcium-based bentonite with weak expansion properties is widely available. Therefore, it is necessary to use commercially available sodium-modified calcium-based bentonite and modify it with an organic modifier. The resulting modified bentonite has good expansion and adsorption properties under organic stress and is the main material that provides anti-seepage properties in barrier materials.

[0012] The bentonite organic modifier is a hydrogenated styrene-butadiene-styrene block copolymer or a styrene-butadiene-styrene block copolymer. These two copolymers are thermoplastic elastomers commonly used in the rubber and plastics industry, used to improve the basic properties of rubber and plastics. They are also commonly used hydrophobic polymers in the chemical industry. In this technical solution, they are organic modified materials for bentonite materials, with a purity of not less than 90%, a styrene content of not less than 18%, and an ash content of not more than 1%. They can effectively adsorb organic pollutants in organic pollution sources and swell, effectively protect bentonite particles, and swell to fill pores, thereby improving the chemical compatibility and anti-seepage performance of barrier materials.

[0013] Sodium tripolyphosphate, sodium pyrophosphate and sodium hexaphosphate are common phosphate materials with a phosphate content of not less than 65%. They are often used in inorganic chemical industry, food industry, ceramics, oil drilling, water treatment and other fields. They are a dispersant, metal chelating agent, quality improver, etc. In the present technical scheme, sodium tripolyphosphate, sodium pyrophosphate and sodium hexaphosphate mainly provide the function of improving construction and workability, which can effectively disperse the bentonite particles in the bentonite slurry, solve the agglomeration problem of the bentonite particles, improve the fluidity of the bentonite slurry, and increase the fluidity, so that the barrier material slurry can be injected into the in-situ soil of the organic pollution source at a lower liquid-to-solid ratio.

[0014] The aforementioned method for preparing the vertical barrier material for high-concentration and high-risk organic pollution sources comprises the following steps: Step 1) Weigh the dry powders of commercial sodium-modified calcium-based bentonite, bentonite organic modifier, and bentonite viscosity reducer in the corresponding mass ratios mentioned above.

[0015] Step 2) Add the above dry powders into tap water in sequence, and continue stirring with a cement slurry mixer until the slurry is uniform to form a modified bentonite slurry. The liquid-to-solid ratio of the modified bentonite slurry is controlled according to the fluidity of the slurry. Generally speaking, the fluidity of the slurry is preferably controlled to be 150~250mm.

[0016] Step 3) Add the modified bentonite slurry in step 2) into the in-situ soil of the organic pollution source in a corresponding mass ratio, and continuously stir the mixture using a cement mortar mixer until the mixture has a uniform color to form the final vertical barrier material.

[0017] Among them: the particle size of commercial sodium modified bentonite is not less than 200 mesh, the free expansion volume is not less than 16ml / 2g, and the liquid limit is not less than 250%.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following specific beneficial effects: (1) The anti-seepage performance of the material under the stress of high-concentration and high-risk organic pollution sources meets the requirement that the organic matter permeability coefficient is less than 10 -7 cm / s anti-seepage requirement (Technical Specifications for Vertical Barriers of Industrial Polluted Sites (HG / T 20715-2020)): that is, when the organic pollutants in my country account for no more than 10% of the organic pollution sources, the permeability coefficient of the vertical barrier material can still be kept below 10 under the infiltration of contaminated soil from organic pollution sources and high-risk non-aqueous organic matter. -7 cm / s.

[0019] (2) The material has good construction and workability, and can be constructed through trenchless construction methods, thereby avoiding the volatile organic compounds generated during the construction process that harm human health and environmental safety: that is, under the same liquid-solid ratio conditions, the fluidity of the modified bentonite slurry is significantly improved compared to the fluidity of the traditional bentonite slurry. This makes it easier to pump the modified bentonite into the in-situ soil of the pollution source, solving the problem of difficult on-site engineering construction.

[0020] (3) The vertical barrier material only requires simple mixing during its preparation process, and does not require high temperature, high pressure and grinding treatment. It has good industrialization potential, is easy to construct on site, is convenient to process, and significantly reduces the implementation cost. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments: Example

[0022] The following is an example prepared based on the method for preparing vertical barrier materials for high-concentration and high-risk organic pollution sources, as shown in Table 1. Among them, the in-situ soil of the organic pollution source is self-made according to the situation that the maximum pollution concentration of organic pollution sources in known organic pollution sites in my country is not higher than 10% as mentioned above. Commercially available No. 0 diesel is set to simulate organic pollutants, and the pollutant concentration is set to 10% of the maximum pollutant concentration. The soil is sandy soil in the floodplain area of ​​the Yangtze River, that is, 10% diesel-contaminated sandy soil. The particle size of commercial sodium-modified bentonite is 200 mesh, the free expansion volume is 18ml / 2g, and the liquid limit is 262%. The purity of hydrogenated styrene-butadiene-styrene block copolymer is 98%, the styrene content is 29%, and the ash content is 0.8%; the purity of sodium tripolyphosphate is 98%. In order to explore the construction and workability, anti-seepage and blocking performance of vertical barrier materials for high-concentration and high-risk organic pollution sources, fluidity experiments, flexible wall penetration tests, and toxicity leaching tests were carried out. It should be noted that the construction and workability are for the modified bentonite slurry simulating trenchless construction, while the anti-seepage and retardation performance is for the final vertical barrier material formed.

[0023] Therefore, the present invention designs a series of comparison examples and embodiments of mud and vertical barrier materials. The comparison examples and embodiments of mud are shown in Table 1.

[0024] The mud-control example is composed of common commercial sodium-modified bentonite and tap water. The mud-embodiment example is composed of commercial sodium-modified calcium-based bentonite, bentonite organic modifier hydrogenated styrene-butadiene-styrene block copolymer, bentonite viscosity reducer sodium tripolyphosphate and tap water. Wherein, the content of tap water is designed to be 500% of the total dry mass in the mud material. The fluidity values ​​of the mud are shown in Table 1. The results show that the fluidity values ​​of the mud-embodiment example are significantly higher than the fluidity values ​​of the mud-control example. And the fluidity value increases significantly with the increase of sodium tripolyphosphate content, decreases significantly with the increase of bentonite content, and increases slightly with the increase of hydrogenated styrene-butadiene-styrene block copolymer content. This is attributed to the strong dispersibility of sodium tripolyphosphate, the strong water absorption of bentonite and the self-hydrophobicity of hydrogenated styrene-butadiene-styrene block copolymer. In addition, the fluidity values ​​of the mud-example and the mud-control example are both 150~250mm, indicating that the construction and workability of the mud can be achieved when the tap water content is designed to be 500% of the total dry mass of the mud material, and subsequent tests can be performed based on this water content.

[0025] Table 1 Mud fluidity values

[0026] The control examples and embodiments of the vertical barrier materials are shown in Table 2. It should be noted that the control examples and embodiments of the vertical barrier materials are composed of the corresponding control examples and embodiments of the mud in Table 1 and the in-situ soil of the organic pollution source.

[0027] Table 2 Design of vertical barrier material dosage (dry mass ratio)

[0028] In order to explore the anti-seepage performance of vertical barrier materials under high-concentration and high-risk organic pollution sources, a flexible wall penetration test was carried out. Commercially available No. 0 diesel was used as the pollutant penetration solution. The hydraulic gradient of penetration was controlled to be 50, the effective stress was 18.3 kPa, and finally the chemical solution penetration termination condition proposed by ASTM D7100 was achieved. See Table 2 for details. The permeability coefficients of the barrier materials in the embodiments all meet the requirements of less than 10 -9 m / s limit value requirement, and the permeability coefficient of the barrier material-control example cannot meet the limit value of less than 10 -9 The limit value requirement of m / s. The permeability coefficient of the barrier material-implementation example is about 3-4 orders of magnitude lower than the permeability coefficient of the barrier material-control example, which is mainly attributed to the excellent swelling ability, gel ability, adsorption ability and blocking ability of the hydrogenated styrene-butadiene-styrene block copolymer modified bentonite for organic pollutants. After the hydrogenated styrene-butadiene-styrene block copolymer modified bentonite absorbs diesel, a hydrogenated styrene-butadiene-styrene block copolymer composite bentonite gel is formed, which can effectively block the pores and significantly reduce the permeability coefficient of the barrier material. In addition, sodium tripolyphosphate plays a role in protecting the bentonite to a certain extent inside the barrier material, thereby appropriately reducing the permeability coefficient of the barrier material.

[0029] In order to further explore the environmental safety performance of vertical barrier materials for high-concentration and high-risk organic pollution sources, toxic leaching tests of control examples and embodiments of medium vertical barrier materials were carried out, that is, the leaching of non-aqueous phase organic matter in vertical barrier materials for high-concentration and high-risk organic pollution sources under deionized water immersion conditions. The specific test is to place the samples obtained from Examples 1 to 8 and Control Examples 1 to 2 in a chemically resistant 500-mesh stainless steel mesh, which can effectively wrap the barrier material without blocking the migration of the liquid, and soak it in deionized water for 7 days, test the total amount of organic matter leached from the barrier material and the proportion of the total amount of organic matter in the barrier material, and then judge the toxic leaching of the barrier material. Among them, the leaching rate of the barrier material-embodiment is 0, while the leaching rate of the barrier material-control example is between 11-36%. This is also attributed to the excellent swelling ability, gel ability, adsorption ability and blocking ability of hydrogenated styrene-butadiene-styrene block copolymer modified bentonite for organic pollutants.

[0030] In summary, the present invention discloses a vertical barrier material for high-concentration and high-risk organic pollution sources and a preparation method thereof. The novel vertical barrier material can directly utilize the soil of high-concentration and high-risk organic pollution sources and effectively block high-concentration organic pollutants.

[0031] It should be understood that the above is only a preferred embodiment of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, but these improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A vertical barrier material for high-concentration and high-risk organic pollution sources, characterized in that: include: Organically contaminated in-situ soil, commercial sodium-modified calcium-based bentonite, bentonite organic modifier, bentonite viscosity reducer; the mass ratio of the above four materials is 100:8~12:1~3:0.1~0.25; among them, the in-situ soil of the organic pollution source is obtained based on an in-situ non-excavation method.

2. A vertical barrier material for high-concentration and high-risk organic pollution sources according to claim 1, characterized in that: The particle size of commercial sodium modified bentonite shall not be less than 200 mesh, the free expansion shall not be less than 16ml / 2g, and the liquid limit shall not be less than 250%; The bentonite organic modifier is a hydrogenated styrene-butadiene-styrene block copolymer or a styrene-butadiene-styrene block copolymer, which is used to enhance the adsorption and expansion capacity of bentonite for organic matter; wherein the hydrogenated styrene-butadiene-styrene block copolymer has a purity of not less than 90%, a styrene content of not less than 18%, and an ash content of not more than 1%; The bentonite viscosity reducer is any one of sodium tripolyphosphate, sodium pyrophosphate and sodium hexaphosphate, with a phosphate content of not less than 65%, and is used to improve the fluidity of bentonite slurry.

3. The method for preparing a vertical barrier material for high-concentration and high-risk organic pollution sources according to claim 1, characterized in that: The following steps are involved: Step 1) weighing dry powders of commercial sodium-modified calcium-based bentonite, bentonite organic modifier, and bentonite viscosity reducer in corresponding mass ratios; Step 2) Add the above dry powders to tap water in sequence, and continue stirring with a cement slurry mixer until the slurry is uniform to form a modified bentonite slurry. The liquid-to-solid ratio of the modified bentonite slurry is controlled according to the fluidity of the slurry, and the fluidity of the slurry is controlled to be 150-250 mm; Step 3) Add the modified bentonite slurry in step 2) into the in-situ soil of the organic pollution source in a corresponding mass ratio, and continuously stir the mixture with a cement mortar mixer until the color of the mixture is uniform, thereby forming the final pollution source vertical barrier material.

4. Use of the vertical barrier material for high-concentration and high-risk organic pollution sources as described in claim 1 for blocking high-concentration and high-risk organic pollution sources.

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