Biochar-zero-valent iron enhanced bentonite-based vertical barrier material for combined polluted underground water as well as preparation method and application of biochar-zero-valent iron enhanced bentonite-based vertical barrier material

Abstract

The invention provides a biochar-zero-valent iron enhanced bentonite-based vertical barrier material for combined polluted underground water, which comprises sodium modified calcium bentonite and sandy soil, and also comprises biochar and slow-release zero-valent iron particles, and the slow-release zero-valent iron particles are formed by mixing and stirring micron-sized zero-valent iron and sodium alginate. Related preparation methods and uses are also provided. The anti-seepage performance of the biochar-zero-valent iron enhanced bentonite-based vertical barrier material for combined polluted underground water meets the anti-seepage requirement that the permeability coefficient is lower than 10 <-9 > cm / s under the stress of heavy metal, chlorinated hydrocarbon and micro-plastic combined polluted underground water, heavy metal can be effectively reduced and precipitated, chlorinated hydrocarbon is dechlorinated, and micro-plastic is adsorbed; therefore, the concentration of composite pollutants in underground water is reduced, and the long-acting performance of the vertical barrier material is improved.

Description

Technical Field

[0001] The present invention relates to the fields of environmental engineering and geotechnical engineering technology, and in particular to the field of groundwater vertical barrier material technology, specifically to a biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater, and its preparation method and application. Background Art

[0002] Through resource integration, technological collaboration, and policy innovation, industrial parks have not only enhanced the intensiveness of industrial production but also become important vehicles for high-quality regional economic development, playing a key role in promoting industrial upgrading and sustainable development. However, due to inadequate anti-seepage measures at the bottom of some industrial parks, illegal wastewater discharge, rainwater erosion, or accidental leaks, a variety of pollutants have entered the groundwater. During their migration, these pollutants undergo physical adsorption, chemical reactions, or bioaccumulation, resulting in complex pollution, further exacerbating groundwater ecological risks and making remediation more difficult.

[0003] In industrial parks with dense concentrations of industries such as chemical engineering, metallurgy, electronics manufacturing, and plastics processing, groundwater is commonly contaminated by a combination of heavy metals (such as arsenic, lead, and cadmium), chlorinated hydrocarbon organic pollutants (such as trichloroethylene and tetrachloroethylene), and microplastics. This pollution primarily stems from wastewater discharge, material leakage, and solid waste landfills during industrial production. Heavy metals primarily originate from process wastewater from smelting and electroplating, while chlorinated hydrocarbons primarily come from production processes such as solvent cleaning and chemical synthesis. Microplastics enter groundwater through waste from plastic product processing and industrial wastewater containing plastic additives.

[0004] The above three types of pollutants form a complex pollution system in groundwater through physical adsorption, chemical complexation and biofilm enrichment. Microplastics act as carriers to adsorb heavy metals and organic pollutants due to their high specific surface area and hydrophobicity. Their synergistic migration effect significantly enhances the environmental persistence and ecotoxicity of pollutants. The redox reaction of chlorinated hydrocarbons and heavy metal arsenic may change the toxic form, posing a complex threat to groundwater quality safety and surrounding ecological receptors.

[0005] Existing treatment technologies are mostly designed for single pollutants, and have problems such as low treatment efficiency, high cost and secondary pollution. In addition, research on the synergistic migration mechanism, ecotoxicological effects and joint treatment technologies of pollutants in complex pollution systems is still insufficient. There is an urgent need to develop efficient, in-situ treatment materials for groundwater heavy metal-chlorinated hydrocarbon-microplastic complex pollution to meet the urgent needs of groundwater environmental governance.

[0006] Bentonite-based vertical barrier technology, a core engineering measure for groundwater pollution control at industrial sites, offers significant advantages in controlling single pollution sources by constructing a dense physical barrier to block pollutant migration pathways. However, this technology presents significant performance degradation risks when faced with high concentrations of heavy metals, chlorinated hydrocarbons, and microplastics in groundwater. Heavy metal ions can cause chemical corrosion and structural damage to the barrier material, chlorinated hydrocarbons can easily penetrate traditional barrier materials through molecular diffusion and dissolution, and microplastics can alter the pore structure and permeability of the barrier material through physical blockage and interfacial adsorption. The synergistic effects of these three types of pollutants not only accelerate the barrier material's failure process but also create "preferred flow pathways" for pollutant migration, resulting in a more than 50% reduction in the barrier performance of traditional barrier materials against complex pollution systems. Therefore, there is an urgent need to develop modified bentonite barrier materials with enhanced barrier properties for combined heavy metal, chlorinated hydrocarbon, and microplastic pollution.

[0007] Zero-valent iron (ZVI) groundwater remediation technology has become a research hotspot in the field of groundwater remediation due to its efficient reduction and degradation capabilities for organic pollutants and its reduction and precipitation effects on heavy metals. However, existing zero-valent iron technology still faces bottlenecks such as limited reaction rate, easy clogging of pore structure, and long-term passivation and deactivation during engineering applications, and there is a lack of systematic research on the synergistic transformation mechanism of pollutants in complex composite pollution systems. Therefore, there is an urgent need to develop a new zero-valent iron composite material system that has both efficient reaction activity, anti-clogging ability and long-term stability to break through the limitations of traditional technologies and provide innovative solutions for the deep treatment of composite contaminated groundwater in industrial pollution sites.

[0008] Biochar has significant advantages in the remediation of groundwater contamination by heavy metals, chlorinated hydrocarbons and microplastics due to its porous structure, high specific surface area and abundant surface functional groups: its surface functional groups can effectively adsorb heavy metal ions (such as Pb 2 +、Cd 2 +), the porous structure has a physical interception effect on microplastics, and can also act as an electron donor to promote the biodegradation or chemical reduction reaction of chlorinated hydrocarbons. However, the adsorption capacity of biochar for hydrophobic chlorinated hydrocarbons is limited, and its performance is easily degraded due to heavy metal saturation or organic coverage during long-term operation. In addition, there is a lack of systematic research on the synergistic / antagonistic effects between pollutants in complex pollution systems, making it difficult to achieve simultaneous and efficient removal of multiple pollutants. Therefore, there is an urgent need for breakthroughs through material modification, functional design or combined remediation technologies.

[0009] Therefore, facing the application scenario of high-concentration heavy metal, chlorinated hydrocarbon and microplastic composite pollution in groundwater, biochar, zero-valent iron and bentonite all have their own advantages and disadvantages; however, the combined development of the three into new materials has the application prospect of being suitable for the isolation of high-concentration composite pollution in groundwater. Therefore, the development of biochar-zero-valent iron reinforced bentonite barrier materials with both anti-seepage and adsorption properties is of great significance. Summary of the Invention

[0010] In order to overcome the shortcomings of the above-mentioned prior art, one object of the present invention is to provide a biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater, which has an anti-seepage performance under the stress of composite contaminated groundwater of heavy metals, chlorinated hydrocarbons and microplastics, and a permeability coefficient of less than 10 -9 cm / s anti-seepage requirements, can effectively reduce and precipitate heavy metals, dechlorinate chlorinated hydrocarbons and adsorb microplastics, thereby reducing the concentration of complex pollutants in groundwater, improving the long-term performance of vertical barrier materials, and is suitable for large-scale promotion and application.

[0011] Another object of the present invention is to provide a method for preparing a biochar-zero valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater. The anti-seepage performance of the biochar-zero valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater prepared by the method meets the requirements of a permeability coefficient of less than 10 -9 cm / s anti-seepage requirements, can effectively reduce and precipitate heavy metals, dechlorinate chlorinated hydrocarbons and adsorb microplastics, thereby reducing the concentration of complex pollutants in groundwater, improving the long-term performance of vertical barrier materials, and is suitable for large-scale promotion and application.

[0012] Another object of the present invention is to provide an application of a biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater. The biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater is used to vertically block groundwater contaminated by heavy metals, chlorinated hydrocarbons and microplastics, and the anti-seepage performance meets the permeability coefficient of less than 10 -9 cm / s anti-seepage requirements, can effectively reduce and precipitate heavy metals, dechlorinate chlorinated hydrocarbons and adsorb microplastics, thereby reducing the concentration of complex pollutants in groundwater, improving the long-term performance of vertical barrier materials, and is suitable for large-scale promotion and application.

[0013] To achieve the above objectives, in a first aspect of the present invention, a biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater is provided, comprising sodium-modified calcium-based bentonite and sand. The barrier material further comprises biochar-loaded slow-release zero-valent iron, wherein:

[0014] The biochar-loaded slow-release zero-valent iron is prepared by the following method:

[0015] (1) mixing micron-sized zero-valent iron and sodium alginate and stirring to obtain sustained-release zero-valent iron particles;

[0016] (2) The biochar and the slow-release zero-valent iron particles are mixed and stirred to obtain the biochar-loaded slow-release zero-valent iron.

[0017] Preferably, the mass ratio of the sodium-modified calcium-based bentonite, the biochar and the slow-release zero-valent iron particles is 100:30:7.5, the mass ratio of the micron-sized zero-valent iron and the sodium alginate is 6:1, and the ratio of the total mass of the sodium-modified calcium-based bentonite, the biochar and the slow-release zero-valent iron particles to the mass of the sand is 1:10.

[0018] Preferably, the particle size of the sodium-modified calcium-based bentonite is less than 0.075 mm, the free expansion capacity of the sodium-modified calcium-based bentonite is not less than 15 ml / 2 g, the 30 min filtration loss of the sodium-modified calcium-based bentonite is not higher than 14 mL, and the liquid limit of the sodium-modified calcium-based bentonite is not less than 200%.

[0019] Preferably, the carbon content of the biochar is 60% to 70% by weight, and the specific surface area of ​​the biochar is between 300m 2 / g~1000m 2 / g, and the mesopore ratio of the biochar is between 30% and 50%.

[0020] Preferably, the purity of the micron-sized zero-valent iron is not less than 90%, the particle size of the micron-sized zero-valent iron is between 10 μm and 100 μm, and the specific surface area of ​​the micron-sized zero-valent iron is between 1 m 2 / g~ / g.

[0021] Preferably, the purity of the sodium alginate is not less than 95%, and the viscosity of a 1% by weight aqueous solution of sodium alginate at 20° C. is between 50 mPa·s and 300 mPa·s.

[0022] In a second aspect of the present invention, a method for preparing the above-mentioned biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater is provided, which is characterized by comprising the following steps:

[0023] (A) mixing the biochar-loaded slow-release zero-valent iron and the sodium-modified calcium-based bentonite and stirring to obtain biochar-zero-valent iron-enhanced bentonite;

[0024] (B) uniformly mixing the biochar-zero-valent iron enhanced bentonite and the sand.

[0025] Preferably, in step (A), the stirring speed is between 300 rpm and 500 rpm, and the stirring time is 60 minutes.

[0026] In the third aspect of the present invention, a biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater is provided, which is characterized in that it is prepared using the above-mentioned preparation method of the biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater.

[0027] In a fourth aspect of the present invention, there is provided an application of the above-mentioned biochar-zero-valent iron reinforced bentonite-based vertical barrier material for compositely contaminated groundwater in vertically blocking groundwater compositely contaminated by heavy metals, chlorinated hydrocarbons and microplastics.

[0028] The beneficial effects of the present invention are mainly:

[0029] 1. The biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater of the present invention comprises sodium-modified calcium-based bentonite and sand, and also comprises biochar-loaded slow-release zero-valent iron. The biochar-loaded slow-release zero-valent iron is prepared by the following method: (1) mixing micron-sized zero-valent iron and sodium alginate and stirring to obtain slow-release zero-valent iron particles; (2) mixing biochar and slow-release zero-valent iron particles and stirring to obtain biochar-loaded slow-release zero-valent iron. The biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater of the present invention has an anti-seepage performance that satisfies the permeability coefficient of less than 10 under the stress of composite contaminated groundwater of heavy metals, chlorinated hydrocarbons and microplastics. -9 cm / s anti-seepage requirements, can effectively reduce and precipitate heavy metals, dechlorinate chlorinated hydrocarbons and adsorb microplastics, thereby reducing the concentration of complex pollutants in groundwater, improving the long-term performance of vertical barrier materials, and is suitable for large-scale promotion and application.

[0030] 2. The preparation method of the biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater of the present invention comprises the following steps: (A) mixing biochar-loaded slow-release zero-valent iron and sodium-modified calcium-based bentonite and stirring to obtain biochar-zero-valent iron-enhanced bentonite; (B) uniformly mixing the biochar-zero-valent iron-enhanced bentonite and sand. The anti-seepage performance of the biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater prepared by this method meets the permeability coefficient of less than 10 -9 cm / s anti-seepage requirements, can effectively reduce and precipitate heavy metals, dechlorinate chlorinated hydrocarbons and adsorb microplastics, thereby reducing the concentration of complex pollutants in groundwater, improving the long-term performance of vertical barrier materials, and is suitable for large-scale promotion and application.

[0031] 3. The application of the biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater of the present invention in vertically blocking heavy metal, chlorinated hydrocarbon and microplastic composite contaminated groundwater, and the anti-seepage performance satisfies the permeability coefficient of less than 10 -9 cm / s anti-seepage requirements, can effectively reduce and precipitate heavy metals, dechlorinate chlorinated hydrocarbons and adsorb microplastics, thereby reducing the concentration of complex pollutants in groundwater, improving the long-term performance of vertical barrier materials, and is suitable for large-scale promotion and application.

[0032] These and other objects, features and advantages of the present invention are fully reflected in the following detailed description and drawings, and can be achieved by the means, devices and their combinations particularly pointed out in the summary of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 3 is a graph showing the change in permeability coefficient of the vertical barrier materials of Examples 1 to 3 and Comparative Examples 1 to 3.

[0034] Figure 2 It is a curve chart of the adsorption rate change of heavy metals, chlorinated hydrocarbons and microplastics by the vertical barrier materials of Examples 1 to 3 and Comparative Examples 1 to 3, wherein the three rectangular columns in each example or comparative example represent the adsorption rates of heavy metals, chlorinated hydrocarbons and microplastics respectively. DETAILED DESCRIPTION

[0035] In order to solve the problem of anti-seepage failure and insufficient adsorption of traditional vertical barrier materials in high-concentration heavy metal, chlorinated hydrocarbon and microplastic composite pollution scenarios, and to provide a new solution for emergency control and long-term treatment of high-risk composite contaminated groundwater, the inventors conducted in-depth and extensive research on traditional sodium-modified calcium-based bentonite, biochar and zero-valent iron (ZVI), and thus proposed a biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater. Its anti-seepage performance under the stress of heavy metal, chlorinated hydrocarbon and microplastic composite contaminated groundwater meets the permeability coefficient of less than 10 -9 cm / s anti-seepage requirements (Technical Specifications for Vertical Barriers in Industrial Polluted Sites (HG / T 20715-2020)), which can effectively reduce and precipitate heavy metals, dechlorinate chlorinated hydrocarbons, and adsorb microplastics, thereby reducing the concentration of complex pollutants in groundwater and improving the long-term performance of vertical barrier materials.

[0036] The present invention first provides a biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater, comprising sodium-modified calcium-based bentonite and sand. The biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater also includes biochar-loaded slow-release zero-valent iron, wherein:

[0037] The biochar-loaded slow-release zero-valent iron is prepared by the following method:

[0038] (1) mixing micron-sized zero-valent iron and sodium alginate and stirring to obtain sustained-release zero-valent iron particles;

[0039] (2) The biochar and the slow-release zero-valent iron particles are mixed and stirred to obtain the biochar-loaded slow-release zero-valent iron.

[0040] Micron-sized ZVI is dry-mixed with sodium alginate to form slow-release zero-valent iron particles. The gel formed by sodium alginate in water has strong encapsulation properties, fully encapsulating the ZVI particles and allowing for their slow release. This inhibits ZVI particle aggregation, enhances their mobility, improves their ability to reduce and precipitate heavy metals, and dechlorinate chlorinated hydrocarbons, thereby extending their service life. Biochar not only increases the dispersibility of the slow-release ZVI particles by loading them, creating a synergistic effect, but also absorbs microplastics through electrostatic and anchoring interactions.

[0041] The mass ratio of the sodium-modified calcium-based bentonite, the biochar and the slow-release zero-valent iron particles, the mass ratio of the micron-sized zero-valent iron and the sodium alginate, and the ratio of the total mass of the sodium-modified calcium-based bentonite, the biochar and the slow-release zero-valent iron particles to the mass of the sand can be determined as needed. Preferably, the mass ratio of the sodium-modified calcium-based bentonite, the biochar and the slow-release zero-valent iron particles is 100:30:7.5, the mass ratio of the micron-sized zero-valent iron and the sodium alginate is 6:1, and the ratio of the total mass of the sodium-modified calcium-based bentonite, the biochar and the slow-release zero-valent iron particles to the mass of the sand is 1:10.

[0042] The particle size, free expansion volume, 30-min filtration loss and liquid limit of the sodium-modified calcium-based bentonite can be determined as needed. Preferably, the particle size of the sodium-modified calcium-based bentonite is less than 0.075 mm, the free expansion volume of the sodium-modified calcium-based bentonite is not less than 15 ml / 2 g, the 30-min filtration loss of the sodium-modified calcium-based bentonite is not higher than 14 mL, and the liquid limit of the sodium-modified calcium-based bentonite is not less than 200%.

[0043] The carbon content, specific surface area and mesopore ratio (particle size is between 2nm and 50nm) of the biochar can be determined as needed. Preferably, the carbon content of the biochar is 60% by weight to 70% by weight, and the specific surface area of ​​the biochar is between 300m 2 / g~1000m 2 / g, the mesopore ratio of the biochar is between 30% and 50%. The surface of the biochar has a rough structure such as gullies, wrinkles, and protrusions, and biochar derived from lignocellulose (sawdust, straw, etc.) is preferred.

[0044] The purity, particle size and specific surface area of ​​the micron-sized zero-valent iron can be determined as needed. Preferably, the purity of the micron-sized zero-valent iron is not less than 90%, the particle size of the micron-sized zero-valent iron is between 10 μm and 100 μm, and the specific surface area of ​​the micron-sized zero-valent iron is between 1 m 2 / g~5m 2 / g.

[0045] The purity of the sodium alginate and the viscosity of a 1% by weight aqueous solution of sodium alginate at 20°C can be determined as needed. Preferably, the purity of the sodium alginate is not less than 95% (analytical grade), and the viscosity of a 1% by weight aqueous solution of sodium alginate at 20°C is between 50 mPa·s and 300 mPa·s.

[0046] In the step (1), the stirring speed and time can be determined as needed. Preferably, in the step (1), the stirring speed is between 300 rpm and 500 rpm, and the stirring time is 30 minutes.

[0047] In the step (2), the stirring speed and time can be determined as needed. Preferably, in the step (2), the stirring speed is between 300 rpm and 500 rpm, and the stirring time is 30 minutes.

[0048] The present invention also provides a method for preparing the above-mentioned biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater, comprising the following steps:

[0049] (A) mixing the biochar-loaded slow-release zero-valent iron and the sodium-modified calcium-based bentonite and stirring to obtain biochar-zero-valent iron-enhanced bentonite;

[0050] (B) uniformly mixing the biochar-zero-valent iron enhanced bentonite and the sand.

[0051] In the step (A), the stirring speed and time can be determined as needed. Preferably, in the step (A), the stirring speed is between 300 rpm and 500 rpm, and the stirring time is 60 minutes.

[0052] The present invention also provides a biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater, which is prepared using the above-mentioned method for preparing the biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater.

[0053] The present invention also provides an application of the above-mentioned biochar-zero-valent iron reinforced bentonite-based vertical barrier material for compositely contaminated groundwater in vertically blocking groundwater compositely contaminated by heavy metals, chlorinated hydrocarbons and microplastics.

[0054] In order to more clearly understand the technical content of the present invention, the following examples are specifically described in detail. It should be understood that the specific examples described herein are merely illustrative of the present invention and are not intended to limit the present invention. Unless otherwise stated, the instruments, drugs, reagents, etc. used in the following examples can be obtained by conventional commercial means.

[0055] In the Examples and Comparative Examples:

[0056] The sandy soil is selected from the floodplain area of ​​the Yangtze River, dried in an oven at 105°C for 24 hours, and then sieved through a 2mm diameter sieve to obtain the sandy soil that passes through the sieve.

[0057] Example 1

[0058] The biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater was prepared by the following method:

[0059] Step 1) Preparation of sustained-release zero-valent iron: Micronized ZVI (secondary reduced iron powder, Jinan Xingming Industry and Trade Co., Ltd.) and biopolymer sodium alginate (Yuanfeng Chemical Sodium Alginate, Shaoguan Chengfeng Chemical Co., Ltd.) were weighed at a mass ratio of 6:1 and mixed in a beaker. The mixture was stirred at 300 rpm for 30 minutes to obtain sustained-release zero-valent iron particles. The micronized zero-valent iron had a purity of 98%, a particle size of 200 mesh (0.075 mm), and a specific surface area of ​​3 m 2 / g; Sodium alginate purity is 98%, and the viscosity of a solution formed by dissolving 1% sodium alginate in water at 20°C is 180mPa·s;

[0060] Step 2) Preparation of biochar-loaded slow-release zero-valent iron: The slow-release zero-valent iron particles prepared in step 1) were mixed with biochar (Henan Xingnuo Environmental Protection Materials Co., Ltd., Xingnuo Biochar) at a mass ratio of 1:4 in a beaker, and stirred at 400 rpm for 30 minutes to obtain biochar-loaded slow-release zero-valent iron, wherein the biochar contained 70% carbon by weight and had a specific surface area of ​​800 m 2 / g, the mesopores (particle size between 2nm and 50nm) of the biochar account for 45%, the surface has rough structures such as gullies, wrinkles, and protrusions, and the biochar is sourced from wheat straw;

[0061] Step 3) Preparing biochar-zero-valent iron-enhanced bentonite: The biochar-loaded slow-release zero-valent iron prepared in step 2) and sodium-modified calcium-based bentonite (common commercial sodium-modified calcium-based bentonite from Jurong Mufeng Bentonite Processing Plant) were mixed in a beaker at a mass ratio of 37.5:100, and stirred at 500 rpm for 60 minutes to obtain a biochar-zero-valent iron-enhanced bentonite, wherein the sodium-modified calcium-based bentonite had a particle size of less than 0.075 mm, a free expansion capacity of 16 ml / 2 g, a 30-min filtration loss of no more than 12.5 mL, and a liquid limit of 212%;

[0062] Step 4) Preparation of biochar-zero-valent iron-enhanced bentonite barrier material: The biochar-zero-valent iron-enhanced bentonite prepared in step 3) is evenly mixed with sand in a mass ratio of 1:10, and an appropriate amount of tap water is added to obtain the final biochar-zero-valent iron-enhanced bentonite barrier material.

[0063] Example 2

[0064] The biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater was prepared by the following method:

[0065] Step 1) Preparation of sustained-release zero-valent iron: Weigh micron-sized ZVI (AVIC Zhongmai flagship store, AVIC Zhongmai high-purity iron powder) and biopolymer sodium alginate (Shaoguan Chengfeng Chemical Co., Ltd., Yuanfeng Chemical Sodium Alginate) at a mass ratio of 6:1, mix in a beaker, and stir at 400 rpm for 30 minutes to obtain sustained-release zero-valent iron particles. The micron-sized zero-valent iron has a purity of 95%, a particle size of 150 mesh, and a specific surface area of ​​2 m 2 / g; the purity of sodium alginate is 98%, and the viscosity of a solution formed by dissolving 1% sodium alginate in water at 20°C is 180mPa·s;

[0066] Step 2) Preparation of biochar-loaded slow-release zero-valent iron: The slow-release zero-valent iron particles prepared in step 1) were mixed with biochar (Henan Coconut Carbon Environmental Protection Materials Co., Ltd., Coconut Carbon Beauty Biochar) at a mass ratio of 1:4 in a beaker, and stirred at 500 rpm for 30 minutes to obtain biochar-loaded slow-release zero-valent iron, wherein the biochar contained 60% carbon by weight and had a specific surface area of ​​600 m 2 / g, the mesopores (particle size ranges from 2nm to 50nm) of the biochar account for 38%, and the surface has rough structures such as gullies, wrinkles, and protrusions. The biochar is sourced from rice husks;

[0067] Step 3) Preparing biochar-zero-valent iron-enhanced bentonite: The biochar-loaded slow-release zero-valent iron prepared in step 2) and sodium-modified calcium-based bentonite (common commercial sodium-modified calcium-based bentonite from Jurong Mufeng Bentonite Processing Plant) were mixed in a beaker at a mass ratio of 37.5:100, and stirred at 400 rpm for 60 minutes to obtain a biochar-zero-valent iron-enhanced bentonite, wherein the sodium-modified calcium-based bentonite had a particle size of less than 0.075 mm, a free expansion volume of 16 ml / 2 g, a 30-min filtration loss of no more than 12.5 mL, and a liquid limit of 212%;

[0068] Step 4) Preparation of biochar-zero-valent iron-enhanced bentonite barrier material: The biochar-zero-valent iron-enhanced bentonite prepared in step 3) is evenly mixed with sand in a mass ratio of 1:10, and an appropriate amount of tap water is added to obtain the final biochar-zero-valent iron-enhanced bentonite barrier material.

[0069] Example 3

[0070] The biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater was prepared by the following method:

[0071] Step 1) Preparation of sustained-release zero-valent iron: Micronized ZVI (secondarily reduced iron powder, Jinan Xingming Industry and Trade Co., Ltd.) and biopolymer sodium alginate (Yuanfeng Chemical Sodium Alginate, Shaoguan Chengfeng Chemical Co., Ltd.) were weighed at a mass ratio of 6:1 and mixed in a beaker. The mixture was stirred at 500 rpm for 30 minutes to obtain sustained-release zero-valent iron particles. The micronized zero-valent iron had a purity of 98%, a particle size of 200 mesh (0.075 mm), and a specific surface area of ​​3 m 2 / g; Sodium alginate purity is 98%, and the viscosity of a solution formed by dissolving 1% sodium alginate in water at 20°C is 180mPa·s;

[0072] Step 2) Preparation of biochar-loaded slow-release zero-valent iron: The slow-release zero-valent iron particles prepared in step 1) were mixed with biochar (Henan Coconut Carbon Environmental Protection Materials Co., Ltd., Coconut Carbon Beauty Biochar) at a mass ratio of 1:4 in a beaker, and stirred at 300 rpm for 30 minutes to obtain biochar-loaded slow-release zero-valent iron, wherein the biochar contained 60% carbon by weight and had a specific surface area of ​​600 m 2 / g, the mesopores (particle size ranges from 2nm to 50nm) of the biochar account for 38%, and the surface has rough structures such as gullies, wrinkles, and protrusions. The biochar is sourced from rice husks;

[0073] Step 3) Preparing biochar-zero-valent iron-enhanced bentonite: The biochar-loaded slow-release zero-valent iron prepared in step 2) and sodium-modified calcium-based bentonite (common commercial sodium-modified calcium-based bentonite from Jurong Mufeng Bentonite Processing Plant) were mixed in a beaker at a mass ratio of 37.5:100, and stirred at 300 rpm for 60 minutes to obtain a biochar-zero-valent iron-enhanced bentonite, wherein the sodium-modified calcium-based bentonite had a particle size of less than 0.075 mm, a free expansion capacity of 16 ml / 2 g, a 30-min filtration loss of no more than 12.5 mL, and a liquid limit of 212%;

[0074] Step 4) Preparation of biochar-zero-valent iron-enhanced bentonite barrier material: The biochar-zero-valent iron-enhanced bentonite prepared in step 3) is evenly mixed with sand in a mass ratio of 1:10, and an appropriate amount of tap water is added to obtain the final biochar-zero-valent iron-enhanced bentonite barrier material.

[0075] Comparative Example 1

[0076] Without adding biochar-loaded slow-release zero-valent iron, the sodium-modified calcium-based bentonite (same as in Example 1) and sand (same as in Example 1) were evenly mixed to obtain a bentonite-based vertical barrier material that was not reinforced with biochar-loaded slow-release zero-valent iron, wherein the mass ratio of the sodium-modified calcium-based bentonite to the sand was 1:10.

[0077] Comparative Example 2

[0078] The sustained-release zero-valent iron (same as in Example 1) and the sodium-modified calcium-based bentonite (same as in Example 1) were mixed in a beaker at a mass ratio of 37.5:100, and stirred at 500 rpm for 60 minutes to obtain zero-valent iron-enhanced bentonite; the prepared zero-valent iron-enhanced bentonite was evenly mixed with sand at a mass ratio of 1:10, and an appropriate amount of tap water was added to obtain the final zero-valent iron-enhanced bentonite barrier material.

[0079] Comparative Example 3

[0080] Biochar (same as in Example 1) and sodium-modified calcium-based bentonite (same as in Example 1) were mixed in a beaker at a mass ratio of 37.5:100, and stirred at 500 rpm for 60 minutes to obtain biochar-enhanced bentonite; the prepared biochar-enhanced bentonite was evenly mixed with sand at a mass ratio of 1:10, and an appropriate amount of tap water was added to obtain the final biochar-enhanced bentonite barrier material.

[0081] Example 4

[0082] To investigate the anti-seepage and adsorption properties of vertical barrier materials under the stress of groundwater contaminated by a combination of heavy metals, chlorinated hydrocarbons, and microplastics, flexible wall permeation tests and batch adsorption tests were conducted. The combined contaminated groundwater was simulated by calcium chloride solution at a concentration of 20 mmol / L for heavy metals, trichloroethylene at a concentration of 50 mg / L for chlorinated hydrocarbons, and polyethylene at a concentration of 50 mg / L for microplastics. Uncontaminated groundwater was simulated by deionized water.

[0083] (1) In order to explore the anti-seepage performance of vertical barrier materials under the stress of groundwater contaminated by heavy metals, chlorinated hydrocarbons and microplastics, a flexible wall penetration test was carried out. The penetration solutions were simulated solutions of uncontaminated and compositely contaminated groundwater, respectively. The hydraulic gradient of penetration was controlled to be 10 and the effective stress was 15 kPa. The termination conditions of the test met the chemical solution penetration requirements proposed by ASTM D7100.

[0084] The vertical barrier materials of Examples 1 to 3 and Comparative Examples 1 to 3 were mixed with water and then placed into the sample chamber of the flexible wall permeameter. The test was started according to the hydraulic gradient, effective stress and permeation solution as above. The permeability coefficient results of each vertical barrier material are shown in Figure 1 The results show that under the infiltration of uncontaminated groundwater simulation solution, the comparative examples 1 to 3 and examples 1 to 3 are all lower than 10 -9 m / s; However, under the stress of composite contaminated groundwater simulation solution, the values ​​of Examples 1 to 3 were still lower than 10 -9 m / s, wherein the higher the purity of zero-valent iron, the smaller the particle size, the larger the specific surface area, and the greater the carbon content of biochar, the larger the specific surface area, and the larger the proportion of mesopores, the lower the permeability coefficient of the corresponding enhanced bentonite-based vertical barrier material; while Comparative Examples 1 to Comparative Examples 3 exceed the specified value requirements, among which the permeability coefficient of Comparative Example 3 is slightly lower than that of Comparative Example 2, and both are lower than Comparative Example 1.

[0085] (2) In order to explore the adsorption performance of vertical barrier materials under the stress of groundwater contaminated by heavy metals, chlorinated hydrocarbons and microplastics, a batch adsorption test was carried out. The batch adsorption test referred to the ASTM D4646 specification. The test solution was a simulated solution of composite contaminated groundwater, and the solid-liquid ratio was controlled at 1:20.

[0086] The vertical barrier materials of Examples 1 to 3 and Comparative Examples 1 to 3 were mixed with water and stirred. An appropriate amount was weighed and poured into a 250 mL plastic bottle. Then, heavy metal, chlorinated hydrocarbon and microplastic composite contaminated groundwater with a corresponding solid-liquid ratio was added. The mixture was shaken for 24 hours, and the supernatant was then taken to test the concentrations of heavy metals, chlorinated hydrocarbons and microplastics. The adsorption results of various pollutants by each vertical barrier material are shown in Figure 2. Figure 2The adsorption rates of Examples 1 to 3 are similar, among which the higher the purity of zero-valent iron, the smaller the particle size, the larger the specific surface area, and the greater the carbon content, the larger the specific surface area, and the larger the proportion of mesopores in the biochar, the higher the adsorption rate of the corresponding enhanced bentonite-based vertical barrier material; the adsorption rates of Comparative Examples 1 to 3 are generally low. Compared with Comparative Example 1, Comparative Example 2 significantly increases the adsorption rate of heavy metals and chlorinated hydrocarbons, and Comparative Example 3 significantly increases the adsorption rate of microplastics.

[0087] Therefore, the present invention discloses a biochar-zero-valent iron-enhanced bentonite-based barrier material for composite contaminated groundwater and its preparation method. The biochar-loaded slow-release zero-valent iron effectively reduces the concentration of heavy metals, chlorinated hydrocarbons, and microplastics in groundwater, greatly enhancing the anti-seepage and adsorption properties of the bentonite-based vertical barrier material for composite contaminated groundwater, improving its long-term performance, and solving the problems of anti-seepage failure and insufficient adsorption of traditional barrier materials in scenarios of composite contamination by heavy metals, chlorinated hydrocarbons, and microplastics, providing a new solution for emergency control and long-term management of high-risk composite contaminated groundwater by heavy metals, chlorinated hydrocarbons, and microplastics.

[0088] Compared with the existing technology, the present invention achieves synergistic anti-seepage adsorption of groundwater contaminated by heavy metals, chlorinated hydrocarbons, and microplastics through the innovative design of biochar-zero-valent iron reinforced bentonite-based vertical barrier materials. The specific advantages are as follows:

[0089] (1) By preparing slow-release zero-valent iron, the micron-sized ZVI particles are slowly released, effectively inhibiting their agglomeration, enhancing their mobility, and improving the zero-valent iron's ability to reduce and precipitate heavy metals and dechlorinate chlorinated hydrocarbons in groundwater, thereby reducing the concentrations of heavy metals and chlorinated hydrocarbons in groundwater and improving the long-term performance of zero-valent iron.

[0090] (2) By preparing biochar loaded with slow-release zero-valent iron, the high specific surface area, porous structure and rough surface characteristics of biochar are used to carry slow-release zero-valent iron, thereby increasing its dispersion and synergistically enhancing its efficiency. At the same time, biochar absorbs microplastics through electrostatic and anchoring effects, thereby reducing the concentration of microplastics in groundwater.

[0091] (3) By improving bentonite with biochar-loaded slow-release zero-valent iron, the concentrations of heavy metals, chlorinated hydrocarbons, and microplastics in groundwater were reduced, thereby solving the problem of high-concentration complex pollution stressing bentonite. This enabled the bentonite to have both anti-seepage barrier and adsorption capabilities, greatly expanding the application scenarios of biochar-zero-valent iron enhanced bentonite.

[0092] In summary, the biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater of the present invention has an anti-seepage performance that satisfies the requirement of a permeability coefficient of less than 10 under the stress of composite contaminated groundwater of heavy metals, chlorinated hydrocarbons and microplastics. -9cm / s anti-seepage requirements, can effectively reduce and precipitate heavy metals, dechlorinate chlorinated hydrocarbons and adsorb microplastics, thereby reducing the concentration of complex pollutants in groundwater, improving the long-term performance of vertical barrier materials, and is suitable for large-scale promotion and application.

[0093] It can be seen that the objectives of the present invention have been fully and effectively achieved. The functional and structural principles of the present invention have been demonstrated and illustrated in the embodiments. The embodiments may be modified as desired without departing from the principles described. Therefore, the present invention includes all variations within the spirit and scope of the claims.

Claims

1. A biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater, comprising sodium-modified calcium-based bentonite and sand, characterized in that: The biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater also includes biochar-loaded slow-release zero-valent iron, wherein: The biochar-loaded slow-release zero-valent iron is prepared by the following method: (1) mixing micron-sized zero-valent iron and sodium alginate and stirring to obtain sustained-release zero-valent iron particles; (2) The biochar and the slow-release zero-valent iron particles are mixed and stirred to obtain the biochar-loaded slow-release zero-valent iron.

2. The biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater according to claim 1, characterized in that: The mass ratio of the sodium-modified calcium-based bentonite, the biochar and the slow-release zero-valent iron particles is 100:30:7.5, the mass ratio of the micron-sized zero-valent iron and the sodium alginate is 6:1, and the ratio of the total mass of the sodium-modified calcium-based bentonite, the biochar and the slow-release zero-valent iron particles to the mass of the sand is 1:

10.

3. The biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater according to claim 1, characterized in that: The particle size of the sodium-modified calcium-based bentonite is less than 0.075 mm, the free expansion capacity of the sodium-modified calcium-based bentonite is not less than 15 ml / 2 g, the 30 min filtration loss of the sodium-modified calcium-based bentonite is not higher than 14 mL, and the liquid limit of the sodium-modified calcium-based bentonite is not less than 200%.

4. The biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater according to claim 1, characterized in that: The carbon content of the biochar is 60% to 70% by weight, and the specific surface area of ​​the biochar is between 300m 2 / g~1000m 2 / g, and the mesopore ratio of the biochar is between 30% and 50%.

5. The biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater according to claim 1, characterized in that: The purity of the micron-sized zero-valent iron is not less than 90%, the particle size of the micron-sized zero-valent iron is between 10 μm and 100 μm, and the specific surface area of ​​the micron-sized zero-valent iron is between 1 m 2 / g~5m 2 / g.

6. The biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater according to claim 1, characterized in that: The purity of the sodium alginate is not less than 95%, and the viscosity of a 1% by weight sodium alginate aqueous solution at 20° C. is between 50 mPa·s and 300 mPa·s.

7. A method for preparing a biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater according to any one of claims 1 to 6, characterized in that: The following steps are involved: (A) mixing the biochar-loaded slow-release zero-valent iron and the sodium-modified calcium-based bentonite and stirring to obtain biochar-zero-valent iron-enhanced bentonite; (B) uniformly mixing the biochar-zero-valent iron enhanced bentonite and the sand.

8. The preparation method according to claim 7, wherein In the step (A), the stirring speed is between 300 rpm and 500 rpm, and the stirring time is 60 minutes.

9. A biochar-zero-valent iron-enhanced bentonite-based vertical barrier material for composite contaminated groundwater, characterized in that: The barrier material is prepared by the method for preparing a biochar-zero-valent iron reinforced bentonite-based vertical barrier material for composite contaminated groundwater according to any one of claims 7 to 8.

10. Use of a biochar-zero-valent iron reinforced bentonite-based vertical barrier material for compositely contaminated groundwater as described in any one of claims 1 to 6 and claim 9 in vertically blocking groundwater compositely contaminated by heavy metals, chlorinated hydrocarbons and microplastics.

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