A polymer-modified soil composite anti-seepage material and its on-site heat-source-free synthesis method

Abstract

The present invention provides a polymer-modified soil composite anti-seepage material and an on-site heat-source-free synthesis method thereof. The on-site heat-source-free synthesis method of the polymer-modified soil composite anti-seepage material of the present invention comprises the following steps: mixing water, anionic polymer monomer A, polymer monomer B containing a hydrophilic group, a cross-linking agent, bentonite, an initiator, and a filler, and reacting to obtain an anti-seepage material. The present invention adopts an oxidation-reduction initiation system to initiate in-situ polymerization of the hydrophilic polymer monomer between bentonite crystal sheets, and can be directly synthesized under engineering site conditions, eliminating the trouble of heating and passing inert gas in traditional preparation methods, and does not require drying, crushing, screening and other operations. It not only ensures the integrity of the polymer network and obtains more excellent anti-seepage performance, but also greatly simplifies the preparation process and shortens the preparation time. The present invention overcomes the shortcomings of existing modified bentonite anti-seepage materials, such as cumbersome preparation, long time consumption, and high cost.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental geotechnical engineering, and in particular to a polymer-modified soil composite anti-seepage material and an on-site heat-source-free synthesis method thereof. Background Art

[0002] The main component of bentonite is montmorillonite crystals, with a chemical composition of Al2O3·4SiO2·3H2O. It is a 2:1 layered aluminosilicate composed of two layers of silicon-oxygen tetrahedrons sandwiching a layer of aluminum-oxygen octahedrons. The octahedrons and tetrahedrons are connected by shared oxygen atoms. The geometric space between the montmorillonite crystal layers is called the interlayer domain, with a width of 0.96 to 2.14 nm. This layered stacking structure gives bentonite a specific surface area of ​​600 to 800 m 2 / g. According to the different cations in the interlayer domain, bentonite is divided into calcium-based bentonite, sodium-based bentonite and sodium calcium-based bentonite. The surface of bentonite is negatively charged and can adsorb water or other polar molecules into the interlayer domain through weak interactions, thereby expanding the interlayer domain of montmorillonite. As the number of water molecules adsorbed between the layers increases, the montmorillonite sheets gradually separate and osmotic swelling occurs, which is manifested macroscopically as the volume expansion of the bentonite particles. Due to the high specific surface area and high expansion multiple of bentonite, it is often used as the core material of anti-seepage and pollution interception materials (such as soil-bentonite vertical barrier walls, geosynthetic clay liners (GCLs), compacted clay liners, etc.) in environmental geotechnical engineering. It is widely used in industrial solid waste landfills, domestic waste landfills, tailings ponds and various contaminated sites to prevent the migration of pollutants within the site and avoid pollution to the surrounding environment. However, the water absorption and expansion properties of natural bentonite materials are significantly reduced under corrosive conditions such as high salt, strong acid, and strong alkali, resulting in a significant deterioration of their anti-seepage barrier properties and an inability to form an effective anti-fouling barrier. They need to be modified to achieve an effective anti-seepage effect.

[0003] There are two main methods for modifying bentonite: physical bentonite-polymer blending and in-situ bentonite polymerization. Physical bentonite-polymer blending involves mixing bentonite and a hydrophilic polymer in a dry state to create a bentonite-polymer composite (BPC). When used for barrier purposes, the polymer absorbs and swells in water or saline solution, forming a gel that fills the gaps between bentonite particles, making the composite more compact and achieving excellent barrier properties. Tian et al. (K. Tian, ​​WJ Likos, CH Benson. Polymer Elution and Hydraulic Conductivity of Bentonite-Polymer Composite Geosynthetic ClayLiners. Journal of Geotechnical and Geoenvironmental Engineering, 2019, 145(10): 04019071) tested the anti-seepage performance of GCL made of BPC and natural sodium bentonite (Sodium Bentonite, NaB), respectively. The results showed that the permeability coefficient of BPC GCL to chemical solutions was 1 to 4 orders of magnitude lower than that of NaB GCL. SEM images showed that the blockage of bentonite pores by polymer hydrogel was the reason for the lower permeability coefficient of BPC GCL. The physical blending method can make up for the disadvantage of insufficient swelling of bentonite particles in chemical solutions, but the interfacial effect between bentonite and polymer in BPC materials is weak, and serious polymer elution problems are prone to occur in actual engineering use, that is, the polymer is separated from the pores of bentonite, which greatly deteriorates its anti-seepage barrier properties (C.Wire, T.Abichou.Investigating Factors InfluencingPolymer Elution And The Mechanism Controlling The Chemical Compatibility OfGCLs Containing Linear Polymers.Geotextiles and Geomembranes, 2021, 49(4):1004-1018). In situ polymerization modification of bentonite refers to inserting monomers, initiators and catalysts into the interlayers of montmorillonite crystals, and then initiating monomer polymerization. The polymer overcomes the Coulomb force between the montmorillonite sheets and stretches them apart to obtain intercalated or even stripped polymer in situ modified bentonite.In-situ polymerization-modified bentonite has excellent anti-seepage properties and is not prone to polymer elution like BPC. However, since free radicals are highly sensitive to oxygen, they are usually synthesized under an inert environment. The in-situ preparation process requires the bentonite raw materials, which are originally in a dry powder state, to be re-wetted, stirred, heated, reacted, dried, crushed, screened, and other processes. The operation is cumbersome, time-consuming, costly, and only suitable for factory production. The crushing process will also destroy the polymer network between the montmorillonite flakes, thereby affecting the anti-seepage performance of the polymer-modified bentonite anti-seepage material.

[0004] In summary, it is necessary to invent a new modification method that can avoid the shortcomings of the above two types of modification methods and combine the advantages of the two methods, that is, a polymer-modified bentonite solution that has a simple preparation process, excellent anti-seepage performance, is not prone to polymer elution, and is suitable for large-scale direct preparation at engineering sites. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides an on-site heat-source-free synthesis method of a polymer-modified soil composite anti-seepage material. The method utilizes a redox initiation system to generate free radicals at room temperature or even low temperature, and can initiate in-situ polymerization of polymerization monomers between bentonite layers without additional heating. The reducing agent can consume the oxygen in the reaction system, so the polymerization process does not need to be carried out under an inert atmosphere. At the same time, the resulting product does not need to undergo drying, crushing, screening and other procedures before it can be directly poured into an anti-seepage barrier. The preparation process is simple, the anti-seepage performance is excellent, the cost is low, and there is no need for pre-production in a factory. Instead, it is suitable for large-scale preparation directly at the engineering site.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a formula of a polymer-modified soil composite anti-seepage material, comprising the following raw materials: water, anionic polymer monomer A, polymer monomer B containing a hydrophilic group, a cross-linking agent, bentonite, an initiator, and a filler.

[0008] Preferably, the anion of the anionic polymerizable monomer A comprises at least one of a sulfonate group and a carboxylate group;

[0009] The carboxylate group includes at least one of acrylate, methacrylate, and maleate.

[0010] Preferably, the hydrophilic group of the hydrophilic group-containing polymer monomer B includes at least one of an amino group and a quaternary amino group.

[0011] Preferably, the anionic polymerizable monomer A comprises at least one of sodium acrylate and sodium methacrylate;

[0012] The polymerizable monomer B includes at least one of 2-acrylamide-2-methylpropanesulfonic acid and dimethylaminoethyl acrylate.

[0013] Preferably, the crosslinking agent includes at least one of N,N'-vinylbisacrylamide, N,N'-methylenebisacrylamide, diacetone acrylamide, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, caprolactone acrylate, alginate acrylate, and divinylbenzene.

[0014] Preferably, the bentonite includes at least one of sodium bentonite, calcium bentonite, and sodium calcium bentonite.

[0015] Preferably, the initiator is a redox initiator, which includes an oxidizing agent and a reducing agent, and the oxidizing agent includes at least one of hydrogen peroxide, persulfate, and hydroperoxide;

[0016] The reducing agent includes at least one of ferrous salts, cuprous salts, sodium bisulfite, sodium sulfite, sodium thiosulfate, alcohol, amine, oxalic acid, and glucose;

[0017] The mass ratio of the oxidizing agent to the reducing agent is (0.05-10):1;

[0018] And / or, the filler includes at least one of graded fine sand, graded tailings sand, graded silt, graded construction waste, and graded engineering slag; the average particle size d of the filler is 50 It is 0.1mm~1mm.

[0019] Preferably, the mass ratio of the water to the bentonite is (0.5-10):1;

[0020] The mass ratio of the anionic polymerizable monomer A to the hydrophilic group-containing polymerizable monomer B is (10-800):30;

[0021] The mass ratio of the anionic polymerizable monomer A to the cross-linking agent is (100-900):1;

[0022] The mass ratio of the initiator to the anionic polymerization monomer A is (0.05-5):100;

[0023] The mass ratio of the filler to the bentonite is (0-90):10;

[0024] The mass ratio of the anionic polymerization monomer A to the water is (5-20):100.

[0025] In a second aspect, the present invention further provides an on-site heat-source-free synthesis method of the polymer-modified soil composite anti-seepage material, comprising the following steps:

[0026] Water, anionic polymer monomer A, polymer monomer B containing hydrophilic groups, crosslinking agent, bentonite, initiator and filler are mixed and reacted to obtain polymer modified soil composite anti-seepage material.

[0027] Preferably, the reaction temperature is 5-60°C.

[0028] The polymer-modified soil composite anti-seepage material and its on-site heat-source-free synthesis method of the present invention have the following beneficial effects compared with the prior art:

[0029] 1. The present invention provides a method for directly synthesizing a polymer-modified soil composite anti-seepage material in the absence of a heat source at a construction site. The method uses a redox initiation system to replace the thermal initiation system used in conventional polymer-modified bentonite synthesis methods. On the one hand, the redox initiation system generates free radicals from an initiator through redox reactions, significantly reducing the activation energy. Thus, free radicals that initiate monomer polymerization can be generated at lower temperatures, making the method suitable for heat-free preparation at construction sites. On the other hand, the reducing agent in the redox initiation system consumes oxygen in the reaction system, allowing free radicals that are highly sensitive to oxygen to initiate polymerization normally, eliminating the need for the polymerization process to be conducted under an inert atmosphere.

[0030] 2. The on-site heat-source-free synthesis method of the polymer-modified clay composite anti-seepage material provided by the present invention does not require drying, crushing, screening, and other processes during its preparation. On the one hand, the drying and crushing processes will destroy the polymer network structure, thereby affecting the anti-seepage barrier performance of the material; on the other hand, the drying, crushing, screening, and other series of processes are time-consuming, energy-consuming, and costly. Especially when preparing in large quantities, it is extremely difficult to quickly crush and screen the product. The polymer-modified bentonite anti-seepage material prepared according to the present invention can be directly used in anti-seepage barrier systems, significantly reducing the number of steps, lowering costs, shortening time, and improving efficiency. Test results show that it has excellent anti-seepage barrier performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0032] Figure 1 Schematic diagram of the reaction mechanism of polymer-modified bentonite in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be understood as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0036] The embodiment of the present application provides a polymer-modified soil composite anti-seepage material, which includes the following raw materials: water, anionic polymer monomer A, polymer monomer B containing hydrophilic groups, a cross-linking agent, bentonite, an initiator, and a filler.

[0037] In some embodiments, the anion of the anionic polymerizable monomer A comprises at least one of a sulfonate group and a carboxylate group;

[0038] The carboxylate group includes at least one of acrylate, methacrylate, and maleate.

[0039] In some embodiments, the hydrophilic group of the hydrophilic group-containing polymeric monomer B includes at least one of an amino group and a quaternary amino group.

[0040] In some embodiments, the anionic polymerizable monomer A comprises at least one of sodium acrylate and sodium methacrylate;

[0041] The polymerizable monomer B includes at least one of 2-acrylamide-2-methylpropanesulfonic acid and dimethylaminoethyl acrylate.

[0042] Specifically, the anions in the anionic polymerizable monomer A can electrostatically interact with the cations between the montmorillonite sheets, allowing them to be adsorbed into the interlayer domains of the montmorillonite, achieving in situ polymerization. The hydrophilic group in the hydrophilic monomer B is at least one of an amino group and a quaternary amino group. Hydrophilic groups are atomic groups that readily associate with water, significantly enhancing the hydrophilicity of the polymer-modified bentonite, thereby improving the impermeability and barrier properties of the modified bentonite.

[0043] In some embodiments, the crosslinking agent includes at least one of N,N'-vinylbisacrylamide, N,N'-methylenebisacrylamide, diacetone acrylamide, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, caprolactone acrylate, alginate acrylate, and divinylbenzene. The crosslinking agent forms a crosslinked network with the polymer through covalent bonds, thereby increasing the stability and mechanical strength of the polymer.

[0044] In some embodiments, the bentonite comprises at least one of sodium bentonite, calcium bentonite, and sodium calcium bentonite.

[0045] In some embodiments, the initiator is a redox initiator, which includes an oxidizing agent and a reducing agent, wherein the oxidizing agent includes at least one of hydrogen peroxide, a persulfate (such as ammonium persulfate), and a hydroperoxide;

[0046] The reducing agent includes at least one of ferrous salts, cuprous salts, sodium bisulfite, sodium sulfite, sodium thiosulfate, alcohol, amine, oxalic acid, and glucose;

[0047] The mass ratio of the oxidant to the reducing agent is (0.05-10):1.

[0048] Specifically, the redox initiator has a low activation energy and can generate free radicals at a lower temperature, thereby initiating in situ polymerization of the monomer without heating. At the same time, the reducing agent will also consume oxygen in the system, so that the polymerization process no longer needs to be carried out under an inert atmosphere.

[0049] In some embodiments, the filler comprises at least one of graded fine sand, graded tailings sand, graded silt, graded construction waste, and graded engineering slag; the average particle size of the filler is d 50 It is 0.1mm~1mm.

[0050] In some embodiments, the filler is at least one of graded fine sand, graded tailings sand, graded silt, graded construction waste, and graded engineering slag, and its maximum particle size is less than 3 mm and the average particle size d 50 It is between 0.1mm and 1mm, and has good gradation (uniformity coefficient Cu>6, gradation coefficient Cc is between 1 and 3).

[0051] In some embodiments, the mass ratio of water to bentonite is (0.5-10):1;

[0052] The mass ratio of the anionic polymerizable monomer A to the hydrophilic group-containing polymerizable monomer B is (10-800):30;

[0053] The mass ratio of anionic polymerization monomer A to crosslinking agent is (100-900):1;

[0054] The mass ratio of the initiator to the anionic polymerization monomer A is (0.05-5):100;

[0055] The mass ratio of filler to bentonite is (0-90):10;

[0056] The mass ratio of anionic polymerization monomer A to water is (5-20):100.

[0057] Based on the same inventive concept, the present invention also provides an on-site heat-source-free synthesis method of the above-mentioned polymer-modified soil composite anti-seepage material, comprising the following steps:

[0058] Water, anionic polymer monomer A, polymer monomer B containing hydrophilic groups, crosslinking agent, bentonite, initiator and filler are mixed and reacted to obtain polymer modified soil composite anti-seepage material.

[0059] In some embodiments, the reaction temperature is 5-60°C.

[0060] In some embodiments, the on-site heat-free synthesis method of the above-mentioned polymer-modified soil composite anti-seepage material includes the following steps: adding water, anionic polymerization monomer A, polymerization monomer B containing hydrophilic groups, cross-linking agent, bentonite, initiator, and filler into a reaction container, mixing and stirring thoroughly until uniform, and pouring the mixture directly into the bottom lining anti-seepage layer, the top covering anti-seepage layer, the vertical barrier wall and other anti-seepage barriers, and after sufficient reaction, a polymer-modified soil composite anti-seepage material with excellent anti-seepage performance can be obtained.

[0061] The present invention provides a method for directly synthesizing a polymer-modified soil composite anti-seepage material in the absence of a heat source at a construction site. The method uses a redox initiation system to replace the thermal initiation system of the existing traditional polymer-modified bentonite synthesis method. On the one hand, the redox initiation system causes an initiator to generate free radicals through redox reactions, and its activation energy is greatly reduced. Therefore, free radicals that initiate monomer polymerization can be generated at a lower temperature, which is suitable for heat-free preparation at the construction site. On the other hand, the reducing agent in the redox initiation system can consume oxygen in the reaction system, so that free radicals that are highly sensitive to oxygen can normally initiate polymerization, eliminating the need for the polymerization process to be carried out under an inert atmosphere. The on-site heat-free synthesis method of the polymer-modified soil composite anti-seepage material provided by the present invention does not require drying, crushing, screening and other processes during its preparation. On the one hand, the drying and crushing processes will destroy the polymer network structure, thereby affecting the anti-seepage barrier properties of the material. On the other hand, the series of processes such as drying, crushing, and screening are time-consuming, energy-consuming, and costly. In particular, when large-scale preparation is carried out, rapid crushing and screening of the product is extremely difficult. The polymer-modified bentonite anti-seepage material prepared according to the present invention can be directly applied to the anti-seepage barrier system, which greatly reduces the number of processes, reduces costs, shortens time, and improves efficiency. Test results show that it has excellent anti-seepage barrier performance.

[0062] The following further describes the on-site heat-free synthesis method of the polymer-modified soil composite anti-seepage material of the present application with specific examples. This section further illustrates the present invention in conjunction with specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means adopted in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0063] Example 1

[0064] The present invention provides an on-site heat-free synthesis method of a polymer-modified soil composite anti-seepage material, comprising the following steps:

[0065] Add 100 mL of water to a three-mouth reaction kettle, then add 16.826 g of sodium acrylate, 2.46 g of 2-acrylamide-2-methylpropanesulfonic acid, 0.058 g of triethylene glycol dimethacrylate, and then add 45 g of sodium calcium bentonite (without fillers such as graded sand). After sufficient stirring, add 0.289 g of ammonium persulfate and 0.289 g of sodium bisulfite and stir until uniform. The mixture is fully reacted at room temperature (25°C) to obtain a synthesized polymer-modified soil composite anti-seepage material.

[0066] Example 2

[0067] The present invention provides an on-site heat-free synthesis method of a polymer-modified soil composite anti-seepage material, comprising the following steps:

[0068] 1L of water was added to the three-mouthed reactor, followed by 130.85g of sodium methacrylate, 19.13g of dimethylaminoethyl acrylate, 0.45g of N-N'methylenebisacrylamide, 450g of sodium calcium bentonite, 3600g of graded sand (average particle size d 50 The obtained composite anti-seepage material is prepared by adding 0.25 g hydrogen peroxide and 0.25 g sodium thiosulfate after thorough stirring and stirring until uniform. The obtained composite anti-seepage material is obtained by thorough reaction at room temperature (25°C).

[0069] Example 3

[0070] The present invention provides an on-site heat-free synthesis method of a polymer-modified soil composite anti-seepage material, comprising the following steps:

[0071] 100 mL of water was added to the three-mouthed reactor, followed by 9.8154 g of sodium methacrylate, 1.435 g of dimethylaminoethyl acrylate, 0.034 g of N-N'methylenebisacrylamide, and then 45 g of sodium calcium bentonite, 270 g of graded tailings sand (average particle size d 50 The obtained composite anti-seepage material is prepared by adding 0.169 g of hydrogen peroxide and 0.169 g of sodium thiosulfate after thorough stirring and stirring until uniform. The obtained composite anti-seepage material is obtained by thorough reaction at room temperature (25°C).

[0072] Comparative Example 1

[0073] This comparative example provides a method for synthesizing a polymer-modified bentonite anti-seepage material, comprising the following steps:

[0074] Under a nitrogen atmosphere, 100 mL of water was added to a three-necked reactor, followed by 16.826 g of sodium acrylate, 2.46 g of 2-acrylamide-2-methylpropanesulfonic acid, and 0.058 g of triethylene glycol dimethacrylate. 45 g of sodium calcium bentonite was added, stirred thoroughly, and 0.578 g of ammonium persulfate was added and stirred until uniform. The reactor was placed in a 70 ° C oil bath for full reaction, and the reaction product was taken out, dried, ground, and sieved. The polymer-modified bentonite was uniformly mixed in a mass ratio of 1:1 with a mesh size of 100 to 200 mesh and above 200 mesh to obtain a polymer-modified bentonite anti-seepage material.

[0075] The preparation method of the polymer-modified bentonite in this comparative example is basically the same as that in Example 1, except that this comparative example does not use a redox initiation system, but instead initiates polymerization by heating, and it is necessary to ensure that the reaction system is an oxygen-free environment, and the product needs to be dried, crushed, and sieved to obtain the polymer-modified bentonite anti-seepage material.

[0076] Comparative Example 2

[0077] This comparative example provides a method for synthesizing a polymer-modified bentonite anti-seepage material, comprising the following steps:

[0078] 5.13 mL (3 g) of acrylic acid and 8.7 mL of 0.2 g / mL sodium hydroxide were added to 36.3 mL of water. After acid-base neutralization, 0.04 g of N,N'-vinylbisacrylamide and 3 g of N,N'-diethylacrylamide were added and stirred until completely dissolved. 60 g of calcium bentonite was added and vigorously stirred under a nitrogen atmosphere to mix the solution and bentonite evenly. 0.108 g of ammonium persulfate was added and reacted at room temperature for 3 h to obtain a product. The product was dried, crushed and sieved to obtain a polymer-modified bentonite anti-seepage material.

[0079] The preparation method of the polymer-modified bentonite described in this comparative example is similar to that in Example 1 in that neither method requires heating to initiate the polymerization reaction. The differences are: 1) the initiation mechanisms of the two are different; 2) this comparative example requires a series of operations such as drying, grinding, and screening of the product to obtain a polymer-modified bentonite anti-seepage material that can be used in engineering projects.

[0080] Comparative Example 3

[0081] This comparative example provides a method for synthesizing a polymer-modified bentonite anti-seepage material, comprising the following steps:

[0082] 18.8 mL of acrylic acid and 38.8 mL of 0.2 g / mL sodium hydroxide were added to 111 mL of water. After acid-base neutralization, 0.1 g of N-N' vinyl bisacrylamide was added and stirred until completely dissolved. 60 g of calcium bentonite was added and vigorously stirred under a nitrogen atmosphere to mix the solution and bentonite evenly. 0.36 g of ammonium persulfate was added and the temperature was raised to 70°C. The reaction was carried out for 3 h to obtain a product. The product was dried, crushed and sieved to obtain a polymer-modified bentonite anti-seepage material.

[0083] The preparation method of the polymer-modified bentonite described in this comparative example differs from that in Example 1 in that: 1) the initiation mechanisms of the two are different, and 2) the comparative example requires a series of operations such as drying, grinding, and screening of the product to obtain a polymer-modified bentonite anti-seepage material that can be used in engineering.

[0084] Performance Testing

[0085] The permeability coefficient of the polymer-modified bentonite was tested using deionized water, sodium hydroxide solution (pH = 12), nitric acid solution (pH = 3), and artificially synthesized coal combustion product leachate (ionic strength I = 178 mM), wherein the coal combustion product leachate was synthesized by dissolving reagent-grade CaSO4, Na2SO4, MgSO4, K2SO4, NaCl, and CaCl2 in deionized water, and its chemical composition is shown in Table 1; the permeability coefficient was determined by a flexible wall permeability test according to the decreasing head and constant tail method in ASTM D5084, a standard developed by the American Society for Testing and Materials. The permeability coefficients of the polymer-modified bentonite anti-seepage materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2.

[0086] Table 1 - Chemical composition of coal combustion product leachate

[0087]

[0088] Table 2 - Permeability coefficients of anti-seepage materials prepared in different embodiments

[0089]

[0090] The preparation methods of the anti-seepage materials in Examples 1 to 3 and Comparative Examples 1 to 3 are compared as shown in Table 3 below.

[0091] Table 3 - Comparison of preparation methods of anti-seepage materials in different embodiments

[0092]

[0093]

[0094] As can be seen from Table 2, the permeability coefficients of the four different permeates in the examples and comparative examples are all lower than the 5×10 -11m / s, and the anti-seepage performance of the embodiment is better than that of the comparative example. Comparative Examples 1 and 3 adopt a thermal initiation system, as shown in Table 3. The preparation process needs to ensure an inert atmosphere, and the initiator is decomposed by heating to generate free radicals to initiate polymerization. The product needs to be dried, crushed, and sieved to obtain the modified bentonite anti-seepage material. The preparation process is cumbersome, time-consuming and energy-consuming, and costly, and is not suitable for large-scale preparation on the engineering site. In comparison, the present invention has more advantages, namely, the application of a redox initiation system reduces the reaction activation energy, so that the synthesis can be carried out without a heat source, and the reducing agent can react with oxygen to ensure the activity of free radicals that are highly sensitive to oxygen in the reaction system. After synthesis, there is no need for drying, crushing, or sieving. It can be directly applied to the anti-seepage and anti-fouling barrier on the engineering site, has more excellent anti-seepage barrier performance, and its permeability coefficient is about 10 times lower than that of Comparative Examples 1 and 3. In Comparative Example 2, a free radical reaction accelerator is selected to decompose the initiator to produce free radicals. No heating is required, but the preparation must be carried out under an inert atmosphere, and the product must be dried, crushed, and sieved. According to the permeability coefficient measurement results in Table 2, the permeability coefficient of Example 1 is significantly lower than that of Comparative Example 2, which indicates that the drying, crushing, and screening processes have an adverse effect on the anti-seepage performance. Further, it is speculated that the drying and crushing processes will destroy the polymer network structure and reduce the structural integrity of the composite material. In comparison, the present invention has more excellent anti-seepage barrier properties.

[0095] Further, Figure 1 Schematic diagram of the reaction mechanism of polymer-modified bentonite in Example 1 of the present invention.

[0096] from Figure 1 It can be seen that the Na + , Ca 2+ Electrostatic adsorption is generated, and the polymer monomer 2-acrylamide-2-methylpropanesulfonic acid containing hydrophilic groups and the cross-linking agent triethylene glycol dimethacrylate are uniformly dispersed in the montmorillonite layer domain. At the same time, the redox initiation system generates free radicals in the initiator (NH4)2S2O8 through redox action and initiates the polymerization of the monomer between the montmorillonite layer domains. Under the action of the cross-linking agent, a polymer network is formed to obtain a polymer in-situ modified bentonite nano-composite anti-seepage material.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for synthesizing a polymer-modified soil composite anti-seepage material on-site without heat source, characterized in that: The following steps are involved: Mixing water, anionic polymer monomer A, polymer monomer B containing a hydrophilic group, a crosslinking agent, bentonite, an initiator, and a filler, and reacting the mixture to obtain a polymer-modified soil composite anti-seepage material; The anionic polymerizable monomer A comprises at least one of sodium acrylate and sodium methacrylate; The polymerizable monomer B includes at least one of 2-acrylamide-2-methylpropanesulfonic acid and dimethylaminoethyl acrylate; The cross-linking agent includes at least one of N,N'-methylenebisacrylamide and triethylene glycol dimethacrylate; The initiator is a redox initiator, which includes an oxidizing agent and a reducing agent, and the oxidizing agent includes at least one of hydrogen peroxide and ammonium persulfate; The reducing agent includes at least one of sodium bisulfite and sodium thiosulfate; The mass ratio of the oxidizing agent to the reducing agent is (0.05-10):1; The filler comprises at least one of graded fine sand, graded tailings sand, graded silt, graded construction waste, and graded engineering slag; the average particle size of the filler is d 50 0.1mm~1mm; The mass ratio of the water to the bentonite is (0.5-10):1; The mass ratio of the anionic polymerizable monomer A to the hydrophilic group-containing polymerizable monomer B is (10-800):30; The mass ratio of the anionic polymerizable monomer A to the cross-linking agent is (100-900):1; The mass ratio of the initiator to the anionic polymerization monomer A is (0.05-5):100; The mass ratio of the filler to the bentonite is (0-90):10; The mass ratio of the anionic polymerization monomer A to the water is (5-20):

100.

2. The on-site heat-free synthesis method of the polymer-modified soil composite anti-seepage material according to claim 1, characterized in that: The reaction temperature is 5-60°C.

3. The on-site heat-free synthesis method of the polymer-modified soil composite anti-seepage material according to claim 1, characterized in that: The bentonite includes at least one of sodium-based bentonite, calcium-based bentonite, and sodium-calcium-based bentonite.

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