Polymer modified bentonite, method for preparing the same, and polymer modified bentonite gasket

Abstract

The application belongs to the technical field of anti-seepage materials, and discloses a polymer modified bentonite and a preparation method thereof.The method is as follows: bentonite is slurried by adding water, then acrylamide is added, and a composite initiator is added under stirring at 5-20 DEG C to react for 60-150 min; a mixed emulsion is added dropwise, the dropwise adding time is 5-7 h, and the reaction is continued for 30-60 min, and the product is dried to obtain the polymer modified bentonite.The mixed emulsion is prepared by preparing a mixed solution with a total mass concentration of 5-15 wt% of polyacrylamide, an emulsifier and polyacrylonitrile, and dispersing the mixed solution into a mixed emulsion with a particle size of 100-500 nm.The application further provides a gasket containing the polymer modified bentonite.The polymer modified bentonite prepared by the preparation method has good salt resistance, good anti-seepage effect and good stability, and the polymer modified bentonite gasket prepared therefrom is suitable for anti-seepage and isolation of a landfill or a roadbed.

Description

Technical Field

[0001] This invention belongs to the field of seepage prevention materials technology, and particularly relates to polymer-modified bentonite, its preparation method and polymer-modified bentonite lining. Background Technology

[0002] Bentonite, due to its expansibility, adsorption, and ion exchange capacity, is widely used in engineering, environmental, and civil engineering fields, especially in landfills, where bentonite liners are commonly used for seepage prevention, providing reliable and long-term protection for groundwater, air, and soil. However, traditional bentonite liners only perform well in clean water. In actual landfill sites, there are often pollutants such as inorganic salts and organic matter. When traditional bentonite is soaked in these pollutants, it loses water and shrinks, increasing porosity and reducing its barrier properties, leading to poorer or even ineffective seepage prevention. Furthermore, bentonite liners around landfills are also subject to erosion by rainwater, causing bentonite particles to separate, settle, and aggregate, further increasing pore size and leading to side leakage. In addition, as transportation engineering extends to special soil areas such as cold regions, saline soil regions, and soft soil regions, roadbed engineering faces problems such as moisture migration, salt erosion, and frost heave deformation. While natural bentonite has low permeability, its performance deteriorates easily under high salinity and complex environmental conditions, making it unsuitable for use in roadbeds. Summary of the Invention

[0003] The purpose of this invention is to provide a polymer-modified bentonite that is resistant to leaching and salt immersion, and has good seepage prevention effect.

[0004] The technical solution of this invention is as follows: A method for preparing polymer-modified bentonite includes the following steps: Step 1: Add water to bentonite to make a slurry, and adjust its pH to 6.5-7.5; then add acrylamide, stir to dissolve and mix evenly, and continue stirring for at least 15 minutes. The amount of acrylamide added is 0.25-1.0 wt% of the bentonite. The temperature is maintained at 5-20℃, and the composite initiator is added while stirring at 300-600 rpm, so that the content of the composite initiator in the reaction system is 0.1-1.0 wt%, and the reaction is carried out for 60-150 minutes; the composite initiator is a mixture of redox initiator and azo initiator; Step 2: Add the mixed emulsion dropwise to the reaction system over a period of 5-7 hours. After the addition is complete, continue the reaction for 30-60 minutes. Throughout the reaction process, maintain the temperature of the reaction system at 5-20°C and keep the stirring speed at 300-600 rpm. The method for preparing the mixed emulsion is as follows: Weigh acrylamide, emulsifier, and polyacrylonitrile, wherein the acrylamide is 0.75-9.0 wt% of bentonite, the polyacrylonitrile is 1.0-4.0 wt% of bentonite, and the emulsifier is 0.5-1.5 wt% of bentonite; dissolve acrylamide and emulsifier in water to form solution A, dissolve polyacrylonitrile in an organic solvent to form solution B, mix solutions A and B to form a mixed liquid with a total mass concentration of 5-15 wt% of polyacrylamide, emulsifier, and polyacrylonitrile, and homogenize under high pressure or disperse by ultrasonication to prepare a mixed emulsion with a diameter of 100-500 nm; Step 3: Freeze-dry or low-temperature vacuum-dry the product to obtain polymer-modified bentonite.

[0005] In the preparation method of polymer-modified bentonite of the present invention, in step one, acrylamide monomer is directly introduced into the aqueous slurry of bentonite. Acrylamide diffuses in the solution and enters the crystal layers of bentonite with water molecules, binding with bentonite through hydrogen bonds and intermolecular forces to form active centers for polymerization. After adding an initiator, at a low temperature of 5-20°C, the uniformly dispersed active centers slowly polymerize to form short-chain polyacrylamide. These short-chain polyacrylamides are inserted between the crystal layers of bentonite, becoming active reaction sites for further grafting and chain extension. In step two, a mixed emulsion is added dropwise to the reaction system. The emulsifier in the mixed emulsion emulsifies acrylamide and polyacrylonitrile into small droplets of 100-500 nm. During the dropwise addition, the small emulsion droplets come into contact with the active reaction sites of the short-chain polyacrylamide, resulting in graft polymerization and block polymerization. The insertion of polyacrylonitrile increases the mechanical strength of the polymer. The slow, controlled dropwise addition allows for a slow and controlled reaction rate, thus favoring the grafting and chain-promoting reaction. A low stirring speed of 300-600 rpm further promotes the increase of the polymer's molecular weight. Additionally, the addition of polyacrylonitrile reduces the self-polymerization rate of acrylamide, facilitating the formation of longer-chain polymers. In the resulting polymer-modified bentonite, the polymer is embedded between the bentonite crystal layers, held in place by the interlayer structure, and firmly bonded to the bentonite, filling the micropores of the bentonite particles. This polyacrylonitrile-grafted acrylamide polymer forms a three-dimensional network structure, firmly wrapping and encapsulating the bentonite, preventing the gel structure from collapsing and segregating due to water erosion. When used for seepage prevention, the bentonite absorbs water and, under the constraint of the polymer network, expands to a limited extent into a gel-like viscous state, preventing water molecules from passing through and forming a relatively dense water-blocking layer. Due to the constraint of the polymer network structure, the structure is dense, and Na... + Ca 2+ It is difficult for metal ions to enter, thus avoiding the exchange between external metal ions and interlayer ions, preventing external metal ions from damaging the water-blocking layer, playing a good anti-seepage role, and facilitating the anti-seepage of polymer-modified bentonite under high salt conditions and salt leaching resistance.

[0006] Preferably, in step two, the mixed emulsion is added at a variable rate: 1 / 6 of the total amount of mixed emulsion is added in the first 1 / 3 of the time period, 1 / 3 of the total amount of mixed emulsion is added in the middle 1 / 3 of the time period, and 1 / 2 of the total amount of mixed emulsion is added in the last 1 / 3 of the time period.

[0007] By adding the mixed emulsion using a variable-rate dropping method, the orderly addition of the reactive monomer acrylamide is controlled, and the amount of acrylamide monomer added is gradually increased. This ensures that the reaction is most favorable for increasing polymer chain length during the first 1 / 3 of the time period at the lowest concentration, which helps to grow a strong network structure, improves the density and rigidity of the network structure, improves the overall impermeability and stability, and reduces the risk of bentonite particles swelling and being lost in water. The acrylamide monomer added at a faster rate in the later stage is conducive to the generation of new shorter-chain polymers that fill the micropores and network structure of the bentonite particles, which is more conducive to the formation of a filled water-blocking layer.

[0008] Preferably, the emulsifier is carboxymethyl cellulose, hydroxypropyl cellulose, or a salt of both. The organic solvent for polyacrylonitrile can be dimethylformamide, dimethyl sulfoxide, or sulfolane.

[0009] Preferably, the molar ratio of the redox initiator to the azo initiator is 10:1 to 100:1.

[0010] Preferably, the redox initiator is a combination of persulfate and sodium bisulfite; the azo initiator is azobisisobutyronitrile, azodicarbonamide, or azobisisobutyronitrile.

[0011] Preferably, inorganic nanomaterials are added to the bentonite in step one, and the inorganic nanomaterials are... Bentonite nanosheets or graphene oxide. The addition of inorganic nanomaterials can further enhance impermeability and mechanical strength.

[0012] The present invention also provides a polymer-modified bentonite, which is prepared by the above method.

[0013] This invention also provides a polymer-modified bentonite liner containing the aforementioned polymer-modified bentonite. Because the polymer-modified bentonite prepared by the above method is present in the liner of this invention, one end of the polymer in the polymer-modified bentonite is inserted between the crystal layers of the bentonite to form a long chain containing polyacrylonitrile insertions. This forms a three-dimensional network structure encapsulated within the bentonite, making it more resistant to leaching and salt immersion. Therefore, the polymer-modified bentonite liner of this invention has better seepage prevention performance and can be used for sidewall seepage prevention. The preparation method of the polymer-modified bentonite liner can employ methods commonly used in the prior art, combining polymer-modified bentonite with geotextiles to form the bentonite liner. This liner can improve the material's resistance to chemical erosion, structural stability, and environmental adaptability, and can be used for roadbed seepage prevention and isolation, etc.

[0014] The beneficial effects of this invention are as follows: The polymer-modified bentonite preparation method of this invention first forms active centers for polymerization reaction between the crystal layers of bentonite, then extends the chain at low temperature and embeds polyacrylonitrile into the polymer to enhance its mechanical properties. A three-dimensional network structure is formed in the micropores and on the surface of the bentonite particles, firmly encapsulating the bentonite and preventing structural collapse and segregation caused by water erosion. The polymer-modified bentonite prepared by this invention is resistant to salt leaching, has good seepage prevention effect, and good stability, making it more suitable for manufacturing polymer-modified bentonite liners for seepage prevention and isolation in landfill sites or roadbeds. Detailed Implementation

[0015] The present invention will now be described in detail with reference to the embodiments. Example 1

[0016] A polymer-modified bentonite is prepared by the following method: Step 1: Take bentonite with a particle size of 0.075-2 mm, add water to the bentonite to make a slurry, purge with nitrogen for 20 minutes, and then adjust its pH value to 6.5; then add acrylamide, stir to dissolve and mix evenly, and continue stirring for 15 minutes, wherein the amount of acrylamide added is 0.25 wt% of the bentonite.

[0017] The composite initiator was added to the reaction system at 5-10℃ and 300 rpm with stirring. The composite initiator was a combination of sodium persulfate, sodium bisulfite and azobisisobutyronitrile in a molar ratio of 1:1:0.1, and the amount of composite initiator added was 0.5 wt% in the reaction system. The reaction was carried out at 5-10℃ and 300 rpm for 60 minutes with stirring. During the reaction, nitrogen was used to purge oxygen.

[0018] Step 2, Preparation of the mixed emulsion: Weigh acrylamide, carboxymethyl cellulose, and polyacrylonitrile, wherein acrylamide is 2.0 wt% of bentonite, polyacrylonitrile is 1.0 wt% of bentonite, and carboxymethyl cellulose is 0.5 wt% of bentonite. First, dissolve acrylamide and carboxymethyl cellulose in water to form solution A, then dissolve polyacrylonitrile in dimethyl sulfoxide to form solution B. Mix solutions A and B to form a mixed solution with a total mass concentration of 5 wt% for polyacrylamide, carboxymethyl cellulose, and polyacrylonitrile. Homogenize under high pressure or disperse ultrasonically to prepare a mixed emulsion with a thickness of 100–500 nm.

[0019] The mixed emulsion was added dropwise to the reaction system at a uniform rate over a period of 5 hours. After the addition was completed, the reaction was continued for another 30 minutes. The temperature of the reaction system was maintained at 5-10℃ throughout the reaction process, and the stirring speed was maintained at 300 rpm. Nitrogen was used to purge oxygen during the reaction.

[0020] Step 3: Freeze-dry the product to obtain polymer-modified bentonite. Example 2

[0021] The only difference between this embodiment and Embodiment 1 is the addition of the mixed emulsion in step two. In this embodiment, a variable-speed addition method is used, specifically: 1 / 6 of the total amount of the mixed emulsion is added in the first 1 / 3 of the time period, 1 / 3 of the total amount of the mixed emulsion is added in the middle 1 / 3 of the time period, and 1 / 2 of the total amount of the mixed emulsion is added in the last 1 / 3 of the time period.

[0022] The remaining steps are exactly the same as in Example 1. Example 3

[0023] A polymer-modified bentonite is prepared by the following method: Step 1: Take bentonite with a particle size of 1-3 mm and add water to the bentonite to make a slurry. Purge with nitrogen for 20 minutes, then adjust the pH value to 7.5; then add acrylamide, stir to dissolve and mix evenly, and continue stirring for 20 minutes, wherein the amount of acrylamide added is 0.5 wt% of the bentonite.

[0024] The composite initiator was added to the reaction system at 5-10℃ and 500rpm with stirring. The composite initiator was a combination of sodium persulfate, sodium bisulfite and azobisisobutyronitrile in a molar ratio of 1:1:0.01. The amount of composite initiator added was 0.1wt% in the reaction system. The reaction was carried out at 5-10℃ and 500rpm for 100 minutes with stirring. During the reaction, nitrogen was used to purge oxygen.

[0025] Step 2, Preparation of the mixed emulsion: Weigh acrylamide, sodium carboxymethyl cellulose, and polyacrylonitrile, wherein acrylamide is 0.75 wt% of bentonite, polyacrylonitrile is 2.0 wt% of bentonite, and sodium carboxymethyl cellulose is 1.5 wt% of bentonite. First, dissolve acrylamide and sodium carboxymethyl cellulose in water to form solution A, then dissolve polyacrylonitrile in dimethyl sulfoxide to form solution B. Mix solutions A and B to form a mixed solution with a total mass concentration of 10 wt% for polyacrylamide, sodium carboxymethyl cellulose, and polyacrylonitrile. Homogenize under high pressure or disperse ultrasonically to prepare a mixed emulsion with a thickness of 100–500 nm.

[0026] The mixed emulsion was added dropwise to the reaction system over a total of 6 hours, using a variable-rate addition method: 1 / 6 of the total mixed emulsion volume was added during the first 2 hours, 1 / 3 during the middle 2 hours, and 1 / 2 during the last 2 hours. After the addition was completed, the reaction was continued for 30 minutes. Throughout the entire reaction process, the reaction system temperature was maintained at 5-10℃, and the stirring speed was kept at 500 rpm. Oxygen was removed by purging with nitrogen during the reaction.

[0027] Step 3: The product is dried under low temperature and vacuum to obtain polymer-modified bentonite. Example 4

[0028] A polymer-modified bentonite is prepared by the following method: Step 1: Take bentonite with a particle size of 1-3 mm and add water to make a slurry. Purge with nitrogen for 20 minutes, then adjust the pH to 7.0; then add acrylamide, stir to dissolve and mix evenly, and continue stirring for 20 minutes, wherein the amount of acrylamide added is 1.0 wt% of the bentonite.

[0029] The composite initiator was added to the reaction system while stirring at 10-15℃ and 600 rpm. The composite initiator was a combination of sodium persulfate, sodium bisulfite and azobisisobutyronitrile in a molar ratio of 1:1:0.05. The amount of composite initiator added was 1.0 wt% in the reaction system. The reaction was carried out at 10-15℃ and 600 rpm for 150 minutes, and nitrogen was used to purge oxygen during the reaction.

[0030] Step 2, Preparation of the mixed emulsion: Weigh acrylamide, hydroxypropyl cellulose, and polyacrylonitrile, wherein acrylamide is 9.0 wt% of bentonite, polyacrylonitrile is 3.0 wt% of bentonite, and hydroxypropyl cellulose is 1.0 wt% of bentonite. First, dissolve acrylamide and hydroxypropyl cellulose in water to form solution A, then dissolve polyacrylonitrile in dimethyl sulfoxide to form solution B. Mix solutions A and B to form a mixed solution with a total mass concentration of 15 wt% for polyacrylamide, hydroxypropyl cellulose, and polyacrylonitrile. Homogenize under high pressure or disperse ultrasonically to prepare a mixed emulsion with a thickness of 100–500 nm.

[0031] The mixed emulsion was added dropwise to the reaction system at varying rates over a period of 7 hours. The varying rates were as follows: 1 / 6 of the total volume of the mixed emulsion was added during the first 2 hours, 1 / 3 during the middle 3 hours, and 1 / 2 during the last 2 hours. After the addition was completed, the reaction was continued for 60 minutes. Throughout the reaction, the temperature of the reaction system was maintained at 10-15°C, and the mixture was stirred at 600 rpm. Oxygen was removed by purging with nitrogen during the reaction.

[0032] Step 3: Freeze-dry the product to obtain polymer-modified bentonite. Example 5

[0033] A polymer-modified bentonite is prepared by the following method: Step 1: Take bentonite with a particle size of 1-3 mm, add water to the bentonite to make a slurry, purge with nitrogen for 20 minutes, and then adjust its pH value to 6.5; then add acrylamide, stir to dissolve and mix evenly, and continue stirring for 25 minutes, wherein the amount of acrylamide added is 0.75 wt% of the bentonite.

[0034] The composite initiator was added to the reaction system at 15-20℃ and 300 rpm with stirring. The composite initiator was a combination of sodium persulfate, sodium bisulfite and azobisisobutyronitrile in a molar ratio of 1:1:0.1. The amount of composite initiator added was 0.5 wt% in the reaction system. The reaction was carried out at 15-20℃ and 300 rpm for 60 minutes with stirring. During the reaction, nitrogen was used to purge oxygen.

[0035] Step 2, Preparation of the mixed emulsion: Weigh acrylamide, sodium hydroxypropyl cellulose, and polyacrylonitrile, wherein acrylamide is 4.0 wt% of bentonite, polyacrylonitrile is 4.0 wt% of bentonite, and sodium hydroxypropyl cellulose is 1.0 wt% of bentonite. First, dissolve acrylamide and sodium hydroxypropyl cellulose in water to form solution A, then dissolve polyacrylonitrile in dimethyl sulfoxide to form solution B. Mix solutions A and B to form a mixed solution with a total mass concentration of 5 wt% for polyacrylamide, sodium hydroxypropyl cellulose, and polyacrylonitrile. Homogenize under high pressure or disperse ultrasonically to prepare a mixed emulsion with a thickness of 100–500 nm.

[0036] The mixed emulsion was added dropwise to the reaction system over a total of 6 hours using a variable-rate addition method, as follows: 1 / 6 of the total volume of the mixed emulsion was added during the first 2 hours, 1 / 3 during the middle 2 hours, and 1 / 2 during the last 2 hours. After the addition was completed, the reaction was continued for 30 minutes. Throughout the entire reaction process, the reaction system temperature was maintained at 15-20℃, and the stirring speed was kept at 300 rpm. Nitrogen was used to purge oxygen during the reaction.

[0037] Step 3: Freeze-dry the product to obtain polymer-modified bentonite.

[0038] Comparative Example 1 A polymer-modified bentonite was prepared. The difference between this comparative example and Example 1 is that no acrylamide was added in step one; all the acrylamide was added in step two, as detailed below: Step 1: Take bentonite with a particle size of 0.075-2 mm, add water to the bentonite to make a slurry, purge with nitrogen for 20 minutes, and then adjust its pH value to 6.5.

[0039] The composite initiator was added to the reaction system at 5-10℃ and 300 rpm with stirring. The composite initiator was a combination of sodium persulfate, sodium bisulfite and azobisisobutyronitrile in a molar ratio of 1:1:0.1. The amount of composite initiator added was 0.5 wt% in the reaction system. The reaction was carried out at 5-10℃ and 300 rpm for 60 minutes with stirring. During the reaction, nitrogen was used to purge oxygen.

[0040] Step 2, Preparation of the mixed emulsion: Weigh acrylamide, carboxymethyl cellulose, and polyacrylonitrile, wherein acrylamide is 2.25 wt% of bentonite, polyacrylonitrile is 1.0 wt% of bentonite, and carboxymethyl cellulose is 0.5 wt% of bentonite. First, dissolve acrylamide and carboxymethyl cellulose in water to form solution A, then dissolve polyacrylonitrile in dimethyl sulfoxide to form solution B. Mix solutions A and B to form a mixed solution with a total mass concentration of 5 wt% for polyacrylamide, carboxymethyl cellulose, and polyacrylonitrile. Homogenize under high pressure or disperse ultrasonically to prepare a mixed emulsion with a thickness of 100–500 nm.

[0041] The mixed emulsion was added dropwise to the reaction system at a uniform rate over a period of 5 hours. After the addition was completed, the reaction was continued for another 30 minutes. The temperature of the reaction system was maintained at 5-10℃ throughout the reaction process, and the stirring speed was maintained at 300 rpm. Nitrogen was used to purge oxygen during the reaction.

[0042] Step 3: Freeze-dry the product to obtain polymer-modified bentonite.

[0043] Comparative Example 2 A polymer-modified bentonite is prepared by the following method: Step 1: Take bentonite with a particle size of 0.075-2 mm, add water to the bentonite to make a slurry, purge with nitrogen for 20 minutes, and then adjust its pH value to 6.5; then add acrylamide, stir to dissolve and mix evenly, and continue stirring for at least 15 minutes, wherein the amount of acrylamide added is 0.25 wt% of the bentonite.

[0044] The composite initiator was added to the reaction system at 5-10℃ and 300 rpm with stirring. The composite initiator was a combination of sodium persulfate, sodium bisulfite and azobisisobutyronitrile in a molar ratio of 1:1:0.1. The amount of composite initiator added was 0.5 wt% in the reaction system. The reaction was carried out at 0-5℃ and 30 rpm for 60 minutes with stirring. During the reaction, nitrogen was used to purge oxygen.

[0045] Step 2: Weigh out acrylamide in an amount equal to 2.0 wt% of bentonite and prepare an aqueous solution of acrylamide with a mass concentration of 5 wt%.

[0046] The above-mentioned acrylamide aqueous solution was added dropwise to the reaction system at a uniform rate over a period of 5 hours. After the addition was completed, the reaction was continued for 30 minutes. The temperature of the reaction system was maintained at 5-10℃ throughout the reaction process, and the stirring speed was maintained at 300 rpm. Nitrogen was used to purge oxygen during the reaction.

[0047] Step 3: Freeze-dry the product to obtain polymer-modified bentonite.

[0048] Comparative Example 3 A polymer-modified bentonite was prepared. The difference between this comparative example and Example 1 is the method of adding the mixed emulsion in step two. In this comparative example, the obtained mixed emulsion was added to the reaction system at one time, and then the reaction was carried out by stirring at 300 rpm for 5 hours and 30 minutes. The temperature was maintained at 5-10℃ throughout the reaction process, and nitrogen was used to purge oxygen during the reaction.

[0049] Everything else is exactly the same as in Example 1.

[0050] Comparative Example 4 A polymer-modified bentonite was prepared. The difference between this comparative example and Example 1 is the stirring speed during the reaction process. In this comparative example, all stirring speeds were 800 rpm, and the rest were exactly the same as in Example 1.

[0051] Comparative Example 5 The bentonite with a particle size of 0.075-2 mm used in Example 1 was used directly as the sample.

[0052] The bentonite samples obtained from each embodiment and comparative example were tested, and the test results are recorded in Table 1. The specific test methods are as follows: 1. Separation test Take 20g of bentonite sample, add 400g of water, stir thoroughly and let stand for 60min. Centrifuge at 4000rpm for 15min. Take the supernatant and measure its viscosity at 20℃, which is the viscosity of the separated liquid. The results are shown in Table 1.

[0053] 2. Salt resistance test Take 105g of bentonite sample and place it in a flexible wall permeameter containing 0.25 mol / L CaCl2 solution (150 mm in diameter) and soak for 24-48 hours to ensure complete hydration. The soaking temperature should be controlled at 18 ± 2 ℃. During the experiment, ensure that the upper and lower surfaces of the material are flat and well-sealed.

[0054] Head difference: 150-160 mm, until the flow rate stabilizes. Collect the lower effluent and record the volume at time intervals. Calculate the average value after the flow rate stabilizes. Calculate the permeability coefficient (permeability coefficient 1) and record the result in Table 1.

[0055] 3. Permeability test Take 105g of bentonite sample and place it in a 150mm diameter flexible wall permeameter. Add water and soak for 24-48 hours to ensure full hydration of the bentonite sample. Control the soaking temperature at 18 ± 2℃. During the test, ensure that the upper and lower surfaces of the material are flat and well-sealed.

[0056] Head difference: 100-150 mm, until the flow rate stabilizes. Collect the lower effluent and record the volume at time intervals. Calculate the average value after the flow rate stabilizes. Calculate the permeability coefficient (permeability coefficient²) and record the result in Table 1.

[0057] Table 1

[0058] As can be seen from the data in Table 1, the polymer-modified bentonite prepared by the method of the present invention has a low viscosity of the precipitate measured in the segregation test. This indicates that the polymer-modified bentonite prepared by the present invention is not easily separated from the organic polymer during centrifugation. The polymer is embedded between the crystal layers of bentonite and is sandwiched between the layers, and is firmly bonded to the bentonite without separation. It has high resistance to loss and good stability.

[0059] In salt resistance and permeability tests, the polymer-modified bentonite prepared using the method of this invention also exhibited smaller permeability coefficients 1 and 2, demonstrating better salt resistance and permeability resistance. In contrast, the segregation solutions obtained from Comparative Examples 1 to 4 (which did not use the method of this invention) had higher viscosity, resulting in greater separation of the polymer and bentonite during centrifugation, poor leaching resistance, and poor stability. In the salt resistance and permeability tests, the bentonite prepared using the method of this invention also exhibited larger permeability coefficients 1 and 2, demonstrating poorer salt resistance and permeability resistance. It is evident that the polymer-modified bentonite prepared using the method of this invention has a three-dimensional network structure formed in the micropores and on the surface of the bentonite particles, firmly encapsulating the bentonite and effectively preventing structural collapse and segregation. It exhibits good stability, salt resistance, and excellent permeability resistance, making it more suitable for manufacturing polymer-modified bentonite liners for landfill sites or roadbed seepage prevention and isolation.

[0060] It should be noted that the descriptions of these embodiments are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described above can be combined with each other as long as they do not conflict with each other. In addition, the above are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

Claims

1. A method for preparing polymer-modified bentonite, characterized in that, Includes the following steps: Step 1: Add water to bentonite to make a slurry, and adjust its pH to 6.5-7.5; then add acrylamide, stir to dissolve and mix evenly, and continue stirring for at least 15 minutes. The amount of acrylamide added is 0.25-1.0 wt% of the bentonite. The temperature is maintained at 5-20℃, and the composite initiator is added while stirring at 300-600 rpm, so that the content of the composite initiator in the reaction system is 0.1-1.0 wt%, and the reaction is carried out for 60-150 minutes; the composite initiator is a mixture of redox initiator and azo initiator; Step 2: Add the mixed emulsion dropwise to the reaction system over a period of 5-7 hours. After the addition is complete, continue the reaction for 30-60 minutes. Throughout the reaction process, maintain the temperature of the reaction system at 5-20°C and keep the stirring speed at 300-600 rpm. The method for preparing the mixed emulsion is as follows: Weigh acrylamide, emulsifier, and polyacrylonitrile, wherein the acrylamide is 0.75-9.0 wt% of bentonite, the polyacrylonitrile is 1.0-4.0 wt% of bentonite, and the emulsifier is 0.5-1.5 wt% of bentonite; dissolve acrylamide and emulsifier in water to form solution A, dissolve polyacrylonitrile in an organic solvent to form solution B, mix solutions A and B to form a mixed liquid with a total mass concentration of 5-15 wt% of polyacrylamide, emulsifier, and polyacrylonitrile, and homogenize under high pressure or disperse by ultrasonication to prepare a mixed emulsion with a diameter of 100-500 nm; Step 3: Freeze-dry or low-temperature vacuum-dry the product to obtain polymer-modified bentonite.

2. The method for preparing polymer-modified bentonite as described in claim 1, characterized in that, In step two, the mixed emulsion is added dropwise at a variable rate: 1 / 6 of the total amount of mixed emulsion is added in the first 1 / 3 of the time period, 1 / 3 of the total amount of mixed emulsion is added in the middle 1 / 3 of the time period, and 1 / 2 of the total amount of mixed emulsion is added in the last 1 / 3 of the time period.

3. The method for preparing polymer-modified bentonite as described in claim 1, characterized in that, The emulsifier is carboxymethyl cellulose, hydroxypropyl cellulose, or a salt of both.

4. The method for preparing polymer-modified bentonite as described in claim 1, characterized in that, The molar ratio of the redox initiator to the azo initiator is 10:1 to 100:

1.

5. The method for preparing polymer-modified bentonite as described in claim 4, characterized in that, The redox initiator is a combination of persulfate and sodium bisulfite; the azo initiator is azobisisobutyronitrile, azodicarbonamide, or azobisisobutyronitrile.

6. The method for preparing polymer-modified bentonite according to any one of claims 1 to 5, characterized in that, In step one, inorganic nanomaterials are added to the bentonite. The inorganic nanomaterials are... Bentonite nanosheets or graphene oxide.

7. A polymer-modified bentonite, characterized in that, It is made by any one of the methods of claims 1-6.

8. A polymer-modified bentonite liner, characterized in that, It contains the polymer-modified bentonite of claim 7.

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