A carbon-modified clay-based salt-resistant seepage-proof material and its preparation method

Abstract

This invention discloses a method for preparing a carbon-modified clay-based salt-resistant and seepage-proof material. Natural bentonite is ground, washed with water to remove coarse particles, and then subjected to sodium treatment in NaCl solution. After washing and drying, sodium-based bentonite powder is obtained. The obtained sodium-based bentonite powder is dispersed in deionized water, sheared to achieve layer exfoliation, and centrifuged to remove undispersed large particles, resulting in a highly dispersed nanosheet liquid. An organic amine is dissolved in the nanosheet liquid, the pH is adjusted to 8.5-9.0, and the mixture is heated to 60-80℃ for intercalation reaction for 4-24 hours. After washing and drying, organic amine-modified bentonite is obtained. The organic amine-modified bentonite is mixed with water to obtain wet soil, which is placed in a fixed-bed adsorber and CO2 gas is introduced to allow the organic amine-modified bentonite to fully adsorb CO2. The modified bentonite after CO2 adsorption is pressed into shape according to a set compaction degree to obtain the carbon-modified clay-based salt-resistant and seepage-proof material.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering and materials technology, and specifically relates to a clay-based salt-resistant seepage-proof material. Background Technology

[0002] Bentonite is a layered silicate mineral widely used in seepage control systems in solid waste landfills such as landfills and tailings ponds due to its excellent swelling properties, ion exchange capacity, and ultra-low permeability. Its abundant adsorption capacity and low cost make it an ideal choice for clay-based seepage control materials. However, under high-salt environments (such as landfill leachate and tailings leachate), the swelling performance and pore-sealing ability of bentonite significantly decrease, leading to a significant increase in its permeability coefficient and weakened seepage control function, thus severely affecting its long-term service performance.

[0003] Studies have shown that when bentonite is exposed to environments containing high concentrations of polyvalent salt ions, it is prone to particle flocculation and microstructural damage, leading to pore enlargement and failure of the impermeable interface, making it difficult to meet the requirements for long-term safe operation of solid waste landfills. To improve its salt resistance, various modification methods have been proposed, such as adding inorganic salt modifiers, polymer composites, or cationic surface modifiers. While these methods can alleviate the effects of high salt on bentonite to some extent, their effectiveness is limited and they cannot fundamentally solve the interfacial stability problem under the combined action of high salt and multiple ions, nor can they endow the material with carbon capture or emission reduction functions.

[0004] Meanwhile, bentonite and its main constituent mineral, montmorillonite, have also shown significant potential in the field of carbon dioxide capture and storage due to their rich interlayer structure and specific surface area. Natural montmorillonite's adsorption of CO2 is primarily physical adsorption, with limited adsorption capacity, and its strong hydrophilicity makes it difficult to effectively interact with non-polar CO2. To improve its adsorption performance, organic amines (such as quaternary ammonium salts, aliphatic amines, and imidazoles) are commonly used for interlayer organic modification. Modification introduces CO2-loving active sites, adjusts the specific surface area and pore structure, and significantly enhances its chemical adsorption capacity. However, these adsorbents are mostly reversible adsorption agents; CO2 is prone to desorption under certain conditions, making long-term fixation impossible and failing to meet the stability requirements of carbon sequestration. Therefore, relying solely on the seepage prevention function of bentonite or the CO2 adsorption function of montmorillonite is insufficient to simultaneously meet the current dual requirements for interfacial stability and carbon emission reduction capacity of seepage prevention materials in high-salt environments. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon-modified clay-based salt-resistant seepage-proof material and its preparation method. It can utilize multivalent cations in a high-salt environment to achieve permanent CO2 mineralization and fixation, while sealing the pores of the material itself and enhancing structural stability. This effectively solves the technical problem of traditional bentonite's easy failure in a high-salt environment and significantly improves its seepage-proof performance and durability in a high-salt environment.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] A method for preparing a carbon-modified clay-based salt-resistant and seepage-proof material includes the following steps:

[0008] (1) Take natural bentonite, grind it, wash it with water to remove coarse particles, add NaCl solution for sodium treatment, wash it and dry it to obtain sodium-based bentonite powder;

[0009] (2) The obtained sodium-based bentonite powder was dispersed in deionized water, and the shearing dispersion was used to achieve the peeling of the sheets. The centrifugation was used to remove the large undispersed particles to obtain a highly dispersed nanosheet liquid.

[0010] (3) Dissolve the organic amine in the nanosheet liquid, adjust the pH to 8.5-9.0, heat to 60-80℃ for intercalation reaction for 4-24 hours, wash and dry to obtain organic amine modified bentonite;

[0011] (4) The organic amine modified bentonite is mixed with water to obtain wet soil, which is placed in a fixed bed adsorber and CO2 gas is introduced to allow the organic amine modified bentonite to fully adsorb CO2.

[0012] (5) The modified bentonite after adsorbing CO2 is pressed into shape according to the set compaction degree to obtain carbon-modified clay-based salt-resistant seepage prevention material.

[0013] According to the above scheme, the concentration of NaCl solution for sodium treatment in step 1 is 0.5-1.0 mol / L, the temperature is 40-60℃, and the stirring time is 2-4 hours.

[0014] According to the above scheme, the drying temperature in step 1 is 60-80℃, the drying time is 8-12 hours, and after drying, the material is ground and passed through a 200-mesh sieve.

[0015] According to the above scheme, the mass ratio of sodium-based bentonite powder to deionized water in step 2 is 1:(50-100).

[0016] According to the above scheme, after shearing and dispersing in step 2, ultrasonic treatment is used for 10-60 minutes to promote the peeling of the lamellae.

[0017] According to the above scheme, a polar solvent is added to the nanosheet liquid obtained in step 2 to improve the dispersion effect.

[0018] According to the above scheme, the organic amine mentioned in step 3 is one or a combination of triethylenetetramine, ethylenediamine, diethylenetriamine, and dodecylamine.

[0019] According to the above scheme, in step 3, add organic amine at a rate of 1-3 times the cation exchange capacity (CEC) of bentonite; at the same time, add dispersing aid and heat to 40-60℃ to improve dissolution efficiency.

[0020] According to the above scheme, step 3, the intercalation reaction is supplemented with ultrasound to improve efficiency, and the reaction is allowed to stand for more than 12 hours after completion.

[0021] According to the above scheme, the moisture content of the wet soil in step 4 is about 5-10 wt%.

[0022] According to the above scheme, in step 4, the fixed bed adsorption temperature is 25-40℃, and the adsorption time is 1-3 hours.

[0023] According to the above scheme, the negative carbon fixation of the organic amine modified bentonite obtained in step 4 is 2-8 wt%.

[0024] This invention also provides a carbon-modified clay-based salt-resistant impermeable material, prepared using the above-described method. Furthermore, it provides the application of this carbon-modified clay-based salt-resistant impermeable material as an impermeable layer in landfills.

[0025] This invention proposes a synergistic mechanism based on "organic intercalation-CO2 adsorption-mineralization precipitation-interfacial self-healing" to construct a carbon-negative clay-based impermeable interface material, significantly improving the structural stability and impermeability of bentonite in high-salt environments; it also achieves the transformation and long-term sequestration of CO2 into a stable carbonate form. First, natural bentonite is modified into sodium-based bentonite. Under the combined action of mechanical force and ultrasound, the interlayer structure of sodium-based bentonite peels apart, expanding its large specific surface area and providing space for subsequent organic amine modification of the bentonite interface. Through cation exchange reaction, triethylenetetramine (TETA) is grafted onto the interface of the bentonite lamellar structure, introducing abundant amine sites to enhance the material's chemisorption capacity for CO2; simultaneously, by controlling the degree of cation exchange reaction, the interlayer spacing and hydrophilicity are adjusted, retaining a certain degree of swelling performance and maintaining impermeability. In high-salt environments or landfill leachate, multivalent cations (such as Ca2+) can effectively absorb CO2. 2+ Mg 2+It participates in the mineralization reaction. This reaction takes place in the confined space between bentonite layers. Due to the confinement effect, the interlayer space promotes the formation of small crystal nuclei. At the same time, the slow seepage rate of landfill leachate is conducive to the formation of nano-sized CaCO3 and other precipitates. Nano-sized calcium carbonate crystals are generated in the interlayer or micropores, sealing the micropores in situ and significantly reducing permeability. It can achieve a "self-sealing-self-repairing" effect, enhancing its salt-resistant sealing performance as an impermeable material. At the same time, it can achieve long-term carbon stability sequestration, avoiding the leakage risks of geological and marine storage. In addition, the generated nano-calcium carbonate strengthens the framework structure through physical bonding, improves the interfacial resistance to damage, and endows the material with long-term structural stability and erosion resistance.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] Significantly enhances the CO2 adsorption capacity of bentonite, endowing it with negative carbon function. Synergistic intercalation modification with water-soluble organic amines (such as TETA) and PEG significantly improves the chemisorption capacity of bentonite for CO2; intercalation forms an ordered structure, stabilizes amine sites, improves adsorption selectivity and immobilization efficiency, and realizes an integrated negative carbon process of CO2 capture, mineralization, and sequestration; after CO2 adsorption, nano-sized CaCO3 can be induced to form in the pores or interlayers, achieving long-term carbon fixation and demonstrating good potential for green carbon sequestration.

[0028] To enhance the structural stability and impermeability of materials in high-salt environments, nano-carbonates (such as CaCO3 and MgCO3) formed during CO2 mineralization cement bentonite sheets, enhancing their mechanical strength and interfacial stability. Polyvalent cations in high-salt wastewater react with CO2 to form precipitates, which in situ block seepage channels in the pores, creating a microscopic "self-healing" effect and improving the material's low permeability and structural stability in high-salt environments. Organic intercalation modification controls the interlayer space, retaining some expansibility and dispersibility, ensuring good sealing performance even in wet applications.

[0029] It features multiple synergistic functions, a green process, and wide applicability. The process is simple, can be carried out in an aqueous phase, has mild reaction conditions, uses inexpensive raw materials, and has good scalability and engineering adaptability. The modified bentonite can meet the molding strength requirements without additional sand mixing, making it easy to construct. It effectively utilizes emitted CO2 and mixed ion leachate from landfills, realizing the resource utilization of solid waste and reducing environmental pollution. The finished product can be widely used in environmental engineering scenarios requiring long-term salt resistance and seepage prevention, such as landfills, tailings ponds, and saline-alkali land.

[0030] This invention synergistically improves the performance of clay-based seepage prevention systems from three dimensions: material interface structure regulation, efficient CO2 adsorption and conversion, and high-salt environment adaptation. It has the three-in-one functional characteristics of "carbon fixation, seepage prevention, and strength improvement", takes into account environmental friendliness and engineering feasibility, and has broad prospects for promotion. Attached Figure Description

[0031] Figure 1 : Schematic diagram of bentonite layer peeling.

[0032] Figure 2 Schematic diagram of grafting organic amines onto the surface of bentonite sheets.

[0033] Figure 3 : Schematic diagram of the generation of nano-calcium carbonate precipitate in high-salt solution according to the present invention. Detailed Implementation

[0034] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0035] A specific embodiment provides a carbon-modified clay-based salt-resistant and seepage-proof material:

[0036] I. Preparation of homogeneous ionic sodium-based bentonite:

[0037] (1) Bentonite pretreatment: Take natural bentonite (e.g., 100 g), grind and sieve (<200 mesh) to improve reactivity; if it contains a lot of impurities, wash with water and settle to remove coarse particles and sand, discard the supernatant and take fine particles. (2) Sodium treatment: Prepare NaCl solution (sodium agent), weigh an appropriate amount of NaCl and dissolve it in a certain amount of deionized water to prepare a NaCl solution with a concentration of 0.5 mol / L; add bentonite to the NaCl solution and stir at 40-60℃ for 2-4 hours (can be extended to 12 hours to improve exchange efficiency) to promote the exchangeable Ca in montmorillonite minerals. 2+ Mg 2+ Equal exchange to Na + Let stand for 24 hours to complete sodium ion exchange and fractional sedimentation. (3) Washing and drying: Wash with deionized water 3-5 times until the filtrate is close to neutral to ensure that excess Na + Remove the wet bentonite sample; place the wet bentonite sample in a drying oven and dry it at 60-80℃ for 8-12 hours; after drying, grind it and pass it through a 200-mesh sieve to obtain homogenized sodium-based bentonite powder.

[0038] II. Dispersion and exfoliation of sodium-based bentonite to increase interlayer spacing:

[0039] (1) Preparation of suspension: Sodium-based bentonite is added to deionized water at a ratio of 1:50 and stirred to form a uniform suspension; (2) High-energy dispersion and exfoliation: The interlayer structure is exfoliated by strong mechanical force using a high-speed shear disperser; then, it is treated with an ultrasonic cleaner or probe-type ultrasonic instrument for 10-60 minutes to promote the exfoliation of the layers; (3) Centrifugation to remove large particles: The dispersed suspension is centrifuged in a centrifuge to remove large particles that are not dispersed in the layers, and highly dispersed nanosheet liquid is obtained. To improve the dispersion effect, a small amount of polar solvent (such as ethanol, dimethyl sulfoxide DMSO, etc.) that is compatible with sodium-based montmorillonite can be added to the aqueous solution and heated and stirred to reduce the interlayer force and facilitate the separation of the layers. See the attached diagram for a schematic diagram of bentonite layer exfoliation. Figure 1 As shown.

[0040] III. Organic amine intercalation modification to construct a CO2-loving active interface:

[0041] (1) Preparation of organic amine solution: Dissolve triethylenetetramine (TETA) or other organic amines in a solution prepared by the above method to obtain highly dispersed nanosheet liquid, according to 1-3 times the CEC (cation exchange capacity) of bentonite. Heat to 40-60℃ to improve solubility, and dissolve by magnetic stirring. Add 2-4 g / L polyethylene glycol (PEG-200) as a dispersant, and adjust the pH to 8.5-9.0 with 0.1 mol / L NaOH to promote amine protonation (-NH4+). 3+ (2) Intercalation reaction via cation exchange: The above-mentioned dispersed bentonite nanosheet liquid and organic amine mixture are stirred at 60-80℃ for 4-24 hours, and ultrasound can be used to improve the intercalation efficiency; let stand for 12 hours to age, so that the organic amine can fully react with the exchangeable cation Na between the montmorillonite sheets. + Exchange occurs, and the amines are uniformly grafted onto the surface of the bentonite sheets. (3) Washing and drying: Wash 3-5 times with an ethanol-water (1:1) mixture to remove unreacted amines and impurities. Dry at 60-80℃, or vacuum drying if available. Grind and sieve (<200 mesh) to obtain organic amine-modified bentonite. See attached diagram for a schematic diagram of organic amine grafting onto the surface of bentonite sheets. Figure 2 As shown.

[0042] IV. CO2 Adsorption and Carbon Negation Treatment:

[0043] (1) Pre-hydration treatment: The dried organic amine modified bentonite is pre-hydrated to prepare wet soil with a water content of about 10%, which can achieve the maximum adsorption performance of CO2. (2) CO2 adsorption reaction: The wet soil is placed in a fixed bed adsorber, and pure CO2 gas (≥99.5%, flow rate 50-100 mL / min) is introduced and reacted at 25-40℃ for 1-3 hours. This allows the bentonite surface and organic amine groups to fully adsorb CO2, and the amount of negative carbon fixed can reach 2-8 wt%.

[0044] V. Interfacial sedimentation enhancement during the formation and operation of the seepage barrier layer:

[0045] (1) Compaction molding: The modified bentonite after adsorbing CO2 is pressed into shape according to the set compaction degree. The resulting carbon-modified clay-based salt-resistant seepage-proof material adsorbs a large amount of CO2 during the preparation process. Under the action of high-salt leachate (such as landfill leachate), the Ca in the liquid 2+ Mg 2+ Isovalent cations react with HCO3 generated after CO2 adsorption in modified bentonite - / CO3 2- The reaction results in the in-situ formation of nano-precipitates such as CaCO3 and MgCO3. These precipitates grow in a confined space between the lamellar structures and within the pores, effectively sealing microchannels and enhancing interfacial stability and salt resistance. This achieves an integrated "CO2 adsorption-mineralization-sealing" process, improving the material's long-term seepage prevention and carbon fixation functions. Because nano-calcium carbonate is generated during CO2 mineralization, it cements the lamellar structure of bentonite, significantly enhancing the mechanical properties of the seepage prevention material. Therefore, no additional sand addition is needed to improve strength, and the molded material exhibits excellent mechanical properties and micro-density. A schematic diagram of the formation of nano-calcium carbonate precipitates in high-salt solutions using the carbon-modified clay-based salt-resistant seepage prevention material of this invention is attached. Figure 3 As shown.

[0046] Example 1

[0047] (1) Take 100 g of natural bentonite, grind it and sieve it through a 200-mesh sieve. Wash it with water and let it settle to remove coarse particles and sand, etc. Discard the supernatant and take the fine particles. Prepare a 0.5 mol / L NaCl solution, add the bentonite to the NaCl solution, stir at 50℃ for 3 hours, and let it stand for 24 hours to complete sodium ion exchange and fractional sedimentation. Wash it with deionized water until the filtrate is close to neutral, put it in a drying oven to dry, grind it and sieve it through a 200-mesh sieve to obtain homogenized sodium-based bentonite powder.

[0048] (2) Add the obtained sodium-based bentonite to deionized water at a ratio of 1:50, stir to form a uniform suspension, use a high-speed shear disperser to peel off the interlayer structure, and then use an ultrasonic cleaner or probe ultrasonic instrument to treat for 60 minutes to promote the peeling of the sheets; put the dispersed suspension into a centrifuge for centrifugation to remove large particles of undispersed sheets and obtain highly dispersed nanosheet liquid.

[0049] (3) Take 3 times the amount of triethylenetetramine according to the CEC of bentonite and dissolve it in the above highly dispersed nanosheet liquid. Heat to 60°C, add 4 g / L polyethylene glycol as a dispersing agent, adjust the pH to 8.5 with 0.1 mol / L NaOH, heat to 70°C and stir for 12 hours. Let stand for 12 hours to age, wash with ethanol / water (1:1) mixture, vacuum dry, grind and sieve through 200 mesh to obtain organic amine modified bentonite.

[0050] (4) The above-mentioned dried organic amine modified bentonite was pre-hydrated to prepare wet soil with a water content of 10%, placed in a fixed bed adsorber, and pure CO2 gas (≥99.5%, flow rate 100 mL / min) was introduced and reacted at 40℃ for 2 hours to allow the bentonite surface and organic amine groups to fully adsorb CO2.

[0051] (5) The modified bentonite after adsorbing CO2 is pressed into shape according to the set compaction degree to obtain carbon-modified clay-based salt-resistant seepage prevention material.

[0052] Comparative Example 1

[0053] Repeat steps (1), (2), and (3) of Example 1. The organic amine modified bentonite is pre-hydrated to prepare wet soil with a water content of 10%. Then, it is pressed into shape according to the set compaction degree to obtain clay-based seepage-proof interface material.

[0054] The impermeable materials prepared in Example 1 and Comparative Example 1 were applied to a simulated high-salt environment, and their salt resistance and impermeability were tested. The impermeable layer was pressed and molded with a compaction degree of 90% and a thickness of 10 mm; the simulated leachate (high-salt aqueous solution) contained: Na + =3000 mg / L, Ca 2+ =800 mg / L, Mg 2+ =500 mg / L; water head pressure was 30 cm, temperature was 25℃; the permeability coefficient was tested using the equal head method, and the test was conducted by continuous soaking and permeation for 30 days. The test results are shown in Table 1.

[0055] Table 1

[0056]

[0057] Example 1 showed a slight decrease in permeability under high salinity, indicating that the CO2 adsorbed under the action of leachate continued to undergo in-situ CaCO3 / MgCO3 precipitation reaction, blocking the micropores of the layered structure and effectively enhancing impermeability. In contrast, Comparative Example 1 did not undergo CO2 adsorption treatment and lacked precipitation reaction, resulting in significant changes in the microstructure under high salinity, with the appearance of large pores, which increased the permeability by two orders of magnitude.

[0058] Samples of the geomembrane that had been continuously soaked and permeated in a high-salt environment for 30 days were taken and subjected to mechanical property tests. The test methods used were unconfined compressive strength test and direct shear strength test (four-piece shear apparatus, normal consolidation conditions). All samples were tested under the same compaction conditions. The test results are shown in Table 2.

[0059] Table 2

[0060]

[0061] In Example 1, the adsorbed CO2 forms carbonate precipitates, which cement the layers and pores, significantly improving compressive strength and cohesion. Its structure is more dense and stable, capable of withstanding higher compressive and shear loads, making it particularly suitable for seepage-proof sealing structures under long-term buried and heavily loaded environments.

Claims

1. A method for preparing a carbon-modified clay-based salt-resistant seepage-proof material, characterized in that... Includes the following steps: (1) Take natural bentonite, grind it, wash it with water to remove coarse particles, add NaCl solution for sodium treatment, wash it and dry it to obtain sodium-based bentonite powder; (2) The obtained sodium-based bentonite powder was dispersed in deionized water, and the shearing dispersion was used to achieve the peeling of the sheets. The centrifugation was used to remove the large undispersed particles to obtain a highly dispersed nanosheet liquid. (3) Dissolve the organic amine in the nanosheet liquid, adjust the pH to 8.5-9.0, heat to 60-80℃ for intercalation reaction for 4-24 hours, wash and dry to obtain organic amine modified bentonite; (4) The organic amine modified bentonite is mixed with water to obtain wet soil, which is placed in a fixed bed adsorber and CO2 gas is introduced to allow the organic amine modified bentonite to fully adsorb CO2. (5) The modified bentonite after adsorbing CO2 is pressed into shape according to the set compaction degree to obtain carbon-modified clay-based salt-resistant seepage prevention material.

2. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... In step 1, the concentration of the NaCl solution used for sodium treatment is 0.5-1.0 mol / L, the temperature is 40-60℃, and the stirring time is 2-4 hours.

3. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... In step 1, the drying temperature is 60-80℃ and the drying time is 8-12 hours. After drying, the product is ground and passed through a 200-mesh sieve.

4. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... In step 2, the mass ratio of sodium-based bentonite powder to deionized water is 1:(50-100).

5. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... In step 2, after shearing and dispersing, ultrasonic treatment is used for 10-60 minutes to promote the peeling of the lamellae.

6. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... Adding a polar solvent to the nanosheet liquid obtained in step 2 improves the dispersion effect.

7. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... The organic amine mentioned in step 3 is one or any combination of triethylenetetramine, ethylenediamine, diethylenetriamine, and dodecylamine.

8. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... Step 3: Add organic amine at a rate of 1-3 times the cation exchange capacity of bentonite; at the same time, add dispersing agent and heat to 40-60℃ to improve dissolution efficiency.

9. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... Step 3 involves using ultrasound to enhance the efficiency of the intercalation reaction, followed by standing for at least 12 hours after the reaction is complete.

10. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... The moisture content of the wet soil described in step 4 is 5-10 wt%.

11. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... Step 4: Fixed bed adsorption temperature 25-40℃, adsorption time 1-3 hours.

12. The preparation method of the carbon-modified clay-based salt-resistant seepage-proof material as described in claim 1, characterized in that... The negative carbon fixation of the organic amine-modified bentonite obtained in step 4 is 2-8 wt%.

13. A carbon-modified clay-based salt-resistant seepage-proof material, prepared by the method for preparing carbon-modified clay-based salt-resistant seepage-proof material according to any one of claims 1-12.

14. The application of the carbon-modified clay-based salt-resistant impermeable material of claim 13 as an impermeable layer in landfills.

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