Bentonite with anion and cation adsorbability, preparation method and anti-seepage liner

Abstract

The invention provides bentonite with anion and cation adsorbability, a preparation method and an anti-seepage liner, and belongs to the field of environmental governance, the method comprises the following steps: uniformly mixing sodium bentonite with deionized water, and controlling the water content of the mixture to be 80-120% to obtain a sodium bentonite pretreated substance; dissolving a chelating agent and ion exchange resin in deionized water to prepare a modifier dispersion liquid; stirring the sodium bentonite pretreatment substance and the modifier dispersion liquid until the materials are fully and uniformly mixed; transferring the mixed material to a constant-temperature environment for standing; and drying the material after standing in a drying oven to obtain the modified sodium bentonite. The modified sodium bentonite prepared by the method has the capability of efficiently adsorbing anion and cation pollutants at the same time. The adsorption capacity of typical heavy metal cations can be increased by two times or more, and effective adsorption and fixation of harmful anions are synchronously realized.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation, and in particular to a bentonite with both anion and cation adsorption properties, its preparation method, and an impermeable liner. Background Technology

[0002] Currently, the annual output of solid waste is enormous, with industrial solid waste continuing to increase year by year. Sanitary landfill, as the mainstream method of solid waste disposal, faces the challenge of treating leachate generated from the degradation of waste within the landfill. This leachate typically contains high concentrations of harmful metal cations (such as Zn). 2+ Mg 2+ Cd 2+ ) and anions (such as CrO4) 2- Cr2O7 2- SO4 2- Of particular concern is that landfill leachate often has high ionic strength (I) or low relative abundance (RMD) of certain ions. This extremely harsh chemical environment poses a serious challenge to existing composite impermeable liner systems (typically geomembranes / geotextiles with sodium bentonite).

[0003] The primary risk of failure in existing seepage control systems stems from chemical compatibility issues. When leachate intrudes into the bentonite layer, the high concentrations of cations (especially polyvalent cations) and anions in the leachate undergo strong ion exchange and double-layer compression with the bentonite (whose main active component is montmorillonite). This significantly reduces the interlayer repulsion of montmorillonite crystals, severely inhibiting its expansion performance and consequently causing a dramatic increase in the permeability coefficient of the bentonite layer (up to several orders of magnitude). Once the bentonite barrier, as the core seepage control material, fails, harmful anionic and cationic pollutants will significantly diffuse and migrate, seriously threatening the safety of groundwater and soil environments surrounding the landfill, and leading to a significant decline in the long-term performance and service life of the entire seepage control system.

[0004] Therefore, developing a novel modified sodium-based bentonite technology that can effectively adsorb and fix harmful anions and cations in leachate while maintaining low permeability, thereby significantly improving the chemical stability and long-term barrier performance of bentonite in leachate environments with high ionic strength and complex ionic composition, has significant practical engineering significance and broad application prospects for solving the key technical bottlenecks of existing anti-seepage liners, ensuring the long-term environmental safety of landfills, and extending the service life of the system. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a bentonite with both anion and cation adsorption properties, its preparation method, and an anti-seepage liner.

[0006] This invention provides a method for preparing bentonite with both anion and cation adsorption properties, comprising: mixing sodium-based bentonite with deionized water until uniform, controlling the water content of the mixture to be 80%~120%, to obtain a sodium-based bentonite pretreated material; dissolving a chelating agent and an ion exchange resin in deionized water to prepare a modifier dispersion; stirring the sodium-based bentonite pretreated material and the modifier dispersion until the materials are fully and uniformly mixed; transferring the mixed material to a constant temperature environment for standing; and placing the standing material in an oven for drying to obtain modified sodium-based bentonite.

[0007] According to the present invention, a method for preparing bentonite with both anionic and cationic adsorption properties is provided, wherein the sodium-based bentonite has a montmorillonite mineral content of more than 70% and a free expansion coefficient of more than 24 ml / 2g.

[0008] According to the present invention, a method for preparing bentonite with both anion and cation adsorption properties is provided, wherein the total amount of deionized water used in sodium-based bentonite and deionized water used in chelating agent is 80% to 120% of the dry weight of the sodium-based bentonite.

[0009] According to the present invention, a method for preparing bentonite with both anion and cation adsorption properties is provided, wherein the total amount of chelating agent and ion exchange resin added is 2.0% to 10.0% of the dry weight of the sodium-based bentonite. According to the present invention, a method for preparing bentonite with both anionic and cationic adsorption properties is provided, wherein the sodium-based bentonite pretreatment material and the modifier dispersion are stirred at a speed of 75 rpm to 100 rpm.

[0010] According to the present invention, a method for preparing bentonite with both anion and cation adsorption properties is provided, wherein the chelating agent and the ion exchange resin can both function effectively within a pH range of 4-14.

[0011] According to the present invention, a method for preparing bentonite with both anionic and cationic adsorption properties is provided, wherein the chelating agent includes disodium ethylenediaminetetraacetate.

[0012] The present invention also provides a bentonite with both anion and cation adsorption properties, which is prepared by any of the above-mentioned bentonite preparation methods with both anion and cation adsorption properties.

[0013] The present invention also provides a seepage-proof liner with both anion and cation adsorption properties, comprising a modified sodium-based bentonite layer laid from the above-mentioned bentonite and a geomembrane layer laid on the modified sodium-based bentonite layer.

[0014] According to the present invention, a seepage-proof liner with both anionic and cationic adsorption properties is provided, wherein the geomembrane layer is directly laminated in contact with the upper surface of the bentonite layer.

[0015] This invention provides bentonite with both anionic and cationic adsorption properties, its preparation method, and a seepage-proof liner. Through synergistic modification using chelating agents and ion exchange resins, the modified sodium-based bentonite possesses the ability to efficiently adsorb both anionic and cationic pollutants. It is particularly effective against typical heavy metal cations (such as Zn). 2+ The adsorption capacity can be increased by 2 times or more, and the adsorption capacity of harmful anions (such as CrO4) can be simultaneously improved. 2- Effective adsorption and fixation of ). Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A schematic flowchart illustrating the method for preparing bentonite with both anionic and cationic adsorption properties provided by the present invention. Figure 2 A schematic diagram of the preparation process of the seepage-proof liner with both anion and cation adsorption properties provided by the present invention; Figure 3 A schematic diagram of the structure of the seepage-proof liner with both anionic and cationic adsorption properties provided by the present invention; Figure 4 The modified sodium-based bentonite and unmodified sodium-based bentonite provided by this invention are used to compare the cations (Zn) 2+ Comparison of adsorption kinetic curves; Figure 5 The modified sodium-based bentonite and unmodified sodium-based bentonite provided by this invention, at different initial concentrations, affect the cationic (Zn) 2+ A comparison chart of adsorption efficiencies; Figure 6 A comparison of the adsorption kinetics curves of modified sodium bentonite and unmodified sodium bentonite for anions (Cr(VI)) provided by the present invention. Figure 7 A comparison of the adsorption efficiency of modified sodium bentonite and unmodified sodium bentonite for anions (Cr(VI)) at different initial concentrations provided by this invention. Figure 8 A comparison of the permeability coefficients of modified sodium-based bentonite and unmodified sodium-based bentonite in a leachate environment with high ionic strength and low relative abundance (RMD) provided by the present invention. Figure 9A comparison of the permeability coefficients of the impermeable liner made of modified sodium bentonite and the liner made of unmodified sodium bentonite in a leachate environment with high ionic strength and low relative abundance (RMD). In the diagram: 1-Geomembrane layer, 2-Chlorinating agent, 3-Ion exchange resin, 4-Sodium bentonite. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0019] This application aims to address the core problem of the sharp increase in permeability coefficient of existing sodium-based bentonite-based seepage liners in high ionic strength and complex leachate environments due to the combined effects of cation exchange erosion (especially high-valence heavy metal cations) and anion erosion.

[0020] High concentrations of cations in leachate (especially polyvalent heavy metal cations such as Zn) 2+ Cd 2+ ) and anions (such as CrO4) 2- SO4 2- This causes ion exchange and double-layer compression in bentonite (whose main active component is montmorillonite), resulting in a strong inhibition of its expansion properties.

[0021] Current sodium-based bentonite liners have low adsorption and blocking efficiency for key harmful anionic and cationic pollutants in leachate, and cannot effectively prevent their diffusion and migration. During long-term service, the chemical stability of the impermeable layer decreases due to continuous erosion by leachate, resulting in a significant decline in its impermeability and threatening long-term environmental safety.

[0022] The following is combined Figures 1-9 This invention describes the bentonite with both anion and cation adsorption properties, its preparation method, and the seepage-proof liner. Figure 1 This is a schematic flowchart of the method for preparing bentonite with both anion and cation adsorption properties provided by the present invention, as shown below. Figure 1 As shown, the present invention provides a method for preparing bentonite with both anion and cation adsorption properties, comprising: 101. Mix sodium-based bentonite with deionized water until homogeneous, and control the water content of the mixture to 80%~120% to obtain sodium-based bentonite pretreated material.

[0023] In some embodiments, the sodium-based bentonite contains more than 70% montmorillonite and has a free expansion coefficient greater than 24 ml / 2 g.

[0024] The first step is raw material pretreatment. For example, 1 kg of commercial sodium-based bentonite with a montmorillonite content ≥80% and a free expansion coefficient of 32 ml / 2 g is selected and ground through a 100-mesh sieve. The sieved bentonite is then dried at 105℃ for 8 hours to remove free water.

[0025] Next is the preparation of bentonite slurry. Take 150g of dried bentonite, add 150mL of deionized water (moisture content ≈100%, where the moisture content is the mass moisture content), and mechanically stir to form a uniform slurry.

[0026] 102. Dissolve the chelating agent and ion exchange resin in deionized water to prepare a modifier dispersion.

[0027] In some embodiments, the total amount of deionized water used in sodium-based bentonite and deionized water used in chelating agents is 80% to 120% of the dry weight of the sodium-based bentonite.

[0028] In some embodiments, the total amount of the chelating agent and ion exchange resin added is 2.0% to 10.0% of the dry weight of the sodium-based bentonite. This step involves preparing the modifier dispersion. Weigh out 3g of disodium ethylenediaminetetraacetate (EDTA-2Na) and 7.5g of anion exchange resin, dissolve them in 500mL of deionized water, and ultrasonically disperse for 30 minutes.

[0029] 103. Stir the sodium-based bentonite pretreated material and the modifier dispersion until the materials are fully and evenly mixed.

[0030] This step involves mixing and modification. In some embodiments, the sodium-based bentonite pretreated material and the modifier dispersion are stirred at a speed of 75 rpm to 100 rpm. The modifier dispersion of 102 can be slowly added to the bentonite slurry of 101, and then stirred in a high-speed mixer at a speed of 75 rpm to 100 rpm for 1 hour.

[0031] 104. Transfer the mixed materials to a constant temperature environment and let them stand.

[0032] This step involves a static reaction. Transfer the mixture to a constant temperature chamber, such as setting it to 60℃ and letting it stand for 24 hours.

[0033] 105. Place the settled material in an oven and dry it to obtain modified sodium-based bentonite.

[0034] Finally, the material is dried at 105℃ for 8 hours, then ground through a 0.5mm sieve to obtain modified sodium-based bentonite.

[0035] The present invention provides a method for preparing bentonite with both anionic and cationic adsorption properties. Through the synergistic modification using chelating agents and ion exchange resins, the modified sodium-based bentonite possesses the ability to efficiently adsorb both anionic and cationic pollutants. It is particularly effective against typical heavy metal cations (such as Zn). 2+ The adsorption capacity can be increased by 2 times or more, and the adsorption capacity of harmful anions (such as CrO4) can be simultaneously improved. 2- Effective adsorption and fixation of ).

[0036] Excellent permeability stability under extreme leachate conditions: Modified sodium-based bentonite maintains extremely low permeability even in extreme leachate environments with high ionic strength and containing various harmful anions and cations. Its permeability coefficient can be stably maintained at ≤1×10⁻⁶. -9 m / s, meeting strict seepage prevention requirements, significantly better than the sharp deterioration of the permeability coefficient of traditional bentonite in such environments.

[0037] The long-term seepage prevention mechanism is clear and reliable: Chelating agent function: Through its strong complexing / chelating ability, it locks in metal cations (especially polyvalent heavy metal ions) in the leachate, effectively preventing these cations from exchanging with the cations between the bentonite and montmorillonite crystal layers, thereby protecting the expansion properties of montmorillonite from being damaged.

[0038] Function of ion exchange resin: Through its inherent ion exchange groups, it efficiently adsorbs and fixes harmful anion and cation pollutants in leachate, reducing their diffusion and migration into the deeper bentonite layer and the underlying environment.

[0039] Synergistic effect: The two modifiers work together to greatly alleviate the erosion of bentonite structure by harmful ions in leachate, ensuring that the modified sodium-based bentonite layer maintains its low permeability and structural stability during long-term service, and significantly improving the long-term service performance and service life of the liner system.

[0040] Ion exchange resins are activated by their supported permanently positively charged groups (such as quaternary ammonium groups -N). + (CH3)3) for anionic contaminants in leachate (such as CrO4) 2- SO4 2- It generates strong electrostatic attraction and selectively replaces and fixes high-charge-density anions through ion exchange reactions. Simultaneously, its porous framework structure physically adsorbs and mechanically traps anion complexes, preventing anions from eroding the active sites of bentonite. This process synergistically removes anions that compress the electrical double layer, repairs the surface potential of montmorillonite, thereby inhibiting crystal collapse and permeability deterioration. Combined with chelating agents, it forms a synergistic anion-cation barrier network, significantly improving the long-term seepage prevention stability of the liner under extreme leachate environments.

[0041] In some embodiments, the chelating agent and the ion exchange resin are required to function effectively within a pH range of 4-14. The chelating agent and ion exchange resin selected as modifiers are required to function effectively within a wide pH range (approximately 4-14).

[0042] In some embodiments, the chelating agent comprises disodium ethylenediaminetetraacetate (EDTA). Disodium EDTA binds to Zn via a hexadecanaline ligand (4 carboxyl oxygen + 2 amino nitrogen). 2+ / Cd 2+ Plasma forms a stable chelating ring (log K>18), blocking heavy metals from contacting the bentonite lattice and simultaneously chelating Zn in the leachate. 2+ / Mg 2+ To maintain the double-layer structure.

[0043] The present invention also provides a bentonite with both anion and cation adsorption properties, which is prepared by any of the above-described methods for preparing bentonite with both anion and cation adsorption properties.

[0044] The present invention also provides a seepage-proof liner with both anion and cation adsorption properties, comprising a modified sodium-based bentonite layer laid from the above-mentioned bentonite and a geomembrane layer laid on the modified sodium-based bentonite layer.

[0045] In some embodiments, the geomembrane layer is directly laminated in contact with the upper surface of the modified sodium-based bentonite.

[0046] Specifically, the modified sodium-based bentonite can be laid in layers, and the geomembrane layer 1 can be directly laminated onto the upper surface of the modified sodium-based bentonite layer to form the final composite seepage-proof liner structure. The geomembrane layer 1 can be obtained by laying a high-density polyethylene (HDPE) geomembrane. The seepage-proof liner manufacturing process in conjunction with the above embodiments is as follows: Figure 2 As shown in the diagram, the structure of the seepage-proof liner is as follows: Figure 3 As shown, the modified sodium-based bentonite layer includes chelating agent 2, ion exchange resin 3, and sodium-based bentonite 4.

[0047] The adsorption performance was verified: like Figure 4 , Figure 5As shown, the equilibrium adsorption capacity of the modified bentonite samples for Zn(II) increases with increasing equilibrium concentration. The increase is non-linear; at lower equilibrium concentrations, the slope of the increase is steeper, but as the equilibrium concentration increases, the slope gradually decreases, and the adsorption curve flattens. This is because as the Zn(II) concentration increases, the modified bentonite continuously adsorbs Zn(II), and the adsorption rate decreases when the surface adsorption sites approach saturation. Each sample reaches its maximum equilibrium adsorption capacity at an initial concentration of 100 mg / L. The maximum adsorption capacity of sodium-based bentonite is 0.9889 mg / g, while the maximum adsorption capacity of modified sodium-based bentonite is 2.1246 mg / g, which is 2.15 times that of unmodified bentonite.

[0048] like Figure 6 , Figure 7 As shown, the equilibrium adsorption capacity of modified bentonite samples for Cr(VI) in typical leachate increases with increasing equilibrium concentration. The increase is non-linear; at lower equilibrium concentrations, the slope of the increase is steeper, but as the equilibrium concentration increases, the slope gradually decreases, and the adsorption curve flattens. This is because as the Cr(VI) concentration increases, modified bentonite continuously adsorbs Cr(VI), and the adsorption rate decreases when the surface adsorption sites approach saturation. Sodium-based bentonite and modified sodium-based bentonite reach their maximum equilibrium adsorption capacity at an initial concentration of 100 mg / L, which are 0.0282 mg / g and 2.8660 mg / g, respectively, 101.63 times that of the unmodified sodium-based bentonite sample.

[0049] like Figure 8 , Figure 9 The core data on seepage prevention performance shown are in the presence of Zn. 2+ / Mg 2+ In leachate environments, the initial permeability coefficient of modified bentonite was not significantly different from that of the unmodified system (both < 10). -7 The high expansion rate (cm / s) of sodium-based bentonite is the primary factor driving its short-term seepage prevention performance. However, in the modified system, the low expansion characteristics of the resin and EDTA-2Na lead to the formation of local micropores at the bentonite particle-modifier interface, resulting in a slightly higher degree of seepage pathway development compared to the pure bentonite system. However, the measured data ( Figure 8 This confirms that the difference remains within the acceptable range for the project—the permeability coefficient of the modified soil is 5.02 × 10⁻⁶. -8 (cm / s) is only slightly lower than that of unmodified soil (3.8×10 cm / s). -8 The increase in cm / s is less than 1 time, and both are far below the national standard limit (10). -7 cm / s). It is worth noting that when modified bentonite and geomembrane form a composite liner ( Figure 9The physical barrier effect of the geomembrane can effectively compensate for the interfacial porosity effect, reducing the system permeability coefficient to 1.61 × 10⁻⁶. -9 The speed of cm / s is an order of magnitude higher than that of a single bentonite layer in terms of seepage prevention efficiency, highlighting the advantages of structural synergy.

[0050] The present invention experimentally tested the properties of the modified bentonite prepared in the above embodiments, including the adsorption, free swelling index, specific surface area, average pore diameter, total pore volume, and permeability of the modified bentonite.

[0051] (1) Adsorption properties of modified bentonite In this embodiment, the adsorption capacity of the modified bentonite material for Zn(II) in Zn(II) solution was studied through batch adsorption experiments. The adsorption characteristics of bentonite for Zn(II) before and after modification and the change law of the maximum adsorption amount were analyzed and compared.

[0052] (2) Free expansion index of modified bentonite.

[0053] The free expansion index can assess the expansion characteristics of bentonite in solution. This example is performed in accordance with ASTM D5890.

[0054] (3) Specific surface area, average pore diameter and total pore volume of modified bentonite.

[0055] Specific surface area reflects the adsorption capacity and reactivity of tailings, while average pore diameter and pore size distribution reflect properties such as permeability and selectivity of modified bentonite. In this embodiment, the BSD-PS2 specific surface area and pore size analyzer manufactured by Best Instruments Technology (Beijing) Co., Ltd. was used for measurement.

[0056] (4) Permeability of modified bentonite.

[0057] In this embodiment, the permeability of the adsorbent bentonite modified material in extreme leachate was studied through a flexible wall permeability test. The permeability characteristics of bentonite before and after modification and the variation of the permeability coefficient with confining pressure were analyzed and compared.

[0058] The embodiments described above are merely illustrative, and some or all of the solutions can be selected to achieve the purpose of this invention according to actual needs. Those skilled in the art can understand and implement these embodiments without any creative effort.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing bentonite with both anion and cation adsorption properties, characterized in that, include: Sodium-based bentonite is mixed evenly with deionized water, and the water content of the mixture is controlled to be 80%~120% to obtain sodium-based bentonite pretreated material. A chelating agent and an ion exchange resin were dissolved in deionized water to prepare a modifier dispersion. The sodium-based bentonite pretreated material and the modifier dispersion were stirred until the materials were fully and uniformly mixed. Transfer the mixed materials to a constant temperature environment and let them stand. The material, after being left to stand, is placed in an oven and dried to obtain modified sodium-based bentonite.

2. The method for preparing bentonite with both anion and cation adsorption properties according to claim 1, characterized in that, The sodium-based bentonite contains more than 70% montmorillonite and has a free expansion coefficient greater than 24 ml / 2g.

3. The method for preparing bentonite with both anion and cation adsorption properties according to claim 1, characterized in that, The total amount of deionized water used in the sodium-based bentonite and the chelating agent is 80% to 120% of the dry weight of the sodium-based bentonite.

4. The method for preparing bentonite with both anion and cation adsorption properties according to claim 1, characterized in that, The total amount of the chelating agent and ion exchange resin added is 2.0% to 10.0% of the dry weight of the sodium-based bentonite.

5. The method for preparing bentonite with both anion and cation adsorption properties according to claim 1, characterized in that, The sodium-based bentonite pretreated material and the modifier dispersion are stirred at a speed of 75 rpm to 100 rpm.

6. The method for preparing bentonite with both anion and cation adsorption properties according to claim 1, characterized in that, Both the chelating agent and the ion exchange resin are effective within a pH range of 4-14.

7. The method for preparing bentonite with both anion and cation adsorption properties according to claim 1, characterized in that, The chelating agent includes disodium ethylenediaminetetraacetate.

8. A bentonite possessing both anion and cation adsorption properties, characterized in that, It is prepared by the method for preparing bentonite with both anionic and cationic adsorption properties as described in any one of claims 1-7.

9. A leak-proof liner with both anion and cation adsorption properties, characterized in that, It includes a modified sodium-based bentonite layer laid with the bentonite as described in claim 8 and a geomembrane layer laid on the modified sodium-based bentonite layer.

10. The waterproof liner with both anionic and cationic adsorption properties according to claim 9, characterized in that, The geomembrane layer is directly laminated in contact with the upper surface of the modified sodium-based bentonite.

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