Study on chemical compatibility of bentonite under the action of cation and stress of hazardous waste leachate

Bentonite is widely used for the construction of anti-seepage barriers in hazardous waste landfills due to its excellent anti-seepage performance, but its impermeability is usually affected by leachate and stress. Different concentrations of cationic solutions were set up by leachate sampling and analysis to investigate the influence law of actual leachate components on the anti-seepage performance of bentonite. Ca²⁺ was chosen as the characteristic cation, and the variation rule of the bentonite permeability coefficient under different stress conditions was studied. Meanwhile, the influence law of chemical compatibility of bentonite was elucidated under the action of leachate composition and stress combined with Zeta potential and DLVO theoretical calculation. The results show that the concentration of Al³⁺, Fe³⁺, Zn²⁺, Ni²⁺, Cu²⁺, Fe²⁺, Mn²⁺ in the leachate is in the range of 0-0.20 mmol/L, which has less influence on the expansion and permeability characteristics of bentonite. The concentration of Mg²⁺, Ca²⁺, K⁺, Na⁺ is in the range of 0.20-50 mmol/L, and Ca²⁺ has more influence on the expansion capacity and permeability characteristics of bentonite. When the concentration increases from 1 mmol/L to 50 mmol/L, the permeability coefficient rapidly increases from 1.15×10⁻⁷ cm/s to 6.34×10⁻⁶ cm/s. Ca²⁺ concentration and stress usually affect the permeability characteristics of hydrated bentonite by affecting its porosity, and the permeability coefficient gradually decreases with increasing pressure under the same Ca²⁺ concentration conditions. Zeta potential and DLVO theoretical analysis indicate that the increase in Ca²⁺ concentration leads to a decrease in the negative potential on the surface of bentonite and thickness of the double layer of bentonite, which decreases the interlayer spacing of montmorillonite in bentonite, and then depress the swelling and permeability characteristics of bentonite. Therefore, the solidification and stabilization process of hazardous waste during the landfill process should be optimized, to reduce Ca²⁺ content in the leachate at the source. Meanwhile, new bentonite composite materials should be developed to improve the impermeability of bentonite in Ca²⁺ as well as other salt solutions to prevent and control the risk of leakage of hazardous waste landfills.