Straightforward preparation of Ca-bentonite/polymer nanocomposite by confining salt-resistant copolymers into montmorillonite interlayers

Calcium bentonites (CaB), rich in European and Asian countries, are potential barrier materials for landfill leachate containment. However, CaB has to be converted into sodium bentonite (NaB) by Na-activation so as to facilitate intercalation modification. In this study, salt-resistant poly(acrylic acid-N, N-diethyl acrylamide) [P(AA-DEA)] was designed to intercalate and graft CaB by in situ polymerization without prior Na-activation. By this design, acrylic acid monomers were first adsorbed into interlayers of Ca-montmorillonite (Ca-MT) through the electrostatic complexation with Ca 2+ , dislodging Ca 2+ from montmorillonite surfaces. Then, ammonium ions of N, N-diethyl acrylamide were adsorbed into Ca-MT interlayers. Swelling index of the obtained CaB/P(AA-DEA) nanocomposite in aggressive coal combustion product (CCP) leachate is 15.8 mL/2g, which is as high as 3.4 times that of CaB. CaB/P(AA-DEA)-based geosynthetic clay liners (GCLs) exhibit very low hydraulic conductivity (1.6✕10 −12  m/s) to CCP leachate, which is as low as 3.3% that of the U.S. standard requirement and ∼4 orders of magnitude lower than that of CaB-based GCL. Polymer elution of CaB/P(AA-DEA)-8% in CCP leachate is as low as 1.9% that of the dry mixed samples.