Advection, Diffusion, and Sorption Characteristics of Inorganic Chemicals in GCL Bentonite

Because of its low permeability and high swelling characteristics, bentonite is used in various hydraulic barrier systems, including geosynthetic clay liners (GCLs). In order to increase their long-term resistance to contamination, bentonites may be amended during manufacturing through mixing with soluble polymeric compounds. The resulting materials are referred to as polymer-treated, chemically-enhanced, or contaminant-resistant clays, and are arguably resistant to a host of inorganic chemicals. In this study, the advection, diffusion, and sorption characteristics of untreated and polymer-treated bentonite clays are examined. The response of bentonite clays to single and multi-species solutions at various concentrations is evaluated using permeability, diffusion, chemical titration, and index tests. Long-term advection properties are determined from flexible and rigid wall permeability tests, where both chemical and hydraulic equilibrium are established. The results indicate the high dependence of performance on sample homogeneity, pre-hydration conditions, and, to a lesser extent, polymer treatment. The cation exchange capacity and the clay plasticity appear to be more reliable than the swell index as indicators of the hydraulic performance of bentonite permeated with inorganic chemicals.