Adsorptive selectivity of organic-cation-modified bentonite for nonionic organic contaminants

The mineral surface of Wyoming bentonite was modified by replacing inorganic ions with four quaternary ammonium cations in an amount equal to 40 percent of the cation-exchange capacity of the bentonite. The four quaternary ammonium cations used were tetramethylammonium (TMA), tetraethylammonium (TEA), benzyltrimethylammonium (BTMA), and benzyltriethylammonium (BTEA). Sorption of benzene, tetrachloromethane, trichloroethene, 1,2-dichlorobenzene, and naphthalene to the modified sorbents from water at 20 °C was investigated. All five solutes were sorbed strongly by TEA-, BTMA-, and BTEA-bentonite, but only benzene and tetrachloromethane were strongly sorbed by TMA-bentonite. The sorption isotherms are distinctly nonlinear and the magnitude of sorption is not correlated with the solute's aqueous solubility. In contrast, sorption of trichloroethene, 1,2-dichlorobenzene, and naphthalene to TMA-bentonite was negligible relative to benzene and tetrachloromethane sorption. The apparent absence of solute selectivity by TEA-, BTMA-, and BTEA-bentonite, along with their large sorption capacities, indicates that these sorbents can potentially be useful as components of landfill liners or slurry walls to decrease the mobility of a variety of nonionic organic contaminants.