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Sorption of nonionic organic contaminants to single and dual organic cation bentonites from water.

Wyoming bentonite was modified by the exchange of one or two classes of quaternary ammonium cations for inorganic ions. Sorption of tetrachloromethane, trichloroethene, and benzene to the resulting organobentonites from water at 10 and 30 °C was studied. The first class of quaternary ammonium cations studied are characterized by short-chain alkyl or aryl functional groups and include tetramethyl-, tetraethyl-, and benzyltriethylammonium cations. The second class of quaternary ammonium cations studied are characterized by the following structure : (CH 3 ) 3 -N + -R where R is a 10-, 12-, 14-, 16-, or 18-carbon alkyl chain. Nonionic solute sorption to bentonite exchanged with cations from the first class (in an amount equal to 40% of cation-exchange capacity) is caused primarily by adsorption. When a second organic cation from the second class is also exchanged onto this sorbent in an amount equal to 20, 40, or 60% of cation-exchange capacity, the long-chain alkyl functional groups cause two effects. First, the alkyl chains interfere with nonionic solute adsorption to the bentonite mineral surface modified by the tetramethyl-, tetraethyl-, or benzyltriethylammonium cations. Second, the alkyl chains create a partition medium for sorption of the nonionic solutes. Solute uptake by adsorption decreases, and solute uptake by partition increases as the amount of organic cations from the second class exchanged onto the bentonite increases from 0 to 60% of cation-exchange capacity. Solute uptake by adsorption decreases, and solute uptake by partition increases as the length of the alkyl chain of the quaternary ammonium cation increases from 12 to 14 carbon atoms. In general, the reduction in solute uptake by adsorption caused by the long-chain alkyl functional groups is greater than the increased solute uptake by partition. Therefore, the net effect of the exchange of the second class of organic cations to the bentonite mineral surface is a reduction in nonionic solute sorption.