Cosorption of organic contaminants from water by hexadecyltrimethylammonium-exchanged clays

Abstract

The characteristics of organoclays as sorbents for neutral organic contaminants (NOCs) in aqueous systems containing multiple solutes were evaluated by measuring the sorption of trichloroethylene on hexadecyltrimethylammonium (HDTMA) exchanged illite and smectite in the absence and presence of carbon tetrachloride, nitrobenzene and ethyl ether. Trichloroethylene partitioned into HDTMA-derived phases present on the external surfaces of the clay particles manifesting type III isotherms. Carbon tetrachloride functioned to increase the solvency of the external HDTMA phase, and hence enhanced sorption of trichloroethylene. Nitrobenzene solvated HDTMA resulting in a more vertical orientation of the C-16 alkyl chains and interlayer expansion. This rendered the interlamellar region of HDTMA-smectite accessible for trichloroethylene sorption, and nitrobenzene sorption simultaneously increased the solvency of HDTMA phase for trichloroethylene. Ethyl ether sorption suppressed the uptake of trichloroethylene by decreasing the solvency of HDTMA phase for trichloroethylene. Sorption of trichloroethylene also facilitated sorption of carbon tetrachloride and nitrobenzene. The results suggest that multiple organic compounds generally produce a synergistic effect on the uptake of NOCs from water by HDTMA-clays, and support multiple mechanisms controlling the sorption process.