Reactions of neutral, nonpolar organic contaminants with clay minerals

Vapor phase sorption/desorption of the neutral, nonpolar organic compounds, EDB and TCE, by a number of clay minerals revealed a strong hysteresis ; the amounts sorbed in 1 to 2 hours were not desorbed completely even after 100 hours. Both sorption and desorption were rapid initially, for several hours, and then continued for days at a slow rate. The rapid sorption was considered to occur on external surfaces of the clay aggregates and the slow sorption within the intraaggregate micropores. The observed rates of sorption and desorption were described by a two compartment model. The compartments were assumed to be in series with transfer between the compartments and with the gas phase following first order kinetics. The rate constants were varied to give the best fit with the observed time course of sorption and desorption. In general, the rate constants for the rapid sorption were found to be several orders of magnitude greater than those for the slow sorption. The slow desorption from the intraaggregate micropores is likely responsible for the observed persistence of these contaminants in soils.Sawhney B.L., Gent M.P.N. Reactions of neutral, nonpolar organic contaminants with clay minerals. In: Proceedings of the 9th international Clay Conference, Strasbourg, 1989. Vol I : Clay-organic interactions. Clay minerals in soils. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1990. pp. 45-50. (Sciences Géologiques. Mémoire, 85