Mechanisms for Trichloroethylene Vapor Sorption onto Soil Minerals

Partition coefficients were determined for trichloroethylene (TCE) vapor (P/P o <2% or concentration <10 mg L −1 ) for several minerals over a wide range of moisture contents. For oven‐dried minerals, surface area was found to be a good indicator of the sorptive capacity of the solid phase. As moisture content was increased, the partition coefficients of TCE vapor decreased by several orders of magnitude, attained a minimum, and then gradually increased. Mechanisms of TCE vapor sorption were proposed corresponding to three regions of sorbent moisture content. In Region 1, from oven‐dried conditions to one monolayer coverage of water on the solid surface, direct solid‐vapor sorption was evident with strong competition between water and TCE for adsorption sites on the sorbents. In Region 2, between a monolayer coverage to approximately five layers of water molecules, likely interactions between TCE vapor and water include sorption of TCE onto surface‐bound water and limited TCE dissolution into sorbed water with some “salting out” effects caused by water structure. In Region 3, extending from a minimum of approximately five layers of water molecules to the water retention capacity of the soil, TCE dissolution into condensed water‐dominated vapor uptake along with sorption at the water solid interface. Thermodynamic data and the development of a simple model were used to interpret the above processes. Application of Henry's Law to model TCE interaction with the soil water was possible only after five layers of water molecules have formed.