EFFECTS OF TEMPERATURE ON TRICHLOROETHYLENE DESORPTION FROM SILICA-GEL AND NATURAL SEDIMENTS .1. ISOTHERMS

Aqueous phase isotherms were calculated from vapor phase desorption is otherms measured at 15, 30, and 60 degrees C for trichloroethylene on a silica gel, an aquifer sediment, a soil, a sand fraction, and a clay and silt fraction, all at 100% relative humidity. Isosteric heats of adsorption (Q(st)(q)) were calculated as a function of the sorbed conc entration, q, and examined with respect to the following mechanisms: a dsorption on water wet mineral surfaces, sorption in amorphous organic matter (AOM), and adsorption in hydrophobic micropores. Silica gel, s and fraction, and clay and silt fraction 60 degrees C isotherms are ch aracterized by a Freundlich region and a region at very low concentrat ions where isotherm points deviate from log-log linear behavior. The l atter is designated the non-Freundlich region. For the silica gel, val ues of Q(st)(q) (9.5-45 kJ/mol) in both regions are consistent with ad sorption in hydrophobic micropores. For the natural solids, values of Q(st)(q) in the Freundlich regions are less than or equal to zero and are consistent with sorption on water wet mineral surfaces and in AOM. In the non-Freundlich regions, diverging different temperature isothe rms with decreasing q and a Q(st)(q) value of 34 kJ/mol for the clay a nd silt fraction suggest that adsorption is occurring in hydrophobic m icropores. The General Adsorption Isotherm is used to capture this ads orption heterogeneity.