INVESTIGATION OF THE EFFECT OF MOISTURE ON THE SORPTION AND DESORPTION OF CHLOROBENZENE AND TOLUENE FROM SOIL

The sorption isotherms of chlorobenzene and toluene on a standard EPA soil at different relative humidities were measured using a dynamic te chnique based on frontal analysis chromatography. At 0% relative humid ity, the isotherms were BET (Brunauer-Emmett-Teller) type II isotherms , indicating monolayer coverage of the surface followed by multilayer coverage. As the relative humidity increased, the shape of the isother m became progressively a type III isotherm, indicating weaker adsorben t/adsorbate interactions. The presence of water greatly reduced the or ganic uptake by soil, especially at low organic concentrations. The ef fect of humidity was attributed to adsorptive displacement of the orga nic by water. A mechanistic approach was considered to evaluate the co ntribution of the possible sorption mechanisms to the total sorption. It was found that adsorption at the gas-liquid interface was important and that dissolution in liquid water and partitioning into organic ma tter from the adsorbed water phase were negligible. The BET theory for adsorption of binary gas mixtures on solid surfaces successfully repr esented the data in the relative humidity range 0-50% and relative org anic pressure range 0-30%. The effect of humidity on the desorption pr ofile was investigated, and it was found that the efficiency of extrac tion was increased when using a water-saturated gas stream for desorpt ion instead of a dry gas stream.