Rapid prediction of long-term rates of contaminant desorption from soils and sediments

A method using heated and superheated (subcritical) water is described for rapid prediction of long-term desorption rates from contaminated geosorbents. Rates of contaminant release are measured at temperatures between 75 and 150 degrees C using a dynamic water desorption technique. The subcritical desorption rate data are then modeled to calculate apparent activation energies, and these activation energies are used to predict desorption behaviors at any desired ambient temperature. Predictions of long-term release rates based on this methodology were found to correlate well with experimental 25 degrees C desorption data measured over periods of up to 640 days, even though the 25 degrees C desorption rates were observed to vary by up to 2 orders of magnitude for different geosorbent types and initial solid phase contaminant loading levels. Desorption profiles measured under elevated temperature and pressure conditions closely matched those at 25 degrees C and ambient pressure, but the time scales associated with the high-temperature measurements were up to 3 orders of magnitude lower. The subcritical water technique rapidly estimates rates of desorption-resistant contaminant release as well as those for more labile substances. The practical implications of the methodology are significant because desorption observed under field conditions and ambient temperatures typically proceeds over periods of months or years, while the high temperature experiments used for prediction of such field desorption phenomena can be completed within periods of only hours or days.