Contaminant migration in engineered clay barriers due to heat and moisture redistribution under freezing conditions

Abstract

In this study, the effect of temperature distribution and its influence on contaminant migration in a silty clay soil were examined. Three series of freezing-column tests were performed with three different fluids: distilled water, municipal waste leachate, and heavy metal – leachate solution. It was found that temperature distribution as a function of space and time was similar in all tests, most likely as a result of the limited amount of fluid intake. Moisture redistributions were varied as a function of experiment duration and the type of fluid used. The amount of fluid intake was directly related to the freezing time and the temperature gradient in the freezing column. The amount of unfrozen water content, ion concentration and temperature gradient were the controlling parameters that contributed to the contaminant transport in the frozen illitic silty clay soil. Na+-concentration profiles were mostly dependent on water movement in the soil column. The behaviour of Ca2+ and Mg2+ cations was similar to Na+; their concentrations in the soil solution decreased with freezing time due to ion exchange. The large accumulations of Pb2+, Zn2+, Cu2+, and Cd2+ in the lower 10 mm of the soil column occurred as a result of cation exchange and precipitation mechanisms. Key words : unsaturated, osmotic, diffusion, buffer, exchange, transport.