pH influence on sorption characteristics of heavy metal in the vadose zone

Sorption is an important process in the modelling and prediction of the mov ement of heavy metals in unsaturated clay barriers. This experimental study investigates the effect of pH changes in the acidic range on the sorption characteristics of heavy metals such as: lead, copper and zinc in an unsatu rated soil. A series of one-dimensional coupled solute and moisture leachin g column tests, using different heavy metal solutions, were conducted on an unsaturated illitic soil at varying pH values. Variations of volumetric wa ter content (VWC) with distance were measured for different time durations, and concentrations of heavy metals in the liquid and solid phases were ana lysed. Partitioning coefficient profiles of contaminants along the soil col umn were determined for each individual layer in the soil. Results from column leaching tests showed that the sorption characteristics of heavy metals are controlled by many factors which should be taken into consideration, i.e. the VWC, time of wetting, soil pH, and the influent hea vy metal concentrations. Simplification of Kd as a constant and of the VWC as a linear function cannot be considered a good assumption and may lead to an improper evaluation of the sorption phenomena and also to serious error s in predicting contaminant transport through unsaturated soils. (C) 2001 E lsevier Science B.V. All rights reserved.