Extraction kinetics of six heavy metals from contaminated clay soils

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Abstract
The rate of the extraction of four heavy metals (Cu, Nl, Pb and Zn) from artificially polluted and waste site clay soils is determined in a 0.1 N HCl solution. A two‐reaction model is developed that describes the rate of extraction at a constant pH and at a constant temperature by two processes: a fast, irreversible reaction that is first‐order in the metal concentration in the clay and a slow, reversible first‐order reaction. The influence of the temperature on the extraction rate is measured over a range of 5 to 80°C for Ni extraction from an artificially polluted clay soil. Calculated values for the energy of activation suggest that the extraction process is rate‐limited by a diffusion process in the porous soil particles, but chemical limitations seem probable in case of the older contaminations in the waste site soils.