Heavy Metal Sorption by Different Estonian Soil Types at Low Equilibrium Solution Concentrations

Batch sorption experiments were conducted with heavy metal solutions in 0.01 M CaCl2 at low equilibrium concentrations of Cu, Pb, Cd, and Cr in 10 different intact soil samples. Metal solid/liquid distribution coefficients Kd were determined from the adsorption isotherms obtained. Their values varied over a range from 57 to 53 000 mL/g. The soils used in the experiment were chosen according to their organic matter content and origin to represent differential behaviour with regard to heavy metal sorption. Correlations of Kd with soil parameters were observed together with varying sorption behaviour of metal cations to different soil types. Desorption of metals from soil phase to solution was found to be very small, suggesting that at least during the initial period after the metal pollutants have reached the soil surface they accumulate in the top humus layer. Heavy metal desorption into the water phase also depends on the character of the metal and on soil type.