Adsorption Kinetics of Cadmium and Zinc as Influenced by Some Calcareous Soil Properties

ABSTRACT: Adsorption process is very important in determining zinc (Zn) and cadmium (Cd) availability and fate in soil. Time-dependent adsorption characteristics of toxic concentrations of Zn and Cd were studied in ten calcareous soils throughout shaking periods of 1 to 1440 min. Patterns of Zn and Cd adsorption rates were investigated by using seven kinetic models. Results showed that the patterns consisted of an initial fast sorption rates throughout the first two hours followed by much slower rates reactions. Power function was the best fitted model describing Zn and Cd adsorption in the soils studied. It assumed that soil factors controlling Zn and Cd adsorption are almost similar and clay and organic matter are probably the main sites for adsorption of these metals. In most shaking periods Cd adsorption rate was higher than that of Zn demonstrating higher capability of Cd in competition with Zn for occupying adsorption sites.