Effect of organic matter and clay content on cadmium adsorption in calcium-saturated soils from semi-arid region

The effect of organic matter and clay content on adsorption of Cd on soil samples from semi-arid region was investigated. Three soil samples, varying in organic matter and clay content, were made homoionic with Ca. The Ca-homoionic soil samples were equilibrated with solutions having a wide range of Ca+Cd at 500 μmol L⁻¹ total electrolyte concentration. The per cent adsorption of Cd decreased with increasing concentration of Cd in equilibrium solution. The values of distribution coefficient,K_d, also followed a similar trend as that of per cent adsorption. Higher organic matter soil had higher percentage of Cd adsorption as compared to low organic matter soil. Langmuir and Freundlich adsorption isotherms were fitted to the data. Langmuir adsorption isotherm was resolved into two parts i.e., part-I (0–100 μmol L⁻¹) and part-II (100–500 μmol L⁻¹) concentration. Effect of organic matter content on Cd adsorption was found to be dominating whereas effect of clay content was secondary.