ISOTHERMS OF CADMIUM SORPTION DENSITY

To study Cd sorption, 16 soil samples of different chemical soil reactions were taken and analyzed for their physical and chemical properties. Adsorption of ethylene glycol monoethyl ether (EGME) and N2 were determined to establish the specific surface area of the soils. The sorption of Cd was modeled on a per-mass basis using the Langmuir and Freundlich equations as well as per-surface area basis. Traditional sorption isotherms reveal the relation between the amount of Cd sorbed and the Cd concentration in the soil solution only for the soil under study and can therefore not be applied, or can be applied only with restrictions, to other soils. To meet the aim of modeling Cd sorption and mobility for other soils or locations differing greatly in their properties, we attempted to establish a generalizing sorption isotherm for soils of entirely different composition of the solid phase. On the basis of characteristic values the 16 soil samples taken were grouped into three different reaction types (aluminum-hydroxide, silicate, and carbonate-buffer range). The generalizing Cd sorption density isotherms for these different soil groups introduced in the following provide a useful mathematical model for the quantity-intensity relation of Cd in soils that differ greatly in their specific surface area and their composition.