Zinc(II) Sorption Characteristics of Soils in Predominant Smectite, Illite and Kaolinite Clay Minerals

Abstract

The purpose of the present study was to evaluate the adsorption behaviour of zinc in soils dominated with smectite, illite and kaolinite. The linear Langmuir model is more suitable for the adsorption of Zn ions onto the soils since it had higher coefficient of determination value compared with that of the linear Freundlich model. The maximum sorption capacity of illite for Zn ions was determined from the Langmiur equation and found to be 11.38, 10.23 and 8.50 mg g^-1 for smectite, illite and kaolinite soils, respectively. The dimensionless equilibrium parameter or separation factor (R_L) approaches zero as the C_o (initial concentration) value is increased, indicating that the adsorption of Zn(II) ions onto the clay fractions is less favourable. The Dubinin- Redushckevich (D-R) model was also applied equilibrium data to identify the type of sorption (chemically or physically) of Zn ions onto the soils. The bonding energies for ion-exchange mechanism (E, kJ mol^-1) calculated from D-R parameter β (the activity coefficient related to mean adsorption energy) was found as 11.9, 10.6 and 10.1 kJ mol^-1 for smectite, illite and kaolinite soils, respectively. The calculated E value in these soils indicated that the type of sorption of Zn ions onto the soils was predominantly chemical in nature according to typical ranges of bonding energy. From the obtained results, it can be concluded that the Zn ions adsorption on soils rich in smectite was higher compared with the adsorption on the other soils.