Characterization of Zinc Adsorption in Some Soils of India

Abstract Laboratory studies were conducted to characterize Zn adsorption in some soils varying in texture using a wide range of equilibrating Zn concentrations. The fit of adsorption data was tested both in Freundlich and Langmuir isotherms. The Langmuir isotherm was resolved into two linear portions. Binding energy coefficients ( K ) were higher and adsorption maxima ( b ) were lower in part I than part II of the curves for both soils. b values were higher and K values were lower for loam than sand. The Freundlich isotherm was also resolved into three distinct portions having different K and n values. The adsorption pattern at different concentrations indicated differential bonding energies for adsorbed Zn, and occurrence of precipitation reactions along with adsorption in these soils, even before saturation of cation exchange capacity (CEC). The results showed the limitations in describing Zn adsorption through Langmuir or Freundlich adsorption isotherms in such soils of pH ⩾ 8 at 6 ppm Zn concentrations due to precipitation. Zinc adsorption exceeded CEC at equilibrating Zn concentration of 10 −2 M . The soil texture did not affect the nature of adsorption curves but more Zn was adsorbed by loam than sand showing the effect of the number of adsorption sites.