Binding and Adsorption Energies of Heavy Metal Ions with Hapli-Udic Argosol and Ferri-Udic Argosol Particles

Abstract

Gibbs free binding energy and adsorption energy between cations and charged soil particles were used to evaluate the interactions between ions and soil particles. The distribution of Gibbs free adsorption energies could not be determined experimentally before the development of Wien effect measurements in dilute soil suspensions. In the current study, energy relationships between heavy metal ions and particles of Hapli-Udic Argosol (Alfisol) and Ferri-Udic Argosol were inferred from Wien effect measurements in dilute suspensions of homoionic soil particles (< 2μm) of the two soils, which were saturated with ions of five heavy metals, in deionized water. The mean Gibbs free binding energies of the heavy metal ions with Hapli-Udic Argosol and Ferri-Udic Argosol particles diminished in the order of Pb 2+ > Cd 2+ > Cu 2+ > Zn 2+ > Cr 3+, where the range of binding energies for Hapli-Udic Argosol (7.25-9.32 kJ mol −1) was similar to that for Ferri-Udic Argosol (7.43-9.35 kJ mol −1). The electrical field-dependent mean Gibbs free adsorption energies of these heavy metal ions for Hapli-Udic Argosol and for Ferri-Udic Argosol descended in the order: Cu 2+≥Cd 2+≥Pb 2+ > Zn 2+ > Cr 3+, and Cd 2+ > Cu 2+ > Pb 2+ > Zn 2+ > Cr 3+, respectively. The mean Gibbs free adsorption energies of Cu 2+, Zn 2+, Cd 2+, Pb 2+, and Cr 3+ at a field strength of 200 kV cm −1, for example, were in the range of 0.8-3.2 kJ mol −1 for the two soils.