Wien Effect Determination of Adsorption Energies between Heavy Metal Ions and Soil Particles

Abstract

Gibbs mean free adsorption energies between cations and charged soil particles are a measure of physicochemical 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 present study, energy relationships between heavy metal ions and particles of yellow‐brown and black soils (an Alfisol and a Mollisol) were inferred from Wien effect measurements in dilute suspensions, in deionized water, of homoionic soil particles (<2 μm) of the two soils saturated with ions of five heavy metals. The results show that the mean Gibbs free binding energies of the heavy metal ions with yellow‐brown and black soil particles diminish in the order Pb 2+ > Zn 2+ ≥ Cu 2+ > Cd 2+ > Cr 3+ , where the range of binding energies for yellow‐brown soil (5.39–8.54 kJ mol −1 ) is less than that for black soil (8.39–9.88 kJ mol −1 ). The electrical field‐dependent mean Gibbs free adsorption energies of these heavy metal ions for yellow‐brown and black soils descend in the order Cu 2+ > Cd 2+ > Pb 2+ > Zn 2+ > Cr 3+ and Cu 2+ > Zn 2+ > Pb 2+ > Cd 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 150 kV cm −1 , for example, are in the range of 0.5 to 2.1 kJ mol −1 for the two soils.