Binding of cadmium at the goethite aqueous interface

Abstract

The adsorption of cadmium ionic species at the goethite aqueous interface was measured as a function of pH. The electrokinetic properties of the system were also investigated. The surface complexation model was used for interpretation, and the association of cadmium species with negatively charged surface sites was considered. The electrostatic potential affecting the state of the surface species was calculated from the electrokinetic potential by Gouy-Chapman theory introducing the electrokinetic plane separation as an adjustable parameter. It was found that singly charged cadmium species are adsorbed on negatively charged surface sites with the corresponding equilibrium adsorption constant log K = 13.3 ± 0.35. The capacitance of the Helmholtz layer was found to be between 2 and 2.5 F m-2. © Springer-Verlag 1999.