Surface complexation modeling of metal adsorption onto goethite in aqueous systems

The triple layer surface complexation model has been used to model the adsorption behavior of copper(II), lead(II), and zinc (II) onto goethite as function of pH, total dissolved metal concentration, the surface area of goethite, and ionic strength. A single reaction involving adsorption of Me^{2+ onto negative surface site (SOH + Me2+ SOMe⁺ + H+) as an inner-sphere complex proved successful in describing adsorption of copper, lead, and zinc under the experimental conditions. The estimated values of the weighted average equilibrium constant of above the reactions are 101.95, 101.19, and 100.34 for copper, lead, and zinc, respectively. The adsorption equilibrium constants were related to the first hydrolysis constant by a linear free-energy relationship.}