RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

Adsorption of lead ionic species at the goethite aqueous interface, as well as the electrokinetic properties of the system, were measured as a function of pH. The interpretation was based on the Surface Complexation Model assuming that association of lead species with negatively charged surface sites takes place. The electrostatic potential affecting the state of the surface species was obtained from the electrokinetic potential by Gouy–Chapman theory introducing the electrokinetic slipping plane as an adjustable parameter. It was found that singly charged lead species (PbOH⁺) are bound to negatively charged surface sites with the equilibrium adsorption constant log K_a=14±0.2. The capacitance of the Helmholtz layer was found to be C₁=0.4±0.1 F m⁻². These findings were confirmed by employing the standard triple layer model (TLM).