Temperature dependence of cadmium adsorption on oxides. I. Experimental observations and model analysis

The influence of temperature on the adsorption of cadmium on rutile (TiO₂) and hematite (α-Fe₂O₃) is measured at different values of the (initial) surface charge density and salt concentration. The formation of cadmium hydroxo-complexes in solution is simultaneously investigated. Experimental adsorption results are analyzed in terms of the Frumkin-Fowler-Guggenheim model, using a Gouy-Stern double layer picture. Thermodynamic analysis points to a great similarity between the binding of Cd²⁺ with hydroxyl groups on the surface and with OH^- ions in solution. Both processes are entropically driven.