Electrochemical properties of Fe and Al hydroxides as affected by different supporting electrolytes

Potentiometric titration curves of Fe and Al hydroxides, carried out in presence of different electrolytes (KCI, Kbr, KI, KNO3, KCIO4) were elaborated by the Stern theory through a computered program. The zero points of charge (zpc), calculated from the intersection point of the titration curves at different ionic strenght, varied from pH 7.10 to pH 7.65 for Fe hydroxides and from pH 9.10 pH 9.45 for Al hydroxi des. For Fe compounds, a good match was found between the experimental values and those calculated by the Stern model. High deviations were observed only with KCIO4, in whose presence a lowering of the zpc was registered. Also in Al hydroxides the proposed model was not reliable below zpc, indicating that the surface interac tions are somewhat involved in specific adsorption phenomena.