Effect of Anions (Cl−, SO2−4) on the Interfacial Properties of Akaganeite (β-FeOOH) in Aqueous Electrolyte Solutions

The point of zero charge (pH pzc ) of the sample (β-FeOOH) is shifted from 7.50 to 8.20 and 8.55, respectively, in KCl and K 2 SO 4 electrolyte media. Intrinsic surface acidity and complexation constants have been calculated by single and double extrapolation methods using Potentiometrie titration data obtained for different concentrations of KCl and K 2 SO 4 in aqueous media. Complexation con stants for K + , Cl − and SO 2− 4 have also been calculated from adsorption data by the same two methods. Close agreement exists between the two sets of values. Chloride ions form SOH 2− 4 – Cl − surface complexes on a β-FeOOH surface, whereas sulphate ions form two types of surface complex i.e. SOH + 2 – SO 2− 4 and SOH + 2 – SO 4 H − . Various parameters such as σ 0 , ψ 0 , ψ d , dσ 0 /dψ 0 , etc. associated with the electrical double layer at the oxide/aqueous KCl and K 2 SO 4 electrolyte solution interface have been calculated from Potentiometrie and adsorption data, and are discussed.