Effect of Anions (Cl −,SO 2− 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 K₂SO₄ 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 K₂SO₄ in aqueous media. Complexation con stants for K⁺, Cl⁻ and SO²⁻₄ have also been calculated from adsorption data by the same two methods. Close agreement exists between the two sets of values. Chloride ions form SOH²⁻₄ – Cl⁻ surface complexes on a β-FeOOH surface, whereas sulphate ions form two types of surface complex i.e. SOH⁺₂ – SO²⁻₄ and SOH⁺₂ – SO₄H⁻. Various parameters such as σ₀, ψ₀, ψ_d, dσ₀/dψ₀, etc. associated with the electrical double layer at the oxide/aqueous KCl and K₂SO₄ electrolyte solution interface have been calculated from Potentiometrie and adsorption data, and are discussed.