RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

The present paper deals with the interfacial behaviour of two samples of hydrous oxides of iron, namely, amorphous hydrated oxide (FeOOH·xH₂O) and akaganeite (β-FeOOH) in aqueous KNO₃ solution. The samples have been characterised by various physico-chemical methods. Both potentiometric and reverse potentiometric (salt) titration methods give similar values of pH_pzc, these being 7.05±0.1 for the amorphous variety and 7.15±0.1 for β-FeOOH. Electrophoretic measurements show that the i.e.p. and pH_pzc of the two samples are almost identical. Intrinsic surface acidity and complexation constants have been calculated by both single and double extrapolation methods using potentiometric titration data. Both methods give similar values of ΔpK^int_a and Δ*K^int_complex. Various parameters of the electrical double layer have been calculated from the site-binding model and are compared with the experimentally found values.