Surface Behaviour of β-FeOOH: Point of Zero Change and Interactions with Anions and Cations

Abstract

The acid-base dissociation behaviour of the surface of β-FeOOH in aqueous suspension has been investigated by potentiometric titration. The zero point of charge of the electrical double layer of the oxide/solution interface (pH = 7·6 ± 0·1 in KNO 3 , NaNO 3 and LiNO 3 electrolytes) coincides with the pH of the isoelectric point, determined by the solid addition method. Chloride and sulphate anions are strongly adsorbed on the β-FeOOH surface and thus modify the balance of positive and negative groups on the surface. The sequence of interaction of monovalent cations with the surface is K + = ≤ Na + ≤ Li + . β-FeOOH appears to behave essentially in the same manner as found previously for α-FeOOH.