Reduction and Oxidation of Fe³⁺ in Dioctahedral Smectites—III. Oxidation of Octahedral Iron in Montmorillonite

Abstract

Abstract Structural Fe 2+ in montmorillonite is readily oxidized by contact with water, salt solutions or on mild heating. This is shown clearly by the Mössbauer spectra and is associated with a sharpening of the infrared absorption near 880 cm −1 . It was inferred that this band comprises the Fe 2+ —OH—Al and Fe 3+ —OH—Al deformations. The rate at which oxidation occurs depends on the exchangeable cations. High acidity of the interlayers is conducive to oxidation, as is contact with Cu 2+ -containing solutions or concentrated H 2 O 2 solutions. The results show clearly that any chemical treatment of montmorillonite causes changes in the oxidation state of structural iron.