Moessbauer studies of oxidation-reduction reactions of absorbed and structural iron in smectite clay minerals

By applying Moessbauer spectroscopy to measuring the isomeric shifts and quadrupole splitting in clay materials, the Fe2+ and Fe3+ chemical states can be unambiguously determined. At the same time, the signal intensity related to the lattice dynamics and bondstrength of the iron probe. These phenomena are used to distinguish between the structurally bound and exchangeable iron ion in clay materials; different configurations of sapporite, attapogyte and bentonite were studied. By the determination of temperature dependence of Moessbauer spectra, it was observed that the signal corresponding to exchangeable iron disappears between 200 and 300 K, depending on the material. This is correlated with the melting layered water in clays, and indicates that the exchangeable iron ions are attached to this water. The experimental results are interpreted using the Debye model