A Mossbauer study of the role of iron impurities in the high temperature reactions of kaolinite minerals

Abstract

Mossbauer spectroscopy was used to study the valence and bonding changes of iron in (a) lattice sites, and (b) cation exchange sites during thermal treatment of kaolinite and halloysite. Lattice iron which is initially in octahedral sites occurs in octahedral and tetrahedral sites at the completion of the thermal reactions. At temperatures below 650°C some divalent ions in cation exchange positions become trivalent and assume octahedral co-ordination, which they retain until the later stages of mullite formation. The implications of the work on the high temperature reaction mechanism and structural sequence are discussed.