Mössbaur Studies of Iron in Illite and Montmorillonite

Abstract

Three-layer type iron bearing clay minerals, Illite and Montmorillonite, have been analyzed by Mössbauer effect with a view to find the oxidation state, coordination symmetry and site distortion of the iron ion. Furthermore, these samples were treated with concentrated solutions of Fe(NO₃)₃, pH 0.1 to study the exchange of cations. It is concluded that in the natural samples of Montmorillonite and Illite, Fe³⁺ ion is in the alumina octahedra in place of Al³⁺ ion. In the case of Montmorillonite, treated with ferric nitrate solution, the iron ion is taken up in three inequivalent sites of cubic symmetry: into the vacant sites of Si tetrahedra as [FeO₄]⁻⁻, in the basal plane and on the broken edges. In the case of Illite, the main exchange location for Fe³⁺ is the broken edge and only a small amount goes into the basal plane.