Location and migration of cations in Cu2+-adsorbed montmorillonite

Abstract

Location of Cu2+ ion in Cu2+-adsorbed montmorillonite have been studied by electron paramagnetic resonance (EPR), supplemented by X-ray diffraction (XRD) and differential thermal analysis (DTA). In the EPR spectra of Cu2+-adsorbed montmorillonite, three signals, corresponding to Cu2+ ion, have been simultaneously recorded. Some Cu2+ ion seemed to replace the original interlayer metal cations and some entered into the hexagonal cavities. A small fraction of Cu2+ ion penetrated into the octahedral vacancies. There were two ways for the adsorption of Cu2+ ion by montmorillonite — exchangeable and specific. On heating, the hydrated Cu2+ ion in the interlayer loses the coordinating water and then enters into the hexagonal cavities. When the heating temperature further increased, dehydroxylation occurs, which facilitates Cu2+ ion in the hexagonal cavities to penetrate into the octahedral vacancies.