Location and migration of cations in Cu 2+-adsorbed montmorillonite

Abstract

Locations of Cu 2+ ion in Cu 2+-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 Cu 2+-adsorbed montmorillonite, three signals, corresponding to Cu 2+ ion, have been simultaneously recorded. Some Cu 2+ ions seemed to replace the original interlayer metal cations and some entered into the hexagonal cavities. A small fraction of Cu 2+ ions penetrated into the octahedral vacancies. There were two ways for the adsorption of Cu 2+ ion by montmorillonite — exchangeable and specific. On heating, the hydrated Cu 2+ 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 Cu 2+ ion in the hexagonal cavities to penetrate into the octahedral vacancies.