Physico-chemical characterization of Cu²⁺-exchanged sepiolite

Copper-sepiolites exchanged at different levels have been studied by ESR, IR, and TG. The results indicate that in the unheated samples the Cu 2+ ions are located in octahedral edge positions. After dehydration, the Cu 2+ ions occur in two positions with different environments. Some of the Cu 2+ ions lose the two molecules of coordinated water in one step, at low dehydration temperatures, and adopt a square pyramidal geometry. Other Cu 2+ ions lose the coordination water in two steps, at lower temperature than the natural sepiolite, and adopt a tetrahedral symmetry.