Surface Hydroxyl Site Density on Spinel-typeλ-MnO₂ as a Measure of Ion-Exchange Capacity

Abstract

Lambda-manganese dioxide (λ-MnO₂), a spinel-type oxide, has lattice vacancies with a size equal to that of lithium ions, and incorporates lithium ions selectively from aqueous solutions. Oxide surfaces in water are hydroxylated by hydration, and the surface hydroxyl groups adsorb ions non-selectively by ion exchange, interfering with the selective incorporation of lithium ions. In this investigation, the surface hydroxyl groups on λ- MnO₂ were determined by the Grignard method as a measure of ion-exchange capacity. The surface hydroxyl site densities obtained were compared with the calculated value for the closest packing of hydroxyl groups, and the formation of hydroxyl groups was explained by neutralization of surface oxide ions by water.