Infrared Study of Exchangeable Cation Hydration in Montmorillonite

Abstract Infrared absorption spectra in the 3000 cm ‐1 and 1600 cm ‐1 regions are reported for thin films of Na‐, K‐, Li‐, and Ca‐Wyoming bentonite previously dehydrated over P 2 O 5 and over LiCl · H 2 O at room temperature. The spectra of Na‐ and K‐clay exhibited very similar features in the 3000–3500 cm ‐1 region, which, together with other data, lead to the proposal that the exchangeable cations on these montmorillonites are dehydrated at relative humidities less than about 11%. The spectra of Li‐ and Ca‐clay are very different from those of Na‐ and K‐clay. A sharp doublet structure appears to be centered near 3650 cm ‐1 and the absorption in the 3000–3500cm ‐1 region generally is much deeper and broader. These differences are interpreted as evidence of the hydration of the exchangeable cations Li + and Ca 2+ at relative humidities less than about 11%. The conclusions drawn here are in agreement with previous findings based on infrared, differential thermal analysis, and desorption isotherm studies.