Interlayer cation effects on the hydration state of smectite

Abstract

BET surface area measurements and XRD and TG analysis were performed on a mixed-layer illite/smectite with 11 percent illite, exchanged with different cations (Li, Na, K, Cs, Mg, Ca, Sr, and Ba), at 30 percent relative humidity. The analyses showed that the exchange cation affects the surface area of clays and so influences the amount of water that can be adsorbed on the clay outer surface. This factor must be taken into account when assessing the actual amount of interlayer water. Most of the exchanged samples studied are homogeneous systems with either one or two water layers in every interlayer. The K-clay, however, is a mixed-layer of one water layer and dehydrated interlayers. D-spacing varies depending on the interlayer cation even when the overall hydration state remains the same. This implies that the density of adsorbed water in a hydrated interlayer depends on the interlayer cation. The study seems to indicate that for Li-, Na-, Mg-, Ca-, Sr-, and Ba-smectite the number of water moles per half formula unit in the interlayer of a fully hydrated smectite (100 percent relative humidity) is approx 4.5.