Kinetics of Cesium Sorption by Clay Minerals

Abstract

AbstractTime course and the processes in the sorption of cesium from dilute solutions by illite, montmorillonite and vermiculite saturated with Ca or K and in the absence of excess saturating cation were investigated.Cesium sorbed by illite and montmorillonite quickly reached an approximate equilibrium; the Cs sorbed by montmorillonite did not change with time while the Cs sorbed by illite changed only slightly. On the other hand, the Cs sorbed by vermiculite did not reach an equilibrium even after 500 hr. Cesium sorbed by Ca‐vermiculite continued to increase while the Cs sorbed by K‐vermiculite decreased.Since the sorption of Cs by illite is limited to the external planar surfaces and interlattice edges only, equilibrium is quickly reached. Equilibrium in montmorillonite is attributed to its expanded lattice which makes all exchange sites equally available and permits exchange readily. The increased Cs sorption by Ca‐vermiculite, on the other hand, is attributed to the different sorption rates by different exchange sites: initial fast sorption on external surfaces and edges followed by slow diffusion into the interlayers. The decreased Cs sorption by K‐vermiculite is perhaps associated with the collapse of the partially hydrated vermiculite in suspension to 10A.