The Impact of pH and Ion Exchange on 133Cs Adsorption on Vermiculite

Abstract

Many studies have shown that the adsorption of ions like K and Cs on 2:1 clay minerals can prompt the collapse of their interlayers and render the adsorbing ions nonexchangeable. This study sought to better understand this unique adsorption mechanism through the generation of an adsorption envelope for Cs adsorption on vermiculite and the exploration of the kinetics of interlayer collapse. The collapse of the vermiculite interlayer was confirmed via X-ray diffraction (XRD), and the timing of interlayer collapse was determined by placing Cs in competition with K at different time intervals. The adsorption envelope for Cs on vermiculite showed that although H competition does affect the adsorption of Cs on vermiculite, the effect of this competition is quite limited, even at very low pH values. This hypothesis is supported by the fact that XRD demonstrated a significant decrease in interlayer dimension after Cs adsorption. Finally, kinetics experiments showed that the irreversible adsorption of K and the collapse of the interlayer may take place on a much longer time scale than previously considered.