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

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-133 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.