Sorption of cesium on granite under aerobic and anaerobic conditions

Abstract

This study focused on the determination of distribution coefficients (K d) of 137Cs under aerobic (∼21% O2) and anaerobic conditions (1−10 ppm O2) which might be found in the deep geologic environment. The anaerobic conditions were simulated in a glove box filled with highly pure argon (99.9%). Both batch tests and solid-phase analyses, including X-ray diffraction, N2-BET surface area, and polar-microscopy/autoradiography were employed for analyzing the sorption of 137Cs on granite, which is the potential host rock for waste disposal in Taiwan. Before starting batch tests, the rock samples were placed in the glove box for one week, and the E h values of experimental liquids were periodically measured until the E h value decreased below 0 mV. The sorption of 137Cs was studied at various concentrations in synthetic groundwater. The Freundlich sorption isotherm seems to be adequate to quantitatively describe the sorption of Cs for the concentration ranges (i.e., 10-3−10-6 M) conducted in both conditions. The distribution coefficient (K) obtained from the two-week batch tests indicated no obvious difference in two systems and the values of K and n are similar. In addition, sorption onto a specific host rock was found to be dependent on its mineralogical components. The photos obtained from polar-microscopy/autoradiography analyses showed that biotite is the principal mineral component responsible for the sorption of 137Cs onto granite.