Interaction mechanism of radioactive cesium on Beishan granite

Abstract

As an important fission product in the uranium nuclear fission, radioactive cesium (RCs) is one of the key nuclides in the high-level radioactive waste (HLW) disposal. The microscopic mechanism of interaction between Beishan granite and RCs is very essential for the performance and safety evaluation of the HLW disposal. In this article, batch experiments, electron probe microanalysis (EPMA), X-ray absorption fine structure spectroscopy (EXAFS) and micro-X-ray fluorescence (μ-XRF) spectroscopy had been used in studying the interaction between Beishan granite and RCs under different conditions. EPMA and μ-XRF confirmed that biotite and albite/microcline were controlling the retardation of RCs in Beishan granite. EXAFS analysis showed that Cs(I) adsorbed on Beishan granite and albite/microcline mainly as the formation of outer-sphere complexes, while more inner-sphere complexes when adsorbed on biotite. Since the high content of albite/microcline (about 70%) in Beishan granite, the sorption of Cs(I) on albite/microcline cannot be negligible. The general adsorption mode (GAM) for Cs adsorption can quantitatively describe and predict the adsorption-desorption behaviors of Cs(I) on Beishan granite. Groundwater with higher salinity could inhibit the fixation of Cs(I) on Beishan granite to some extent. However, the frayed edge sites on Beishan granite were still effective to trace RCs, and less affected by Beishan groundwater.