Transport behaviors of Cs+ in granite porous media: Effects of mineral composition, HA, and coexisting cations

Abstract

The transport of radiocesium (RCs) in granite has attracted great concerns for the consideration of a long-term safety assessment and performance evaluation of the nuclear waste disposal repository. In this study, the transport behaviors of Cs+ in granite were addressed and quantified by column experiments, sequential extraction, and a convection-dispersion equation model. The transport of Cs+ in granite experienced at least two stages including a rapid increase and a slow increase stages. The retardation of Cs+ in granite obviously became higher as biotite content increased. However, a consistent breakthrough plateau and almost overlapped breakthrough curves were observed under different feldspar contents, which suggested that the transport behaviors of Cs+ in granite was quite close to feldspar. Compared to Na+, K+ could effectively inhibit Cs+ adsorption and facilitate the mobility of Cs+ in granite column. In the presence of Sr2+, the transport of Cs+ was provoked in the granite column mainly due to the high competition effects. Humic acid (HA) did not obviously change the transport behaviors of Cs+ in granite column; however, HA could weakly change the adsorption species of Cs+ during Cs+ transport in granitic media. Both sequential extraction and two-site non-equilibrium model suggested that feldspar was the main contributor to the weak adsorption sites and biotite was responsible for the strong affinity sites for Cs+ in Beishan granite. The findings could provide important insights into RCs transport and fate in granitic media.