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.

Keywords: Coexisting cations; Cs(+); Granite; Mineral composition; Transport.