Dynamic behavior of sorption of europium onto biotite flakes under the condition of saline groundwater

This study discussed the interaction between Eu and biotite in flakes under the coexistence of Na ions, considering saline groundwater. The sorption experiments were conducted by mixing an Eu solution with Na or K ions and biotite flakes at pH 5. Resultantly, the sorption of Eu gradually increased because of the diffusion into the layered structure of biotite flakes. Thereafter, the sorption amount of Eu with Na ions was less than that without Na ions, and Eu was hardly sorbed with K ions. Additionally, the apparent diffusion coefficients were estimated to be in the order of 10⁻¹³ m²/s based on a two-dimensional diffusion model. These values were lower than the effective diffusion coefficients in plutonic rock, which are employed to assess the performance of geological disposal systems. This indicates that the sorption of Eu in plutonic rock is restricted by the diffusion process in biotite flakes.