Sorption of cesium on weathered biotite: The effects of cations in solution

Phyllosilicate minerals can control the mobility and distribution of nuclear elements in both natural environments and nuclear waste sites owing to their high reactivity. Radioactive ¹³⁷Cs is an important component of nuclear waste and can be used as a tracer for soil erosion assessment; therefore, information regarding the reaction of ¹³⁷Cs with phyllosilicate minerals is necessary to predict its fate in near-surface environments. Here, biotite samples were artificially weathered with low ph solutions containing k, ca, na, mg, rb, and cs. Cations in the solutions had varying effects on both Si release caused by the dissolution of biotite plates and K release influenced by ion exchange, and in addition to resultant Cs sorption on weathered biotite. Na and Mg had the most significant effects on weathering among the cations. Si release, pH increase, and the results of X-ray diffraction (XRD), and scanning electron microscopy (SEM) verified these effects. These two cations influenced the weathering of biotite through the formation of expandable layers. Monovalent cations such as Na, Rb, and Cs were similar to K in radius and charge and had significant effects on interlayer K replacement in the biotite. The results of this study suggest that plate weathering and cation exchange each differently affect Cs sorption on weathered biotite. Weathered biotite that reacted with Na and Mg solutions had the highest amount of Cs sorption owing to the presence of expandable layers. However, the biotite samples that reacted with Cs, Rb, and K had much lower amounts of Cs sorption possibly because these cations fit relatively well on the frayed edge sites in the weathered biotite and therefore blocked additional sorption of Cs.