Fixation of radium by weathered granite from the view point of dependence of ionic size on adsorption reaction

Yamaguchi, Akiko*  ; Kurihara, Yuichi*  ; Tanaka, Kazuya  ; Ohara, Yoshiyuki; Kozai, Naofumi   ; Takahashi, Yoshio*

Clay minerals can adsorb many ions and are abundant at earth surface, which controls dissolved concentrations of various trace ions in natural soil/sediment-water systems. Thus, clay minerals affect various phenomena observed at earth surfaces. In my previous study, it was revealed that ions adsorbed on clay minerals mainly form two types of surface complex, either outer-sphere (OS) or inner-sphere (IS) complex. Furthermore, it was shown that ions smaller than Ba form OS complexes, while ions lager form IS complexes, which suggested that Ba has specific interaction with clay mineral surface. In general, ions forming IS and OS complexes have low and high ion exchangeability, respectively. Therefore, behavior of ion can be predicted by the ionic size. In this study, we focused on the migration of Ra in Ningyo-toge Uranium Mine (Okayama, Japan), where the interaction of Ra with clay minerals can be examined.