Adsorption behavior of radioactive cesium by non-mica minerals

We studied the adsorption behavior of radioactive cesium (Cs) by the non-mica minerals kaolinite, halloysite, chlorite, montmorillonite, mordenite, MnO2, TiO2, Al2O3, and FeOOH to elucidate the environmental behavior of radioactive Cs fallout from the Fukushima Daiichi Nuclear Power Plant in the Tohoku region of Japan. The adsorption and desorption experiments of Cs on the minerals were carried out at the Cs concentrations 1 x 104, 1 x 105, and 2 x 109 mole L1 at pH 5.5. The desorption of Cs from the minerals was examined using 0.1 mole L1 LiCl, NaCl, KCl, RbCl, and CsCl solutions. The sequential desorption was examined using a 0.1 mole L1 LiCl solution, a 1 mole L1 KCl solution, and a 1 mole L1 HCl solution. The distribution coefficient (K d) for the minerals at the Cs concentration 109 mole L1 was in the order of mordenite > illite > montmorillonite, sericite, MnO2, kaolinite, and halloysite > chlorite, TiO2, Al2O3, and FeOOH, differing from the order observed at higher Cs concentrations. After the sequential desorption by the three reagent solutions, the residual fraction of Cs was higher at the Cs concentration 109 mole L1 than at higher concentrations. Approximately 40%, 40%, 50%, and 25% of the adsorbed Cs were residual in montmorillonite, mordenite, MnO2, and kaolinite, respectively, after the sequential desorption. These results strongly suggest that (1) radioactive Cs at 109 mole L1 is more strongly associated with the non-mica minerals than at higher concentrations of 1 x 104 and 1 x 105 mole L1, and (2) the non-mica minerals montmorillonite, mordenite, kaolinite, and MnO2 contributed to the fixation of the radioactive Cs fallout on Fukushima soil.