Mobility of U and REE on colloids in groundwater and its quality-controlled sampling at the Mizunami Underground Research Laboratory

地下水中におけるコロイドによるUとREEの移動性とその採取方法についての研究

宗本 隆志; 大森 一秋; 岩月 輝希  

Munemoto, Takashi; Omori, Kazuaki; Iwatsuki, Teruki

The mobility of colloids and their association with U and rare earth elements (REEs) in deep granitic groundwater were investigated at the Mizunami Underground Research Laboratory. The groundwater and colloids were sampled from boreholes and fractures in the drift wall. For groundwater sampling from boreholes, anthropogenic colloids formed on the borehole wall randomly contaminate groundwater. The mobile anthropogenic colloids can be removed by replacing contaminated groundwater in the borehole. In contrast, groundwater sampled from drift wall, the effects of natural occurring colloids on the groundwater chemistry were almost negligible. Changes in the concentrations of U in the groundwater sampled from boreholes were associated with the anthropogenic colloids. The mobility of U was facilitated by mobile anthropogenic colloids. The REE was concentrated with large particles in the groundwater sampled from fractures in the drift wall and its mobility was associated with natural REE bearing materials originating from deep granitic groundwater. Our results suggest the mobility of analogue elements are facilitated by different colloidal materials in the deep granitic groundwater.