Evaluation of behavior of rare earth elements based on determination of chemical state in groundwater in granite

Yamamoto, Yuhei; Aosai, Daisuke; Mizuno, Takashi   

Chemical state of rare earth elements (REEs) in deep groundwater was determined by combination of ultrafiltration techniques maintaining in-situ pressure and anaerobic conditions, speciation considering contribution of natural organic matters, and finger-printing method using REE pattern of stability constants for probable complexes of REEs in groundwater. Groundwater samples were collected from a borehole at a depth of 200 m in the Mizunami Underground Research Laboratory (MIU), Gifu, Japan. Spectroscopic analysis for colloidal matters on a membrane filter was also conducted to estimate chemical properties of colloidal ligands. Our results suggest that REEs-humic complexes were the dominant chemical states of REEs in groundwater. Presence of humic substance in groundwater was also confirmed by spectroscopic analysis. It is expected that behavior of REEs mainly depends on humic substances.