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Study on the surface complexes of Eu(III) on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS); TRLFS measurement in H$$_{2}$$O/D$$_{2}$$O systems

Ishida, Keisuke; Saito, Takumi*; Aoyagi, Noboru   ; Kimura, Takaumi ; Nagasaki, Shinya*; Tanaka, Satoru*

Eu(III) surface complexes on kaolinite are investigated by TRLFS. It is as a model of clay mineral particles that can be released from engineered barrier of nuclear waste disposal or present as intrinsic aquatic or groundwater colloids. Kaolinite is a 1:1 aluminosilicate that has two reactive sites: Si-O site on the siloxane basal face and Al-O site on gibbsite-like edge face. It is probable that the outer-sphere complexes resulting from cation exchange at the Si-O site, while the inner-sphere complex is formed on the Al-O site. However, the reported lifetime of the inner-sphere complex showed the hydration number is 2.6, which does not agree with the structure of trivalent lanthanide on -Al$$_{2}$$O$$_{3}$$ obtained from EXAFS. This discrepancy may suggest a change of character of coordinating H$$_{2}$$O upon sorption or energy transfer from Eu(III) to the surface. The purpose of this study is to unveil these aspects and address the applicability of TRLFS. At the conference, we show the results of TRLFS measurements of Eu(III) on kaolinite in H$$_{2}$$O/D$$_{2}$$O media and evaluate the roles of the surface as an energy accepter and/or an inhibitor affecting the quenching efficiency of H$$_{2}$$O coordinating to Eu(III) effects of the surface such as energy transfer and the quenching efficiency of H$$_{2}$$O coordinating Eu(III).

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