Study on the surface complexes of Eu(III) on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS); TRLFS measurement in HO/DO systems

時間分解型レーザー誘起蛍光分光法によるカオリナイトに対する3価ユウロピウムの表面錯体に関する研究; 軽水・重水系における測定

石田 圭輔; 斉藤 拓巳*; 青柳 登   ; 木村 貴海 ; 長崎 晋也*; 田中 知*

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

マイクロ秒時間分解レーザー発光分光法によってカオリナイト表面に吸着したEu(III)錯体の吸着反応に伴なう構造変化を観測した。Eu(III)はマイナーアクチニドの化学アナログとして用いた。カオリナイトは放射性廃棄物の処分場と想定される地帯に広がっている天然鉱物である。1:1のアルミノシリケートであるこの鉱物中のシロキサン面とギブサイト様の端面に吸着した構造をpHや塩濃度を変えることで制御し、その様子をレーザー誘起発光によって観測した結果、内圏型と外圏型の吸着形態が分離できた。

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 -AlO obtained from EXAFS. This discrepancy may suggest a change of character of coordinating HO 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 HO/DO media and evaluate the roles of the surface as an energy accepter and/or an inhibitor affecting the quenching efficiency of HO coordinating to Eu(III) effects of the surface such as energy transfer and the quenching efficiency of HO coordinating Eu(III).