Surface speciation of Eu adsorbed on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC)

時間分解レーザー蛍光法とパラレル因子分析法によるユウロピウムのカオリナイトへの吸着形態に関する研究

石田 圭輔*; 斉藤 拓巳*; 青柳 登   ; 木村 貴海 ; 永石 隆二 ; 長崎 晋也*; 田中 知*

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

Time-resolved laser fluorescence spectroscopy is an effective speciation technique for fluorescent metal ions, which can be further extended by the parallel factor analysis. The adsorption of Eu on kaolinite as well as gibbsite as a reference mineral was investigated by TRLFS together with batch adsorption measurements. The PAFAFAC modeling provided the fluorescence spectra, decay lifetimes and relative intensity profiles of three Eu surface complexes with kaolinite; an outer-sphere complex and two inner-sphere complexes. Their intensity profiles qualitatively explained the measured adsorption of Eu. Based on the TRLFS results in varied HO/DO media, it was shown that the outer-sphere complex exhibited more rapid fluorescence decay than Eu aquo ion, because of the energy transfer to the surface. Factor B was an inner-sphere complex, which became dominant at relatively high pH, high salt concentration and low Eu concentration. Its spectrum and lifetime were similar to those of Eu adsorbed on gibbsite, suggesting its occurrence on the edge face of the gibbsite layer of kaolinite. From the comparison with the spectra and lifetimes of crystalline or aqueous Eu(OH), factor C was considered as a poly-nuclear surface complex of Eu formed at relatively high Eu concentration.