title: Surface speciation of Eu3+ adsorbed on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC).
abstract: Time-resolved laser fluorescence spectroscopy (TRLFS) is an effective speciation technique for fluorescent metal ions and can be further extended by the parallel factor analysis (PARAFAC). The adsorption of Eu(3+) 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(3+) surface complexes with kaolinite; an outer-sphere (factor A) complex and two inner-sphere (factors B and C) complexes. Their intensity profiles qualitatively explained the measured adsorption of Eu(3+). Based on the TRLFS results in varied H(2)O/D(2)O media, it was shown that the outer-sphere complex exhibited more rapid fluorescence decay than Eu(3+) 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(3+) concentration. Its spectrum and lifetime were similar to those of Eu(3+) 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)(3), factor C was considered as a poly-nuclear surface complex of Eu(3+) formed at relatively high Eu(3+) concentration.
authors.affiliation: Nuclear Waste Management Organization of Japan, 4-1-23 Shiba, Minato-ku, Tokyo 108-0014, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Ishida
authors.forename: Takumi
authors.initials: T
authors.lastname: Saito
authors.forename: Noboru
authors.initials: N
authors.lastname: Aoyagi
authors.forename: Takaumi
authors.initials: T
authors.lastname: Kimura
authors.forename: Ryuji
authors.initials: R
authors.lastname: Nagaishi
authors.forename: Shinya
authors.initials: S
authors.lastname: Nagasaki
authors.forename: Satoru
authors.initials: S
authors.lastname: Tanaka