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Multivariable factor analysis for time-resolved laser fluorescence spectroscopy of the uranyl adsorption on gibbsite

ギブサイト表面へのウラニルの吸着挙動解明に向けたレーザー分光分析に関する多変数因子分析

佐尾 宏和*; 石田 圭輔; 斉藤 拓巳*; 青柳 登   ; 長崎 晋也*; 田中 知*

Sao, Hirokazu*; Ishida, Keisuke; Saito, Takumi*; Aoyagi, Noboru; Nagasaki, Shinya*; Tanaka, Satoru*

ランタノイド・アクチノイドの溶液中における化学状態は時間分解型レーザ蛍光分光法やX線吸収分光などさまざまな分光手法を用いて評価されている。その際に複数の吸着種の共存や鉱物表面の不均質性のために、計測されたスペクトルから溶液中や固体表面における化学種の数,量的変化などの情報を得るには困難が伴う。本研究では、多成分系である鉱物表面における放射性核種の吸着挙動の解明を行う。多様な化学状態をとるウラニルと単純な構造で核種の吸着モデルとして有用なアルミニウム酸化物であるギブサイトの吸着系に着目した。用いたレーザー分析法は、試料中における対象とする金属イオン濃度が他の分光手法に比べて低い条件で測定可能である。加えて、計測にあたり試料の前処理が必要ないため、天然環境条件下での観測が可能となる。こうした系にPARAFACを適用し、その成分抽出法を確立した結果、化学種を解析上分けることが可能になった。

Structures of the Ln/An in solution and on mineral surfaces have been assessed by various spectroscopic techniques. In a relatively simple system containing a few species in solution this can be done unequivocally. However, on mineral surfaces at relatively high pH or in the presence of ligand molecules measured spectra are hard to interpret because of the co-existence of many species and/or the heterogeneity of the surfaces. In addition spectroscopic measurements involve several parameters, not only spectroscopic parameters like wavelength and delay time, but also chemical parameters like pH and concentrations of reactants. Therefore, the information on the number and relative amounts of different chemical species formed should be pursued in the entire multi-dimensional parameter space and one needs a systematic approach based on statistical argument for the purpose. The goal of this study is to construct a multivariable analysis method for TRLFS, which can extract the number of components, their pure spectra and the variation of their quantities from a series of spectra measured as a function of wavelength, time and chemical conditions. Uranyl sorption on gibbsite is studied by TRLFS as a test system for this purpose. It has been shown that the spectral shapes of uranyl on gibbsite varies as the delay time of the detector increases and as pH of the solution is changed, suggesting the presence of multiple sorption complexes of uranyl on gibbsite. The obtained TRLFS spectra are processed by the fixed-size window evolving factor analysis to extract the number of statistically meaningful components, followed by nonlinear least square regression for the deconvolution of temporally varying spectra.

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