Speciation Studies of Metals in Trace Concentrations: The Mononuclear Uranyl(VI) Hydroxo Complexes

Abstract

A direct luminescence spectroscopic experimental setup for the determination of complex stability constants of mononuclear uranyl(VI) hydrolysis species is presented. The occurrence of polynuclear species is prevented by using a low uranyl(VI) concentration of 10–8 M (2.4 ppb). Time-resolved laser-induced fluorescence spectra were recorded in the pH range from 3 to 10.5. Deconvolution with parallel factor analysis (PARAFAC) resulted in three hydrolysis complexes. A tentative assignment was based on thermodynamic calculations: UO22+, UO2(OH)+, UO2(OH)2, UO2(OH)3–. An implementation of a Newton–Raphson algorithm into PARAFAC allowed a direct extraction of complex stability constants during deconvolution yielding log(β1M,1°C)1:1 = −4.6, log(β1M,1°C)1:2 = −12.2, log(β1M,1°C)1:3 = −22.3. Extrapolation to standard conditions gave log(β0)1:1 = −3.9, log(β0)1:2 = −10.9, and log(β0)1:3 = −20.7. Luminescence characteristics (band position, lifetime) of the individual mononuclear hydroxo species were derived to serve as a reference data set for further investigations. A correlation of luminescence spectroscopic features with Raman frequencies was demonstrated for the mononuclear uranyl(VI) hydroxo complexes for the first time. Thereby a signal-to-structure correlation was achieved and the complex assignment validated.

Mononuclear Hydroxo Carbonato Complexes of Np(V), Np(VI), and U(VI): A Density Functional Study

“…More recent measurements of the complexation constants of the carbonato complexes[8c], are in line with these results. Recent measurements of the complexation constants of the hydroxo complexes at low uranium concentrations show a weaker increase than the accepted values measured at higher uranium concentrations, with factors of 1.69 for the dihydroxo and 2.11 for the trihydroxo complexes. Although our model calculations correspond to infinite dilution, the agreement with the results for low uranium concentration is worse, Table .…”

Detection and identification of solids, surfaces, and solutions of uranium using vibrational spectroscopy

“…Current limitations include deconvolution of overlapping vibrational bands in the narrow uranyl spectral window [152] and the relatively low signals from vibrational modes compared to signal collected using other methods, such as fluorescence spectroscopy [247]. Spectral deconvolution techniques can overcome the limitation of unresolved spectral features, and additional computational assessment can provide supporting information on vibrational band assignments and questions related to electronic structure of the uranium cation.…”

“…This review has highlighted the importance of how vibrational spectroscopy can provide insight into uranium chemistry and speciation, but there is an opportunity for the development of new methodologies and techniques that can lead to additional advancements in characterization and detection. Current limitations include deconvolution of overlapping vibrational bands in the narrow uranyl spectral window [152] and the relatively low signals from vibrational modes compared to signal collected using other methods, such as fluorescence spectroscopy [247]. Spectral deconvolution techniques can overcome the limitation of unresolved spectral features, and additional computational assessment can provide supporting information on vibrational band assignments and questions related to electronic structure of the uranium cation.…”

High-Gradient Magnetic Separation of Compact Fluorescent Lamp Phosphors: Elucidation of the Removal Dynamics in a Rotary Permanent Magnet Separator

“…Thus, the emission spectrum, especially when combined with the luminescence decay, carries information about the phosphor and is a unique fingerprint of it. The TRLFS data were analyzed using parallel factor analysis (PARAFAC, N-way toolbox for Matlab [22]), which was previously successfully used for TRLFS data of ionic f-elements [23,24]. Here, we demonstrate the use of TRLFS in combination with PARAFAC for the quantification of an individual phosphor's concentration when suspended in a mixture with other phosphors.…”