Chemometric and Statistical Analysis of Uranium(VI) Hydrolysis at Elevated U(VI) Concentrations

Abstract

26 UV-Vis spectra of U(VI) samples in the pH range 2.4 to 4.8 and U(VI) concentration range 6 · 10"' M to 2 · 10" 4 M in 0.1 M aqueous Perchlorate solutions are analyzed simultaneously by model free techniques, e.g. factor analysis, target rotation and non-parametric statistics. Within the investigated range of conditions, three factors only are found to be significantly contributing. UOHaq), (U0 2 ) 2 (0H)r and (U0 2 ),(0H)í are found as the relevant species. A single component spectrum of the (U0 2 )I(0H)Î species is derived with a molar absorption of ε, 5 = 474±7 1 mor' cm"' at the absorption maximum at 429.0 nm of the low-energy electronic transition of uranium(VI). The complete set of 26 spectra is simultaneously interpreted by Target Factor Analysis. The evaluated formation constants are lg K22 = -6.14,±0.08« of (U0 2 ) 2 (0H)r from 21 observations and lg K', 5 = -17.14 2 ±0.13" of (U0 2 ) 3 (0H)J from 14 observations. Owing to the importance of pH determination in evaluating thermodynamic data of hydrolysis species, a rigorous statistical approach to the evaluation of pH by a multistandard calibration procedure is chosen.

Stoichiometry of uranyl hydrolysis reaction in acidic aqueous solutions from the evidence of oxygen exchange kinetics

“…Our data on uranyl hydrolysis in acidic aqueous solutions are close to Meinrath's data [19]. Based on the analysis of electronic absorption spectra of aqueous uranyl solutions at 550 nm, Meinrath concluded that this spectrum is initiated by a superposition of spectra of three uranyl species.…”

Lifetime and fluorescence quantum yield of uranium(VI) species in hydrolyzed solutions

“…Noise reduction was achieved by averaging multiple scans. Interpretation of these spectra by factor analysis [13] suggested three species, in agreement with previous results [13,14] Lifetimes are measured after excitation with a dye-laser pulse at 420 nm. Laser pulse energy was about 100 µJ.…”

“…It has been shown previously that these formation constants are not in agreement with similar other assessments of U(VI) hydrolytic behaviour and also discrepant with direct speciation by using UV-Vis and laser-induced fluorescence spectroscopy [13][14][15]18,19,26].…”

“…The properties of the 13 spectra are investigated by abstract factor analysis (AFA) [13][14][15]17] with some results summarized in Table 1. AFA is a model-free technique that allows inference into UV-Vis absorption data without a priori assumptions and is recently applied to hydrolyzed U(VI) solutions [13][14][15]18,19]. Main advantage of factor analysis techniques is the model-free approach and strong commitment to statistical criteria.…”

Direct spectroscopic speciation of schoepite-aqueous phase equilibria

“…Hence, single component spectra of relevant hydrolysis species have been evaluated by chemometric techniques in undersaturated systems. 4,5 In these studies, only three species are found to be supported by the spectroscopic data in a pH and U(VI) concentration range, where evidence for further species has been claimed in literature -even though with considerable scatter. 6,7 0236 5731/98/USD 17.00 9 1998 Akaddmiai Kiad6, Budapest All rights ' reserved In the following, application of these UV-Vis single component spectra to solid-aqueous phase equilibrium of UO3"2H20(s) under 0.03 kPa CO 2 (air) is reported.…”