CHEMOMETRIC AND STATISTICAL-ANALYSIS OF URANIUM(VI) HYDROLYSIS AT ELEVATED U(VI) CONCENTRATIONS

26 UV-Vis spectra of U(VI) samples in the pH range 2.4 to 4.8 and U(VI ) concentration range 6 . 10(-3) M to 2 . 10(-4) M in 0.1 M aqueous pe rchlorate solutions are analyzed simultaneously by model free techniqu es, e.g. factor analysis, target rotation and non-parametric statistic s. Within the investigated range of conditions, three factors only are found to be significantly contributing. UO22+(aq), (UO2)(2)(OH)(2)(2) and (UO2)(3)(OH)(5)(+) are found as the relevant species. A single c omponent spectrum of the (UO2)(3)(OH)(5)(+) species is derived with a molar absorption of epsilon(35) = 474 +/- 7 l mol(-1) cm(-1) at the ab sorption maximum at 429.0 nm of the low-energy electronic transition o f uranium(VI). The complete set of 26 spectra is simultaneously interp reted by Target a Factor Analysis. The evaluated formation constants a re lg K'(22) = -6.14(s) +/- 0.08(8) of (UO2)(2)(OH)(2)(2+) from 21 obs ervations and lg K'(35) = -17.14(2) +/- 0.13(8) of (UO2)(3)(OH)(5)(+) from 14 observations. Owing to the importance of pH determination in e valuating thermodynamic data of hydrolysis species, a rigorous statist ical approach to the evaluation of pH by a multistandard calibration p rocedure is chosen.