Hydrolysis of Uranium(VI) at Variable Temperatures (10−85 °C)

• Published in: Journal of the American Chemical Society 2004-05, Vol.126 (17), p.5515-5522
• Main Authors: Zanonato, PierLuigi, Di Bernardo, Plinio, Bismondo, Arturo, Liu, Guokui, Chen, Xueyuan, Rao, Linfeng
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; Inorganic chemistry and origins of life; Kinetics and mechanism of reactions
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0398666

The hydrolysis of uranium(VI) in tetraethylammonium perchlorate (0.10 mol dm-3 at 25 °C) was studied at variable temperatures (10−85 °C). The hydrolysis constants (*β n , m ) and enthalpy of hydrolysis (ΔH n , m ) for the reaction mUO2 2+ + nH2O = (UO2) m (OH) n (2 m - n )+ + nH+ were determined by titration potentiometry and calorimetry. The hydrolysis constants, *β1,1, *β2,2, and *β5,3, increased by 2−5 orders of magnitude as the temperature was increased from 10 to 85 °C. The enthalpies of hydrolysis, ΔH 2,2 and ΔH 5,3, also varied:  ΔH 2,2 became more endothermic while ΔH 5,3 became less endothermic as the temperature was increased. The heat capacities of hydrolysis, ΔC p (2,2) and ΔC p (5,3), were calculated to be (152 ± 43) J K-1 mol-1 and −(229 ± 34) J K-1 mol-1, respectively. UV/Vis absorption spectra supported the trend that hydrolysis of U(VI) was enhanced at elevated temperatures. Time-resolved laser-induced fluorescence spectroscopy provided additional information on the hydrolyzed species at different temperatures. Approximation approaches to predict the effect of temperature were tested with the data from this study.