The hydrolysis of uranium (VI) in tetraethylammonium perchlorate (0.10 mol dm(-3) at 25 C) was studied at variable temperatures (10-85 degreesC). The hydrolysis constants (*betan,m) and enthalpy of hydrolysis (DeltaHn,m) for the reaction MUO22+ + nH(2)O = (UO2)(m)(OH)n((2M-n)+) + nH(+) were determined by titration potentiometry and calorimetry. The hydrolysis constants, *beta(1,1),*beta(2,2),and *beta(5,3), increased by 2-5 orders of magnitude as the temperature was increased from 10 to 85 degreesC. The enthalpies of hydrolysis, DeltaH(2),(2) and DeltaH(5,3), also varied: DH(2,2) became more endothermic while DeltaH(5,3) became less endothermic as the temperature was increased. The heat capacities of hydrolysis, DeltaC(p(2,2)) and DeltaC(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.

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

ZANONATO, PIER LUIGI;DI BERNARDO, PLINIO;
2004

Abstract

The hydrolysis of uranium (VI) in tetraethylammonium perchlorate (0.10 mol dm(-3) at 25 C) was studied at variable temperatures (10-85 degreesC). The hydrolysis constants (*betan,m) and enthalpy of hydrolysis (DeltaHn,m) for the reaction MUO22+ + nH(2)O = (UO2)(m)(OH)n((2M-n)+) + nH(+) were determined by titration potentiometry and calorimetry. The hydrolysis constants, *beta(1,1),*beta(2,2),and *beta(5,3), increased by 2-5 orders of magnitude as the temperature was increased from 10 to 85 degreesC. The enthalpies of hydrolysis, DeltaH(2),(2) and DeltaH(5,3), also varied: DH(2,2) became more endothermic while DeltaH(5,3) became less endothermic as the temperature was increased. The heat capacities of hydrolysis, DeltaC(p(2,2)) and DeltaC(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.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2466162
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