14305-55-6Relevant articles and documents
Stoichiometries and thermodynamic stabilities for aqueous sulfate complexes of U(VI)
Vercouter, Thomas,Vitorge, Pierre,Amekraz, Badia,Moulin, Christophe
, p. 2180 - 2189 (2008)
The formation constants of UO2SO4 (aq), UO 2(SO4)22-, and UO 2(SO4)34- were measured in aqueous solutions from 10 to 75°C by time-resolved laser-induced fluorescence spectroscopy (TRLFS). A constant enthalpy of reaction approach was satisfactorily used to fit the thermodynamic parameters of stepwise complex formation reactions in a 0.1 M Na+ ionic medium: log10 K1(25°C) = 2.45 ± 0.05, ΔrH1 = 29.1 ± 4.0 kJ·mol-1, log10 K 2(25°C) = 1.03 ± 0.04, and ΔrH 2 = 16.6 ± 4.5 kJ·mol-1. While the enthalpy of the UO2(SO4)22- formation reaction is in good agreement with calorimetric data, that for UO 2SO4 (aq) is higher than other values by a few kilojoules per mole. Incomplete knowledge of the speciation may have led to an underestimation of ΔrH1 in previous calorimetric studies. In fact, one of the published calorimetric determinations of ΔrH1 is here supported by the TRLFS results only when reinterpreted with a more correct equilibrium constant value, which shifts the fitted ΔrH1 value up by 9 kJ·mol -1. UO2(SO4)34- was evidenced in a 3 M Na+ ionic medium: log10 K 3(25°C) = 0.76 ± 0.20 and ΔrH3 = 11 ± 8 kJ·mol-1 were obtained. The fluorescence features of the sulfate complexes were observed to depend on the ionic conditions. Changes in the coordination mode (mono- and bidentate) of the sulfate ligands may explain these observations, in line with recent structural data.
Formation of excited uranyl ion in oxidation of U(IV) with xenon trioxide in aqueous solutions of H2SO4 and HClO4: I. Influence of sulfate anions
Khamidullina,Lotnik,Kazakov
, p. 131 - 135 (2008/10/09)
Kinetic and chemiluminescent parameters of U(IV) oxidation with xenon trioxide in 1 M H2SO4 were studied in relation to complexation of U(IV) with SO42- anions. The rate constant of oxidation of the sulfate comp
The effect of temperature on the quenching of the photoluminescence of the uranyl ion in liquid, supercooled, and solid aqueous solutions of sulfuric acid
Lotnik,Khamidullina,Kazakov
, p. 1170 - 1174 (2007/10/03)
The effect of temperature on the lifetime τ of electron-excited uranyl ions (UO22+)* in aqueous H2SO4 (0.2-5.0 M) solutions of UO2SO4 was studied over the temperature range from 77 to 300 K. The activation parameters for the temperature quenching of the photoluminescence (PL) of the electron-excited uranyl ion (UO22+)* were obtained. The temperature dependences of the (UO22+)* PL decay constant (k = 1/τ) obeys the Arrhenius equation only at T > 265 K for a 0.5 M H2SO4 solution and at T > 280 K for a 5 M H2SO4 solution. The temperature dependences of τ for the uranyl ion obtained while cooling the solutions from 300 to 77 K and during their heating exhibit extrema. DTA measurements show that the positions of these extrema coincide with the temperatures of the phase transitions in the samples. The effect of the phase transitions on the temperature dependence of τ is associated with not only the molecular mobility change caused by the phase transition (temperature quenching) but also the concentration quenching of (UO22+)*.
