The double chlorides of tetravalent actinides and cesium, Cs2AnCl6 (An=U, Np, or Pu), have been studied as starting materials for the preparation of intermetallides, of AnAln (n=2,3 or 4) by interaction with aluminium. The reactions were performed in an inert atmosphere at a temperature of 600–900°C with various reactant ratios. To develop a convenient method for the preparation of Cs2 AnCl6 compounds, their solubilities have been measured in water-organic solvents containing methanol, acetone or acetonitrile up to 60 vol.%. The presence of organic components in the range of 50–60 vol % make the solubilities of Cs2AnCl6 low enough to obtain high yields of the compounds. On the basis of the results presented a new method for preparation of actinide intermetallides and alloys is proposed.
The process of platinum-catalyzed uranium(VI) reduction with hydrazine in sulfuric acid media has been studied. The influence of sulfuric acid and hydrazine concentrations, and temperature on the reaction rate were investigated. A new reaction mechanism is proposed. The process allows to obtain pure U(IV) sulfate solutions with concentrations of up to 0.3 mol·l–1. Further increase of initial U(VI) concentrations is limited by the reductant solubility in sulfuric acid media.
Authors:H. Abdunnabi, S. Nikitenko, and T. Afonasieva
The kinetics of oxidation of uranium(IV) monofluoride complex by nitrous acid in nitric acid solution have been studied. The experiments were carried out at constant ionic strength of 2M (HNO3 and NaNO3) and temperature in the range of 18–47 °C. The rate of reaction was determined spectrophotometrically at a wavelength of 621 nm, at which the molar extinction coefficients of UF3+ and UF
are the same. It was shown that reaction orders for [HNO2] and [HNO3] are equal to 0.12 and 0.39, respectively. The values of activation parameters H and S are determined to be 83 kJ mol–1 and 75 J (mol·K)–1, respectively. The rate order of the reaction studied has a weak direct dependence on [H+] in contrary to the strong and reverse dependence in the absence of fluoride ions. In conclusion, fluoride ions may strongly stabilize the U(IV) in nitric acid solutions.