The precipitation of ammonium uranyl carbonate (AUC): Thermodynamic and kinetic investigations

The aim of this study is to determine the predominant chemical reaction during precipitation of ammonium uranyl carbonate (AUC) based on thermodynamic analysis and to investigate its kinetics. Four chemical reactions were considered. The Gibbs free energies, ΔrG°(T) derived from the Ulich calculations as a function of temperature have been determined between 293.15 K and 353.15 K. The predominant chemical reaction of AUC precipitation was UO2(NO3)2·6H2O(aq) + 6NH3(g) + 3CO2(g) → (NH4)4UO2(CO3)3(s) + 2NH4NO3(aq) + 3H2O(l). According to the AUC precipitation kinetics results, the reaction best fits a second order rate equation. The rate constants k2 were calculated at 313.15 K and 330.15 K and the activation energy Ea determined using the Arrehenius equation was found as 17.4 kJ/mol.