Kinetic studies of isothermal decomposition of (NH4)4UO2(CO3)3 to uranium oxide

The ammonium uranyl carbonate, (NH4)4UO2(CO3)3, is an important material used in UO2 and U3O8 ceramics production for the nuclear fuel fabrication. Thermal study and kinetic analysis of ammonium uranyl carbonate conversion under isothermal conditions has been studied in air atmosphere to obtain the tri-uranium octoxide (U3O8), using muffle furnace equipment, UV–visible spectrophotometer, gas adsorption, Hg porosimetry, laser granulometry, and optic spectroscopy. The textural properties (specific surface area, morphology, pore size, grain size, inter-particular porosity, and intra-particular porosity) and characteristics (uranium content and stoichiometry) of the prepared samples were estimated from the physical–chemical characterization. The kinetic parameters were estimated by a fitting of the experimental data. The activation energy Ea , frequency factor A , and reaction rate constants k were calculated from the conventional and iso-conversion kinetic models and were within the range of literature values. The activation energy average values are 36.69 and 30.36 kJ mol−1 by conventional and iso-conversion models, respectively.