Mechanism of UO2(NO3)(2)center dot 6H(2)O Decomposition under the Action of Microwave Radiation: Part 2

Products of UO2(NO3)(2)center dot 6H(2)O decomposition under the action of microwave radiation (MWR) were studied by thermal gravimetric analysis, X-ray phase analysis, IR spectroscopy, and electron microscopy. The results of physicochemical studies of these decomposition products were compared to the published data for various uranium compounds, including UO2(NO3)(2)center dot 6H(2)O. Apart from gaseous products, the final products of decomposition of 2-10 g of UO2(NO3)(2)center dot 6H(2)O under the action of MWR for 35 min (the maximal process temperature, 170-320 degrees C, is attained in the first 2-5 min of irradiation) are uranyl hydroxonitrate UO2(OH) NO3 and uranium trioxide UO3 or their hydrates. The results obtained are consistent with the mechanism suggested in our previous paper and involving the reactions (1) UO2(NO3)(2)center dot 6H(2)O -> UO2(OH) NO3 + 5H(2)O + HNO3 and (2) UO2(OH) NO3 -> UO3 + HNO3. The physicochemical study confirms the conclusions on the composition of products of UO2(NO3)(2)center dot 6H(2)O decomposition under the action of MWR, made previously on the basis of chemical studies. The only precursor of UO3 in microwave treatment of UO2(NO3)(2)center dot 6H(2)O is UO2(OH) NO3 (or its hydrates). This is the main difference between the courses of uranyl nitrate decomposition under the conditions of microwave and convection heating. In the latter case, uranyl nitrate and its hydrates also participate in the formation of UO3.