Reduction of UO22+ by H2

The reactivity of H2 towards UO22+ has been studied experimentally using a PEEK coated autoclave where the UO22+ concentration in aqueous solution containing 2 mM carbonate was measured as a function of time at pH2∼40 bar. The experiments were performed in the temperature interval 74–100 °C. In addition, the suggested catalytic activity of UO2 on the reduction of UO22+ by H2 was investigated. The results clearly show that H2 is capable of reducing UO22+ to UO2 without the presence of a catalyst. The reaction is of first order with respect to UO22+. The activation energy for the process is 130 ± 24 kJ mol−1 and the rate constant is k298K=3.6×10−9 l mol−1 s−1. The activation enthalpy and entropy for the process was determined to 126 kJ mol−1 and 16.5 J mol−1 K−1, respectively. Traces of oxygen were shown to inhibit the reduction process. Hence, the suggested catalytic activity of freshly precipitated UO2 on the reduction of UO22+ by H2 could not be confirmed.