Reduction of UO 22+ by H 2

Abstract

The reactivity of H 2 towards UO 2 2+ has been studied experimentally using a PEEK coated autoclave where the UO 2 2+ concentration in aqueous solution containing 2 mM carbonate was measured as a function of time at p H 2 ∼40 bar. The experiments were performed in the temperature interval 74–100 °C. In addition, the suggested catalytic activity of UO 2 on the reduction of UO 2 2+ by H 2 was investigated. The results clearly show that H 2 is capable of reducing UO 2 2+ to UO 2 without the presence of a catalyst. The reaction is of first order with respect to UO 2 2+. The activation energy for the process is 130 ± 24 kJ mol −1 and the rate constant is k 298K=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 UO 2 on the reduction of UO 2 2+ by H 2 could not be confirmed.