Study on the Kinetics of Catalytic Hydrogenation of U(VI) in Nitric Acid Solution Using a Bubble Reactor

The kinetics of hydrogenation/reduction of uranium [U(VI)] has been investigated using a platinum catalyst loaded on silica substrates in a bubble column reactor at atmospheric pressure and room temperature. Effects of catalyst loading, hydrogen flow rate, and concentrations of nitric acid and hydrazine have been investigated. Several kinetic models are derived based on the Langmuir–Hinshelwood mechanism and each of them are evaluated. The experimental results indicate that the surface reaction between dissolved hydrogen and adsorbed reactants on the catalyst surface is the rate controlling step in the hydrogenation of uranyl ion. To test the applicability of the developed rate expression, the mass balance equations for uranium, nitric acid, and hydrogen around the bubble reactor have been solved numerically. The comparison of experimental and predicted results showed a reasonably good agreement.