Deposition of Uranium Oxide Following the Reduction in Weak Acid Solution Using Electrochemical Quartz Crystal Microbalance (EQCM)

We investigated the deposition of U(IV) following a valence change of U as electrodeposition using an electrochemical quartz crystal microbalance. When measurements of the reduction of U(VI) in a weak acid solution were performed, deposits of U(IV) were observed on the electrode surface. From deposition rates, pH dependence of deposition rates, and oxidation potentials of deposits, we proposed the following deposition mechanism. The deposition is divided into the three phases; First, in the induction phase, U(IV) produced by the disproportionation forms U(IV) hydroxide nucleus. Next, in the growth phase, U(IV) deposits begin to grow. In this phase, the deposits catalyze the reduction of U(V) to U(IV), resulting an increase in the reduction current. Finally, in the transformation phase, U(IV) hydroxide species transform into UO2 having more stable state.