The Microparticulation with the valence change of uranium in a weakly acid solution

Ouchi, Kazuki  ; Otobe, Haruyoshi  ; Kitatsuji, Yoshihiro  

In previous study, it was found that microparticles of U(IV) formed in reduction process of U(V) enhanced the rate of the disproportionation and the electrolytic reduction of U(V). In this study, we investigated the relationship between reduction process and formation of microparticles by measuring electrochemical quartz crystal microbalance (EQCM). When EQCM measurements of the reduction of U(VI) in a weakly acid solution were performed, the frequency was changed negatively. This indicates that aggregates of U(IV) were formed on the electrode surface. We consider that aggregates form in the three steps from deposition rates; the induction step (start deposition), metastable aggregation step (temporary fast rate) and stable aggregation step (constant rate). The pH dependence of the deposition rate was investigated. When pH was higher, the deposition rates at metastability and stability step were high. This suggests that a U hydroxide relates to the formation of aggregates.