Electrode reaction of Np in a weakly acidic solution

Kitatsuji, Yoshihiro  ; Ouchi, Kazuki  ; Otobe, Haruyoshi  

Electrolytic reactions of Neptunium ions in a weakly acid solution were investigated by using gold electrode. It was reported previously that electrolytic reduction of Neptunium (V) ion based on mediator reaction with Np(III)/Np(IV) couple was observed in the acidic solution when bulk electrolysis was carried out at the potential around -0.2 V versus Ag/AgCl reference electrode. The reduction of Np(V), however, was not observed at the pH higher than 2. This is attributable to low reaction rate of electron exchange reaction between Np(V) and Np(III). Electrode reaction of Np(V) at more negative potential was investigated by cyclic voltammetry. The current peak due to reduction of Np(V) was observed at ca. -0.75 V, and oxidation current was appeared at +0.5 V. The reactions was determined to be reduction of Np(V) and oxidation of deposited species of reduction product of Np on the electrode. It was found that stripping current due to oxidation of deposit was saturated in spite of longer preelectrolysis time. This phenomenon is different from uranium.