Oxidation state and extraction of neptunium with TBP

The change of Np oxidation state in nitric acid and the effect of nitrous a cid on the oxidation state were analyzed by spectrophotometry, solvent extr action, and electrochemical methods. The Np extraction with 30 vol.% TBP wa s enhanced by the adjustment of the Np oxidation state using a glassy carbo n fiber column electrode system. The knowledge of electrolytic behavior of nitric acid was important because the nitrous acid affecting the Np redox r eaction was generated during the adjustment of the Np oxidation state. The Np solution used in this work consisted of Np(V) and Np(VI) but no Np(IV). The ratio of NP(V) in the range of 0.5M similar to5.5 M nitric acid was 32% similar to 19%. The electrolytic oxidation of Np(V) to NpO(VI) in the solut ion enhanced the Np extraction efficiency about five times higher than with out electrolytic oxidation. It was confirmed that the nitrous acid in a con centration of less than about 10(-5) M acted as a catalyst to accelerate th e chemical oxidation reaction of Np(V) to Np(VI).