Authors:Kwang-Wook Kim, Eil-Hee Lee, In-Kyu Choi, Jae-Hyung Yoo, and Hyun-Soo Park
The electrochemical redox behavior of nitric acid was studied using a glassy carbon fiber column electrode system, and its reaction mechanism was suggested and confirmed in several ways. Electrochemical reactions in less than 2.0M nitric acid was not observed. However, in more than 2.0M nitric acid, the reduction of nitric acid to nitrous acid occurred and the reduction rate was slow so that the nitric acid solution had to be in contact with an electrode for a period of time long enough for an apparent reduction current of nitric acid to nitrous acid to be observed. The nitrous acid generated in more than 2.0M nitric acid was rapidly and easily reduced to nitric oxide by an autocatalytic reaction. Sulfamic acid was confirmed to be effective to destroy the nitrous acid. At least 0.05M sulfamic acid was necessary to scavenge the nitrous acid generated in 3.5M nitric acid.
Authors:Kwang-Wook Kim, Kee-Chan Song, Eil-Hee Lee, In-Kyu Choi, and Jae-Hyung Yoo
The change of Np oxidation state in nitric acid and the effect of nitrous acid on the oxidation state were analyzed by spectrophotometry, solvent extraction, and electrochemical methods. The Np extraction with 30 vol.% TBP was enhanced by the adjustment of the Np oxidation state using a glassy carbon fiber column electrode system. The knowledge of electrolytic behavior of nitric acid was important because the nitrous acid affecting the Np redox reaction 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 0.5M5.5 M nitric acid was 32%19%. The electrolytic oxidation of Np(V) to Np(VI) in the solution enhanced the Np extraction efficiency about five times higher than without electrolytic oxidation. It was confirmed that the nitrous acid in a concentration of less than about 10–5 M acted as a catalyst to accelerate the chemical oxidation reaction of Np(V) to Np(VI).