Equilibrium of nitrous acid-catalyzed oxidation of neptunium in nitric acid-tbp extraction system

Osamu Tochiyama, Yoshinobu Nakamura, Yasushi Katayama, Yasushi Inoue

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34 Citations (Scopus)


The redox equilibrium of neptunium with nitric and nitrous acids, [[inline]] was studied in 3 to 6 M nitric acid solutions by 30 vol% TBP-dodecane extraction. The equilibrium distribution ratio of neptunium was shown to be expressed by D=D6R/(l+R), where R is [Np(VI)]/[Np(V)] and D6the distribution ratio of pure Np(Vl). To examine the dependence of the apparent concentration constant for the reaction, on nitric acid concentration. the redox potentials of HNO3HNO2solutions were measured which revealed that the activity correction on H+, NO3-, HNO2and H2O was effective enough to give an ideal Nernst relationship for the potential of HNO3HNO2 With using the activity coefficient quotient, Y=ys2(yuaw)1/2(ys: stoichiometric activity coefficient of nitric acid, yu: activity coefficient of HNO2, aw: rational activity of water), the apparent concentration constant Kappwas shown to be expressed by Kapp=KmixY, where [[inline]] and log Kmix=-2.77 and log Y=-0.13, 0.02 and 0.28 for [HNO3]t=3, 4 and 6 M, respectively.

Original languageEnglish
Pages (from-to)50-59
Number of pages10
JournalJournal of Nuclear Science and Technology
Issue number1
Publication statusPublished - 1995 Jan
Externally publishedYes


  • Activity coefficient
  • Neptunium
  • Nitric acid
  • Nitrous acid
  • Ph value
  • Purex process
  • Redox potential
  • Redox reaction
  • Solvent extraction
  • TBP

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Nuclear Energy and Engineering


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