Equilibrium of Nitrous Acid-Catalyzed Oxidation of Neptunium in Nitric Acid-TBP Extraction System.

• TOCHIYAMA Osamu

  Department of Nuclear Engineering, Faculty of Engineering, Tohoku University

• NAKAMURA Yoshinobu

  Department of Nuclear Engineering, Faculty of Engineering, Tohoku University

• KATAYAMA Yasushi

  Department of Nuclear Engineering, Faculty of Engineering, Tohoku University

• INOUE Yasushi

  Department of Nuclear Engineering, Faculty of Engineering, Tohoku University

Abstract

The redox equilibrium of neptunium with nitric and nitrous acids, <BR>NpO₂⁺+(3/2)H⁺+(1/2)NO₃^-=NpO₂²⁺+(1/2)HNO₂+(1/2)H₂O<BR>was studied in 3 to 6M nitric acid solutions by 30vol% TBP-dodecane extraction. The equilibrium distribution ratio of neptunium was shown to be expressed by D=D₆R/(1+R), where R is [Np(VI)]/[Np(V)] and D₆ the distribution ratio of pure Np(VI). To examine the dependence of the apparent concentration constant for the reaction, <BR>K_app=[NP(VI)][HNO₂]^1/2/[Np(V)][HNO₃]_t²<BR>on nitric acid concentration, the redox potentials of HNO₃/HNO₂ solutions were measured which revealed that the activity correction on H⁺, NO₃^-, HNO₂ and H₂O was effective enough to give an ideal Nernst relationship for the potential of HNO₃/HNO₂. With using the activity coefficient quotient, Y=y_S²/(y_ua_w)^1/2(y_S: stoichiometric activity coefficient of nitric acid, y_u: activity coefficient of HNO₂, a_w: rational activity of water), the apparent concentration constant K_app was shown to be expressed by K_app=K_mixY, where <BR>K_mix=[Np(VI)]{HNO₂}^1/2{H₂O}^1/2/[NP(V)]{H⁺}^3/2{NO₃^-}^1/2<BR>and log K_mix=-2.77 and log Y=-0.13, 0.02 and 0.28 for [HNO₃]_t=3, 4 and 6M, respectively.

Journal

• Journal of Nuclear Science and Technology

  Journal of Nuclear Science and Technology 32 (1), 50-59, 1995

  Atomic Energy Society of Japan

Keywords

• neptunium
• nitric acid
• nitrous acid
• Purex process
• redox reaction
• redox potential
• solvent extraction
• activity coefficient
• TBP
• pH value

Details

• CRID: 1390001204093950592
• NII Article ID: 10002071908
• NII Book ID: AA00703720
• DOI: 10.3327/jnst.32.50
• COI: 1:CAS:528:DyaK2MXjt1KlsLo%3D
• ISSN: 18811248
• ISSN: 00223131
• Text Lang: en
• Data Source:
  • JaLC
  • Crossref
  • CiNii Articles
• Abstract License Flag: Disallowed