### Abstract

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=D_{6}R/(l+R), where R is [Np(VI)]/[Np(V)] and D_{6}the 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 HNO_{3}HNO_{2}solutions were measured which revealed that the activity correction on H^{+}, NO_{3}-, HNO_{2}and H_{2}O was effective enough to give an ideal Nernst relationship for the potential of HNO_{3}HNO_{2} With using the activity coefficient quotient, Y=y_{s}^{2}(y_{u}a_{w})^{1/2}(y_{s}: stoichiometric activity coefficient of nitric acid, y_{u}: activity coefficient of HNO_{2}, a_{w}: rational activity of water), the apparent concentration constant K_{app}was shown to be expressed by K_{app}=K_{mix}Y, where [[inline]] and log K_{mix}=-2.77 and log Y=-0.13, 0.02 and 0.28 for [HNO_{3}]_{t}=3, 4 and 6 M, respectively.

Original language | English |
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Pages (from-to) | 50-59 |

Number of pages | 10 |

Journal | Journal of Nuclear Science and Technology |

Volume | 32 |

Issue number | 1 |

DOIs | |

Publication status | Published - 1995 Jan |

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### Keywords

- 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

### Cite this

*Journal of Nuclear Science and Technology*,

*32*(1), 50-59. https://doi.org/10.1080/18811248.1995.9731668