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Journal of Applied Electrochemistry

, Volume 39, Issue 6, pp 827–835 | Cite as

Electrochemical redox reactions of chromium and iron ions in molten NaCl–2CsCl eutectic for pyro-reprocessing of nuclear fuels

  • A. UeharaEmail author
  • O. Shirai
  • T. Nagai
  • T. Fujii
  • H. Yamana
Original Paper
  • 201 Downloads

Abstract

Basic electrochemical and spectroscopic properties of Cr3+, Cr2+, Fe3+, and Fe2+ were studied to analyze the cyclic redox reactions of Cr and Fe, which may decrease the current efficiency of the electro-winning method using NaCl–2CsCl melts. The formal redox potentials of the \( {\text{Cr}}^{3 + } |{\text{Cr}}^{2 + } \) and \( {\text{Fe}}^{3 + } |{\text{Fe}}^{2 + } \) couples, \( E_{{{\text{Cr}}^{{ 3 + }} | {\text{Cr}}^{{ 2 + }} }}^{\circ \prime } \) and \( E_{{{\text{Fe}}^{ 3+ } | {\text{Fe}}^{ 2+ } }}^{\circ \prime } \), in NaCl–2CsCl melts at 923 K were spectroelectrochemically determined to be −0.648 ± 0.005 V and \(-0.140 \pm 0.010\,{\text{V}}\,{\text{vs}} .\,{\text{Cl}}_{2}|{\text{Cl}}^{-} \), respectively. These values were determined by measuring electromotive force and UV–VIS absorption spectra at varying concentration ratios of trivalent and divalent ions. Cyclic voltammetry was also carried out to examine the characteristics of the voltammograms for the \( {\text{Cr}}^{3 + } |{\text{Cr}}^{2 + } \) and \( {\text{Fe}}^{3 + } |{\text{Fe}}^{2 + } \) couples in NaCl–2CsCl melts. The \( E_{{{\text{Cr}}^{3 + } |{\text{Cr}}^{2 + } }}^{\circ \prime } \) determined by the spectroelectrochemical method was close to that determined by cyclic voltammetry \( ( - 0.651 \pm 0.006\,{\text{V}}\,{\text{vs}} .\,{\text{Cl}}_{2} |{\text{Cl}}^{-} ) \). The effect of temperature on the \( E_{{{\text{Cr}}^{3 + } |{\text{Cr}}^{2 + } }}^{\circ \prime } \) in NaCl–2CsCl melts was studied by cyclic voltammetry in the range from 823 to 1,023 K \( (E_{{{\text{Cr}}^{3 + } |{\text{Cr}}^{2 + } }}^{\circ \prime } = 0.00143T-1.971 \pm 0.005\,{\text{V}}\,{\text{vs}} .\,{\text{Cl}}_{2} |{\text{Cl}}^{-} ) \). Diffusion coefficients of Cr3+ and Cr2+, \( D_{{{\text{Cr}}^{ 3+ } }}^{{}} \)and \( D_{{{\text{Cr}}^{ 2+ } }}^{{}} \), were determined between 823 and 1,023 K to be \( D_{{{\text{Cr}}^{3 + } }} = 2.23 \times 10^{ - 3} \,{ \exp }( - 4,\!135/T) \) and \( D_{{{\text{Cr}}^{2 + } }} = 3.34 \times 10^{ - 3} \,{ \exp }( - 4,\!106/T) \), respectively. Molar absorptivities of Cr3+ and Cr2+ in NaCl–2CsCl melts at 923 K were determined to be 77.8 ± 2.4 M−1 cm−1 at 17,670 cm−1 and 48.0 ± 1.4 M−1 cm−1 at 9,170 cm−1, respectively. In addition, the effects of these ions on the cyclic redox reaction of the pyro-reprocessing process were discussed.

Keywords

NaCl–2CsCl Cr Fe Spectroelectrochemistry Cyclic redox reaction Formal redox potential 

Notes

Acknowledgement

We thank Mr. Roy Jacobus for his help in improving the English expressions of this paper.

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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • A. Uehara
    • 1
    Email author
  • O. Shirai
    • 2
  • T. Nagai
    • 3
  • T. Fujii
    • 1
  • H. Yamana
    • 1
  1. 1.Division of Nuclear Engineering Science, Research Reactor InstituteKyoto UniversityKumatoriJapan
  2. 2.Division of Applied Life Science, Graduate School of AgricultureKyoto UniversitySakyo, KyotoJapan
  3. 3.Nuclear Fuel Cycle Engineering LaboratoriesJapan Atomic Energy AgencyTokaiJapan

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