Oxidation states and complex ions of uranium in fused chlorides and nitrates

doi:10.1016/0022-1902(59)80233-5

Journal of Inorganic and Nuclear Chemistry

Volume 9, Issues 3–4, March 1959, Pages 290-301

https://doi.org/10.1016/0022-1902(59)80233-5 Get rights and content

Abstract

Oxidation states of uranium in fused LiClKCl eutectic, pyridinium chloride, and LiNO₃KNO₃ eutectic were characterized spectrophotometrically. The (III), (IV) and (VI) oxidation states of uranium are stable in LiClKCl eutectic. The (IV) and (VI) oxidation states have been observed in pyridinium chloride. In LiNO₃KNO₃ eutectic the (III) and (IV) states are oxidized to the (VI) oxidation state.

It was found that Al as well as U metal reduces U(IV) to U(III) while Mg metal reduces U(III) to U(O) in LiClKCl eutectic. On the basis of these experiments the U(III)-U(O) standard potential versus a 1 M Pt reference electrode can be predicted to lie between −1·77 and −2·58 V. The U(IV)-U(III) potential versus the same electrode can be expected to be more positive than −1·77 V.

Spectrophotometric evidence indicates that U(IV) changes its co-ordination number from six to eight in going from fused pyridinium chloride to LiClKCl eutectic. Changes were observed in the UO₂(II) spectrum on addition of chloride ion to UO₂(II) solutions in LiNO₃KNO₃ eutectic which were correlated with the formation of chlorocomplexes of uranyl ion.

References (21)

D.M. Gruen
J. Inorg. Nucl. Chem.
(1957)
D.M. Gruen
Nature, Lond.
(1956)
D.M. Gruen et al.
B.R. Sundheim et al.
Rev. Sci. Instrum.
(1956)
B.R. Sundheim et al.
J. Chem. Phys.
(1958)
W.J. Buckhard et al.
J. Amer. Chem. Soc.
(1957)
H.A. Laitinen et al.
J. Electrochem. Soc.
(1957)
C.R. Boston et al.
J. Phys. Chem.
(1958)
E.R. Van Artsdalen et al.
J. Amer. Chem. Soc.
(1955)
W.M. Latimer
Oxidation Potentials
(1952)

There are more references available in the full text version of this article.

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^☆: Based on work performed under the auspices of the U.S. Atomic Energy Commission.

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Oxidation states and complex ions of uranium in fused chlorides and nitrates☆

Abstract

J. Inorg. Nucl. Chem.

Nature, Lond.

Rev. Sci. Instrum.

J. Chem. Phys.

J. Amer. Chem. Soc.

J. Electrochem. Soc.

J. Phys. Chem.

J. Amer. Chem. Soc.

Oxidation Potentials