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Yoshinori Suzuki, T. Nankawa, T. Yoshida, Takuo Ozaki, T. Ohnuki, Arokiasamy J. Francis, S. Tsushima, Y. Enokida, I. Yamamoto

Reduction behavior of uranium in the presence of citric acid

Keywords: Uranium-citrate complex, Reduction, Speciation, Column electrode, Absorption spectrum

We examined the reduction behavior of UO₂²⁺ in citrate media at pH 2.0−7.0 by column electrodes. At pH 2.0, UO₂²⁺ was reduced to U(IV) through a one-step reduction process, while it was reduced to U(IV) through a two-step reduction process at pH 3.0−5.0. The reduction potential of UO₂²⁺ shifted to lower values with an increase in pH from 2.0 to 7.0. At pH 6.0 and 7.0, UO₂²⁺ was not reduced to U(IV) completely at the electrode potential above -0.8 V vs . silver/silver chloride electrode. Ultraviolet-visible spectroscopy and speciation calculation of UO₂²⁺ in citrate media indicated that uranium existed as a mixture of UO₂²⁺, [UO₂Cit]^- and [(UO₂)₂Cit₂]^2- at pH 2−3, and a predominant species at pH 3−5 was [(UO₂)₂Cit₂]^2- (H₃Cit: citric acid). At pH 5−7, polymeric complexes, probably, [(UO₂)₃Cit₃]^3- and [(UO₂)₆Cit₆(OH)₁₀]^16- were present. These findings suggest that the reduction of UO₂²⁺ is more difficult by polymerization of UO₂²⁺ with citric acid at higher pHs. Absorption spectra of the reduced complexes showed that U(IV) forms soluble complexes with citric acid at pH 2.0−5.0, and presence of U(V) species was not observed during the reduction of UO₂²⁺.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 94, 09/2006
Pages: 579 - 583

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