Solubility of U(VI) in Highly Basic Solutions

T. Yamamura, A. Kitamura, A. Fukui, S. Nishikawa, T. Yamamoto, H. Moriyama

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The solubility of U(VI) was measured in highly basic solutions (p0Hc = -log[OH] ranges from 3 down to 0) at the ionic strength I = 0.5 - 2.0 M (M: mol dm -3) over a wide range of carbonate ion concentrations C = 1 × 10-3 -0.5 M by both oversaturation and undersaturation methods. In oversaturation experiments, the solubility of U(VI) decreased with increasing equilibration time from 1 week to 1 year, suggesting an increase in the crystallinity of the solid phase with aging. The solid phase was identified as Na2U2O7 · x H2O (x = 3-5) by X-ray diffraction. Undersaturation experiments conducted for 1 month with this solid phase indicated a rapid attainment of equilibrium. These data were well interpreted by considering the formation of [UO2(OH)3]-, [UO2(OH),]2- and [UO2(CO3)3]4-, and the apparent equilibrium constants for [UO (OH)3]- and [UC2(OH)4,]2- were determined with fairly small deviations. Using the evaluated solubility product of Na2U2O7 · x H2O (x = 3-5), the stability constants for the above species were evaluated. The upper limit values of the stability constants of the carbonatohydroxodioxouranium(VI) complexes were also evaluated.

Original languageEnglish
Pages (from-to)139-146
Number of pages8
JournalRadiochimica Acta
Issue number3
Publication statusPublished - 1998


  • Carbonate
  • Equilibrium constant
  • Hydrolysis
  • Solubility
  • Solubility limiting solid phase
  • U(VI)

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry


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