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The hydrolysis of dioxouranium(VI) investigated using EXAFS and 170-NMR

Moll, H.; Reich, T.; Szabo, Z.
The structure of dioxouranium(VI) as a function of pH at different (CH3)4N-OH concentrations has been investigated with the aid of U LIII EXAFS. Polynuclear hydroxo species were identified by an U-U interaction at 3.808 Å at pH = 4.1. The precipitate formed at pH = 7 has a schoepite like structure. In solution at high pH [0.5M (CH3)4N-OH], the EXAFS and data are consistent with the formation of a monomeric four coordinated uranium(VI) hydroxide complex UO2(OH)42- of octahedral geometry. The first shell contains two O atoms with a U=O distance of 1.830 Å, and four O atoms were identified at a U-O distance of 2.266 Å.
In strong alkaline solutions [> 1 M (CH3)4N)-OH], 17O-NMR spectra indicate the presence of two species, presumably UO2(OH)42- and UO2(OH)53-, which are in rapid equilibrium with one another at 268 K in aqueous solution.

Keywords: EXAFS, Uranyl, Hydrolysis, Structure, 17O-NMR
  • Radiochimica Acta 88(2000),411-415

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Permalink: https://www.hzdr.de/publications/Publ-3176
Publ.-Id: 3176