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Bronwyn S. Thomas, Y. Zhang

A kinetic model of the oxidative dissolution of brannerite, UTi₂O₆

The aqueous dissolution of synthetic brannerite (UTi₂O₆) in an open atmosphere has been investigated. Previous data in the literature have been combined with new experimental work, dealing with the release of uranium from brannerite as a function of solution pH and aqueous carbonate species, in oxygenated solutions. From these data we have developed a conceptual model for uranium release from brannerite consisting of two reaction steps: oxidation of surface uranium(IV) atoms, and subsequent detachment of U(VI) atoms into solution, which is catalysed by surface coordination with protons (acidic media) or carbonate species (alkaline media in equilibrium with the atmosphere). A kinetic rate law is derived for this simple reaction mechanism and fitted to experimental data. The resulting predictive equation for uranium release qualitatively describes the pH-dependent behaviour observed in experiment, and quantitatively gives an upper limit for uranium release from brannerite over a range of conditions and experiment types.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 91, 08/2003
Pages: 463

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