Murdoch University Research Repository

Welcome to the Murdoch University Research Repository

The Murdoch University Research Repository is an open access digital collection of research
created by Murdoch University staff, researchers and postgraduate students.

Learn more

Alteration of UO2+x under oxidizing conditions, Marshall Pass, Colorado, USA

Deditius, A.P., Utsunomiya, S. and Ewing, R.C. (2007) Alteration of UO2+x under oxidizing conditions, Marshall Pass, Colorado, USA. Journal of Alloys and Compounds, 444-445 . pp. 584-589.

Link to Published Version:
*Subscription may be required


As a natural analogue of the processes and products of spent nuclear fuel (SNF) alteration, we have examined the sequence of phases that form during the alteration of natural UO2+x in a U-deposit at Marshall Pass, Colorado. We have determined the paragenesis of U(VI)-phases including the fate of trace elements: W, Mo, As, Sb, Cu, Ba, Ce, Y, Pb and Th. Enrichment of trace elements, especially W and Mo, in this system resulted in a unique alteration sequence: uraninite → amorphous U-oxyhydrate gel → schoepite(I)/vandendriesscheite/compreignacite → uranophane → schoepite(II)/"dehydrated" schoepite(I) → Ba-Mo-W-U phase/U-arsenates/U-Sb phase → "dehydrated schoepite" (II) → soddyite/swamboite. In this sequence, the Ba-Mo-W uranyl phase and U-Sb phase are newly characterized phases. These results suggest that the UO2+x alteration, involving higher concentrations of certain radionuclides and metallic compounds, may lead to a different paragenesis of U(VI)-phases, as compared with the expected alteration sequence of UO2 interacting with a typical groundwaters. This was also noted in a previous study of the alteration of Pb-rich uraninite [R.J. Finch, R.C. Ewing, J. Nucl. Mater. 190 (1992) 133-156]. Some trace elements, such as CaO 2.08 wt.%, PbO 1.69 wt.%, WO3 1.39 wt.%, As2O3 0.50 wt.% and MoO3 0.41 wt.%, can locally concentrate, but still form uranyl phases. As a consequence, the mobility of U and radionuclides is governed by the stability of these metal-uranyl phases, such as Pb-oxide hydrates, Ba-uranyl molybdates/ tungstates and U-antimonate.

Item Type: Journal Article
Publisher: Elsevier B.V.
Copyright: © 2007 Elsevier B.V.
Item Control Page Item Control Page