Journal article
Fate of trace elements during alteration of uraninite in a hydrothermal vein-type U-deposit from Marshall Pass, Colorado, USA
Geochimica et Cosmochimica Acta, Vol.71(20), pp.4954-4973
2007
Abstract
Alteration of uraninite from a hydrothermal vein-type U-deposit in Marshall Pass, Colorado, has been examined by electron microprobe analysis in order to investigate the release and migration of trace elements W, As, Mo, Zr, Pb, Ba, Ce, Y, Ca, Ti, P, Th, Fe, Si, Al, during alteration, under both reducing and oxidizing conditions. The release of trace elements from uraninite is used to establish constraints on the release of fission product elements from the UO2 in spent nuclear fuels. Uraninite occurs with two different textures: (1) colloform uraninite and (2) fine-grained uraninite. The colloform uraninite contains 1.04-1.75 wt% of WO3, 0.16-1.70 wt% of As2O3, 0.06-0.88 wt% of MoO3; whereas, the fine-grained uraninite retains 2.25-4.93 wt% of WO3, up to 5.76 wt% of MoO3, and 0.26-0.60 wt% of As2O3. The near constant concentration of incompatible W in the colloform uraninite suggests W-incorporation into the uraninite structure or homogeneous distribution of W-rich nano-domains. Incorporation of W and Mo into the uraninite and subsequent precipitation of uranyl phases bearing these elements are critically important to understanding the release and migration of Cs during the corrosion of spent nuclear fuel, as there is a strong affinity of Cs with W and Mo. Zoning in the colloform texture is attributed to variation in the amount of impurities in uraninite. For unaltered zones, the calculated amount of oxygen ranges from 2.08 to 2.32 [apfu, (atom per formula unit)] and defines the stoichiometry as UO2+x and U4O9; whereas, for the altered zones of the colloform texture, the oxygen content is 2.37-2.48 [apfu], which is probably due to the inclusion of secondary uranyl phases, mainly schoepite. The supergene alteration resulted in precipitation of secondary uranyl minerals at the expense of uraninite. Four stages of colloform uraninite alteration are proposed: (i) formation of an oxidized layer at the rim, (ii) corrosion of the oxidized layer, (iii) precipitation of U6+-phases with well-defined cleavage, and (iv) fracture of the uraninite surface along the cleavage planes of the U6+-phases.
Details
- Title
- Fate of trace elements during alteration of uraninite in a hydrothermal vein-type U-deposit from Marshall Pass, Colorado, USA
- Authors/Creators
- A.P. Deditius (Author/Creator) - University of MichiganS. Utsunomiya (Author/Creator) - University of MichiganR.C. Ewing (Author/Creator) - University of Michigan
- Publication Details
- Geochimica et Cosmochimica Acta, Vol.71(20), pp.4954-4973
- Publisher
- Elsevier BV
- Identifiers
- 991005542296007891
- Copyright
- © 2007 Elsevier Ltd.
- Murdoch Affiliation
- Murdoch University
- Language
- English
- Resource Type
- Journal article
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- Citation topics
- 8 Earth Sciences
- 8.242 Nuclear Geology
- 8.242.1362 Uranium Chemistry
- Web Of Science research areas
- Geochemistry & Geophysics
- ESI research areas
- Geosciences