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Alteration of Coffinite (USiO4) Under Reducing and Oxidizing Conditions

Published online by Cambridge University Press:  19 October 2011

Artur Piotr Deditius ,
Satoshi Utsunomiya  and
Rodney C. Ewing
Artur Piotr Deditius
Affiliation:
deditius@umich.edu, University of Michigan, Geological Sciences, 1100 N. University Ave., Ann Arbor, MI, 48109, United States, 734-763-5344
Satoshi Utsunomiya
Affiliation:
utu@umich.edu, University of Michigan, Geological Sciences, 1100 N. University Ave., Ann Arbor, MI, 48109, United States
Rodney C. Ewing
Affiliation:
rodewing@umich.edu, University of Michigan, Geological Sciences, 1100 N. University Ave., Ann Arbor, MI, 48109, United States
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Abstract

Samples of natural coffinite (USiO4·nH2O) from Grants uranium region, New Mexico were investigated in order to understand the alteration process of coffinite under reducing and oxidizing conditions. Alteration of the primary coffinite under reducing conditions was promoted by organic acids and as a result secondary coffinite precipitated. Subsequently oxidizing fluids altered the coffinite, and (Na,K)-boltwoodite and jáchymovite precipitated with no rare earth elements. Based on the charge balance calculation we suggest that the amount of U6+ in the coffinite is less than 0.2 [apfu] and U6+ is accommodated in the structure via substitution: U4+ + Si4+ ⇔ U6+ + 2(OH)-. The high and variable analysis total of electron microprobe indicates that H2O is not an essential component in coffinite structure. The U-Pb ages of coffinite formation vary from 36.6-0 Ma suggesting that the coffinite has precipitated continuously in this period and organic matter can preserve reducing conditions even when oxidizing conditions dominate.

Keywords

Utransmission electron microscopy (TEM)corrosion
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 985: Symposium NN – Scientific Basis for Nuclear Waste Management XXX , 2006 , 0985-NN01-08
Copyright
Copyright © Materials Research Society 2007

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