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Exafs Spectroscopic Studies of Uranium (VI) Oxide Precipitates

Published online by Cambridge University Press:  10 February 2011

P.G. Allen ,
D.K. Shuh ,
J.J. Bucher ,
N.M. Edelstein ,
C.E.A. Palmer  and
L. N. Marquez
P.G. Allen
Affiliation:
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 Seaborg Institute for Transactinium Science, Lawrence Livermore National Laboratory, Livermore, CA 94551
D.K. Shuh
Affiliation:
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
J.J. Bucher
Affiliation:
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
N.M. Edelstein
Affiliation:
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
C.E.A. Palmer
Affiliation:
Seaborg Institute for Transactinium Science, Lawrence Livermore National Laboratory, Livermore, CA 94551
L. N. Marquez
Affiliation:
Seaborg Institute for Transactinium Science, Lawrence Livermore National Laboratory, Livermore, CA 94551
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Abstract

We have investigated the structures of U(VI) oxides precipitated from room temperature aqueous solutions at low ionic strength as a function of pH. Using the uranium LIII - edge extended x-ray absorption fine structure (EXAFS) as a probe of the local structure around the uranium, a trend is observed whereby the axial oxygen bond lengths from the uranyl groups increase from 1.80 Å at pH=7 to 1.86 Å at pH=11. A concomitant decrease in the equatorial oxygen and nearest-neighbor uranium bond lengths also occurs with increasing pH. Expansion of the linear O=U=O group is seen directly at the L111 absorption edge where multiple scattering resonances systematically shift in energy. EXAFS curve-fitting analysis on these precipitates and a sample of synthetic schoepite indicate that the structure of the species formed at pH=7 is similar to the structure of schoepite. At pH=11, the precipitate structure is similar to that of a uranate.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 432: Symposium S – Aqueous Chemistry and Geochemistry of Oxides , 1996 , 139
Copyright
Copyright © Materials Research Society 1997

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