EXAFS spectroscopic studies of uranium(VI) oxide precipitates

Conference · Mon Apr 01 04:00:00 EST 1996

OSTI ID:464179

Allen, P G ^[1]; Shuh, D K; Bucher, J J ^[2]

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1. Lawrence Berkeley National Lab., CA (United States)
2. Lawrence Berkeley National Lab., CA (United States); and others

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 L{sub III} - 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 {Angstrom} at pH=7 to 1.86 {Angstrom} 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 L{sub III} 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.

• Research Organization: Lawrence Berkeley Lab., CA (United States)
• Sponsoring Organization: USDOE Office of Energy Research, Washington, DC (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 464179
• Report Number(s): LBNL--39934; CONF-960401--73; ON: DE97000627
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AQUEOUS SOLUTIONS
BOND LENGTHS
FINE STRUCTURE
MOLECULAR STRUCTURE
MULTIPLE SCATTERING
PH VALUE
URANIUM OXIDES