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XAFS spectroscopic study of uranyl coordination in solids and aqueous solution

Hillary A. Thompson, Gordon E. Brown and George A. Parks
XAFS spectroscopic study of uranyl coordination in solids and aqueous solution
American Mineralogist (June 1997) 82 (5-6): 483-496

Abstract

To evaluate the ability of X-ray absorption fine structure (XAFS) spectroscopy to elucidate the coordination environment of U (super 6+) at the solid-water interface, we conducted an in-depth analysis of experimental XAFS data from U (super 6+) solid and solution model compounds. Using the ab initio XAFS code FEFF6, we calculated phase-shift and amplitude functions for fitting experimental data. The code FEFF6 does a good job of reproducing experimental data and is particularly valuable for providing phase-shift and amplitude functions for neighboring atoms whose spectral contributions are difficult to isolate from experimental data because of overlap of Fourier transform features. In solid-phase model compounds at ambient temperature, we were able to fit spectral contributions from axial O (1.8 Aa), equatorial O (2.2-2.5 Aa), N (2.9 Aa), C (2.9 Aa), Si (3.2 Aa), P (3.6 Aa), distant O (4.3 Aa), and U (4.0, 4.3, 4.9, and 5.2 Aa) atoms. Contributions from N, C, Si, P, distant O, and distant U (4.9 and 5.2 Aa) are weak and therefore might go undetected in a sample of unknown composition. Lowering the temperature to 10 K extends detection of U neighbors to 7.0 Aa. The ability to detect these atoms suggests that XAFS might be capable of discerning inner-sphere U sorption at solid aluminosilicate-water interfaces. XAFS should definitely detect multinuclear U complexes and precipitates. Multiple-scattering paths are minor contributors to uranyl XAFS beyond k = 3 Aa (super -1) . Allowing shell-dependent disorder parameters (sigma (super 2) ) to vary, we observed narrow ranges of sigma (super 2) values for similar shells of neighboring atoms. Knowledge of these ranges is necessary to constrain the fit of XAFS spectra for unknowns. Finally, we found that structures reported in the literature for uranyl diacetate and rutherfordine are not completely correct.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 82
Serial Issue: 5-6
Title: XAFS spectroscopic study of uranyl coordination in solids and aqueous solution
Affiliation: Stanford University, Department of Geological and Environmental Sciences, Stanford, CA, United States
Pages: 483-496
Published: 199706
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 50
Accession Number: 1997-055740
Categories: Geochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 199718
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