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Title: Biogenic UO_2 _ Characterization and Surface Reactivity

Abstract

Nano-scale biogenic UO{sub 2} is easier to oxidize and more reactive to aqueous metal ions than bulk UO{sub 2}. In an attempt to understand these differences in properties, we have used a suite of bulk and surface characterization techniques to examine differences in the reactivity of biogenic UO{sub 2} versus bulk UO{sub 2} with respect to aqueous Zn(II). Precipitation of biogenic UO{sub 2} was mediated by Shewanella putrefaciens CN32, and the precipitates were washed using two protocols: (1) 5% NaOH, followed by 4 mM KHCO{sub 3}/KCl (NA-wash; ''NAUO2'', to remove surface organic matter), and (2) 4 mM KHCO{sub 3}-KCl (BI-wash; ''BIUO2'', to remove soluble uranyl species). BET surface areas of biogenic-UO{sub 2} prepared using the two protocols are 128.63 m{sup 2}g{sup -1} and 92.56 m{sup 2}g{sup -1}, respectively; particle sizes range from 2-10 nm as determined by FEG-SEM. Surface composition was probed using XPS, which showed a strong carbon 1s signal for the BI-washed samples; surface uranium is > 90% U(IV) for both washing protocols. U L{sub III}-edge XANES spectra also indicate that U(IV) is the dominant oxidation state in the biogenic UO{sub 2} samples. Fits of the EXAFS spectra of these samples yielded half the number of uranium second-shellmore » neighbors relative to bulk UO{sub 2}, and no detectable oxygen neighbors beyond the first shell. At pH 7, the sorption of Zn(II) onto both biogenic and bulk UO{sub 2} is independent of electrolyte concentration, suggesting that Zn(II) sorption complexes are dominantly inner-sphere. Fits of Zn K-edge EXAFS spectra for biogenic UO{sub 2} indicate that Zn(II) sorption is dependent on the washing protocol. Zn-U pair correlations are observed for the NA-washed samples, but not for the BI-washed ones, suggesting that Zn(II) sorbs directly to the UO{sub 2} surface in the first case, and possibly to organic matter in the latter. Further work is required to elucidate the binding mechanism of Zn(II) to bulk UO{sub 2}.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
896938
Report Number(s):
SLAC-PUB-12230
TRN: US200705%%14
DOE Contract Number:
AC02-76SF00515
Resource Type:
Conference
Resource Relation:
Journal Name: AIP Conf.Proc.882:277,2007; Conference: Contributed to 13th International Conference on X-ray Absorption Fine Structure (XAFS13), Stanford, California, 9-14 Jul 2006
Country of Publication:
United States
Language:
English
Subject:
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; URANIUM DIOXIDE; ACTIVATION ENERGY; SAMPLE PREPARATION; SURFACE AREA; PARTICLE SIZE; CHEMICAL COMPOSITION; SORPTIVE PROPERTIES; VALENCE; ZINC; SORPTION; Other,BIO

Citation Formats

Singer, D.M., Farges, F., Brown, G.E., and Jr.. Biogenic UO_2 _ Characterization and Surface Reactivity. United States: N. p., 2007. Web.
Singer, D.M., Farges, F., Brown, G.E., & Jr.. Biogenic UO_2 _ Characterization and Surface Reactivity. United States.
Singer, D.M., Farges, F., Brown, G.E., and Jr.. Wed . "Biogenic UO_2 _ Characterization and Surface Reactivity". United States. doi:. https://www.osti.gov/servlets/purl/896938.
@article{osti_896938,
title = {Biogenic UO_2 _ Characterization and Surface Reactivity},
author = {Singer, D.M. and Farges, F. and Brown, G.E. and Jr.},
abstractNote = {Nano-scale biogenic UO{sub 2} is easier to oxidize and more reactive to aqueous metal ions than bulk UO{sub 2}. In an attempt to understand these differences in properties, we have used a suite of bulk and surface characterization techniques to examine differences in the reactivity of biogenic UO{sub 2} versus bulk UO{sub 2} with respect to aqueous Zn(II). Precipitation of biogenic UO{sub 2} was mediated by Shewanella putrefaciens CN32, and the precipitates were washed using two protocols: (1) 5% NaOH, followed by 4 mM KHCO{sub 3}/KCl (NA-wash; ''NAUO2'', to remove surface organic matter), and (2) 4 mM KHCO{sub 3}-KCl (BI-wash; ''BIUO2'', to remove soluble uranyl species). BET surface areas of biogenic-UO{sub 2} prepared using the two protocols are 128.63 m{sup 2}g{sup -1} and 92.56 m{sup 2}g{sup -1}, respectively; particle sizes range from 2-10 nm as determined by FEG-SEM. Surface composition was probed using XPS, which showed a strong carbon 1s signal for the BI-washed samples; surface uranium is > 90% U(IV) for both washing protocols. U L{sub III}-edge XANES spectra also indicate that U(IV) is the dominant oxidation state in the biogenic UO{sub 2} samples. Fits of the EXAFS spectra of these samples yielded half the number of uranium second-shell neighbors relative to bulk UO{sub 2}, and no detectable oxygen neighbors beyond the first shell. At pH 7, the sorption of Zn(II) onto both biogenic and bulk UO{sub 2} is independent of electrolyte concentration, suggesting that Zn(II) sorption complexes are dominantly inner-sphere. Fits of Zn K-edge EXAFS spectra for biogenic UO{sub 2} indicate that Zn(II) sorption is dependent on the washing protocol. Zn-U pair correlations are observed for the NA-washed samples, but not for the BI-washed ones, suggesting that Zn(II) sorbs directly to the UO{sub 2} surface in the first case, and possibly to organic matter in the latter. Further work is required to elucidate the binding mechanism of Zn(II) to bulk UO{sub 2}.},
doi = {},
journal = {AIP Conf.Proc.882:277,2007},
number = ,
volume = ,
place = {United States},
year = {Wed Jan 03 00:00:00 EST 2007},
month = {Wed Jan 03 00:00:00 EST 2007}
}

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  • Nano-scale biogenic UO2 is easier to oxidize and more reactive to aqueous metal ions than bulk UO2. In an attempt to understand these differences in properties, we have used a suite of bulk and surface characterization techniques to examine differences in the reactivity of biogenic UO2 versus bulk UO2 with respect to aqueous Zn(II). Precipitation of biogenic UO2 was mediated by Shewanella putrefaciens CN32, and the precipitates were washed using two protocols: (1) 5% NaOH, followed by 4 mM KHCO3/KCl (NA-wash; 'NAUO2', to remove surface organic matter), and (2) 4 mM KHCO3-KCl (BI-wash; 'BIUO2', to remove soluble uranyl species). BETmore » surface areas of biogenic-UO2 prepared using the two protocols are 128.63 m2g-1 and 92.56 m2g-1, respectively; particle sizes range from 2-10 nm as determined by FEG-SEM. Surface composition was probed using XPS, which showed a strong carbon 1s signal for the BI-washed samples; surface uranium is > 90% U(IV) for both washing protocols. U LIII-edge XANES spectra also indicate that U(IV) is the dominant oxidation state in the biogenic UO2 samples. Fits of the EXAFS spectra of these samples yielded half the number of uranium second-shell neighbors relative to bulk UO2, and no detectable oxygen neighbors beyond the first shell. At pH 7, the sorption of Zn(II) onto both biogenic and bulk UO2 is independent of electrolyte concentration, suggesting that Zn(II) sorption complexes are dominantly inner-sphere. Fits of Zn K-edge EXAFS spectra for biogenic UO2 indicate that Zn(II) sorption is dependent on the washing protocol. Zn-U pair correlations are observed for the NA-washed samples, but not for the BI-washed ones, suggesting that Zn(II) sorbs directly to the UO2 surface in the first case, and possibly to organic matter in the latter. Further work is required to elucidate the binding mechanism of Zn(II) to bulk UO2.« less
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