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Title: Biogenic UO2 - Characterization and Surface Reactivity

Abstract

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). BET 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.more » 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

Authors:
 [1];  [1];  [2];  [1];  [3]
  1. Surface and Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, California, 94305-2115 (United States)
  2. (France)
  3. (United States)
Publication Date:
OSTI Identifier:
21054612
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 882; Journal Issue: 1; Conference: XAFS13: 13. international conference on X-ray absorption fine structure, Stanford, CA (United States), 9-14 Jul 2006; Other Information: DOI: 10.1063/1.2644500; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; BIOCHEMISTRY; CORRELATIONS; ELECTROLYTES; FINE STRUCTURE; ORGANIC MATTER; PARTICLE SIZE; PH VALUE; POTASSIUM CHLORIDES; PRECIPITATION; REACTIVITY; SCANNING ELECTRON MICROSCOPY; SODIUM HYDROXIDES; SORPTION; SURFACE AREA; URANIUM; URANIUM DIOXIDE; VALENCE; X-RAY PHOTOELECTRON SPECTROSCOPY; X-RAY SPECTROSCOPY

Citation Formats

Singer, David M., Farges, Francois, Laboratoire de Mineralogie, Museum National d'Histoire Naturelle, CNRS UMR 7160, Paris, Brown, Gordon E. Jr., and Stanford Synchrotron Radiation Laboratory, SLAC, MS 69, 2575 Sand Hill Road, Menlo Park, California, 94025. Biogenic UO2 - Characterization and Surface Reactivity. United States: N. p., 2007. Web. doi:10.1063/1.2644500.
Singer, David M., Farges, Francois, Laboratoire de Mineralogie, Museum National d'Histoire Naturelle, CNRS UMR 7160, Paris, Brown, Gordon E. Jr., & Stanford Synchrotron Radiation Laboratory, SLAC, MS 69, 2575 Sand Hill Road, Menlo Park, California, 94025. Biogenic UO2 - Characterization and Surface Reactivity. United States. doi:10.1063/1.2644500.
Singer, David M., Farges, Francois, Laboratoire de Mineralogie, Museum National d'Histoire Naturelle, CNRS UMR 7160, Paris, Brown, Gordon E. Jr., and Stanford Synchrotron Radiation Laboratory, SLAC, MS 69, 2575 Sand Hill Road, Menlo Park, California, 94025. Fri . "Biogenic UO2 - Characterization and Surface Reactivity". United States. doi:10.1063/1.2644500.
@article{osti_21054612,
title = {Biogenic UO2 - Characterization and Surface Reactivity},
author = {Singer, David M. and Farges, Francois and Laboratoire de Mineralogie, Museum National d'Histoire Naturelle, CNRS UMR 7160, Paris and Brown, Gordon E. Jr. and Stanford Synchrotron Radiation Laboratory, SLAC, MS 69, 2575 Sand Hill Road, Menlo Park, California, 94025},
abstractNote = {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). BET 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.},
doi = {10.1063/1.2644500},
journal = {AIP Conference Proceedings},
number = 1,
volume = 882,
place = {United States},
year = {Fri Feb 02 00:00:00 EST 2007},
month = {Fri Feb 02 00:00:00 EST 2007}
}