Biogenic UO_2 _ Characterization and Surface Reactivity

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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; ... continued below

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Singer, D.M.; Farges, F.; Brown, G.E. & Jr. January 3, 2007.

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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}.

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  • 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

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  • Report No.: SLAC-PUB-12230
  • Grant Number: AC02-76SF00515
  • Office of Scientific & Technical Information Report Number: 896938
  • Archival Resource Key: ark:/67531/metadc878257

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  • January 3, 2007

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  • Sept. 22, 2016, 2:13 a.m.

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  • Nov. 22, 2016, 9:20 p.m.

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Singer, D.M.; Farges, F.; Brown, G.E. & Jr. Biogenic UO_2 _ Characterization and Surface Reactivity, article, January 3, 2007; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc878257/: accessed November 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.