Experimental determination of UO2(cr) dissolution kinetics: Effects of solution saturation state and pH

Pierce, Eric M.; Icenhower, Jonathan P.; Serne, R. Jeffrey; Catalano, Jeffrey G.

doi:10.1016/j.jnucmat.2005.05.012

Cited by 75 publications

(46 citation statements)

References 48 publications

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“…À9 mol m À2 s À1 ) was 48-times higher than the rate published for similar conditions (Pierce et al, 2005). This discrepancy can be due to the higher flow rate and the sequential treatment of the UO 2+x material used in our study.…”

Section: +contrasting

confidence: 67%

Comparative dissolution kinetics of biogenic and chemogenic uraninite under oxidizing conditions in the presence of carbonate

Ulrich

Ilton

Veeramani

et al. 2009

Geochimica et Cosmochimica Acta

100

149

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The long-term stability of biogenic uraninite with respect to oxidative dissolution is pivotal to the success of in situ bioreduction strategies for the subsurface remediation of uranium legacies. Batch and flow-through dissolution experiments were conducted along with spectroscopic analyses to compare biogenic uraninite nanoparticles obtained from Shewanella oneidensis MR-1 and chemogenic UO 2.00 with respect to their equilibrium solubility, dissolution mechanisms, and dissolution kinetics in water of varied oxygen and carbonate concentrations. Both materials exhibited a similar intrinsic solubility of $10 À8 M under reducing conditions. The two materials had comparable dissolution rates under anoxic as well as oxidizing conditions, consistent with structural bulk homology of biogenic and stoichiometric uraninite. Carbonate reversibly promoted uraninite dissolution under both moderately oxidizing and reducing conditions, and the biogenic material yielded higher surface areanormalized dissolution rates than the chemogenic. This difference is in accordance with the higher proportion of U(V) detected on the biogenic uraninite surface by means of X-ray photoelectron spectroscopy. Reasonable sources of a stable U(V)-bearing intermediate phase are discussed. The observed increase of the dissolution rates can be explained by carbonate complexation of U(V) facilitating the detachment of U(V) from the uraninite surface. The fraction of surface-associated U(VI) increased with dissolved oxygen concentration. Simultaneously, X-ray absorption spectra showed conversion of the bulk from UO 2.0 to UO 2+x . In equilibrium with air, combined spectroscopic results support the formation of a near-surface layer of approximate composition UO 2.25 (U 4 O 9 ) coated by an outer layer of U(VI). This result is in accordance with flowthrough dissolution experiments that indicate control of the dissolution rate of surface-oxidized uraninite by the solubility of metaschoepite under the tested conditions. Although U(V) has been observed in electrochemical studies on the dissolution of spent nuclear fuel, this is the first investigation that demonstrates the formation of a stable U(V) intermediate phase on the surface of submicron-sized uraninite particles suspended in aqueous solutions.

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Section: +contrasting

confidence: 67%

Comparative dissolution kinetics of biogenic and chemogenic uraninite under oxidizing conditions in the presence of carbonate

Ulrich

Ilton

Veeramani

et al. 2009

Geochimica et Cosmochimica Acta

100

149

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“…Based on X-ray diffraction crystal structure, the U-U distance for large uraninite particles is 3.867 Å (Wyckoff, 1960). Previous EXAFS studies have shown that the U-U distance contracts from 3.86 to 3.87 Å in UO 2 particles larger than $100 nm (O'Loughlin et al, 2003;Pierce et al, 2005) to 3.80-3.84 Å in UO 2 particles smaller than $2 nm (Suzuki et al, 2002;O'Loughlin et al, 2003).…”

Section: Characterization Of U(iv) Precipitatesmentioning

confidence: 87%

The effect of U(VI) bioreduction kinetics on subsequent reoxidation of biogenic U(IV)

Senko

Kelly

Dohnálková

et al. 2007

Geochimica et Cosmochimica Acta

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“…UO 2 is found in natural ore deposits, spent nuclear fuel waste repositories, and in redox permeable reactive barriers designed to promote uranium reduction through abiotic and biologically mediated processes [1]. With regard to biological processes, metal-reducing bacteria can reduce soluble and mobile U(VI) to U(IV), which precipitates as UO 2 [2].…”

Section: Introductionmentioning

confidence: 99%

Biogenic UO2 — Characterization and Surface Reactivity

Singer

Farges

Brown

2007

AIP Conference Proceedings

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Abstract. Nano-scale biogenic UO 2 is easier to oxidize and more reactive to aqueous metal ions than bulk UO 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 2 versus bulk UO 2 with respect to aqueous Zn(II). Precipitation of biogenic UO 2 was mediated by Shewanella putrefaciens CN32, and the precipitates were washed using two protocols: (1) 5% NaOH, followed by 4 mM KHCO 3 /KCl (NA-wash; "NAUO2", to remove surface organic matter), and (2) 4 mM KHCO 3 -KCl (BI-wash; "BIUO2", to remove soluble uranyl species). BET surface areas of biogenic-UO 2 prepared using the two protocols are 128.63 m 2 g -1 and 92.56 m 2 g -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 III -edge XANES spectra also indicate that U(IV) is the dominant oxidation state in the biogenic UO 2 samples. Fits of the EXAFS spectra of these samples yielded half the number of uranium second-shell neighbors relative to bulk UO 2 , and no detectable oxygen neighbors beyond the first shell. At pH 7, the sorption of Zn(II) onto both biogenic and bulk UO 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 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 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 2 .

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Experimental determination of UO2(cr) dissolution kinetics: Effects of solution saturation state and pH

Cited by 75 publications

References 48 publications

Comparative dissolution kinetics of biogenic and chemogenic uraninite under oxidizing conditions in the presence of carbonate

Comparative dissolution kinetics of biogenic and chemogenic uraninite under oxidizing conditions in the presence of carbonate

The effect of U(VI) bioreduction kinetics on subsequent reoxidation of biogenic U(IV)

Biogenic UO2 — Characterization and Surface Reactivity

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