Dissoluton of Biogenic And Synthetic UO(2) Under Varied Reducing Conditions
The chemical stability of biogenic UO{sub 2}, a nanoparticulate product of environmental bioremediation, may be impacted by the particles' surface free energy, structural defects, and compositional variability in analogy to abiotic UO{sub 2+x} (0 {<=} x {<=} 0.25). This study quantifies and compares intrinsic solubility and dissolution rate constants of biogenic nano-UO{sub 2} and synthetic bulk UO{sub 2.00}, taking molecular-scale structure into account. Rates were determined under anoxic conditions as a function of pH and dissolved inorganic carbon in continuous-flow experiments. The dissolution rates of biogenic and synthetic UO{sub 2} solids were lowest at near neutral pH and increased with decreasing pH. Similar surface area-normalized rates of biogenic and synthetic UO{sub 2} suggest comparable reactive surface site densities. This finding is consistent with the identified structural homology of biogenic UO{sub 2} and stoichiometric UO{sub 2.00}. Compared to carbonate-free anoxic conditions, dissolved inorganic carbon accelerated the dissolution rate of biogenic UO{sub 2} by 3 orders of magnitude. This phenomenon suggests continuous surface oxidation of U(IV) to U(VI), with detachment of U(VI) as the rate-determining step in dissolution. Although reducing conditions were maintained throughout the experiments, the UO{sub 2} surface can be oxidized by water and radiogenic oxidants. Even in anoxic aquifers, UO{sub 2} dissolution may be controlled by surface U(VI) rather than U(IV) phases.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 953593
- Report Number(s):
- SLAC-REPRINT-2009-290; ESTHAG; TRN: US201002%%1421
- Journal Information:
- Environ. Sci. Tech. 42:5600,2008, Vol. 42, Issue 15; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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