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Particle size, Associations, and Crystallinity of Bioreduced Uranium phases


EMSL Project ID
3581

Abstract

Due to mining and nuclear-production activities, uranium is an environmental contaminant of great concern; within surface and subsurface environments, uranium predominates in either the (VI) or (IV) oxidation states. The oxidized form exists as the uranyl cation and is significantly more soluble than the reduced state, which generally precipitates as the mineral, uraninite. While reduction of U(VI) to U(IV) is highly desirable, limiting the migration of this hazardous element, and is readily achieved by the metabolic activity of iron and sulfate reducing bacteria, recent evidence illustrate the importance of uranyl speciation on the extent of reduction. In batch experiments, both abiotic and biotic reduction of U(VI) is greatly limited if a Ca-UO2-CO3 complex dominates the aqueous speciation. This species is, in fact, the most stable form of U(VI) in waters equilibrated with atmospheric carbon dioxide levels and calcium concentrations > 0.4 mM from pH 5 to 8. Here, we examined the reactive transport of U(VI) through packed mineral beds of ferrihydrite coated sand inoculated with the iron reducing bacterium Shewanella putrefaciens, strain CN 32. We specifically tested the impact of varying calcium concentrations on the extent of U(VI) reduction and retention.

Project Details

Project type
Exploratory Research
Start Date
2003-06-26
End Date
2004-07-15
Status
Closed

Team

Principal Investigator

Scott Fendorf
Institution
Stanford University

Related Publications

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