Method to Estimate the Contribution of Molecular U(IV) to the Product of U(VI) Reduction

Alessi, D. A., Uster, B., Veeramani, H., Stubbs, J. E., Lezama-Pacheco, J. S., Bargar, J. R. and Bernier-Latmani, R. (2010) Method to Estimate the Contribution of Molecular U(IV) to the Product of U(VI) Reduction. In: Goldschmidt 2010, Knoxville, TN USA, 13-18 June 2010,

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Abstract

The reduction of soluble hexavalent uranium to tetravalent uranium can be catalyzed by bacteria and minerals in the subsurface. A reported end-product of this reduction is the mineral uraninite (UO2), which is desirable because of its low solubility. Although uraninite was long assumed to be the only product of U (VI) reduction, our present work indicates the formation of an adsorbed U (IV) species –dubbed molecular U (IV)– under certain geochemical conditions. The presence of this species was confirmed using X-ray absorpion spectroscopy (XAS). High resolution transmission electon microscopy (HRTEM) with electron diffraction further confirmed a non-crystalline uranium reduction product. The discovery of molecular U (IV) is an important development because this species is likely to be more labile and susceptible to reoxidation than uraninite. Thus, current conclusions about the stability of reduced uranium in the subsurface may need to be reassessed. Here, we propose a wet chemical method to differentiate between molecular U (IV) and uraninite in environmental samples which may contain a mixture of the two. The method utilizes a concentrated bicarbonate solution to extract molecular U (IV) from Shewanella oneidensis MR-1 cells, biogenic and chemogenic Fe (II) solid phases, and contaminated sediments over the course of several hours. To calibrate the method, U (IV) is extracted from known mixtures of uraninite and monomeric U (IV). Our results show that molecular U (IV) is efficiently removed from biological cells and Fe (II) phases by bicarbonate extraction, without affecting uraninite stability. Both extracted and unextracted samples were analyzed using XAS to validate the results of the extraction. Our extraction method provides a rapid alternative to XAS analysis to estimate molecular U (IV) in environmental samples.

Item Type:Conference Proceedings
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Veeramani, Dr Harish
Authors: Alessi, D. A., Uster, B., Veeramani, H., Stubbs, J. E., Lezama-Pacheco, J. S., Bargar, J. R., and Bernier-Latmani, R.
College/School:College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
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