Products of Abiotic U(VI) Reduction by Biogenic Magnetite and Vivianite

Veeramani, H., Alessi, D. S., Suvorova, E. I., Lezama-Pacheco, J. S., Stubbs, J. E., Dippon, U., Kappler, A., Bargar, J. R. and Bernier-Latmani, R. (2010) Products of Abiotic U(VI) Reduction by Biogenic Magnetite and Vivianite. In: Goldschmidt 2010, Knoxville, TN USA, 13-18 June 2010,

Abstract

Reductive immobilization of uranium by stimulation of dissimilatory metal-reducing bacteria (DMRB) has been extensively investigated as a remediation strategy for subsurface U (VI) contamination. These bacteria gain energy by reducing oxidized metals as terminal electron acceptors, often using organic electron donors. Thus, when evaluating the potential for in situ uranium remediation, it is important to understand how the presence of alternative electron acceptors affects U (VI) remediation and the long term reactivity of reduced uranium. Iron, an abundant metal in the subsurface, represents a substantial sink for electrons from DMRB, and the reduction of Fe (III) leads to the formation of dissolved Fe2+ or to reactive biogenic Fe (II)- and mixed Fe (II)/Fe (III)- mineral phases. Consequently, indirect abiotic U (VI) reduction by reactive forms of biogenic Fe (II) minerals could be a potentially important process for uranium immobilization. The DMRB Shewanella putrefaciens CN32 was used to synthesize two biogenic Fe (II)-bearing minerals: magnetite and vivianite, which were characterized by XRD, HRTEM and Mössbauer spectroscopy. The present work elucidates abiotic molecular scale redox reactions between biogenic magnetite, vivianite and uranium. While both biogenic magnetite and vivianite reduced U (VI) completely, XAS analysis indicated dramatic differences in speciation of the reduced uranium phase in each case. Biogenic magnetite favored formation of structurally ordered crystalline UO2 and biogenic vivianite led to the formation of a molecular adsorbed U (IV) species, even though UO2 has generally been considered to be the sole end product of U (VI) reduction. Molecular U (IV) species is potentially more labile than UO2 in sub-oxic environments and thus may affect the long-term stability of reduced uranium species post-remediation. This observation suggests that the the speciation of reduced uranium is strongly influenced by the bulk mineralogical composition in the surrounding environment.

• Item Type: Conference Proceedings
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Veeramani, Dr Harish
• Authors: Veeramani, H., Alessi, D. S., Suvorova, E. I., Lezama-Pacheco, J. S., Stubbs, J. E., Dippon, U., Kappler, A., 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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