Abiotic U(VI) Reduction by Biogenic Mackinawite

Veeramani, H., Qafoku, N. P., Kukkadapu, R., Pruden, A., Murayama, M., Monsegue, N. and Hochella Jr, M. F. (2012) Abiotic U(VI) Reduction by Biogenic Mackinawite. In: Goldschmidt 2012, Montreal, Canada, 24-29 June 2012,

Abstract

Biostimulation of dissimilatory metal and/or sulfate reducing bacteria (DMRB and DSRB) has been extensively researched as a remediation strategy for mitigating subsurface uranium [U(VI)] contamination. These bacteria derive energy by reducing oxidized metals as terminal electron acceptors by utilizing organic substrates as electron donors. Iron [Fe(III)], an abundant subsurface element, represents a substantial sink for electrons from DMRB, and the reduction of Fe(III) leads to the presence of dissolved Fe(II) and/or reactive biogenic Fe(II)- and mixed Fe(II)/Fe(III)- mineral phases. Likewise, reduction of other electron acceptors such as sulfates by DSRB leads to the formation of sulfide-bearing minerals in subsurface environments. Thus, when evaluating the potential for insitu uranium remediation in heterogeneous subsurface media, it is important to understand how the presence of alternative electron acceptors such as Fe(III) and sulfate affect U(VI) remediation and the long term behavior and reactivity of reduced uranium. Consequently, abiotic U(VI) reduction by reactive forms of biogenic Fe(II) and sulfide-bearing minerals will be a potentially important process for uranium immobilization. In this study, amendment of Fe(III) and sulfate to a culture of Shewanella putrefaciens CN32 (DMRB) bacterium, resulted in the production of biogenic mackinawite, a Fe(II)-bearing sulfide mineral. This biogenic mineral was systematically characterized by X-ray powder diffraction (XRD), electron microscopy (SEM, TEM, HRTEM) and Mössbauer spectroscopy. Batch experiments involving biogenic mackinawite and U(VI) were carried out at room temperature under strict anoxic conditions. Following complete reduction of uranium (determined by ICP analysis), the biogenic mackinawite was analyzed by a suite of analytical techniques including X-ray absorption spectroscopy (XAS), SEM, HRTEM and Mössbauer spectroscopy to determine the speciation of uranium and concomitant phase transformation(s) with respect to mackinawite. SEM and selected area electon diffraction (SAED) analyses showed reduction of U(VI) to nanoparticulate UO2 on the surface of biogenic mackinawite. These findings are consistent with XANES analysis that indicate reduction of U(VI) to U(IV) and μXRF analysis that was used to map iron and uranium in the sample. Determining the speciation of uranium is critical to success of a remediation strategy. The present work elucidates abiotic molecular scale redox interactions between biogenic mackinawite and uranium.

• Item Type: Conference Proceedings
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Veeramani, Dr Harish
• Authors: Veeramani, H., Qafoku, N. P., Kukkadapu, R., Pruden, A., Murayama, M., Monsegue, N., and Hochella Jr, M. F.
• College/School: College of Science and Engineering > School of Engineering > Infrastructure and Environment