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Abiotic reduction of U(VI) by sorbed Fe(II) and the implications for field-scale bioremediation at the Rifle IFC project site


EMSL Project ID
30463

Abstract

Bioremediation of uranium-contaminated sites has recently been explored as a potentially effective groundwater treatment option. The injection of an organic carbon substrate such as acetate stimulates metal reducing bacteria resulting in iron reduction and removal of uranium from the groundwater, presumably by reduction of mobile U(VI) to insoluble U(IV). The efficacy of this technique has been demonstrated at the Rifle, CO integrated field challenge site. There are both biotic and abiotic pathways of U(VI) reduction, and the relative importance of abiotic U(VI) reduction by Fe(II) produced during reductive dissolution of Fe(III) mineral phases is currently unknown. The objectives of the proposed work are 1) to understand the reactivity and kinetic behavior of U(VI) reduction by adsorbed Fe(II), and 2) to assess the relevance of abiotic U(VI) reduction to field-scale processes during biostimulation at Rifle. Our experimental approach will be to characterize both the adsorption and redox reactions of Fe(II) and U(VI) with pure solid phases under anaerobic conditions. We will investigate the adsorption behavior of Fe(II) and U(VI) on different sorbates and the effect of competitive adsorption between the two surface species using a non-redox-reactive proxy for Fe(II). Then we will study the effect of different sorbates on the reduction of U(VI) by enriched 57Fe(II) using Mossbauer spectroscopy, SEM, XANES, EXAFS, and XPS techniques. The mineral phases used will be an aluminum oxide (non-reactive solid phase), a well-characterized clay (such as nontronite), and Fe-oxides, such as goethite, and stoichiometric magnetite [mixed Fe(II)-Fe(III) oxide]. Depending on the results of the pure phase study, we will also examine the effects of natural Rifle sediment on the reaction. The combination of wet chemical techniques and state-of-the-art instrumentation at EMSL will make this type of study possible.

Project Details

Project type
Large-Scale EMSL Research
Start Date
2008-09-22
End Date
2009-09-30
Status
Closed

Team

Principal Investigator

Kate Campbell
Institution
US Geological Survey, Menlo Park

Team Members

James Davis
Institution
US Geological Survey, Menlo Park