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The effect of aging on the stability of microbially-reduced uranium in natural sediments

DOI: 10.1021/acs.est.8b07023 DOI Help

Authors: Luca Loreggian (Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML) , Agnes Novotny (Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML) , Sophie Louise Bretagne (Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML) , Barbora Bartova (Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML) , Yuheng Wang (Northwestern Polytechnical University) , Rizlan Bernier-latmani (Environmental Microbiology Laboratory (EML), EPFL-ENAC-IIE-EML)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Environmental Science & Technology

State: Published (Approved)
Published: November 2019
Diamond Proposal Number(s): 17472

Abstract: Reductive immobilization of uranium has been explored as a remediation strategy for the U-contaminated subsurface. Via the in-situ biostimulation of microbial processes, hexavalent U is reduced to less soluble tetravalent species which are immobilized within the sediments. Although the mineral uraninite (UO2) was initially considered the dominant product of biological reduction, non-crystalline U(IV) species (NCU(IV)) are found to be abundant in the environment, despite their greater susceptibility to oxidation and remobilization. However, it has been recently proposed that, through aging, NCU(IV) might transform into UO2, which would potentially enhance the stability of the reduced U pool. In this study, we performed column experiments to produce NCU(IV) species in a natural sediment mimicking the environmental conditions during bioremediation. Bioreduced sediments retrieved from the columns and harboring NCU(IV), were incubated in static microcosms under anoxic conditions, to allow the systematic monitoring of U coordination by X-ray absorption spectroscopy (XAS) over 12 months. XAS revealed that, under the investigated conditions, the speciation of U(IV) does not change over time. Thus, because NCU(IV) is the dominant species in the sediments, bioreduced U(IV) species remain vulnerable to oxidation and remobilization in the aqueous phase even after a 12-month aging period.

Journal Keywords: Non-crystalline tetravalent uranium; aging effect; transformation; X-ray absorption spectroscopy; uraninite

Subject Areas: Chemistry, Biology and Bio-materials, Environment

Instruments: I20-Scanning-X-ray spectroscopy (XAS/XES)

Other Facilities: Stanford Synchrotron Radiation Lightsource (SSRL)