Issue 41, 2015

Effects of supplemental organic carbon on long-term reduction and reoxidation of uranium

Abstract

Bioreduction of mobile uranyl(VI) (UO22+) to sparingly soluble uraninite (U(IV)O2(s)) is a strategy that has been proposed for in situ remediation of uranium contaminated aquifers. That strategy faces the challenge of reoxidation of uraninite, with consequent release of soluble uranyl when the stimulation of U(VI) bioreduction is terminated. We tested the effects of supplemental organic carbon (ethanol) addition on the long-term reduction and subsequent reoxidation of uranium. In 620 days (31 pore volumes) flow-through bioreduction experiments with 1 or 10 mM ethanol, no obvious difference was observed in effluent U(VI), effluent nitrate, and effluent sulfate. However, a higher concentration of ethanol (10 mM) supported more extensive sulfate reduction to sulfide compared to lower ethanol (1 mM). Upon completion of bioreduction experiments, U(IV) in both 1 and 10 mM ethanol-fed columns was resistant to reoxidation upon addition of oxygenated water to the columns for 110 days (182 pore volumes). Columns that received a higher concentration of ethanol (10 mM) exhibited less U(IV) reoxidation in the presence of nitrate compared to 1 mM ethanol-fed column sediments, and similar results were observed in batch reoxidation experiments in which O2 was used as an oxidant. Our results demonstrate that supplemental organic carbon could protect biogenic U(IV) from remobilization upon intrusion of oxidants.

Graphical abstract: Effects of supplemental organic carbon on long-term reduction and reoxidation of uranium

Supplementary files

Article information

Article type
Paper
Submitted
11 Feb 2015
Accepted
26 Mar 2015
First published
26 Mar 2015

RSC Adv., 2015,5, 32210-32216

Author version available

Effects of supplemental organic carbon on long-term reduction and reoxidation of uranium

F. Luan, G. Zhang, J. M. Senko and W. D. Burgos, RSC Adv., 2015, 5, 32210 DOI: 10.1039/C5RA02550H

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