U(VI) reduction in sulfate-reducing subsurface sediments amended with ethanol or acetate

Abstract

An experiment was conducted with subsurface sediments from Oak Ridge National Laboratory to determine the potential for reduction of U(VI) under sulfate-reducing conditions with either ethanol or acetate as the electron donor. The results showed extensive U(VI) reduction in sediments supplied with either electron donor, where geochemical and microbiological analyses demonstrated active sulfate reduction.

Fig 1

Concentrations of ethanol, acetate, nitrate, sulfate, 0.5 M HCl-extractable Fe(II), aqueous U(VI), and NaHCO₃-extractable U(VI) during the initial phase of the sediment slurry experiment designed to drive the slurries into sulfate-reducing conditions.

Fig 2

(A and B) Concentrations of ethanol (panel A only), acetate, sulfate, and 0.5 M HCl-extractable Fe(II) in ¹³C-labeled ethanol (A)- or ¹³C-labeled acetate (B)-amended slurries during the second (sulfate-reducing) phase of the sediment slurry experiment; panel B also shows sulfate and Fe(II) concentrations in unamended (control) slurries. (C and D) Concentrations of aqueous U(VI) and NaHCO₃-extractable U(VI) in ethanol- or acetate-amended or unamended (control) slurries during the second phase of the sediment slurry experiment.

Fig 3

(A) Relative abundances determined by GC-FID. (B) δ¹³C values for PLFAs determined by GC-IRMS. All data are from the ¹³C-labeled ethanol- and ¹³C-labeled acetate-amended slurries from the second phase of the experiment. All δ¹³C values for the control (unamended) slurries were between 0 and −21‰ and are not shown in panel B. Individual components of the summed PLFA ¹³C peaks, as inferred from parallel PLFA mass quantifications (see the text), are indicated in panel A.