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Center for Biofilm Engineering
Abstract:
"Reduction of Uranium (VI) under Sulfate-Reducing Conditions in the
Presence of Fe(III)-(hydr)oxides"
04-014 Hexavalent uranium [U(VI)] dissolved in a modified lactate-C medium was treated
under anoxic conditions with a mixture of an Fe(III)-(hydr)oxide mineral
(hematite, goethite, or ferrihydrite) and quartz. The mass of
Fe(III)-(hydr)oxide mineral was varied to give equivalent Fe(III)-mineral
surface areas. After equilibration, the U(VI)-mineral suspensions were
inoculated with sulfate-reducing bacteria, Desulfovibrio desulfuricans
G20. Inoculation of the suspensions containing sulfate-limited medium yielded
significant G20 growth, along with concomitant reduction of sulfate and U(VI)
from solution. With lactate-limited medium, however, some of the uranium that
had been removed from solution was resolubilized in the hematite treatments and,
to a lesser extent, in the goethite treatments, once the lactate was depleted.
No resolubilization was observed in the lactate-limited ferrihydrite treatment
even after a prolonged incubation of 4 months. Uranium resolubilization was
attributed to reoxidation of the uraninite by Fe(III) present in the (hydr)oxide
phases. Analysis by U L3-edge XANES spectroscopy of mineral specimens
sampled at the end of the experiments yielded spectra similar to that of
uraninite, but having distinct features, notably a much more intense and
slightly broader white line consistent with precipitation of nanometer-sized
particles. The XANES spectra thus provided strong evidence for SRB-promoted
removal of U(VI) from solution by reductive precipitation of uraninite.
Consequently, our results suggest that SRB mediate reduction of soluble U(VI) to
an insoluble U(IV) oxide, so long as a suitable electron donor is available.
Depletion of the electron donor may result in partial reoxidation of the U(IV)
to soluble U(VI) species when the surfaces of crystalline Fe(III)-(hydr)oxides
are incompletely reduced.
Sani, R.K., B.M. Peyton, J.E. Amonette, and G.G. Geesey, "Reduction of Uranium
(VI) under Sulfate-Reducing Conditions in the Presence of Fe(III)-(hydr)oxides,"
Geochimica et Cosmochimica Acta 68(12):2639-2648 (2004). |
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