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Reoxidation of reduced uranium with iron(III) (hydr)oxides under sulfate-reducing conditions.

Environmental science & technology (2005-05-06)
Rajesh K Sani, Brent M Peyton, Alice Dohnalkova, James E Amonette
ABSTRACT

In cultures of Desulfovibrio desulfuricans 620 the effects of iron(III) (hydr)oxides (hematite, goethite, and ferrihydrite) on microbial reduction and reoxidation of uranium (U) were evaluated under lactate-limited sulfate-reducing conditions. With lactate present, G20 reduced U(VI) in both 1,4-piperazinediethanesulfonate (PIPES) and bicarbonate buffer. Once lactate was depleted, however, microbially reduced U served as an electron donor to reduce Fe(III) present in iron(III) (hydr)oxides. With the same initial amount of Fe(III) (10 mmol/L) for each iron(III) (hydr)oxide, reoxidation of U(IV) was greater with hematite than with goethite orferrihydrite. As the initial mass loading of hematite increased from 0 to 20 mmol of Fe(III)/L, the rate and extent of U(IV) reoxidation increased. Subsequent addition of hematite [15 mmol of Fe(III)/L] to stationary-phase cultures containing microbially reduced U(IV) also resulted in rapid reoxidation to U(VI). Analysis by U L3-edge X-ray absorption near-edge spectroscopy (XANES) of microbially reduced U particles yielded spectra similar to that of natural uraninite. Observations by high-resolution transmission electron microscopy, selected area electron diffraction, and energy-dispersive X-ray spectroscopic analysis confirmed that precipitated U associated with cells was uraninite with particle diameters of 3-5 nm. By the same techniques, iron sulfide precipitates were found to have a variable Fe and S stoichiometry and were not associated with cells.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
PIPES, ≥99% (titration)
Sigma-Aldrich
PIPES, BioPerformance Certified, suitable for cell culture
Sigma-Aldrich
PIPES, BioXtra, for molecular biology, ≥99.5% (T)
Sigma-Aldrich
PIPES, BioXtra, ≥99% (titration)
Sigma-Aldrich
PIPES sodium salt, ≥99% (titration)
SAFC
PIPES, PharmaGrade, Manufactured under appropriate controls for use as a raw material in pharma or biopharmaceutical production, suitable for cell culture

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