title: Reoxidation of reduced uranium with iron(III) (hydr)oxides under sulfate-reducing conditions.
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.
authors.affiliation: Department of Chemical Engineering, Center for Multiphase Environmental Research, Washington State University, Pullman, Washington 99164-2710, USA.
authors.forename: Rajesh K
authors.initials: RK
authors.lastname: Sani
authors.forename: Brent M
authors.initials: BM
authors.lastname: Peyton
authors.forename: Alice
authors.initials: A
authors.lastname: Dohnalkova
authors.forename: James E
authors.initials: JE
authors.lastname: Amonette
mesh_terms: D017738:Alkanesulfonic Acids; D001639:Bicarbonates; D045285:Desulfovibrio desulfuricans / Q000378:metabolism* / Q000648:ultrastructure; D005290:Ferric Compounds / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D010084:Oxidation-Reduction; D010879:Piperazines; D013057:Spectrum Analysis / Q000379:methods; D014501:Uranium / Q000378:metabolism*; D014965:X-Rays
chemical_list: D017738:Alkanesulfonic Acids; D001639:Bicarbonates; D005290:Ferric Compounds; D010879:Piperazines; C000499:ferric oxide; C021024:ferric hydroxide; D019344:Lactic Acid; D014501:Uranium; C008916:piperazine-N,N'-bis(2-ethanesulfonic acid)