Reductive biotransformation of Fe in shale–limestone saprolite containing Fe(III) oxides and Fe(II)/Fe(III) phyllosilicates

Abstract

A <2.0-mm fraction of a mineralogically complex subsurface sediment containing goethite and Fe(II)/Fe(III) phyllosilicates was incubated with Shewanella putrefaciens (strain CN32) and lactate at circumneutral pH under anoxic conditions to investigate electron acceptor preference and the nature of the resulting biogenic Fe(II) fraction. Anthraquinone-2,6-disulfonate (AQDS), an electron shuttle, was included in select treatments to enhance bioreduction and subsequent biomineralization. The sediment was highly aggregated and contained two distinct clast populations: (i) a highly weathered one with ''sponge-like'' internal porosity, large mineral crystallites, and Fecontaining micas, and (ii) a dense, compact one with fine-textured Fe-containing illite and nano-sized goethite, as revealed by various forms of electron microscopic analyses. Approximately 10-15% of the Fe(III) TOT was bioreduced by CN32 over 60 d in media without AQDS, whereas 24% and 35% of the Fe(III) TOT was bioreduced by CN32 after 40 and 95 d in media with AQDS. Little or no Fe 2+ , Mn, Si, Al, and Mg were evident in aqueous filtrates after reductive incubation. Mö ssbauer measurements on the bioreduced sediments indicated that both goethite and phyllosilicate Fe(III) were partly reduced without bacterial preference. Goethite was more extensively reduced in the presence of AQDS whereas phyllosilicate Fe(III) reduction was not influenced by AQDS. Biogenic Fe(II) resulting from phyllosilicate Fe(III) reduction remained in a layer-silicate environment that displayed enhanced solubility in weak acid. The mineralogic nature of the goethite biotransformation product was not determined. Chemical and cryogenic Mö ssbauer measurements, however, indicated that the transformation product was not siderite, green rust, magnetite, Fe(OH) 2 , or Fe(II) adsorbed on phyllosilicate or bacterial surfaces. Several lines of evidence suggested that biogenic Fe(II) existed as surface associated phase on the residual goethite, and/or as a Fe(II)-Al coprecipitate. Sediment aggregation and mineral physical and/or chemical factors were demonstrated to play a major role on the nature and location of the biotransformation reaction and its products.

Advances in Geochemical Testing of Key Contaminants in Residual Hanford Tank Waste

“…Note the spectral areas of the sextet in 77 K spectrum and the outer sextet in the 12 K spectrum are (Kukkadapu et al 2005) (doublet at RT and sextet at 77 K and 12 K with similar features). The sextet feature is not likely to be due to hematite/maghemite, and definitely not due to lepidocrocite, based on derived Mössbauer parameters.…”

Uranium reduction and microbial community development in response to stimulation with different electron donors

“…Fe(II) in the sediments was measured in an anaerobic glove box (3% H 2 , 97% N 2 ) by adding 0.2-0.3 g of sediment to 5 mL 0.5 N HCl, extracting for 24 h Kukkadapu et al 2006) and analyzing as described above. Total reducible Fe concentration in the sediments was determined in the same manner as the sediment associated Fe(II) concentration, except that 0.2 mL of 6.25 N hydroxylamine hydrochloride was added to the 0.5 N HCl solution at a final concentration of 0.25 N prior to the sediment addition ).…”

Identification of iron-reducing microorganisms in anoxic rice paddy soil by 13C-acetate probing

“…In a number of studies, goethite reduction was either undetectable or goethite was reduced only to a small extent (Lovley and Phillips, 1986, 1987, 1988Kukkadapu et al, 2006;Komlos et al, 2007), whereas goethite was reduced considerably on biostimulation in a subsurface sediment (Stucki et al, 2007). In Italian rice field soil, neither goethite nor Al-goethite added to soil slurries was microbially reduced after 180 days of incubation (Qu et al, 2004).…”