minerals Article Effects of Fe(III) Oxide Mineralogy and Phosphate on Fe(II) Secondary Mineral Formation during Microbial Iron Reduction Edward J. O’Loughlin 1,* , Maxim I. Boyanov 1,2 , Christopher A. Gorski 3,†, Michelle M. Scherer 3 and Kenneth M. Kemner 1 1 Biosciences Division, Argonne National Laboratory, Lemont, IL 60439-4843, USA;
[email protected] (M.I.B.);
[email protected] (K.M.K.) 2 Institute of Chemical Engineering, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria 3 Department of Civil and Environmental Engineering, University of Iowa, Iowa City, IA 52242-1527, USA;
[email protected] (C.A.G.);
[email protected] (M.M.S.) * Correspondence:
[email protected]; Tel.: +1-630-252-9902 † Present address: Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, State College, PA 16802-7304, USA. Abstract: The bioreduction of Fe(III) oxides by dissimilatory iron-reducing bacteria may result in the formation of a suite of Fe(II)-bearing secondary minerals, including magnetite (a mixed Fe(II)/Fe(III) oxide), siderite (Fe(II) carbonate), vivianite (Fe(II) phosphate), chukanovite (ferrous hydroxy car- bonate), and green rusts (mixed Fe(II)/Fe(III) hydroxides). In an effort to better understand the factors controlling the formation of specific Fe(II)-bearing secondary minerals, we examined the effects of Fe(III) oxide mineralogy, phosphate concentration, and the availability of an electron shuttle (9,10-anthraquinone-2,6-disulfonate, AQDS) on the bioreduction of a series of Fe(III) oxides (akaganeite, feroxyhyte, ferric green rust, ferrihydrite, goethite, hematite, and lepidocrocite) by Shewanella putrefaciens CN32, and the resulting formation of secondary minerals, as determined by Citation: O’Loughlin, E.J.; Boyanov, X-ray diffraction, Mössbauer spectroscopy, and scanning electron microscopy.