MICROBIAL REDUCTION OF Fe(III) IN THE FITHIAN AND MULOORINA ILLITES: CONTRASTING EXTENTS AND RATES OF BIOREDUCTION

Abstract-Shewanella putrefaciens CN32 reduces Fe(III) within two illites which have different properties: the Fithian bulk fraction and the <0.2 mim fraction of Muloorina. The Fithian illite contained 4.6 % (w/w) total Fe, 81 % of which was Fe(III). It was dominated by illite with some jarosite (-32 % of the total Fe(llI)) and goethite (11 % of the total Fe(lll)). The Muloorina illite was pure and contained 9.2 % Fe, 93 % of which was Fe(III). Illite suspensions were buffered at pH 7 and were inoculated with CN32 cells with lactate as the electron donor. Select treatments included anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle. Bioproduction of Fe(II) was determined by ferrozine analysis. The unreduced and bioreduced solids were characterized by M6ssbauer spectroscopy, X-ray diffraction and transmission electron microscopy. The extent of Fe(IIl) reduction in the bulk Fithian illite was enhanced by the presence of AQDS (73%) with complete reduction ofjarosite and goethite and partial reduction of illite. Mbssbauer spectroscopy and chemical extraction determined that 21-25 % of illite-associated Fe(III) was bioreduced. The extent of bioreduction was less in the absence of AQDS (63%) and only jarosite was completely reduced with partial reduction of goethite and illite. The XRD and TEM data revealed no significant illite dissolution or biogenic minerals, suggesting that illite was reduced in the solid state and biogenic Fe(II) from jarosite and goethite was either released to aqueous solution or adsorbed onto residual solid surfaces