SURFACE-CHEMISTRY AND MORPHOLOGY OF POORLY CRYSTALLINE IRON SULFIDES PRECIPITATED IN MEDIA CONTAINING SULFATE-REDUCING BACTERIA

This study characterizes the surface chemistry and morphology of poorl y crystalline iron sulfides precipitated in a chemically defined growt h media for sulfate-reducing bacteria. The precipitates were analyzed by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Based on XRD results, the prec ipitates exhibit only incipient crystallization with a single broad di ffraction peak at about 5 Angstrom, characteristic of disordered macki nawite. The iron sulfides generally exhibit a platy habit with particl es 100 to 300 nm in diameter; these particles appear often in 1 to 2 m u m spherical aggregates. The XPS results indicate that the Fe(2p(3/2) ) spectrum for poorly crystalline iron sulfide can be fitted with Fe(I I) and Fe(III) components, both corresponding to Fe-S bond types, The absence of oxide oxygen in the O(1s) spectrum and Fe(III)-O bond types in the Fe(2p(3/2)) spectrum supports the conclusion that the poorly c rystalline iron sulfides are composed of both ferric and ferrous iron coordinated with monosulfide, with lesser amounts of disulfide and pol ysulfides also present. These results suggest that the precipitates po ssess a surface composition similar to greigite, with the remaining mi neral mass composed of disordered mackinawite. (C) 1998 Elsevier Scien ce B.V.