Iron sulfide minerals crystallization in the presence of oxidatizing agent and clay minerals in media containing sulfate-reducing bacteria
Description
This study aimed to synthesize Fe-sulfides in cultures of sulfate-reducing bacteria consortium under laboratory conditions with the time, Fe:S ratio, and addition or lack of oxidizing agent and/or clay mineral matrix. Here we sought to determine the role that SRM plays in iron sulfide mineral formation using a series of lab-based incubations that included live cultures and abiotic treatments. In the present contribution, the sulfate-reducing microorganisms were cultured with sulfur to investigate the effect of the oxidant agent on the nature of iron sulfides formed. In addition, the effect of the presence of a crystallization matrix, in the form of clay minerals, on the process of formation or morphology of crystallizing iron sulfides was investigated.These results allow an understanding of the evolution and mechanisms of pyrite formation in sulfate-reducing consortia cultures and discuss implications for natural environments.
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Diffraction patterns were acquired from 4° to 78° with a 2θ step of 0.0263°, at 40 kV and 30 mA with Co Kα radiation on a PANalytical X’Pert Pro MPD diffractometer equipped with a PIXcel3D detector mounted in Bragg-Brentano configuration. The total time of registration for one sample was 4 hours. Mineral phase identification was performed by comparing peak positions and relative intensities against powder diffraction databases in the Profex 5.0.2 extended with the COD database. Samples were imaged without sputter coating using a scanning electron microscope coupled with a focused ion beam (FIB) ZEISS Auriga 60 and a ZEISS Sigma VP scanning electron microscope. The current parameters of the observations were: current intensity 4 pA, excitation voltage 8-20 kV, working distance 7.5 mm. The observations were carried out using backscattered electron (BSE) and reflected electron (SE) detectors to obtain the maximum imaging resolution. Elemental characterizations were performed by energy dispersive X-ray spectrometry (EDS) at 15 kV and the same working distance. Data were processed using the software Genesis (EDAX). Thermal analysis-mass spectrometry (TA-MS) was carried out on the post-culture sediments. The apparatus used for the tests was a SDT Q600 (TA INSTRUMENTS) linked to a GSD 320 Omnistar quadrupole mass spectrometer (Quadera Software, MID function).