The formation of iron sulfide is a strong indicator of its relevant reducing environments and occurs in a wide range of geological settings, from marine sediments to lacustrine, riverine, estuarine, and groundwater systems. Through previous studies, it has been known that the initial phase of iron-sulfide precipitates from an aqueous solution is amorphous or poorly crystalline and of nanoscale sizes. What remains mysterious, however, is how the initial phase of iron sulfide transforms in terms of morphology and crystal structure along with time and with slight changes in redox conditions. This knowledge gap is further compounded by the unknown differences that may or may not exist in biogenic versus abiogenic iron-sulfide phases, both restricting us from fully understanding the roles of iron-sulfide nanoparticles in biogeochemical processes. The main purpose of our current study is to capture the morphological and structural changes in the abiogenic and biogenic iron sulfides in situ using a combination of analytical tools, including X-ray diffraction, small angle X-ray scattering, and transmission electron microscopy. For the abiotic experiments, we added aqueous sulfide solution to that of Fe2+ or Fe3+ at controlled rates, imitating the sulfide production rates in the biological system. By using two types of iron cations, we intend to evaluate how the different sources (anoxic vs. oxic) of iron may affect the formed phases of iron sulfide. For the biogenic samples, sulfate-reducing bacteria of Desulfovibrio desulfuricans are grown to provide sulfide to precipitate iron in similar aqueous setups as the abiotic system. Preliminary results showed that using different types of iron cations (Fe2+ vs. Fe3+) could lead to abiogenic iron sulfide of different morphologies. The results of this study will have implication for understanding the origin and fate of iron sulfide nanoparticles in a multitude of geochemical settings.

In-situ morphological and structural transformation of abiogenic and biogenic iron-sulfide nanoparticles: An X-ray scattering and transmission electron microscopy study

255th National Meeting (2018)

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