Fe(III) (oxy)hydroxides and pyrite (FeS2) are formed in a variety of environments. In this study, we present data on the biotic formation of Fe(III) solids via planktonic iron oxidizing bacteria (FeOB) from the oxic – anoxic transition zone of the Chesapeake Bay and data on the abiotic formation of pyrite and iron-silicate materials formed at hydrothermal vents. Cultures of two FeOB strains from the Chesapeake Bay form Fe(III) solids in amorphous sheaths that emanate from the FeOB cell. Electron microscopy data show that they consist of nanoparticles that aggregate into sizes from 100 nm to greater than 1 mm. In and below the oxic – anoxic transition zone of the Chesapeake Bay, these particles must be extremely reactive as the total soluble iron concentration is 5 mM and the oxygen concentration below 3 mM. In a catalytic oxygen-iron-sulfide catalytic cycle, hydrogen sulfide below the zone reacts with these biologically formed Fe(III) solids to resupply the Fe(II) necessary for the maintenance of the FeOB in this transition zone. We discuss mechanistic details of the surface reaction of Fe(III) amorphous solids with hydrogen sulfide species. We also present results on pyrite nanoparticle and aggregates found at different vents including the first meter from the vent orifice, and describe the slow oxidation kinetics of synthesized pyrite with oxygen in seawater. Also, we provide evidence for the formation of iron silicate and other materials, which indicate that reverse weathering occurs in the reaction zone above the vent orifice that undergoes rapid cooling.

Natural oxidized and reduced iron nanoparticles in the marine environment

251st National Meeting (2016)

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