Fe(II) oxidation has been extensively studied under a wide range of aqueous conditions since iron plays a major role in the various (bio)geochemical processes and its redox speciation heavily participates in controlling the fate and transport of other inorganic and organic substances. Recently, a few studies have investigated the redox behaviors of Fe (e.g., dissolution of Iron oxides) under freezing conditions and showed that the reaction rates were considerably enhanced. As some chemical reactions can follow different pathways in the cryogenic environment, the rate and extent of Fe(II) oxidation may also be far from those under the normal aqueous conditions. This study examined cryogenic Fe(II) oxidation under dark and acidic conditions (pH 2.0 – 5.0), where its abiotic reaction without any catalyst is known to be sluggish. The solution pH was adjusted with or without a buffer. For each ice sample, 10 mL of 50 μM Fe(II) solution in a range of electrolyte concentrations (0 – 10 mM NaNO<sub>3</sub>) was placed in an ethanol bath at -20 degC and rapidly thawed in lukewarm water after a predetermined reaction time. Preliminary results showed that Fe(II) oxidation was substantially accelerated upon freezing under only limited conditions examined in this study. In addition, the solid phases formed by cryogenic Fe(II) oxidation were distinctly different from those formed at room temperature under otherwise the same conditions.

Fe(II) oxidation in aqueous solution under freezing conditions

2019 Fall National Meeting

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