Iron geochemical cycling and abiotic reactivity in natural groundwater is dependent on several environmental variables, including ionic strength, acidity, and minerals present. This work describes how reactivity of iron oxide minerals is affected by ionic strength and the presence of unreactive minerals. Aggregate size and adsorption of Fe(II) on the mineral surface were both affected by increasing ionic strength at low pH. At high CaCl<sub>2</sub> concentration, aggregates were micrometers in scale, and adsorption of Fe(II) was significantly inhibited. Quinone reduction by Fe(II) sorbed on the surface was unfavorable in acidic brine. In contrast, quinone oxidation by the iron oxide mineral was favored at high ionic strength. In heterogeneous mineral mixtures, addition of kaolinite either increased or decreased the reaction rate of adsorbed Fe(II), depending on the mass loading of kaolinite. These results reveal the importance of small changes in environmental variables on our interpretations of iron redox reactivity in natural waters.

Redox reactions and contaminant degradation by Fe(II) and iron oxides in complex groundwater systems

249th National Meeting (2015)

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