Reactions between dissolved Fe(II) and crystalline Fe(III) oxide minerals during biogeochemical cycling results in mineral transformations controlled by localized growth and dissolution processes. Ions common in natural aquatic systems, such as phosphate and sulfate, are known to adsorb to mineral surfaces and alter growth and dissolution mechanisms. We have investigated how phosphate and sulfate interact with Fe(II) during adsorption onto hematite and goethite. Both oxoanions enhance Fe(II) adsorption. Fe(II) increases sulfate adsorption but has little effect on phosphate adsorption. ATR-FTIR spectra show that Fe(II) alters the adsorption mechanism of phosphate but not sulfate. This suggests that enhanced Fe(II) adsorption by these oxoanions is the result of different processes, with phosphate and Fe(II) forming ternary surface complexes and sulfate influencing Fe(II) adsorption through surface electrostatic effects. These common oxoanions are thus predicted to have different effects on iron oxide mineral transformations and trace element repartitioning during biogeochemical iron cycling.

Interactions of phosphate and sulfate with aqueous Fe(II) on Fe(III) oxide surfaces

245th National Meeting (2013)

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