Nanogoethite formation from oxidation of Fe(II) sorbed on aluminum oxide: Implications for contaminant reduction

Abstract

Ferrous iron [Fe(II)] bound to mineral surfaces has been shown to reduce several important groundwater contaminants, but little is known of the nature of the newly formed, insoluble ferric iron [Fe(III)] and whether it influences the heterogeneous contaminant reduction process. To explore how the formation and evolution of the Fe oxidation products influences contaminant reduction, we measured the kinetics of nitrobenzene reduction by Fe(II) sorbed on α-Al2O3 while simultaneously characterizing the Fe oxidation product with Mössbauer spectroscopy and electron microscopy. After a brief period of slow kinetics, the onset of nitrobenzene reduction coincided with a change in particle suspension color from white to yellow-ocher due to formation of nanogoethite rods (α-FeOOH) from oxidation of sorbed Fe(II). Formation of nanogoethite on the α-Al2O3 particles appears to promote the rapid reduction of nitrobenzene. Our results show that nanogoethite crystals can form rapidly by heterogeneous Fe(II) oxidation, and formation of goethite can profoundly influence contaminant reduction rates by Fe(II). © 2010 American Chemical Society.