PNNL

Abstract

Biogeochemical transformation (inclusive of dissolution) of iron (hydr)oxides resulting from dissimilatory reduction has a pronounced impact on the fate and transport of nutrients and contaminants in subsurface environments. Despite the reactivity noted for pristine (unreacted) minerals, iron (hydr)oxides within native environments will likely have a different reactivity owing in part to changes in surface composition. Accordingly, here we explore the impact of surface modifications induced by phosphate adsorption on ferrihydrite reduction by Shewanella putrefaciens under static and advective flow conditions. Alterations in surface reactivity induced by phosphate adsorption change the extent, nearly linearly, and pathway of iron biomineralization. Magnetite is the most appreciable mineralization product while minor amounts of vivianite and green rust-like phases are formed in systems having high aqueous concentrations of phosphate, ferrous iron, and biogenic bicarbonate. Goethite and lepidocrocite, characteristic biomineralization products at low ferrous-iron concentrations, are inhibited in the presence of adsorbed phosphate. Considering deviations in reactivity of iron (hydr)oxides with changes in surface composition is important for deciphering mineralization pathways under native conditions and predicting reactive characteristics.