title: Influence of Dissolved Silicate on Rates of Fe(II) Oxidation.
abstract: Increasing concentrations of dissolved silicate progressively retard Fe(II) oxidation kinetics in the circum-neutral pH range 6.0-7.0. As Si:Fe molar ratios increase from 0 to 2, the primary Fe(III) oxidation product transitions from lepidocrocite to a ferrihydrite/silica-ferrihydrite composite. Empirical results, supported by chemical kinetic modeling, indicated that the decreased heterogeneous oxidation rate was not due to differences in absolute Fe(II) sorption between the two solids types or competition for adsorption sites in the presence of silicate. Rather, competitive desorption experiments suggest Fe(II) was associated with more weakly bound, outer-sphere complexes on silica-ferrihydrite compared to lepidocrocite. A reduction in extent of inner-sphere Fe(II) complexation on silica-ferrihydrite confers a decreased ability for Fe(II) to undergo surface-induced hydrolysis via electronic configuration alterations, thereby inhibiting the heterogeneous Fe(II) oxidation mechanism. Water samples from a legacy radioactive waste site (Little Forest, Australia) were shown to exhibit a similar pattern of Fe(II) oxidation retardation derived from elevated silicate concentrations. These findings have important implications for contaminant migration at this site as well as a variety of other groundwater/high silicate containing natural and engineered sites that might undergo iron redox fluctuations.
authors.affiliation: School of Civil and Environmental Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia.|Institute for Environmental Research, Australian Nuclear Science and Technology Organisation , Locked Bag 2001, Kirrawee DC, New South Wales 2232, Australia.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Kinsela
authors.affiliation: School of Civil and Environmental Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: Adele M
authors.initials: AM
authors.lastname: Jones
authors.affiliation: School of Civil and Environmental Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia.|Institute for Environmental Research, Australian Nuclear Science and Technology Organisation , Locked Bag 2001, Kirrawee DC, New South Wales 2232, Australia.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Bligh
authors.affiliation: School of Civil and Environmental Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: An Ninh
authors.initials: AN
authors.lastname: Pham
authors.affiliation: School of Civil and Environmental Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: Richard N
authors.initials: RN
authors.lastname: Collins
authors.affiliation: Institute for Environmental Research, Australian Nuclear Science and Technology Organisation , Locked Bag 2001, Kirrawee DC, New South Wales 2232, Australia.
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Harrison
authors.affiliation: Institute for Environmental Research, Australian Nuclear Science and Technology Organisation , Locked Bag 2001, Kirrawee DC, New South Wales 2232, Australia.
authors.forename: Kerry L
authors.initials: KL
authors.lastname: Wilsher
authors.affiliation: Institute for Environmental Research, Australian Nuclear Science and Technology Organisation , Locked Bag 2001, Kirrawee DC, New South Wales 2232, Australia.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Payne
authors.affiliation: School of Civil and Environmental Engineering, The University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: T David
authors.initials: TD
authors.lastname: Waite
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds; D007501:Iron / Q000737:chemistry; D010084:Oxidation-Reduction; D017640:Silicates / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D017640:Silicates; D007501:Iron