title: Synergistic effect of reductive and ligand-promoted dissolution of goethite.
abstract: Ligand-promoted dissolution and reductive dissolution of iron (hydr)oxide minerals control the bioavailability of iron in many environmental systems and have been recognized as biological iron acquisition strategies. This study investigated the potential synergism between ligands (desferrioxamine B (DFOB) or N,N'-Di(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED)) and a reductant (ascorbate) in goethite dissolution. Batch experiments were performed at pH 6 with ligand or reductant alone and in combination, and under both oxic and anoxic conditions. Goethite dissolution in the presence of reductant or ligand alone followed classic surface-controlled dissolution kinetics. Ascorbate alone does not promote goethite dissolution under oxic conditions due to rapid reoxidation of Fe(II). The rate coefficients for goethite dissolution by ligands are closely correlated with the stability constants of the aqueous Fe(III)-ligand complexes. A synergistic effect of DFOB and ascorbate on the rate of goethite dissolution was observed (total rates greater than the sum of the individual rates), and this effect was most pronounced under oxic conditions. For HBED, macroscopically the synergistic effect was hidden due to the inhibitory effect of ascorbate on HBED adsorption. After accounting for the concentrations of adsorbed ascorbate and HBED, a synergistic effect could still be identified. The potential synergism between ligand and reductant for iron (hydr)oxide dissolution may have important implications for iron bioavailability in soil environments.
authors.affiliation: †Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305, United States.
authors.forename: Zimeng
authors.initials: Z
authors.lastname: Wang
authors.affiliation: ‡Department of Environmental Geosciences, University of Vienna, 1010 Vienna, Austria.
authors.forename: Walter D C
authors.initials: WD
authors.lastname: Schenkeveld
authors.affiliation: ‡Department of Environmental Geosciences, University of Vienna, 1010 Vienna, Austria.
authors.forename: Stephan M
authors.initials: SM
authors.lastname: Kraemer
authors.affiliation: §Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, United States.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Giammar
mesh_terms: D000085:Acetates / Q000737:chemistry; D000327:Adsorption; D001205:Ascorbic Acid / Q000737:chemistry; D003676:Deferoxamine / Q000737:chemistry; D005029:Ethylenediamines / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D016014:Linear Models; D008903:Minerals / Q000737:chemistry*; D010084:Oxidation-Reduction; D019163:Reducing Agents / Q000032:analysis; D012995:Solubility; D013696:Temperature
chemical_list: D000085:Acetates; D005029:Ethylenediamines; D058085:Iron Compounds; D008024:Ligands; D008903:Minerals; C524457:N,N'-di(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid; D019163:Reducing Agents; C094886:goethite; D007501:Iron; D003676:Deferoxamine; D001205:Ascorbic Acid