HR: 1340h
AN: B33C-1048    [Abstracts]
TI: Comparison of Rates of Abiotic, Biotic, Reductive and Non-reductive Dissolution of Fe(III) (Hydr)oxides: Toward Simple Models of Reactivity
AU: * JANG, J
EM: jehun@psu.edu
AF: Center for Environmental Kinetics Analysis, 2217 EES Building The Pennsylvania State University, University Park, PA 16802 United States
AU: Brantley, S L
EM: brantley@essc.psu.edu
AF: Center for Environmental Kinetics Analysis, 2217 EES Building The Pennsylvania State University, University Park, PA 16802 United States
AB: Reductive dissolution of Fe(III) (hydr)oxides regulates the mobility of iron and the redox buffer capacity of anoxic natural waters. The process consists of multiple elementary steps, such as the reaction between reductant and the Fe(III) center, electron transfer from reductant to Fe(III) center, and detachment of reduced Fe(II) from the surface. In this study, surface-area normalized dissolution rates (mol Fe/m²/s) of Fe(III) (hydr)oxide minerals that were measured as a function of experimental conditions (e.g., pH, ligand concentration, reductant concentration, presence of microorganisms) were compiled and plotted against pH. The rate of abiotic, proton-promoted, non-reductive dissolution defines the lower limit for the compiled dissolution rates. Rates of dissolution of Fe(III) oxides as a function of pH in the absence of complexing ligands were roughly similar, regardless of mineralogy. Both abiotic and biological reductive processes showed greatly increased dissolution rates compared to abiotic non-reductive dissolution, but those rates did not exceed the dissolution rate of FeO as estimated using a theoretical prediction. The dissolution rate for FeO was estimated based on the observation that dissolution rates of divalent metal oxides vary consistently with the first-order rate coefficient for water exchange in the inner-coordination sphere of the hydrated metal ions. This result is consistent with a model that suggests that after reduction occurs, a mixed-valence solid-solution of Fe(II) and Fe(III) exists at the mineral surface. Fe(II) release is enhanced relative to Fe(III) release due to the significant difference between bond strengths of Fe(II)O and Fe(III)O. This simple model may allow limits to be placed on rates of reduction of metal oxides in the environment.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0419 Biomineralization
DE: 0434 Data sets
SC: Biogeosciences [B]
MN: Fall Meeting 2005