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  • Title: Redistribution of Electron Equivalents between Magnetite and Aqueous Fe2+ Induced by a Model Quinone Compound AQDS.
    Author: Peng H, Pearce CI, N'Diaye AT, Zhu Z, Ni J, Rosso KM, Liu J.
    Journal: Environ Sci Technol; 2019 Feb 19; 53(4):1863-1873. PubMed ID: 30673270.
    Abstract:
    The complex interactions between magnetite and aqueous Fe2+ (Fe2+(aq)) pertain to many biogeochemical redox processes in anoxic subsurface environments. The effect of natural organic matter, abundant in these same environments, on Fe2+(aq)-magnetite interactions is an additional complex that remains poorly understood. We investigated the influence of a model quinone molecule anthraquinone-2,6-disulfonate (AQDS) on Fe2+(aq)-magnetite interactions by systematically studying equilibrium Fe2+(aq) concentrations, rates and extents of AQDS reduction, and structural versus surface-localized Fe(II)/Fe(III) ratios in magnetite under different controlled experimental conditions. The equilibrium concentration of Fe2+(aq) in Fe2+-amended magnetite suspensions with AQDS proportionally changes with solution pH or initial AQDS concentration, but independent of magnetite loadings through the solid concentrations that were studied here. The rates and extents of AQDS reduction by Fe2+-amended magnetite proportionally increased with solution pH, magnetite loading, and initial Fe2+(aq) concentration, which correlates with the corresponding change of reduction potentials for the Fe2+-magnetite system. AQDS reduction by surface-associated Fe(II) in the Fe2+-magnetite suspensions induces solid-state migration of electron equivalents from particle interiors to the near-surface region and the production of nonmagnetic Fe(II)-containing species, which inhibits Fe2+(aq) incorporation or electron injection into the magnetite structure. This study demonstrates the significant influence of quinones on reductive activity of the Fe2+-magnetite system.
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