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Formation of Green Rust Sulfate: A Combined in Situ Time-Resolved X-ray Scattering and Electrochemical Study

DOI: 10.1021/la903935j DOI Help

Authors: Imad Ahmed (University of Lancaster) , Liane G Benning (University of Leeds) , Gabriella Kakonyi (University of Leeds) , Aryani Sumoondur (University of Leeds) , Nicholas Terrill (Diamond Light Source) , Sam Shaw (University of Leeds)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Langmuir , VOL 26 (9)

State: Published (Approved)
Published: February 2010
Diamond Proposal Number(s): 883

Abstract: The mechanism of green rust sulfate (GR-SO4) formation was determined using a novel in situ approach combining time-resolved synchrotron-based wide-angle X-ray scattering (WAXS) with highly controlled chemical synthesis and electrochemical (i.e., Eh and pH) monitoring of the reaction. Using this approach,GR-SO4 was synthesized under strictly anaerobic conditions by coprecipitation from solutions with known FeII/FeIII ratios (i.e., 1.28 and 2) via the controlled increase of pH. The reaction in both systems proceeded via a three-stage precipitation and transformation reaction. During the first stage,schwertmannite (Fe8O8(OH)4.5(SO4)1.75) precipitated directly from solution at pH 2.8?4.5. With increasing pH (>5), Fe2+ ions adsorb to the surface of schwertmannite and catalyze its transformation to goethite (?-FeOOH) during the second stage of the reaction. In the third stage, the hydrolysis of the adsorbed Fe2+ ions on goethite initiates its transformation to GR-SO4 at pH >7. The GR-SO4 then continues to crystallize up to pH ?8.5. These results suggest that with an FeII/FeIII ratio of ?2 in the initial solution the structural FeII/FeIII of the GR-SO4 will be close to that of the starting composition.

Subject Areas: Environment, Chemistry

Instruments: I22-Small angle scattering & Diffraction