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Nitrate Reduction in the Presence of Wüstite

Department of Agronomy, University of Kentucky, N-122G Agricultural Science Building-North, Lexington, KY 40546-0091

View larger version (20K): [in a new window]   Fig. 1. (a) Nitrate reduction to NH4+ and NO2– by FeO(s) at a constant pH 6.45. The small inset shows NO2– reduction by FeO(s) in a separate experiment over a 4-h interval under similar conditions. (b) Production of NH4+ vs. consumption of NO3– for the reaction of NO3– with FeO(s) at a constant pH 6.45. The solid line represents a linear least square regression fit of the data. Error bars indicate ±range of duplicate runs; bars not visible are smaller than the symbols.

View larger version (25K): [in a new window]   Fig. 2. X-ray diffraction (XRD) patterns of (a) control experiments where NO3– was not added to FeO(s) in MES [2-(N-morpholino)ethane sulfonic acid] at constant pH 6.45, and (b) reaction product at constant pH 6.45, 10 g L–1 FeO(s), and 1 mM NO3–. In (a), peaks at 2.49, 2.15, and 1.52 Å represent the diagnostic d-spacings for wüstite. In (b), peaks at 2.97, 2.53, 2.10, 1.71, 1.61, and 1.48 Å represent the d-spacings for magnetite, and peaks at 2.49, 2.15, and 1.52 Å represent the d-spacings for unreacted wüstite.

View larger version (94K): [in a new window]   Fig. 3. Scanning electron micrographs of (a) unreacted FeO(s) and (b and c) reacted FeO(s) in MES [2-(N-morpholino)ethane sulfonic acid] at constant pH 6.45. Bars show the length unit.

View larger version (21K): [in a new window]   Fig. 4. Initial rate plots to determine apparent reaction order for (a) NO3–, (b) [H+], and (c) [FeO]. The different initial NO3– concentrations were 0.9, 9.5, and 14.7 mM, pH values were 5.45, 6.45, and 7.45, and FeO(s) concentrations were 10, 5, and 1 g L–1. The solid line represents a linear least square regression fit of the data.

View larger version (18K): [in a new window]   Fig. 5. Temperature study showing (a) Arrhenius and (b) Eyring plots describing NO3–, reduction by FeO(s) at a constant pH 6.45, solid-phase concentration 10 g L–1, and initial NO3– concentration 1 mM.