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.