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.