Role of carbonate speciation on the oxidation of Fe(II) by H2O2

A unified model for Fe(II) speciation and oxidation by hydrogen peroxide is described. This model uses ion-ion-specific interactions with classic ion pair formation theory to describe ferrous iron speciation under conditions typical of natural waters. The speciation data were then utilized to evalua te the species-specific rates of Fe(II) oxidation by hydrogen peroxide for a range of media compositions. At a pH below 5.0, the oxidation rate of Fe( II) is well described in terms of the Fe2+ However, for a pH above 5, the F e(CO3) complex is the most kinetically active species. Combining these new Fe(II)-H2O2 rates with rates for Fe(II) oxidation by molecular oxygen, a co rrelation between one-electron transfer rates and the Delta G of electron t ransfer was established. This correlation is consistent with the Marcus the ory of electron transfer. The model for Fe(II) oxidation by molecular oxyge n and hydrogen peroxide allows the prediction of steady-state hydrogen pero xide concentrations that will result from the oxidation of micromolar level s of Fe(II). The greatest hydrogen peroxide production by Fe(II) oxidation is predicted in freshwater systems with low total alkalinity. (C) 2000 Else vier Science B.V. All rights reserved.