Influence of pyrogallol on the catalytic effects of Fe3+ during Fe2+ oxidation with atmospheric oxygen

One of the most common methods for the removal of iron from water is oxidation of the ferrous iron to the ferric form by atmospheric oxygen. Ferric hydroxide yielding from hydrolysis of ferric iron precipitates which is settled and filtered out from the water. The oxidation rate of the ferrous iron is affected by several factors such as the concentrations of Fe2+, Fe3+, and oxygen, pH, temperature, organic matter, and other ions present in the solution. Considerable concentrations of dissolved iron can be preserved in aerobic aquatic systems in the presence of organic species of natural origin. Organic species such as tannic acid, gallic acid, and others can completely retard the oxidation of Fe2+ for several days, even under an oxygen partial pressure of 0.21 atm. In this study, the effect of Fe3+ on Fe2+ oxidation in water containing pyrogallol was simulated and investigated experimentally in two stages. In the first stage, catalytic effect of Fe3+ on Fe2+ oxidation has been investigated, experimentally. In the second stage, it has been studied how pyrogallol affects the oxidation of Fe2+ and the catalytic effect of Fe3+. Without pyrogallol, the oxidation rate of Fe2+ was enhanced by increasing Fe3+ concentration. The catalytic effect of Fe3+ clearly decreased and almost vanished in the presence of pyrogallol. This is considered to be a result of pyrogallol-forming complexes with Fe3+.