The oxidation of Fe2+ with oxygen in sulfate solutions was studied in the presence of T. ferrooxidans. To measure the chemical activity of bacteria, and the oxidation rate of iron, the redox potentials of solutions were continuously monitored during the experiments. The redox potentials were simultaneously monitored on the platinum and pyrite indicator electrodes. The redox potential versus time curves were further used to calculate the basic kinetic parameters, such as the reaction orders, the activation energy, and the frequency factor. It was found that under atmospheric conditions, and at Fe2+ < 0.001M, T < 25°C, and at pH above 2.2, the oxidation of iron is governed by the following rate expression: [equation image] Below pH = 2.2, the oxidation rate is independent of H+ Concentration.