The oxidation kinetics of Fe 2+ ions to Fe 3+ in concentrated H 2 SO 4 –FeSO 4 solutions was studied with isothermal and isobaric experiments carried out in a laboratory-scale pressurized autoclave. The experiments were performed at temperatures between 60 and 130°C, and the oxygen pressures between 4 and 10 bar. The kinetic results revealed that the oxidation rate increases with temperature and pressure. A rate equation was derived for the oxidation process, based on the assumption that stepwise complexation of Fe 2+ with dissolved oxygen is rate determining. The rate equation has the form r = a 1 c 2 FeII c O /(1+ a ′= c FeII ), where c FeII and c O are the concentrations of Fe 2+ ions and dissolved oxygen, respectively a 1 and a ′ are experimentally determined kinetic parameters. A comparison of the experimental data with the model fit revealed that the proposed rate equation is applicable for the prediction of the Fe 2+ -oxidation kinetics in acidic solutions.