Oxidation Kinetics of Ferrous Sulfate over Active Carbon

Catalyzed oxidation kinetics of dissolved Fe²⁺ ions to Fe³⁺ over active carbon in concentrated H<INF>2</INF>SO<INF>4</INF>−FeSO<INF>4</INF> 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 pressure of oxygen (O<INF>2</INF>) was varied between 4 and 10 bar. The kinetic results revealed that the oxidation rate was enhanced by increasing the temperature and pressure and that the catalytic and noncatalytic oxidations proceed as parallel processes. A rate equation was obtained for the catalytic oxidation process, based on the assumption that the oxidation of Fe²⁺ with adsorbed oxygen is rate determining. The rate equation for the catalytic oxidation has the simplified form r = k‘ ‘c<INF>Fe</INF>c<INF>O</INF>^0.5/(K<INF>O</INF>‘‘c<INF>O</INF>^0.5 + 1) where c<INF>Fe</INF> and c<INF>O</INF> are the concentrations of Fe²⁺ ions and dissolved oxygen, respectively, and k‘ ‘ and K<INF>O</INF>‘‘ are experimentally determined kinetic parameters. The total oxidation rate was simulated by including a previously determined rate equation for the noncatalytic oxidation into the global model, from which the kinetic parameters of the catalytic oxidation rate were determined. A comparison of the model fit with the experimental data revealed that the proposed rate equation is applicable for the prediction of the Fe²⁺ oxidation kinetics in acidic ferrous sulfate solutions.