Oxidation kinetics of dithionate compound in the leaching process of manganese dioxide with manganese dithionate

Manganese dithionate (MnS2O6), formed in the leaching process of pyrolusite slurry with SO2, is a concern because of its ability to decrease the purity of MnSO4 (industrial raw material). Information regarding the oxidation and recovery of dithionate ion is scarce. In this study, we investigated the leaching process of MnO2 with MnS2O6 in the liquid phase. The leaching reaction presented one way to oxidize MnS2O6. The most suitable operating parameters on the oxidation efficiencies of MnS2O6 were established as follows: MnO2 dosage, 21.7 g L−1; agitation speed, 450 rpm; initial H2SO4 concentration, 1.81 mol L−1; initial MnS2O6 concentration, 28.5 g L−1; and reaction temperature, 372.5 K. Under the optimum conditions, the removal efficiency of 97.55% for MnS2O6 was obtained in 30 min. The experimental results showed that increasing the initial concentrations of MnS2O6 and H2SO4 and the reaction temperature resulted in a decrease in the content of MnS2O6. The dithionate oxidation process could be well modeled by the shrinking core model with an inert product layer, which indicated that the process was controlled by the interfacial chemical reaction. The reaction orders with respect to initial H2SO4 concentration and initial MnS2O6 concentration were 1.64 and 0.18, and the activation energy was 60.1 kJ mol−1 as well as pre-exponential factor was 5.9 × 106.