Novel Process of Reduction Roasting Manganese Ore with Sulfur Waste and Extraction of Mn by Acid Leaching

Manganese dioxide is typically reduced to a bivalent state before being extracted; here, sulfur is considered an efficient reductant and sulfur–based reduction has been industrialized in China. In this study, the reaction mechanism between MnO₂ and gaseous sulfur was investigated. Thermodynamically, the reduction of MnO₂ by gaseous sulfur is feasible. The predominant phase diagram as functions of temperature and input S₂(g) fraction in the S₂–MnO₂ system was calculated. Experimental validation showed that MnO₂ was reduced stepwise to low-valence manganese oxides and manganese sulfate. The phase composition of the roasted products was complex, and MnS was inevitably formed. The valence state as well as microstructure of manganese dioxide during reduction roasting were also investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS). The reaction process could be described by an unreacted nuclear model. Manganese was extracted by sulfuric acid solution after reduction by sulfur waste. In sulfuric acid, 95.2 wt% Mn extraction was achieved, using a roasting temperature of 450 °C, roasting time of 30 min, and S₂/MnO₂ molar ratio of 0.40. With the same conditions, low Fe extraction was achieved. On the other hand, in deionized water, 24.3 wt% Mn extraction was achieved, confirming the formation of MnSO₄.