Fundamental investigation on the precise regulation of pyrolusite ore phase transformation

To achieve the rational utilization of low-grade co-associated complex manganese ore resources, this paper systematically elucidated the mechanism of the phase transformation process of roasting in a reducing atmosphere with pyrolusite ore (MnO₂) as the research object. According to the single-factor experiment results, the divalent manganese (Mn²⁺) reduction rate of the roasted product obtained as 95.30% at a roasting time of 25 min, a roasting temperature of 700°C, a CO concentration of 20at% and a total gas volume of 500 mL·min^-1, in which the manganese was mainly in the form of manganosite (MnO). Scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) demonstrated the microstructural evolution of the roasted products, and the reduction of pyrolusite ore was completed gradually from the surface to the core. Thermodynamic calculations, X-ray photoelectron spectroscopy(XPS), and X-ray diffractometry (XRD) elucidated that the phase transformation of pyrolusite follows MnO₂→Mn₂O₃→Mn₃O₄→MnO phase by phase and that the reduction of manganese oxides in each valence state proceeds simultaneously.