Precise regulation of the phase transformation for pyrolusite during the reduction roasting process

The mechanism involved in the phase transformation process of pyrolusite (MnO2) during roasting in a reducing atmosphere was systematically elucidated in this study, with the aim of effectively using low-grade complex manganese ore resources. According to single-factor experiment results, the roasted product with a divalent manganese (Mn2+) distribution rate of 95.30% was obtained at a roasting time of 25 min, a roasting temperature of 700 degrees C, a CO concentration of 20at%, and a total gas volume of 500 mL center dot min-1, in which the manganese was mainly in the form of manganosite (MnO). Scanning electron microscopy and Brunauer-Emmett-Teller theory demonstrated the microstructural evolution of the roasted product and the gradual reduction in the pyrolusite ore from the surface to the core. Thermodynamic calculations, X-ray photoelectron spectroscopy, and X-ray diffractometry analyses determined that the phase transformation of pyrolusite followed the order of MnO2 -> Mn2O3 -> Mn3O4 -> MnO phase by phase, and the reduction of manganese oxides in each valence state proceeded simultaneously.