Effect of microwave heating on the microstructures and kinetics of carbothermal reduction of pyrolusite ore

This article focuses on the development of phase transformation and morphology of low-grade pyrolusite during carbothermal reduction using microwave heating. The XRD, SEM and EDS results show that selective carbothermal reduction of Mn_xO_y and Fe_xO_y in pyrolusite is easy to realize with microwave heating, which can reduce MnO₂ to MnO, and Fe₂O₃ to Fe₃O₄, rather than FeO. It was also observed that the phases of Mn₂O₃, Mn₃O₄ and MnO appear at 300 °C, 450 °C and 500 °C, respectively. The MnO phase, formed by the accumulation of MnO sphere particle with a diameter of 266.75–420.05 nm, is loose and porous. At a temperature of 750 °C, the Mn₂SiO₄ layer of about 316 nm in thickness, tightly wrapping SiO₂ particle is generated at the interface between MnO and SiO₂ embedded with MnO. Above 650 °C, Fe₂O₃ in pyrolusite can be transformed into a very dense Fe₃O₄ phase.