Investigation on microwave carbothermal reduction behavior of low-grade pyrolusite

Abstract

Applying microwave heating, in substitution for conventional industrial process heating, renders energy-saving and clean efficient for mineral reduction. In this work, the behavior of low-grade pyrolusite during microwave-assisted heating was systematically investigated, and the phase transformation of pyrolusite during the reduction process was characterized by TG-DTG-DSC and XRD; meanwhile, a model for the reduction mechanism was proposed, with a three-stage reduction process identified. Results indicated that manganese oxide (MnO) powder can be efficiently prepared, and the reduction ratio presented positive relationships with reduction temperature and heating time, obtaining with a high reduction ratio value of 94.4% achieved at 600 °C within a duration time of 40 min. XRD analysis confirmed that the phase transformation during the reduction process followed the conversion sequence as MnO2→Mn2O3→Mn3O4→MnO, and the iron oxides was almost converted to Fe3O4. It was proved that low-grade pyrolusite can be reduced effectively and efficiently to manganese oxide at lower temperature and shorter duration time by microwave heating.