Microwave Dielectric Properties and Reduction Behavior of Low-Grade Pyrolusite

Manganese ore is an important mineral having a strategic role in the development of the national economy and society. In this study, the dielectric properties, heating curve, crystal structure, and reduction ratio of a low-grade pyrolusite were investigated. The dielectric constant, dielectric loss factor, and loss tangent coefficient of low-grade pyrolusite at room temperature were evaluated using the resonant cavity perturbation method, yielding values of 5.854, 0.146, and 0.0249, respectively. Owing to the excellent microwave absorption properties of low-grade pyrolusite with 10% coal (22 g), it could be heated to a temperature of 800°C within 200 s. X-ray diffraction results confirmed that MnO2 was partially transformed into MnO at 450°C, while, at 650°C, no diffraction peak of MnO2 was observed. At a reduction temperature of 550°C, a reduction ratio of MnO2 to MnO of 96.65% could be achieved within a holding time of 50 min. This study demonstrates that the microwave carbothermal reduction of a low-grade pyrolusite is efficient, and thus could promote the clean production and sustainable development of the manganese industry.