Pyrolusite was carbothermally reduced using coal by microwave heating, and the crystal structures and microstructures of the samples were characterized after microwave heating using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). When the reductants proportion was of 10 percent, the reduction temperature was of 800 °C and the holding time was of 40 minutes, the reduction ratio of MnO₂ to MnO was 97.2%, and Fe₂O₃ was almost completely transformed to Fe₃O₄ and there was no Fe(II) produced. Moreover, it was found that the low-grade pyrolusite was carbothermally reduced using microwave heating with lower temperature and shorter processing time. These results show that microwave heating can be applied effectively and efficiently to the carbothermal reduction processes of low-grade pyrolusite.

The microwave absorption properties of a material depend largely on the dielectric properties of the material being heated. Therefore, the influences of temperature on the dielectric constant (ε′), loss factor (ε′′), loss tangent (tan δ_d) and penetration depth (D_P) of steelmaking dust at frequencies of 1064 MHz and 2423 MHz were measured. Three steelmaking dust samples were studied. The effects of temperature on the dielectric properties of the samples were insignificant at temperatures below 600 °C. However, above this temperature, a rapid rise in the values of the dielectric properties of the samples was observed. Comparing the thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) results and mass spectra (MS) of the dusts with their dielectric properties revealed that the changes in the dielectric values of the dusts were associated with the thermal decomposition of calcium carbonate and the release of CO/CO₂ gases. Furthermore, the increase in the electrical conductivity of the samples at high temperature resulted in increased dielectric values. The behavior of the loss tangent of the samples with increasing temperature coincided with the behavior of the loss factor. The penetration depth decreased with an increase in temperature at both frequencies, while an increase in the dielectric properties caused a significant decrease in the penetration depth. The results indicated that steelmaking dusts have good microwave absorbing properties owing to their carbon and iron oxide contents.