Reduction of High-Grade Pyrolusite by Pyrolyzed Biomass in Vacuum

High-grade pyrolusite was reduced via biomass vacuum pyrolysis with corn straw as a reductant. Thermogravimetry–differential scanning calorimetry (TGA–DSC) was adopted for differential thermal analysis of raw materials. X-ray diffraction (XRD), inductively coupled plasma (ICP-OES), and scanning electron microscopy (SEM) were used to analyze the phase, chemical composition, and morphology of the raw materials and reducing slags. Based on the thermomechanical analysis, influences of the reduction temperature, reduction time, pyrolusite–corn straw mass ratio, cross-sectional diameter of briquettes of raw mix, and residual pressure in the system on the manganese (Mn) reduction rate were studied. The results show that the reduction rate of pyrolusite reaches 96.8% when the reduction temperature, reduction time, pyrolusite–corn straw mass ratio, and residual pressure are 600 °C, 90 min, 5:1, and 500 Pa, respectively. XRD results of the reducing slag indicate that the reduction process of pyrolusite with corn straw as the reductant successively experiences phase transformation of MnO₂ → Mn₂O₃ → Mn₃O₄ → MnO.