Dielectric characterisation and reduction properties of the blending mixtures of low-grade pyrolusite and waste corn stalks in the microwave field

Abstract Recently, pyrometallurgical reduction of low-grade pyrolusite is one of the potential techniques for expanding the resources for manganese. However, the process has a high cost on fossil energy and produces a large amount of greenhouse gases. This work proposed a novel method of using biomass, namely corn stalks, to reduce and roast low-grade pyrolusite under microwave field to provide positive alternatives for fossil energy. The microwave-assisted reduction was studied systematically, and the corresponding mechanism was also studied by thermodynamic analysis and dielectric properties analysis. Results indicated that co-pyrolysis reduction characteristics of the mixtures were mainly divided into three stages: the pre-reaction stage (25 °C–196 °C), activated pyrolysis reduction stage (196 °C–480 °C), and carbonisation stage (>430 °C). The mechanism of MnO2 reduction is attributed to reductive volatiles (H2, CO, CH4) and the fixed carbon (C) produced by biomass pyrolysis. Meanwhile, the reduction efficiency of Mn can achieve 97.2% at 650 °C for 60 min with 25% corn stalks, indicating efficient pyrolusite reduction by microwave heating. These results enrich the fundamental knowledge on the corresponding industrial technology development.