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.