This article focuses on the development of phase transformation and morphology of low-grade pyrolusite during carbothermal reduction using microwave heating. The XRD, SEM and EDS results show that selective carbothermal reduction of MnxOy and FexOy in pyrolusite is easy to realize with microwave heating, which can reduce MnO2 to MnO, and Fe2O3 to Fe3O4, rather than FeO. It was also observed that the phases of Mn2O3, Mn3O4 and MnO appear at 300 °C, 450 °C and 500 °C, respectively. The MnO phase, formed by the accumulation of MnO sphere particle with a diameter of 266.75–420.05 nm, is loose and porous. At a temperature of 750 °C, the Mn2SiO4 layer of about 316 nm in thickness, tightly wrapping SiO2 particle is generated at the interface between MnO and SiO2 embedded with MnO. Above 650 °C, Fe2O3 in pyrolusite can be transformed into a very dense Fe3O4 phase.
Bibliographical noteFunding Information:
Financial supports from the Key Projects in the National Science & Technology Pillar Program during the Twelfth Five-year Plan Period (No.: 2015BAB17B00 ), Specialized Research Fund for the Doctoral Program of Higher Education (No.: 20125314120014 ) and the Applied Foundation Fund of Yunnan Province of China (No.: 2012FD015 ), and the Hunan Provincial Science and Technology Plan Project , China (No. 2016TP1007 ) were sincerely acknowledged.
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- Carbothermal reduction
- Microwave heating
- Phase transformation