Replacing fossil energy by utilizing biomass as carbon source to convert metal oxides has meaning for reduction of minerals. Microwave pyrolysis of walnut shell for reduction process of low-grade pyrolusite was proposed. Thermogravimetric analysis indicated biomass pyrolysis process for reduction of pyrolusite was divided into four phases identified by temperatures: dehydration stage (<150 °C), pre-pyrolysis stage (150 °C–290 °C), curing decomposition stage (290 °C–480 °C) and carbonization stage (>480 °C), and manganese recovery reached 92.01% at 650 °C for 30 min with 18% walnut shell. The strongest preferential orientation of MnO was appeared, with good crystalline structure and no MnO2 and FeO peaks detected. The product surface became loose and porous with numerous cracks, pits and holes, and molten granules were interconnected and stacked with regular shape. The methods propose new idea of selective reduction of pyrolusite based on biomass pyrolysis by microwave heating.
Bibliographical noteFunding Information:
Financial supports from the National Natural Science Foundation of China (No: U1802255 ), the Key Projects in the National Science & Technology Pillar Program during the Twelfth Five-year Plan Period (No. 2015BAB17B00 ), the Hunan Provincial Science and Technology Plan Project, China (No. 2016TP1007 ), and Innovative Research Team (in Science and Technology) in University of Yunnan Province were sincerely acknowledged.
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- Biomass pyrolysis
- Low-grade pyrolusite
- Microwave heating
- Phase transformation
- Thermal behavior