Co-pyrolysis of biomass with Red Mud: An efficient approach to improving bio-oil quality and resourceful utilization of the iron in Red Mud

Co-pyrolysis of biomass with Red Mud was used to boost up the quality of the produced bio-oil and recover iron from Red Mud. The influences of five different biomass species and impregnation pretreatment were investigated. It was found that co-pyrolysis could significantly improve the bio-oil quality, decreasing the acidity from 173.28 to 1.18 mg KOH/g due to the decarboxylation of carboxylic acids into ketones under the catalysis of Red Mud and boosting up the HHV from 20.05 to 31.80 MJ/kg with an energy efficiency of 72.56%. Meanwhile, the soluble alkalinity of Red Mud declined from 65.34 to 5.26 mg HCl/g, which is very crucial to mitigate the harmfulness and perniciousness to the environment. The characterizations of XRD, 57Fe Mossbauer spectroscopy and XPS confirmed that the weak magnetic Fe2O3 and FeOOH in Red Mud could be completely transformed into stronger magnetic Fe3O4. For this reason, the magnetic separation iron recovery reached up to 92.25% with iron grade of 66.12%. The findings in the research not only open the avenue for efficient biomass conversion to high quality fuels, but also provide an efficient approach to resourceful utilization of Red Mud.