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, 57 Fe Mössbauer spectroscopy and XPS confirmed that the weak magnetic Fe 2 O 3 and FeOOH in Red Mud could be completely transformed into stronger magnetic Fe 3 O 4 . 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.