Direct reduction of iron ore using biomass biochar: Reduction rate, microstructural and morphological analysis

•Biomass pyrolysis char is capable of reducing Fe2O3 to metallic iron at 1000 °C.•Biochar gasification with release of CO and CO2 takes place during Fe2O3 reduction.•Reduction degree of Fe2O3 with biomass is comparable with that obtained with H2.•Reduced iron particles show a sponge-like microstructure with gangue elements.•Reduction of Fe2O3 with biomass is faster than reduction with H2 for T > 890 °C. Direct Reduction Iron (DRI) of a natural hematite (Khumani Iron Ore, KIO), by lignocellulosic biomass (Mischantus Giganteous, MIS), has been carried out in a thermogravimetric apparatus (TGA) coupled with evolved gas analysis (EGA) at different temperatures (750–1200 °C) and weight ratios. The microstructural and morphological changes of KIO have been also investigated by means of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Biomass pyrolysis is scarcely influenced by the presence of iron up to 500 °C. At higher temperatures, the biochar left behind pyrolysis of biomass acts as reducing agent resulting in progressive reduction from hematite (Fe2O3) to metallic iron and, in parallel, gasification of the fixed carbon with release of CO2 and mainly CO. The reduction degree of KIO with biomass turns out to be comparable or even higher than that obtained with gaseous H2 mixtures above ∼ 900 °C. XRD shows that Fe2O3 is completely reduced to metallic iron at 1000 °C. Reduced iron particles show well-developed porosity, with formation of a sponge-like microstructure; EDX metal maps reveal a re-distribution of contaminants in the iron particles after complete reduction. Accumulation of gangue elements, Si, promotes the formation of inorganic rich micro-spheres within the iron sponge-like architecture.