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

• Biomass pyrolysis char is capable of reducing Fe 2 O 3 to metallic iron at 1000 °C. • Biochar gasification with release of CO and CO 2 takes place during Fe 2 O 3 reduction. • Reduction degree of Fe 2 O 3 with biomass is comparable with that obtained with H 2. • Reduced iron particles show a sponge-like microstructure with gangue elements. • Reduction of Fe 2 O 3 with biomass is faster than reduction with H 2 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 (Fe 2 O 3 ) to metallic iron and, in parallel, gasification of the fixed carbon with release of CO 2 and mainly CO. The reduction degree of KIO with biomass turns out to be comparable or even higher than that obtained with gaseous H 2 mixtures above ∼ 900 °C. XRD shows that Fe 2 O 3 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.