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

Abstract

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.