Thermodynamic Assessment of Phase Transformation during Carbothermic Ilmenite Using Non-Carbonization Palm Kernel Shell Biomass

Abstract

Based on the thermodynamic assessment, this study aims to investigate the reduction behavior of carbothermic ilmenite using Non-Carbonization Palm Kernel Shell biomass (PKS-B). Phase transformation, equilibrium phases, and spontaneity reactions during reduction were systematically evaluated. The effect of PKS-B addition in metallic iron and TiO2-rutile formation temperature are investigated, respectively. Based on thermodynamic results, ilmenite was dissociated indirectly by volatile matter of biomass to FeO and TiO2 at 400°C to 600°C. Subsequently, biomass carbon took the reduction directly to Fe above 600°C. The metallization degree of Fe was almost close to 100% at 1200°C and 1000°C when adding half and one-time mol ratio of the stoichiometry of PKS-B. In addition, the Fe phase was consistent with the reduction of TiO2 to form Ti-suboxides such as Ti3O5 and Ti2O3 provided by adding PKS-B above half along with reduction temperature above 1100°C. The formation of TiN from Ti-suboxides was more spontaneous than via TiO2 due to the presence of N2 as confirmed by Gibbs free energy change. Thus, the ilmenite reduction pathway using PKS-B was dissociation and reduction first, then continued by the nitridation process. Furthermore, the nitriding competes with the reduction process, where Fe nitrides are formed at low temperatures while Ti nitrides and metallic Fe are formed at high temperatures.