Process optimization, characterization and kinetics of the reduction roasting of a low-grade iron ore with rice straw as a sustainable reductant

Abstract

Iron ore reduction releases a significant amount of greenhouse gases due to coal-based reductants. This communication aims to tackle this challenge by proposing rice straw as a substitute for coal in the reduction roasting of a typical low-grade Indian iron ore with 51.4 % Fe. The usage of rice straw has another advantage because it is a biomass residue produced in large quantities in agricultural countries like India, often lacking viable applications and being primarily incinerated, leading to various environmental problems. X-ray diffraction and optical microscopic studies revealed that the iron ore sample consists of goethite and hematite as the ironbearing minerals having a complex association with the gangue silicate phases, making the physical separation of iron values challenging. Reduction roasting using rice straw followed by magnetic separation successfully generated an iron ore concentrate with about 65 % Fe and a Fe recovery of 77 % at a roasting temperature of 800 degrees C and a residence time of 45 min. Characterization studies involving optical microscopy, scanning electron microscopy, and thermogravimetric studies explained the phase transformation of the iron ore as a function of the reducing conditions correlating it with the grade and recovery of iron at different levels of operating parameters. Kinetics studies indicated that the biomass-assisted reduction behaviour of the iron ore can be divided into three stages, each following a different model.