Reduction Mechanism and Kinetics of a Low Grade Iron Ore-coal Composite Pellets Improved by Sodium Salt

Abstract

Reduction behavior of low grade iron ore-coal composite pellets was investigated in the temperature range of 850–1000°C. Effects of the sodium salt addition on the reduction behavior and kinetics were researched. Reduction samples were analyzed by applying X-ray Diffraction (XRD) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS) to reveal its function mechanism. Results demonstrated that composite pellets without sodium salt showed poor reduction performance at lower temperatures (below 950°C) for most of wustite phase transferred into fayalite rather than iron. Raising reduction temperature can restrain fayalite formation to some extent, but the effect was limited. However, the reduction process of wustite to iron was improved by sodium salt in temperature range of 950–1000°C for its favourable inhibiting effect on formation of fayalite. SEM-EDS analysis of reduced samples revealed that sodium salt also enhanced the growth of newly formed metallic iron particles. The reduction process of composite pellets was diffusion controlled reaction in the temperature range of 850°C–1000°C. The activation energy decreased from 545.06 kJ/mol to 135.77 kJ/mol as 3 wt% of sodium salt was applied.