Effect of impurity oxides on CWF (CaFe3O5) formation in lime magnetite pellets – part I: thermodynamic assessments and experimental investigations

Lime magnetite pellets (LMPs) containing CWF phase (CaFe3O5) provide potential feed materials for ironmaking. In this paper, the effects of typical impurity oxides inherent to magnetite ores such as Al2O3, MgO and SiO2 on the formation of CWF in LMPs have been investigated. The thermodynamics of the Ca–Fe–O–X systems (X = Al, Mg or Si) were assessed followed by time-series experiments using natural and synthetic materials. The X-Ray Diffraction (XRD) results indicated a significant decrease in CWF percentage by over 45 wt-% and 18 wt-% with the addition of 5 wt-% SiO2 and 2 wt-% Al2O3, respectively due to the formation of α’ Ca2SiO4 and Ca2(Al, Fe)2O5 phases. A 5 wt-% decrease in CWF amount was observed for 2 wt-% MgO added LMPs. In summary, the presence of impurity oxides limits the formation of CWF, which may affect the suitability of LMPs for industrial application.