Effect of impurity oxides on CWF (CaFe 3 O 5 ) formation in lime magnetite pellets – part I: thermodynamic assessments and experimental investigations

Abstract

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.