Reduction enhancement mechanisms of low iron grade ore-coal composite pellets by sodium salt

Method of reduction roasting with iron ore-coal composite pellets was adopted to deal with high silicon content-low iron grade ore, and sodium salt was used to enhance the reduction process. Effects of temperature, reduction time and mass fraction of sodium salt on reduction behavior were researched. Gas analysis was used to investigate effect of sodium salt on the reduction process. Effects of CO volume fraction on thermodynamic of reduction of FeO and formation of fayalite were analyzed, and SEM and XRD were applied to analyse microstructures and composition of reduced pellets. The results show that FeO may react with SiO2 and form fayalite which can hardly be reduced again. Increasing CO volume fraction can improve the reduction of FeO, and thus decrease the formation of fayalite. Reduction of iron oxide can be facilitated effectively by sodium salt, which can be attributed to the fact that sodium improves the gasification reaction of carbon and increases CO volume fraction, which promotes the reduction of FeO. Reduced pellets with metallization ratio of 56.74% can be obtained with ratio of m(C)/m(Fe) 0.4, mass fraction of sodium salt 3% and reduces at 950℃ for 30 min. TFe in the magnetic separation concentrate and iron recovery are 74.16% and 74.57%, respectively. © 2019, Central South University Press. All right reserved.