Investigation of transformations of low-grade manganese ore during the roasting process

ABSTRACT The transformations of low-grade manganese ore were investigated during roasting in the air at different temperatures up to 1200°C. The transformations were followed up by XRD and TGA-DTA. Moreover, the morphology and magnetic properties were determined by SEM and VSM. It was observed that MnO2 transformed to the lower oxide Mn5O8 at 500°C and then to bixbyite (Mn2O3) at 600°C. Finally, the bixbyite decomposed to hausmannite (Mn3O4) at 800°C. Increasing the roasting temperature to 900°C induced a reaction between hematite and hausmannite and led to the formation of a small amount of solid solution of the ferrite spinel MnFe2O4. Further increase in temperature to 1000°C led to the formation of a solid solution of braunite (Mn7SiO12) which decomposed to rhodonite (MnSiO3) at 1200°C. The magnetic susceptibility of the original ore gradually increased with the roasting temperature, from 0.119 × 10−3 at ambient temperature to a maximum value of 80 × 10−3 at 1200°C.