Beneficiation studies of a difficult to treat iron ore using conventional and microwave roasting

Abstract

This work illustrates the reduction roasting and magnetic separation studies of a complex Indian iron ore with 57% Fe that could not be upgraded to >61% Fe using a flow sheet comprising of the conventional unit operations like scrubbing, jigging, magnetic separation or flotation. The sole reason of the poor response to physical beneficiation was mainly attributed to the inadequate liberation of iron as visualized under the reflected light microscope, which revealed the fine dispersion of silica particles within the hematite grains and vice versa. In order to overcome this problem, the ore was subjected to reduction roasting using conventional as well as microwave heating followed by magnetic separation. The effects of different process variables such as reductant concentration, time, and temperature during the process of roasting were studied and subsequently optimized using the Taguchi statistical design. Optical microscopy and X-ray diffraction (XRD) studies of the roasted mass confirmed the formation of magnetite with simultaneous disappearance of the hematite and goethite phases. In the microwave roasting process, the reduction could be achieved in a considerably shorter time as compared to the conventional roasting, and the formation of undesired non-magnetic iron minerals like fayalite was limited as well. In both the processes, it was possible to achieve an iron ore concentrate having 63–65% Fe accompanied by ~85–90% weight recovery.