Influence of feed mineralogical characteristics on the reduction behavior of low-grade iron ores

Reduction roasting followed by magnetic separation has become a major beneficiation technique to utilize low and lean-grade iron ore resources. However, the fundamentals of the reduction nature of iron ore are complex and largely depend upon the mineralogical characteristics of the raw material. In order to ascertain the complexities involving the phase transformation and reducibility nature of iron ores, experiments were conducted on four mineralogically different iron ores such as crushed fines, slime, BHQ and BHJ samples to examine their responses in terms of recovery and their enrichment in Fe content. The representative samples of each class were undergone through identical experimental conditions (850 degrees C temperature, 30 min resident time, 10% noncoking coal used as reductant) and it was observed that the crushed fines and slime showed the highest degree of reducibility while the BHQ and BHJ samples responded moderately to the process. Mineralogical characterization of both BHQ and BHJ show the presence of hematite mineral phases in the non-magnetic fractions, indicating the necessity of higher reductant content as well as residence time than the crushed fines and slimes. In essence, the banded ores require a higher temperature and reducing environment than the hematite and goethite-rich feed materials for higher magnetite conversion. In addition, the advantages of reduction roasting followed by magnetic separation process over direct magnetic separation process is highlighted in detail.