A Comparative Study of Dry Grinding Kinetics of Hematite Ore: Impact of Low-Temperature Hydrogen-Based Magnetization Roasting

A comparative study is reported on the kinetics of dry grinding on a natural hematite ore (Fe: 51.6% and SiO2: 16.9%) before and after magnetization roasting at 375°C (20 min; H2). Dry grinding of initial and magnetized ores was carried out in a ball mill (0-30 min). Particle sizes were determined using sieve analysis and laser diffraction methods. Average particle sizes had reduced by 7% after the magnetization roasting. During the initial stages of grinding, the magnetization process had increased the grinding rate of ores by 30% compared to initial ores. The formation of microcracks, observed in SEM micrographs, were attributed to the release of moisture and density differences, and played an important role in particle break-ups, size reductions and enhanced grinding rates. The aggregation of small particles was also noted after 30 min. Computations based on Tovarov’s model showed that the rate of formation of the optimal class (0.045+0.020 mm) for reverse flotation was 4.4 times higher for the magnetized ore; sludge formation of class (-0.002+0.001 mm) was also 2.5 times slower due to aggregation. This study has shown that magnetization roasting coupled with dry grinding could be used to transform low-grade hematite ores into high value magnetite resources currently in great demand in steelmaking.