Application of low-temperature reduction by hydrogen for enhancing the magnetic characteristics of several iron ores

The conversion of non-magnetic or weakly magnetic constituents of iron ores into the magnetic ‘magnetite’ phase was investigated using partial reduction by hydrogen at temperatures below 400 °C. The examined four commercial iron ores from Russian and Chinese deposits have significant differences in their compositions and morphologies. All ore samples were crushed using mechanical abrasion in a stamp and sieved with a mesh size of 1.5 mm. Reduction was carried out in a tube furnace under isothermal conditions at 375 and 400 °C for one hour. To study the kinetics of the reduction process, non-isothermal studies of selected ores were сonducted using a thermogravimetric analyzer with heating to 800 °C at a heating rate of 10 °C/min in hydrogen flow. The authors made a detailed characterization of the annealed products using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy to determine the magnetic characteristics of initial and partially reduced ores. X-ray diffraction patterns showed hematite peaks in the initial samples; both magnetite and metallic iron peaks were detected in the samples reduced at 375 and 400 °C. Such behavior was observed for all four samples under investigation. The most important result of the study is the confirmation of an order of magnitude increase in saturation magnetization for hematite ores, in addition the reduced ore samples show soft magnetic properties with average coercive force values ​​of approximately 20 kA/m. Application of the low-temperature reduction by hydrogen to iron-containing ores is very promising for production of the materials that could later be subjected to enrichment using magnetic separation methods.