Synergistic Effect of Ball Milling and Heat Treatment for Synthesis of Magnetite from Blue Dust

The present work reports sustainable synthesis of magnetite from blue dust- a secondary fragile mineral resource of iron ore, which is mostly found in open cast iron ore mines. Blue dust mainly contains hematite (Fe₂O₃). With an aim to produce magnetite, blue dust is ball milled utilizing a WC-lined jar and balls up to 25 hours. Phase analysis showed peaks corresponding to the hematite phase. With milling, the peak broadening was observed, which is due to the reduction of crystallite size and an increase in the microstrain. The saturation magnetization (M_s) of blue dust increased significantly from 0.8 emu/g in the unmilled state to ~ 14 emu/g after 25 hours of milling. Further, the 25 hours milled blue dust was mixed with Fe in a 4:1 molar ratio and the reaction milling of the mixture was performed for milling durations up to 10 hours. The milled products obtained at various intervals of milling time were characterized, which indicates the presence of hematite phase only. This affirms that the ball milling of blue dust in the presence of Fe was not sufficient to induce the formation of magnetite. The maximum value of M_s (33 emu/g) was noted for 5 hours reaction milling of blue dust and Fe. Subsequent heat treatment of 5 hours milled blue dust and Fe at 750 °C under Ar atmosphere resulted in the formation of magnetite phase with an increase of M_s to 70 emu/g. Altogether, this study demonstrates the synergistic effect of ball milling and heat treatment of blue dust and iron for phase transformation from hematite to magnetite.

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