Beneficiation of low-grade, goethite-rich iron ore using microwave-assisted magnetizing roasting

Microwave-assisted reduction roasting of a goethite-rich, reject iron ore waste stream (-2 mm) was used to produce a high-grade concentrate. Reduction roast experiments were conducted at 370 ?C, 450 ?C, 600 ?C and 1000 ?C under gas atmospheres of 30:70 and 40:60 CO/CO2, with a soak time of 20 min. Goethite was converted to hematite above 370 ?C under both gas mixtures while at the higher roasting temperatures, increasing amounts of magnetite formed. Roasting conditions for the best conversion of goethite to synthetic magnetite were 600 ?C in a gas atmosphere of 40:60 CO/CO2, with a soak time of 20 min. Laboratory-based magnetic separations in a Davis tube indicated that a blast furnace grade (+62 wt% Fe) pellet concentrate could be produced with an acceptable iron recovery of > 88 wt%. Under both gas atmospheres, a higher reduction temperature of 1000 ?C achieved a greater conversion of goethite to magnetite but resulted in over-reduction and the generation of w?stite, fayalite and Fe-rich spinel phases with different magnetic susceptibilities that are expected to make subsequent beneficiation difficult. Further processing to optimize the microwave-assisted magnetizing roast and the magnetic separation conditions can be expected to maximize the efficiency of upgrading the iron content in low grade goethite-rich iron ores.

Automated summary

Microwave-assisted reduction roasting of reject iron ore waste stream rich in goethite was used to produce high-grade concentrate, with optimal conditions leading to conversion of goethite to synthetic magnetite. Higher reduction temperatures led to greater conversion of goethite to magnetite, but caution is needed to avoid over-reduction which could complicate subsequent beneficiation processes.