Effects of various factors on gangue removal in alkaline hydrothermal treatment of iron ores

Abstract

The upgrading technology of low-grade iron ores by alkaline treatment was investigated in this study. The basic experiments (evaluation of the effects of solvent types, treatment temperature, holding time, solvent concentration, particle size, and solid–liquid ratio) were carried out with the alkaline hydrothermal treatment in a small batch-type reactor. The gangue removal rate in the 5 M NaOH hydrothermal treatment increased with the increase in treatment temperature, and about 90% of Si, Al, and P could be removed below 250 °C. The gangue removal rate tended to increase with the increase in NaOH concentration, the decrease in particle size, and the decrease in solid–liquid ratio. The order of the removal rate was P < Al < Si. The optimum conditions for alkaline hydrothermal treatment were found to be as follows: particle size, <500 μm; solvent, NaOH; solvent concentration, >0.1 M; solid–liquid ratio, ≤1.2; heating temperature, ≥150 °C; and holding time, 30 min. According to the results of XRD and N2 adsorption measurements of the treated ores, the gangue removal from low-grade iron ores, the improvement of Fe quality (higher Fe content), and densification were possible by alkaline hydrothermal treatment.