Process Optimization for Gangue Removal from Low-Grade Iron Ore by a Flow-Type Reactor with a NaOH Solution

This research aims to develop technology that can improve low-grade iron ore containing a large amount of α-FeOOH and gangue to the same level as the high-grade iron ores that are conventionally used. The main goal is to optimize the alkaline hydrothermal treatment conditions for iron ore when using a flow-type reactor for constructing a development framework for an upgrading process for low-grade iron ore. Gangue removal extents during 5 M NaOH hydrothermal treatment increased with increasing treatment temperature, with around 80% of Si, Al, and P removed by treatment at 250 °C. The removal extents also increased with increasing NaOH concentration, decreasing particle size, and decreasing solid-liquid ratio. The ore species was found to have virtually no effect on gangue removal by alkaline hydrothermal treatment. Based on the results obtained, the optimal parameters for gangue removal were a particle size of <1000 μm, a solvent concentration of >0.1 M, and a heating temperature of 250 °C. The FeOOH present in the iron ore changed to Fe2O3 after alkaline hydrothermal treatment. Furthermore, this method was also effective for gangue removal from sorted particles with a large gangue content.