Beneficiation of rejects slime of iron ore by means of sequential leaching

The present research work has been conducted to remove gangue contents from rejects slime of iron ore, having particle size < 20 mu m by circulating leaching with aqueous hydrofluoric acid (HF) followed by nitric acid (HNO3) washing. Effects of acid concentration, slurry ratio, reaction time, stirring speed and temperature on gangue removal have been examined. The gangue contents (alumina and silica) are reduced from 13 weight percentage (wt.%) to around 1 wt.%. The iron value has also been increased from 58.74 wt.% to 68.47 wt.% with more than 95% iron recovery. The gangue matter remaining after leaching consists mainly of aluminium and silicon, which is most likely encapsulated in the goethite phase. The leaching kinetics has also been studied to establish an overall leach-rate equation. The shrinking core model is very suitable to describe the kinetics of gangue removal.