The removal of alumina and silica from iron rejects slime by chemical leaching

A hydrometallurgical method of alumina and silica gangue removal from rejects slime of iron ore by alkali and acid leaching is proposed. Up to about 80% gangue is removed by chemical leaching with sodium hydroxide, sulphuric, hydrochloric and nitric acids. Although sulphuric acid is the most effective among the acids, it suffers from a substantial loss of iron. Sodium hydroxide is the most effective leachant at 95 °C with an optimum concentration of 5 M NaOH for 2 h. The iron value of the leached slime improved from 58.8% to 67.5% and contained < 2% Al2O3. s parameters were optimized by circulating and staged leaching with different concentrations of sodium hydroxide (1.25–7.25 M). The leaching kinetics shows that the principal reaction of alumina + silica is first order with respect to hydroxide ions.