Beneficiation of High-Aluminium-Content Hematite Ore by Soda Ash Roasting

High-aluminium-content iron ore is one of typical intractable iron ores, and magnetic separation and floatation processes are found impracticable to remove alumina from the ore effectively. In this article, a new process, roasting with addition of soda followed by leaching, is developed to remove aluminium from the ore. Results show that Al2O3 content decreases from 8.16% in raw ore to 2.13% in iron concentrate, and total iron grade increases from 48.92 to 63.21% when the ore is roasted at 1000 degrees C for 15min with the addition of 14.0% (wt.) sodium carbonate. Mechanisms of aluminium-iron separation were studied by using XRD, SEM, and thermodynamic methods, and it is shown that aluminium is transformed into sodium aluminosilicate, sodium aluminate, and corundum during roasting; sodium aluminate is able to be leached by water, so is sodium aluminosilicate by dilute acid solution, while corundum remains in the iron concentrate.