Novel Process for Alumina Extraction via the Coupling Treatment of Coal Gangue and Bauxite Red Mud

A novel process for the coupling treatment of coal gangue and red mud is reported. Red mud containing 23.4% Al2O3, 19.1% SiO2, and 9.4% Na2O by weight was used as the blended ingredients of coal gangue for alumina extraction. Calcination of coal gangue with the addition of Na2CO3 at 850 degrees C could obtain more than 90% of Al2O3 extraction. Nevertheless, the high consumption of Na2CO3 is equivalent to the same weight amount of coal gangue. Both nepheline and sodium aluminum silicate formed during the process have the molecular structure of NaAlSiO4. The 1:1:1 of the theory molar ratio of Na, Al, and Si suggested that the minimum consumption of Na2CO3 might be obtained at the optimal Al/Si molar ratio of 1:1. Red mud with an Al/Si molar ratio of 1.44 mixed with coal gangue with a ratio of 0.64 was used to extract alumina. The results showed that red mud could adjust the Al/Si molar ratio of coal gangue to an appropriate value and Na2O in red mud was also used to partly substitute for Na2CO3 required for coal gangue activation, which consequently decreased the consumption of Na2CO3 from 100% to 12.1-20.5%.