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% Al 2 O 3, 19.1% SiO 2, and 9.4% Na 2 O by weight was used as the blended ingredients of coal gangue for alumina extraction. Calcination of coal gangue with the addition of Na 2 CO 3 at 850 °C could obtain more than 90% of Al 2 O 3 extraction. Nevertheless, the high consumption of Na 2 CO 3 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 NaAlSiO 4 . The 1:1:1 of the theory molar ratio of Na, Al, and Si suggested that the minimum consumption of Na 2 CO 3 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 Na 2 O in red mud was also used to partly substitute for Na 2 CO 3 required for coal gangue activation, which consequently decreased the consumption of Na 2 CO 3 from 100% to 12.1–20.5%.