Effect of Na2CO3 additive on the activation of coal gangue for alumina extraction

•We discussed the activation effect of Na2CO3 on coal gangue.•Na2CO3 react with aluminosilicates in coal gangue to form nepheline at 600~900 °C.•Na2CO3 improved the dissolution of Al2O3 and made SiO2 enriched in the residue.•Na2CO3 facilitate the decomposition of AlO6 and SiO4 network in coal gangue.

The effect of Na2CO3 additive on the activation of coal gangue for alumina extraction was investigated. The discussion on the action mechanisms was performed by the means of TG-DSC, XRD and XRF. The results showed that the calcined coal gangue with the addition of Na2CO3 improved the alumina extraction significantly. At the calcination temperatures of 800–900 °C with Na2CO3 to coal gangue weight ratios of 0.8–1, the alumina extractions of > 90% were obtained. There were reactions between Na2CO3 and coal gangue during the calcination to form nepheline, which improved the dissolution of Al2O3 in acid and enriched SiO2 concentration in the residue during the acid leaching process. Na2CO3 could attack AlO6 and SiO4 network in coal gangue owing to the compensation charge effect, and therefore facilitate the decomposition of coal gangue.