A prospective process for alumina extraction via the co-treatment of coal fly ash and bauxite red mud: Investigation of the process

A prospective alumina extraction process of co-treatment of coal fly ash (CFA) and red mud (RM) was proposed. The effects of RM on the alumina dissolution, the consumption of Na2CO3, the mineral transformation during the calcination, the compositions and properties of the acid-leached residue were investigated systematically by means of TG-DSC, XRD and MAS-NMR. Results showed that the comprehensive dissolution of Al2O3 in CFA and RM reached 90.4%. The consumption of Na2CO3 reduced about 80% for CFA-RM-Na2CO3 system as opposed to that for CFA-Na2CO3 system. The TG-DSC and XRD results revealed that the interactions among CFA, RM and Na2CO3 mainly occur at above 800 degrees C, and as a result the active phases involving nepheline and zeolite formed. The consistent results were presented further by MAS-NMR analysis that the calcined CFA-RM-Na2CO3 sample showed the Al-IV and Si-IV coordination in nepheline and zeolite at 850 degrees C. The formed nepheline and zeolite are acid soluble phases and the formed acid-leached residues contain > 90% SiO2, which facilitate the further utilization of the residue. This work is expected to provide a clear understanding of the alumina extraction process of the CFA-RM-Na2CO3 reaction system.