Alumina extraction from red mud by CaCO3 and Na2CO3 sinter process

Abstract

An investigation of the application of the CaCO3 and Na2CO3 sinter process to extract alumina from red mud has been carried out. In the sintering stage, the optimal operating conditions have been obtained for highest extraction of alumina. The chemical composition of red mud is 16.07% Al2O3, 53.75% Fe2O3, 8.25% SiO2, 3.83% Na2O, 4.24% TiO2, 1.48% CaO, 0.15% V2O5, 0.157% MnO, 0.02% MgO, 0.085% Ga2O3, 0.007% ZnO, 0.099% K2O and 11.83% LOI along with rare earth elements in ppm level. During the process of sintering-leaching the minerals and alumina phases present in red mud like gibbsite, gibbsite co-existing with boehmite, alumino-goethite, boehmite and sodalite is converted to soluble sodium meta-aluminate as well as stable phases of calcium ferrite, titanate and silicate. The effect of CaCO3 and Na2CO3 additive, sintering temperature, sintering time and leaching time on the efficiency of alumina extraction from red mud were investigated. Studies show that it was possible to extract alumina from red mud with approximately 97.64% extraction efficiency at a sintering temperature of 1100 oC for 4 hr with red mud, CaCO3 and Na2CO3 in mole ratio of 1:0.20:0.25 followed by leaching with suitable caustic concentration. The formation of Na2CaSiO4, Ca2SiO4, CaTiO3 and Ca2Fe2O5 enhance alumina extraction efficiency. X-Ray diffractometer (XRD) and scanning electron microscopy (SEM) studied confirm the formation of Na2CaSiO4, Ca2SiO4, CaTiO3 and Ca2Fe2O5.