Extraction of alumina from Iraqi colored kaolin by lime-sinter process

In this work lime -sinter method was investigated to recover alumina from Iraqi colored kaolinitic claystone. The claystone was intimately mixed with limestone and the mixture was sintered. The annealed sintered material dusts to a fine powder which required no grinding. This material was leached with sodium carbonate solution, and an alumina extract (sodium aluminate solution) was obtained. By bubbling carbon dioxide gas into this extract solution, gibbsite [Al(OH)3] precipitated and on calcinations at 1350 °C ,alumina in the form of alpha (α – Al2O3) of high purity (98%) can be obtained. In the course of this investigation, the effect of sintering temperature and time, concentration of sodium carbonate solution, leaching time and sintered powder to sodium carbonate solution ratio were studied. About 85% of the alumina in the claystone was extracted at the optimum conditions. The alumina obtained in this method assaying 98% Al2O3, 1.45% SiO2, 0.04% Fe2O3, and 0.13% CaO and, 0.15% Na2O