ABSTRACT
Solid state, phase transformation mechanism during the thermal decomposition of kaolin-limestone mixture sintered at different temperatures were investigated. The effect of sintering temperature on the phase transformation and alumina extraction efficiency were studied. Sintering of the mixture was carried out in the temperature range 800-1400°C, followed by leaching with sodium carbonate solution. Leaching was carried out under the following conditions; sodium carbonate solution concentration of 120 g/l at a temperature of 70°C for 30 minutes and at a stirring speed of 600 rpm. During sintering, kaolinite decomposes and transferred into the metakaolinite phase, which in turn reacts with the decomposed calcium carbonate and forms at a certain temperature calcium aluminate phases (12CaO.7Al2O3) that are readily soluble in sodium carbonate solution. The obtained results indicate that is the sintering temperature has a significant effect on the phase transformation and the efficiency of alumina extraction. Low sintering temperatures are not enough for the main phase transformations and the formation of readily soluble forms of calcium aluminate. It is clear that, increasing the temperature to 1360°C increases the degree of extraction of alumina in the solution to 80.49%. At the same time, the increase in the sintering temperature has a positive effect on the degree of completion of the self-disintegration process.
