Synthesis of high purity aluminium hydroxide and alumina from Bayer's gibbsite and aluminium salts

In this study, high purity alumina was produced from Bayer's gibbsite (Al(OH)3) and aluminum salts (Al(NO3)3.9H2O, AlCl3.6H2O) via hydrothermal synthesis, combustion synthesis and precipitation from acid solution. From these different types of synthesis systems, different level of purity of alumina was aimed. Hydrothermal synthesis was performed at 200°C with both grinded Bayer's gibbsite and Al(NO3)3.9H2O, and as a result boehmite (AlOOH) was precipitated. Then, boehmite powder was calcined at 1250°C to obtain α-Al2O3. At combustion synthesis; Al(NO3)3.9H2O, urea and citric acid were used to have a desired solution. Mixed solution was put into 550°C heated furnace and waited there approximately 20-30 min. to obtain alumina. After this step, obtained alumina was calcined at 1200°C and amorphous alumina change into crystallized and pure α-Al2O3. At last, Bayer's gibbsite was dissolved in concentrated HCl (37%) acid and then AlCl3 salt was obtained by evaporation from the solution. α-Al2O3 was formed by calcination at 1200°C from the AlCl3 salt. After these studies, all alumina powders' purity level was analyzed and there is no differences between purity level of these alumina powders. Purity level of these formed alumina powders was around 99.95%. Only difference has been monitored between these alumina powders was particle morphology and particle size. Keywords: Bayer gibbsite, α-Al2O3, hydrothermal synthesis, Al(NO3)3.9H2O, AlCl3, calcination, combustion synthesis, high purity