Synthesis of α-alumina from a less common raw material

A nanostructured alpha-Al2O3 with particle size lower than 100 nm was obtained from a hazardous waste generated in slag milling process by the aluminium industry. The route developed to synthesize alumina consisted of two steps: in the first one, a precursor of alumina, boehmite, gamma-AlOOH was obtained by a sol-gel method. In the second step, the alumina was obtained by calcination of the precursor boehmite (xerogel). Calcination in air was performed at two different temperatures, i.e. 1,300 and 1,400 A degrees C, to determine the influence of this parameter on the quality of resulting alumina. X-Ray diffraction patterns and transmission electron microscopy images of calcined powers revealed beside corundum the presence of transition aluminas and some rest of amorphous phase in the sample prepared at 1,300 A degrees C. The increase of the calcinations temperature to 1,400 A degrees C favors the formation of an almost single-phase corundum powder. The transition of theta- to alpha-Al2O3 was followed by means of infrared spectroscopy, since it is accompanied by the disappearance of the IR band frequencies associated with tetrahedral sites (AlO4 sites), giving rise to a spectrum dominated by Al3+ ions in octahedral sites (AlO6) characteristic of corundum.