Synthesis of gamma alumina from Kankara kaolin using a novel technique

• Gamma alumina was synthesized from Kankara kaolin using a novel synthesis technique.
• Crystalline gamma alumina phase began to develop at calcination temperature of 600°C.
• A BET surface area of 102 m2/g was obtained after calcination at 900°C.
• XRF showed 91.02 wt.% alumina and the XRD pattern was similar to that of typical commercial gamma alumina.
• Thermal analysis at 30–900°C range showed that the material was thermally stable.

Synthesis of gamma alumina from Kankara kaolin using simple novel dealumination, precipitation and calcination steps and the product characterization have been presented. The raw clay was wet beneficiated, metakaolinized and dealuminated. Amorphous aluminum hydroxide was precipitated from the aluminum sulfate produced, using sodium hydroxide solution as the precipitating agent. Chemical, mineralogical, physiochemical, morphological and thermal analyses of the products were carried out using XRF, XRD, BET, FTIR, SEM, TEM and TGA/DTA. The aluminum hydroxide produced was subjected to thermal treatment at variable calcination temperatures in the range of 300 to 900°C, gradual phase transformation was observed, a fully formed gamma alumina phase was observed at 900°C. XRF analysis of the various materials at each stage of processing showed a progressive trend of increase in Al2O3 content, at calcination of 900°C the Al2O3 content was 91.02 wt.%. The XRD pattern of the alumina obtained at 900°C was similar to that of commercial gamma alumina. The BET surface area, pore volume and pore diameter of the as-synthesized gamma alumina were 102.6 m2/g, 0.0305 cm3/g and 11.89 Å respectively and the crystal size was 10 nm. This novel process is an industrially feasible alternative to the conventional Bayer process, and it offers a solution to the environmental hazards posed by the wastes generated by the Bayer process.