Synthesis of gamma alumina from Kankara kaolin using a novel technique

Abstract

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 91.02wt.%. 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 102.6m2/g, 0.0305cm3/g and 11.89Å respectively and the crystal size was 10nm. 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.