LEACHING OF FINE AND PELLETIZED NATAL KAOLIN USING SULFURIC-ACID

The kinetics of sulphuric acid leaching of calcined kaolin were studied. The kaolin ore used is from the province of Natal in South Africa and has been identified as an economic source of aluminium. The rate of aluminium removal from fine metakaolin was explored under different conditions of temperature and acid concentration. From the experimental data, an intrinsic leach model was developed and the kinetic parameters measured. The leach reaction was found to be first order with respect to the unleached aluminium and the leach rate was strongly temperature dependent. An activation energy of 67.4 kJ/mol was measured, which correlates with those values determined by other workers. An acid effect was observed and an acid term of order n included in the model. This acid term is an extension on other models found in the literature. Industrially counter-current packed bed leaching of metakaolin is an alternative to co-current leaching of fine metakaolin. Therefore, the effect of pelletisation was investigated under similar leach temperatures and acid concentrations used in the fine metakaolin test work. The effect of pellet size was examined and the leach rate found to be directly proportional to pellet diameter. From the experimental data, this leach rate is chemical reaction controlled and not limited by diffusion through the porous product layer. A shrinking core model was fitted to the data and satisfactorily describes the pellet leach rate. In the pellet model, the intrinsic leach reaction at the shrinking core is described by the rate constant, k, and acid term, of order n, taken from the fine metakaolin leach work.