Leaching Kinetics for Recovering Alumina from Waste Tricalcium Aluminate Generated after Filtration of Bayer’s Liquor

Abstract

A study was performed on the leaching kinetics to recover the alumina from Tricalcium aluminate (TCA) generated as waste after removal of suspended red mud particles in the Bayer process by different concentrations of Na2CO3 solution at different temperatures and solid:liquid ratios. The influences of initial sodium carbonate and stirring speed on reaction rate constant were examined and the corresponding apparent activation energy was calculated. The results indicate that the leaching process is a first order reaction, and the reaction rate constant 8.64×10–6 mol/(L.m). Optimization of recovery and minimization of Na2CO3 in liquor were studied, and the dissolution rate of TCA and conversion of CaCO3 also increases. The apparent activation energy is 52.86 kJ/mol, and temperature has great influence on the leaching rate of TCA. The leaching rate is controlled by diffusion of reacting reagents in the solid product layer. A higher leaching rate of TCA is obtained by higher temperature and/or lower solid g/l during leaching process..