Oxidative Leaching of Akpugo Kaolinite for Alumina Recovery and Kinetic Modeling

摘要

In this work, the kinetics of alumina recovery from Akpugo kaolinite in nitric acid and hydrogen peroxide binary solution are investigated. Parameters considered in the study include the leaching temperature, hydrogen peroxide concentration, stirring rate, solid/liquid (S/L) ratio, and particle size. The fraction of alumina dissolved increases with increase in leaching temperature, hydrogen peroxide concentration, and stirring rate, from 47.6 to 87.3 for temperatures of 30 and 90 degrees C; 48 to 85.6 for concentrations of 2 and 10 M; and 49.8 to 86.8 for stirring rates of 90 and 540 rpm. The fraction of alumina dissolved, however, decreases with increase in S/L ratio and particle size, from 86.6 to 50.2 for solid/liquid ratios of 20 and 45 g/L and 87.6 to 49.3 for particle sizes of < 75 and < 425 mu m. The experimental data fitted into the product layer diffusion model while surface chemical reaction was the rate-determining step. Activation energy was estimated to be 26.56 kJ/mol while the Arrhenius constant of 25.01 s(-1) was estimated. About 87.1 alumina dissolution rate was recorded at the optimum conditions. The overall reaction constant was estimated to be 8.883 s(-1). Post-leaching analysis of the leached residue by XRD revealed the presence of illite and quartz. GRAPHICS .