Kinetics of Owhe kaolinite leaching for alumina recovery in hydrochloric acid solution

Abstract

Recovery of alumina from kaolinite presents a sustainable alternative to its recovery from bauxite, a major source of alumina which is depleting in quantity globally. Owhe kaolinite proves to be a reliable resource for this process given its rich alumina content. This study focused on the leaching of alumina from Owhe kaolinite in hydrochloric acid (HCl) solution. Effects of parameters such as acid concentration, stirring rate, leaching temperature, particle diameter and solid/liquid (S/L) ratio, were investigated. The experimental data was analyzed using relevant kinetic models to establish the best model of fit. Alumina leaching rate increased as the temperature, stirring rate, and acid concentration increased, and decreased with increase in solid/liquid ratio and particle diameter. The experimental results fitted into the solid film diffusion model while chemical reaction was found to be the rate-determining step, with activation energy (Ea) of 34.79 kJ/mol and a pre-exponential factor of 120.37 s–1. The result revealed an average alumina leaching rate of 85 % with an overall reaction constant of 0.983 s–1. Post-leaching analysis by energy dispersive spectrophotometer (EDS) also confirms over 80 % alumina leaching rate, which is in line with the experimental result. Hence, hydrochloric acid proved to be a viable lixiviant for alumina recovery from Owhe kaolinite.

Keywords

• Metal dissolution
• Rate-determining step
• Activation energy
• Kinetic models
• Rate constant
• Leaching rate