Assessment of calcined Owhe kaolinite for potential alumina recovery via nitric acid route

Abstract

In this study, the leaching of alumina from Owhe kaolinite was investigated with nitric acid (HNO3) solution as the leachant. The variables investigated in the leaching study comprise the reaction temperature, acid concentration, stirring speed, particle size, solid/liquid (S/L) ratio, and reaction time. The kinetics of the leaching was analyzed with relevant kinetic models. The percentage of alumina leached increased as the temperature, acid concentration, and stirring speed increased, and decreased as the solid/liquid ratio and particle size increased. The surface chemical reaction was found to be the rate-controlling step while the activation energy (Ea) of 33.81 kJ/mol and Arrhenius constant of 257.34 s−1 were obtained. About 84.1 % alumina leaching rate was obtained at the optimal conditions while the overall rate constant was obtained as 2.099 s−1. The energy dispersive spectrophotometer (EDS) analysis of the residue showed that 79.86 % silicon, 6.41 % of aluminium, 5.24 % of titanium, and 2.69 % of potassium were the main elements found in the residue. X-ray diffraction (XRD) results of the residues obtained from the leaching reaction indicated the presence of quartz, davyne, sanidine, garnet, and kaolinite. From the results obtained, nitric acid was established as a good lixiviant for alumina recovery from Owhe kaolinite.

Keywords

• Kaolinite
• Nitric acid
• Kinetics
• Leaching
• Alumina