KINETICS AND MECHANISMS OF NITRIC ACID LEACHING OF ALUMINA FROM AMAGUNZE CLAY

Abstract

This study was concerned with the physicochemical characterization and kinetics study of Amagunze clay
dissolution in nitric acid. The effects of acid concentration, temperature, particle size, stirring speed and solid/liquid
ratio on the leaching of alumina from Amagunze clay were investigated. The X-ray fluorescence data revealed the
presence of Al2O3 and SiO2 as major oxides. Metals such as Mg, K, Ca, andTi exist as minor elements while Cr, Zn,
Mn and Sr exist as traces. The analysis of Amagunze clay by X-ray diffraction revealed the presence of microline
and quartz. The FTIR result confirmed the results of XRF and XRD analysis by revealing the presence of relevant
functional groups. Results of the leaching studies showed that alumina dissolution in nitric acid increased with
increasing concentration of nitric acid, temperature and stirring rate, and decreased with increasing particle diameter
and solid/liquid ratio. In 10M HNO3, at a temperature of 363K using 75μm particle diameter with solid/liquid ratio
of 20g/L and stirring speed of 540 rpm, about 85.4% of alumina dissolved in 150 minutes. The activation energy,
reaction order and Arrhenius constant calculated at the conditions above were 15.36 KJ/mol, 0.41, 0.586 s-1,
respectively. The mechanism of dissolution of alumina was established to follow the shrinking core model for the
surface chemical reaction mechanism. The XRD analysis of the post-leaching residue revealed the presence of
microline and quartz. Hence, Amagunze clay has proved to be a viable alternative source for alumina production.