The Thermal Activation of Nsu Clay for Enhanced Alumina Leaching Response

Abstract

The thermal activation conditions for enhancing the leaching of alumina from Nsu clay from south-eastern Nigeria was investigated. The clay assayed 28.9% and 50.59% , comprising mainly kaolinite mineral (82.6%) and quartz (12.5%). Thermal activation rendered the alumina in the clay acid-soluble by transforming the clay from its crystalline nature to an amorphous phase or metakaolinite. The clay samples were heated at calcination temperatures of 500, 600, 700, 800, and 900 °C at holding times of 30, 60, and 90 minutes. Uncalcined clay samples and samples calcined at 1000 °C (holding for 60 minutes) were used in the control experiments. Leaching of alumina from the resulting clay calcines passing 300 μm sieve (-50 mesh) was done in 1M hydrochloric acid solution at room temperature using a solid/liquid ratio of 0.02g/ml and shaking speed of 100 rpm. The solubility data given by the fraction of Al ion taken into leach solution showed that the clay calcined at 700 °C (holding for 60 minutes) responded most to leaching. In general, it was observed that samples calcined for 60 minutes responded better than those held for 30 or 90 minutes. The activation energies for leaching the clay calcines were 29.50, 32.92, 26.71, 30.18, 29.18, and 33.24 kJ/mol for samples calcined for 60 minutes at 500, 600, 700, 800, 900, and 1000 °C, respectively. The activation energy of leaching for the uncalcined sample was 35.07 kJ/mol. Thus, calcines produced at 700 °C (holding for 60 minutes) had the highest leaching response for alumina and the lowest leaching activation energy of 26.71 kJ/mol. It is concluded therefore that Nsu kaolinite clay should be best calcined for alumina yield by heating up to 700 °C and holding for 60 minutes at that temperature. The clay deposit can be used as alternative resource for alumina production.