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.
Highlights
Primary aluminium is produced by the electrolytic reduction of alumina (Al2O3) in the popular Hall-Héroult process [1] [2] [3] [4]
The chemical composition shows that the clay contains 50.59% silica, 28.9% alumina, loss on ignition (LOI) of 12.7% while impurity or accessory oxides make-up the balance of 7.81% (Table 1)
The thermal treatment conditions required for transforming Nsu clay to metakaolinite for enhanced leaching response was investigated
Summary
Primary aluminium is produced by the electrolytic reduction of alumina (Al2O3) in the popular Hall-Héroult process [1] [2] [3] [4]. The alumina used is usually refined from bauxite, the traditional ore for aluminium [5] [6]. About 90 percent of the world production of bauxite is used for making alumina, most of which is consumed in the manufacture of aluminium. The West African subregion holds the largest bauxite resources in the world [11] [12] [13]. The U.S Geological Survey put the world bauxite reserve at about 55 billion tonnes with West Africa having the highest share of 32% [10]. Countries in the sub-region (Nigeria’s neighbours) hold about one-third of the world’s bauxite reserves, and the resource is sold at locally unfavourable internationally competitive prices [10]. Only the occurrence of bauxitic clay is SciPress applies the CC-BY 4.0 license to works we publish: https://creativecommons.org/licenses/by/4.0/
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