Determination of the Calcination Procedure Required to Activate Edda Clay for Optimal Leaching of Alumina

Nigeria is the highest consumer of aluminium in Africa but lacks bauxite deposits. The replacement of bauxite alumina with other alumina bearing resources (clays in particular) has been proposed. The present study investigated the thermal treatment required to activate Edda clay from southeastern Nigeria for optimal leaching of alumina. The clay is composed mainly of kaolinite and quartz, assaying 24.65% Al2O3 and 52.81% SiO2. Thermal activation of the clay prior to leaching transformed the crystalline kaolinite mineral to an amorphous phase (metakaolinite) in which the alumina became soluble. Clay samples passing 300 μm sieve were calcined at temperatures of 500°C, 600°C, 700°C, 800°C, and 900°C at holding times of 30, 60, and 90 minutes in each case. The uncalcined clay and sample heated at 1000°C (for 60 minutes) were used in the control experiments. Leaching of alumina from the resulting clay calcines was done in 1 M hydrochloric acid solution at room temperature using a solid/liquid ratio of 0.02 g/ml and shaking speed of 100 rpm. The solubility data based on the percentage of Al ions taken into leach solution showed that the sample calcined at 700°C (for 60 minutes) responded to leaching better than other samples. Samples calcined for 60 minutes at all temperatures studied were found to respond more than those held for 30 or 90 minutes. Studies on the activation energy of leaching revealed that calcines produced at 700°C (for 60 minutes) had both the highest leaching response (49.96% after 1 hour at leaching temperature of 100°C) and the lowest activation energy of 24.47 kJ/mol. It is concluded therefore that Edda kaolinite clay should be thermally activated for alumina yield by heating up to 700°C and holding for 60 minutes. The clay deposit is therefore a potential alternative resource for alumina production.

Effect of Calcination Condition on Thermal Activation of Ibere Clay and Dissolution of Alumina

Bauxite deposits for production of alumina are lacking in Nigeria and there is an aluminium smelter plant in the country which requires alumina for its operation. Development of alternative alumina resource using clays that are abundant in the country is the focus of this paper. The thermal activation of Ibere clay from southeastern Nigeria for optimal leaching of alumina was investigated. The clay assayed 28.52% Al2O3 and 51.6% SiO2, comprising mainly kaolinite mineral and quartz or free silica. The alumina locked up in the clay structure was rendered acid-soluble by thermal activation which transformed the clay from its crystalline nature to an amorphous, anhydrous phase or metakaolinite. The clay samples were heated at calcination temperatures of 500°C, 600°C, 700°C, 800°C, 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. The result of leaching the clay calcines in 1 M hydrochloric acid solution at room temperature, showed that the clay calcines produced at 600°C (holding for 60 minutes) responded most to leaching. Samples calcined for 60 minutes also responded better than those held for 30 or 90 minutes. Based on activation energy studies, it was observed that calcines produced at 600°C (for 60 minutes) had both the highest leaching response (50.27% after 1 hour at leaching temperature of 100°C) and the lowest activation energy of 24.26 kJ/mol. It is concluded therefore that Ibere kaolinite clay should be best calcined for alumina dissolution by heating up to 600°C and holding for 60 minutes at that temperature. The clay deposit has potential for use as alternative resource for alumina production in Nigeria where bauxite is scarce.

Conditions for Thermal Activation of Ngwo Clay as an Alternative Resource for Alumina

The thermal activation of Ngwo clay from southeastern Nigeria for optimal leaching of alumina was investigated. The clay assayed 24.63% Al2O3 and 52.15% SiO2, comprising mainly kaolinite mineral and free silica or quartz. The alumina locked up in the clay structure was rendered acid-soluble by thermal activation which transformed the clay from its crystalline nature to an amorphous, porous phase or metakaolinite. The clay samples were heated at calcination temperatures of 500°C, 600°C, 700°C, 800°C, 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. After leaching the resulting clay calcines in 1 M hydrochloric acid solution at room temperature, it was observed that the clay calcines produced at 700°C (holding for 60 minutes) responded most to leaching. Samples calcined for 60 minutes also responded better than those held for 30 or 90 minutes. Based on activation energy studies, it was observed that calcines produced at 700°C (for 60 minutes) had both the highest leaching response (51.84%?after 1 hour at leaching temperature of 100°C) and the lowest activation energy of 25.03 kJ/mol. It is concluded therefore that Ngwo kaolinite clay should?be best calcined for alumina dissolution by heating up to 700°C and holding for 60 minutes at that temperature. The clay deposit has potential for use as alternative resource for alumina production in Nigeria where bauxite is scarce.