KINETICS OF THE EXTRACTION OF ALUMINA AND IRON OXIDE FROM OZORO CLAY

AUTHOR: ORUGBA OGHENERO HENRY

DEPARTMENT: CHEMICAL ENGINEERING

AFFILIATION: NNAMDI AZIKIWE UNIVERSITY, AWKA

Clay which is one of the most abundant raw materials in nature is a very rich source of alumina and iron oxide. The direct application of this mineral in the dissolution process yields very poor result due to small surface area. This research was directed towards the modification of the clay mineral from Ozoro and investigating the thermodynamics and kinetic model of their dissolution. The clay relatively 33.90% alumina and 12.0% iron oxide. The raw and modified clay was characterized using the X-Ray florescence (XRF) for chemical composition, the Fourier Transform Infrared spectroscopy (FTIR) for the determination of effect of heat treatment and SEM for determination of surface area. In order to determine the best calcinations temperature and period in the thermal activation process, temperature range of 400 to 900oC and period of 30mins to 180mins were investigated. The calcined samples were ground to particle size of 0.045mm and leached with 3M H2SO4 for 90mins and the best calcinations conditions were found to be 700oC at 1hr since this gave the highest yield for the two metals. For the leaching kinetics of the clay using HCl, H2SO4 and HNO3, the clay was subjected to the best calcinations conditions. The resulting samples was ground to different particle sizes, and at different concentrations of the solvents, liquid to solid weight ratio, stirring speed and leaching temperature, the dissolution kinetics were investigated. The dissolution kinetic data were analyzed using the various forms of the shrinking core model. The values of K were calculated and the activation energy, the order of reaction and thermodynamic data were obtained. The Response Surface Methodology (RSM) based on the central composite rotatable design (CCRD) was used to optimize the leaching of both alumina and iron oxide from the clay. The characterization showed that Ozoro clay is kaolinitic in nature. Analysis of the dissolution data showed that the process increased with increased calcinations temperature, leaching temperatures, stirring speed, liquid-solid ratio and solvent concentration but with decreased particle size. Results showed that alumina dissolution in HCl and HNO3 conform to the liquid film diffusion model, but in H2SO4, product layer diffusion model and the activation energies were respectively 35.32, 25.43 and 31.44KJ/Mol. Iron dissolution in HCl and HNO3 conform to the liquid film diffusion model, but in H2SO4, product layer diffusion model and the activation energies were respectively 34.003, 32.60 and 38.88KJ/Mol. Maximum yield of alumina of 90.48% was achieved in leaching with H2SO4 at calcinations temperature 582.33oC; leaching temperature 67.92oC; concentration 1.92mol/dm3; liquidsolid ratio 10.78cm3/g and stirring speed289.54rpm. Maximum iron yield of 84.91% was achieved in leaching with H2SO4 at calcinations temperature 662.72oC; leaching temperature 59.76oC; concentration 2.06mol/dm3; liquid-solid ratio 9.99cm3/g and stirring speed 373.60rpm. The results from this study showed that heat treatment of the Ozoro clay increased both alumina and iron yield. Hence, application of the simple and low cost modification techniques employed in this study has shown that Ozoro clay is a rich source of both alumina and iron.

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