Determination of Optimal Yield of Alumina From Local Clays by Factorially-Designed Experiments

摘要

Leaching by use of factorial design experiment was used to investigate the effect of process variables on the yield of alumina obtainable from four local clays from four different locations in Nigeria. Characterization of these clays obtained from previous work was observed in this order: Ikot-Abasi, Enito II, Akpugo and Awgbu containing 56.00%, 8.45%, 25.28% and 14.43% Al 2 O 3 respectively. Fractional factorial design was used to develop a mathematical model used in the investigation. The process variables whose effect on alumina leaching investigated were: acid concentration (2M and 10M), calcinations Temperature (200 o C and 1000 o C), calcinations time (15 and 75 minutes), leaching time (20 and 100 minutes) and particle size (75 and 1000μm) with the experiment conducted at constant boiling temperatures of the acids used (Nitric and Acetic acid). On optimization of the model developed from the factorial design experiment, optimal leaching conditions for each clay samples were obtained with corresponding yields of alumina presented as follows: Ikot-Abasi clay and nitric acid – yield of 78.86% alumina; Ikot-Abasi and Acetic – yield of 50.26% alumina; Enito II and nitric acid – yield of 53.14% alumina; Enito II clay and acetic acid – yield of 30.23% alumina; Awgbu clay and nitric acid – 62.74% alumina yield; Awgbu clay and acetic acid – alumina yield of 43.24%; Akpugo clay and nitric acid – alumina yield 75.43%; Akpugo clay and acetic acid – alumina yield 41.98%. The values of the yields obtained from the model optimization were validated by conducting the leaching experiment again in the laboratory under the optimized process conditions and were observed to closely match with a deviation ranging from 0.21 to 5.55%. From the results obtained, it was observed that the best yield was gotten from Ikot-Abasi clay which contained the highest percentage of alumina content.