Comparative Study on the Adsorptive Capacity of Water Hyacinth and Palm Kernel Shell on Heavy Metals

Abstract

The adsorptive capacity of activated water hyacinth (AWH) and palm kernel shell (APKS) on lead (Pb⁺⁺) and iron (Fe⁺⁺) was studied. The zinc chloride activated carbons were characterized under pH and iodine number, moisture content, particle size, specific gravity, bulk density, porosity and volume of void. The results showed that APKS has a pH of 6.36 with iodine number of 510mg/g, where as the AWH has a pH of 7.67 and iodine number of 620mg/g.

Batch adsorption studies were also carried out under varying experimental conditions of pH of the solutions, contact time of the carbons and metal ions, and initial concentration of Pb⁺⁺ and Fe⁺⁺ solutions. The results showed that the highest percentage removal of 99.85 occurred at pH = 8 by AWH on Fe⁺⁺ and the lowest percentage removal of 3.026 by AWH on the same metal. On the effect of contact time, it was found that the equilibrium time for the sorption was at 60mins with the percentage removal of 99.59 by AWH on Fe and lowest % removal of 23.27 by APKS on Fe⁺⁺. On the effect of initial concentration, the results showed that the adsorption of Fe increases with the initial concentration, while that of Pb⁺⁺ decreases with increase in initial concentration. The Langmuir and Freundlich adsorption models were used for the mathematical description of adsorption equilibrium as well. It was deduced from the plot that the Langmuir isotherm fitted for modeling the adsorption by APKS on Pb⁺⁺ and Fe⁺⁺ while the Langmuir and Freundlich model for lead by AHW gave relative close correlation coefficient of 0.692 and 0.771 respectively, but was totally inadequate for modeling that of iron.