ISSN : 0976-8505
The potential to remove Ni(II) and Pb(II) from aqueous solutions through biosorption using Escherichia coli immobilized in agarose was investigated. The effects of pH, contact time, initial concentration and temperature on the adsorption of Ni(II) and Pb(II) were studied. The optimum pH value was found to be 6 for Ni(II) and Pb(II) adsorption. The equilibrium experiment data were analyzed using Langmuir, Freundlich and Temkin isotherm models. The equilibrium data obeyed Langmuir isotherm with high correlation coefficient better than Freundlich and Temkin adsorption isotherms. From the Langmuir model, the maximum uptake capacities of Escherichia coli immobilized in agarose gel for Ni(II) were found to be 58.49 ± 0.69 mg g-1 63.28 ± 3.41 mg g-1 and 69.69 ± 1.23 mg g-1 at 298K, 308K and 318K respectively. While for Pb(II) they were found to be 40.30 ± 4.38 mg g-1, 48.26 ± 3.82 mg g-1 and 60.25 ± 0.37 mg g-1 at 298K, 308K and 318K respectively. Increment in adsorption capacity with increasing temperature indicated that the adsorption process is endothermic in nature. Thermodynamic parameter Δ calculated for the two metals were found to be positive confirming the endothermic nature of the adsorption process. Δ were negative indicating the reaction is spontaneous and Δ obtained were positive indicating significant change in the internal structure of the adsorbent. The dependence of adsorption on time data were fitted with pseudo first order, pseudo-second-order and elovich kinetic models. The data fitted pseudo-second-order kinetic model with high correlation indicating that the adsorption processes were chemisorptions. The result indicated that Escherichia coli immobilized in agarose gel was suitable for biosorption of Ni(II) and Pb(II) from aqueous solution.
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