Comparative study on batch equilibrium biosorption of Cd(II), Pb(II) and Zn(II) using plantain (Musa paradisiaca) flower: kinetics, isotherm, and thermodynamics

Kemi Damilola Ogundipe and Adesola Babarinde

Abstract

The potential of plantain (Musa paradisiaca) flower to remove Cd(II), Pb(II) and Zn(II) from aqueous solutions has been investigated under different process parameters like pH, contact time, biomass dose and initial metal ion concentration. The optimum pH for the biosorption of each of the metal ions is pH 6. The kinetic data obtained were subjected to four kinetic models, among which the pseudo-second order kinetic model was found to be the best model that describes the biosorption of each of the metal ions. The equilibrium sorption data were fitted into Langmuir, Freundlich, Temkin and D-R isotherms. In each case, the Freundlich isotherm model gave the best fit giving the sorption intensity (n) values of 1.17, 0.91 and 0.90 which indicate favourable sorption of Cd(II), Pb(II) and Zn(II), respectively. The heat of the sorption process was estimated from Temkin Isotherm model and the mean free energy was estimated from D-R isotherm model to be 312.81Jmol-1, 223.61Jmol-1 and 316.55Jmol-1 for Cd(II), Pb(II) and Zn(II), respectively. Thermodynamically, the biosorption of each of the metal ions is endothermic and the order of spontaneity of the biosorption process being Cd(II) > Zn(II) > Pb(II). Similarly, positive change in entropy was observed for each, the order of disorderliness is Cd(II) > Zn(II) = Pb(II).