Comparative study on the biosorption of Pb(II), Cd(II) and Zn(II) using Lemon grass (Cymbopogon citratus): Kinetics, isotherms and thermodynamics

A comparative study on the biosorption of Pb(II), Cd(II) and Zn(II) using Lemon grass (Cymbopogon citratus) was investigated under various physicochemical parameters. Optimisation studies were carried out using batch biosorption studies. The biosorption of each of the metal ions was found to be pH-dependent. Kinetic study showed that each biosorption process followed the pseudo-second-order kinetic model. The sorption of each metal ion was analysed with Freundlich, Langmuir, Temkin and Dubinin-Radushkevich (D-R) isotherm models, in each case, the equilibrium data were best represented by Freundlich isotherm model. Thermodynamic parameters such as standard Gibbs free energy (？G？), standard enthalpy (？H？), standard entropy (？S？) and the activation energy (A) were calculated. The biosorption of each metal ion was spontaneous and the order of spontaneity of the biosorption process being Zn(II) > Cd(II) > Pb(II). Similarly, the change in entropy shows that the order of disorder is Cd(II) > Zn(II) > Pb(II). In each case, the value of activation energy obtained shows that each process is a diffusion-controlled adsorption process.