Biosorption equilibrium, kinetic and thermodynamic modelling of naphthalene removal from aqueous solution onto modified spent tea leaves

The object of this study was to investigate the feasibility of using modified spent tea leaves to remove naphthalene from its aqueous solution under batch mode. The effects on the removal process of physical factors, such as initial naphthalene concentration, contact time, biosorbent dosage, pH and temperature, have been evaluated. The equilibrium biosorption data were analyzed by the Langmuir, Freundlich, Temkin and DubininRadushkevich (DR) adsorption isotherm models. These models provided a good fit to the experimental data, but the Langmuir isotherm model provided the best correlation (R-2=0.993) to the experimental data. The biosorption kinetic data of naphthalene were analyzed by pseudo-first-order, pseudo-second-order and intra-particle diffusion and surface mass transfer kinetic models. These four kinetic models fitted the biosorption kinetic data well, but the pseudo-first-order kinetic model gave the best fit. The activation energy (E-a) was found to be 15.89 kJ per mole and the thermodynamic properties of the biosorption process, such as the Gibbs free energy, enthalpy and the entropic change of biosorption, were also evaluated. It was established that the biosorption process was spontaneous, feasible and endothermic in nature.