Kinetics and thermodynamics of lead(II) adsorption on vermiculite

The kinetics and thermodynamics of Pb(II) adsorption on vermiculite have been studied by the sets of experiments at various conditions (temperature, initial lead concentration and adsorption time). The structures of the vermiculite before and after Pb(II) adsorption were measured using X-ray diffraction (XRD), thermogravimetric analysis (TA), and X-ray photoelectron spectroscopy (XPS). Adsorption of Pb(II) was strongly affected by pH. First order kinetics model best described the reaction rate, and the adsorption capacity calculated by the model was consistent with that actual measurement. Isotherms for the adsorption of Pb(II) on vermiculite were developed and the equilibrium data fitted well to the Langmuir and Freundlich models. Thermodynamic parameters such as enthalpy, entropy, and free energy were calculated using the Van't Hoff equations. The thermodynamics of Pb(II) on vermiculite indicates the spontaneous and endothermic nature of adsorption. Quantitative desorption of Pb(II) from vermiculite was found to be more than 40% which facilitates the sorption of metal by ion exchange.