Study of Thermodynamic Parameters in Adsorption of Lead, Copper and Cadmium Metal Ions by Plant Sorbents

This research was carried out in laboratory scale using dried leaves powder of Thuja andPopulus as sorbents to remove lead, copper and cadmium ions from aqueous solution. The effect of temperature on metal ions removal by sorbents was evaluated, the equilibrium data was fitted by Langmuir, Freundlich and Dubinin-radushkevich isotherms and thermodynamic constants were determined. For this purpose, solutions with different concentration of ionic metals were prepared. Sorbent amount equal to 10 gr/lit, pH = 5 and detention time 60 minutes for all sorbents were adjusted. Studied temperatures were 20, 25, 35, 45 ºC. The results have shown that increasing the initial concentration, increases the adsorption capacity. The Langmuir model was found to best describe the data, although some adsorption processes were described with more than one model. This research indicated that the adsorption of metal ions by Populus was endothermic and adsorption of them by Thuja was exothermic processes. Determination of the thermodynamic parameters, Gibbs free energy (ΔGº) and the mean adsorption free energy (Ea) showed that the adsorption of metal ions by two plants was physical.