The values of thermodynamic parameters such as free energy of adsorption (ΔG0), heat of adsorption (ΔH0), and standard entropy changes (ΔS0) provide information about the nature of removal lead process. The results are given in Table 4. The Gibbs free energy indicates the degree of spontaneity of the sorption process. ΔH0 and ΔS0 were obtained from the slope and intercept of a plot of ln Kd against 1/T ( Fig. 3).