A Comparative Study of the Sorption of Cd(II) and Pb(II) Ions from Aqueous Solution by Local Bentonite and Clinoptilolite

Local clay (bentonite) and a zeolite (clinoptilolite) have been characterized and used for the removal of Pb(II) and Cd(II) ions from aqueous solutions using batch sorption experiments. Parameters such as the equilibrium time, the effect of pH and temperature were studied. The sorption capacities of the two sorbents were calculated by fitting the Langmuir adsorption model to the experimental data points. Metal ion sorption by zeolite [q(0) Pb(II) = 0.515 mmol/g, q(0) Cd(II) = 0.392 mmol/g] was higher than that by bentonite [q(0) Pb(II) = 0.436 mmol/g, q(0) Cd(II) = 0.381 mmol/g]. The removal of Pb(H) ions was much greater than that of Cd(II) ions under identical experimental conditions. The negative values of the Gibbs' free energy change (Delta G(0)) demonstrate the spontaneous nature of the sorption process with both sorbents, while the positive values of the enthalpy change (Delta H(0)) indicate that the sorption process was endothermic in nature.