Adsorption–Desorption of Cd(II) and Pb(II) on Ca-Montmorillonite

The adsorption and desorption of Cd­(II) and Pb­(II) on Ca-montmorillonite have been investigated. The maximum removal efficiency of Cd­(II) reaches 98% at the initial concentration of 50.00 mg L–1, while it is about 70% for Pb­(II) at the initial concentration of 58.79 mg L–1. Experimental results indicate that adsorption reactions of Cd­(II) and Pb­(II) on Ca-montmorillonite agree well with second-order kinetics and the Langmuir isotherm model. Cd­(II) and Pb­(II) on Ca-montmorillonite are successfully desorbed by NaCl solution of high concentration. Data shows that desorption efficiencies are mainly influenced by the concentration of NaCl and temperature. The optimum desorption concentrations of NaCl for Cd­(II) and Pb­(II) are 1 mol L–1 and 3 mol L–1, respectively, where the adsorption efficiencies can reach 93% and 83%. The results of 4-time consecutive adsorption–desorption show that the method of desorption by NaCl solution is efficient and practical. Samples before and after adsorption or desorption have been characterized by X-ray diffraction, which are consistent with the results mentioned above.