Pb(II) AND Cd(II) EXTRACTION BY CROSS LINKED POLYSTYRENE THIOUREA

Abstract

This study aims to investigate the Lewatit TP 214, which is a chelating ion-exchange polymer containing the thiourea group, for the sorption of Pb(II) and Cd(II) ions from aqueous solutions. The thiourea function is chemically bonded to the matrix of the styrene-divinylbenzene polymer. The effects of parameters such as the concentration, pH level, contact time, ionic strength and temperature were investigated. The results showed more affinity of resin towards cadmium than lead cations. The maximum uptake values of Pb(II) and Cd(II) were 55.59 mg.g -1 and 81.75 mg.g -1 , respectively. The resin used in this study exhibited a good sorption potential at initial pH values, i.e. pH = 4.1 and pH = 6.1, for Pb(II) and Cd(II), respectively, at room temperature. The extraction kinetics, for both cations Pb(II) and Cd(II), was best described by the pseudo second order model. This study showed that the diffusion of moving boundary particles fits well the experimental data (r > 0.99) for the sorption of both Pb(II) and Cd(II) ions. The Langmuir isotherm fits better the obtained equilibrium data compared to the Freundlich isotherm. The thermodynamic data for the sorption of Pb(II) and Cd(II), on the Lewatit 214 resin, indicate that the process is endothermic for Pb(II) (∆H = + 8.94 kj.mol -1 ), while it is exothermic for Cd(II) (∆H = - 51.65 kj.mol -1 ). In addition, the thermodynamic study showed also negative ∆G values, indicating that the sorption process of both Pb(II) and Cd(II) ions is spontaneous.