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Investigation of zinc and lead removel from aqueous solutions using clinoptilolite

Moralı, Nihan
Natural zeolites, especially clinoptilolite, have the ability of removing certain cations from wastewater by utilizing ion exchange and adsorption. In this study, clinoptilolite originated from Bigadiç, Balıkesir deposit was investigated in its natural and conditioned form for its effectiveness in removing Zn2+ and Pb2+ ions from aqueous solutions. In addition, relevant mechanisms involved in heavy metal removal by clinoptilolite were examined in this study. Throughout this work, equilibrium and kinetic studies were performed with as-received and conditioned clinoptilolite, having particle size of 0.15 ا 0.80 mm. Conditioning aimed to replace exchangeable cations (Na+, K+, Ca2+, Mg2+) on clinoptilolite with a cation that is more willing to undergo ion exchange. The results of equilibrium studies revealed that clinoptilolite had different capacities for Zn2+ and Pb2+ ions. Clinoptilolite had high capacity for Pb2+ ions, whereas lower capacities were attained for Zn2+. Conditioning with concentrated NaCl solution increased the removal capacity for both metals. Maximum capacities attained were 0.14 meq/g (as-received) and 0.39 meq/g (conditioned) for Zn2+, and 0.51 meq/g (as-received) and 1.10 meq/g (conditioned) for Pb2+. Furthermore, kinetic studies performed under pH-uncontrolled and pH-controlled conditions revealed that heavy metal removal can not only be explained by ion exchange. These studies also indicated that Zn2+ ions were weakly bound to clinoptilolite structure, whereas there was a strong bonding between Pb2+ ions and clinoptilolite structure. To examine possible removal mechanisms, relationship between exchangeable ions released from clinoptilolite structure and Zn2+ and Pb2+ ions removed from aqueous solutions were investigated during equilibrium and kinetic studies. For equilibrium studies, it was observed that the higher the heavy metal equilibrium