Review of the Natural, Modified, and Synthetic Zeolites for Heavy Metals Removal from Wastewater

In this study, the adsorption behavior of natural (clinoptilolite) zeolites with respect to Co(2+), Cu(2+), Zn(2+), and Mn(2+) has been studied in order to consider its application to purity metal finishing wastewaters. The batch method has been employed, using metal concentrations in solution ranging from 100 to 400 mg/l. The percentage adsorption and distribution coefficients (K(d)) were determined for the adsorption system as a function of sorbate concentration. In the ion exchange evaluation part of the study, it is determined that in every concentration range, adsorption ratios of clinoptilolite metal cations match to Langmuir, Freundlich, and Dubinin-Kaganer-Radushkevich (DKR) adsorption isotherm data, adding to that every cation exchange capacity metals has been calculated. It was found that the adsorption phenomena depend on charge density and hydrated ion diameter. According to the equilibrium studies, the selectivity sequence can be given as Co(2+) > Cu(2+) > Zn(2+) > Mn(2+). These results show that natural zeolites hold great potential to remove cationic heavy metal species from industrial wastewater.