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

Low-cost zeolite sorbents, which have unique ion exchange and sorption properties, have been investigated as candidates for cost-effective removal of heavy metals from waste solution. Waste products from various industries are employed to prepare or modify zeolite for the improvement of adsorption capacity. In this review, the applications of natural, modified, and synthetic zeolite in removal of heavy metals from waste water solutions are summarized, and the removal efficiency on the same individual heavy metal is compared. It is unique in comparison with the existing literature reviews that three kinds of zeolites, including natural, modified, and synthetic zeolite, are used to remove the same heavy metal for comparative analysis, so a suitable adsorbent could be selected according to the properties of the wastewater in applications. Compared to natural zeolite, modified and synthetic zeolites have higher cation exchange capacities and sorption performance. Sorption process of three kinds of zeolites was generally spontaneous and endothermic, and removal mechanism of heavy metal ions was by adsorption and ion exchange processes. In summary, zeolites are effective adsorbent materials with great potential applications to remove heavy metals from waste water.