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The Physicochemical Characteristics of Natural Zeolites Governing the Adsorption of Pb2+ from Aqueous Environment

The aim of this study is to investigate the effect of natural zeolites characteristics on the adsorption capacity of Pb2+ from an aqueous environment. The used natural zeolites were originated from 3 regions in Indonesia. i.e. Bayah, Banten (coded as ZB) and two samples from South Lampung (coded as ZL-1 and ZL-2) and Nanggung, Bogor (ZN). The characteristics of each natural zeolite were evaluated through a series of detailed analysis including XRD, FTIR, XRF, SEM and N2 physisorption. It was revealed that ZB, ZL-1 and ZL-2 were dominated by clinoptilolite (HEU) frameworks while the major phase of ZN was mordenite (MOR) type. From XRF data, the three natural zeolites (ZB, ZL-1 and ZN) possessed a comparable Si/Al ratio (ca. 5.5 to 6) whereas ZL-2 had slightly lower Si/Al ratio (ca. 4). We found that, at comparable Si/Al ratio, clinoptilolite frameworks has a higher adsorption capacity of Pb2+ compared to that of mordenite due to the compatibility of Pb2+ inside the pores of clinoptilolite. Lower Si/Al ratio of natural zeolite tended to show higher adsorption capacity of Pb2+ since the net charge of zeolite frameworks became more negative. These two factors, the framework type and the Si/Al ratio, are significant for the adsorption capacity. Another factor, i.e. surface area, had no certain effect on the adsorption capacity in this case.