Removal of Pb2+ from water by using Na-Y zeolites prepared from Egyptian kaolins collected from different sources

Abstract

This article aims to study the effect of the chemical composition of the Egyptian kaolins on the performance of the low cost kaolin-based zeolites toward Pb2+ removal. In this work, different Egyptian kaolins collected from Saint Catherine, Kalabsha and Dehessa (KS, KK and KD, respectively) were used in the preparation of the corresponding Na-Y zeolites (ZS, ZK and ZD). X-ray Fluorescence (XRF), X-ray diffraction (XRD) and atomic absorption analyses were recorded. XRF and XRD indicate that the zeolitic contents in the prepared samples are proportional to the kaolinite contents in the corresponding kaolins. The difference in the removal efficiency between zeolites depends on the experimental conditions. Generally, the order of Pb2+ loading and Na+ release is ZS>ZK>ZD, which is in accordance with the zeolitic contents in each sample. From sorption isotherms, maximum sorbed amounts of Pb2+ were 299.6, 299.3 and 260.6meq/100g for ZS, ZK and ZD, respectively. Comparison with previous studies shows that the maximum loading capacities of zeolites are higher than the commonly used; and it is also comparable to ion exchange resins.For all zeolites, in Pb2+ loading experiments, the relation between released and loaded equivalents of positive charges was not stoichiometric. We concluded that the loading process involves competition between three processes: (a) precipitation of some Pb2+as hydroxides, (b) ion exchange and (c) chemisorption of Pb2+on zeolite surfaces. During Pb2+ loading processes, the equivalent amount of loaded Pb2+ is always higher than that of the released Na+ suggesting the predominance of the chemisorption mechanism.