pH Dependence of Lead Adsorption on Zeolites

Abstract

The adsorption of Pb on zeolites A4, X, Y and mordenite was studied at various initial pH with the purpose of assessing the pH dependence of Pb adsorption. The adsorption was conducted using 0 - 0.6 mM Pb(NO 3)2 in the presence of 100 mM NH 4 NO 3 and pH adjustment done using HNO 3 . The coexisting NH 4 NO 3 served as a representative of other cations available in nature. The study was conducted at initial solution pH ranging from 3 - 5. Adsorption results were analyzed using Langmuir isotherm analysis. Adsorption was noted to be dependent on pH with increasing adsorption as pH increased from 3 - 5 for zeolites A4, X and Y. The adsorption of Pb on mordenite on the other hand did not show any dependence on pH since it was almost constant within the studied pH range. The adsorptive capacities were 2500, 2000, 588 and 179 mmol · kg -1 for A4, X, Y and mordenite, respectively. The results of this study can be used in designing or planning for the clean-up of polluted water using adsorption techniques. An important attribute of these findings was that the samples studied were shown to have the capacity of removing even very low concentration of Pb, a property which is hardly achievable by most adsorbents.