Influence of modulus of alkaline activator on the removal of Pb2+ by mesoporous geopolymer adsorbent.

Abstract

In this study, we synthesised metakaolin-based mesoporous geopolymer adsorbent and investigated the effect of alkaline activator modulus (molar ratios of SiO2/Na2O) on Pb2+ adsorption. The geopolymer prepared using 1.2 M alkaline activator performs excellent Pb2+ removal with a maximum adsorption capacity of 172.71\u2005mg g-1. The pseudo-second-order model fit the adsorption kinetics satisfactorily, indicating that the adsorption process is dominated by chemical adsorption. The adsorption data appropriately fit the Langmuir isotherm model. The contributions of adsorption methods corresponding to the total quantity adsorbed declined in the following order: EDTA extraction (formation of Pb aluminium oxide and Pb-containing amorphous materials) > residual fraction (Pb stabilisation in the tetrahedral aluminosilicate network) > ion exchange. Overall, the alkaline activator modulus significantly influenced the Pb2+ adsorption characteristics of the geopolymer adsorbent.