Synthesis of zeolite-supported microscale zero-valent iron for the removal of Cr6+ and Cd2+ from aqueous solution

Zeolite-supported microscale zero-valent iron (Z-mZVI) was synthesized and used to remove heavy metal cation (Cd2+) and anion (Cr6+) from aqueous solution. Transmission electron microscope (TEM) confirmed that mZVI (100-200 nm) has been successfully loaded and efficiently dispersed on zeolite. Atomic absorption Spectroscopy (AAS) revealed the amount of stabilized mZVI was about 13 wt.%. The synthesized Z-mZVI has much higher reduction ability and adsorption capacity for Cr6+ and Cd2+ compared to bare nanoscale zero-valent iron (nZVI) and zeolite. Above 77% Cr6+ and 99% Cd2+ were removed by Z-mZVI, while only 45% Cr6+ and 99% Cd2+ were removed by the same amount iron of nZVI, and 1% Cr6+ and 39% Cd2+ were removed by zeolite alone with an initial concentration of 20 mg/L Cr6+ and 200 mg/L Cd2+. The removal of Cr6+ by Z-mZVI follows the pseudo first-order kinetics model, and Xray photoelectron spectroscopy (XPS) analysis confirmed that Cr6+ was reduced to Cr3+ and immobilized on the surface of Z-mZVI. The removal mechanisms for Cr6+ include reduction, adsorption of Cr3+ hydroxides and/or mixed Fe3+/Cr3+ (oxy)hydroxides. The pseudo-second-order kinetic model indicated that chemical sorption might be rate-limiting in the sorption of Cd2+ by Z-mZVI. This synthesized Z-mZVI has shown the potential as an efficient and promising reactive material for removing various heavy metals from wastewater or polluted groundwater. (C) 2015 Published by Elsevier Ltd.