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

• Z-mZVI has better performance on Cr6+ and Cd2+ removal than pure zeolite and nZVI.
• XPS test confirmed the reduced Cr3+ production was immobilized by Z-mZVI.
• The Cd2+ adsorption data were well described by pseudo-second order kinetic model.
• Z-mZVI can remove Cr6+ and Cd2+ from wastewater at a fairly rapid rate.

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 1.3 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 9% 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 X-ray 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.

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