Removal of Pb(II) from aqueous solution by a zeolite-nanoscale zero-valent iron composite

The effectiveness of nanoscale zero-valent iron (nZVI) to remove heavy metals from water is reduced by its low durability, poor mechanical strength, and tendency to form aggregates. A composite of zeolite and nanoscale zero-valent iron (Z-nZVI) overcomes these problems and shows good potential to remove Pb from water. FTIR spectra support nZVI loading onto the zeolite and reduced Fe⁰ oxidation in the Z-nZVI composite. Scanning electron micrographs show aggregation was eliminated and transmission electron micrographs show well-dispersed nZVI in chain-like structures within the zeolite matrix. The mean surface area of the composite was 80.37m²/g, much greater than zeolite (1.03m²/g) or nZVI (12.25m²/g) alone, as determined by BET-N₂ measurement. More than 96% of the Pb(II) was removed from 100mL of solution containing 100mg Pb(II)/L within 140min of mixing with 0.1g Z-nZVI. Tests with solution containing 1000mg Pb(II)/L suggested that the capacity of the Z-nZVI is about 806mg Pb(II)/g. Energy-dispersive X-ray spectroscopy showed the presence of Fe in the composite; X-ray diffraction confirmed formation and immobilization of Fe⁰ and subsequent sorption and reduction of some of the Pb(II) to Pb⁰. The low quantity of Pb(II) recovered in water-soluble and Ca(NO₃)₂-extractable fractions indicate low bioavailability of the Pb(II) removed by the composite. Results support the potential use of the Z-nZVI composite in permeable reactive barriers.