Mechanism insights into enhanced Cr(VI) removal using nanoscale zerovalent iron supported on the pillared bentonite by macroscopic and spectroscopic studies

Abstract

NZVI was supported on a pillared bentonite (Al-bent) to enhance the reactivity of NZVI and prevent its aggregation. The performance and mechanisms of the combined NZVI/Al-bent on removing hexavalent chromium (Cr(VI)) was investigated by batch and XAFS experiments. The batch investigations indicated that Cr(VI) could be almost completely removed by NZVI/Al-bent after 120min. The efficiency was not only much higher than that by NZVI (63.0%), but also superior to the sum of NZVI reduction and Al-bent adsorption (12.4%). Besides, NZVI/Al-bent exhibited good stability and reusability, and Al-bent could reduce the amount of iron ions released into the solution. XANES results provided evidence that NZVI/Al-bent could reduce Cr(VI) entirely into Cr(III), while NZVI reduced Cr(VI) partly into Cr(III) with a trace of Cr(VI) adsorbed on the corrosion products. The structure of Cr(VI)-treated NZVI/Al-bent determined with EXAFS revealed the formation of Cr–Al/Si bond, suggesting that some insoluble Cr(III) species might be transferred to the surface of Al-bent, therefore the precipitates on iron surface could be greatly reduced. The results demonstrated that Al-bent plays a significant role in enhanced reactivity and stability of NZVI, and may shed new light on design and fabrication of supported NZVI for environmental remediation.