Insights into environmental remediation of heavy metal and organic pollutants: Simultaneous removal of hexavalent chromium and dye from wastewater by zero-valent iron with ligand-enhanced reactivity

Abstract

The pollution of heavy metal and organic pollutants is a global environmental issue. Up to now, the simultaneous removal of heavy metal and organic pollutants is still a great challenge. The removal of heavy metal and organic pollutants by zero-valent iron (ZVI) has been extensively studied, but the removal efficiency of pollutants is low using single ZVI for remediation application. In this paper, a low-cost method by ZVI in presence of ethylenediaminetetraacetic acid (EDTA) and oxalate ligands has been developed to simultaneously remove Cr(VI) and dye from wastewater. This innovative process combines the reduction of Cr(VI) to Cr(III) with the reduction/oxidation of the dye by ZVI with the aid of ligand. EDTA and oxalate ligands can significantly increase the removal efficiency of Cr(VI) and dye since the ligands can accelerate ferrous iron oxidation and increase the generation of hydroxyl radical. In contrast, oxalate ligand possessed better removal efficiency in simultaneous removal process than EDTA, and oxalate generated lower TOC than EDTA. At the optimal conditions, the removal efficiency higher than 98% for Cr(VI) and higher than 81% for dye was observed in presence of 3.0mM oxalate. X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy and UV–visible spectrometer were used to study the reaction mechanism among Cr(VI), ZVI and dye in presence of ligand.