Simultaneous removal of Cr(VI) and 2,4-dichlorophenol from water using the zero-valent iron–aminotriacetic acid system

Abstract

Zero valent iron (ZVI) can remove complex organic pollutants and heavy metals during water purification. However, the oxide film formed on its surface leads to passivation, which reduces the complete exposure of the reaction sites. Aminotriacetic acid (NTA) as a complexing agent is considered to be a good choice for inhibiting the surface passivation of ZVI due to its simple operation, economic feasibility and rapid reaction. The removal efficiency of pollutants and influencing factors (pollutant concentration, iron dosage, NTA concentration, and pH) were investigated in the ZVI/NTA system. Cr(VI) and 2,4-dichlorophenol (2,4-DCP) were simultaneously removed in the ZVI/NTA system with removal efficiencies of 98.1 % and 94.3 % within 120 min, respectively. Cr(VI) removal was mainly ascribed to the reduction ability of bare ZVI, whereas 2,4-DCP removal was ascribed to the •OH generated during the reaction between Fe(II) and H2O2. Quenching and molecular probe experiments confirmed the participation of •OH in 2,4-DCP removal. X-ray photoelectron spectroscopy analysis further confirmed the mutual conversion of Fe(II)/Fe(III) in the ZVI/NTA system, which contributes to the generation of •OH. In the ZVI/NTA system, Cr(VI) and 2,4-DCP were more easily removed under weak acidic conditions. Moreover, the TOC removal efficiency reached 75 % within 120 min, indicating decreased toxicity of this pollutant. As for the 2,4-DCP degradation, the intermediates 2-chlorohydroquinone, 1,2,4-trihydroxyphenol, hydroquinone, phenol, benzene, and acetic acid were detected. This research provides a new approach for simultaneously removing complex organic pollutants and heavy metals.