Preparation of formic acid modified industrial zero-valent iron (FA-ZVIbm) for CdII-EDTA removal: CdII capturing and self-enhanced oxidative degradation of EDTA

Abstract

Cadmium (Cd) contamination is highly toxic to human health, and the complexed Cd in wastewater is tricky to remove owing to its stable chelating structure. In this study, industrial zero-valent iron (ZVI) was modified by ball-milling with tiny formic acid (FA), and the as-prepared sample (FA-ZVIbm) was attempted in the treatment of CdII-ethylenediaminetetraacetic acid (CdII-EDTA). Little FA addition to ball-milling could dramatically improve the performance of FA-ZVIbm towards CdII-EDTA elimination and raise the elimination rate constant by more than 200 times. Results ascertained that the (HCOO)2FeII shell formed on FA-ZVIbm promoted CdII-EDTA decomplexation and activation of dissolved O2 to reactive oxygen species (ROS) for oxidative degradation of EDTA ligands. CdII-EDTA was instantly decomplexation by Fe3+ replacement, and the decomplexed Cd2+ was rapidly captured by FA-ZVIbm. At the same time, the EDTA ligands underwent oxidative degradation, avoiding the re-chelation ecological hazard. Interestingly, we found that replacement decomplexation has a synergistic mechanism for activating dissolved O2 to ROS, facilitating oxidative destruction of EDTA ligands. Furthermore, the FA-ZVIbm fixed-bed reactor could remediate CdII-EDTA contaminated environmental water one-stop, and the effluent stably meets the emission standards. This study demonstrated that FA-ZVIbm could be a viable approach for CdII-EDTA decontamination and clarified the remediation mechanism.