Ball-milled zero-valent iron with formic acid for effectively removing Cu(II)-EDTA accomplished by EDTA ligands oxidative degradation and Cu(II) removal

Heavy metal complexes in industrial wastewater are challenging to be removed by conventional methods arising from their stable chelating structure. In this study, zero-valent iron (ZVI) was ball-milled with tiny formic acid (FA), and the as-prepared sample (FA-ZVI bm ) was attempted to eliminate a model heavy metal complex of Cu(II)-ethylenediaminetetraacetic acid (Cu(II)-EDTA). The addition of FA to ball-milling could dramatically enhance the performance of ball-milled ZVI (ZVI bm ) towards Cu(II)-EDTA removal and increase the removal rate constant by 80 times. This conspicuous improvement of Cu(II)-EDTA elimination was attributed to the ferrous formate (Fe(HCOO) 2 ) shell formed on the surface of FA-ZVI bm . Results revealed that the Fe(HCOO) 2 shell facilitated the activation of O 2 to reactive oxygen species (ROS) and the leaching of Fe 3+ . Cu(II)-EDTA was decomplexed through both oxidative destruction and Fe 3+ replacement, and the released Cu 2+ was reduced by FA-ZVI bm and immobilized synchronously. Meanwhile, the ligands underwent oxidative degradation by ROS, thus avoiding the re-chelation ecological risk. Impressively, FA-ZVI bm could achieve cyclic treatment of actual copper complex wastewater and possessed promising advantage in treatment cost. This study would offer a promising approach for eliminating Cu(II)-EDTA through EDTA ligands degradation and synchronous Cu(II) removal, moreover to shed light on the decomplexation mechanism.