Simultaneous decomplexation in blended Cu(II)/Ni(II)-EDTA systems by electro-Fenton process using iron sacrificing electrodes

Abstract

This research explored the application of electro-Fenton (E-Fenton) technique for the simultaneous decomplexation in blended Cu(II)/Ni(II)-EDTA systems by using iron sacrificing electrodes. Standard discharge (0.3 mg L^-1 for Cu and 0.1 mg L^-1 for Ni in China) could be achieved after 30 min reaction under the optimum conditions (i.e. initial solution pH of 2.0, H₂O₂ dosage of 6 mL L^-1 h^-1, current density of 20 mA/cm², inter-electrode distance of 2 cm, and sulfate electrolyte concentration of 2000 mg L^-1). The distinct differences in apparent kinetic rate constants (k_app) and intermediate removal efficiencies corresponding to mere and blended systems indicated the mutual promotion effect toward the decomplexation between Cu(II) and Ni(II). Massive accumulation of Fe(Ⅲ) favored the further removal of Cu(II) and Ni(II) by metal ion substitution. Species distribution results demonstrated that the decomplexation of metal-EDTA in E-Fenton process was mainly contributed to the combination of various reactions, including Fenton reaction together with the anodic oxidation, electro-coagulation (E-coagulation) and electrodeposition. Unlike hypophosphite and citrate, the presence of chlorine ion displayed favorable effects on the removal efficiencies of Cu(II) and Ni(II) at low dosage, but facilitated the ammonia nitrogen (NH₄⁺-N) removal only at high dosage.

Keywords: Decomplexation; Electro-Fenton; Metal species; Metal-EDTA; Mutual promotion effect.