Decomplexation of Cu(II)-EDTA by UV/persulfate and UV/H2O2: Efficiency and mechanism

Heavy metal-organic complexes are widely present in natural water and industrial effluents. Currently, the widely employed strategy for removal of metal-organic complexes is to combine oxidative decomplexation with further precipitation or adsorption of the released metals. (OH)-O-center dot and SO4 center dot- based advanced oxidation processes (AOPs) are very promising in water purification. However, to the best of our knowledge, there is no open literature concerning the decomplexation efficiency of metal-organic complexes based on SO4 center dot- as yet. In this study, a typical SO4 center dot- based technology, i.e., UV/PS (persulfate) process, was applied to investigate its decomplexation of Cu(II)-EDTA in water, and the final Cu(II) removal during the subsequent alkaline precipitation was used as a reference of the decomplexation efficiency. UV/H2O2 was employed for comparison throughout the study. Effect of the oxidant dosage, pH, and coexisting substances on the decomplexation was evaluated, and the degradation mechanism was particularly concerned. The results show that degradation of Cu(II)-EDTA by SO4 center dot- and (OH)-O-center dot follows a similar pathway, i.e., successive decarboxylation, while the decomplexation efficiency of UV/PS is much higher than UV/H2O2 under similar conditions. Meanwhile, the coexisting substances (Cl-, NO3-, and NOM) exerted less inhibition on the decomplexation of UV/PS than UV/H2O2. The above advantages of UV/PS are mainly attributed to the better selectivity of SO4 center dot- as well as its higher yield of active species. Similarly, satisfactory performance was observed for Cu-citrate and Cu-nitrilotriacetate removal from aqueous solution and for Cu(II) removal from a real electroplating effluent as well, further demonstrating the promising applicability of the UV/PS based combined process in water decontamination from Cu-organic complexes. (C) 2016 Elsevier B.V. All rights reserved.