Decomplexation efficiency and mechanism of Cu(II)–EDTA by H2O2 coupled internal micro-electrolysis process

Internal micro-electrolysis (IE) coupled with Fenton oxidation (IEF) was a very effective technology for copper (Cu)–ethylenediaminetetraacetic acid (EDTA) wastewater treatment. However, the mechanisms of Cu2+ removal and EDTA degradation were scarce and lack persuasion in the IEF process. In this paper, the decomplexation and removal efficiency of Cu–EDTA and the corresponding mechanisms during the IEF process were investigated by batch test. An empirical equation and the oxidation reduction potential (ORP) index were proposed to flexibly control IE and the Fenton process, respectively. The results showed that Cu2+, total organic carbon (TOC), and EDTA removal efficiencies were 99.6, 80.3, and 83.4%, respectively, under the proper operation conditions of iron dosage of 30 g/L, Fe/C of 3/1, initial pH of 3.0, Fe2+/H2O2 molar ratio of 1/4, and reaction time of 20 min, respectively for IE and the Fenton process. The contributions of IE and Fenton to Cu2+ removal were 91.2 and 8.4%, respectively, and those to TOC and EDTA removal were 23.3, 25.1, and 57, 58.3%, respectively. It was found that Fe2+-based replacement–precipitation and hydroxyl radical (•OH) were the most important effects during the IEF process. •OH played an important role in the degradation of EDTA, whose yield and productive rate were 3.13 mg/L and 0.157 mg/(L min−1), respectively. Based on the intermediates detected by GC-MS, including acetic acid, propionic acid, pentanoic acid, amino acetic acid, 3-(diethylamino)-1,2-propanediol, and nitrilotriacetic acid (NTA), a possible degradation pathway of Cu–EDTA in the IEF process was proposed.