Enhanced ozonation of Cu(II)-organic complexes and simultaneous recovery of aqueous Cu(II) by cathodic reduction

The removal of toxic heavy metals, which are usually complexed with organic ligands in real wastewater , is still a challenge currently. The green oxidant O 3 has been widely applied in the oxidation of pollutants, but suffers from the dependency of HO· yield on water chemistry and also low recovery of metals. Here, we developed a new method, namely electrolysis-O 3 -GF-Ti, for efficiently removing the complexed Cu(II) via HO· oxidation and for simultaneously recovering Cu using graphite felt coated Ti mesh (GF-Ti) as the cathode. For Cu(II)-EDTA decomplexation, this process achieved more than 80% of TOC removal and 90% of Cu(II) recovery, which was significantly more efficient than those of electrolysis , ozonation or electrolysis-O 3 -Ti. The cathodic O 3 reduction was responsible for the efficient production of HO· in the process, as proved by the simultaneous enhanced decomposition of O 3 and degradation of HO· probe ( p -chlorobenzoic acid) but insignificant formation of H 2 O 2 by electrolysis. Mechanism study with HPLC spectrum and mass spectrometry evidence combined with SEM-EDX and XRD analysis revealed electrolysis-O 3 -GF-Ti of Cu(II)-EDTA was a stepwise decarboxylation process, and the formed decomplexed Cu(II) intermediates were reduced as Cu 0 at the GF-Ti surface. The results of cathodic characterization and continuous 5-cycle experiments demonstrated GF-Ti is an excellent renewable cathode. Moreover, over 90% of Cu was recovered in treatment of Cu(II) complexed with different chelators (nitrilotriacetic acid, citrate, tartrate, etc.), and more than 80% from authentic electroplating wastewater. This study would provide a promising alternative for destruction of metal complexes and recovery of heavy metals. • The yield of HO· from O 3 was enhanced by about 71 times on the GF-Ti cathode. • Electrolysis-O 3 -GF-Ti showed high efficiency in decomplexation of Cu(II) complexes. • More than 90% of Cu(II) in terms of Cu 0 was recovered. • GF-Ti cathode exhibited high activity and good reusability. • Electrolysis-O 3 -GF-Ti was capable of recovering Cu from electroplating effluent.