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

Abstract The removal of toxic heavy metals, which are usually complexed with organic ligands in real wastewater, is still a challenge currently. The green oxidant O3 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-O3-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-O3-Ti. The cathodic O3 reduction was responsible for the efficient production of HO· in the process, as proved by the simultaneous enhanced decomposition of O3 and degradation of HO· probe (p-chlorobenzoic acid) but insignificant formation of H2O2 by electrolysis. Mechanism study with HPLC spectrum and mass spectrometry evidence combined with SEM-EDX and XRD analysis revealed electrolysis-O3-GF-Ti of Cu(II)-EDTA was a stepwise decarboxylation process, and the formed decomplexed Cu(II) intermediates were reduced as Cu0 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.