A low-voltage electroreduction strategy for efficient and cost-effective recovery of metal Cu from Cu(II)-EDTA...

Electroreduction can simultaneously decomplex metal-organic complexes and recover metals. However, most current systems operate at high voltages that trigger side reactions such as hydrogen and oxygen evolution, or rely on expensive noble metal-modified electrodes, limiting their practical applicability. Here, we developed a low-voltage (2 V) electroreduction system using an economical and commercially available 200-mesh high-purity Ti mesh as the cathode to achieve reduction of Cu(II)-EDTA and efficient recovery of Cu. The process obtained complete removal of Cu(II)-EDTA and 99.6% recovery of total Cu within 90 min at the conditions of 2 V and pH = 2, with a specific energy consumption of 9.2 kWh/kg for Cu recovery, substantially lower than the values reported in available technologies. Cyclic voltammetry, electrochemical impedance spectroscopy, radical quenching and trapping experiments revealed that Cu(II)-EDTA was reduced at the Ti mesh cathode via a direct electron transfer (DET) pathway. Subsequently, the released free EDTA was stepwise decarboxylated via anodic oxidation. The system maintained effective Cu recovery from Cu(II)-EDTA solution across the pH range of 2-10 and from other various Cu complexes such as Cu(II)-NTA and Cu(II)-citrate. However, the presence of high concentrations of NOM may inhibit Cu recovery to some extent. When applied to real electroplating wastewater with Cu(II) concentration exceeding 100 mg/L, the system still enabled effective Cu recovery and sustained a decomplexation efficiency of over 80% during 120 h of continuous flow operation.