Electrochemical decomplexation of Cu(II)-citrate and copper recovery via peroxymonosulfate activation with N,O co-doped carbon felt cathode.

The copper-citrate complex (Cu(II)-CA) poses environmental risks due to its aqueous stability, while monofunctional electrodeposition fails to synchronize decomplexation and ligand mineralization. This study adopted a nitrogen and oxygen co-doped carbon felt (N,O/CF) as the cathode for Cu(II)-CA electrodeposition and peroxymonosulfate (PMS) electro-activation, achieving Cu(II)-CA decomplexation, CA mineralization and Cu recovery simultaneously. The synergistic decomplexation mechanism-mediated by electrodeposition and reactive species-enabled complete decomplexation of Cu(II)-CA within 100 min. This strategy enabled both CA mineralization and Cu recovery to reach 90 % under optimal conditions across the pH range of 3.5 to 9.5. The decomplexation reaction was inhibited by the following compounds in decreasing order: fulvic acid, HCO3-, NH4+, NO3-, H2PO4-, Cl-, SO42-. The -O-O- and -SO3H groups of PMS can coordinate with the Cu(II)-CA complex through electron transfer to the central Cu(II). This interaction facilitated the formation of a PMS-Cu(II)-CA complex with low adsorption energy on the N,O/CF surface. The favorable adsorption promoted electrochemical activation of PMS, leading to the generation of reactive species. These radicals accelerated the oxidative decomplexation of Cu(II)-CA, releasing free Cu2+, which were subsequently electrodeposited for copper recovery. The system also demonstrated excellent performance in treating real electroplating wastewater, achieving removal efficiency of total organic carbon (TOC) and effective recovery of both Cu and Ni.