A one-step strategy for Cu(II)-EDTA decomplexation and copper precipitation via microwave-alkaline synergistic activation of persulfate

Stable heavy metal complexes are ubiquitous in industrial wastewater. Decomplexation is an essential step to release free heavy metal ions from heavy metal complexes before removing them via alkaline precipitation. In this study, the activation of peroxydisulfate (PDS) by microwave irradiation (MW) and NaOH (MW+NaOH+PDS) was systematically studied for Cu(II)-EDTA decomplexation. The effects of initial pH, oxidant dosage, microwave power, and NaOH dosage on Cu(II)-EDTA decomplexation were comprehensively evaluated. Among these, oxidant dosage showed the most significant effect on Cu(II) removal efficiency, highlighting the critical role of oxidant concentration in promoting Cu(II)-EDTA decomplexation. A detailed comparison was conducted, showing that the MW + PDS process achieved higher Cu removal efficiency than MW + H 2 O 2 over a broader pH range (2–12) using lower oxidant dosage than the MW + H 2 O 2 system. Furthermore, the synergistic activation of PDS by microwave irradiation and NaOH significantly enhanced reactive oxygen species (ROS) generation, including SO 4 •– , OH • , and O 2 •– , thereby accelerating Cu(II)-EDTA decomplexation. Using a molar ratio of [NaOH] 0 /[PDS] 0 = 2:1, MW + NaOH + PDS system enabled simultaneous Cu(II)-EDTA decomplexation and Cu precipitation, resulting in a residual Cu concentration of 0.2 mg/L (99.9% removal) and a final pH of 6.52, both meeting the Chinese discharge standard (GB 21900–2008). Compared with previously reported PDS activation systems, the MW + NaOH + PDS system achieved ultrafast and highly efficient Cu removal without requiring transition-metal catalysts or complicated dual-oxidant systems. In addition, the precipitates generated in the MW + NaOH + PDS system exhibited more compact and better sedimentation properties. Finally, the biotoxicity was significantly reduced after treatment, indicating good environmental compatibility.