A Novel Method for Continuous Deep Removal of Copper Citrate from Saline Wastewater: Synergy of Nano-Zirconium Loaded Resin and Optimized Electric Field

Copper-plating wastewater often contains Cu(II) as stable complexes (e.g., Cu-Citrate) coexisting with high salinity (>1000 mg/L), which limits removal by conventional electrodeionization (EDI). Here, we developed an advanced EDI system using a nanocomposite anion exchange resin loaded with hydrated zirconium oxide (nAER-HZO) for efficient Cu-Citrate removal. Compared with conventional EDI without HZO, the EDI-nAER-HZO achieved 1.5–2.3 times higher removal across different saline conditions. Response surface methodology (RSM) optimization yielded an optimal removal rate of 80.12% at voltage = 1.47 V, pH = 6.19, flow rate = 56.01 mL/min, and resin dosage = 0.118 g. Mechanistic analysis revealed that ion exchange was the dominant removal pathway, where HZO formed stable Zr–O–Cu-Citrate complexes, resisting salt interference. Additionally, the electric field reduced local ionic strength by driving salt ions away from the resin, expanding the electrical double layer (EDL) thickness from 0.051 to 8.85 nm, which weakened ion shielding and enhanced the selective adsorption capacity of nAER-HZO by 38.8%. The system maintained 77.8% removal efficiency after 30 regeneration cycles. Life cycle assessment showed a low carbon footprint (2.64 kg of CO2-eq/t), indicating strong environmental advantages. This work offers an efficient and sustainable strategy for removing heavy metal complexes from saline industrial wastewater.