Green Regeneration and Resource Recovery of Nickel-Plating Waste Solution: A Synergistic Study of Electrodialysis and Advanced Oxidation

Electroless nickel plating is a chemical deposition process in which nickel ions within a plating solution are reduced by a chemical reducing agent and subsequently deposited onto the surface of a solid substrate. Chemical nickel-plating wastewater contains substantial amounts of phosphorus as well as abundant nickel resources. In this study, electrodialysis coupled with advanced oxidation techniques was utilized for the efficient recovery of nickel and phosphorus from spent nickel-plating solutions. The end-of-life tank solution from chemical nickel plating was treated via electrodialysis to remove harmful phosphite and sulfate ions, enabling the purified solution to be reused in plating production by supplementing it with appropriate amounts of sodium hypophosphite and nickel sulfate. Subsequently, the concentrate generated from electrodialysis was treated using peroxydisulfate (PDS)-based advanced oxidation technology to break nickel complexation and simultaneously promote the oxidation of hypophosphite and phosphite ions. Finally, Ca(OH)2 was employed as a precipitating agent to effectively recover phosphorus from the treated concentrate. From an economic perspective, optimal process conditions were determined as follows: a current density of 20 mA/cm2, concentrate-to-dilute water volume ratio of 1:1, current speed of 1.0 m3/h, and a sodium sulfate concentration in concentrate of 20 g/L. Under these conditions, the migration rates of H2PO2− and HPO32− ions reached 67.3% and 62.53%, respectively, whereas Ni2+ exhibited significantly lower mobility at only 6.77%. The purified wastewater recovered approximately 60% of its initial plating activity. Regarding the concentrate—which is a by-product of electrodialysis—the hypophosphite ions were nearly completely oxidized using a PDS dosage of 0.3 mol/L. Furthermore, when the Ca/P molar ratio was adjusted to 2.0, total phosphorus (TP) and nickel (Ni) removal efficiencies exceeded 98% and 93%, respectively.