Electrocatalysis coupled super-stable mineralization for the efficient treatment of phosphorus containing plating wastewater

Abstract

The automotive, electronics, and aerospace sectors use electroless nickel plating (ENP) technology for surface treatment. Hypophosphite, a widely used reducing agent in ENP, generates large volumes of hypophosphate (H₂PO₂^-) and nickel ions (Ni²⁺) in its wastewater which poses potential risks to human health. However, it is a highly challenging task to remove and recycle the H₂PO₂^- and Ni²⁺ from such wastewater. In this study, a novel electrocatalysis coupled super-stable mineralization process was developed for the treatment of phosphorus-containing ENP wastewater. The electrocatalytic system, utilizing commercial lead dioxide and stainless steel as the anode and cathode, separately, achieved remarkable results in simultaneously removing H₂PO₂^- and recycling valuable Ni²⁺ ions from ENP wastewater, with a 99.1 % oxidation efficiency for H₂PO₂^- to PO₄^3- and a high recovery rate of 99.8 % for nickel. In order to meet industrial emission standards, layered double hydroxide (CaAl-LDH) and its calcined derivatives (CaAl-900) were employed as super-stable mineralizers for the further treatment of total phosphorus (TP) and residual Ni²⁺ in the wastewater. The mechanism underlying the enhanced treatment of ENP wastewater was elucidated through free radical quenching experiments, revealed superoxide radicals (·O₂^–) as the primary active species. It is noteworthy that the successful treatment of actual ENP wastewater was achieved, meeting standard discharge requirements. This study provides novel insights for achieving resource-efficient wastewater treatment and promoting environmentally friendly electroplating industries.