Simultaneous and efficient removal of organic Ni and Cu complexes from electroless plating effluent using integrated catalytic ozonation and chelating precipitation process in a continuous pilot-scale system

In the industrial electroless metal plating process, efficient removal of organic-Ni and -Cu complexes from electroless plating effluent (EPE) remains a huge challenge. In this study, a novel and feasible process of heterogeneous catalytic ozonation combined with heavy metal chelation is proposed for the effective removal of organic-Ni and -Cu complexes from EPE. The method was evaluated in a continuous pilot-scale system (CPSS). Results show that the adoption of synchronous bi-directional flow enhanced the removal of total Ni and Cu. Under optimal conditions, the total Ni and Cu in the effluent decreased to 0.1 and 0.3 mg L-1, respectively, meeting the Chinese discharge standard requirements. The CPSS indicated that efficient removal of total Ni and Cu (>95%) was consistently achieved for 300 days using the proposed process. Mechanistic analysis demonstrated that ethylenediamine tetraacetic acid-Ni (EDTA-Ni) and citrate-Cu (CA-Cu) were the main complexes present in EPE. Furthermore, there were 10 transformation products and their related pathways were also identified. The decomplexation of EDTA-Ni was found to be difficult, with its final products principally existing in the complexed states, while CA-Cu was readily broken down, releasing Cu (II) that can be easily chelated. Overall, these findings provide valuable and novel insights into the removal of organic-Ni and -Cu, supporting the practical application of the proposed process in advanced EPE treatment and other industrial wastewater treatment systems.

Automated summary

A novel process of heterogeneous catalytic ozonation combined with heavy metal chelation was proposed for the effective removal of organic-Ni and -Cu complexes from electroless plating effluent. The method was successfully evaluated in a continuous pilot-scale system, showing over 95% removal of total Ni and Cu under optimal conditions for 300 days. The study provides valuable insights into complexation mechanisms and transformation products, supporting the practical application of the proposed process in industrial wastewater treatment systems.