Hydrometallurgical electroleaching of waste printed circuit boards using batch or continuous redox mediator activation

The growing volume of electronic waste and increasing interest in the urban mine urges the sustainable recovery of valuable and critical metals from waste printed circuit boards (PCBs). Indirect electroleaching, using a reversible redox mediator (RM), offers a promising low‑reagent hydrometallurgical alternative. In this work, we compare Fe³⁺/Fe²⁺ mediated electroleaching of shredded waste PCBs (< 1 mm particle size) operated in continuous-mode (in situ RM regeneration) versus batch-mode (pre‑activated RM). Leaching characteristics were evaluated in sulfate‑ and chloride‑based electrolytes for both shredded waste PCB material and a simulated metal mixture as a model system to decouple matrix effects. Continuous‑mode operation performed with 50 mM Fe 2+ enabled near-complete dissolution of major base metals (Cu, Sn, Ni, Zn) within 12–24 h. In contrast, batch-mode leaching using 300 mM pre-activated (10% stoichiometric excess) significantly accelerated kinetics, achieving near-complete dissolution within 2–3 h in sulfate media and less than 1 h in chloride media. Considering the upscaled operations, continuous- versus batch-mode processes have certain advantages and disadvantages over each other. The factors considered include process robustness, electrode fouling risk, and improved compatibility with fluctuating renewable electricity supply. These considerations support batch‑activated mediated leaching as a possible route for scalable and flexible hydrometallurgical PCB recycling.