Electrolyte circulation: Metal recovery from waste printed circuit boards of mobile phones by alkaline slurry electrolysis

Alkaline slurry electrolysis has been verified as an effective method for metal recovery from waste printed circuit boards (WPCBs). However, the electrolyte that remains after slurry electrolysis contains high concentrations of metal, which can cause pollution without suitable treatment. Most importantly, the metals in the electrolyte are not completely recovered, resulting in wasted resources and increased costs. Here, the feasibility of circulating this electrolyte and its effect on copper recovery, current efficiency, and purity, is discussed. We also describe in detail the migration and transformation of copper and other metals, such as nickel, zinc, and lead, during the preparation of high-purity cathode copper from mobile phone WPCBs (WPCB-MPs) using an ammonia-ammonium chloride slurry electrolysis system. Experimental results from 19 cycles of electrolyte reuse show that copper is mainly distributed in the cathode products, whereas other metals are mainly distributed in the electrolyte and anode residues. With an increase in the number of cycles, the concentration of other metals in the electrolyte gradually increased, showing metal enrichment. The current efficiency fluctuates but is usually >90%. In addition, the copper recovery rate and purity were essentially unaffected, being >99% and >99.9% for all 20 runs, respectively, and all the cathode copper foils were easily peeled off. This study demonstrated that electrolytes can be reused for metal recycling from WPCB-MPs by alkaline slurry electrolysis without decreasing Cu purity, Cu recovery rate, and current efficiency. Thus, this study provides a green and cost-effective process for recycling resources from e-waste.