Influence of physical conditioning on copper dissolution Behavior and acid utilization during static nitric acid leaching of waste PCBs

Copper recovery from waste printed circuit boards (WPCBs) is often limited by poor metal accessibility caused by polymeric and glass-fibre encapsulation, resulting in inefficient acid utilisation. In this study, density-based segregation using a gas–solid fluidized bed (GSFB) was combined with static nitric acid leaching to isolate the effect of physical pre-treatment on copper dissolution. Physical conditioning of the nominal 250–500 µm sieve fraction increased the copper content from 29.57 wt% to 80.7 wt% without additional comminution. Under identical leaching conditions, the conditioned feed showed significantly higher copper dissolution and acid utilisation than the unsegregated feed. At 4 M HNO 3 after 1 h, the accessibility enhancement factor (AEF) and acid utilisation gain (AUG), which quantify improvements in copper dissolution per unit feed mass and per unit volume of leaching solution, respectively, were both approximately 3. The conditioned feed also exhibited rapid early-stage dissolution owing to improved copper accessibility, whereas diffusion-related limitations became increasingly important as leaching progressed. SEM–EDS and FTIR analyses showed a substantial reduction in the non-metallic fraction, changes consistent with improved copper accessibility, and progressive surface evolution during leaching. Overall, the results demonstrate that physical conditioning and the associated improvement in copper accessibility enhance static nitric acid leaching beyond the effect of increasing acid concentration alone. Consequently, comparable copper dissolution was achieved using 1 M HNO 3 for the conditioned feed and 3–4 M HNO 3 for the unsegregated feed, demonstrating that comparable leaching performance can be achieved at a lower initial HNO 3 concentration following physical conditioning.