Pilot-scale comminution of waste printed circuit boards (WPCB) in a shared e-scrap/biomass facility: Linking process streams to post-cleaning residuals

Dual-use user facilities that preprocess both e-scrap and biomass must manage metal-bearing dust hazards and verify cleaned equipment to prevent cross-contamination. This study introduces a risk-informed e-scrap mechanical preprocessing workflow that traces metals from process outputs to post-cleaning residuals on equipment. The workflow involves multiple unit operations with dust control and was demonstrated by processing mixed waste printed circuit boards to produce five <2 mm particle and vacuum-dust streams spanning pre-, coarse-, and fine milling. Each stream was size-classified into 7 fractions and analyzed with inductively coupled plasma (ICP). Results show stream chemistry was dominated by copper, which was strongly enriched in fine-milled particles, while vacuum dust streams were enriched in matrix-associated elements (aluminum/calcium) and exhibited stronger fine-fraction enrichment for several metals of occupational concern. Cadmium showed the clearest dust signature, concentrating in fine-milling dust while remaining non-detected in retained particles. After cleaning, nine “worst-case” locations on equipment were wipe-sampled for ICP and benchmarked against conservative surface limits. Results show all concerned elements were below limits or non-detected, supporting readiness for biomass preprocessing. This end-to-end process-to-residual validation framework can be adopted by other dual-use facilities and pinpoint value metal-enriched streams for recovery and impurity-bearing dust/fines streams to be managed.