Development of a shear grinding machine for enhanced liberation of copper from waste PCBs

A shear grinding machine was developed to achieve enhanced liberation of copper from waste printed circuit boards (PCBs) through controlled shear-based comminution. Unlike previous approaches focused primarily on impact grinding, this study presents a comprehensive quantitative evaluation of the liberation performance of a newly developed shear-based grinding machine specially designed to exploit layered structure. The machine utilizes vertically aligned disks with corrugated surfaces to apply targeted shear stress at material interfaces. Liberation performance was quantitatively evaluated through particle size distribution analysis using Population Balance Model (PBM), Fractional Degree of Liberation (FDL), and copper grade distributions. Results revealed first-order breakage kinetics with disk clearance primarily controlling particle size reduction. Rotational speed significantly influenced liberation efficiency, where FDL reached over 85 % at 1000 μm particle size with 600 rpm, compared to conventional methods requiring size reduction below 355 μm for equivalent liberation. The copper grade was enriched to 37.32 % in the 500-1000 μm fraction at 600 rpm, more than doubling the feed grade of 16.96 %. This demonstrates that targeted shear forces effectively exploit PCBs' inherent structure anisotropy, enabling efficient metal recovery at coarser particle sizes while reducing energy consumption and material losses associated with fine grinding. Representing the first systematic application of interfacial-targeted grinding for PCB recycling, this approach offers potential applications extending beyond PCBs to other critical waste streams, including lithium-ion battery black mass and multi-material electronic components.