Unveiling the Release Mechanism of Pollutants during the Crushing Process of Waste Printed Circuit Boards

Waste printed circuit boards (WPCBs) are hazardous wastes but also valuable resources. Mechanical crushing is widely used to recycle WPCBs. Some pollutants are released during the crushing, but the release mechanisms have been rarely reported. Herein, the experimentation results with the theoretical analysis can well explain the release mechanism of pollutants during the crushing of WPCBs. According to the size distribution of material in different crushing conditions, the collision analysis can describe the crushing process and illustrate the energy changes during the crushing. The energy changes in crack extension indicate that the reduced energy transferred to WPCBs results in a decrease in concentration and size of airborne particles with the crushing proceeding. Besides, the energy changes during the crushing illustrate the release mechanism of organic substances. In the early period of crushing, all branched chains on benzenes are broken to form phenol at the high energy. In the late period of crushing, phenol homologs are largely generated at the low energy. Moreover, the release behavior of triphenyl phosphate is relative to the accumulated energy during the crushing. This study provides a theoretical basis for the release of pollutants during the crushing process of WPCBs.