A cost-effective strategy for metal recovery from waste printed circuit boards via crushing pretreatment combined with pyrolysis: Effects of particle size and pyrolysis temperature

Abstract

The dramatic increase in global generation of e-wastes has become a great challenge for sustainable development, and strategies for efficient and environmental-friendly recycling and disposal of e-waste are of great demand. A cost-effective strategy of crushing pretreatment combined with pyrolysis to recover metals from waste printed circuit boards (WPCBs) has been developed. Effects of particle size and pyrolysis temperature on metal recovery were explored. The optimal combination of less energy consumption and higher metal recovery was obtained when the pretreated particle size was 4.0 cm and pyrolysis temperature was 330 °C. The Cu and Sn were recovered as zero-valent copper and tin-copper alloy with the recovery efficiency of 92.38 and 99.80 wt%, respectively. Brominated pollutants are easily controlled when pretreated particle size is larger than 2.0 cm and pyrolysis temperature is below 400 °C. Under the optimal crushing pretreatment and pyrolysis conditions, the bromine contents in the pyrolysis products of solid residues, liquid tar, and gas were 45.45 wt%, 38.70 wt%, and 15.85 wt%, respectively. The structure of WPCBs was destroyed at 275–525 °C due to decomposition of brominated epoxy resins (BERs), which could be accurately characterized by 8 dominating reactions through pyrolysis kinetics analysis. The main reactions took place at conversion of 0.14 and 0.15, corresponding to a pyrolysis temperature of 306–342 °C. Thus, the interlayer bonding force of WPCBs significantly decreased, contributing to effective separation of metals in WPCBs.