Deportment of Metals from E-Waste PCBs towards Alloy and Slag Phases during Smelting Using CaO-Al2O3-SiO2-B2O3 Slags

Abstract

Printed circuit boards (PCBs) from antiquated electronic goods were processed by a pyrometallurgical route to produce and separate alloy and slag phases. The process involved initial size reduction of PCBs, followed by pyrolysis at 500 °C for 6 h and finally smelting of the solid materials in an electric furnace. A preliminary smelting test was performed at 1600 °C to estimate the composition of the slag generated. In later kilogram-scale smelting experiments, B2O3 flux was added along with CaO and SiO2 to decrease the liquidus temperature required to smelt the PCBs. The level of fluxing was adapted from earlier phase equilibria studies of the CaO-Al2O3-SiO2-B2O3 slag system. Results showed that the flux decreased the melting temperature and assisted the recovery of most valuable metals within the alloy phase at 1350 °C smelting temperature. The alloy phase recovered 99.8% of Cu, 99% of Sn, and 100% of precious metals (Au, Ag, Pt). A fluxing strategy for smelting high Al2O3 containing e-waste PCBs was proposed based on the experimental findings of this research.