Environmentally friendly hydrometallurgical recovery of tin and lead from waste printed circuit boards: Thermodynamic and kinetics studies

The aim of this research was to develop an environmentally friendly fiowsheet to recover Sn and Pb, which are two well-known hazardous elements, from waste printed circuit boards (PCBs), resulting in solving an environmental issue besides reproducing high-value metals. In the leaching process, the highest Sn and Pb recoveries of 88% and 99% were achieved by using 2 M hydrochloric acid (HCl) at an agitation rate of 500 RPM at 75 degrees C. Thermodynamic evaluations were employed successfully to confirm the leaching results. The kinetics studies indicated that the reaction mechanism shifted from a mixed control model (surface reaction control and diffusion through product layer) to the diffusion control, by increasing the agitation rate. The temperature and acid concentration controlled the dissolution by the diffusion mechanism. Production of an ash layer on the particle surface suppressed Sn and Pb dissolution as a result of enhancing both the temperature and acid concentration. The results of the kinetics modeling have been validated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) studies. The activation energies for Sn and Pb were found to be 39.49 and 50.60 kJ/mol, respectively. The Fourier-transform infrared spectroscopy (FTIR) indicated the presence of alkyne and alkyl halides, as well as carboxylic and aromatic components, in the pregnant leach solution. The metallic Sn-Pb product was obtained by using Al-based heat sink scrap separated from the same PCBs via the cementation method. The SEM and X-ray mapping studies were carried out to characterize this product. The selectivity of the cementation method for Sn and Pb was confirmed by the above mentioned methods. (C) 2019 Elsevier Ltd. All rights reserved.