André F.m. NOGUEIRA1, Ana R. F. CARREIRA1, Sílvia J.r. VARGAS2, Paula BRANDÃO1, Helena PASSOS1, Nicolas SCHAEFFER1, João A. P. COUTINHO1
1University of Aveiro, Aveiro, Portugal
2Purdue University, West Lafayette, United States
E-waste is a source of valuable base and precious metals, making its exploration a key step in reducing the environmental impact of modern electronics and establishing a circular market for critical and rare materials. Gold is one of such materials present in e-waste in greater concentrations than the primary ores from which it is mined, providing a strong justification for its recycling. In this work, the use of a quaternary ammonium ionic liquid (IL) as a precipitating agent for the selective recovery of gold from an aqua regia leachate of printed circuit boards was investigated. A suitable IL was selected considering the cation’s apolar volume and geometry as well as counter-anion selection. The precipitation was optimized in regard to time, the IL to Au molar ratio, temperature and aqua regia dilution. IL to gold ratio and dilution were found to be the key factors driving the precipitation. Optimized conditions were applied to a real leachate sample, resulting in a gold salt with a metallic content of over 90% gold and yield of 64%. The same IL was used to establish an acidic aqueous biphasic system for the recovery of Au for higher acid concentration, demonstrating two possible avenues of Au recovery depending on the leachate condition. The technique presented herein allows for the selective separation of gold using relatively simple materials and techniques with a lower reagent use than what is required with other gold separation techniques employing ILs.
Acknowledgments: This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC).