Sensitivity of Gold Lixiviants for Metal Impurities in Leaching of RAM Printed Circuit Boards

The importance of gold recovery from waste printed circuit boards is continuously increasing due to raising gold prices and demand as well as the need for innovative and flexible recycling methods for this complex waste stream. The state-of-the-art recycling process aims at the pyrometallurgical recovery of noble metals, mainly using a copper collector. Different technical limitations justify the application of a hydrometallurgical process alternative for recovering gold. The direct application of gold lixiviants on comminuted PCBs is hardly possible due to the high concentration of metal impurities. As a solution, most researchers propose hydrometallurgical separation of disturbing base metals prior to gold extraction. For this, different leaching systems with aggressive chemicals can be applied, often leaving residual base metal concentrations behind. Within this study, two different leaching parameter sets were investigated to separate base metals and determine the impact of residual base metals on subsequent gold recovery. The gold lixiviants that were applied for comparison were thiosulfate, thiourea, iodine-iodide, NBS, and cyanide. It was found that thiosulfate and thiourea are less sensitive than other lixiviants to metal impurities. When base metals are separated completely, gold recovery is strongly improved, and cyanide also achieves a good gold recovery.

Automated summary

The importance of gold recovery from waste printed circuit boards is increasing due to higher gold prices, demand, and the need for innovative recycling methods. The state-of-the-art recycling process focuses on pyrometallurgical recovery of noble metals using a copper collector. However, a hydrometallurgical process is proposed as an alternative due to technical limitations and high metal impurity concentration. This study investigates different leaching parameters to separate base metals and determine their impact on subsequent gold recovery. Thiosulfate and thiourea are found to be less sensitive to metal impurities, while cyanide achieves good gold recovery when base metals are completely separated.