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

Abstract

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.

Investigation of the Impact of Electrochemical Hydrochlorination Process Parameters on the Efficiency of Noble (Au, Ag) and Base Metals Leaching from Computer Printed Circuit Boards

“…It is noted that, as a result of physical pretreatment, the precious metals present in the raw material in small or trace quantities are partially lost both in the mass of metal dust and plastic particles [3,10]. Cyanides, thiosulfates, thiourea, and halides are used in hydrometallurgical techniques [9,11]. The mechanisms of the reactions of precious metal leaching from PCBs with these reagents, and progress in hydrometallurgical technologies, are presented in a number of reviews published in the last decade [12][13][14][15][16][17].…”

“…This reagent is considered as an alternative to cyanide for the leaching of gold from refractory ores [24]. Research results on the use of thiourea for leaching gold from waste PCBs [21,25,26] and different types of random-access memory (RAM) sticks [11] are also reported. The selectivity of the leaching of gold by thiourea increases in the absence of base metals.…”