A closed loop recycling strategy for sustainable recovery of group 11 metals (Cu, Au, and Ag) from waste PCBs: An amalgamation of low-temperature NH4Cl roasting, HCl leaching and cementation

Abstract

Circular economy is not a choice but a necessity for every sector with growing demand and limited resources. E-waste, being considered as a strategic resource because of its enriched metallic content the implementation of effective utilization is necessary, but not at the cost of the environment. Therefore, to maximize resource recovery and minimize environmental impact, a closed-loop approach was proposed for the recovery of group 11 metals from waste printed circuit boards (WPCBs). Herein, a combination of low-temperature NH4Cl roasting, HCl leaching, and cementation methods was employed for the separation of metals. The NH4Cl roasting assisted in altering metals to metal chlorides, whereas HCl solvates produced metal chlorides. Ultimately, cementation methods were employed for individual separation of metals from leached solution. The obtained results revealed that >98% Cu, 86% Ag, and 76% Au were extracted under optimum conditions (Temperature of 260 °C, roasting time of 2.5 h, NH4Cl dose of 2 g/g, and 2 M HCl). Further, a three-step cementation technique was employed for the separation of Au, Ag, and Cu using Ag, Cu, and Fe as sacrificial metals, respectively. Finally, all the reagents used in the process were recovered in the form of NH4Cl and Fe(OH)2 making a closed-loop process.