First Gold Recovery from PCBs through en-thiosulfate Leaching and Selective Adsorption with Carbon

Abstract Eco-friendly gold extraction from printed circuit boards (PCBs) is highly attractive due to the increasing demand for gold in various fields. The conventional Cu2+-NH3-S2O32− method for PCBs involves polluting NH3 gas and requires additional copper. This study explored a new eco-friendly alternative using ethylenediamine (en) and thiosulfate to extract gold from CPU (the PCB material used in this study). The results showed that 81% of gold in CPUs could be successfully leached out after 48 hours, using 10 mM ethylenediamine and 0.2 M thiosulfate. Various analyses, including SEM, ICP, XPS, were conducted to further investigate the process. It was found that the metal in CPU was Au(0)→Ni(II)→Cu(0) from the outside to the inside, and possible gold leaching mechanism was related to the oxidization of Cu(en)22+ produced from CPU’s defective position and the presence of S2O32−. As for Au(S2O3)23− recovery, different from our previous study, it is necessary to add a small amount of ethylenediamine (en) except for carbon and thiosemicarbazone (TSC); consequently, a gold adsorption efficiency of 99% was achieved. In summary, the leaching method proposed in this work solved the problem of NH3 pollution of traditional one and achieves green, efficient, and selective gold adsorption from CPU leaching solution through a simple method, which is hopeful to replace the traditional unfriendly Cu-NH3-S2O32−.