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⁻.