Recycling gold from printed circuit boards gold-plated layer of waste mobile phones in “mild aqua regia” system

Abstract

Traditional mechanical pretreatment and hydrometallurgy is the mainstream technology to recycle gold from waste printed circuit boards (PCBs). However, this method is cumbersome and often employs toxic/harsh chemicals. In the present study, gold was easily recycled from PCBs gold-plated layer of waste mobile phones (WMPs) in DMF-CuCl2-CaCl2 (DMF: dimethyl formamide) system what we call “mild aqua regia” without pretreatments or enrichment process, and the reaction system could be cyclic utilized. In such reaction system, gold could be recycled through leaching, precipitation and filtration. The reaction parameter optimization and reaction mechanisms were studied. Under the optimized conditions, the gold leaching rate and precipitation rate could reach over 99%. DMF plays a significant role in the leaching system. As a typical polar aprotic solvent, DMF cannot solvate Cl−. Thus, “Cl−” exists in a “naked state”, and it can easily react with Au. Besides, Au (III) could generate a complex through the complexation with DMF which could result in the redox potentials reduce and move the equilibrium to the Au leaching side. In summary, this study provided a fundamental basis as well as practical guidance for recovering precious metals from waste electrical and electronic equipment in an efficient manner.