Professor National Cheng Kung University Tainan, Tainan, Taiwan (Republic of China)
Printed circuit boards (PCBs) are one of the core components in electronic wastes (e-wastes). Acid-washing and open incineration for recycling of precious metals from PCB wastes may cause serious environmental pollution such as emissions of polychlorinated or polybrominated dioxins/furans. Recycling of precious metals (e.g., copper and gold) from PCBs by pyrometallurgy or hydrometallurgy processes frequently suffers from relatively high energy consumption, high cost and high secondary pollution risk. Capacitive deionization (CDI), which applies a potential voltage between parallel activated carbon (AC)-based electrodes to trap and store ions by electrosorption in the electrical double layers, has drawn much attention. Capacitive deionization has the advantages of high energy-efficiency, low-cost and environmental-friendly. Thus, in this study, new fluidized capacitive deionization (FdCDI) method using additional fluidized AC electrodes between parallel electrodes was developed to concentrate copper and silver separated from selective extraction of e-wastes by green solvent citric acid. Also, a feasibility study for photoelectrocatalytic (PEC) reduction of copper and gold ions (i.e., Cu2+ and Ag+) to metals was performed. In the PEC process, photoexcited electrons were transferred to photocathode through the external circuit for generation of electricity, and simultaneously conducted reduction for recycling of copper and silver metals with efficiencies of 79% and 62%, respectively. Apparently, the cost-effective green method for recycling precious metals from e-wastes is chemically feasible.