Concentration of precious metals from waste printed circuit boards using supergravity separation

Printed circuit boards (PCBs) comprise valuable metals, precious metals, and hazardous materials. Thus, they are considered both attractive secondary sources of metals and environmental pollutants. This study is based on the selective separation of Pb-Sn, Sn-Cu, and Cu-Zn alloys, where supergravity separation was used to concentrate precious metals (i.e., Ag, Au, and Pd) from PCBs in Cu-Zn alloy and final residue. The temperature and gravity coefficient were found to have great influence on the concentration of precious metals in said alloy and residue. At the optimized temperature of 1300 °C, gravity coefficient of 1000, and separation time of 5 min, the Ag, Au, and Pd contents in the Cu-Zn alloy increased by 1.65, 2.05, and 1.54 times, respectively, compared to their concentrations in the original PCBs, while those in the final residue increased by 0.63, 1.02, and 2.62 times, respectively. By combining an appropriate hydrometallurgical process with the present supergravity separation and concentration of precious metals, this clean and efficient process provides a new pathway to recycle valuable metals and prevent environmental pollution by PCBs.