Supergravity separation for recovering Pb and Sn from electronic waste

Reverse flotation efficiency and mechanism of various collectors for recycling waste printed circuit boards

Reverse flotation was used to recover metal components from waste printed circuit boards (PCBs). The micro-morphology and chemical composition analysis of raw materials indicated that waste PCBs are mainly composed of glass fibers, ceramics and valuable metals. The effects of collector dosage and temperature on flotation efficiency were investigated and evaluated. The flotation results using various collectors showed that the efficient recovery of metal components could be achieved via reverse flotation with the diesel oil (DO) dosage of 370-1110 g/t, composite collector (CC) dosage of 370-740 g/t and laurylamine (LAM) dosage of 740 g/t, respectively. The suitable temperature should be controlled at around 20 °C for these collectors. The results also indicated that the selectivity of DO for nonmetal particles was stronger than that of CC and LAM. In summary, reverse flotation is a feasible and environmental approach for disposal of waste PCBs.

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.