Supergravity separation for recovering metals from waste printed circuit boards

Abstract

The recovery of metals from electronic waste has become increasingly important due to environmental concerns and potential risks to the supply of strategic raw materials. Electronic waste, especially waste printed circuit boards from a variety of sources, is of inherently high complexity in composition, phase, and physiochemical properties. Waste PCBs contain valuable metals and multiple toxic substances, motivating a search for processes or technologies to allow their cost-effective and environmental recycling. A novel process was developed, using supergravity separation to recover valuable metals (Pb, Sn, Zn, and Cu) from granulated computer printed circuit boards. A three-step separation process was adopted to selectively recover metals or alloys and to concentrate precious metals. Total recovery values for Pb, Sn, Zn, and Cu were 96.37%, 92.32%, 93.71%, and 97.90%, respectively. The mass fraction of (Pb+Sn) in Pb-Sn alloy, (Sn+Cu) in Sn-Cu alloy, and (Cu+Zn) in Cu-Zn alloy reached 94.84%, 85.18%, and 84.73%, respectively, during the individual separation steps. Compared with the contents of Au (44ppm), Ag (124ppm), and Pd (6.5ppm) in the computer printed circuit boards, the contents of Au, Ag, and Pd in the residues after three-step separation were concentrated to 150ppm, 550ppm, and 12ppm, respectively. By a combination of appropriate hydrometallurgical process and supergravity separation of metals or alloys, this process can achieve closed-loop, clean recycling of electronic waste with significant efficiency.