Study on metals recovery from discarded printed circuit boards by physical methods

Abstract

Study on discarded printed circuit boards (PCBs) reutilization has important significance and application values, which can not only achieve secondary resources recycling, but also prevent environment pollution. Physical methods show great potential and advantages on discarded PCBs reutilization comparing with chemical and biological methods. In the paper, an effective physical method was introduced to recover metals from discarded PCBs. A double-toothed roll shear and a hammer crusher were employed to achieve liberation of metals from other components contained in the PCBs. Metals of -2+0.074 mm in PCBs were recovered by a conventional high tension electrostatic separator, while metals in the -0.074 mm were reclaimed by enhanced gravity concentrator (Falcon concentrator). Experimental study indicates that the liberation mechanism of printed wiring boards (PWBs) and integrated cards (ICs) can be explained by dispersion liberation accompanied disengaging liberation and ideal metal liberation degree is around 0.5 mm, while the liberation mechanism of slots can be explained by disengaging liberation. For -2+0.5mm feed PCBs, the integration efficiency of 89.32% can be achieved when power supply voltage is 27 KV, roller rotation speed being 80 rpm and three corona electrodes and one static electrode applied; for -0.5+0.074 mm feed, the corresponding integration efficiency is 71.14 % when power supply voltage is 22 KV, roller rotation speed 150 rpm and one corona electrodes and one static electrode used; the integration efficiency of -0.074 mm PCBs is 80.77 % if slurry concentration is 40 g/l with water pressure of 0.01 MP and rotation speed of 50 Hz. Based on experimental study, the innovative flowsheet of "mechanical shredding + screening + electrostatic separation + Falcon centrifugal separation" was brought forward to recover metals from discarded PCBs.