New technology for recovering residual metals from nonmetallic fractions of waste printed circuit boards

Recycling of waste printed circuit boards is important for environmental protection and sustainable resource utilization. Corona electrostatic separation has been widely used to recycle metals from waste printed circuit boards, but it has poor separation efficiency for finer sized fractions. In this study, a new process of vibrated gas-solid fluidized bed was used to recycle residual metals from nonmetallic fractions, which were treated using the corona electrostatic separation technology. The effects of three main parameters, i.e., vibration frequency, superficial air flow velocity, and fluidizing time on gravity segregation, were investigated using a vibrating gas-solid fluidized bed. Each size fraction had its own optimum parameters. Corresponding to their optimal segregation performance, the products from each experiment were analyzed using an X-ray fluorescence (XRF) and a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). From the results, it can be seen that the metal recoveries of -1 + 0.5 mm, -0.5 + 0.25 mm, and -0.25 mm size fractions were 86.39%, 82.22% and 76.63%, respectively. After separation, each metal content in the -1 + 0.5 or -0.5 + 0.25 mm size fraction reduced to 1% or less, while the Fe and Cu contents are up to 2.57% and 1.50%, respectively, in the -0.25 mm size fraction. Images of the nonmetallic fractions with a size of -0.25 mm indicated that a considerable amount of clavate glass fibers existed in these nonmetallic fractions, which may explain why fine particles had the poorest segregation performance. (C) 2017 Elsevier Ltd. All rights reserved.