Mathematical analysis of the gas–solid fluidized bed separation of metals and nonmetals from waste PCB powders

Abstract

Modern society is generating increasing quantities of waste printed circuit boards (PCBs). Together with the complicated components of high values, the treatment of waste PCBs has been a heavily researched and difficult topic in the disposal of waste electrical and electronic equipment (WEEE). The application of an air separation technology to produce comminuted PCB particles can achieve efficient separation of metal and nonmetallic fractions for further treatment and purification. With the advantages of a simple operation, environmental-soundness, and avoidance of secondary pollution, this technology is of great significance in the recycling of waste PCBs. In this paper, the air separation principles of waste PCB particles in a fluidized bed were mathematically analyzed. The shape factor of metal and non-metallic particles and the uneven airflow velocity distribution in the radial dimension were considered, and the formula for metal grade and yield were deduced. Experiments were designed and performed to obtain metal grade and yield data, which were compared with the calculation results. The calculated grade is in good agreement with the experimental results. The presented mathematical analysis can act as a guide for the engineering design and operating configuration of air separation for waste PCB particles in determining the terminal velocity and for selecting the particle size, feed volume, and discharging height.