Waste Electrical and Electronic Equipment (WEEE) recycling has raised increasing concern around the world due to requirement from legal regulations, environmental impact associated with recycling process and economic benefit from resource recovery. Most of the current recycling practices employ energy intensive wet hydrometallurgy process that generate secondary waste, which requires further treatment.
This thesis investigates the potential application of two dry separation techniques, vertical vibratory separation and pneumatic separation, for the recycling of WEEE. Both processes provide dry density based particle separation to concentrate metallic fractions from shredded WEEE hence reduce the energy and chemical consumption in the following smelting process, and reduce the overall environmental impact in recycling. Printed Wiring Boards (PWBs) represent the most complex components of WEEE, waste computer motherboards and were selected as sample materials for this investigation. Artificial shredded samples with different densities have also been prepared to explore the effect of density difference on particle separation.
Research work on vibration induced particle segregation originated from the famous ‘Brazil Nuts Effect’ and ‘reverse Brazil Nuts Effect’. The movement pattern of granular material under vibration is affected by particle size and density. Previous research at University of Nottingham showed vertical vibratory separation to be a promising environmental friendly mechanical separation method for recycling metallic fraction from shredded WEEE stream. A pilot scale thin cell vibratory separator has been developed to investigate the potential for WEEE recycling applications. To better understand the density effect on vibration separation, artificial shredded sample particles with different densities have been chosen to mimic metallic and non-metallic fractions in WEEE. Experimental results showed the effect of environmental humidity on separation results was highly relevant. Vibratory separation test within a controlled environment and the addition of solid lubricant were conducted. Relative humidity and solid lubricant were proven to be effective on improving flowability of granular system hence successful vibratory separation. The effect of particle size on vibratory separation has also been investigated with bronze and glass spheres in various size range.
Jigging is one of the oldest gravity concentration techniques, which separates materials based on specific gravity by vibration and the pulsation of fluid through a bed of materials. Pneumatic jigging is capable of separating coarse material within a very narrow density range, which makes it suitable as a pre-treatment process for WEEE recycling. The work presented in this thesis investigates the potential application of pneumatic jigging in metal recovery from shredded PWBs. Research work started with separation experiment on a pilot scale pneumatic jig developed by University of Nottingham Ningbo, China. Shredded PWBs have been successfully separated into non-metallic fraction (consisting of glass fibre, fluffs, and plastic pieces) and metallic fraction. Jigging operation parameters like sample bed height, superficial air velocity, air pulsation frequency has been established from pilot scale separation experiment. Industrial prototype pneumatic jigging has been developed for the recycling of metallic fraction from WEEE.
|Date of Award
|8 Jul 2019
- Univerisity of Nottingham
|Nichola James Miles (Supervisor) & Philip Hall (Supervisor)
- particle separation
- vibratory separation
- pneumatic separation