Electronic printed circuit boards (PCBs) are complex assemblies with a lot of electronic components and materials. Large quantities of electronic equipment are manufactured every year around the world. Major portion is in the form of consumer electronics such as television receivers, computers and mobile phone handsets. Large volumes of printed circuit boards are obsoleted every year in television receivers, computers, mobile phones handsets, etc. and these must eventually be recycled or disposed of. Recycling of printed circuit boards is done for recovery of precious metals such as gold, silver, copper, lead, zinc, steel, aluminum, tin, nickel, etc. from PCBs.
Why Recycling of Printed Circuit Boards (PCB)
Almost every piece of electronic equipment has its electronic components mounted by soldering onto a fibre-based epoxy printed circuit board (PCB) or similar with the interconnecting wiring provided by tracks of copper on that board. The solder is usually a mixture of lead and tin. Along with all the components, the printed circuit boards contain precious metals such as gold, silver, copper, lead, zinc, steel, aluminum, tin, nickel, etc. Land-filling of these metals is thus not only a waste of valuable resources, but also a potential hazard.
Certainly gold, palladium, silver and copper can earn revenue, but the other metals recovered are hardly in worthwhile quantities. It is possible to recover all the metallic elements on a printed circuit board such as the copper (and any nickel) and the tin and lead from the solder. There may also be smaller quantities of precious metals, such as gold, palladium and silver. Flame retardants can also be recovered. However, there may be hazards associated with certain types of components, containing mercury or beryllia.
What is the Process for Recycling of Printed Circuit Boards (PCB)
There are many different processes for recycling printed circuit boards and many more being proposed as time goes on, but difficulties arise with the economics of such processes and with the very large mix of materials contained in the boards. However a typical process is:
- Partial disassembly by hand to remove hazardous materials such as batteries and other large components.
- Shredding to reduce particle size to a few mm or smaller.
- Separation of different materials
- Magnetic separation for ferrous metals
- Magnetic separation for some copper alloys
- Eddy current separation for non-ferrous metals
- Triboelectric or density based separation for plastics
- Jigging to separate light and heavy non-ferrous metals
- Smelting to refine out small fractions of valuable metals such as gold
This would seem to be a complex process given the relatively small volume involved. Indeed, it is argued that disassembling printed circuit boards has a relatively low environmental benefit relative to some of the other activities such as collection of metal dominated products (refrigerators and washing machines) and CRT glass recycling.