Electronic circuits in discarded computers, cellphones and other devices could be recycled less harmfully using a technique developed by researchers in China. Unlike current methods, it can be used to reclaim valuable metals such as copper without releasing toxic fumes into the air.

Printed circuit boards (PCBs) are made from insulating layers of fibreglass and resin with electronic components and interconnecting circuitry on top. The number of PCBs being manufactured worldwide is growing by around 9% every year, with China and Taiwan alone producing more than 200 million square metres of circuitry each year.

Only a small numbers of PCBs are recycled. They are typically put into copper smelters, which risks releasing harmful toxic fumes. Most circuit boards are simply incinerated or thrown into landfill, which releases toxic pollutants such as heavy metals and dioxins into groundwater and the atmosphere.

Researchers from Shanghai Jiao Tong University, China, believe their recycling solution could reduce these problems. It involves crushing boards and using a high-voltage electric field to separate metallic and non-metallic materials. The metals can then be reclaimed by distilling in a vacuum while the non-metal components can be compacted into plates for use as building materials.

Pulverised circuits

The researchers experimented with 400 kilograms of waste PCBs collected from electronic repair depots and household waste. A machine with rotating cutters crushed the boards and a hammer grinder pulverised them into pieces smaller than 1millimetre in diameter.

This process detached the metallic and non-metallic components from the boards. The large difference in their electrical conductivity meant they could then be separated using a high-voltage electric field.

Derek Fray at the University of Cambridge, UK, who researches materials processing and recycling, says such innovation will be important to recover the resources from discarded circuitry. "This is an interesting technique that can be a part of a portfolio of technologies to treat PCBs," he told New Scientist.

Fray acknowledges that the method would reduce the toxic fumes produced when reclaiming metals, but he notes that there are other factors to consider.

For example, he suggests that smelting could recover some metals other than copper more effectively. It also uses less energy than vacuum distilling. "The gases [produced] by smelting may be toxic, but one assumes that they have the technology to deal with this problem," he says.