E-waste recycling process developed to stop environmental contamination

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A new recycling process has been developed for printed circuit boards (PCBs) that should reduce their impact on environment.

Typically composed of 30 per cent metallic and 70 per cent non-metallic particles, PCBs support and connect all of the electrical components of a device.

The metallic components are easy to recover from crushed circuit boards using magnetic and high-voltage electrostatic separations, but the non-metallic particles including resins, reinforcing materials, brominated flame retardants and other additives are much more difficult to sequester.

The brominated flame retardants are added to prevent PCBs from catching fire. But they have also been linked to endocrine disorders and foetal tissue damage for people living in areas contaminated with them.

Once they have served their purpose, the boards are often just burned or buried in landfills, polluting the air, soil and water.

Researchers from Sun Yat-sen University in Guangzhou China have been developing a process that can safely remove the flame retardants from waste PCBs to alleviate this problem.

They used a ball-milling method to break down these potentially harmful compounds, enabling safer disposal.

The PCBs were first crushed and their metallic components removed. The non-metallic particles were then placed into a ball mill – a rotating machine that uses small agate balls to grind up materials.

They also added iron powder, which prior studies had shown was helpful for removing halogens, such as bromine, from organic compounds.

After ball-milling, the bromine content on the surface of the particles had decreased by 50 per cent, and phenolic resin compounds had decomposed.

The researchers determined that during the ball-milling process, iron transferred electrons to flame retardant compounds, causing carbon-bromine bonds to stretch and break.

UN figures showed that increasing consumption of electronics saw the amount of global e-waste reach 41.8m tonnes in 2014 with an expected rise to over 50m tonnes by this year.

The problem has been escalating in Southeast Asia in particular, with the amount of e-waste produced jumping by almost two thirds between 2010 and 2015.