Sun Yat-Sen University scientists have developed a new ball-milling process to break down harmful compounds found in printed circuit boards.
Chief among these are the toxic brominated flame retardants added to printed circuit boards to keep them from catching fire.
The Chinese team’s method, published in ACS Sustainable Chemistry & Engineering, ensures a safer way of disposing circuit boards which are often burned or buried in landfills, polluting the air, soil and water.
Composed of 30% metallic and 70% nonmetallic particles, printed circuit boards support and connect all of the electrical components of a device.
Metallic components can be recovered from crushed circuit boards by magnetic and high-voltage electrostatic separations.
However, nonmetallic particles including resins, reinforcing materials, brominated flame retardants and other additives often get left behind.
Scientists have linked compounds in brominated flame retardants to endocrine disorders and fetal tissue damage.
In order to remedy this, associate professor Jujun Ruan and colleagues have developed a new method to remove the flame retardants from waste printed circuit boards so that they wouldn’t contaminate the environment.
The researchers crushed printed circuit boards and removed the metallic components by magnetic and high-voltage electrostatic separations, as is typically done.
They then put the nonmetallic particles 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 decreased by 50%, and phenolic resin compounds decomposed too.
During the ball-milling process, iron transfers electrons to flame retardant compounds, causing carbon-bromine bonds to stretch and break, resulting in cleaner, disposable circuit boards.
Image and content: Webandi-Pixabay/ACS via Eurekalert
