Toward safer disposal of printed circuit boards 

January 15, 2020

Printed circuit boards are vital components of modern electronics. However, once they have served their purpose, they are often burned or buried in landfills, polluting the air, soil and water. Most concerning are the brominated flame retardants added to printed circuit boards to keep them from catching fire. Now, researchers reporting in ACS Sustainable Chemistry & Engineering have developed a ball-milling method to break down these potentially harmful compounds, enabling safer disposal.

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, leaving behind nonmetallic particles including resins, reinforcing materials, brominated flame retardants and other additives. Scientists have linked compounds in brominated flame retardants to endocrine disorders and fetal tissue damage. Therefore, Jujun Ruan and colleagues wanted to develop a 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. Then, they 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 had decreased by 50%, 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. 

The authors acknowledge funding from the 111 Project, the Natural Science Foundation of Guangdong Province, China and the Pearl River Star of Science and Technology.

The study is freely available as an ACS Editor's Choice article here.

For more research news, journalists and public information officers are encouraged to apply for complimentary press registration for the ACS Spring 2020 National Meeting & Exposition in Philadelphia.

The American Chemical Society (ACS) is a nonprofit organization chartered by the U.S. Congress. ACS' mission is to advance the broader chemistry enterprise and its practitioners for the benefit of Earth and its people. The Society is a global leader in providing access to chemistry-related information and research through its multiple research solutions, peer-reviewed journals, scientific conferences, eBooks and weekly news periodical Chemical & Engineering News. ACS journals are among the most cited, most trusted and most read within the scientific literature; however, ACS itself does not conduct chemical research. As a specialist in scientific information solutions (including SciFinder® and STN®), its CAS division powers global research, discovery and innovation. ACS' main offices are in Washington, D.C., and Columbus, Ohio.

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