Researchers at Rice University have developed a new technique to efficiently recycle electronic waste and harvest critical minerals using rapid heating.
Most electronic devices use flame-retardant plastic. The plastic is formulated from a critical metal called antimony.
However, recapturing antimony is typically a challenging task since it first has to be released from the plastic. As it is released, other compounds can form, such as organic bromides, which are toxic and difficult to capture. However, the organic bromides can also be reused and have applications in industrial chemicals when safely captured.
“Conventionally heating the plastic releases the antimony in a volatile and difficult-to-collect form as well as creating and releasing hazardous organic bromide compounds,” Leo Haoxin Ye, first author of the paper and a graduate student at Rice, said in a news release. “Other options are risky or more impractical, such as using strong acids, organic solvents or multistep treatment options.”
To address this issue, leading Rice chemistry professor James Tour, Ye and their team adapted Tour’s flash Joule heating technique, which heats materials to hundreds of degrees Celsius in milliseconds, according to Rice.
The team ground up flame-retardant plastic waste and placed it between two sheets of electrically heated carbon paper before using what’s known as isothermal-clamped flash Joule heating to release and collect the antimony.
The team found that limiting the time the plastic spent in the high temperature range dramatically reduced the production of the hazardous organic bromide compounds. The plastic remained between 200 degrees and 500 degrees Celsius for only 9.4 milliseconds, according to Rice.
Through the process, the team recovered 90 percent of antimony from tested materials and converted 83 percent of the bromide into hydrogen bromide. Their findings were published this month in the journal Nature Chemical Engineering.
“Isothermal-clamped flash Joule heating could improve the speed, safety and practicality of antimony recovery from discarded flame-retardant plastics,” Tour added in the release. “This represents an important step forward to conserving and reusing our critical antimony supply while also regenerating bromide salts for reuse.”
The study noted that the world is currently trending toward producing 82 million metric tons of flame-retardant plastic waste by 2030, which adds to the fact that e-waste is the fastest-growing solid waste stream in the world.
The research was funded by the Air Force Office of Scientific Research and the U.S. Army Corps of Engineers.
