Flash-heating efficiently recycles precious metals from e-waste
Electronic waste (or e-waste) is not only a major pollutant in landfill, but huge amounts of useful resources are being thrown away. Engineers at Rice University have now shown that precious metals and rare earth minerals can be recovered by flash-heating ground-up electronics with a zap of electricity.
The annual pursuit of newer, shinier phones makes e-waste the world’s fastest-growing waste stream, with 59 million tons generated in 2019 alone. If cleaning up the environment isn’t motivating enough, then perhaps the financial incentive will be – it’s estimated that all those discarded laptops, Zunes and iPhone 12s contain tens of billions of dollars’ worth of precious metals like gold, silver, copper and platinum. Unfortunately, less than 20 percent of the world’s e-waste is recycled, so the Rice team set out to make this process easier and less expensive.
In previous work the researchers demonstrated a technique called flash joule heating, involving millisecond-long jolts of electricity that heated materials to high temperatures. Originally the team used this to create graphene out of waste products, and later converted carbon from almost any source into either graphene or diamond by alternating the length of the flash.
For the new study, the team turned their attention to the e-waste problem. They started by grinding up old discarded circuit boards into powder, then zapped the mix to heat it to 3,127 °C (5,660 °F). This vaporizes the metals, and the vapors are then piped into a cold trap where they recondense into solid metals. From there, common refining methods can separate the specific metals for use.
The team says that this process can recover over 60 percent of gold in a sample, and over 80 percent of silver, palladium and rhodium. It also removes toxic heavy metals like chromium, arsenic, cadmium, mercury and lead, which can leach into the environment from e-waste in landfill.
Importantly, the researchers say that the process is energy efficient and scalable. It consumes about 939 kWh per ton of material processed, which is one 80th the amount consumed by commercial smelting and one 500th that of furnaces.
“Here, the largest growing source of waste becomes a treasure,” says James Tour, lead researcher on the study. “This will curtail the need to go all over the world to mine from ores in remote and dangerous places, stripping the Earth’s surface and using gobs of water resources. The treasure is in our dumpsters.”
The study was published in the journal Nature Communications. The team describes the process in the video below.
Source: Rice University