Truth be told, this wouldn’t be the first time we’ve talked about flash joule heating. Some folks over at Rice University had already published a study using this process earlier this year, but in that case, they converted carbon into its allotropes, like graphene or diamond. Now, the same team has set its sights on using their novel technique to solve the recycling problem plaguing the electronics industry. Their new study was published in the journal Nature Communications.
As a short reminder, flash joule heating encompasses pulsing jolts of electricity to a target, heating it to very high temperatures in a flash. Before, they had used this to zap carbon into its different forms, like the proposed “material of the future” graphene or the famous diamond. These Rice researchers then rattled their heads to look for new applications for their process, and decided to take it a little bit closer to home.
As the world continuously goes through its seemingly year-long renewal cycle of smartphones and tablets, our stockpile of e-waste also constantly grows with it. In the five years leading up to 2019, the world’s e-waste volume surged by as much as 21%, amounting to about 54 million metric tons of e-waste. This sheer amount of electronic runoff is set to pose a health risk to individuals living close to disposal sites if left unchecked, according to a report from the World Health Organization. And with only about 17% of e-waste reaching formal recycling facilities back in 2019, there is a real need for additional solutions to the problem of our own doing.
Luckily for us, the Rice researchers are already working in our favor by testing their potentially new recycling process. In it, they ground up discarded circuit boards from mobile devices into a powder-like consistency, followed by the addition of additives like Teflon or table salt, and finally carbon black to improve the recovery yield.
The team then used flash joule heating to rapidly heat this e-waste powder up to temperatures of 3,127 °C (5,660 °F). From here, the metal vapors generated by the rapid heating are condensed through a “cold trap,” where they condensed into solid metal particles.
From there, “the reclaimed metal mixtures in the trap can be further purified to individual metals by well-established refining methods,” according to lead author and Rice postdoctoral research associate Bing Deng.
“Since each flash takes less than a second, this is easy to do,” according to Rice chemist and lead author James Tour.
According to the Rice team, their novel process was able to retrieve about 60% of the amount of gold left in a sample, and over 80% of other metals like silver (Ag) and palladium (Pd). And by removing other heavy metals like mercury and lead from the residual product, the process can also help alleviate chemical leaching from e-waste into the environment, according to the authors.
Additionally, the research team considers their process “energy-efficient and scalable,” given that it consumes about 940 kWh (kilowatt-hours) per ton of material—1/80th the energy consumed by commercial smelting plants and 1/500th that of commercial furnaces.
Said Tour: “Here, the largest growing source of waste becomes a treasure. […] 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.”
(For more recycling news, check out how scientists are solving a similar problem with PET bottles using E. coli bacteria.)
References
- Deng, B., Luong, D. X., Wang, Z., Kittrell, C., McHugh, E. A., & Tour, J. M. (2021). Urban mining by flash Joule heating. Nature Communications, 12(1), 5794. https://doi.org/10.1038/s41467-021-26038-9
- Irving, M. (2021, October 6). Flash-heating efficiently recycles precious metals from e-waste. New Atlas. https://newatlas.com/materials/ewaste-flash-heating-recover-precious-metals/
- Urban mining for metals flashes electronic trash into treasure. (2021, October 4). Rice University News and Media Relations; Rice News. https://news.rice.edu/news/2021/urban-mining-metals-flashes-electronic-trash-treasure
- World Health Organization. (2021, June 15). Soaring e-waste affects the health of millions of children, WHO warns. World Health Organization. https://www.who.int/news/item/15-06-2021-soaring-e-waste-affects-the-health-of-millions-of-children-who-warns
