Ellen Phiddian
Cosmos science journalist
A US-based team of chemists has found a more efficient way to extract precious metals from electronics, making e-waste cheaper to recycle.
The study is published in Nature Chemical Engineering.
Traditionally, metals in waste are recycled with hydrometallurgy, which involves soaking in corrosive substances to leach metals out, or pyrometallurgy, which involves heating things to very high temperatures.
While selective, hydrometallurgy creates extra waste streams, while pyrometallurgy is energy intensive and doesn’t produce metals in high purities.
This research still uses heat and additional chemicals, but both are deployed in a more controlled way.
The researchers used chlorination, an industrial process which involves reacting chlorine and oxygen with specific metals in a mixture.
But they added a process called “flash joule heating”, where an electric current passed through a substance can heat it to precise temperatures, very quickly.
Between these two techniques, the team was able to extract more than 85% of specific precious metals, like gallium, indium and tantalum, from e-waste mixtures.
The purity of the mixtures were more than 95%.
The technique dodges the waste problem of hydrometallurgy, and is more selective than pyrometallurgy.
“The incorporation of direct electric heating into the chlorination process represents a potential shift in metallurgy that could minimise supply chain shortage,” write the authors in their paper.
“We are trying to adapt this method for recovery of other critical metals from waste streams,” says co-first author Dr Bing Deng, a former postdoctoral student at Rice University, USA, and now an assistant professor at Tsinghua University, China.
The researchers focussed on e-waste in this study, but they believe the method could be used on other industrial waste and even crude ores from mining.
“This breakthrough addresses the pressing issue of critical metal shortages and negative environmental impacts while economically incentivising recycling industries on a global scale with a more efficient recovery process,” says co-first author Dr Shichen Xu, a postdoctoral researcher at Rice University.
