Researchers innovate sustainable metal-recycling method

Metal recycling can reduce the need for mining, which decreases the environmental damage associated with extracting raw materials such as deforestation, water pollution and greenhouse gas emissions. "Our process offers significant reductions in operational costs and greenhouse gas emissions, making it a pivotal advancement in sustainable recycling," said Tour, the T.T. and W.F. Chao Professor of Chemistry and professor of materials science and nanoengineering.

The research team's work was published in Nature Chemical Engineering on Sept. 25.

Innovative technique

The new technique enhances the recovery of critical metals and builds upon Tour's earlier work in waste disposal using flash Joule heating (FJH). This process involves passing an electric current through a material to rapidly heat it to extremely high temperatures, transforming it into different substances.

The researchers applied FJH chlorination and carbochlorination processes to extract valuable metals, including gallium, indium and tantalum, from e-waste. Traditional recycling methods such as hydrometallurgy and pyrometallurgy are energy-intensive, produce harmful waste streams and involve large amounts of acid.

In contrast, the new method eliminates these challenges by enabling precise temperature control and rapid metal separation without using water, acids or other solvents, significantly reducing environmental harm.

"We are trying to adapt this method for recovery of other critical metals from waste streams," said Bing Deng, former Rice postdoctoral student, current assistant professor at Tsinghua University and co-first author of the study.

Efficient results

The scientists found that their method effectively separates tantalum from capacitors, gallium from discarded light-emitting diodes and indium from used solar conductive films. By precisely controlling the reaction conditions, the team achieved a metal purity of over 95% and a yield of over 85%.

Moreover, the method holds promise for the extraction of lithium and rare Earth elements, said Shichen Xu, a postdoctoral researcher at Rice and co-first author of the study.

"This breakthrough addresses the pressing issue of critical metal shortages and negative environmental impacts while economically incentivizing recycling industries on a global scale with a more efficient recovery process," Xu said.

Other study authors include Jaeho Shin, Yi Cheng, Carter Kittrell, Justin Sharp, Long Qian, Shihui Chen and Lucas Eddy of Rice's Department of Chemistry and Khalil JeBailey of Rice's Department of Materials Science and NanoEngineering.

The Defense Advanced Research Projects Agency, U.S. Army Corps of Engineers, Rice Academy Fellowship and startup funds from Tsinghua supported this study.