New molecule could make metal recovery cleaner and more efficient

Recovering valuable metals from electronic waste, mining streams and industrial waste typically requires large quantities of chemical reagents. Researchers at the University of Illinois Urbana-Champaign have developed a new molecule that could replace much of that chemistry with electricity – a fundamental advance that could potentially make metal recovery cleaner, simpler and more energy efficient.

Led by chemical and biomolecular engineering professor Xiao Su, the team’s findings were reported in ACS Energy Letters.

The study builds on a 2024 breakthrough from Su's research group, which introduced a continuous electrochemically mediated liquid-liquid extraction process, or e-LLE, for recovering gold from electronic waste. That work demonstrated that electricity could replace many of the acids and bases traditionally used in liquid-liquid extraction, a widely used method for separating and purifying metals. However, the process still relied on additional chemical reagents to complete the extraction cycle.

 The new study removes that extra step by redesigning the extraction molecule itself.

Rather than modifying the process, the researchers created a multifunctional molecule that performs three jobs at once: it selectively binds metal ions, carries a permanent electrical charge and remains soluble in the organic phase used during extraction. Because the molecule itself carries charge, it can be directly controlled by electricity, eliminating the need for intermediate chemical reagents.

"The new molecule has a permanent built-in charge that acts as electrolyte, letting the liquid conduct electric current," explained postdoctoral researcher Deborah Schmitt, a co-author of the paper. "That's what allows the redox reactions to be driven by electricity instead of chemicals. This work completely electrifies a separation process that industry heavily depends on chemical reagents to perform."

"This is the first time we've been able to run electrochemical solvent extraction the way we dreamed of," Su said. "We charge the molecule, it binds the metal, moves it into the organic phase, and then electricity releases it again.”

By directly electrifying the extraction process, the new system reduces chemical consumption by one to two orders of magnitude while simplifying the overall extraction cycle. Because electricity replaces intermediate chemical reagents, the approach has the potential to reduce both chemical waste and energy use.

In laboratory demonstrations, the researchers used the new molecule to selectively recover gold from electronic-waste leachates – solutions produced when valuable metals are dissolved from discarded electronics. Although gold served as a demonstration case, the study's broader contribution is establishing a set of molecular design principles that can be used to create electrically active extraction molecules for other separations.

"This system can be adapted to selectively recover many different valuable metals, like platinum-group metals from spent automotive catalysts and potentially a number of other critical elements from mine tailings or other complex feedstocks," said graduate student and co-author Aderiyike Aguda. "Since the electrochemical platform remains largely the same, the chemistry of the extractant can be tailored to target different metals depending on the application."

“Basically, this work unlocked the fundamentals behind it – how to think about it,” Su said.

The work establishes a new fundamental framework for electrically driven liquid-liquid extraction, and future work will focus on its scale-up for industrial use. The researchers are already exploring new molecule designs and pursuing collaborations to introduce computational modeling and artificial intelligence for accelerated discovery.

"I'm really excited about this work because I think it shows one more step toward demonstrating that electrochemistry can actually offer scalable, minimal-waste separations," he said. "With growing attention on critical minerals and supply chains, it’s a step toward rethinking how we recover metals in a way that's cleaner and fully electrified."

The study was funded by the U.S. Department of Energy Office of Science, Basic Energy Sciences and the Separation Science Program under Award Number DE-SC0025636. Su is also affiliated with The Grainger College of Engineering, the Beckman Institute for Advanced Science and Technology, Chemistry, and the Prairie Research Institute. He holds the Helen Corley Petit Scholar appointment.

Editor’s Notes:

Xiao Su can be reached at x2su@illinois.edu.

The paper, “Direct Electrification of Liquid–Liquid Extraction by Imparting Fixed Charges onto Selective Redox Active Compounds,” is available online. DOI: 10.1021/acsenergylett.6c01434