Siddarth Kara’s bestseller, “Cobalt Red: How the Blood of Congo Powers Our Lives,” focuses on problems surrounding the sourcing of cobalt, a critical component of lithium-ion batteries that power many technologies central to modern life, from mobile phones and pacemakers to electric vehicles.
“Perhaps many of us have read how lithium-ion batteries are vital for energy storage technologies,” says Eric Schelter, the Hirschmann-Makineni Professor of Chemistry at the University of Pennsylvania. “But how material that make up such batteries are sourced can be concerning and problematic, both ethically and environmentally.”
Schelter says that cobalt mining in the Democratic Republic of Congo, which supplies about 70% of the world’s cobalt, raises concerns due to environmental degradation and unsafe working conditions, and that large-scale mining disrupts ecosystems, can contaminate water supplies, leaving lasting environmental damage. In addition, he notes that a looming cobalt shortage threatens to strain global supply chains as demand for battery technologies continues to grow.
To that end, an area of research his lab has been focusing on is the separation of battery-critical metals like nickel and cobalt. In a new paper, published in the journal Chem, Schelter’s team and collaborators at Northwestern University presented an “easier, more sustainable, and cheaper way to separate both from materials that would otherwise be considered waste.”
“Our chemistry is attractive because it’s simple, works well, and efficiently separates nickel and cobalt—one of the more challenging separation problems in the field,” Schelter says. “This approach offers two key benefits: increasing the capacity to produce purified cobalt from mining operations with potentially minimal environmental harm, addressing the harshness of traditional purification chemicals, and creating value for discarded batteries by providing an efficient way to separate nickel and cobalt.”
The right ingredients for selective separation
Typically, the researchers say, cobalt is often produced as a byproduct of nickel mining by way of hydrometallurgical methods such as acid leaching and solvent extraction, which separates cobalt and nickel from ores. It’s an energy-intensive method that generates significant hazardous waste.
The process Schelter and the team developed to circumvent this is based on a chemical-separation technique that leverages the charge density and bonding differences between two molecular complexes: the cobalt (III) hexammine complex and the nickel (II) hexammine complex.
“A lot of separations chemistry is about manifesting differences between the things you want to separate,” Schelter says, “and in this case we found conditions where ammonia, which is relatively simple and inexpensive, binds differently to the nickel and cobalt hexammine complexes.”
By introducing a specific negatively charged molecule, or anion, like carbonate into the system, they created a molecular solid structure that causes the cobalt complex to precipitate out of the solution while leaving the nickel one dissolved. Their work showed that the carbonate anion selectively interacts with the cobalt complex by forming strong “hydrogen bonds” that create a stable precipitate. After precipitation, the cobalt-enriched solid is separated through filtration, washed with ammonia, and dried. The remaining solution contains nickel, which can then be processed separately.
“This process not only achieves high purities for both metals—99.4% for cobalt and more than 99% for nickel—but it also avoids the use of organic solvents and harsh acids commonly used in traditional separation methods,” says first author Boyang (Bobby) Zhang, a graduate student in Penn’s School of Arts & Sciences and a Vagelos Institute for Energy Science and Technology Graduate Fellow. “It’s an inherently simple and scalable approach that offers environmental and economic advantages.”
Techno-economic and life cycle analyses
In evaluating the real-world applicability of their new method, the team, led by Marta Guron, conducted both techno-economic analysis and life-cycle assessment, with the former revealing an estimated production cost of $1.05 per gram of purified cobalt, substantially lower than the $2.73 per gram associated with a reported separations process.
“We focused on minimizing chemical costs while also using readily available reagents, which makes our method potentially competitive with existing technologies,” Schelter says.
The life-cycle analysis found that eliminating volatile organic chemicals and hazardous solvents allows the process to significantly reduce environmental and health risks, which was supported by metrics like Smog Formation Potential and Human Toxicity by Inhalation Potential, where the process scored at least an order of magnitude better than traditional methods.
“This means fewer greenhouse gas emissions and less hazardous waste, which is a seriously big win for both the environment and public health,” says Zhang.
Cleaner path forward
Owing to how the team accomplished their separation, Schelter says, there’s an exciting fundamental science aspect of this work that he thinks they can take in many different directions, even for other metal separation problems.
“Based on the unique set of molecular recognition principles we identified through the course of this work, I think we can extend this work in many different directions,” he says. “We could apply it to other metal separation problems, ultimately driving broader innovation in sustainable chemistry and materials recovery.”
Eric Schelter is the Hirschmann-Makineni Professor of Chemistry in the Department of Chemistry at the School of Arts & Sciences at the University of Pennsylvania.
Boyang (Bobby) Zhang is a Vagelos Institute for Energy Science and Technology Graduate Fellow in the Schelter Group at Penn Arts & Sciences.
Marta Guron is an adjunct lecturer in the Department of Chemistry and project manager in the Office of Environmental and Radiation Safety.
Other authors are Andrew J. Ahn, Michael R. Gau, and Alexander B. Weberg from Penn and Leighton O. Jones and George C. Schatz of Northwestern University.
This research was supported by the Vagelos Institute for Energy Science and Technology at Penn, Vagelos Integrated Program in Energy Research at Penn, National Science Foundation Center (Award CHE-1925708), Center for Advanced Materials for Energy Water Systems of the U.S. Department of Energy (Grant 8J-30009-0007A), and Research Corporation for Science Advancement (Award #CS-SEED-2024-022).
