As the demand for lithium-ion batteries escalates with the proliferation of mobile phones, electric vehicles, and even pacemakers, key components in these powerhouses, like cobalt, face significant ethical and environmental concerns related to their extraction.
Now, Eric Schelter, the Hirschmann-Makineni Professor of Chemistry at the University of Pennsylvania, and colleagues have pioneered a safer, more sustainable technique to extract elements critical to battery-powered technologies.
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 address these pressing issues, Schelter’s lab is actively researching the separation of battery-critical metals like nickel and cobalt. In a recent paper published in the journal Chem, he and his team, in collaboration with researchers at Northwestern University, introduced an innovative method that offers a more sustainable, cost-effective, and simpler way to extract these vital metals from materials that would typically be deemed waste.
This technique not only enhances the recycling potential of battery materials but also contributes to minimizing environmental impact, thereby paving the way for a more responsible approach to resource utilization in the battery industry.
“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.”
Researchers indicate that 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 approach developed by Schelter and the team relies on a chemical-separation process that utilizes the differences in charge density and bonding characteristics between two molecular complexes: the cobalt (III) hexamine complex and the nickel (II) hexamine 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 hexamine complexes.”
By introducing a specific negatively charged molecule or anion, such as carbonate, into the system, a remarkable molecular solid structure is formed. This innovation causes the cobalt complex to precipitate out of the solution while allowing the nickel complex to remain dissolved.
Their research highlights the selective interaction of the carbonate anion with the cobalt complex, as it establishes strong “hydrogen bonds” that lead to a stable and identifiable precipitate. After precipitation, the cobalt-enriched solid is separated through filtration, washed with ammonia, and dried. The remaining solution, which contains nickel, can then be processed separately.
A step-by-step process for separating cobalt (Co) from nickel (Ni): Starting with mixed metal chlorides, mild conditions form hexammine complexes. Adding an anionic receptor, like carbonate, selectively precipitates cobalt, leaving nickel in the filtrate. Credit: Bobby Zhang/University of Pennsylvania
“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.”
The research team, led by Marta Guron, evaluated the practical application of their innovative method by conducting a techno-economic analysis alongside a life-cycle assessment. Their findings indicated a production cost of $1.05 per gram for purified cobalt, which is notably lower than the $2.73 per gram cost associated with an existing 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 assessment underscored the substantial environmental and health advantages of their approach. By eliminating hazardous solvents and volatile organic compounds, their method not only minimizes risks but also scores impressively better in metrics like Smog Formation Potential and Human Toxicity by Inhalation Potential, achieving at least an order of magnitude improvement over conventional processes.
“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.
According to Schelter, the method the team used for their separation presents a fascinating fundamental science element that he believes can be explored in various directions, even pertaining to other issues related to metal separation.
“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.”
Journal reference:
Boyang Zhang, Alexander B. Weberg, Andrew J. Ahn, Marta Guron, Leighton O. Jones, Michael R. Gau, George C. Schatz, Eric J. Schelter. A sustainable cobalt separation with validation by techno-economic analysis and life-cycle assessment. Chem, 2024; DOI: 10.1016/j.chempr.2024.10.028