[Image above] Example of cemented carbide cutting tools. Researchers are investigating ways to extract tungsten and cobalt from these tools after they are decommissioned so the valuable metals can be reused. Credit: Make Everything, YouTube
Lithium is often the first material that people think of when it comes to potential resource shortages in the energy storage market. But there is another core battery material at risk of long-term supply constraints as well—cobalt.
Cobalt stabilizes the cathode in lithium-ion batteries by compensating for the charge when lithium ions arrive or depart during cycling. Perhaps surprisingly for some readers, there typically is more cobalt in this battery type than lithium.
Cobalt mining comes with a long list of challenges, however, both environmentally and ethically. In the Democratic Republic of the Congo, where some of the world’s largest cobalt mines are located, high concentrations of cobalt have even been linked to the death of crops and fish in fields and lakes near the mines. Additionally, the reliance on forced labor and child labor in cobalt mining is a well-known and widespread issue.
Researchers are working to advance new battery types that do not rely on cobalt. But it will take time before this technology is ready to make up a significant share of the energy storage market. Until then, manufacturers will need ways to source cobalt more sustainably.
Recovering cobalt from devices that have reached the end of their life is one option. It is estimated that more than 3.3 million metric tons of critical materials will be recovered annually from secondary sources, such as end-of-life equipment and electronic waste, by 2045.
Research is underway on recovering cobalt and other metals from battery scraps in an environmentally friendly manner. Another product that cobalt can be recovered from is cemented carbide tools, where it is used as the cementing phase between the tungsten carbide grains.
In a recent paper, researchers from Beijing University of Technology and Xiamen Tungsten Co. experimented with recovering tungsten and cobalt from cemented carbide scrap using molten salt electrochemical extraction.
Molten salt electrolysis is a relatively low-temperature process in which an electric current is passed through a molten salt to facilitate chemical reactions. Researchers have explored using this method to make the production of certain materials more sustainable, such as white phosphorus, as well as to recycle carbon dioxide into new products.
In the recent study, the researchers explain that they previously used this method successfully to extract tungsten and cobalt in studies here, here, and here. However, in this previous work, the electrolysis process was carried out in an argon atmosphere. This time, they aimed to carry out the process in air, “which can simplify the equipment to some extent and enhance its practical applicability,” they write.
For this study, a two-electrode system was used for all air-based electrolysis experiments. A tungsten carbide cobalt (WC-23Co) block or tungsten rod was used as the soluble anode, and a copper plate was used as the cathode. Both cathode and anode were immersed in molten salt (sodium tungstate, Na2WO4) at 900°C to a depth of 15 mm.
For comparison, some experiments were carried out in an argon protective atmosphere using a three-electrode system. The working and reference electrodes were platinum wires, and the counter electrode was a tungsten rod.
Testing confirmed that both tungsten and cobalt could be successfully separated and extracted by three-stage constant-current electrolysis in an air atmosphere. Additionally, compared to experiments in the argon atmosphere, the dissolution rate could be accelerated by increasing the air flow rate in the air atmosphere. The dissolution rate remained steady after the air flow rate reached 0.2 L/min.
“It can be concluded that electrolysis in an air atmosphere may be a viable option,” the researchers conclude.
The paper, published in International Journal of Refractory Metals and Hard Materials, is “Study on the air atmosphere molten salt electrolytic extraction of tungsten and cobalt from cemented carbide scrap” (DOI: 10.1016/j.ijrmhm.2024.106636).
