Rare-earth metals are a key component in many modern technologies, yet mining and purifying them is not only expensive and labor-intensive, but devastating to the environment.
“Everybody’s heard of blood diamonds,” says Eric Schelter, an associate professor in the Department of Chemistry in the School of Arts & Sciences, “but maybe people haven’t heard of blood cobalt, or tantalum, or lithium for that matter.”
Although there is a huge incentive to recycle rare-earth metals, the current method of separating them is expensive and energy-consuming, takes weeks, and requires massive amounts of solvents.
Because of the cost and inefficiency of this process, rare-earth metals are currently only recycled at a rate of about 1 percent.
In a previous study, Penn researchers pioneered a process that could enable the efficient recycling of two rare-earth metals—neodymium and dysprosium—which are found in the small, powerful magnets in many high-tech devices.
In a new paper published in the Proceedings of the National Academy of Sciences, the researchers extend the method to the entire series of rare-earth metals.
The paper focused on one pairing in particular, europium and yttrium, which could enable scientists to recycle rare-earth metals from compact fluorescent light bulbs. Being able to recycle materials from these bulbs would not only keep mercury out of the environment, but also allow companies to get value out of the waste.
The research was led by Schelter, along with graduate students Justin Bogart and Zeke Cole. Connor Lippincott, an undergraduate student in the Vagelos Integrated Program in Energy Research, and Patrick Carroll, director of the X-Ray Crystallography Facility, also contributed to the study.
The new method minimizes the amount of waste generated and the amount of time and energy needed. To do this, the researchers designed a ligand to bind the ions in mixtures. The chemical compounds that form as a result are slightly different for each type of ion. For example, in mixtures of two types of elements, one is soluble in organic solvents, while the other is not. This allows the researchers to simply filter them, separating one of the metal cations from the other.
“Our thinking was if we could take the magnets or some material that comes out of the magnets and then apply a very simple chemical method, we could purify the rare-earths out of them directly and complement existing sources in the supply chain with this new one through simple chemistry,” Schelter says.
Schelter believes that there will eventually be a push by companies that are socially conscious to implement ethically sourced materials and manufacturing practices. He says the impact of this research is in taking steps to return materials to the supply chain at the end of their useful life as a consumer product.
“We shouldn’t just be throwing so much material away,” Schelter says. “There’s still a lot of value to it. I think that as part of a sustainable approach to manufacturing and developing a ‘circular’ economy, we should think about the impact and value of materials at every point along their lifecycle, and how we can efficiently and effectively bring them back to useful raw materials once they’re at the end of their product life.”