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Materials

Ionic Liquid Helps Recycle Rare Earths

Liquid-liquid extraction separates rare-earth metal ions from transition metals and could serve as a method to recycle magnets

by Stephen K. Ritter
March 25, 2013 | APPEARED IN VOLUME 91, ISSUE 12

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Credit: Tom Vander Hoogerstraete
Vials containing ionic liquid and aqueous phases efficiently separate transition metals from rare-earth metals, as shown in these before and after shots.
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Credit: Tom Vander Hoogerstraete
Vials containing ionic liquid and aqueous phases efficiently separate transition metals from rare-earth metals, as shown in these before and after shots.

Rare-earth magnets are indispensable components in computer hard drives, wind turbines, audio speakers, and electric vehicles. Because of the insecure supply chain and price fluctuations of rare-earth metals, scientists are interested in developing efficient, safe, and environmentally friendly methods for recycling magnets to recover the metals. Tom Vander Hoogerstraete, Koen Binnemans, and coworkers at the University of Leuven, in Belgium, have come up with such a method, one that relies on extracting the metals with an ionic liquid (Green Chem., DOI: 10.1039/c3gc40198g). A common way to separate metal ions is by liquid-liquid extraction of acidic aqueous solutions of dissolved metal ions with an organic solvent containing an extraction agent. Rather than using a volatile, flammable solvent as is customary, the Leuven researchers tried ionic liquids, which are nonvolatile, nonflammable organic-based salts with low melting points. By using a tetraalkylphosphonium chloride ionic liquid, which functions as both a solvent and extraction agent, the researchers separated cobalt from samarium and iron from neodymium with better than 99.98% efficiency. They focused on those metal combinations because samarium-cobalt and neodymium-iron-boron magnets are two of the most common types of rare-earth magnets. After the extractions, the researchers stripped the cobalt and iron out of the ionic liquid so they could reuse it.

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