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A New Degree Of Separation For Rare-Earth Metals

Recycling: Chemists design and prepare a nitroxide ligand that selectively binds neodymium over dysprosium to recover the metals

by Stephen K. Ritter
June 8, 2015 | APPEARED IN VOLUME 93, ISSUE 23

Rare-earth metals are important for making many electronic devices and permanent magnets, yet commodity amounts of the elements can be in short supply. This situation has prompted metal suppliers to ramp up recycling of consumer products as an alternative to mining. To that end, chemists have developed several approaches for separating mixtures of rare-earth metals so they can be reblended in the necessary proportions for different applications. In the latest example, Eric J. Schelter and coworkers at the University of Pennsylvania report the design and synthesis of a nitroxide-based ligand that selectively binds neodymium over dysprosium in mixtures of the two elements derived from permanent magnets (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201501659). The nitroxide ligand forms a size-sensitive aperture when it binds the metals. In solutions of neodymium and dysprosium triflate salts, the ligand prefers the larger neodymium cation, forming a soluble complex as the less soluble complex formed from the smaller dysprosium cation precipitates. The team developed a complete recycling process to recover the two metals and reuse the ligand. According to the researchers, the new approach offers a simpler, less expensive alternative to redox chemistry, acid leaching processes, and ionic liquid extraction currently being used and explored for recycling rare earths.

This tripodal nitroxide ligand (left) wraps up neodymium (right) to separate it from dysprosium.


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Steve Ritter (June 23, 2015 3:08 PM)
Andrew McGhie, a UPenn colleague of Schelter's and a spontaneous poet, crafted these lines after reading this article:

Gimme Schelter

Gimme Schelter, for he's the man
Who separates rare earths as fast as one can
For that all he needs is a simple ligand
And a tridentate nitroxide is at his command
So far he has separated two rare earths
Neodymium from Dysprosium dependent on girth
For each complex dimerizes differently
Which changes a lot their solubility
The Neodymium completely enters into solution
While Dysprosium precipitates with good resolution
Thus 50:50 powder mixtures can yield
Ninety-five percent pure metals. His fame, it is sealed
So a fortune awaits the brilliant inventor
Of this new technology, he’s right at the center

Andrew Roxburgh McGhie 06.20.2015

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