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Metal-binding polymer continues to surprise

New details on the chemistry of poly(amidoxime) sorbents could help optimize the extraction of valuable metals from seawater

by Stephen K. Ritter
November 27, 2017 | APPEARED IN VOLUME 95, ISSUE 47

National lab researchers exploring poly(amidoxime)’s metal-binding abilities found that the material prefers vanadium ions over uranium ions, and that vanadium binds very strongly and exclusively to cyclic imide-dioxime units.

The world’s oceans contain more than 4 billion tons of uranium, an amount that could supply fuel for nuclear power production for centuries. The trick is how to harvest the metal ions, which occur at a dilute 3.3 ppb in the vast and deep blue sea.

Chemists have long been developing polymeric materials that selectively absorb uranium, gold, and other valuable metals from seawater. For uranium, researchers have focused on sorbent mats made from poly(amidoxime)s in which the nitrogen-oxygen functional groups in the polymers selectively bind uranium ions.

In a new study, Alexander S. Ivanov of Oak Ridge National Laboratory (ORNL) and coworkers report a nuance in this chemistry: poly(amidoxime)s actually bind vanadium ions better than uranium ions. This observation could lead to developing better materials for plucking uranium out of seawater, Ivanov says, but also help in efforts to mine the oceans for metals like vanadium and lithium, which are used in batteries, rather than using environmentally destructive surface mining (Nat. Commun. 2017, DOI: 10.1038/s41467-017-01443-1).

By using a combination of titration, X-ray spectroscopy, and computer simulation, ORNL researchers in collaboration with Lawrence Berkeley National Laboratory and UC Berkeley found that the cyclic imide-dioxime units in poly(amidoxime)s preferentially bind V5+ over UO22+. They also found that linear amidoxime units in the polymers don’t bind V5+ but do bind UO22+. This knowledge should help researchers design polymers for more efficient capture of uranium, vanadium, and other metals.



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Steve Ritter (December 4, 2017 3:57 PM)
Andrew McGhie, a UPenn chemist, has struck again by penning his poetic thoughts about a C&EN article:

A Shakespearean Sea Sonnet

There is more Uranium in the sea
Four billion tons at 3 ppb, it’s known
And Ivanov of ORNL’s Chemistry
Has suitable sorbent mats now grown
Composed of poly(amidoxime)
Which binds Uranium to a high degree
It is truly a research worker’s dream
And it is even better at Vanadium selectivity
Which binds to cyclic imide-dioxime units
Much better than Uranium
While linear poly(amidoxime) units
Bind UO2 cations better than Vanadium
And so, with further research, we’ll see
Uranium captured more efficiently

Andrew Roxburgh McGhie 11.29.2017

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