Chelating agent selectively grabs uranium from oceans

The world’s oceans contain some 4 billion metric tons of dissolved uranium. That’s roughly 1,000 times as much as all known terrestrial sources combined, and enough to fuel the global nuclear power industry for centuries. But the oceans are so vast, and uranium’s concentration in seawater is so low—roughly 3 ppb—that extracting it remains a formidable challenge. That task may have just become easier thanks to a new adsorbent material based on a bioinspired chelating agent (Nat. Commun. 2019 DOI: 10.1038/s41467-019-08758-1).

Researchers have been looking for ways to extract uranium from seawater for more than 50 years. In the 1980s, surveys pointed to amidoxime-type chelating agents, which have a knack for latching onto uranyl ions, the aqueous form of uranium.

Nearly 20 years ago, the Japan Atomic Energy Agency (JAEA) confirmed that amidoxime-functionalized polymers could soak up uranium reliably even under harsh marine conditions. But that type of adsorbent has not been implemented on a large scale because it has a higher affinity for vanadium than uranium. Separating the two ions raises production costs.

Alexander S. Ivanov of Oak Ridge National Laboratory, together with colleagues there and at Lawrence Berkeley National Laboratory and other institutions, may have come up with a solution. Using computational methods, the team identified a highly selective triazine chelator known as H₂BHT that resembles iron-sequestering compounds found in bacteria and fungi. Starting with low-cost reagents, the team prepared fibers containing polyethylene and polyacrylic acid, functionalized them with H₂BHT (shown), and analyzed their performance as adsorbents.

H₂BHT exhibits little attraction for vanadium but has roughly the same affinity for uranyl ions as amidoxime-based adsorbents do. And in contrast to amidoxime adsorbents—which are tough to recycle because of the acid treatment needed to further purify uranium they gather—the new adsorbent can be regenerated with mild carbonate solution and reused.

JAEA’s Masashi Kaneko offers high praise for the study. H₂BHT’s high selectivity and uranium uptake capacity, coupled with molecular insights from the team’s analyses, may lead to improved methods for recovering uranium from seawater, he says.