Using high-energy
X-rays, researchers discovered uranium is bound
by adsorbent
fibers in an unanticipated fashion.
(December 17, 2015) An
ultra-high-resolution technique used for the first time to study polymer fibers
that trap uranium in seawater may cause researchers to rethink the best methods
to harvest this potential fuel for nuclear reactors.
The work of a team led by Carter Abney, a Wigner Fellow at
the Department of Energy’s Oak Ridge National Laboratory, shows that the
polymeric adsorbent materials that bind uranium behave nothing like scientists
had believed. The results, gained through collaboration with the University of
Chicago and detailed in a paper published in Energy & Environmental
Science, highlight data made possible with X-ray Absorption Fine Structure
spectroscopy performed at the Advanced Photon Source. The APS is a DOE Office
of Science User Facility at Argonne National Laboratory.
“Despite the low concentration of uranium and the presence
of many other metals extracted from seawater, we were able to investigate the
local atomic environment around uranium and better understand how it is bound
by the polymer fibers,” Abney said.
Surprisingly, the spectrum for the seawater-contacted
polymer fibers was distinctly different from what was expected based on small
molecule and computational investigations. Researchers concluded that for this
system the approach of studying small molecule structures and assuming that
they accurately represent what happens in a bulk material simply doesn’t work.
It is necessary to consider large-scale behavior to obtain
the complete picture, highlighting the need for developing greater
computational capabilities, according to Abney.
“This challenges the long-held assumption regarding the
validity of using simple molecular-scale approaches to determine how these
complex adsorbents bind metals,” Abney said. “Rather than interacting with just
one amidoxime, we determined multiple amidoximes would have to cooperate to
bind each uranium molecule and that a second metal that isn’t uranium also
participates in forming this binding site.”
An amidoxime is the chemical group attached to the polymer
fiber responsible for binding uranium.
Abney and colleagues plan to use this knowledge to design
adsorbents that can harness the vast reserves of uranium dissolved in seawater.
The payoff promises to be significant.