PNNL

Researchers at PNNL exposed the ORNL-developed fibers to Pseudomonas fluorescens and used the Advanced Photon Source at Argonne National Laboratory to create a 3-D X-ray microtomograph, determining that the fiber structure was not damaged by the organism.

The world's oceans hold more than four billion tons of uranium—enough to meet global energy needs for the next 10,000 years. But for half a century researchers have tried to mine uranium from seawater with limited success—until now. A braid of polyethylene fibers developed by researchers from Oak Ridge National Laboratory (ORNL) and tested by PNNL has shown the capacity to hold 5.2 grams of uranium per kilogram of adsorbent in 49 days of natural seawater exposure.

To chronicle this and other successes in “Uranium in Seawater”, a special issue of Industrial & Engineering Chemistry Research was recently published. Major contributions came from researchers supported by DOE's Office of Nuclear Energy.

The Seawater Uranium Recovery program, initiated by DOE in 2011, includes a multidisciplinary team from national laboratories, universities, and research institutes that address the fundamental challenges of economically extracting uranium from seawater. Within five years this team has developed new adsorbents that reduce the cost of extracting uranium from seawater by a factor of three to four.

"Synthesizing a material that's superior at adsorbing uranium from seawater required a multi-disciplinary, multi-institutional team including chemists, computational scientists, chemical engineers, marine scientists and economists," said Sheng Dai, who has technical oversight of the ORNL uranium from seawater program. "Computational studies provided insight into chemical groups that selectively bind uranium. Thermodynamic studies provided insight into the chemistry of uranium and relevant chemical species in seawater. Kinetic studies uncovered factors that control how fast uranium in seawater binds to the adsorbent. Understanding adsorbent properties in the laboratory is key for us to develop more economical adsorbents and prepare them to grab as much uranium as possible."

Bound by a Braid PNNL researchers at the Marine Sciences Laboratory in Sequim, Wash. pack flow-through columns with fibers of adsorbent material. The columns are exposed to seawater to test how well the material collects uranium.

That teamwork culminated in the creation of braids that contain a uranium-attracting chemical called amidoxime. So far, testing has been conducted with real seawater at PNNL’s Marine Sciences Laboratory, Woods Hole Oceanographic Institution in Massachusetts, and the University of Miami in Florida. Gary Gill, PNNL researcher, coordinated the testing sites.

"Understanding how the adsorbents perform under natural seawater conditions is critical to reliably assessing how well the uranium adsorbent materials work," Gill said. "In addition to marine testing, we assessed how well the adsorbent attracted uranium versus other elements, adsorbent durability, whether buildup of marine organisms might impact adsorbent capacity, and we demonstrated that most of the adsorbent materials are not toxic. PNNL also performed experiments to optimize release of uranium from the adsorbents and adsorbent re-use using acid and bicarbonate solutions."

The program continues to make significant advances, producing adsorbents with even higher capacities for grabbing uranium. In recent tests, more than 6 grams of uranium per kilogram of adsorbent was achieved after 56 days in natural seawater— an adsorbent capacity that is 15 percent greater than the outcome highlighted in the special edition.

To learn more about the success of the program, read the PNNL-ORNL joint press release.