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Heavy metal fishing

New technology at ORNL may secure nuclear energy for hundreds of years

Scientists envision anchoring hundreds of long HiCap fibers in the sea for 30 to 60 days . Then a wireless signal would cause them to float to the sur face where trapped uranium could be recovered and the fibers reused. Illustration: Andy Sproles

Scientists envision anchoring hundreds of long HiCap fibers in the sea for 30 to 60 days . Then a wireless signal would cause them to float to the sur face where trapped uranium could be recovered and the fibers reused. Illustration: Andy Sproles

For decades, researchers have searched for a way to extract the oceans' estimated 4 to 5 billion tons of uranium. The element rolls in the waves, crashes on the beaches and tickles the toes of beachgoers everywhere, but it could never be captured cheaply enough or in sufficient quantities for energy or defense applications.

With the help of surface-area-enhancing techniques developed and patented by Florida-based Hills Inc., Oak Ridge National Laboratory researchers are creeping closer to unlocking the limitless energy stores buried in the waves.

The Department of Energy is interested in ensuring the United States continues to have uranium for nuclear power and national security. With nuclear power providing more than 20 percent of the nation's energy supply, running out of uranium is simply not an option.

"Scientists have forecast that eventually there will be a tremendous shortage in nuclear fuel if we continue to mine it only on land," said Sheng Dai, technical lead on the ORNL project.

Mining uranium on land involves either physically removing or chemically dissolving the element from a limited number of ore sources. Removing uranium from seawater is safer and recovers the same elemental form of uranium found on land.

"If we could recover uranium from seawater, we could provide enough nuclear energy to supply the whole world for hundreds of years," Dai said.

The goal of extracting uranium from the oceans began with research and development projects in the 1960s, with Japan conducting the majority of the work. DOE became a major player in this research area in 2010, when Hills and ORNL began tinkering with the surface areas of plastic fibers. The adsorbent fiber the team developed was designed to recognize and selectively trap dissolved uranium.

Hills, an innovator in the field of fiber technologies, helped ORNL researchers increase the surface area of the adsorbents by incorporating complex ridges and folding patterns into the plastic material. These modifications and other processing improvements resulted in HiCap Adsorbents, a 2012 R&D 100 Award winner and patent-pending technology. HiCap harvests uranium seven times faster than its competitors—and reduces the initial $1,230 cost of removing one kilogram of uranium from seawater by up to 50 percent.

ORNL's new technology is made from polyethylene fibers—the same material used to make grocery bags and milk cartons. Researchers can melt, spin and braid these plastic fibers. Afterward, they can zap it with an electron beam to open grafting sites and chemically add metal-catchers called amidoxime groups. These modifications turn this everyday plastic into "a fancy heavy-metal fisherman," said Yatsandra Oyola, a member of ORNL's research team.

Despite recent progress, researchers acknowledge additional work is needed to make the technology commercially viable. Fishing for uranium is still five times more expensive than mining it on land, but as land reserves are depleted and uranium prices rise, the technology will become more attractive. The notable cost reduction provided by HiCap suggests that, with additional tweaks, the product could be the key to ensuring nuclear energy security for generations. The ability to extract uranium from seawater, no matter the expense, will allow the government to make decisions about the future of nuclear power with the confidence that the material will be available in the long term.

"The government often funds projects that are developing technologies like HiCap that won't be commercialized immediately," said Erich Schneider, a project collaborator from the University of Texas at Austin. "They are trying to develop it to the point that, if in the future we run out of uranium on land, a company can take the adsorbents off the shelf and quickly commercialize them."

Laboratory tests have shown that collecting uranium is as easy as submerging the product in water for minutes or several days, said Chris Janke, one of HiCap's inventors and a member of ORNL's research team. Scientists envision dropping many metal chains tied to hundreds of 60-meter-long adsorbent fibers into the sea—packing the seabed with row upon row of HiCap Adsorbent fibers and creating something resembling an underwater cornfield. The HiCap field could extend for thousands of square miles along the sea floor, covering an area comparable to two Rhode Islands.

Uranium would be harvested after 30 to 60 days. Ships would float over the submerged fibers and wirelessly detach them from the chains by sending a signal from a handheld device, allowing the fibers to float to the surface. At that point the fibers and any trapped uranium could easily be scooped up and shipped back to labs. Chemists could then extract the uranium from the fibers and regenerate the adsorbents so the fibers could be reused.

Researchers from seven universities and a variety of national laboratories are collaborating with ORNL's team to improve the uranium extraction process. They are focusing their efforts on using carbon-based materials instead of polyethylene fibers, alternative chemical coatings to amidoxime and less harsh chemical treatments for stripping metals. Other researchers are determining HiCap's potential environmental impacts and performing economic analyses.

"We are just scratching the surface on what this product is capable of," Janke said. "The product design will have to be a compromise among binding capacity, durability, amount of chemical groups and price."

In the meantime the adsorbents originally created to catch uranium from seawater can take center stage in environmental cleanup efforts and the recovery of precious metals.

Because HiCap's adsorbents are selective for heavy metals other than just uranium, the technology can be used to extract toxic or valuable dissolved metals from a variety of water sources worldwide. Nets fashioned from HiCap adsorbents and placed throughout contaminated streams could selectively remove other heavy metals, improving water quality and rehabilitating aquatic ecosystems.

"It's a very competitive product for certain types of environmental remediation and metal recovery applications because it's not that expensive to make," Janke said. Researchers believe the heavy metal waste collected can be recycled, potentially allowing HiCap adsorbents to start paying for themselves.

No matter the need, HiCap—or an improved version of the technology—can change the game for a wide variety of applications.

"We have a material that we know can work," Janke said. "Now we just need to figure out the best places to use it and make sure that it's deployed effectively." —Jennifer Brouner