SAN FRANCISCO, Feb. 18 (Xinhua) -- Researchers at Stanford University have create a conductive hybrid fiber incorporating carbon and amidoxime in their search of a new way of extracting uranium from seawater.
It has been long known that uranium dissolved in seawater combines chemically with oxygen to form uranyl ions with a positive charge. Extracting these uranyl ions involves dipping plastic fibers containing a compound called amidoxime into seawater. The uranyl ions essentially stick to the amidoxime. When the strands become saturated, the plastic is chemically treated to free the uranyl, which then has to be refined for use in reactors.
While how practical this approach depends on three main variables, namely how much uranyl sticks to the fibers, how quickly ions can be captured and how many times the fibers can be reused, the Stanford researchers improved on all three variables: capacity, rate and reuse.
By sending pulses of electricity down the newly created hybrid fiber, the researchers altered the properties of the fiber so that more uranyl ions could be collected.
"Concentrations (of uranium in seawater) are tiny, on the order of a single grain of salt dissolved in a liter of water," said Yi Cui, a materials scientist and co-author of a paper in Nature Energy. "But the oceans are so vast that if we can extract these trace amounts cost effectively, the supply would be endless."
Postdoctoral scholar Chong Liu oversaw the lab tests that compared Stanford's amidoxime-carbon hybrid fibers with today's amidoxime fibers. First she tested how much uranyl each type of fiber could hold before reaching saturation. She found that by the time the standard amidoxime fiber had become saturated, Stanford's amidoxime-carbon hybrid fibers had already adsorbed 9 times as much uranyl and were still not saturated. What's more, the electrified fiber captured three times as much uranyl during an 11-hour test using seawater from Half Moon Bay, about an hour from Stanford, and had three times the useful lifespan of the standard amidoxime.
The findings build on years of research in Japan and China, as well as at the Oak Ridge National Laboratory and the Pacific Northwest National Laboratory in the United States.
Professor Steven Chu, a Nobel Prize-winning physicist and co-author of the Nature Energy article, said research on seawater extraction has to proceed in parallel with reactor safety and waste disposal challenges. "For much of this century, some fraction of our electricity will need to come from sources that we can turn on and off. I believe nuclear power should be part of that mix, and assuring access to uranium is part of the solution to carbon-free energy," he said.
Nuclear power currently generates 20 percent of electricity in the United States and 13 percent worldwide.
"We need nuclear power as a bridge toward a post-fossil-fuel future," Chu, a former U.S. secretary of energy who encouraged seawater extraction research before he left the Department of Energy (DOE) to return to Stanford, was quoted as saying Friday in a news release from Stanford. "Seawater extraction gives countries that don' t have land-based uranium the security that comes from knowing they'll have the raw material to meet their energy needs."
Hailing the new findings as big steps toward practicality, Cui acknowledged that "we have a lot of work to do still."