Transforming seawater into a viable fuel may sound like a dream, up there with turning water into wine—but there may be something in it.
This is the conclusion of a team of researchers from China, who have developed a new way to extract nuclear fuel from the world’s oceans.
While nothing to worry about next time you take a trip to the beach, radioactive uranium is found in seawater in extremely low concentrations, in the form of uranyl ions.
Lead author and chemist professor Rui Zhao of the Northeast Normal University in Changchun, China, told Newsweek: “Uranium is an inherent element in the oceans.”
It is thought to have gotten there, he added, from the erosion of “rocks and soil when the Earth began.”
The main fuel for nuclear power stations, the researchers note, is uranium. This element’s advantage is that all of its forms are unstable and naturally breakdown by radioactive decay.
This makes uranium atoms easy to split—a process scientists call “fission”—which releases energy in the process. This energy is used to turn water into steam, which drives a turbine, which creates electricity.
At present, uranium is mined from rocks, but the problem is that uranium ore deposits are finite.
As the team explained in their study, “the limited uranium resource reserves on land have become a serious obstacle to sustainable nuclear energy industry development.”
However, Zhao and his colleagues think we could use another source of this precious element instead—albeit one that is very spread out.
They said: “Comfortingly, the uranium reserves in seawater are estimated to be 4.5 billion tons—nearly 1,000 times larger than terrestrial uranium reserves.”
“Uranium extraction from natural seawater is critical to addressing the shortage of uranium resources,” Zhao said. However, he added, a problem comes in the fact that getting uranyl ions out of water is a “giant challenge!”
Scientists have developed various materials for performing this trick—yet existing solutions have been limited by not having enough surface area to effectively trap the ions.
To overcome this, Zhao and his team set out to develop a material with loads of microscopic nooks and crannies that could be used to make a uranium-capturing electrode.
(Perhaps familiar from school classes on how batteries work, electrodes are terminals that conduct electrical current into and out of medium—whether that be the “electrolyte” in a battery cell, or seawater in the case of the researcher’s system.)
To start with, the team used carbon fibers to weave a flexible cloth, which they then coated and treated with special compounds.
The result was a porous structure with many tiny pockets in which an uranium-grabbing adsorbent known as “amidoxime” can nestle and easily trap the target uranyl ions.
To demonstrate the potential of their system, the team put it through its paces processing both uranium-spiked and natural seawater collected from the Bohai Sea, which lies on China’s east coast.
In their setup, the cloth serves as the negative electrode, while a graphite rod served as its positive counterpart. A cyclic current was run between the pair.
Operating over the course of 24 days, the researchers found that the electrodes were able to extract 12.6 milligrams of uranium per gram of water.
This prospective fuel appeared as a bright uranium-based substance that precipitated out from the seawater onto the cathode cloth.
The coated materials, they said, outperformed most of the other uranium-extracting materials also tested for comparison’s sake.
Furthermore, the researchers reported that using electrochemistry to trap uranyl worked roughly three times faster than allowing the ions to accumulate naturally on the cloths.
There are some limitations to the concept, Zhao cautioned, with the uranium concentration of the world’s oceans being very low, at just 3.3 parts per billion of seawater.
“If the uranium in the seawater can be fully extracted, producing one gram of uranium needs 303,000 liters of seawater,” he said.
This is the equivalent of more than 3,000 bathtubs of water.
To keep a nuclear reactor in fuel, Zhao conceded, “the seawater demand is huge!”
Nevertheless, the team concluded, the study provides “an effective strategy for uranium extraction from seawater through the electrochemical process.”
With their initial study complete, the researchers are now looking to refine their electrode design.
Zhao added: “Moreover, we also want to test the performance in a real ocean environment.”
The technique could easily be scaled up, he explained, and used to operate a facility floating on the ocean surface that could be powered by solar, tidal or wind energy.
Source: Newsweek
