Since the 1960s, researchers have been turning their sights to an unlikely place to harvest uranium: the ocean. Now an Australian-led team has taken the prospect of sea-based uranium harvesting one step closer using materials that are cheap and easy to make.
As the planet begins to slowly move away from carbon-based fuel sources, alternative energy sources begin to come to the fore. While solar, wind and hydroelectric technologies tend to steal the spotlight in this space, nuclear power remains a strong contender. In fact, in 2017, it contributed about 10% of the world's energy production, and in 2022, 8 GW of new nuclear power was integrated into the global grid.
The key to nuclear power generation is uranium, an element found on land in only a handful of countries whose underground supplies will continue to dwindle as nuclear power plants proliferate. However, this is not the case with underwater replenishment. It is estimated that the amount of elements in the world's oceans is about 4.5 billion tons, while the amount on land is only about 6 million tons. This is enough to generate electricity around the world for thousands of years.
However, recovering all the uranium has proven tricky because its concentration in seawater is extremely low.
Scientists at Oak Ridge National Laboratory have had early success with fibers doped with amidoxime chemical groups that have an affinity for uranium. Stanford researchers later electrified the fibers, capturing more of the radioactive elements. Recently, Pacific Northwest National Laboratory was able to extract 5 grams of yellowcake (a uranium powder) from seawater using a special type of acrylic yarn.
Still, these methods are not sufficient to harvest uranium on an industrial scale, which is necessary for nuclear power plants around the world. Trying to find a material that can capture uranium without trapping other sea-based elements has been a challenge.
To overcome these difficulties, researchers at the Australian Nuclear Science and Technology Organization (ANSTO), the University of New South Wales and other colleagues turned to layered double hydroxides (LDH). These relatively easy-to-make materials consist of layers of positively and negatively charged ions. The team doped these LDHs with various chemicals, including neodymium, terbium, and europium, soaked them in seawater, and analyzed the results using enhanced imaging with X-ray absorption spectroscopy.
The researchers found that when neodymium was combined with LDH, the resulting compound was able to capture uranium from seawater as well as more than 10 other more abundant elements. These include sodium, calcium, magnesium and potassium, and are approximately 400 times more abundant than uranium. This selectivity, along with the low cost of producing LDH-doped materials, greatly contributes to the possibility of large-scale harvesting of uranium from seawater, the researchers say.
"These findings demonstrate that doping engineering of LDH provides a simple, efficient way to control selectivity and produce adsorbents capable of challenging separations, such as the extraction of uranium from seawater," the researchers wrote in the study, which has been published as a cover story in the journal Energy Advances.