Extracting uranium from seawater – could it provide a reliable energy source?
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Researchers at the Chinese Academy of Sciences may have found the potential to guarantee a long-term supply of uranium from seawater with a new material that can absorb 20 times more uranium from the world’s oceans than previous approaches.
In the past, experiments have focused on sheets of acrylic fibre that can extract small amounts of the element from the sea, but uranium’s low concentration in water – about 3 parts per billion – make it a challenge to refine on top of the process being very capital intensive.
Still, around 400 billion tonnes of uranium is found in the Earth’s sea, which is 500 times the amount known to exist in land-based ores.
And breakthroughs such as this will continue to be needed to facilitate the world’s push towards decarbonisation, with the research team stating this new method could provide a reliable energy source to last thousands of years at current rates of consumption.
Linsen Yang and his colleagues at the Chinese Academy of Sciences created a polymer membrane with small channels that branch into even smaller tunnels, mirroring the way that blood vessels bifurcate into ever-smaller passages within mammalian organs and limbs.
The material was impregnated with a compound called amidoxime, which binds to uranium ions and then passed water laced with uranium through the material and used X-ray photoelectron spectroscopy to detect whether the element was captured.
What they found was that the membrane not only absorbed up to 20 times as much as previously developed materials did but it could also be cleaned with hydrochloric acid, which extracts 98 per cent of the uranium – meaning the material could be used for long periods of time.
Other critical minerals found in the ocean, such as lithium, have also been widely explored for extraction.
Back in June, a group of researchers at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia used an electrochemical cell containing a ceramic membrane made from lithium lanthanum titanium oxide (LLT) to extract high-purity lithium from seawater.
Its crystal structure, containing holes, allowed lithium ions to pass through while blocking larger metal ions.
The cell contains three compartments – seawater flows into a central feed chamber, where positive lithium ions pass through the LLTO membrane into a side compartment that contains a buffer solution and a copper cathode coated with platinum and ruthenium.
Negative ions then exit the feed chamber through a standard anion exchange membrane, passing into a third compartment containing a sodium chloride solution and a platinum-ruthenium anode.
The cell generates hydrogen gas at the cathode and chlorine gas at the anode, driving the transport of lithium through the LLTO membrane, where it accumulates in the side-chamber.
This lithium-enriched water then becomes the feedstock for four more cycles of processing, eventually reaching a concentration of more than 9,000 ppm.
According to the researchers, the cell would only need US$5 of electricity to extract 1 kilogram of lithium from seawater.
But as exciting as these breakthroughs are, Tim Buckley, director of energy finance at the Institute for Energy Economics and Financial Analysis (IEEFA) says not only is the cost of commercialisation not discussed, but an obscene amount of seawater would be needed to undergo the extraction process.
“To me we don’t have to look at getting three parts of uranium out of the water, it sounds very speculative,” he said.
“What we do know is that solar is already the low-cost source of electricity – it is clean, it is cheap, it is domestic, and it is only going to get dramatically cheaper over time, as will the cost of wind, the cost of lithium-ion batteries and electric vehicles.
“As a result, the energy transition is going to accelerate.
“We’ve already seen how it is a massive disruptor – about 10 per cent in annual deflation of power generation costs.”
And where there is high radiation and low population density, Buckley said solar will kill nuclear, coal, and fossil fuels.
“By that I’m talking about India, Chile, Mexico, Texas, and most of all Australia – solar will be a massive disruption because it is so low cost and so deflationary.”
However, Buckley added uranium is going to play a material part of the Chinese electricity system going forward.
“China is a massive fossil fuel importer, they have a decarbonisation pledge – they are committed to nuclear and will well and truly be able to fund the capital cost of trying to commercialise something like this.
“But how long is a piece of string?”