Chinese researchers have developed a new material – inspired by the fractal networks of blood vessels – that they say can extract 20 times more uranium from seawater than other approaches.
Uranium, a naturally occurring radioactive element, is mostly used to fuel nuclear power plants. As demand grows for nuclear power globally, the need for uranium is also increasing.
It is a finite resource, but since the oceans are estimated to hold more than 4.5 billion tonnes of uranium – about 1,000 times more than the reserves on land – extracting it from seawater could potentially be a more sustainable approach to nuclear power.
However, there are very low concentrations of uranium in seawater – estimated at 3.3 micrograms per litre – making it far more difficult and expensive to extract from the oceans than to mine from the ground.
Scientists saw the potential to use oceanic uranium to fuel nuclear energy in the 1950s, but it took until the 1980s for Japanese researchers to develop a way to extract it – using a chemical compound called amidoxime to bind to floating uranium particles.
The new research, led by scientists at the Chinese Academy of Sciences, was focused on improving the adsorption capacity of this compound. Their findings were published in the journal Nature Sustainability in late November.
The scientists created a porous membrane that was modelled on fractals found in nature, like blood vessels. They found that the membrane – which was saturated in amidoxime – was significantly more efficient in extracting uranium than other materials used previously, with an adsorption capacity 20 times higher.
“Fractals such as blood vessels are ubiquitous in biological systems. They allow for the optimised exchange and transformation of substances. It has inspired us in designing new adsorbents,” Yang Linsen, lead author of the study, said in a statement.
Over a four-week period, they found that 1 gram of the membrane extracted up to 9.03 milligrams of uranium from natural seawater – among the highest yield using a membrane method.
“Our work provides a universal method for enhancing the applicability of porous polymers as efficient membrane-based uranium sorbents,” the study said.
Yang and his co-authors did not immediately respond to email inquiries about the study.
The material developed by the Chinese team could be seen as equal to or superior to many contemporary adsorbents, according to a separate article on the study in the same journal by Alexander Wiechert and Sotira Yiacoumi from the Georgia Institute of Technology, and Costas Tsouris of Oak Ridge National Laboratory.
But they said the study did not mention the effect of biofouling – where organisms build up on submerged surfaces – on the membrane, saying it could have an impact on the material’s uranium adsorption capacity.
They also noted that the membrane adsorbed a number of other molecules from the seawater – not just uranium – such as vanadium, iron, zinc and copper, so a method to separate them would be needed.
“However, the current progress, alongside efforts by other researchers from around the globe actively investigating this topic, draws us closer and closer to the development of a practicable adsorbent,” the US-based scientists said.
Climate change has accelerated the development of nuclear power in many countries, especially in China. The country had about 50 gigawatts of installed nuclear capacity at the end of last year, with 18.5GW under construction. Beijing plans to have 120GW of installed nuclear capacity by 2030 – or 8 per cent of China’s power generation, up from 5 per cent last year.
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