Scientists from India announced last week that they have successfully extracted uranium from natural seawater. The uranium mined from the earth and used for the production of fuel for nuclear power plants (NPPs) is a depleting resource, while the World Nuclear Association estimates land-based uranium reserves to be around 5.9 million tonnes. These uranium reserves are expected to be exhausted within a century.
Instead, seawater is estimated to contain around 4.5 billion tonnes of uranium, although scientists have been grappling with the issue of the technology for its cost-effective extraction. Uranium concentration in seawater at around only 3 micrograms per litre makes its extraction a highly challenging task, as well as a very costly affair since it requires processing massive amounts of seawater.
Uranium recovery from seawater is considered extremely challenging owing to its very low concentration. According to the World Nuclear Association, uranium concentrations in seawater are significantly lower than those found on land. Thus, the challenge would be extracting the uranium economically at such low parts per million.
Scientists at the Indian Institute of Science Education and Research (IISER), Pune, have been working to extract uranium from seawater and have recently published their findings in the journal of the Royal Society of Chemistry. Researchers have for long been faced with the challenge of developing a proper adsorbent to extract uranium from seawater that combines the features of high capacity, excellent selectivity, and ultra-fast kinetics.
This team of scientists at IISER have developed a sponge-like macroporous adsorbent Metal-Organic Framework (MOF) which showed high uranium extraction capabilities. They managed to capture 95 percent of uranium within two hours, which is in sharp contrast to the other existing adsorbents.
The IISER scientists collected seawater from the Arabian Sea off the coast of Mumbai for uranium extraction, and the adsorbent resulted in a record uranium uptake capacity of 28.2 mg per gram in only 25 days, which “satisfies the remarkable uranium extraction from seawater standard only in 2 days compared to existing adsorbents, including commercially available materials reported so far”, according to their findings.
Lead scientist Sujit K. Ghosh, told reporters that “combined with exceptional selectivity, record capacity, ultrafast kinetics, and long service life, this material could be a potential candidate for the efficient extraction of uranium from natural seawater. The selective ion exchanged harvesting method introduces the concept of extracting uranium from natural seawater which may lead to an unlimited supply of uranium at an economically affordable cost.”
“The design is such that the macroporous nature allows uranium cation to enter and remain inside the natural trap site which gets created inside the MOF (Metal-Organic Framework)”, Ghosh added.
“With rising global energy demand and environmental concerns associated with fossil fuels, sustainable energy supply to the global community remains a great challenge. Large-scale uranium extraction from seawater (UES) is widely considered as reconciliation to increasing global energy demand and climate change crises”, the group of IISER scientists said in their paper.
Last year, an Indian scientist from the Central Salt and Marine Chemicals Research Institute, Shilpi Kushwaha, was conferred the Young Scientist Award for her work in developing a method to extract uranium from secondary sources such as seawater and acidic effluents using crystalline thin films and polymer nanorings.
“We have been able to extract uranium from acidic effluent as well as seawater. In future, we will try to make it cost-effective after improvisation so that uranium can be extracted on a larger scale and is commercially viable”, Kushwaha said.
“The demand for energy is increasing day by day. It’s expected that in the near future the demand for nuclear energy will increase worldwide as it is carbon neutral. However, the uranium reserves are limited and it is estimated that it would be exhausted in over 100 years”, she said.
“Uranium extraction from seawater (UES) is amongst the seven chemical separations processes where progress would lead to global gains. UES provides additional benefits to the energy security of any country. It is independent of terrestrial uranium ore which reduces the concerns of environmental damage from land-based mining”, she added.
According to Kushwaha, the heavy metal extracted from seawater is at par with the similar experiments done globally. Some years back, the US Department of Energy (DOE) noted that, in the 1990s, the Japan Atomic Energy Agency pioneered materials that hold uranium as it is stuck, or adsorbed, onto surfaces of the material submerged in seawater.
Subsequently, the DOE put together a team from US national laboratories, universities and research institutes to address the challenges of economically extracting uranium from seawater. The team has developed new adsorbents that reduce the cost of extracting uranium from seawater by three to four times, according to the DOE. It said that one adsorbent material developed had the capacity to hold 5.2 grams of uranium per kilogram of adsorbent in 49 days of natural seawater exposure.