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| Fig. 1: Extracting uranium from the ocean is difficult because the ocean is so vast. (Source: P. Voigt) |
Currently, due to the expensive infrastructure of mining land uranium, only ten countries are responsible for 94% of the world's uranium extraction. [1] The limited reserves of terrestrial uranium has caused a political motivation to find novel sources of uranium. [2] Developing country are increasing their dependence on nuclear power, which they view as a source of large amounts of reliable power that reduces carbon emissions and pollution levels. [3] Therefore, there have been a surge in dependence on the harvesting of uranium from seawater to continue viability of nuclear power generation, particularly to power emerging economies.
The worlds oceans contain 3 parts per billion of uranium, which is about 3 milligrams of uranium per cubic meter. [4] Assuming we could recover half of this resource, this much uranium could support 6,500 years of nuclear capacity. [5]
Even though there is a large supply of uranium in seawater, there are political and physical challenges in oceanic uranium extraction. [1] The ocean's 4.5 billion ton supply of uranium is in the form of ions, or more specifically water-soluble uranyl (UO22+) which is present at a very low concentration (14 nM). [2] The low concentration is then dissolved in an extremely large volume of water (all the world's oceans) which span 1.3 billion cubic km. [4] Then, the uranyl is tightly bound by carbonate and other anions, and exists in seawater, where there are many other metal ions at much higher concentrations (for example 10 mM calcium). [6] These two properties make extracting the uranium extremely difficult. To meet these challenges, recent research publications cited advances and presented alternative methods in extracting uranyl from seawater. [6]
Not only is extraction difficult, it is also very costly. Separating the uranium ions from other more abundant metal ions requires high affinity, selectivity and the ability to deal with an enormous volume of water. [6] This has presented several design and physics challenges which a few physicists have explored. Japanese research suggests the lowest possible cost to extract uranium is 25,000 Yen per kilogram of uranium or 230 USD per kilogram of uranium (at current exchange rate April 2018, 1 USD = 108 JPY). The price of this uranium is 3 times more than the current price of uranium, and it is expected that the actual recovery price would be about 10 times the current price of uranium. [5]
The deviation from nuclear energy as a source of power has created a chain reaction of rising costs. [7] Many companies who produced the parts for the reactors went under and research on more cost effective ways of extracting uranium declined. [7] Fossil fuels and gas became cheaper removing the need to find new sources, more efficient sources of fuel. Yet for some developing nations, they still rely almost entirely on nuclear energy. As countries like China and Russia continue building new technology, uranium extraction from seawater could see more efficiency and lower costs in the near future. [3]
© Paige Voigt. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. Emsley, Nature's Building Blocks: An A to Z Guide to the Elements (Oxford University Press, 2002).
[2] C. Akahori, and M. Holloway, eds. "A New Nuclear Era: The U.S. Role in the Shifting Global Energy Landscape," University of Washington, 2017.
[3] "Uranium 2014: Resources, Production and Demand," International Atomic Energy Agency, 2014.
[4] N. Seko et al., "Aquaculture of Uranium in Seawater by a Fabric-Adsorbent Submerged System." Nucl. Technol. 144, 274 (2003).
[5] K. Ferguson, "Uranium Extraction from Seawater", Physics 241, Stanford University, Winter 2012.
[6] M. Tamada et al., "Cost Estimation of Uranium Recovery from Seawater with System of Braid Type Adsorbent," Trans. At. Energy Soc. Jpn. 5, 358 (2006) [in Japanese].
[7] P. Fairley, "Why Don't We Have More Nuclear Power?" Technology Review, 28 May 15.