The world’s estimated reserves of uranium are only 6 million tons and with the growing demand for reliable energy free of greenhouse emissions leading to more and more nuclear plants being built, that supply may not last very long. Some estimates place the time before all the uranium is gone at between 50 and 200 years. However, the oceans of the world contain 4.5 billion tons of uranium dissolved in seawater. That’s enough to last something on the order of 6,500 years. The tricky bit is getting it out, but a team at Oak Ridge National Laboratory, Tennessee has come a step closer to economically extracting uranium from seawater with a new material that is much more efficient than previous methods.
Ever since it was learned how much precious metal is dissolved in seawater, scientists, engineers, visionaries and con men have dreamed of ways to extract it. In the 1920s, popular science editor Hugo Gernsback graced the covers of his magazines with fanciful floating factories hauling giant sheets of gold out of the briny deep. Since the 1960s, almost a dozen nations have studied ways of making the dream a reality. The Japanese have been particularly successful with the the Japan Atomic Energy Research Institute having some success in extracting uranium using mats of woven polymer fibers in 2002, but at a cost three times the market price of the metal at the time. That is the basic problem – you can get the metal out, but it costs more than it’s worth.
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Now a team at Oak Ridge is working to bring down those costs by devising a more efficient method of extraction. The Oak Ridge team’s approach is based on their examination of how plastic and chemical groups are bound together. From this, they determined that it was possible to enhance the uranium-extracting characteristic of the uranium-loving amidoxime chemical groups in their high-capacity reusable adsorbent, which they combined with a Florida company's high-surface-area polyethylene fibers. These fibers have a small diameter with high surface areas and a variety of shapes. Tailoring the size and shape of the fibers increases their adsorption capacity. The fibers are bombarded with radiation, which react with chemicals that have a high affinity for particular metals. The result is a little uranium sponge.
Using the material, called Hicap, is simply a matter of immersing it in seawater. As it sits in the water, the material grabs on to the uranium ions and deposits them on the surface of its fibers. Once a sufficient amount of uranium is adsorbed, the material is removed and the metal extracted with acid. "We have shown that our adsorbents can extract five to seven times more uranium at uptake rates seven times faster than the world's best adsorbents," said Chris Janke, one of the inventors and a member of Oak Ridge’s Materials Science and Technology Division. HiCap is also reusable as, after the extraction process, it can be regenerated with potassium hydroxide.
The results of the Oak Ridge team were verified by researchers at Pacific Northwest National Laboratory’s Marine Sciences Laboratory in Sequim, Washington, and were presented a last Wednesday’s meeting of the American Chemical Society in Philadelphia. The material is a long way from making uranium as common as pig iron, but it does demonstrate that extracting it from the oceans may no longer be a con man’s dream.