Scientists extract uranium from seawater

In 2011 the DOE put together a team from U.S. national laboratories, universities and research institutes to address the challenges of economically extracting uranium from seawater. Now, the team has developed new adsorbents that reduce the cost of extracting uranium from seawater by three to four times, according to the energy department, which first released their results in April. 

The DOE explains the technology and results in a press release from the DOE’s Oakridge National Laboratory:

That teamwork culminated in the creation of braids of polyethylene fibers containing a chemical species called amidoxime that attracts uranium. So far, testing has been conducted in the laboratory with real seawater; but the braids are deployable in oceans, where nature would do the mixing, avoiding the expense of pumping large quantities of seawater through the fibers. After several weeks, uranium oxide–laden fibers are collected and subjected to an acidic treatment that releases, or desorbs, uranyl ions, regenerating the adsorbent for reuse. Further processing and enriching of the uranium produces a material to fuel nuclear power plants.

Marine testing at PNNL showed an ORNL adsorbent material had the capacity to hold 5.2 grams of uranium per kilogram of adsorbent in 49 days of natural seawater exposure—the crowning result presented in the special issue (published in the journal Industrial & Engineering Chemistry Research).

How much uranium is in the ocean? According to the DOE press release the oceans hold more than four billion tons of uranium— “enough to meet global energy needs for the next 10,000 years if only we could capture the element from seawater to fuel nuclear power plants.” While that sounds like a lot of potential nuclear fuel, a quick check of the World Nuclear Association website shows that uranium concentrations in seawater are significantly lower than those found on land. The real challenge, therefore, would be extracting the uranium economically at such low parts per million.

For example uranium exists in the Earth’s continental crust in concentrations of 2.8 parts per million, versus 0.003 parts per million in seawater. The highest-grade uranium ore, for example in Saskatchewan’s Patterson Lake region, has concentrations of 200,000 parts per million. The World Nuclear Association estimates there is a total of 5.9 million tonnes of uranium available, none of it presumably calculated from seawater; the four largest producers, in descending order, are Australia, Kazakhstan, Russia and Canada.

Supply of uranium. Graphic from the World Nuclear Association.

In 2014 a team of German geochemists found a way to extract rare earth metals from the solid nodes of iron and manganese found strewn across much of the deep ocean floor.

The nodules, called ferromanganese deposits, build slowly over time as dissolved iron and manganese in seawater attaches to seafloor sediments.

Researchers claimed they were able to extract up to 80% of four rare earth metals from ferromanganese nodules by refining their ore-leaching method.