The Pacific Northwest National Laboratory (PNNL) in association with LCW Supercritical Technologies has made an important breakthrough for the nuclear industry by extracting 5 grams of powdered uranium, called yellowcake, from ordinary seawater. The new process uses inexpensive, reusable acrylic fibers and could one day make nuclear energy effectively unlimited.
Along with salt, a liter of seawater also contains sulfates, magnesium, potassium, bromide, fluoride, gold, and uranium. There isn't much of the latter – something like 3 micrograms per liter (0.00000045 ounces per gallon), but when you consider how big the ocean is, that works out to 500 times more uranium in the sea than could be mined on land – that's 4 billion tons, or enough to run a thousand 1-gigawatt fission reactors for 100,000 years.
The tricky bit is how to get the uranium out of the water. One approach developed by the Japan Atomic Energy Institute used polymer mats that would draw the uranium atoms out of solution. But this was very expensive, and a cheaper process that involved doping polymers with amidoxime and then irradiating them was developed at Oak Ridge National Laboratory.
While this showed more promise, PNNL and Idaho-based LCW took it a step further by taking ordinary acrylic yarn and converting it into a uranium adsorbent. The exact details of the process haven't been released, but PNNL says that the yellowcake sample shows that not only does the technique work, but that the acrylic can be cleaned and reused.
In addition, the technique can even use waste fibers for a greater cost savings and that analysis shows that seawater extraction could be competitive with land mining at present prices.
For the test, the yarn was placed in tanks and seawater circulated over it. As the water flowed, the yarn fibers extracted the uranium by chemically bonding it to a molecule. After processing, the result was five grams of uranium oxide or yellowcake.
"For each test, we put about 2 lb (1 kg) of the fiber into the tank for about one month and pumped the seawater through quickly, to mimic conditions in the open ocean," says Gary Gill, a researcher at PNNL. "LCW then extracted the uranium from the adsorbent and, from these first three tests, we got about five grams — about what a nickel weighs. It might not sound like much, but it can really add up."
Another thing that could add up is the fact that the uranium dissolved in seawater is in a state of pseudo-equilibrium. That is, so long as it remains at its present level, no more will be absorbed from the rocks that form the seabed. If large scale extraction were implemented over thousands of years, that concentration would fall, and more uranium would leach out of the rock. That's a potential 100 trillion tons or enough to satisfy Earth's energy needs for the next billion years ... by which time the human race will probably have moved on.
In addition to uranium extraction, PNNL says that the technique could also be used to clean up waterways contaminated by heavy metals. In the meantime, LCW is seeking to license the technique and is finding funding for large scale tests in the warm waters of the Gulf of Mexico.
The video below shows the recent PNNL tank test.
Source: PNNL
