Researchers from the Pacific Northwest National Laboratory (PNNL) and LCW Supercritical Technologies have created for the first time five grams of yellowcake, using acrylic fibers to extract it from seawater.
Yellowcake is a powdered form of uranium used to produce fuel for nuclear power production. Typically it is found from mining underground uranium, but this has environmental challenges. However, extracting it from the oceans is not nearly as toxic to the environment.
"This is a significant milestone," said Gary Gill, a researcher at PNNL, a Department of Energy national laboratory and the only one with a marine research facility, located in Sequim, Washington. "It indicates that this approach can eventually provide commercially attractive nuclear fuel derived from the oceans -- the largest source of uranium on earth."
The team developed an acrylic fiber which attracts and holds on to dissolved uranium naturally present in ocean water. This chemically modified inexpensive “yarn” was converted into an adsorbent which is selective for uranium. Researchers said even waste yarn can be used to create the polymer fiber. The adsorbent properties of the material are reversible and the captured uranium is easily released to be processed into yellowcake.
The better news is that the process could be competitive with the cost of uranium produced through land-based mining. Also, the fibers could likely be used one day to clean up toxic waterways themselves with the potential to extract vanadium, an expensive metal used in large-scale batteries, from the oceans instead of mining it from the ground.
PNNL researchers have conducted three separate tests of the adsorbent’s performance by exposing it to large volumes of seawater from Sequim Bay next to its Marine Sciences Laboratory. The water was pumped into a tank about the size of a large hot tub.
"For each test, we put about two pounds of the fiber into the tank for about one month and pumped the seawater through quickly, to mimic conditions in the open ocean," Gill said. "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."
Seawater contains about three parts per billion of uranium and it is estimated that there is at least four billion tons of uranium in seawater—about 500 times the amount of uranium known to exist in land-based ore that must be mined.
The next step is to conduct further tests in the Gulf of Mexico, where the water is much warmer. The warmer water allows the fibers to perform much better and extraction rates in the Gulf are expected to be three to five times higher.