First grams of uranium extracted from sea water
It has been known for many years that there is more uranium available in the world’s sea water than can foreseeably be produced from land-based mines, if only it could be extracted. Now, for the first time, researchers at Pacific Northwest National Laboratory and LCW Supercritical Technologies have created five grams of yellowcake (70–90% U3O8) — a powdered form of uranium used to produce fuel for nuclear power production — using acrylic fibres to extract it from sea water.
"This is a significant milestone," said Gary Gill, a researcher at PNNL. "It indicates that this approach can eventually provide commercially attractive nuclear fuel derived from the oceans — the largest source of uranium on earth."
LCW Supercritical Technologies (LCW), an Idaho-based clean energy company, developed an acrylic fibre that attracts and holds on to dissolved uranium naturally present in ocean water.
"We have chemically modified regular, inexpensive yarn to convert it into an adsorbent which is selective for uranium, and is efficient and re-usable," said Chien Wai, President of LCW. "PNNL's capabilities in evaluating and testing the material have been invaluable in moving this technology forward."
The adsorbent material is inexpensive, according to Wai. In fact, he said, even waste yarn can be used to create the polymer fibre. The adsorbent properties of the material are reversible, and the captured uranium is easily released to be processed into yellowcake. An analysis of the technology suggests that it could be competitive with the cost of uranium produced through land-based mining.
PNNL researchers have conducted three separate tests of the adsorbent's performance to date by exposing it to large volumes of sea water 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 fibre into the tank for about one month and pumped the sea water through quickly, to mimic conditions in the open ocean," said Gill. "LCW then extracted the uranium from the adsorbent and, from these first three tests, we got about five grams. It might not sound like much, but it can really add up."
Gill notes that sea water contains about three parts per billion of uranium. It's estimated that there is at least four billion tons of uranium in sea water, which is about 500 times the amount of uranium known to exist in land-based ores1, which must be mined.
Mining of underground uranium has environmental challenges not encountered with extracting it from the oceans. And Wai said the fibres, which have affinity for more heavy metals than just uranium, can likely be used one day to clean up toxic waterways themselves. He said the fibres also have potential to extract vanadium, an expensive metal used in large-scale batteries, from the oceans instead of mining it from the ground.
- OECD 2018, Uranium 2016: Resources, Production and Demand, <https://www.oecd-nea.org/ndd/pubs/2016/7301-uranium-2016.pdf>
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