August 21, 2012

Oakridge Absorbents five to seven times better at extracting uranium from seawater

Fueling nuclear reactors with uranium harvested from the ocean could become more feasible because of a material developed by a team led by the Department of Energy's Oak Ridge National Laboratory.

The combination of ORNL's high-capacity reusable adsorbents and a Florida company's high-surface-area polyethylene fibers creates a material that can rapidly, selectively and economically extract valuable and precious dissolved metals from water. The material, HiCap, vastly outperforms today's best adsorbents, which perform surface retention of solid or gas molecules, atoms or ions. HiCap also effectively removes toxic metals from water, according to results verified by researchers at Pacific Northwest National Laboratory.

"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 ORNL's Materials Science and Technology Division.

New Scientist - To make this process more economical, ORNL chemical scientist Sheng Dai says US researchers used plastic fibres with 10 times more surface area than the Japanese design, allowing for a greater degree of absorption on a similar platform.

They tested their new design at the PNNL's marine testing facility in Washington State. The results show the new design cuts the production costs of a kilogram of uranium extracted from seawater from $1232 to $660.

While extracting uranium from seawater is still five times more expensive than mining uranium from the Earth, the research shows that seawater uranium harvesting could be a much-needed economic backstop for the nuclear industry moving forward into the 21st century.



HiCap effectively narrows the fiscal gap between what exists today and what is needed to economically extract some of the ocean's estimated 4.5 billion tons of uranium.

What sets the ORNL material apart is that the adsorbents are made from small diameter, round or non-round fibers with high surface areas and excellent mechanical properties. By tailoring the diameter and shape of the fibers, researchers can significantly increase surface area and adsorption capacity. This and ORNL's patent pending technology to manufacture the adsorbent fibers results in a material able to selectively recover metals more quickly and with increased adsorption capacity, thereby dramatically increasing efficiency.

"Our HiCap adsorbents are made by subjecting high-surface area polyethylene fibers to ionizing radiation, then reacting these pre-irradiated fibers with chemical compounds that have a high affinity for selected metals," Janke said.

After the processing, scientists can place HiCap adsorbents in water containing the targeted material, which is quickly and preferentially trapped. Scientists then remove the adsorbents from the water and the metals are readily extracted using a simple acid elution method. The adsorbent can then be regenerated and reused after being conditioned with potassium hydroxide.

In a direct comparison to the current state-of-the-art adsorbent, HiCap provides significantly higher uranium adsorption capacity, faster uptake and higher selectivity, according to test results. Specifically, HiCap's adsorption capacity is seven times higher (146 vs. 22 grams of uranium per kilogram of adsorbent) in spiked solutions containing 6 parts per million of uranium at 20 degrees Celsius. In seawater, HiCap's adsorption capacity of 3.94 grams of uranium per kilogram of adsorbent was more than five times higher than the world's best at 0.74 grams of uranium per kilogram of adsorbent. The numbers for selectivity showed HiCap to be seven times higher.

"These results clearly demonstrate that higher surface area fibers translate to higher capacity," Janke said.

ORNL researchers conducted field tests of the material at the Marine Sciences Laboratory of Pacific Northwest National Laboratory in Sequim, Wash., and at the Rosenstiel School of Marine and Atmospheric Science and Broad Key Island in collaboration with the University of Miami.

Prior Nextbigfuture coverage of uranium from Seawater work

In marine science, current strength is sometimes measured in “Sverdrups”, a unit that corresponds to one million tons of water per second, or 3 × 10^13 tons of water per year.

Ugo, a critic of uranium from seawater used locations and methods that make the case for uranium from seawater 100 to 1000 times worse than better plans and methods.

Ugo looks at the Strait of Gibraltar which carries a current of about 1 Sverdrup. Japan has proposed various scaling up plans for uranium from seawater They look at the Black Current (42 Sverdrup, 42 times stronger than the current Ugo looked at) in the ocean off of Japan and how much materials it is moving. They would put uranium extraction materials in its path and collect uranium and other resources as they are moved past the materials that would trap the resources.

Ugo assumed recovering one kilogram of uranium, therefore, would require processing at least 3 tons of membranes per year.

Ugo calculates using the ratio of 5 kWh/kg for energy expenditure in fishing, and assuming the yield and the conditions reported by Seko , we can calculate a total energy expenditure of about 1000 TWh/year for processing the membranes to give sufficient amounts to fuel the present needs of the nuclear industry. This is close to the total energy that could be produced by the extracted uranium, ca. 2600 TWh/year. An energy gain (EROEI) of 2.6 is larger than unity, but it is too low for the process to be of practical interest.

Japan is looking at offshore processing, which would save the fuel costs of bringing the absorbent from the ocean to a land based facility

Ugo also bases his calculations on once through reactors. Switching to advanced breeder reactors or extensive reprocessing can increase the efficiency of uranium usage by 60 times.

A Japanese plan for scaling up extracting uranium from seawater



Japan has lab scale work for extraction of uranium from seawater that is about twice the current cost of traditionally mined uranium using cotton dipped in juice with a lot of tannins.

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