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May 2011

Keeping Up with the f-Block

Pushing the limits in actinide science

Jessica Morrison

(Top) Nanoclusters are created on a small scale and optimized through thousands of syntheses.

(Bottom) Structural image of NDTB-1 showing porous nature of the framework compound.

At the Materials Science of Actinides Energy Frontier Research Center, scientists are uncovering mechanisms that produce novel actinide-based compounds with chemistries relevant to the nuclear fuel cycle and environmental remediation. As the demand for power generation increases, gaining efficiency through fuel reprocessing and the safe storage of used fuel are hot topics in the nuclear industry.

“The actinides are the least explored and understood elements on the periodic table,” says Peter Burns, Director of the Materials Science of Actinides EFRC, “owing to the importance of 5f electrons [outer shell electron complexity], relativistic electron effects, and nuclear instability.”

Actinide nanoclusters could simplify the nuclear fuel cycle: Actinide nanoclusters, ranging in diameter from 1.8 to 3.1 nanometers, are made by reacting depleted uranium with peroxide under basic conditions. Quickly precipitating uranium from solution, these clusters have the potential to eliminate the need for organic-based separations, a process that creates more liquid waste, in the nuclear fuel cycle.

Postdoctoral researcher Jie Ling has been instrumental in synthesizing a suite of uranium-based nanocluster compounds. Ling’s natural curiosity and experience working with carbon-based nanomaterials lend themselves to bench-top successes.

On the experimental nature of working in uranium chemistry, Ling remarks, “I worked with uranium chemistry for four years while pursuing my Ph.D., but I never thought a uranium compound could form as an isolated nanoscale structure.” This formation was unexpected because sheet structures are the predominant formation for hexavalent uranium compounds.

Rare cationic compound selectively removes long-lived technetium: Removing radioactive contaminants from waste sites and the surrounding environment is another area of research at the edge of understanding in actinide science. Doctoral candidate Shuao Wang has synthesized a rare cationic compound that selectively removes technetium –  TcO4- – from solution.

Technetium-99, a radioactive fission product of the uranium nuclear fuel cycle with a half-life of more than 200,000 years, forms an anionic complex making it difficult to remove during traditional separations processes.

In laboratory studies, Wang’s thorium borate compound (NDTB-1) selectively removes TcO4- from solution even in the presence of excess chloride and nitrate ions, Cl- and NO3-. This discovery led to a patent for a compound that is the first of its kind for technetium-99 removal.

According to Wang, the challenge in actinide chemistry is fundamental. “Our experimental results cannot be answered by classical chemical theories.”

More Information

Ling J, J Qiu, JES Szymanowski, and PC Burns. 2011. “Low-symmetry uranyl pyrophosphate cage clusters.” Chemistry: A European Journal 17, 2571-2574. DOI: 10.1002/chem.201003481.

Wang SA, EV Alekseev, DW Juan, WH Casey, BL Phillips, W Depmeier, and TE Albrecht-Schmitt. 2010. “NDTB-1: A supertetrahedra cationic framework that removes TcO4- from solution.” Angewandte Chemie International Edition 49(6), 1057-1060. DOI: 10.1002/anie.200906397.

Acknowledgments

These projects have been supported by the Materials Science of Actinides Center, an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Office of Basic Energy Sciences, the DOE Heavy Elements Program and the Deutsche Forschungsgemeinschafit.

About the author(s):

More Information

Ling J, J Qiu, JES Szymanowski, and PC Burns. 2011. “Low-symmetry uranyl pyrophosphate cage clusters.” Chemistry: A European Journal 17, 2571-2574. DOI: 10.1002/chem.201003481.

Wang SA, EV Alekseev, DW Juan, WH Casey, BL Phillips, W Depmeier, and TE Albrecht-Schmitt. 2010. “NDTB-1: A supertetrahedra cationic framework that removes TcO4- from solution.” Angewandte Chemie International Edition 49(6), 1057-1060. DOI: 10.1002/anie.200906397.

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.