Diamylamylphosphonate Solvent Extraction of Am(VI) from Nuclear Fuel Raffinate Simulant Solution

Abstract

The separation of hexavalent americium from the lanthanides in simulated PUREX raffinate solution using 1 M diamylamylphosphonate in dodecane extraction was investigated. Hexavalent americium was prepared using room-temperature sodium bismuthate oxidation. Under these conditions the majority of the lanthanides were not oxidized and remained inextractable. A separation factor of ∼50 was provided for americium from europium over the nitric acid concentration range 6–7 M. Cerium was the exception with oxidation to Ce^IV resulting in its co-extraction with Am^VI. However, since americium is readily reduced to Am^III it was easily stripped with a dilute acidic solution of hydrogen peroxide. Although hydrogen peroxide also reduces cerium, it does so slowly, and a selective americium strip was achieved, with a separation factor of as high as 35. Alternatively, since americium spontaneously reduced in the loaded organic phase, samples allowed to stand for 2 hours could be selectively stripped of americium by contact with 1 M HNO₃ containing no additional reagents. Further, the separation was demonstrated using solutions containing macro-amounts of cerium and americium. The implications for use in fuel cycle separations are discussed.

Keywords:

• Americium
• americium oxidation
• americium extraction
• minor actinides
• separation
• sodium bismuthate
• phosphonate

ACKNOWLEDGMENT

Work supported by the U.S. Department of Energy, Assistant Secretary for Nuclear Energy, under the Fuel Cycle Research and Development Minor Actinide Separations σ-team; DOE Idaho Operations Office Contract DE-AC07-05ID14517. The authors thank E.P. Horwitz, for initially suggesting the use of DAAP as an Am^VI extraction ligand.