Development of an improved environmental actinide separation method

Author

Rose Ann Boll

Date of Award

5-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

George K. Schweitzer

Abstract

The focus of this research project was on the separation of five actinide elements (Th, U Np. Pu, and Am) from each other in aqueous media. Many of the current separation techniques are cumbersome, time consuming, costly, create large volumes of waste, and have moderate recoveries. In developing a separation method, the unique chemistries of the actinides were taken into consideration. These include oxidation state variation, complexation, trace element behavior, hydrolytic behavior and matrix interactions.

The overall process for the determination of actinides in environmental samples can be divided into five general steps: sample solubilization, elimination of matrix interferences, separation of the actinide ions from each other, preparation of separated fraction for counting, and alpha particle counting of the separated samples. Each of these steps was investigated.

The majority of the investigations in this project relates to the most difficult step, the separation of the actinide ions from each other. Selective coprecipitations using zirconium phenylarsonate, calcium-magnesium-yt trium fluorides, neodymium fluoride, and metal iodates were tried. These were unsatisfactory because good percents recovery required large amount of precipitate which resulted in poorly resolved spectra. The new ElChroM TRU-Resin™ extraction resin was investigated and showed good promise for the separation of the actinide ions. Therefore, various tests were conducted in order to develop a separation procedure using the TRU- Resin™ resin. These investigations included evaluations of different eluting reagents, adjustments in the concentration of reagents, separations in the presence of high concentrations of certain actinide ions, changes in pH, and the effects of different redox reagents. The various trials were evaluated by percents recovery of the actinide ions.

The final developed method utilizes a single-one milliliter TRU-Resin™ resin column. In order to cleanly recover the five actinides from a solubilized soil matrix, the sample is passed through the column twice. The sample is first loaded in 5.0-M HCI with hydrogen peroxide as the redox reagent. This allows the Am and most matrix ions to pass through the column. The Th is eluted first using 1.3-M HCl, then the Np and Pu are eluted together with 0.030-M oxalic acid in 0.5-M HCI. Finally, the U is eluted with 0.10-M ammonium oxalate. A calcium-oxalate coprecipitation is performed on the Am sample and the dissolved precipitate is then reloaded onto the TRU-Resin™ column in 3.0-M HNO₃ with ascorbic acid as the redox reagent. The overall procedure requires approximately 1.5 working days to perform with percents recovery of the five tested actinides in the 80-100% range.

Recommended Citation

Boll, Rose Ann, "Development of an improved environmental actinide separation method. " PhD diss., University of Tennessee, 1996.
https://trace.tennessee.edu/utk_graddiss/9662