Supercritical fluid extraction of plutonium and americium from soil using thenoyltrifluoroacetone and tributylphosphate complexation

Samples of clean soil from the source used to backfill pits at the Idaho Na tional Engineering and Environmental Laboratory's Radioactive Waste Managem ent Complex were spiked with Pu-239 and Am-241 to evaluate ligand-assisted supercritical fluid extraction as a decontamination method. The actual soil in the pits has been subject to approximately three decades of weathering since it was originally contaminated. No surrogate soil can perfectly simul ate the real event, but actual contaminated soil was not available for rese arch purposes. However, fractionation of Am and Pu in the surrogate soil wa s found to be similar to that previously measured in the real soil using a sequential aqueous extraction procedure. This suggests that Pu and Am behav ior are similar in the two soils. The surrogate was subjected to supercriti cal carbon dioxide extraction, in the presence of the fluorinated beta dike tone thenoyltrifluoroacetone (TTA), and tributylphosphate (TBP). As much as 69% of the Pu and 88% of the Am were removed from the soil using 3.2mol% T TA and 2.7 mol % TBP, in a single 45 minute extraction. Extraction conditio ns employing a 5 mol % ethanol modifier with 0.33 mol % TTA and 0.27 mol % TBP resulted in 66% Pu and 68% Am extracted. To our knowledge, this is the first report of the use of supercritical fluid extraction (SFE) for the rem oval of actinides from soil.