Supercritical Fluid Extraction of Plutonium and Americium from Soil Using β-Diketone and Tributyl Phosphate Complexants

摘要

Supercritical fluid extraction (SFE) of plutonium and americium from soil was demonstrated using supercritical fluid carbon dioxide solvent augmented with organophosphorus and beta-diketone complexants. Soil from a radioactive waste management site in Idaho was spiked with plutonium and americium, chemically and radiologically characterized, then extracted with supercritical fluid carbon dioxide at 2,900 psi and 65°C. The organophosphorus reagent tributyl phosphate (TBP) and the beta-diketone thenoyltrifluoroacetone (TTA) were added to the supercritical fluid as complexing agents. A single 45 minute SFE with 2.7 mol% TBP and 3.2 mol% TTA provided as much as 88% +-6 extraction of americium and 69%+-5 extraction of plutonium. Use of 5.3 mol% TBP with 6.8 mol% of the more acidic beta-diketone hexafluoroacetylacetone (HFA) provided 95% +-3 extraction of americium and 83% +- 5 extraction of plutonium in a single 45 minute SFE at 3,750 psi and 95°C. Sequential chemical extraction techniques were used to chemically characterize soil partitioning of plutonium and americium in pre-SFE soil samples. Sequential chemical extraction techniques demonstrated that spiked plutonium resides primarily (69% +- 2) in the sesquioxide fraction with minor amounts being absorbed by the oxidizable fraction (18% +- 1) and residual fractions (8% +-1). Post-SFE soils subjected to sequential chemical extraction characterization demonstrated that 97% +- 3 of the oxidizable, 79% +- 2 of the sesquioxide and 80% +-2 of the residual plutonium could be removed using SFE. These preliminary results show that SFE may be an effective solvent extraction technique for removal of actinide contaminants from soil.