Americium maximum concentrations

Additional work in progress includes optimization of parameters affecting the oxalate precipitation step this includes determination of the chloride concentration required to solubilize lead the oxalate ion concentration required for maximum americium recovery with minimum impurity precipitation precipitate aging and hydrogen ion concentrations that will minimize americium solubility yet maximize impurity solubilization. 

Maximum extraction occurs from 1 to 3 M HNO3 into o-nitrophenyl-hexyl-ester and the following separation factors were measured with respect to trivalent americium for 1 mM ligand concentration and 10-4 M metal ions Sf(Am/Ln or Cm) = 2.00 (La), 52 (Ce), 1.72 (Nd), 2.78 (Sm), 5.15 (Eu), 7.15 (Cm). Following this study numerous CMPO-substituted calix[4]arenes have been synthesized and tested. 

The usual effect of increasing the acid concentration is reported to be an increase in the (due to increased amounts of the extractable MA3 in the aqueous phase) followed by a decrease in the (due to formation of the extractant-HNC adduct), resulting in a maximum extraction at an acid concentration between 2 and 6 M. However, one study has noted an increase in americium extraction at nitric acid concentrations from 12 to 16 M. These data are not consistent with the usual view of americium distribution dependence on nitric acid and nitrate concentration, and the authors hypothesize that a TBP HN03 adduct, which is a stronger extractant for americium than TBP alone, is formed above 8 M HNO3 and an organic-phase complex of Am(N03)3 (TBP mHNC ) is formed rather than Am(N03)3 nTBP (26). While one may not absolutely discount this possibility, additional factors such as the extraction of HAm(N03) and deviations from ideal activities in such concentrated acid solutions should definitely be considered. 

When 3.5 mo % of the acidic beta-diketone hexafluoroacetylacetone was used in combination with 2.7 mol% tributyl phosphate, 76% 2 of the plutonium and 93% 1 of the americium could be extracted in a single 45 minute extraction at 65 °C. When the ligand concentrations were increased to 6.8 mol% hexafluoroacetylacetone and 5.3 mol% tributyl phosphate, and the extraction temperature was increased to 95 °C, a maximum of 83% 5 plutonium and 95% 3 americium were extracted. The SFE results for the TBP - HFA system are given in Table II. 

---