Tributylphosphate Extraction Behavior of Bismuthate-Oxidized Americium

Abstract

Higher oxidation states of americium have long been known; however, options for their preparation in acidic solution are limited. The conventional choice, silver-catalyzed peroxydisulfate, is not useful at nitric acid concentrations above about 0.3 M. We investigated the use of sodium bismuthate as an oxidant for Am (3+) in acidic solution. Room-temperature oxidation produced AmO 2 (2+) quantitatively, whereas oxidation at 80 degrees C produced AmO 2 (+) quantitatively. The efficacy of the method for the production of oxidized americium was verified by fluoride precipitation and by spectroscopic absorbance measurements. We performed absorbance measurements using a conventional 1 cm cell for high americium concentrations and a 100 cm liquid waveguide capillary cell for low americium concentrations. Extinction coefficients for the absorbance of Am (3+) at 503 nm, AmO 2 (+) at 514 nm, and AmO 2 (2+) at 666 nm in 0.1 M nitric acid are reported. We also performed solvent extraction experiments with the hexavalent americium using the common actinide extraction ligand tributyl phosphate (TBP) for comparison to the other hexavalent actinides. Contact with 30% tributyl phosphate in dodecane reduced americium; it was nevertheless extracted using short contact times. The TBP extraction of AmO 2 (2+) over a range of nitric acid concentrations is shown for the first time and was found to be analogous to that of uranyl, neptunyl, and plutonyl ions.

Americium(III) oxidation by copper(III) periodate in nitric acid solution as compared with the action of Bi(V) compounds of sodium, lithium, and potassium

“…In any of these cases, the challenge is oxidizing the Am and maintaining the higher oxidation state during the separation step. It was first demonstrated in the 1970s, and more recently confirmed, that Am(III) can be oxidized to Am(VI) by sodium bismuthate (NaBiO 3 ) in a nitric acid solution [3][4][5][6], which, unlike sodium persulfate, does not lose its oxidative efficiency at greater than 0.5 mol/L concentration of HNO 3 [7][8][9]. One of the disadvantages of NaBiO 3 as an oxidant for Am(III) is a slow dissolution rate and its limited solubility in HNO 3 .…”

Separation of oxidized americium from lanthanides by use of pillared metal(IV) phosphate-phosphonate hybrid materials

“…We were unable to reproduce a reported literature preparation [2], but the following process did give stable Am(V). First, 230 mg of Na 2 S 2 O 8 was added to a 1 mL of roughly 0.1 M HClO 4 containing 2.23 × 10 −4 mols of 243 Am in a narrow window 1 cm screw cap cuvette.…”

“…For the interested reader a recent review article has just been published on the higher oxidation states of Am [15]. Only a handful of reports have been published discussing the synthesis and stabilization of oxidized Am [2,[16][17][18][19][20][21][22][23][24][25][26][27][28]. In acidic media the pentavalent americium is highly unstable and readily reduces to Am(III).…”

“…Cs + and Sr 2+ need to be removed to reduce the heat load as they are highly radioactive with ∼ 30-year half-lives. Americium and curium need to be separated from the lanthanides generated during fission and further separate americium from curium with an aim to implement transmutation into fuel cycle technologies [2]. It is highly desirable to implement transmutation process as this will greatly reduce the radiotoxicity of the high-level-waste [3].…”

Separation of curium from americium using composite sorbents and complexing agent solutions

“…Americium(VI) can be separated from curium(III) by Am(VI) extraction with bis(2,6-dimethyl-4-heptyl)phosphoric acid (HD(DIBM)P) [27,28], tributyl phosphate (TBP) [29,30], or dibutyl butyl phosphonate (DBBT) [31]. On the other hand, Am(V) is not extracted under the conditions when Cm(III) is, for example by 2-thenoyltrifluoroacetone (TTA) [32] or its synergistic mixture with tri-noctylphosphine oxide (TOPO) [33].…”