Interlayer confinement mediated oxidation of americium by sodium bismuthate and stability of its higher redox states in acidic solution.

Mutual separation of trans-plutonium actinides (Ans) from lanthanides (Lns) or adjacent Ans is challenging as they exhibit great chemical similarity. Selective Am oxidation-based Am–Lns or Am–Cm separation strategies give very high separation factors. There exist several reports on different aspects of Am3+ oxidation by NaBiO3·xH2O (x = 2–3), which suggests that the oxidation mechanism is still not well understood. We, therefore, carefully performed several experiments taking advantage of the difference in the redox chemistry of Eu3+ and Am3+. The ion exchange of Eu3+ with the interlayer Na+ in NaBiO3 was confirmed by an ionic strength variation experiment. The shift in the 001 peak of NaBiO3 in XRD and the appearance of peaks corresponding to the trivalent Ln ions in XRF after Ln3+ loading give direct evidence for Na+ exchange with Ln3+. The stability of the higher oxidation state of Am was monitored spectrophotometrically. The experimental investigations also suggested the role of Am3+ → AmO22+ transformation in NaBiO3·xH2O (x = 2–3) dissolution even at pH ∼ 1, which otherwise is difficult to achieve even with >1 M HNO3. The role of colloidal NaBiO3 particles and dissolved BiO3− in controlling or stabilizing different oxidation states of Am was also discussed. [ABSTRACT FROM AUTHOR]