Abstract
Formo‐ and aceto‐hydroxamic acids are very effective reagents for stripping tetravalent actinide ions such as Np(IV) and Pu(IV) ions from a tri‐butyl phosphate phase into nitric acid. Distribution data for Np(IV) in the presence of these hydroxamate ions have now been accumulated and trends established. Stability constants for aceto‐hydroxamate complexes of Np(IV) and Np(V) ions have also been determined in a perchlorate medium, and these reaffirm the affinity of hydroxamate ligands for actinide (IV) ions over actinyl (V,VI) ions.
Acknowledgements
The authors wish to thank G. Brown (Nexia Solutions) and Analytical Services, Sellafield Ltd., for assistance in the course of this work. This work was funded by BNFL and the Nuclear Decommissioning Authority.
Notes
1Note that the wavelengths of the proposed 1∶1 Np(V)‐AHA peak in and the 1∶3 Np(IV)‐AHA peak in are coincident (∼988 nm). In , an assignment of the 988 nm absorption to Np(IV) rather than Np(V) is supported by: (1) the Full Width at Half Maximum (FWHM) is 22 nm, which is two times higher than a FWHM of 11 nm in the 1∶1 Np(V)‐AHA complex in ; (2) the molar absorptivity of the 1∶1 complex of Np(V) is 380 M−1cm−1, so if we assume that the 988 nm peak in the Np(IV) titration experiment belongs to the 1∶1 Np(V)‐AHA complex, it gives an expected optical absorbance for this species of 0.00219 (M)×380 (M−1cm−1)×1 (cm) ×1 (yield)=0.83. This disagrees with an experimentally measured value of ∼0.092. Clearly other solution phase structural studies would be more conclusive but these were outside the current scope.