Modelling Np(IV) Solvent Extraction between 30% Tri-Butyl Phosphate and Nitric Acid in the Presence of Simple Hydroxamic Acids

Formo- and aceto-hydroxamic acids are very effective reagents for stripping tetravalent actinide ions from a tri-butyl phosphate phase into nitric acid. A model describing the partitioning of actinide (IV) ions has been derived accounting for reactions in the aqueous and solvent phases, including complex formation with nitrate and hydroxamate ions. Predicted distribution ratios for Np(IV) are compared with experimental data in the presence of aceto-hydroxamate ions. Additionally, a value of 0.473 (+/- 0.004) kgmol-1 for the Np(IV) ion interaction coefficient with nitrate ions (epsilon Np4+-NO3-) was determined.