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Distribution data for the partition of nitric acid between nitric acid solution and a solvent phase comprising various combinations of TODGA, octanol, and inert kerosene diluent have been generated, covering a range of conditions from 0 to 9 mol/L HNO3(aq), 0–100% octanol, 0–0.4 mol/L TODGA over a temperature range from 10°C to 50°C. The data have been used to derive a model describing the nitric acid equilibrium between the phases suitable for incorporation in process models of the innovative SANEX process, for example. For the nitric acid/octanol/diluent system, it was found that an accurate prediction of nitric acid distribution could be achieved using a model allowing 1:1, 1:2, and 1:3 nitric acid/octanol adducts. For the nitric acid/TODGA/diluent system, the best models were found to be those allowing 4:1, 3:1, 2:1, 1:1, and 2:2 nitric acid/TODGA adducts. Superimposing the models for nitric acid distribution into the individual extractants and comparing with experimental results for the nitric acid/octanol/TODGA system showed systematic differences indicative of antagonistic and synergistic effects applying in the ranges 0.5–1.5 mol/L HNO3 and >1.5 mol/L HNO3, respectively. These effects were modelled by the inclusion of 0:1:2, 1:1:1, 2:1:3, and 3:1:2 nitric acid/TODGA/octanol adducts. The effect of temperature on nitric acid extraction was well described by an Arrhenius type expression with an activation energy of −25.7 kJ/mol. No diluent dependence was found for nitric acid extraction. [ABSTRACT FROM AUTHOR]

The tridentate diglycolamide ligandN,N,N′,N′-tetraoctyl diglycolamide (TODGA) shows many interesting properties and is a very good extractant for the minor actinides (MAs) and lanthanides but, due to its low loading capacity, requires a phase modifier when used in a solvent extraction process. Consequently, applications of TODGA in conjunction with tri-butyl phosphate (TBP) in novel DIAMEX and SANEX processes for recovering MAs have been reported. However, TODGA and TBP also extract nitric acid and this has a significant influence on process performance. Here new distribution data for the extraction of nitric acid into solvent phases containing TODGA and TBP have been collected and modeled using an equilibrium-based approach accounting for nitric acid activities in the aqueous phase. Models for the extraction of nitric acid using the individual extractants were obtained using a variety of complexes and these were then combined to give the extraction of the mixed TODGA and TBP solvent. Using this approach, the nitric acid extraction of the mixed TODGA/TBP system can be reliably reproduced indicating that no significant synergistic or antagonistic complexes are formed in solution. [ABSTRACT FROM PUBLISHER]

The Grouped Actinide Extraction (GANEX) process is being developed for actinide recycling within future nuclear fuel cycles. Interactions between potential solvents and macro-concentrations of plutonium are one of the most important issues in defining the GANEX process. Surprisingly, plutonium loading of diglycolamide (DGA) based solvents such as tetra-octyl DGA (TODGA) causes precipitation rather than a conventional third phase, in direct contrast to results with U(VI), Th(IV) or lanthanide ions. Various DGA based solvent systems have been screened for their plutonium loading capacity and 0.2 M TODGA with 0.5 M DMDOHEMA in a kerosene diluent is selected as the optimum solvent formulation of those tested. Plutonium can be relatively easily stripped from this solvent using aqueous acetohydroxamic acid but this is very acid dependent in the low acidity region. [ABSTRACT FROM PUBLISHER]