The structure of tributyl phosphate solutions: Nitric acid, uranium (VI), and zirconium (IV)

Diffusion, rheology, and small angle neutron scattering (SANS) data for organic phase 30 v/v %tributyl phosphate (TBP) samples containing varying amounts of water, nitric acid, and uranium or zirconium nitrate were interpreted from a colloidal perspective to give information on the types of structures formed by TBP under different conditions. Taken as a whole, the results of the different analyses were contradictory, suggesting that these samples should be treated as molecular solutions rather than colloids. This conclusion is supported by molecular dynamics (MD) simulations showing the existence of small, molecular aggregates in TBP samples containing water and nitric acid. Interpretation of TBP and nitric acid diffusion measurements from a molecular perspective suggest that nitric acid and metal species formed are consistent with the stoichiometric solvates that have traditionally been considered to exist in solution. (C) 2017 Elsevier B.V. All rights reserved.