Transport behaviour of water and nitric acid in tributyl phosphate/n-dodecane mixtures

Abstract

The diffusion coefficients of water and nitric acid in different mixtures of tributyl phosphate (TBP)/n-dodecane were measured with the aid of an analytical ultracentrifuge, in order to elucidate the transport behaviour in the organic phase of the PUREX process. Measurements were made at 298 K for different solute concentrations, the TBP content of the organic solutions being varied from pure TBP to a 30/70 (v/v) TBP/n-dodecane mixture. The Stokes' radii and the molecular volumes of the solute particles were evaluated for each system from diffusion coefficients and viscosity by an approximate method based on Stokes' law. Comparisons of the molecular volumes obtained from diffusion with those from density measurements showed that, in the presence of n-dodecane, aggregares of the particles are formed, which consist of water and nitric acid bound to TBP molecules. In pure TBP, however, the diffusion of water was faster, indicating that the molecules then move separately by a slipping mechanism.