Effect of the diluents on the interaction between components in the binary mixtures of organophosphorus acid and tertiary amine

In the extraction of rare earth elements (REEs) from chloride solutions by binary mixtures of organophosphorus acid and tertiary amine, the acid-base equilibria in the mixtures and the nature of the diluents affected the synergistic effect. In order to correlate the interaction in the mixtures with the dielectric constant of the diluents, the FT-IR spectra together with the viscosities of individual extractants and binary mixtures in three diluents (n-hexane, xylene, and toluene) were analyzed. The excess viscosities of the mixtures in different diluents were obtained as a function of composition. The IR spectra and excess viscosity data indicated that the interaction between acidic and amine extractants in the binary mixture grew stronger as the dielectric constant of a diluent became lower.