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The diluent has influence on the intensity and nature of interaction among the constituents during solvent extraction. The physico‐chemical property of the phase where diluent is present required examination for optimizing the extraction conditions. The assessment of extraction efficiency is done on the basis of interaction between extractant and diluent. Densities, dielectric constants, and refractive indices have been measured for the binary mixture of octanoic acid/tri‐n‐butyl phosphate (TBP) with n‐hexane at T=303, 308 and 313 K over the whole constitution range. The dielectric constant, molar polarisation, refractive index and molar refraction values are maximum at 0.7674 mole fraction of octanoic acid and at 0.6577 of tri‐n‐butyl phosphate in binary mixture with n‐hexane. The values were used to further find out the molar polarization, molar refraction, correlation factor and excess Gibbs free energy. The excess values of the different properties were evaluated and fitted to the Redlich‐Kister polynomial equation. Negative values of ϵE were observed for octanoic acid and n‐hexane binary mixture at 308 and 313 K suggesting the dipoles were not aligned. For tri‐n‐butyl phosphate and n‐hexane binary mixture, positive ϵE values indicated the reduced number of aligned dipoles. The correlated motion of dipoles was explained by calculating the g values using Kirkwood‐Frohlich equation with the aid of dielectric and refractive index values of the pure solutes. [ABSTRACT FROM AUTHOR]

Solvent extraction is one of the hydro metallurgical techniques adopted due to its ease for efficient separation of metal ions. The separation and extraction of metals are enabled using privileged metal distribution between the aqueous and organic phase. Commercially available solvent extractants and recently the designer solvents like ionic liquids have gained adequate attention in the area of separation science for the retrieval of different metal ions. Diluents play an important role by ensuring the improved hydrodynamics of the extraction system. The physico‐chemical characteristics of the organic phase solution need to be scrutinized thoroughly in order to optimize the extraction conditions. Investigation on the interaction between extractant and diluent at molecular level is vital for the assessment of extraction efficiency. Density, viscosity, dielectric constant, refractive index, conductivity, and acoustic properties provide evidence on the molecular organizations between these unlike molecules. The aim of this review is to project on the importance of physical, chemical, and thermodynamic properties for fabricating an efficient combination of extractants‐diluents to achieve maximum extraction output. [ABSTRACT FROM AUTHOR]