Modeling activity coefficients in alkali iodide aqueous solutions using the extended Debye-Huckel theory

A recently developed extended Debye-Huckel (EDH) theory which allows for concentration variation of electrolyte solution static permittivity (I.Yu, Shilov, A.K. Lyashchenko, 2015) is employed to predict activity coefficients in alkali metal iodide (LiI, NaI, ICI, and CsI) aqueous solutions at ambient conditions. Calculations without parameter fitting have shown a semiquantitative agreement with experimental data, reproducing the nonmonotonic concentration dependence of activity coefficients for Lit, NaI, and ICI solutions. A good agreement with experimental data was obtained for NaI-water mixtures in the concentration range up to 7 mol/kg. The correct ordering of activity coefficients for the salts with different cations was also reproduced and explained as resulting not only from decreasing solvation in the series LiI > NaI > KI > CsI but also due to increasing ion pairing with increasing cation size. The applicability limits of the EDH theory are outlined. (C) 2017 Elsevier B.V. All rights reserved.