Mixing Enthalpies and Ion-Interaction Models for the Ternary Aqueous Systems Containing Lithium Borates at 298.15 K and 101.325 kPa

A microcalorimeter TAM IV was used to determine the mixing enthalpies for the four ternary systems of LiBO2 (aq) + LiCl/Li2SO4 (aq) and LiB5O8 (aq) + LiCl/Li2SO4 (aq) at 298.15 K and 101.325 kPa. The mixing enthalpies were measured over an ionic strength range from 0.20 to 2.40 mol·kg–1 with the constant ionic strength fraction at 0.5. The profiles of mixing enthalpies against ion strength for the four systems were revealed. However, LiBO2 (aq) + LiCl (aq) and LiB5O8 (aq) + LiCl/Li2SO4 (aq) are endothermic, and the system LiBO2 (aq) + Li2SO4 (aq) exhibits the opposite result. Similarly, the mixing enthalpies of these four systems increase with the increasing of ionic strength. Compared with Cl–, the existence of SO42– has a greater impact on the stability of the binary system (LiBO2 + H2O), indicating that the interaction between SO42– and B(OH)4– is much greater than that between Cl– and B(OH)4–. Besides, the Pitzer mixed ion-interaction parameters of θL and ΨL were obtained accurately, which is significant to guide the separation of lithium and boron from salt lakes.