Isopiestic measurements of water activities and thermodynamic modeling for CuCl2−MCl2−H2O (M = Mg, Ca) ternary system at t = 298.15 K

Abstract

Water activities of the CuCl 2 −MCl 2 −H 2 O ( M = Mg, Ca) ternary systems and their sub-binary systems have been measured by the isopiestic method at 298.15 K. The maximum concentrations of the CuCl 2 −H 2 O, MgCl 2 −H 2 O and CaCl 2 −H 2 O binary systems are 5.28 mol•kg −1 , 5.25 mol•kg −1 and 6.61 mol•kg −1 , respectively. The concentrations of mixture solution rang from 0.91 mol•kg −1 to 5.69 mol•kg −1 for CuCl 2 −MgCl 2 −H 2 O system, and 1.29 mol•kg −1 to 6.87 mol•kg −1 for CuCl 2 −CaCl 2 −H 2 O system. The measured water activities of the sub-binary systems are consistent with the experimental results reported in literature. The measured equal water activities in the ternary systems strongly deviate from the Zdanovskii-Stokes-Robinson (ZSR) lines. The Pitzer model, Pitzer-Simonson-Clegg (PSC) model and Reaction model were selected to correlate and predict the water activity obtained in this work and the solubility reported in literature for the CuCl 2 −MCl 2 −H 2 O ( M = Mg, Ca) ternary systems at 298.15 K. It was found that, the Pitzer model and PSC model cannot consistently represent these thermodynamic properties, with the binary and mixing parameters that already reported or fitted in this work. However, the Reaction model, representing the different competition association ability of common-anions and water molecules with different cations, can successfully predictethe water activity and solubility isotherms in these ternary systems at 298.15 K with binary parameters only. Applying the Reaction model, some examples of the Cu-bearing species distribution as a function of MgCl 2 (CaCl 2 ) molalities are given and used to account for how the structure variation of a electrolyte solution influences its macroproperties.