Phase equilibria and thermodynamic properties of phases in the manganese methanesulfonate – methanesulfonic acid – water system: experiment and calculations

The cross section of the phase diagram of the Mn(CH3SO3)2–CH3SO3H–H2O system at 298.15 K is obtained by the isothermal solubility method. The Mn(CH3SO3)2∙2H2O dihydrate is shown to be in equilibrium with solutions containing from 0 to 58 wt% acid. In this ternary system, the bulk properties of solutions at 298.15 K are obtained for a number of compositions, and in its subsystem Mn(CH3SO3)2–H2O they are obtained in the temperature range 288.15 K – 323.15 K. A semi-empirical Laliberté approach is used to describe the bulk properties. The water activities in the temperature range 288.15-323.15 K are calculated by the static method using the measurement results of the saturated vapor pressure. In the Mn(CH3SO3)2–CH3SO3H–H2 system, the possibility of estimating the solubility and activity of water using only the binary parameters of the Pitzer-Simonson-Clegg model for the liquid phase and the known solubility constant at 298.15 K is checked. It is shown that only binary parameters are insufficient for adequate prediction of solubility, it is necessary to take into account at least one parameter of ternary interaction.