Phase Equilibria in Water–Methanesulfonic Acid–Nickel (Cobalt) Methanesulfonate Systems: Experiment and Modeling

Novel solubility and VLE data were obtained for Ni(CH3SO3)2 and Co(CH3SO3)2 in acidic solutions. The isothermal solubility method was used to obtain an isothermal cross section at 298.15 K for Ni(CH3SO3)2–CH3SO3H–H2O and Co(CH3SO3)2–CH3SO3H–H2O systems. Ni(CH3SO3)2·12H2O is the stable solid phase in nonacidic solutions, and it is acidic up to 20 wt % methanesulfonic acid (MSA). Co(CH3SO3)2·6H2O is the stable phase in solutions with 0–20 wt % MSA, while Ni(CH3SO3)2·6H2O is the stable phase only in acidic solutions with 20–40 wt % MSA. In both systems, Me(CH3SO3)2·4H2O (Me = Co, Ni) is a form stabilized in equilibria solutions only in the presence of acid (from 20 and 40 wt % MSA for Me = Co and Ni). Me(CH3SO3)2·4H2O solubility reaches ∼5 wt % in acidic solutions with an acid content, which decreases in the row Ni > Zn > Co > Cu. Water vapor pressure was measured in the 288.15–308.15 K range to calculate water activity. The Pitzer–Simonson–Clegg model was used for liquid phase modeling. Ternary parameters were evaluated for the first time, which are needed for a correct solubility prediction. The water activity is predicted with a higher accuracy without ternary parameters. The solubility constant for Co(CH3SO3)2·6H2O was reevaluated, and for Ni(CH3SO3)2·4H2O it was estimated at 298.15 K.