Solid–Liquid Phase Equilibrium in the Na₂CO₃+Na₂SO₄+H₂O System at 298.15 K and 101 kPa by Isothermal Titration Microcalorimetry

Abstract

Phase diagrams of aqueous saline systems constitute the cornerstone of the brine puri cation industry. Although ternary phase diagrams may be studied using many experimental methods, the developed isothermal titration microcalorimetry (ITC) approach is simple, generic, and can be extended to the investigation of phase diagrams of multi-salt aqueous solutions and other related systems. In this study, the phase equilibrium of one complex ternary system, Na 2 CO 3 Na 2 SO 4 H 2 O, with several hydrated salts and a double salt, was determined using ITC with the aid of X-ray diffraction, di erential scanning calorimetry, and thermogravimetry. The isobaric and isothermal titration methods can not only determine the boundaries of di erent phase regions by changes in the slope of the heat evolved vs. time plot or in the slope of the observed heat vs. solvent concentration plot, but also provide additional information regarding the hydration heat of ions and hydrates, dissolution heat, and dilution heat. The use of ITC can be extended to complex systems after optimization of data processing.