Thermodynamic Properties of NaCl-HCl(aq) and HCl-NaCl-KCl(aq) at a Temperature of 298.15 K

The aim of this study was to expand the application of the hygrometric method to systems that contain volatile electrolytes, specifically, aqueous hydrochloric acid solutions used in hydrometallurgical processes. To achieve this, the Pitzer–Simonson–Clegg model was combined with the hygrometric method to determine the thermodynamic properties of the NaCl-HCl-H2O and NaCl-KCl-HCl-H2O systems. Water activity and solubility were measured at a temperature of 298.15 K and at total ionic strengths ranging from 0.3 to 7.5 mol/kg. The solid state was characterized by using powder X-ray diffraction (XRD). The predicted mean ionic activity coefficient of HCl and the solubilities of mineral salts MCl (M+ = Na+, K+) in aqueous hydrochloric acid solutions containing sodium chloride or sodium and potassium chloride were consistent with previously published literature data as well as the solubility measurements obtained in this study.