Desalination by cooling and freezing of seawater and groundwater: thermodynamic aspect of the liquid-solid equilibrium

This work focuses on the study of the effect of water composition on the physical properties and thermodynamics of the liquid-solid equilibrium during the desalination process by cooling and freezing. The study was conducted with synthetic ionic aqueous solutions and two real systems, namely seawater from the Atlantic Ocean and groundwater from the coastal area between Ouled Ghanem and Sidi Abed (El Jadida Province, Morocco). The compositions of 73 groundwater wells were grouped statistically in three different classes. The calculation code FREZCHEM based on the thermodynamic model of Pitzer was used to estimate the following properties: activity coefficients, osmotic coefficient, ion composition, salinity, solid phases formed and their appearance temperatures at the liquid-solid equilibrium. The thermodynamic study has quantified the effect of composition and salinity on the freezing temperature, the mass of ice produced and the precipitation temperature of gypsum and mirabilite which alter the purity of ice in the desalination process.