Kinetics of Freeze Crystallization and Eutectic Freeze Crystallization in Binary Aqueous Solutions of Na ₂ SO ₄ , MgSO ₄ , and CuSO ₄

In this study, freezing, salt, and eutectic freeze crystallization (EFC) were investigated for concentrating aqueous solutions and recovering Na2SO4, MgSO4, and CuSO4 hydrates from aqueous sulfate solutions with a batch time of 15 min. Experiments were conducted on samples with varying initial concentrations relative to their eutectic point (EP) conditions for Na2SO4, MgSO4, and CuSO4 at molalities (mol/kg water) of [0.1, 0.2, 0.298 (EP), 0.4, 0.5], [1.4, 1.6, 1.738 (EP), 2, 2.5], and [0.6, 0.7, 0.837 (EP), 1, 1.1], respectively. Temperature and electrical conductivity responses were measured and calibrated against the concentration. Final concentration increases were highest with solutions below the EP and lowest at the EP. A CFD study conducted for a large-scale crystallization model of the 10 m3 jacketed tank equipped with an anchor-type scraper at different tip speeds showed that velocity profiles remain unchanged, while the temperature variation is doubled, and the mixing power required is up to 10 times lower at 22.5 rpm compared to 45 rpm, respectively.