Effects of Halide Anions on Water Desalination Based on Crystallization Methods: Freezing and Tetrahydrofuran Hydrate Formation

In this study, water desalination was performed using the freezing method and Tetrahydrofuran hydrate formation in a stationary reactor. The experimental setup includes two coaxial cylinders, in which ice crystals deposit outside the cool inner cylinder; thus the salt concentration increases in the residual brine. In order to evaluate the performance of these methods, the removal percentage of salt was measured by the electrical conductivity instrument. The results show that the removal efficiency decreases with an increasing salt concentration in the freezing method while a different trend is observed in the hydrate formation method. As an important result, the salt removal efficiency of the hydrate formation method was higher than the freezing process. Also, to investigate the effect of the anionic size on the salt removal efficiency, the experiments were performed with NaCl, NaBr, NaF, and NaI, which have the same cations. The results show that the performance of desalination improves by increasing the anionic radius. So the dissolved mineral components are removed in the following order: I¯>Br¯>Cl¯>F¯. The removal of salts of a higher size is further by hydrate-based and freezing desalination.