Water purification by freezing and gas hydrate processes, and removal of dissolved minerals (Na+, K+, Mg2+, Ca2+)

This research investigates the potential of crystallization technologies containing the freezing method and process of gas hydrate formation in water desalination processes. For this purpose, component of tetrahydrofuran was used as a hydrate former with hydrate structure II. The initial brine solutions were supplied from salts of NaCl, KCl, CaCl2, MgCl2 and also Caspian seawater. After formation of crystal (ice or hydrate) and separation of those from residual brine solution, the distilled water was produced by melting the crystals. The removal efficiency of salts is estimated in range of 40 to 80% for hydrate-based desalination and freezing processes. The results show that the removal efficiency is further at the lower driving force and lower concentrations of salt. Also the removal efficiency of salts depends on the ionic size and the electrical charge. The removal of Na+ and K+ ions is better than that of Ca2+ and Mg2+ ions by the desalination based on crystallization methods. Moreover, the water desalination process based on hydrate formation requires the lower cooling to provide the requirement driving force beside the higher efficiency. (c) 2015 Published by Elsevier B.V.