Experimental study on the correlation between ion rejection rate and ice growth rate in freeze desalination*

Freshwater scarcity is one of the most urgent problems worldwide, and it is becoming severe due to global warming. Several seawater desalination methods have been developed to mitigate the water crisis. Among them, the freeze desalination method is a membrane-free approach, and thermodynamically, it consumes less energy than distillation methods because the latent heat of water crystallization is less than that of water evaporation. For freeze desalination methods, the ion rejection rate, which is the percentage of ions in the liquid phase, is an important parameter. It should be sufficiently high to generate portable water. However, due to the thermal motion of ions and the moving front of ice, ion trapping in ice reduces the ion rejection rate. To understand the ice growth rate on the ion rejection rate, we conduct experiments to study the quantitative correlation between the ion rejection and ice growth rates. Experiments show that when the ice growth rate exceeds the critical value of 0.283 mm/min, a linear relationship between the ice growth rate and the ion rejection rate is observed. Below this critical value, the ion rejection rate stabilizes at approximately 84.8%. This study provides helpful information for freeze desalination system design and parameter optimization.