Ion migration during freeze-thaw process: A cryo-desalination experiment of saltwater from southern Xinjiang, China

Cryo-desalination is an effective technology of separating freshwater from saline solution. Freeze desalination experiments were conducted using saltwater from southern Xinjiang, China. In gradual freezing and melting experiments, three freezing temperatures were chosen to investigate ion migration pattern during freezing/melting process, and to analyze the key factors governing ion migration under conditions of different ion types (charges, radius) and various initial concentrations. Experimental results showed that in the freezing process of saltwater, the ion migration behaviors appeared a significant correlation with the initial ion concentration, ion radius, and freezing temperature. Monatomic ions with higher concentration and a larger radius were more likely to be “trapped” by ice crystals during freezing at lower temperatures. Sulfate ions were difficult to remove during freezing. Different dissolution concentrations of the ions were evident during melting. Specifically, all the ions were significantly removed from the ice body during the initial melting stage, and ice meltwater type progressively switched from Cl-Na to Cl•SO4-Na during melting. In the process of gradual melting, the ion concentration data of ice meltwater can be well fitted by the ion deviation coefficient equation. The gravity force-driven desalination provides a new algorithm for accurately retaining high-quality ice-melting water.