Brine rejection and crystallite formation upon freezing NaCl aqueous solutions

Studying the freezing of saltwater is of fundamental importance for improving methods of acquiring fresh water from seawater via cryo-desalination, as well as for modeling artic ice and iceberg dynamics due to climate change. Here, we probe with x-ray diffraction the freezing process in NaCl solutions for different salt-water concentrations, ranging from seawater conditions to brine. A simple linear superposition model can well reproduce brine rejection due to ice Ih formation and we quantify the relative ratio between the brine and ice. In addition, we perform molecular dynamics simulations to model the formation of NaCl crystallites and we observe signatures of ion-water cross-correlations due to ion inclusion within the ice Ih lattice evident in the diffraction pattern. This study demonstrates a sensitive method of detecting salt trapped inside the ice in the form of crystallites and can provide valuable insight to improve desalination efficiency from a molecular perceptive.