Desalination by directional freezing: an experimental investigation

Desalination of saline waters by freezing is one of the oldest methods for desalination, which relies on the principle that the ice crystal structure cannot accommodate salts during its formation, and salts are rejected during phase transformation. Despite its numerous merits as compared to thermal desalination processes, such as low energy requirements, minimum corrosion potential and no scale formation on surfaces, and its suitability for remote areas, small societies, and cold regions, yet it has been neglected during the last few decades. In the present work, an investigation was conducted to determine the effect of directional freezing on the salinity of the produced ice. Containers of different configurations and sizes, which were filled with saline water of different initial concentrations, were subjected to gradual freezing, then sliced into several equal sections from top to bottom, and the ice allowed to melt in separate containers, while other configurations were sliced into circular annular sections of different radii, then all the samples were analyzed for NaCl. Variables studied for their effect on the salinity, included container configuration, initial saline concentration (C-i) (5, 15, 25 and 35 g/L), and vertical/radial distances. It was found that concentration increased from periphery to center and from top to bottom. The freezing and solubility curves of NaCl-water system were calculated using the perturbed-chain statistical associating fluid theory (PC-SAFT) with the corresponding melting temperatures and enthalpies of fusion of the pure substances using the binary parameter (ki(j)) of -0.1793 for NaCl-water system.