A Novel Method for Maintaining Low and Constant Salinity in Ice during Desalination of Binary Mixtures Using Directional Top-Cooling Solidification

Abstract

Freezing-based desalination shows potential with lower energy needs and less environmental impact. However, current freezing methods produce ice with inconsistent salt levels, and new solutions are needed. This paper proposes a novel method inspired by Czochralski’s (directional top-cooling solidification) techniques, where motion is introduced during solidification to achieve uniform low salinity in ice. Three distinct setups were employed: setup 1 utilized conventional top-cooling, while setups 2 and 3 incorporated directional top-cooling solidification akin to the Czochralski method. The conventional top-cooling approach often leads to nonuniform salinity distribution within ice structures due to complex convection phenomena, whereas directional top-cooling solidification ensures uniform salinity throughout the ice volume by allowing denser solutes to accumulate at the bottom of the tank. Experimental results demonstrate uniform salinity levels along the lengths of ice, measuring 0.34 ± 0.04 wt % NaCl for 1.7 wt % NaCl solution and 0.7 ± 0.05 wt % NaCl for 3.4 wt % NaCl solution. In multistaging desalination, this saline ice again melts and is further desalinized using the same leads to 0.1 ± 0.05 wt % NaCl, which can be directly used for the drinking stage. Additionally, energy analysis indicates a ∼5% reduction in consumption compared to conventional top-cooling methods, highlighting the technique’s efficiency for sustainable desalination.