Salt recovery from a reverse osmosis brine by eutectic freeze crystallization method for waste brine management

Freeze desalination (FD) is a promising method for the treatment of desalination brines due to its ability to recover clean water and solid salts with a low energy compared to traditional techniques. In this work, eutectic freeze crystallization (EFC) for a reverse osmosis brine was conducted to investigate the feasibility of using EFC for the recovery/removal of different salts such as sodium sulfate (Na₂SO₄), magnesium sulfate (MgSO₄), and sodium chloride (NaCl). An indirect freeze crystallization experiment was conducted on the effect of temperature reduction on multi-component ions of the brine. Additionally, thermodynamic modeling of the brine was developed in order to simulate the experimental setup. Subsequently, a comparison with the experiment was performed to assess the developed theoretical model. Thermal analysis revealed the production of ice and salt crystals like mirabilite (NaSO₄.10H₂O) and hydro-halite (NaCl.10H₂O). The FD achieved high water recovery of approximately 88% with recovered solid salts of NaSO₄.10H₂O and NaCl.10H₂O with yields of 16.7g/L and 79.4 g/L, respectively. Ionic analysis compared with theoretical modeling suggests that components such as sodium, magnesium, and chloride might be recovered as solid hydrates from brine with considerable quantities. The study gives an outlook of the step towards achieving zero liquid discharge resulting in high water recovery, effective use of salt resources as well as brine volume reduction.