Directional amine-based solvent extraction for simultaneous enhanced water recovery, salt separation and effective descaling from hypersaline brines

The feasibility of simultaneous water recovery, salt separation and effective descaling of hypersaline brine was investigated by diisopropylamine (DIPA)-based directional solvent extraction (DSE), using diluted/concentrated seawater with initial saline concentration range of 12–237 g/L at extraction temperatures of 5 and 15 °C, respectively. The water recovery shows an obvious boundary at saline concentration of 115 g/L under dual effect of specific water extraction efficiency and extraction cycles. High Cl − ion concentration in product water is in sharp contrast to the nearly complete removal of SO 4 2− and hardness ions, indicating that DIPA-based DSE process indeed achieved efficient separation and purification of Cl − ion from hypersaline brines. Especially, the radical precipitation of Mg 2+ and Ca 2+ ions in form of Mg(OH) 2 and CaCO 3 demonstrates effective descaling potential, although it leads to more DIPA residues in dewatered raffinate than product water. Moreover, an exponential correlation between the Cl − removal efficiency and specific water extraction efficiency further reveals the intrinsic relationship of water extraction process and transfer of Cl − ion to the product water. Overall, the study provides a novel approach for integrating the water recovery and separation of Cl − ion from ultra-high-salinity brines with radical precipitation of Mg 2+ and Ca 2+ ions in one step.