Magnesium sulphate recovery from seawater nanofiltration brine using photothermal membrane crystallization

Global magnesium (Mg) demand is rising due to its applications in different fields. Seawater, with ~1350 mg/L dissolved Mg, offers a sustainable source. Conventional methods like solar evaporation and chemical precipitation are slow and inefficient alongside fundamental inability to recover pure water. In this regards, Membrane Distillation Crystallization (MDCr) presents a technologically advanced alternative, enabling the simultaneous extraction of Mg and high-purity water. However, MDCr is also limited by high energy consumption and issues like polarization and scaling. Hence, this study introduces photothermal membrane crystallization (PhMCr) as a promising solution to both conventional as well as MDCr related challenges. In this work, PhMCr was explored for the recovery of pure magnesium sulphate heptahydrate (MgSO 4 ·7H 2 O) crystals from last stage of multistage nanofiltration (NF) synthetic retentate. Graphene oxide (GO) coated polyvinylidene fluoride (PVDF) membrane has been utilised for the photothermal experiments. The membrane shows surface temperature of 66.3 °C under 1 sun condition in