Fig. 2: Brine concentration and crystallization processes.

a, Mechanical vapour compression using a thermal evaporation mechanism but powered by electricity. b, Membrane distillation using low-grade heat to concentrate brine to near saturation. c, Electrodialytic crystallization using an electric field to remove ions from the feed and enrich them in a closed brine loop to induce crystallization. d, Solvent extraction desalination leveraging the dependence of water–solvent miscibility on environmental conditions (such as temperature and vapour pressure) to extract water from brine and to produce near pure water. e, Natural evaporation using evaporation pond or its variants with either light-adsorbing materials to enhance photothermal energy conversion or 3D structures to increase evaporation area. These systems are considered passive owing to the lack of electric components for separation or flow circulation. f, Convection-enhanced evaporation with two examples including wind-aided intensified vaporization (WAIV) and a water cannon. These processes are considered semi-active because they have electrical components that do not provide the primary driving force for separation.