Salty water quietly supplies chlorine, iodine and much of our lithium
Brine sounds like something for pickles. Yet run an electric current through salt water and you get chlorine, caustic soda and hydrogen in one go. Iodine and bromine are wrung from brines too, much of the world's lithium sits in them, and cold brine sprays freeze fish on some trawlers.
Brine is simply water heavy with dissolved salt, usually sodium or calcium chloride. Seawater sits near the bottom of the range at about 3.5%, and a fully saturated solution holds about 26%. One groundwater classification draws the line at more than 100,000 milligrams of dissolved solids per litre. In nature it forms when seawater evaporates and leaves minerals like gypsum and halite behind, when those deposits redissolve, or when sea ice freezes and squeezes salt into the leftover liquid. Salty springs at the surface are known as licks.
Chemistry does the rest. Iodide in certain brines is turned into acid and then oxidised to iodine with chlorine; bromine is made the same way and collected because it evaporates so readily. Magnesium can be recovered from waste brine left after potash production, and electrolysis of ordinary salt water yields chlorine gas along with sodium hydroxide and hydrogen.
Salt also lowers the freezing point of water, which makes brine a cheap coolant. A sodium chloride solution reaches its lowest freezing point, −21.1 °C, at 23.3% salt by weight. Large refrigeration plants once pumped it around widely, though its corrosiveness led many to switch to ethylene glycol. The same property lets crews spread it on icy roads, and blacksmiths quench steel in it for more even cooling. Water softeners use it too, soaking their resin beads so sodium displaces the calcium and magnesium they have captured.
The awkward side is disposal. Desalination by reverse osmosis sends back water that can be up to twice as salty as the sea it came from. Being denser, it sinks and spreads along the seabed as a plume, which can harm bottom-dwelling life. Countries such as Spain, Israel, Chile and Australia require diffusers, careful siting and monitoring to keep that plume diluted.
Source: Brine
