Brine consists of concentrated solution of Na and Cl ions.  Sodium chloride per se does not exist in water: it is fully ionized.  Other cations found in various brines include K, Mg, Ca, and Sr.  The latter three are problematic because they form scale and they react with soaps.  Aside from chloride, brines sometimes contain Br and I and, most problematically, .  Purification steps often include the addition of calcium oxide to precipitate solid magnesium hydroxide together with gypsum (CaSO), which can be removed by filtration.  Further purification is achieved by fractional crystallization.  The resulting purified salt is called evaporated salt or vacuum salt.