Treating the solution of different soluble magnesium salts with alkaline water induces the precipitation of the solid hydroxide Mg(OH)2: Mg2+ + 2 OH− → Mg(OH)2 As Mg2+ is the second most abundant cation present in seawater after Na+ , it can be economically extracted directly from seawater by alkalinisation as described here above. On an industrial scale, Mg(OH)2 is produced by treating seawater with lime (Ca(OH)2). A volume of 600 m3 (160, 000 US gal) of seawater gives about 1 tonne (2, 200 lb) of Mg(OH)2. Ca(OH)2 (Ksp = 5.02×10−6)[6] is far more soluble than Mg(OH)2 (Ksp = 5.61×10−12) and drastically increases the pH value of seawater from 8.2 to 12.5. The less soluble Mg(OH) 2 precipitates because of the common ion effect due to the OH− added by the dissolution of Ca(OH) 2:[7] Mg2+ + Ca(OH)2 → Mg(OH)2 + Ca2+ For seawater brines, precipitating agents other than Ca(OH)2 can be utilized, each with their own nuances: Use of Ca(OH)2 can yield CaSO4 or CaCO3, which reduces the final purity of Mg(OH)2. NH4OH, can produce explosive nitrogen trichloride when the brine is used for chlorine production. NaOH as the precipitating agent has longer settling times and is difficult to filter. It has been demonstrated that sodium hydroxide, NaOH, is the better precipitating agent compared to Ca(OH)2 and NH4OH due to higher recovery and purity rates, and the settling and filtration time can be improved at low temperatures and higher concentration of precipitates. Methods involving the use of precipitating agents are typically batch processes.[8] It is also possible to obtain Mg(OH)2 from seawater using electrolysis chambers separated with a cation exchange membrane. This process is continuous, lower-cost, and produces oxygen gas, hydrogen gas, sulfuric acid (if Na2SO4 is used; NaCl can alternatively be used to yield HCl), and Mg(OH)2 of 98% or higher purity. It is crucial to deaerate the seawater to mitigate co-precipitation of calcium precipitates.[9]