MAGNESIUM, BROMINE, AND OTHER PRODUCTS FROM SEA WATER 43 



plied to the header of the filter, causing the cake to drop into a dump pit. This 

 filtration removes approximately half of the remaining water and soluble salts 

 from the crude magnesium hydroxide. 



The filter cake, which contains approximately 25 per cent magnesium hydroxide 

 by weight, is mixed with a dilute magnesium chloride solution and "creamed" 



(Courtesy Dow Chemical Co.) 



Fig. 4-4. How the Dow Chemical Company produces 

 magnesimn metal from sea water. 



to a slurry by agitation and homogenization. This mixture is pumped into tanks 

 where it is neutraUzed with a solution of recycled hydrochloric acid containing 

 a httle sulfuric acid to a pH of 6.5. Part of the resultant 15 per cent magnesium 

 chloride solution is returned to the dump pits for the creaming of the filter cake 

 (crude magnesium hydroxide); the remainder is pumped into storage tanks. 



The magnesium chloride solution is then evaporated by blowing hot gases 

 (products of combustion) through it until a 35 per cent solution is obtained. 

 Evaporative cooling in a vacuum cooler reduces the temperature of the hot con- 

 centrated solution to approximately 122° F (50° C). After cooling, it is passed 

 to tanks where a solution of magnesium sulfate and chloride, made by the neutral- 

 ization of the creamed crude magnesium hydroxide, is added in the amount re- 

 quired to precipitate the calcium from the solution as calcium sulfate. The liquor 

 is held for 24 hours to permit crystallization of the calcium sulfate and sodium 

 chloride. Then it is filtered through Moore filters similar to those used for 



