MAGNESIUM, BROMINE, AND OTHER PRODUCTS FROM SEA WATER 41 



Briefly, the process involves: (1) acidulating sea water with sulfuric acid from 

 a pH of 7.2 to approximately 3.5; (2) oxidizing the acidulated sea water with 

 chlorine to free the bromine from the bromides; (3) blowing the free bromine 

 out of solution with air; and (4) absorbing the bromine in a sulfur dioxide solu- 

 tion, by which the bromine is reduced to hydrobromic acid. The hydrobromic 



CHLORINE 







SULPHUR DIOXIDE WATER 



SEA WATER 



BLOWING-OUT 

 TOWER 



Q 



CHLORINE 



9 



BROMINE VAPOR 



ABSORPTION 

 TOWER 



STEAMING OUT 

 TOWER 



HYDROBROMIC 

 SOLUTION 



CONDE 



NSER 



AIR 



STEAM 



{Courtesy Dow Chemical Co.) 



Fig. 4-2. Flow sheet of the Dow process for producing bromine from sea water. 



acid solution is treated with chlorine to free the bromine again by driving it 

 out of the solution with steam and finally condensing it as a liquid. By this process 

 half of the bromine in sea water can be economically recovered. 



Metallic Magnesium from Sea Water. The Dow Chemical Company began the 

 manufacture of magnesium from sea water at Freeport, Texas, on January 21, 

 1941. This was the first time a metal had been produced in commercial quantities 

 from sea water. Since then the plant at Freeport has been greatly enlarged and 

 another huge plant has been built at Velasco, Texas. The latter, government- 

 owned, is no longer operating. 



The Dow process involves the precipitation of the magnesium as hydroxide, 

 the thickening and washing of this precipitate, the conversion of the magnesium 

 hydroxide into chloride by neutralization with hydrochloric acid, the concentra- 

 tion of the chloride to a 35 per cent solution by evaporation, filtration of this 

 solution, followed by further evaporation and drying, and finally the electrolysis 

 of the fused magnesium chloride to produce metallic magnesium. The exact 

 procedure is briefly described as follows: 



The sea water is drawn from a canal through large grid and rotary screens into 

 a flume and is pumped through a constant-head tank into a reinforced concrete 

 flocculator tank where it is agitated with an excess of milk of lime. Precise control 



