CHAPTER 4 

 Magnesium, Bromine, and Other Products from Sea Water 



The Recovery of By-Products from Bittern 



The Importance of By-Products. Although salt has been produced by the solar 

 evaporation of sea water for many centuries, no important use has been made of 

 the bittern or mother liquor from salt crystallizations until comparatively recent 

 times, when Balard worked out the well-known process for the recovery of sodium 

 sulfate and potassium chloride. This process, with modifications by Merle and 

 Pechiney, is in use today at Giraud-en-Camargue, situated at the mouth of the 

 Rhone River. Although Balard's process was entirely successful at the Giraud salt 

 works, few attempts have been made to utilize salt bitterns elsewhere until re- 

 cently. For a number of years magnesium chloride, magnesium oxychloride 

 cements, and bath salts have been recovered from the bitterns obtained in the 

 California salt works, and during World War I potassium chloride was taken from 

 some salt works. 



The discard of the mother liquors from the salt works represents a tremendous 

 waste; the mother liquor from 100,000 tons of salt contains 2800 tons of potas- 

 sium chloride, 27,300 tons of magnesium chloride (MgCL.BoHO), 16,000 tons 

 of magnesium sulfate (MgSOi.THsO), and 240 tons of bromine. 



Detailed analyses of various bitterns from some California salt works are given 

 in Table 8. 



Balard's Process. About the year 1850 Balard perfected the process, which 

 bears his name, for the recovery of common salt, sodium sulfate, and potassium 

 chloride from the solar-salt bitterns. His process, in general terms, consisted of 

 alternately concentrating and cooling the mother liquor of the sea-salt works, so as 

 to secure by successive crystallizations the three products mentioned and, also, a 

 concentrated magnesium chloride solution. This process is described briefly in the 

 following: 



Bittern of about 1.28 sp. gr. (31.72° Be.) was evaporated to a density of 1.32 

 35.15° Be.); under such conditions it deposited magnesium sulfate containing 

 almost an equivalent amount of sodium chloride. This sets mixtes was converted 

 into nearly pure sodium sulfate and magnesium chloride by dissolving it in water 

 and allowing it to crystallize during cold weather. 



The mother hquor from the sels mixtes was held until cold weather when it was 

 run into shallow concrete tanks; nearly pure magnesium sulfate was deposited. 

 This magnesium sulfate was converted into sodium sulfate by adding 1.5 of its 

 equivalent of sodium chloride and by dissolving it and allowing it to crystallize 

 at a temperature below 32° F (0° C). Nearly pure sodium sulfate was obtained. 



The mother liquor from the magnesium sulfate crystals was stored through 

 the winter and evaporated further during the succeeding spring and summer. This 



37 



