THE RECOVERY OF MINERALS FROM SEA WATER 



By C. M. Shigley, The Dow Chemical Company 



Man's hope to develop power from the sea 

 has not yet been reaHzed, but the prospect of 

 recovery of minerals from that mighty storehouse 

 has long since become real. It is the purpose of 

 this writing to trace the history of the extraction 

 of minerals from the seas, to describe recent large 

 commercial projects for recovering elemental 

 bromine and magnesium from sea water, and to 

 briefly discuss a few of the economic factors in 

 such sea water extraction operations. 



The total volume of the oceans is estimated to 

 be 320 million cubic miles (Armstrong and Miall, 

 1946). Although the salinities of the several seas 

 vary somewhat, the average is approximately 

 35,000 parts of dissolved salts per million, equiv- 

 alent to 165 million short tons per cubic mile. 

 The oceans of the world thus represent a store- 

 house of about 50 million billion tons of dissolved 

 materials. The chloride ion represents 54.8 per- 

 cent of the total salts, the sodium ion 30.4 percent, 

 sulphate 7.5 percent, magnesium 3.7 percent, 

 calcium 1.2 percent, potassium 1.1 percent, 

 carbonate 0.3 percent, and bromide 0.2 percent. 

 Although the sea is believed to contain at least 

 traces of every clement, these eight ions account 

 for over 99 percent of the sea water salts; all 

 other elements total less thaa 1 percent. 



Since the sodium and chloride ions represent 

 sLx-sevenths of the dissolved salts and are the 

 most easily extracted, it is not surprising that they 

 seem to have been involved in the first recovery 

 on record. Sodium chloride, common salt, was 

 undoubtedly the first compound to be removed 

 from sea water and used by man. It is believed 

 that salt was used by cave men at least 5,000 

 years ago. Salt from sea water is mentioned in 

 Chinese writings about 2200 B. C. Aristotle in 

 his Meteorologica wrote of the origin and usefulness 

 of the salts of sea water and described a method 

 of "unsalting" sea water. The ancient Greeks, 

 Romans, and Egyptians were familiar with produc- 

 tion of salt by solar evaporation of sea water. 



Such salt recovery has been common in China, 

 India, and Japan for many centuries, and still 

 continues. Salt from sea water was produced on 

 the Atlantic coast of North America about 1680 

 and on the Pacific coast in 1852. The Atlantic 

 coast industry was short lived, but that on the 

 Pacific coast has thrived to this time. 



The production of crude soda and potash from 

 the ashes of seaweeds was accomplished in Scotland 

 as early as 1720. Iodine was recovered from 

 seaweeds for the first time early in the nineteenth 

 century; magnesia was first prepared on the 

 Mediterranean coast at the end of the century. 

 The records do not indicate any additional progress 

 until 1923 when magnesium cliloride and gypsum 

 were produced from the bitterns from solar evap- 

 oration of the sea water of San Francisco Bay 

 (Seaton 1931). 



These bitterns were first treated with calcium 

 chloride, precipitating the sea water sulfate as 

 calcium sulfate, which was settled and filtered. 

 Concentration of the filtrate, cooling and separa- 

 tion of the residual magnesium sulfate, potash, 

 and other salts by settling and centrifuging, gave 

 a fairly pure magnesium chloride solution which 

 was further concentrated to salable form by boil- 

 ing. The calcium sulfate resulting from the 

 calcium chloride treatment was washed, dried, 

 and sold as gypsum. 



In 1926, the first sea water bromine was recov- 

 ered on a small commercial scale by chlorinating 

 the San Francisco Bay bitterns, steam stripping, 

 condensing, and purifying the product. 



In 1931, the production of potassium chloride 

 by evaporation of the waters of the Dead Sea was 

 inaugurated; in 1932, bromine was recovered on 

 a commercial scale from the residual liquors of 

 the potassium plant using a process similar to that 

 employed for San Francisco bitterns. 



Prior to 1933, the survival of the majority of the 

 projects recovering material from sea water 

 depended upon solar evaporation for initial con- 



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