Though bromine exists in the ocean with a 
concentration only one-twentieth that of magne- 
sium, its price per pound is one-third less than 
magnesium. This apparent anomaly is due to the 
fact that the bromine extraction process is much 
less costly in power, labor, and capital equipment. 
Favorable oceanographic and climatic condi- 
tions are paramount in extracting bromine from 
sea water.”” The following requirements are neces- 
sary: 
—High and constant salinity conveniently avail- 
able. 
—Source free from organic contamination and 
undiluted by major fresh water rivers. 
—Favorable circumstances to dispose of large 
quantities of processed water without mixing with 
unprocessed water. 
—Location in a warm climate since bromine can be 
removed at a greater rate from warm sea water. 
—Location near economical raw material and 
power. For example, in Freeport, chlorine, sulfur, 
heated sea water (cooling water from other Dow 
production facilities), and natural gas are in 
relatively good supply. 
B. Present Techniques for Extraction’ ® 
Techniques for extracting salt and magnesium 
compounds from sea water were mentioned on 
previous pages. Almost 30 per cent of world salt 
production is from sea water, chiefly by solar 
evaporation in open ponds. While some magnesium 
compounds also are produced in this way, most 
are from a process similar to the first steps 
employed in magnesium metal recovery. Being 
more complex processes, the extraction of 
magnesium metal and bromine is described below. 
1. Magnesium Metal 
The only two plants that extract magnesium 
metal from sea water (in Norway and Freeport, 
Texas) employ electrolytic processes, although 
each is different. However, both depend on initial 
2 7Shigley, C. M., op. cit., p: 5. 
8 Mclihenny, W..F., op. cit., p: 123. 
VI-194 
precipitation of magnesium hydroxide from sea 
water; oyster shell is used in Texas and dolomitic 
limestone in Norway. 
In the Dow process in Texas, sea water is 
brought into the plant through a system of flumes 
and intakes and then is screened and chlorinated 
for control of biofouling (Figure 54). Either 
calcined oyster shell or caustic soda from a 
caustic-chlorine electrolytic cell is used to precipi- 
tate magnesium hydroxide. The precipitated 
Figure 54. Sea water intake for magnesium 
extraction. Incoming sea water passes through 
a screen to prevent fish and debris from enter- 
(Dow Chemical photo) 
ing canal. 
RN eet 
: NOTTS acer 
Figure 55. Outdoor settling tanks for magne- 
sium extraction. Lime is slaked with water, 
added to sea water, and pumped to outdoor 
settling tanks. Soluble magnesium in sea water 
reacts with lime to form insoluble magnesium 
hydroxide, which settles to bottom and is re- 
moved for further processing. (Dow Chemical 
photo) 
