156 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



scrubs bromine from the condenser vents. It is 

 preheated in that tower by the addition of live 

 steam. Chlorine equivalent to tliree-fourths of 

 the hydrobromic acid is added with the steam. 

 The liquid mixture then passes to a steam strip- 

 ping column where the remainder of the equivalent 

 chlorine is added and the free bromine is steam 

 distilled out of the solution. The bromme- 

 steam vapor from the top of the tower is con- 

 densed as before, and purification of the liquid 

 bromine so obtained yields a product of quality 

 equal to that of the first described method. 



The hot effluent from the stripping column con- 

 sists of a mixture of hydrochloric and sulphuric 

 acids. It is added to the incoming sea water and 

 under normal conditions supplies approximately 

 two- thirds of the acid requirements of the blowing- 

 out step. 



The factors which determine the competitive 

 position of either or both of these sea water ex- 

 traction processes differ only slightly from those 

 encountered in the consideration of any economic 

 enterprise. One must principally consider location 

 of raw materials, efficiency of the process, materials 

 of construction, and manpower. 



The proper location of a plant utilizing either 

 bromine process is particularly important to the 

 success of the project. A place is required where 

 sea water of high and constant salinity is con- 

 veniently available, free from organic contamina- 

 tion, and undiluted by major fresh-water rivers. 

 It must also possess favorable circumstances for 

 disposing of the large quantities of processed 

 water without mixing with the unprocessed water. 

 Where shallow water and variable currents pre- 

 vail, the intake and effluent systems should be 

 widely separated. Deep water along shore and 

 constantly favorable shore currents lessen the 

 need for such separation. A plant site only slightly 

 above sea level is preferable to reduce pumping 

 costs. 



Since both processes depend on vaporization of 

 bromine, and since the vapor pressure of bromine 

 in sea water varies considerably with temperature, 

 a location in a warm climate is highly desirable. 

 Other things being equal, a blowing-out tower 

 handling 25° C. sea water can operate at a higher 

 rate and can produce approximately twice the 

 amount of bromine as the same tower operating 

 at 10° C. The absorption of the alkali process is 

 also susceptible to temperature effects. Absorber 



losses are five- to fifteen-fold more at 10° C. than 

 at 25° C, depending on the excess alkalinity of 

 the absorbing solution. A location as near as 

 possible to the source of economical raw materials 

 and power and to the point of disposal of the 

 finished product is desirable; but other factors are 

 of secondary importance when compared with the 

 need for favorable oceanographic and climatic 

 conditions. 



Because of the relatively large quantities of raw 

 materials which must be handled in order to 

 obtain each pound of bromine, it is necessary that 

 very close operational control be maintained at 

 aU points. Since reliable indicators and automatic 

 controls have made a large contribution to the 

 success of the large scale recovery of bromine from 

 sea water (Hart 1947), they must be regarded as 

 integral parts of both processes. 



The manufacture of magnesium from sea water 

 is quite different from bromine processes. Magne- 

 sium is taken out of the sea water in an alkaline 

 condition instead of acid and is removed by pre- 

 cipitation rather than blowing out. 



The process is carried out in 10 well-defined 

 steps. In the first step, sea water containing 1,300 

 parts per million magnesium is screened as in the 

 bromine process and is continuously treated with 

 an excess of milk of lime. The lime used in the 

 present operation is prepared by calcining oyster 

 shells at 1,200° to 1,400° C. to produce chemical 

 lime of purity over 96 percent, slaking the lime 

 hot, and settling the calcium hydroxide to a heavy 

 slurry. An excess of 20 percent of the theoretical 

 lime is necessary to keep boron compounds in 

 solution. 



The boron of the sea water, if absorbed by the 

 hydroxide and carried through the process, gives 

 difficulty in the final electrolysis step. The limed 

 sea water is delivered to standard Dorr settling 

 tanks. There the precipitated magnesium hy- 

 droxide settles to the bottom and is drawn off as 

 a thin slurry having a composition of about 12 

 percent magnesium hydroxide by weight. The 

 overflow from the Dorr tanks is discarded; it 

 represents nearly 98 percent of the water and 

 other materials with which the magnesium was 

 originally associated. 



The next step consists of filtering the slurry on 

 Moore batch-type leaf filters. In this step approxi- 

 mately half of the remaining water and soluble 

 materials are separated from the magnesium 



