BROMINE FROM SEA WATER STEWART 



157 



iired by the difference in voltage between a saturated calomel elec- 

 trode and a j^latinum electrode. Figure 4 shows the relationship 

 between the oxidation potential, expressed in volts, and the percent- 

 age of bromine liberated in sea water which contained about 3.5 

 percent total solids in solution and about 60 to 70 parts per million 

 bromine, and which had been acidified to a pH of 3 to 4. The char- 

 acteristic potential under these conditions ranged between 0.88 and 

 0.97 volt. The methods of extracting bromine from sea water, in- 

 volving the control of acidification and oxidation, are protected by 

 patents (3). 



10 20 30 40 50 60 70 80 90 100 110 120 130 140 

 PERCE NTAG E BROMINE LI BERATED 

 F I G. 4 



RELATIONSHIP BETWEEN OXIDATION POTENTIAL AND 

 PERCENTAGE OF BROMINE LIBERATED IN SEA WATER 



After obtaining a clear understanding of the factors which, made 

 for the most efficient liberation of bromine from sea water and devel- 

 opment of satisfactory control methods, the laboratory and semiplant 

 work on the process progressed much more rapidly. This work es- 

 tablished the fact that air, blown countercurrent through a 70 parts 

 per million bromine solution, would remove the halogen sufficiently 

 to leave a concentration as low as 5 parts per million. It was also 

 found that soda ash solution would effectively remove the very low 

 concentration of bromine from the air. In these experiments, per- 

 formed at Midland, Mich., synthetic sea water was used at first, and 

 this was followed by tests made on tank-car shipments of true sea 

 water. The chief result of the small-scale work was the demonstra- 

 tion that more than 50 percent of the bromine in the real sea water 

 could be extracted and actually collected as the pure liquid. The 

 indicated cost of operating the process seemed satisfactorily low. 



