40 MARINE PRODUCTS OF COMMERCE 



tern emerges from the bottom of the tower, milk of lime is added to neutralize a 

 portion of the acid present. The treated bittern then flows into a concrete-lined 

 pond until needed for magnesia recovery. 



The first step in the recovery of magnesia from the bittern is treatment with 

 calcium chloride brine, which produces a precipitate of gypsum (CaS04.2H20) 

 and converts magnesium sulfate into chloride. After the separation of gypsum, a 

 valuable by-product, the "magnesium bittern" is treated with lime, thus produc- 

 ing a precipitate of magnesium hydroxide which is flocculated, thickened, and 

 washed in Dorr thickeners. This reaction regenerates the necessary calcium 

 chloride brine for the treatment of more raw bittern. The washed magnesium 

 chloride is separated in an Oliver filter and calcined at 1832° to 3272° F (1000° 

 to 1800° C), thus obtaining magnesia (MgO). The lime used in precipitating the 

 magnesium hydroxide is made by "burning" in a rotary lime kiln oyster shells 

 dredged from the bottom of San Francisco Bay. 



The gypsum crystals are separated, concentrated, and washed in Dorr thickeners. 

 Then the gypsum is separated by Oliver filters, on which it is given a final wash- 

 ing. The gypsum filter cake drops into a paddle mixer which feeds a cage-type 

 kiln mill and flash drying system. The dried gypsum is drawoi into a "cyclone," 

 from which it is carried by a screw conveyor to storage. 



Minerals Direct from Sea Water 



Introduction. In the ocean there is a vast store of minerals (pages 2 and 4) 

 containing appreciable quantities of at least 50 elements which have been leached 

 from the rocks and soil. For example, in a million pounds of sea water there are 

 approximately 1000 pounds of magnesium and 65 to 70 pounds of bromine. In 

 view of its almost limitless quantity, sea water is a very important potential source 

 of these and many other elements. The difiiculty, of course, is the necessity of 

 separating the minerals from such a large quantity of water. 



The ocean has long been an important source of sodium chloride (common 

 salt) and, for the past century, certain other compounds have been obtained from 

 the bittern as by-products from the manufacture of salt. But the separation of 

 elements direct from sea water is an industry of recent origin, having started in 

 1924 when the Ethyl Corporation began extracting bromine in commercial quan- 

 tities from the ocean. Similar extraction of magnesium was undertaken in 1928 

 by the Dow Chemical Company. 



Bromine from the Ocean. In 1924 the demand for bromine increased greatly, 

 owing to the need for ethylene dibromide to make "ethyl" gasoline. To obtain 

 more bromine the operation of a small plant was begun on the Atlantic Coast; 

 this produced tribromoaniline by the addition of aniline to chlorinated sea water. 

 Later, this process was tried on a boat, but the high cost of the bromine produced 

 did not make continuation of the venture worthwhile. 



Meanwhile, the possibility of adapting the process used for the extraction of 

 bromine from natural brines to the separation of bromine from sea water was 

 being studied. In 1931 the Dow Chemical Company built a pilot plant in North 

 Carolina in which 500 pounds of bromine per day were produced. Eventually, the 

 Ethyl-Dow Chemical Company was organized for the purpose of manufacturing 

 on a large commercial scale bromine and ethylene dibromide from sea water in a 

 plant which was constructed in 1933 near Wilmington, North Carolina. 



