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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



to the gas stream entering the furnace or as hydro- 

 chloric acid at the neutraUzers. 



The properties and uses of magnesium are well- 

 known but warrant brief comment. It is the 

 lightest structural metal commercially available. 

 It is about one-fourth as heavy as iron and two- 

 thirds as heavy as aluminum. When alloyed 

 with small amounts of other metals, such as 

 aluminum, zinc, and manganese, it has a high 

 strength to weight ratio, it is easily fabricated, 

 and it has good corrosion resistance. These 

 properties make it advantageous for use in light 

 weight structures and equipment such as air- 

 planes, truck and trailer bodies, portable tools, 

 hand trucks, ladders, and others too numerous to 

 mention. The high place held by magnesium in 

 the electromotive series of metals makes it out- 

 standing for sacrificial anodes — in other words, 

 sources of current for the protection of buried or 

 submerged metal surfaces against corrosion. One 

 of the more recently developed uses of magnesium 

 is in the field of ferrous metallurgy. Small 

 amounts of magnesium properly added to cast 

 iron prior to pouring give a so-called "nodular 

 cast iron" which has strength and ductility prop- 

 erties similar to those of steel. 



The economic factors involved in the mag- 

 nesium-from-sea-water operation are somewhat 

 different from those of bromine. From an ocean- 

 ographic or climatic standpoint, the location is 

 not so critical. The sea water which must be 

 processed per pound of magnesium is only one- 

 twentieth as much as is required per pound of 

 bromine. The water temperature has little effect 

 on the magnesium recovery. More important is 

 a location favorable to the supply of raw materials 

 and power. The convenient availability of lime 

 and abundant and inexpensive fuel and power are 

 obviously essential for competitive operation. 



The process can achieve a recovery of 85 to 90 

 percent of the magnesium in sea water. The 

 performance of each step represents a compro- 

 mise between high efficiency and high capital 

 cost, and the justifiable recovery must be calcu- 

 lated for the conditions of each plant. The 

 process has the inherent advantage that the 

 majority of the materials can be conveyed by 

 pumping. Most of the steps are continuous and 

 subject to the benefits of automatic control. 



The quantities of sea water and oyster shells 

 used in the process are large. In the Freeport 



plant (following quoted from Schambra, 1945, 

 pp. 4, 6): 



"Sea water flows by tidal surge from deep water in the 

 Gulf of Mexico, through the 40 ft. deep channel dredged 

 into the Freeport harbor. Stone jetties at the mouth of 

 the harbor prevent the surf and shore currents from wash- 

 ing sand into the channel. One mile inshore from the 

 harbor mouth, the plant intake withdraws the raw sea 

 water at a depth of 25 ft. A concrete curtain wall holds 

 back the surface water so that the suction opening is 

 actually between —20.0 ft. and —30.0 ft. elevation. In 

 waters of this locality, stratification of high and low 

 density water occurs, even in the range of specific gravity 

 of 1.000 to 1.026, the difference between fresh water and 

 full strength sea water. The use of a curtain wall permits 

 withdrawal of 80% to 90% full strength sea water when 

 the surface may be nearly fresh water. Due to rains and 

 fresh water intrusion from the Brazos River, the sea water 

 at the intake averages 85% of full strength. 



At the intake, trash, marine plants, and small fish are 

 removed by a triple screening . . . Four Worthington 

 submerged-propeller axial-flow type pumps, each delivering 

 70,000 g. p. m., rai.se the sea water from a varying .sea level 

 to a constant head at elevation 9.0 ft. Each pump dis- 

 charges directly into a unique rotating barrel [Monel] 

 screen . . . made up in wood-framed trays which are 

 bolted to the steel barrel framework. Each tray is care- 

 fully insulated from the barrel by rubber gaskets to mini- 

 mize bi-metal electrolytic corrosion. 



Following the screens, the sea water is chlorinated con- 

 tinuously to a residual of 0.2 to 0.5 p. p. m. free halogen. 

 Growth of marine plants, barnacles, and oysters is pre- 

 vented in this manner . . . Shell [used for the production 

 of lime] is purchased from two dredging companies now 

 working the oyster shell reefs in Galveston bay. Accu- 

 mulated shells of dead oysters lie in irregular reefs in 1 to 

 17 ft. of water, with the thickness of the beds varying 

 from 1 to .30 ft. There are millions of tons of usable shell 

 in Galveston and Matagorda Bays alone. Extensive reefs 

 are found off shore in the Gulf. Newly dredged shell 

 contains mud and sand which are removed by washing 

 on the dredge with sea water. The dredge W. D. Haden 

 has a capacity of 350 tons per hr. of washed shell. Loaded 

 barges of 800 tons capacity are removed by Diesel tug to 

 the Freeport plant . . . The washed shell is fed either to 

 the storage pile or directly to the kiln feed hoppers . . . 

 Each kiln produces 150 tons of lime per day.' 



In conclusion, the large-scale recoveries of bro- 

 mine and magnesium from sea water must not be 

 regarded as merely incidents in the record of 

 scientific progress of the last three decades. They 

 are indicative of a pronounced trend toward using 

 the seas for more of life's needs. 



It is natural that this should be so. The seas, 

 covering three-fourths of the earth's surface and 



' Reproduced with the permission of the American Institute of Chemical 

 Engineers from the Transactions of the A. I. Ch. E,, vol. 41, No. 1, pp. 4, 6. 



