Salt, Chlor-Alkali, and Related Heavy Chemicals
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SODIUM CHLORIDE
Common salt, sodium chloride, occurs in nature in almost unlimited quantities. It is a direct source of chlorine, caustic soda (sodium hydroxide), sodium chlorate, synthetic soda ash (sodium carbonate), sodium metal, and sodium sulfate. Indirectly, it is also the source of hydrochloric acid and a host of sodium salts. It has an imposing list of uses, placing it among the more important substances in the economic world. It is used to preserve meat, fish, and hides; it is a necessary component of the animal diet; it is used in refrigeration systems; and large quantities are used for ice control on highways in colder climates. Salt is used by the soap maker to separate soap from glycerine and lye, and by the dye manufacturer to precipitate dye products. In addition, salt is used extensively for the regeneration of watersoftening resins (see Table 12.1). Salt is mined as a solid in shaft mines with depths of 500-2000 ft, in Michigan, Ohio, *The Dow Chemical Company, Midland, MI. Riegel's Handbook of Industrial Chemistry, lOth Edition
Edited by Kent. Kluwer Academic/Plenum Publishers, New York 2003
New York, Kansas, Louisiana, and Texas. Run-of-the-mine salt contains 98-99 percent NaCl. Over 25 percent of the world's salt is produced in the United States. More frequently, salt is obtained by solution mining. Typically, this is achieved by drilling a well into a salt formation, installing concentric piping into the well, pumping water in one pipe, and retrieving nearly saturated brine from the other pipe. The brine concentration is controlled by the rate of pumping and is kept slightly undersaturated to avoid salting up the brine lines at the wellhead. The brine is purified by chemical treatment, settling, and filtration. Such artificial brines permit a cheaper operating cost and are well adapted to the manufacture of synthetic soda ash, chlor-alkali products, and table salt. Very extensive production of artificial brines is carried out along the U.S. Gulf Coast, principally in Texas and Louisiana where huge domelike deposits of rock sal~ exist in readily accessible areas. Some of these domes are 4 miles in diameter and over 8 miles deep, 1 containing over 100 billion 429
430 RIEGEL'S HANDBOOK OF INDUSTRIAL CHEMISTRY
TABLE 12.1 1996 Uses of Salt in the United States (Millions of Metric Tons) 3 Market Chlor-alkali Highway deicing General industrial Agricultural Food Other chemicals Other uses Total
Consumption 21.3 17.7 3.5 1.6 1.6 1.1
6.0 52.8
TABLE 12.2 U.S. Salt Production in 1996 (Millions of Metric Tons)4 Evaporated salt Rock salt Brine
7.1 13.5 21.5
Total
42.2
Source: Chemical Economics Handbook, Sodium Chloride, SRI International, Menlo Park, CA, 770.8000 P, 1998.
bromide and up to a few hundred parts per Source: Chemical Economics Handbook, Sodium million of iodide. These natural brines are Chloride, SRI International, Menlo Park, CA, 770.8000 mined principally for their bromine content. u, 1998. Salt also is derived from seawater in those places in the world, such as California, wher
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