Industry has appetite for salt

Sunday, September 27, 1987

We eat it, and eat with it, drink it, and drink from it, wear it, take a bath with it, clean our teeth with it, shave with it, look through it, write on it, and drive it. -- From "Romances and Notes on Salt," by William Burton Wilkinson.

The uses of salt in industry aren't infinite, but they're right up there.

Sodium chloride is used for everything from blasting off mill scale in plate-rolling mills to curing fish and meat, from making transparent lenses for laboratory equipment to grinding shark livers.

In detergents, salt adds weight and bulk and is abrasive enough to be used as a scouring agent. At Christmas time, salt is used to make artificial ice and snow for holiday displays. The bright yellow light of burning salt is used by both scientists and fireworks makers.

Salt in oil-drillers' mud, a lubricant for drill bits, prevents the mud from breaking down through starch fermentation.

Salt has three major effects on water it is dissolved in, all of which are used by industry. It lowers water's freezing point, which is why salt sprinkled on ice melts it. It increases water's density, so food packers use brine to grade vegetables according to their buoyancy. It raises water's boiling point, so brine can be made hot enough to strip the skin from potatoes, sweet potatoes, rutabagas and carrots.

The American Salt Institute, based in Alexandria, Va., tracks the use of sodium chloride in five major categories: agricultural, highway clearing, water conditioning, food and industry. Together, those categories account for about 80 percent of the 42.2 million tons of salt consumed each year in the United States.

But the use of salt as sodium chloride is less than half the story. Salt is the cheapest, most plentiful source of the metal sodium and the corrosive gas chlorine, and separating the two elements is as simple as running an electrical current through them under controlled conditions.

The result is a proliferation of different chemical compounds, without which modern industry would be impossible.

The biggest chemical use of salt, according to one Salt Institute spokesman, is the manufacture of caustic soda. That chemical, made by running electric current through brine, is a strong base with many uses.

A soaking in caustic soda - the process is called mercerizing - makes cotton fibers about one-third stronger, and is also used in the preparation of feathers, fur or straw for working. Caustic soda's effect on wood pulp makes newsprint, and makes possible every other type of paper made of wood instead of rag. The chemical is also used in making rayon, cellophane, aluminum and a host of other modern products.

Soda ash, or sodium carbonate, is an indispensable ingredient in glassmaking and ceramics, and is also used in cosmetics, toothpaste and purifying natural gas.

Chlorine is used by itself for pulp and paper manufacturing, water purification, textile bleaching and bromine manufacturing, and in compounds as one of the building blocks of modern chemistry.

Chlorine as hydrochloric acid is used for metal processing and a variety of laboratory uses; as ammonium chloride, it is used in dry batteries, tanning and dying.

Other chlorine compounds serve as explosives, detergents, refrigerants and the deadly mustard gas of World War I. Chloroform is a well-known anesthetic; dichlorobenzene is an insecticide; propylene glycol is an antifreeze.

Assorted sodium compounds smelt nickel, keep hogs and cattle healthy, pickle meat and clean porcelain.