SALT IN INDUSTRY

While we are all aware of the familiar package of Sifto in the home, it may be a surprise to learn that home requirements represent one of the smallest uses of salt. Much greater amounts are used in the food processing industries, such as meat packing, fish processing, bakery products, canneries, pickling, and dairy products to name a few. In these industries salt plays a triple role: it enhances the flavour; acts as a preservative; controls, and/or, takes part in the food making process. For instance, in pickle-making it allows fermentation while prohibiting spoiling; in baking it controls enzyme action; in meat and fish products it inhibits bacterial growth.

Salt preserves food in different ways but mainly by inhibiting bacterial growth through dehydration, chloride ion effects, oxygen removal, carbon dioxide sensitization and interference of growth of proteolytic enzymes. By far the largest use of salt in industry is in the manufacture of chemicals. Some of these chemicals are derived directly from salt and some indirectly.

The principal substances made directly from salt are caustic soda, chlorine and sodium. The principal substances made indirectly are hydrochloric acid, soda ash, and sodium sulphate. There is one more important substance that does not come from salt but is produced in the process of making some of the others, and that is hydrogen.

Caustic soda and chlorine are produced from salt by the electrolysis of brine (a solution of salt and water) and hydrogen, from the water, is a concurrent product of the process. An electric current is passed between two poles and through the salt solution, chlorine is released as a gas at the positive pole, hydrogen is released as a gas at the negative pole, sodium remains in solution to form sodium hydroxide (caustic soda) and is collected in catch basins at the cathode.

These three products are used in a great many ways, either as themselves or as the basis for formation of many further chemicals. They are used in anesthetics, bleaches, cosmetics, explosives, fertilizers, petroleum products, paper products, synthetic fibres, sewage treatment, water treatment, and a host of others.

Sodium is produced by electrolysis of molten salt, which process also liberates hydrogen. Sodium has many uses, a few of them are in case hardening metals, detergents, dyes, ore treatment, photography, tetraethyl lead. Tetraethyl lead is used as an additive in gasoline to ensure better engine performance.

Soda ash (sodium carbonate) results from passing carbon dioxide gas through a solution of salt and ammonia. A by-product of this process is sodium bicarbonate, or baking soda. Sodium carbonate is a very important chemical with a large number of uses. Among them are applications in glass, cosmetics, cleansers, degreasers, fire extinguishers, metal fluxes, ore refining, petroleum, soap, textiles.

Hydrochloric acid is made from reacting sulphuric acid with salt, which also produces sodium sulphate. These chemicals are used in adhesives, ceramics, dyes, pigments, rubber, soap, textiles, and many more. There are a great many other uses for salt in a great many industries; it would not be possible to list them here, as you will remember there are over 14,000.