By Jyotsna Bhatnagar.

Consider this -- everyday, each of planet earth's 5.9 billion inhabitants use salt. We need salt to survive. And while pre-historic man obtained salt from the meat of hunted animals, with the development of agriculture, salt was added to supplement the vegetable and cereal diet leading to the quest for salt becoming a primary motivation in history. Over the past century the annual production of salt world-wide has increased from 10 million tonnes to over 200 million tonnes today.

Nearly 100 countries have salt production facilities ranging from primitive solar evaporation to highly advanced multi-stage evaporation in salt refineries.

In the mid-1800s, salt's value as an important raw material for the chemical industry was also established when the Solvay process in Belgium was successfully used for the conversion of salt to synthetic soda ash.

Today, salt is also the largest mineral feedstock in the world's chemical industry.

Brief history
Salt was in use long before recorded history. Even in the pre-historic ages, animals were known to have foraged trails to natural salt sources to satisfy their need for salt. Ancient man obtained salt from eating animals and later as he turned to farming, he found new sources of salt for his vegetables and crops and to satisfy the body's requirement of the mineral.

Over many millennia, he learnt how salt helped to preserve food, cure hides and heal wounds. About 4,700 years ago, the Chinese Png-tzao-kan-mu, one of the earliest known writings, recorded more than 40 types of salt. Interestingly, it described two methods of extracting and processing salt which are similar to the methods still in use today.

Evidence has also been found of the late Iron Age salt production in many areas of Britain. Of these, only Cheshire remains a major centre for edible white salt production though rock salt is still mined in Teeside and northern Ireland. Cheshire was on a Neolithic trade route, which crossed the salt fields where Iron Age Britishers probably traded Westmoreland stone axe-heads for salt.

According to recorded data, the earliest known Cheshire salt mine was sunk in 1682. In 1781, a purer series of salt beds were identified in Northwich. It is believed that rock salt was used to saturate weak natural brine, increasing its salt content before evaporating in open pans to produce white salt. Mines frequently flooded and collapsed, leaving holes about 30m in diameter and 50m deep. These filled with water rapidly.

The ease of mining meant that new pits were sunk in preference to pumping water from old ones. Flooded mines became natural brine reservoirs and shafts were sunk in them to pump out the brine. Curiously, though a natural resource, salt was taxed from earliest times.

In the 15th century reign of William and Mary, it was taxed by the customs service and by 1805, the year of Trafalgar, taxes had touched an astronomical 30 pounds per tonne. Salt taxes were finally abolished in Britain, in 1825.

It may, however, be noted that despite taxation the salt trade continued to expand and imports of foreign goods created opportunities for cheap export of salt and coal cargoes. The Indian market opened to salt in 1844 and by 1850 over half a million tonnes of white salt was barged down the river Weaver to Liverpool annually.

In 1852, a young engineer John Corbett developed a method to keep the mines watertight and, this transformed the salt mining economics and became the key growth factor for the salt industry in the latter half of the nineteenth century.

By the 1860s Cheshire salt exports to India, North America and Europe exceeded one million tonnes annually. Growth of the chemical trade also increased consumption of salt in Britain.

Present scenario
Over the years, however, Britain has lost its status of being the leading salt producer to the US. In fact, today, the US is the largest salt producer producing an estimated 41.3 million tonnes of salt annually while the UK ranks a lowly ninth in the list of the world's top-ten salt producers. The UK comes even lower than India ranking fourth.

It was in 1614 that the American salt industry started off when the first non-native solar saltworks was established by Jamestown colonists on Smith's Island, Vancouver.

Of the United States' total salt production, nearly half, that is, 21.1 million tonnes is in the form of brine produced by captive brine wells supplying to the chloralkali chemical companies of the US.

The remaining 20 million tonnes is in the form of "dry salt" produced using three main technologies -- solar evaporation of seawater or saline lakewater, solution mining and vacuum pan evaporation and, the conventional deep shaft (rock salt) mining. Currently, the US salt industry operates some 48 salt production plants with major production sites in Louisiana, Ohio, New York, Kansas, Michigan, Utah and California.

Also within the vicinity, the Canadian salt industry produces another 13.43 million tonnes from major rock salt mines in Ontario, Quebec and New Brunswick and from the vacuum pan refineries in Alberta, Saskatchewan, Ontario and Nova Scotia. Nearly three-fourths of the production is rock salt, which is primarily used for highway de-icing.

In Latin America, Mexico accounts for a salt production of 8.4 million tonnes, most of which comes from the world's largest solar facility in Guerrero Negro in Baja California. After the US, China is the second largest salt producer in the world with an annual production of 41.3 million tonnes.