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Solar Salt

M.V.S. Prasad*

Common salt touches the lives of almost everyone. Indian salt industry has made rapid strides during last six decades. From an import dependent nation at the time of Independence, today it ranks third amongst 120 salt producing countries, with an average annual production of about 24 million tonnes. The Indian Salt Industry after meeting country’s domestic requirements of 18 million tonnes, exports about five million tons of salt to 20 countries.

Out of the total of salt produced in the country annually, 70% salt is produced from sea brine and 28% salt comes from subsoil brines and the remaining 2% is produced from lake brines/salt rocks. Mandi in Himachal Pradesh is the only source of rock salt in India. In India, Gujarat, Tamil Nadu and Rajasthan contribute to about 96% of the country’s salt production. Gujarat contributes 75% to the total production, followed by Tamil Nadu (11%) and Rajasthan (10%). Other states such as Andhra Pradesh, Maharashtra, Orissa, Karnataka, West Bengal, Goa, Himachal Pradesh, Diu & Daman also contribute to a small extent. About 62% of the total production is from large salt producers, 28% is contributed by small scale producers and rest by medium scale producers. Most of the salt is produced by private sector only. The Indian salt industry uses labour intensive technology in contrast to high level of mechanization in salt industry of nations like Australia, Canada, France, USA etc. India exports surplus production of salt to the tune of about 35 lakh tonnes on an average. Major countries importing salt from India are Japan, Bangladesh, Indonesia, South Korea, North Korea, Malaysia, U.A.E., Vietnam, Qatar etc.

Nearly 30% of total salt produced goes for human and animal consumption and thus can be a potential carrier of essential micronutrients for combating various diseases normally occurring from deficiency of such nutrients in human body. Salt is also required as a basic feedstock in many of the chemical industries. Worldwide about 60% of the salt produced is used in chemical industry, mostly for producing chlorine, caustic soda and soda-ash which are further utilized in the processes like, organic synthesis, polymer and petrochemicals and petroleum refining etc. and is also required in applications such as de-icing, water treatment or coolants etc.

 The salt content in the oceans is ‘virtually inexhaustible.’ Besides this there are substantial deposits of salt in major salt producing countries. There are mainly three ways of producing salt (a) direct mining of rock salt, (b) forced evaporation of brine, and (c) solar evaporation of brine. The most common and energy efficient method is progressive evaporation and concentration of sea, subsoil or lake brines in various condensing and crystallizing pans utilizing solar energy.

In general, purer the salt the more valuable it is. Moisture in salt, mainly due to the presence of excess impurities of magnesium salts, is also detrimental as it can lead to the caking up of salt besides being an unwanted baggage during transportation of salt. For example, if 10 million tonnes of salt has to be transported from the fields by road, a 4% moisture level in salt would amount to ca. 40,000 unnecessary trips! A dry salt thus helps reduce the carbon footprint.

Over the years a series of inventions have taken place in the area of solar salt. CSIR-Central Salt & Marine Chemicals Research Institute, a premier salt research institute has made a commendable contribution in the development of novel cost effective technologies of high purity solar salt production.

The Indian salt industry in general lacks adoption of novel methods of solar salt production leading to inferior quality of harvested salt than countries such as Australia and Mexico. Improving the quality of such impure salt requires mechanical washing and other chemical treatments. CSIR-Central Salt & Marine Chemicals Research Institute, along with various State Governments and Salt Department, the Government is continuously pursuing the programmme of improving the quality of solar salt in a cluster development fashion as well as in the form of establishment of model salt farms which serve as demonstration units among the salt producers.

Mechanization/modernization of solar salt works and use of saline wastes of various industries during solar salt production will also lead to enhancement in salt productivity. The latter will help not only in improving yield but also in improving the quality of slat and mitigation of environmental hazards generally occurred from discharge of effluent in sea or other at other places. Heavy losses in salt production are incurred as a consequence of unfavourable climatic conditions like heavy rainfall etc. Such issues can be addressed partially by mechanization and automation of solar salts. The mechanization of salt works will not only help in overcoming the problems of shortage of desired manpower engaged in salt production activities but will also help in improving the quality and yield of solar salt.

Indian salt industry is targeting production of 40 million tons salt by 2020 to meet its domestic requirement of 25 million tons an export about 10 million salt. It can be achieved by effective utilization of the available 6.1 lakh acre land and increasing productivity using modern technology. The slat industry is to be mechanized, merger of the salt works to increase the size of operation and use of solar plant in place of traditional electric / diesel power is to be encouraged.

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