Contrary to the popular notion, most of the salt produced is not used in foods. More than 60% of the common salt produced in the country is being utilized for industrial applications, chlor-alkali and soda ash industries being the major consumers. High quality salt is in good demand in the industrial sector not only in India but a broad as well. Hence there is very good marketability for high purity solar salt in the country as well as abroad.
Salt is just produced by drying sea water, but it is not fit for industrial use straightaway. It is not white enough and contains some impurities such as Calcium, Magnesium, Sulphur and heavy metals. This is a problem because the higher levels of Ca, Mg and SO4 impurities, the higher investment in brine purification before processing it for chlor-alkali and soda ash manufacture. This also creates the problem of disposal of flux formed during the brine purification causing environmental pollution. The trace element impurities like Br and I present in salt is highly detrimental for certain industrial applications.
The Central Salt and Marine Chemicals Research Institute (CSMCRI) has developed a technology for cost effective process for the preparation of solar salt of a specification which is ideal for industrial applications, in industries such as chlor-alkali, soda ash and other industries where common salt is a basic raw material, especially wherein both the absolute purity of the salt as well as the ratio of Ca to Mg are important, from sea- and sub-soil brines.
Concentrated brine is clarified with suitable agents and is then allowed to enter the salt crystallizing pans preventing the insoluble fine gypsum particles and earthen impurities from entering the crystallizers along with the brine. There after the pH of the brine is adjusted to an optimum value. The salt crystallized between 25 0Be’ and 28.5 0Be’ is harvested and heap washed. The heap washed salt is found to be of high purity with ideal Ca to Mg ratio suitable for chlor-alkali manufacture. The process is based on the modification of salt crystal morphology during salt crystallization from concentrated brines in the solar pans through controlled nucleation which, in turn, is achieved by preventing the suspended gypsum particles and insoluble impurities from entering the crystallizers along with concentrated brine.
The process is cost effective and can be implemented in any solar salt works under predetermined parameters. It doesn’t require any additional infrastructure and manpower over the existing facilities available at solar salt works.
The technology has been implemented on a scale of >10000 ton of high purity solar salt in a commercially operated solar salt works. The technology has also been successfully implemented in 110 marginal solar salt works in LRK and 170 marginal salt works in region of Gujarat; the process is being implemented in small scale salt works in Rajasthan and Orissa.
The process can be implemented in any solar salt works irrespective of its size provided predetermined parameters are maintained. The additional cost of production works out to < Rs. 10 per ton of salt with subsoil brines of Gujarat and Orissa and <Rs. 50 per ton with the subsoil brine available in Rajasthan.
The process doesn’t require any additional investment over the existing units provided predetermined parameters are maintained. The additional cost of chemicals require for the process works out to Rs. 15 per ton of salt with subsoil brines of Gujarat and Orissa and less than Rs. 50 per ton with the subsoil brine available in Rajasthan.
For details, contact:
Dr. V. P. Mohandas, Scientist & Head, SMC Discipline, CSMCRI, Bhavnagar. Ph. 0278 – 2567039