High Purity Common Salt
Recently I visited CSIR technofest 2010 showcased by Council of Scientific & Industrial Research, New Delhi, at India International Trade Fair in New Delhi, the Capital of India. In this technofest, I have seen a technology “High Purity Common Salt” from Brines in Solar Salt Pans which was developed by CSMCRI (Central Salt & Marine Chemicals Research Institute, Bhavnagar under the aegis of CSIR, New Delhi, India.
We use common salt or sodium chloride or NaCl for our essential diet and in all our cooking purposes. Common salt is a basic raw material for the manufacture of a wide variety of industrial chemicals viz. sodium carbonate (soda ash), sodium hydroxide (caustic soda) and chlorine. Salt is also used in textile, dairy, dyeing, food, fertilizer, leather, paper and pharmaceutical industries.
Solar salt is produced using sea brine, sub-soil brine and lake brine. Salt produced from such brines is contaminated with impurities such as Ca2+, Mg2+, SO42- and heavy metals. Salt is not pure white like purified iodine salt. Soda ash, caustic soda and others have to purify the salt before they use to their purpose and this causes pollution also. The need here is purify salt for required ratios to industrial applications in brine itself by using some chemicals. It is cost effective and without pollution to environment.
Absolute purity of the salt as well as the ratio of Ca to Mg are important, from sea- and sub-soil brines. Sea/subsoil brine as the case may be is concentrated to 24 0Be’ in specially designed solar pans. The concentrated brine is clarified with suitable agents and the clarified brine is 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 salt crystals were made defect free minimizing the chance of entrapment of impurities ensuring the production of high purity solar salt.
The present technology offers a cost-effective process for preparation of high purity common salt having highly reduced levels of the above impurities and with Ca to Mg ratio (w/w) in the range of 2-3 ideal for chlor-alkali, soda ash and other industries where common salt is a basic raw material.
Cost per one tonne comes about >Rs.10 in Gujarat and >Rs.50 in Rajasthan. The product has been tested by various chlor-alkali and soda ash manufacturers and has been certified to be ideal for its industrial applications.
Solar salt producers across any country, chlor-alkali and soda ash manufacturers and all other industrial units where high purity solar salt is the basic raw material will be highly benefited through the implementation of this technology.
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