Technologies Rural Technologies – CSIR 800



An Improved Process of Preparation of Common Salt of High Purity from Brines in Solar Salt Pans



Application / use:


Common salt or sodium chloride or NaCl, apart from being an essential dietary component, 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. Besides, salt is used in textile, dairy, dyeing, food, fertilizer, leather, paper and pharmaceutical industries.


Brief description and salient features of the technology / product:

Solar salt is produced using sea brine, sub-soil brine and lake brine. Salt produced from such brines is invariably contaminated with impurities such as Ca2+, Mg2+, SO42- and heavy metals. Moreover, the salt tends to be less white than desirable. It is, therefore, of great importance to devise means of making purer solar salt in cost-effective manner. The present technology relates to a cost effective process for the preparation of solar salt of a specification which is ideal for industrial applications, 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. 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 process is cost effective and can be implemented in any solar salt works under predetermined parameters.

 

Novelty / innovation those differentiate us from others :

Solar salt manufactured in a traditional way is invariably contaminated with higher levels of Ca, Mg, SO4 and other trace elements which are not ideal for its industrial applications especially in the chlor-alkali and soda ash manufacture. The higher levels of Ca, Mg and SO4 impurities demand 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 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.

 

Major raw materials or resources to be utilized:

The process utilizes sea brine, subsoil brine and other natural brines as being commonly used by solar salt producers. In addition to this most commonly available and cheap chemicals are employed in the process at ppm levels for the production of high purity solar salt.

 

Infrastructure and manpower requirement:

The process doesn’t require any additional infrastructure and manpower over the existing facilities available at solar salt works.

 

Status of the technology:

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 Maliya region of Gujarat; the process is being implemented in small scale salt works in Rajasthan and Orissa.

 

Minimum economic unit size and cost:

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.

 

Total investment:

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 <Rs. 50 per ton with the subsoil brine available in Rajasthan.

 

Technology transfer methodology:

As per CSIR / CSMCRI norms

 

Product acceptability:

The product has been tested by various chlor-alkali and soda ash manufacturers and has been certified to be ideal for its industrial applications.

 

Marketability:

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.

 

Is this technology is location specific? If so give details:

The technology can be implemented in any solar salt works irrespective of its size and location provided predetermined conditions are maintained.

 

Beneficiaries:

Solar salt producers across the 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 the technology.

 

Any other important information:

The technology is cost effective and green not only at the producer level but at the user end also.


Contact person and address:


  1. Dr. V. P. Mohandas, Scientist & Head, SMC Discipline, CSMCRI, Bhavnagar
    E-mail: Dr. V. P. Mohandas, Ph. 0278 – 2567039
  2. Dr. A. M. Bhatt, Scientist, CSMCRI, Bhavnagar
    E-mail : Dr. A. M. Bhatt, Ph. 0278 – 2567760 (Extn. 745)
  3. Dr. Arvind Kumar, Scientist, CSMCRI, Bhavnagar
    E-mail : Dr. Arvind Kumar, Ph. 0278 – 2567760 (Extn. 746)
  4. Dr. I. Mukhopadhyay, Scientist, CSMCRI, Bhavnagar
    E-mail : Dr. I. Mukhopadhyay, Ph. 0278 – 2567760 (Extn. 746)

 

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