Recovery of common salt and marine chemicals from brine

Details Recovery of common salt and marine chemicals from brine Recovery of common salt and marine chemicals from brine

2001-10-29

2004-08-17

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Treating mixture to obtain metal containing compound

Alkaline earth metal

C423S197000, C423S155000, C423S178000, C023S29500G

Reexamination Certificate

active

06776972

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for recovery of common salt and marine chemicals of high purity in integrated manner, which boosts the viability of such recovery. The process is amenable to a wide range of brine compositions but especially attractive for brine compositions that are low in sulphate content and yield impure salt when the conventional process of solar salt production is followed.
BACKGROUND OF THE INVENTION
Certain components of brine have industrial uses. Common salt, 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. Salt is also used in textile, dairy, dyeing, food, fertilizer, paper and pharmaceutical industries. Marine gypsum is used in cement industries and in the preparation of high strength Plaster of Paris. It can also be used as a source of calcium in the preparation of calcium-based siliceous chemicals. Magnesium compounds find applications in agriculture, refractories, pharmaceuticals, rubber, polymer additives and fire retardant. Potash is an essential plant nutrient and chemical grade KCl is used for making other important potash chemicals.
Reference may be made to “Rain Washing of Common Salt Heaps” by M. P. Bhatt, P. S. Jesulpura and K. Sheshadri,
Salt Research and Industry,
10(2), (1974), 13, who have reported that sea salt which is harvested and subjected to rain water washing, has 0.21% w/w Ca, 0.60% w/w sulphate and 0.06% Mg. The salt requires upgradation to reduce the level of calcium and sulphate, especially for use in chloralkali industry.
Reference may be also made to “Fractional Crystallisation of Salts from Sub-soil brines” by V. P. Mohandas, S. J. Gohil, and S. D. Gomkale,
International Journal of Salt Lake Research
6, (1998), 331, who have reported that sub-soil brines of Gujarat, India, typically yield salt contaminated with 0.30-0.40% w/w Ca, 0.80-1.00% w/w sulfate and 0.20-0.30% Mg after harvesting and washing of heaps with a minimum quantity of water. This makes the salt unacceptable for industrial application.
The authors have attributed the higher Ca impurity in salt produced from sub-soil brine to the inherent composition of the brine.
In the article “Washing of Strip Mined Rock and Solar Salt at Leslie Salt Corporation, U.S.A. (Symposium on Salt-1, Vol. 1, The Northern Ohio, Geological Society Incorporation, Cleveland, (1961), 449-464), Woodhill has stated that a washery is useful for reducing calcium, magnesium and sulphate impurities in solar salt. The main disadvantage of the method is that there are 10-15% losses, high capital investment is involved, and the maximum level of reduction of Ca is 70%.
In the article “Manufacture of Salt by Series Feeding System” by R. B. Bhatt, R. M. Bhatt, U. V. Chitnis, P. S. Jesulpura and K. Sheshadri,
Salt Research and Industry,
11, (1979), 9, it has been stated that sea salt can be prepared with lower calcium impurity by adopting series feeding method wherein the brine is subjected to fractional crystallization over narrower density ranges, and the salt is harvested between 27.0-29.5° Be. The drawbacks of this process are that the yield of pure salt is reduced as it is harvested over a narrower density range, and the salt is more contaminated with magnesium sulphate impurity which can only be satisfactorily removed with the help of a washery. Moreover, as found by the present inventors, series feeding does not yield improved quality salt when sub-soil brine is used.
In their patent application (Indian Patent Application No. 315/DEL/95) entitled “A Process for the Preparation of Sodium Chloride containing Low Calcium Impurity from Sea Brine in Solar Salt Works”, M. H. Vyas, H. N. Shah, J. R. Sanghavi, M. R. Gandhi and R. J. Sanghavi have claimed that calcium can be reduced by up to 70% in the harvested salt through treatment with activated starch solution. The drawbacks of the process are that it is not applicable to subsoil brines, and it is also difficult to implement the process in large-scale commercial production because of the large requirement of starch solution. Another drawback is that magnesium and sulphate impurities are still high.
In their patent application (PCT Application filed, 2001) entitled “An improved Process for the Removal of Ca Ions from the brine by Marine Cyanobacteria”, S. Mishra, P. K. Ghosh, M. R. Gandhi, A. M. Bhatt and S. A. Chauhan have claimed the production of low Ca salt from sea/sub-soil brine by mopping up Ca in the brine through certain types of marine cyanobacteria. The drawback of the process is that it is not readily amenable to scale up and magnesium and sulphate impurities would continue to pose a problem.
Besides the drawbacks indicated for the above processes, none of them integrate with subsequent marine chemicals recovery and do not in any way improve the composition of bittern and, therefore, the process of such recovery is tedious as described below.
Potassium chloride is produced most commonly from potash deposits (e.g., Strassford deposits of Germany) either by froth flotation technique or by a hot leaching process. Reference may be also made to the process described in
World Survey of Potash Resources
, The British Sulfur Corporation, London 1985, wherein potash is produced from Dead Sea brine through intermediate formation of carnallite (KCl.MgCl
2
.6H
2
O). However, sea water and sub-soil brines such as exist in India yield kainite (KCl.MgSO
4
.3H
2
O) double salt instead of carnallite because of the much higher sulphate content of the brine.
Reference may be also made to the paper “Potassium from Sea Water—A Daring Venture”, Chemistry & Industry, Nov. 13, 1971, 1309 by J. Kielland wherein it is stated that Dipycrylamine can be used to precipitate potash directly from sea water. The drawback of the process is the extremely high toxicity of the extracting reagent and the difficulty in recycling the extractant.
Reference may be made to “Manufacture of Potassium chloride and byproducts from Sea Bittern” by K. Sheshadri et al. published in
Salt Research and Industry
7, (April-July 1970), 39-44, wherein bittern is further concentrated in solar pans and, after removing crude salt and Sels' mixture (mixture of NaCl and MgSO
4
), mixed salt (NaCl and kainite) is formed in solar pans. Mixed salt is dispersed with high density bittern in proper proportion and heated to a temperature of 110° C. when keiserite (MgSO
4
.H
2
O) is formed which is separated by filtering the slurry under hot conditions. The filtrate is cooled to ambient temperature, when camallite crystallizes out. Camallite is decomposed with water to get a solid mixture of sodium chloride and potassium chloride while magnesium chloride goes into solution. Solid mixture of potassium chloride and sodium chloride is purified using known techniques to produce pure potassium chloride. The drawbacks of this process are: Mixed Salt (containing Kainite) is obtained only after two earlier solid evaporates, i.e., crude salt and Sels mixture are removed separately. This is done by solar evaporation in pans, removal of salts from pans, and pumping of liquid into intermediate pans—all of which are highly labor and energy intensive. In order to produce these salts the bittern has to be concentrated to densities as high as 37.5° Be′ (Sp. Gr. 1.348) which requires longer evaporating period and/or larger area. Secondly, kainite type mixed salt is to be processed further by mixing the same with high-density bittern and using hot extraction technique followed by cooling to extract carnallite from mixed salt. This is a tedious operation and involves high-energy consumption accompanied by loss of potash in various effluent streams. Thirdly, there is considerable loss of valuable magnesium in all the solid evaporates and there is no provision in this process to recover other products like high purity magnesia.
Reference may be also made to the articles by M. K. Raval & K. V. Satyanarayana

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