|Title of Invention||
"A PROCESS FOR RECOVERY OF SODIUM CHLORIDE AND MARINE CHEMICALS FROM BRINE"
|Abstract||The invention relates to recovery of sodium chloride , potassium chloride, concentrated magnesium chloride with enriched bromide, and high purity magnesia form brine in an integrated manner, said process comprises preparation of calcium chloride by reaction of hydrochloric acid generated in the process with limestone, desulphatation of brine with calcium chloride, production of sodium chloride or superior quality in solar pans, solar evaporation of bittern thereby producing carnallite and end bittern, processing carnallite through established processes to produce potassium chloride, recovering end bittern containing highly concentrated magnesium chloride and enriched bromide and calcination of a part of the end bittern after solidification to produce high purity magnesia and hydrochloric acid utilizable in the process.|
|Full Text||The present invention relates to a process for recovery of sodium chloride and marine
chemicals from brine. The process recovers 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
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. Besides, salt is 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 KC1 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, p 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), p 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/ sulphate and
0.20-0.30% Mg after harvesting and washing of heaps with 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), p 449-464), A. 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, p 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 yield of pure salt yield 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
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 sub-soil brines and also difficult to implement in
large-scale commercial production because of the large requirement of starch solution.
Another drawback is that magnesium and sulphate impurities would still be high.
In their patent application (PCT Application filed, 2001) entitled "An improved Process
for the Removal of Ca Jons 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 process, none of them integrate with
subsequent marine chemicals recovery and does 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 floatation technique or by hot leaching process.
Reference may be also made to the process described in World Survey of Potash
Resources, The British Sulphur Corporation, London 1985, wherein potash is produced
from Dead Sea brine through intermediate formation of carnallite (KCl.MgCl2.6H2O).
However, sea water and sub-soil brines such as exist in India yield kainite
(KCl.MgS04.3H2O) 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, 13 Nov. 1971, p 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, April-July 1970,
Vol. 7, page 39-44, wherein bittern is further concentrated in solar pans and after removing
crude salt and Sols' mixts (mixture of NaCI and MgSO4), 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 (MgS04.H2O) is formed which is
separated by filtering the slurry under hot conditions. The filtrate is cooled to ambient
temperature, when carnallite crystallizes out. Carnallite 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 evaporites, i.e.,
crude salt and sels mixt. 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 labour 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
evaporites and there is no provision in this process to recover other products like high
Reference may be also made to the articles by M. K. Raval & K. V. Satyanarayana in
"Bromine Content in Bittern From Salt Works in Kuda-Kutch Region", Salt Research
and Industry, Vol. 4, No. 2, April 1967 pp 56-58 and by M. H. Jadhav and V. V. Chowgule
in "Bromine concentration with rise in Density of Sea Bittern", Fifth International
Symposium on Salt, from which it can be concluded that although there is increase in
bromide concentration in bittern with evaporation, a significant part of the original
bromide content in bittern tends to be lost in the solid evaporites in the course of recovery
of potash via kainite salt as described above. This constrains bromine to be recovered at
29-32°Be' as a result of which its recovery is less efficient, since bromide concentration in
bittern is in the range of 2-4 gL"1.
Reference may be made to "Improved Treatment of Waste Brines" by Chr. Balarew, D.
Rabadjieva and S. Tepavitcharova, (International Symposium on Salt 2000, page 551-554)
for recovery of marine chemicals. The principle drawbacks of this process, which
advocates crystallization of salt followed by removal of magnesium in bittern with lime,
subsequent recovery of potash and recirculation of calcium chloride into bittern for the
purpose of desulphatation, are that salt quality is not improved in any way, and the
recovery of potash would involve removal of large quantities of water which is not feasible
with solar evaporation.
Reference may be made to "Potassium chloride from sea bittern — Part 2, Recovery of
potassium chloride, magnesium sulphate and potassium sulphate" by Gadre G. T., Rao
A.V. and Bhavnagary H. M., Jr. of Sc. Ind. Res., 17(A), 9, (1958), p 376, wherein bittern is
cooled to 10° -5° C to crystallize sulphate ion as epsom salt. The bittern after removal of
sulphate is concentrated to crystallize camallite. The main drawback of this process is that
apart from high cost of refrigeration and bulk handling, the process removes sulphate to a
maximum extent of 50% of sulphate originally present in bittern, which at a later stage will
contaminate camallite rendering the product impure.
According to the present invention, desulphatation of low density brine, i.e., brine prior to
crystallization of salt, with in situ generated calcium chloride or with calcium chloride in
distiller waste is found to be a highly effective solution to all of the drawbacks described in
the prior art. It has been found in the course of the invention that, although calcium
impurity in salt is among the principal concerns which dictates its price and usability in
chloralkali industry, the addition of calcium chloride to brine for the purpose of
desulphatation does not increase calcium impurity of salt but actually decreases it. The
primary reason for this is that addition of calcium chloride forcibly eliminates calcium
sulphate as a precipitate because of the large calcium ion concentration in brine and the
sparing solubility of calcium sulphate. As a result, less calcium sulphate coprecipitates
with common salt during the crystallization of the latter at 25° Be' and beyond. The
residual calcium ia the brine which adheres to the salt crystals is easily washable as it is
primarily in the form of calcium chloride which has much higher solubility than calcium
sulphate. Removal of sulphate also reduces build up of magnesium sulphate impurity in
salt and the adhering magnesium chloride impurity is easily washable. Most remarkably,
sub-soil brine which yields salt of the lowest purity is especially attractive since the
requirement of desulphating chemical is the least and the salt quality can be upgraded to
purity even superior to that obtained presently for sea salt As further established in the
course of the invention, addition of calcium chloride to effect desulphatation does not in
any way deteriorate the characterisitics of the bittern and carnallite can be recovered with
ease. Further, as found in the course of the present invention, desulphatation also allows
steady build-up of bromide concentration in bittern with negligible loss in solid evaporites.
Furthermore, desulphatation allows high purity magnesium chloride to be formed, a part of
which can be converted into magnesium oxide of high purity with concomitant production
of hydrochloric acid which can be utilised for production of calcium chloride. Another
novelty of the present invention is the use of soda ash distiller waste for desulphatation.
Such waste is rich in calcium chloride and sodium chloride both of which are useful in the
methodology of the invention.
The main object of the present invention is to provide an improved and integrated process
for recovery of salt and marine chemicals which is centered around desulphatation of brine
and obviates the drawbacks as detailed above.
Another object of the present invention is to prepare high purity salt, particularly from subsoil
brine, through simple washing of the crystallised salt with water, and at virtually no
extra cost, through the process of integration, and further to prepare salt of very high purity
through only additional incremental cost.
Still another object of the present invention is to integrate salt manufacture with soda ash
production and to use calcium rich distiller waste generated in soda ash plants for the
Still another object is to recover salt and marine chemicals from high density, low sulphate
sub-soil brine so as to maximize salt productivity, minimize requirement of desulphating
chemicals and to achieve the highest differential improvement in salt quality.
Still another object of the present invention is to provide a seeding process for easy
granulation of calcium sulphate leading to the easy separation from brine.
Yet another object of the present invention is to use the carbon dioxide gas produced when
lime stone is dissolved in hydrochloric acid, to produce magnesium carbonate and potassium carbonate in the down stream processes, through well established processes. Yet another object of the present invention is to observe that there is negligible loss of bromine when desulphated bittern is processed by further evaporation to produce carnallite, with the result that bromide can be enriched in the end bittern and can then be processed by the well established methods of bromine recovery which prefer higher concentration of bromide ions for better economy. Summary of invention
The present invention relates to recovery of industrial grade salt and marine chemicals from brine in an integrated manner. The process involves treatment of salt brine with calcium chloride to precipitate calcium sulphate, solar evaporation of desulphated brine in crystallisers to produce salt, solar evaporation of bittern to produce carnallite, decomposition of carnallite to recover sodium chloride and potassium chloride mixture and processing of this solid mixture to produce potassium chloride by known hot extraction technique. End bittern obtained after crystallisation of carnallite is calcined to produce high purity magnesia and hydrochloric acid. Limestone is treated with hydrochloric acid to produce calcium chloride, which is recycled for desulphatation of brine while the carbon dioxide can be recycled for preparation of carbonates of magnesium and potassium by well established routes. Statement of Invention:-
Accordingly, the present invention provides a process for recovery of sodium chloride and
marine chemicals from brine 3-24°Be in integrated manner comprising the steps of:
(i) reacting of 1-12 M hydrochloric acid which is obtained from calcination of
magnesium chloride of end bittern at 600-800°C with calcerous material including
limestone in stoichiometric ratio of one part of limestone with two parts of
hydrochloric acid to prepare calcium chloride of 100-600 g/L concentration required
(ii) treating said brine with calcium chloride as obtained in step (i) to produce granular
calcium sulphate through a seeding process; (iii) separating calcium sulphate from brine;
(iv) evaporating desulphated brine thus obtained in step (iii) in solar pans up to 29-32° Be' to obtain crystal of common salt,
(v) washing salt of step (iv) with water or dilute brine to remove adhering chlorides of
calcium and magnesium; (vi)evaporating bittern obtained in step (iv) in solar pans from density range of 29° Be' to 35.5° Be' to crystallise crude carnallite and thereafter recovering potassium chloride by known techniques; (vii) recovering concentrated end bittern as obtained in step (vi) comprising mainly of
magnesium chloride and enriched bromide; and (viii) solidifying a part of the end bittern and calcining in the temperature range of 600-800°C to produce solid magnesium oxide and hydrochloric acid sufficient for recycling in step (i). In still another embodiment of the present invention, calcium chloride is in distiller waste
of soda ash industry in the concentration of 5-15% CaCl2 in 0.8-1.2 mole of calcium to
sulphate can also be used optionally.
In yet another embodiment of the present invention.treating the desulphated brine as
obtained in step (ii) of claim 1 with barium chloride in 0.80-0.95 mole ratio of barium to
residual sulphate ion to ensure near-complete desulphatation.
In still another embodiment of the present invention, marine chemicals include common
salt, potassium chloride, magnesium chloride enriched with bromide, high purity
magnesia and additionally, calcium sulphate with efficient and integrated manner from sub-soil/sea brine of 3-24° Be' density and sulphate
concentration typically in the range of 5-18 g/L measured at 16°Be'.
In yet another embodiment of the present invention, recovery of said marine products can
be most efficiently undertaken through reduction of sulphate concentration of brine to a
concentration in the range of 0.5-2.0 g/L.
In still another embodiment of the present invention, the reduction of sulphate is achieved
by adding calcium chloride produced in situ.
In yet another embodiment of the present invention, removal of calcium sulphate from
desulphated brine is facilitated through a seeding technique which allows easy granulation
of the resultant calcium sulphate formed.
In still another embodiment of the present invention, sub-soil brine having high sodium
chloride concentration (up to 18°Be') and low sulphate concentration ( is especially suitable as brine source.
In yet another embodiment of the present invention, brines located in the vicinity of soda
ash plants can be treated with the distiller waste containing 5-15% calcium chloride.
In still another em
desulphatation, salt recovery and carnallite production can be carried out readily in the
field in large solar pans.
In yet another embodiment of the present invention, wherein desulphatation allows build
up of bromide concentration in bittern up to 7.5 g/L at 35.5°Be' without any significant
loss of bromide along with crystallized solids during evaporation.
The invention is further explained in the following steps:
(I) Calcium chloride is prepared by reaction between limestone and recycled
hydrochoride acid in leach tank under ambient condition followed by treatment
with a small amount of lime to raise pH to 5.5 and filtration through a bed of
calcium sulphate produced in the process itself to eliminate unwanted colour from
iron impurities. The concentration of calcium chloride solution is preferably
maintained between 410 and 440 gL"1. Calcium chloride is alternatively obtained as
a clear liquid after settling the distiller waste from soda ash industry and having
typical composition of 10-12% CaCl2 and 5-7% NaCl.
(II) Brine, preferably with density in the range of 15° Be'-22° Be' (Sp. Or. 1.11-1.14),
is treated with calcium chloride solution to eliminate calcium sulphate as described
above. This reaction can be carried out in a reaction vessel or preferably in the field
in large solar pans. When undertaken in a reaction vessel, a part of the output slurry
of calcium sulphate is fed back to the vessel as seed. This makes the precipitate
granular, which settles efficiently at the bottom.
(ffl) Desulphated brine is allowed to concentrate in the condenser and then charged into
the crystalliser at around 25° Be' (Sp. Gr. 1.21) whereupon common salt
crystallizes out. Evaporation of thus treated brine in solar pans yields salt of high
purity when washed with small quantities of dilute brine or fresh water in the field
to remove adhering calcium and magnesium chlorides.
(TV) Desulphatation with calcium chloride does not remove sulphate completely from
the brine and small amount of calcium in the form of calcium sulphate coprecipitate
with the crystallized salt. If salt of still higher purity is required, more complete
desulphatation of brine may be carried out with barium chloride whose usage,
however, is minimized because of the first stage of desulphatation with calcium,
chloride. To avoid any contamination of the salt with barium ion, the barium
chloride is used in slightly less than the stoichiometric amount of sulphate present
in the brine following treatment with CaCh, the sulphate concentration typically
being in the range of 1-3 g/L at 24° Be'. It is advisable to carry out desulphatation
with barium chloride in reaction vessels than in the open field.
(V) The mother liquor (bittern) obtained after crystallization of salt having density in
the range of 29-30° Be1 (Sp. Gr. 1.25-1.26) is fed to shallow impermeable solar
pans where it undergoes further solar evaporation. As density rises to 32 to 33° Be'
(Sp.Gr. 1.28-1.284), excess sodium chloride present in original bittern crystallizes
out, which is removed. On further evaporation, camallite double salt (KCl.MgCl-
2.6H2O) crystallizes out at a density of 35 to 35.5° Be' (Sp.Gr. 1.318-1.324) along
with residual NaCl as well established in the prior art.
(VI) Camallite is decomposed with water to remove magnesium chloride and a mixture
of potassium chloride and sodium chloride. Purification of the latter to obtain
potassium chloride is achieved as well established in the prior art. Residual sodium
chloride/potassium chloride is fed back into the camallite pan for enhanced
recovery in the subsequent cycle.
(VH) Bittern obtained after removal of camallite, having a density of up to 35.5°Be' (Sp.
Gr. 1.324), is a concentrated solution of magnesium chloride and is known as end
bittern with magnesium chloride concentration ranging from 400 to 430 gL"1. The
end bittern was analysed for bromide and its concentration found to be 7.5 gL"1
(expressed as elemental bromine), i.e., nearly 3 times the bromide concentration at
29° Be' (Sp.Gr. 1.25) and 1.5 times'the concentration at 32° Be' (Sp.Gr. 1.28)
which is typically'-the density range at which bromine is recovered in many plants.
Since the volume of bittern is reduced by a factor of three in going from 29° Be' to
35.5° Be', there is essentially no loss of bromide during the process of
End bittern is reacted in calcination system at a temperature ranging from 600 to 800° C to
form magnesium oxide and hydrochloric acid by the established process of the equation
MgCl2.6H2O -> MgO + 2HC1 + 5H20
The following examples are given by way of illustration and should not be construed to
limit the scope of the invention:-
In this example brine of 24° Be' (Sp. Gr. 1.198) density, with 5.23 gL"1 and 0.86 gL"1
concentrations of SCU2" and Ca2"1", respectively, was desulphated with calcium chloride.
Calcium chloride was prepared by dissolving limestone in concentrated hydrochloric acid
followed by addition of lime in order to neutralize residual acid and precipitate out iron
impurities. After settling, the decanted solution was filtered over a bed of calcium sulphate
to yield a colorless solution with calcium chloride content estimated as 444 gL"1. 3.6 L of
brine was treated with 0.068 L of calcium chloride solution. After removal of calcium
sulphate, which afer washing contained 0.45% Cl"1, desulphated brine was found to contain
1.73 gL'1 of SC>42". A part of desulphated brine was concentrated by solar evaporation till a
density of 29° Be' (Sp. Gr. 1.25) was reached and most of the common salt crystallized
out. The common salt, on chemical analysis, contained 0.2% Ca2+ whereas the salt without
desulphatation had 0.35% Ca2+. The second part of desulphated brine of 24° Be' was
treated with barium chloride in such a manner that 80% of residual sulphate content of
brine was precipitated as barium sulphate. The brine was decanted and concentrated by
solar evaporation till density of 29° Be' (Sp.Gr. 1.25) was achieved. Calcium content of
the crystallised sodium chloride was found to be in the range of 0.03-0.04% after washing
the salt with minimum quantity of water. The above example clearly shows that
desulphatation of brine first with calcium chloride and then with barium chloride gives
very pure quality salt while economizing on the use of barium chloride.
In this example field scale experiment was conducted to produce salt form sub soil brine in
the salt field itself using calcium chloride prepared as in Example 1 as a desulphating
agent. Subsoil brine of density 16.5° Be' (Sp.Gr. 1.128) had the following chemical
composition: Mg, 6.3 gL"1; Ca 1.17 gL"1; S046.5 gL"1; Cl, 117.0 gL"1; Na, 64.0 gL"1. 50000
L of above brine was treated with 950 L of calcium chloride having a concentration of 440
gL"1 CaCh in condenser pan. The desulphated brine was concentrated to 25° Be' density
and then transferred to crystalliser for salt crystallisation. The common salt crystallised
between density range of 25° Be' (Sp. Gr. 1.121) to 30° Be' (Sp. Gr. 1.26) and was
harvested, heaped and washed with minimum quantity of water to remove the adhering
highly soluble calcium and magnesium impurities. The salt on dry basis was analysed as:
Ca, 0.11% w/w; Mg, 0.09% w/w; SO4, 0.06% w/w; NaCl 99.0% w/w. Total quantity of
washed common salt obtaied in this experiment was approximately 5 tons.
40 L of 29°Be' desulphated bittern with chemical analysis as follows: Mg2"1", 46.0 gL"';
Na+, 44.1 gL"1; K+, 13.9 gL-1; Ca2+, 2.0 gL -'; Cl", 193 gL"1; SO4
2, 2.4 gL'1; Bf, 2.5 gL"1
was poured in shallow pans where it was allowed to concentrate using solar energy.
Initially, this bittern got concentrated to a density of 32.2° Be' when excess salt separated
out which was removed. On further evaporation with solar energy in a second shallow pan
bittern got further concentrated up to a bittern density of 35.5° Be' (specific gravity 1.32).
5.5 kg of crude carnallite separated out with the following probable composition: KC1,
15.00%; MgCl2; 28.22%; CaSO4,0.46%; CaCl2,0.36%; NaCl, 6.2%.
1 kg of the carnallite obtained as above was processed initially with 0.4 kg. of water under
ambient conditions. After separation of solid and liquid phases, solid phase was found to
contain 121.4 g of KC1 thereby indicating a recovery of 79% of KC1 originally present in
carnallite. The reset of it was contained in liquid phase. Since liquid phase indicated KC1
analysis of 41.2 gL-1 which was almost similar to concentration of KC1 in bittern before
formation bf carnallite, it was mixed with that bittern and allowed to concentrate in solar
pans for further recovery of carnallite. This reduced loss of KCl to a great extent The
KCl/NaCl mixture so obtained was processed further using the well known hot extraction
technique to produce potassium chloride containing 97.8% KCl.
After removal of carnallite, 11L of end bittern having chemical analysis as given below
was obtained: Mg2*, 108.7 gL'1; Na+, gL"1, K+, 1.4 gL"1; Ca2+, 1.6 gU1; Cl", 324.5 gL"1;
SO42", 0. gL"1; Bf, 7.5 gL~'; B, 0.11 gL"1. A part of the end bittern was calcined at a
temperature of 600-800° C producing crude magnesium oxide followed by washing with
water to yield magnesium oxide containing 98.5% MgO. Hydrochloric acid produced in
the process as by-product can be recycled for the process of production of calcium chloride
described in Example 1.
In this example 29° Be' bittern obtained after recovery of salt from sub-soil brine was used
as raw material for desulphatation in a reaction vessel. In the reaction vessel, bittern and
calcium chloride flow rates were kept at 0.21 Lmin"1 and 0.013 Lmin'1, thereby producing
9.13 g/minute of solid calcium sulphate in the form of a slurry. 0.06 Lmin"1 of seed slurry
containing 18.26 grain"1 of calcium sulphate was added continously into the reaction
vessel. Two third of the output slurry was recycled into the reaction vessel, as seed, while
one third was used for further processing to enable a continous process to be achieved. The
output calcium sulphate slurry was granular and easily settled to a concentration of 294gL"'
to allow decantation of clear desulphated bittern which is otherwise more difficult.
The desulphatation was scaled up and 2400 litres of such desulphated bittern was obtained
and concentrated in a solar pan. After removing excess sodium chloride at a density of
32.5° Be' (Sp. Gr. 1.288), bittern was further evaporated till carnallite deposited at a
density of 35.5 ° Be' (Sp. Gr. 1.324). A total of 340 kg of camallite crystallized out in the
pan. Chemical analysis of camallite is given below: CaSQt, 0.816%; MgCh, 35.25%;
NaCl, 8.42%; KCI, 15.03%. About 650 litre of end bittern, having following chemical
analysis was obtained after removal of carnallite at a density of 35.5° (Sp. Gr. 1.324): Ca2"1",
2.12 gl/1; Mg2, 113.3 gU1; SO4
2", 0.33 gl/1; Na, 1.50 gL'1; K, 1.10 gL'1; Cl", 336.8 gU1;
Boron as 8,0.1 gl/1.
In the example of Example 1, brine was treated with settled distiller waste of a soda ash
industry. Its composition were as follows: CaCla, 12.9%(w/v); NaCl, 6.6% (w/v). Similar
results as those reported in Example 1 were obtained when the distiller waste was added to
maintain the same ratio of calcium to sulphate as in the example of Example 1.
The main advantages of the present invention are:
(1) Very low sulphate bittern containing 1-3 g/L sulphate at 29° Be', which is known
to yield a simple means of efficient recovery of potassium chloride and magnesium
chloride via intermediate carnallite, can be generated from high sulphate brine such
as sea water and other forms of brine typically in many regions of the world,
through an economic process of desulphatation with the distiller waster of soda ash
industry and with the further advantage of production of superior quality salt. This
is especially applicable where salt production and soda ash production are
integrated such as in several large industries.
(2) The improved process is also most attractive for certain sub soil brines which are
low in sulphate concentration ( high salt concentration but yield poor quality salt with high (>0.3% ) insoluble
(3) Desulphatation of sea brine and such sub soil brine as described above allows
bromide content in the brine to be progressively increased up to 7.5 g/L in 35.5°
Be' end bittern with neglible loss of bromide during the process of concentration.
(4) When integrated with downstream production of magnesia, hydrochloric acid
generated as by-product can be utilized in preparation of calcium chloride from
inexpensive limestone and other inexpesive calcareous raw materials while the
liberated carbon dioxide can be utilized for production of carbonate salts of
potassium and magnesium through well established processes. This is especially
advantageous where there is no accessibility of distiller waste.
(5) Forced desulphatation of brine eliminates the need for elaborate condensers
normally employed to crystallize out rnaximimi possible amount of calcium
sulphate through natural solar concentration.
(6) Sub-soil brine having high sodium chloride concentration (up to 18°Be') and low
sulphate concentration ( maximize productivity, minimise use of desulphating chemical, and maximize the
advantage of the process in terms of salt quality upgradation.
(7) Brines located in the vicinity of soda ash plants can be treated with the distiller
waste containing 5-15% calcium chloride and 1-7% sodium chloride so as to
maximize the cost-effectiveness of the process.
1. A process for recovery of sodium chloride and marine chemicals from brine 3-
24°Be in integrated manner comprising the steps of:
i) reacting of 1-12 M hydrochloric acid which is obtained from calcination of
magnesium chloride of end bittern at 600-800°C with calcerous material
including limestone in stoichiometric ratio of one part of limestone with
two parts of hydrochloric acid to prepare calcium chloride of 100-600 g/L
concentration required for desulphatation; ii) treating said brine with calcium chloride as obtained in step (i) to produce
granular calcium sulphate through a seeding process; iii) separating calcium sulphate from brine; iv) evaporating desulphated brine thus obtained in step (iii) in solar pans up to
29-32° Be' to obtain crystal of common salt-sodium chloride, v) washing salt of step (iv) with water or dilute brine to remove adhering
chlorides of calcium and magnesium; vi) evaporating bittern obtained in step (iv) in solar pans from density range of
29° Be' to 35.5° Be' to crystallise crude carnallite and thereafter recovering
potassium chloride by known techniques; vii) recovering concentrated end bittern as obtained in step (vi) comprising
mainly of magnesium chloride and enriched bromide; and viii) solidifying a part of the end bittern and calcining in the temperature range
of 600-800°C to produce solid magnesium oxide and hydrochloric acid
sufficient for recycling in step (i).
2. A process as claimed in claim 1, wherein calcium chloride is distiller waste of soda ash industry in the concentration of 5-15% CaCl2 in 0.8-1.2 mole of calcium to sulphate can also be used optionally.
3. A process as claimed in claim 1, wherein treating the desulphated brine as obtained in step (ii) of claim 1 with barium chloride in 0.80-0.95 mole ratio of barium to residual sulphate ion to ensure near-complete desulphatation.
4. A process as claimed in claim 1, wherein marine chemicals include common salt, potassium chloride, magnesium chloride enriched with bromide, high purity magnesia and additionally, calcium sulphate with
produced in an efficient and integrated manner from sub-soil/sea brine of 3-24° Be' density and sulphate concentration typically in the range of 5-18 g/L measured at 16°Be'.
5. A process as claimed in claim 1, wherein recovery of said marine products can be most efficiently undertaken through reduction of sulphate concentration of brine to a concentration in the range of 0.5-2.0 g/L.
6. A process as claimed in claim 1, wherein the reduction of sulphate is achieved by adding calcium chloride produced in situ.
7. A process as claimed in claim 1, wherein removal of calcium sulphate from desulphated brine is facilitated through a seeding technique which allows easy granulation of the resultant calcium sulphate formed.
8. A process as claimed in claim 1, wherein sub-soil brine having high sodium chloride concentration (up to 18°Be') and low sulphate concentration ( 9. A process as claimed in claim 1, wherein brines located in the vicinity of soda ash plants can be treated with the distiller waste containing 5-15% calcium chloride.
10. A process as claimed in claim 1, wherein the primary process of desulphatation, salt recovery and carnalllite production can be carried out readily in the field in large solar pans.
11. A process as claimed in claim 1, wherein desulphatation allows build up of bromide concentration in bittern up to 7.5 g/L at 35.5°Be' without any significant loss of bromide along with crystallized solids during evaporation.
12. A process for recovery of sodium chloride and marine chemicals from brine substantially as herein described with reference to examples accompanying this specification.
|Indian Patent Application Number||01689/DELNP/2003|
|PG Journal Number||32/2008|
|Date of Filing||16-Oct-2003|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110001, INDIA.|
|PCT International Classification Number||C01D 3/06|
|PCT International Application Number||PCT/IN01/00185|
|PCT International Filing date||2001-10-22|