Ind. Eng. Chem. Res. 2005, 44, 2903-2907
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APPLIED CHEMISTRY Enrichment of Bromine in Sea-Bittern with Recovery of Other Marine Chemicals Rohit H. Dave and Pushpito K. Ghosh* Salt & Marine Chemicals Discipline, Central Salt and Marine Chemicals Research Institute, Bhavnagar 364002, Gujarat, India
The bromide concentration of sea bittern is 2.0-2.5 g L-1 at 29 0Be´. Evaporation to 34.5-35.0 0 Be´ increases the bromide concentration to the highest achievable level without significant losses in solid precipitates. Br- and K+ concentrations at this point are ca. 4.0 and 25.0 g L-1, respectively. It is reported herein that bromide concentration in bittern can be enhanced to 8.4 g L-1 with 93% recovery. This is achieved by integrating the process of bromide enrichment with recovery of gypsum, carnallite, magnesium hydroxide, and magnesium chloride. The process revolves around desulfatation of bittern with calcium chloride to promote carnallite (KCl.MgCl2‚ 6H2O) formation. Calcium chloride is generated from the reaction of MgCl2 in carnallite decomposed liquor (CDL) with lime. Recycling of the liquor in this manner enables us to recover the bromide that co-precipitates with carnallite and also the K+ lost in CDL during decomposition of carnallite, leading to high yields of both. Introduction
Experimental Work seawater1
The concentration of bromide ion in is 0.065 g L-1. This is in marked contrast to the concentration of ca. 4-6 g L-1 in the Dead sea brine.1 The mother liquor (bittern) obtained upon recovery of common salt from seawater, however, has a higher bromide concentration, typically 2-4 g L-1. This bittern has a density of 29-30 0Be´ (F ) 1.250-1.261), where the relationship between 0Be´ and specific gravity (F) for solution with specific gravity > 1, is given by2
F ) 145/(145 - 0Be´)
(1)
Further evaporation of sea bittern leads to substantial loss of bromide in kainite (KCl.MgSO4‚3H2O),3a whereas in the case of Dead sea brine, a concentration of bromide as high as 12-13 g L-1 is obtained in the bitterns left over after recovery of potash in the form of carnallite (KCl.MgCl2‚6H2O).1,3b Since the economics of recovery of bromine from bitterns by the steam stripping process is linked to the concentration of bromide, we were interested to investigate the possibility of increasing bromide concentration in sea bittern and report herein our efforts in this direction. Notably, it has been possible to attain a bromide concentration as high as 8.4 g L-1 in concentrated sea bittern, with overall recovery of 9092%, by desulfating the sea bittern in a cost-effective manner and integrating bromine production with production of other marine chemicals. Recent applications of desulfatation of brine and bittern developed in our laboratory are the subject of several patents.4-7 * To whom correspondence should be addressed. E-mail:
[email protected]. Fax: +91-278-2567562.
The bittern used in this work was obtained from the Greater Rann of Kutch, India where bromine plants are located. Density of bittern was measured using either a calibrated Beaume´ meter or a specific gravity bottle. The raw bittern had a density of 30.2 0Be´ (sp gr 1.263). Its further concentration was carried out by forced evaporation on a hot plate. Water loss was estimated from the difference in weights of the contents before and after evaporation. Solid precipitates such as gypsum, carnallite, and magnesium hydroxide were separated from the liquid phase by vacuum filtration. The ionic compositions of liquid and solid phases were determined using wellestablished literature procedures.8-10 Ca2+ and Mg2+ were estimated by complexometric titration with E. D. T. A.; K+ and Na+ were estimated by flame photometry; SO42- was estimated by gravimetric method; Cl- was estimated using the Mohr’s method; and Br- was estimated by the method of Willard and Heyn. Preparation of Calcium Chloride from Carnallite Decomposed Liquor/End Bittern. Carnallite was obtained by evaporating desulfated bittern from 34 to 37 0Be´ (sp gr 1.306-1.343). It was then treated with water in the ratio of 1:0.5 (w/w) and stirred for ca. 30 min. The resultant slurry was filtered and the filtrate was treated under gentle stirring with laboratory grade hydrated lime [Ca(OH)22H2O] having purity of ca. 95% (w/w)
MgCl2 + Ca(OH)2 f Mg(OH)2V + CaCl2 (L) (2) The lime quantity taken was ca. 90% of the stoichiometric requirement, which minimized the sliminess of
10.1021/ie049130x CCC: $30.25 © 2005 American Chemical Society Published on Web 04/02/2005
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Table 1. Analysis of Raw Bittern of 30.2 0Be´ (sp gr 1.264) sr.
constituents
concentration % w/v
1 2 3 4 5 6 7
calcium magnesium chloride sulfate sodium potassium bromide
0.04 5.25 19.25 6.62 4.64 1.68 2.46
the mass and allowed for easier filtration. After ensuring that the pH of the reaction mass was in the range of 7.0-7.5, the contents were filtered under vacuum. The magnesium hydroxide residue was washed with water, and the washings were kept separately. The calcium chloride concentration of filtrate was around 250-290 g L-1. Calcium chloride was produced by a similar method from end bittern except that the bittern was diluted (1:1) using the dilute CaCl2-containing washings obtained upon purification of the magnesium hydroxide above. Desulfatation of Raw Bittern. Experiments were conducted either with 0.5 or 1.0 L of bittern. Its sulfate content was determined, and a CaCl2 solution prepared as described above was added in stoichiometric quantity. The resultant desulfated bittern was vacuum filtered. Preparation of Carnallite. A measured quantity of desulfated bittern prepared as described above was taken in a beaker and subjected to forced evaporation on a hot plate. The sample was weighed intermittently and allowed to cool. At each point, the water loss and density of resultant bittern were estimated. From this, the amount of water that needs to be removed to attain a certain density was established. In subsequent studies, the total mass in the beaker was weighed and evaporation discontinued as soon as the correct water loss was registered corresponding to a Beaume´ density of 37.2 0Be´ (sp gr 1.345) of concentrated bittern upon cooling to room temperature. The mass was then allowed to cool to room temperature whereupon the carnallite crystallized out. The resultant slurry was filtered under vacuum. Decomposition of Carnallite. The carnallite obtained as described above was decomposed with water (0.5 parts of water for 1 part of carnallite) as per eq 3. The resultant slurry was vacuum filtered and the filtrate (carnallite decomposed liquor - CDL)
KCl.MgCl2.6H2O f KClV + MgCl2 (L)
(3)
was utilized for production of calcium chloride as described above. The KCl quantity in the NaCl/KClcontaining residue, which is named as carnallite decomposed product (CDP), was subsequently measured. Results and Discussion Table 1 provides details of the raw bittern composition employed in the present work. Table 2 provides data of the Br- and K+ concentration of the bittern (without desulfatation) when it was progressively evaporated up to 36.6 0Be´ (sp gr 1.338). It can be seen that ca. 97.5% of the original bromide is retained in the bittern when evaporation is confined to 35 0Be´ (sp gr 1.318), whereas only 78% of bromide is retained in the bittern when evaporation is continued up to 36.6 0Be´. Losses of K+ are still more drastic beyond this point. It would be evident that bromine recovery is confined to bitterns
having a maximum bromide concentration of 4.0 g L-1 on this account. This, in turn, makes recovery of bromine considerably more energy intensive than is achievable, for example, with Dead sea brine. A marked difference between sea bittern and Dead sea brine is the low concentration of sulfate in the latter.11 This helps to promote carnallite formation.12-15 At the same time, the end bittern has a much higher bromide concentration. The carnallite is decomposed and processed further to yield KCl, whereas the mother liquor is recycled into raw bittern to minimize bromide losses. We therefore reasoned that a cost-effective method of desulfatation of sea bittern may offer the double advantage of easy recovery of potassium in the form of KCl (via carnallite) while at the same time enabling high concentrations of bromide to be obtained in the end bittern without compromising on yield.4,5 Although inexpensive sources of CaCl2 or waste CaCl2, e.g., distiller waste of the solvay process, can be used for desulfatation,14,16 such waste is not always available in the vicinity of the bittern source. We reasoned that the reaction of MgCl2 and lime could be an attractive alternative for production of CaCl2 in salt works.6 We further reasoned that the carnallite decomposed liquor (CDL), which is produced upon decomposition of carnallite, would be an ideal source of MgCl2 for several reasons: (i) reuse of CDL in this manner enables us to recover the bromide salt that cocrystallizes with carnallite and subsequently ends up in CDL upon decomposition of the carnallite, (ii) K+ that is lost in CDL upon decomposition of carnallite can also be recovered, and (iii) the boron concentration in CDL being low,6 the Mg(OH)2 obtained along with CaCl2 can be converted into high grade MgO with minimum purification. Accordingly, the scheme of Figure 1 was devised which summarizes the integrated process. As can be seen from Figure 1, the only raw materials required in the process are sea bittern and hydrated lime; outsourced CaCl2 is required only to initiate the process and is therefore not shown. CDL (containing 245 g L-1 MgCl2) of a previous batch was mixed with an appropriate quantity of end bittern (after dilution of the end bittern so as to attain the same MgCl2 concentration as in CDL) and treated with hydrated lime (0.9 equivalents) so as to recover the requisite quantity of CaCl2 for desulfatation of 0.5 L of raw bittern after filtering off the Mg(OH)2. A total of 0.13 L of desulfating solution, which also contained Br- and K+ (Tables 3 and 4), was treated with 29-30 0Be´ (sp gr 1.25-1.261) raw bittern and the gypsum then filtered to yield clear desulfated bittern. The desulfated bittern was taken in a beaker and heated on a hot plate to boiling temperature. Based on preliminary studies undertaken initially, 0.364 kg of water was boiled off (Table 5 and 6), and then the contents were allowed to cool to room temperature. Upon filtration, crude carnallite and 37.2 0Be´ (sp gr 1.345) end bittern, containing 8.4 g L-1 Br- and negligible quantity of K+ (0.8 g L-1), were obtained. The carnallite was treated with water (0.5 part water for 1 part of carnallite) to obtain CDP (NaCl-KCl mixture) and CDL. The CDL, and part of the end bittern, were once again utilized for preparation of CaCl2 for the next batch of bittern to be desulfated. Data for the second batch are also provided in Tables 3 and 4. The tables also provide relevant input-output analysis, where Brrecoveries in the form of end bittern and CDL, and K+ recovery in the form of CDP and CDL, are considered
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Figure 1. Process for concentration of bromide in sea bittern with recovery of valuable co-products. Figures in brackets indicate Brconcentration and brine volume at various stages of processing. Table 2. Details of Br- and K+ Retention in Sea Bittern (without Desulfatation) as a Function of Beaume´ Density bittern density (0Be´)
volume (L)
water loss during evaporation (kg)
Brconc. (g L-1)
Br- amount wrt initial (%)
K+ conc (g L-1)
K+ amount wrt initial (%)
30.2 35.0 35.7 36.6
0.500 0.302 0.220 0.135
0.227 0.808 0.103
2.46 3.99 5.20 7.20
97.6 92.7 78.9
16.8 25.2 2.10 2.60
90.6 54.9 4.2
Table 3. Br- Content in Raw Bittern, CDL, and End Bittern Based on the Scheme of Figure 1
batch no. 1 2
vol./L and Brconc. (g L-1) of 30.5 0Be´ bittern taken (1)
total Br(g) in (1)
0.500 (2.46) 0.500 (2.46)
vol./L and Brconc. (g L-1) of desulfating solution (2)
1.23
total Br(g) in (2)
0.130 (3.13) 0.137 (3.00)
1.23
vol./L and Brconc. (g L-1) of end bittern (3)
0.41
0.139 (8.4) 0.143 (8.4)
0.41
vol./L and Brconc. (g L-1) in CDL (4)
total Br(g) in (3) 1.17
0.116 (2.70) 0.106 (2.91)
1.20
total Br(g) in (4)
% Brrecovery in form of end bittern and CDL
0.313
90.4
0.31
92.1
Table 4. K+ Content in Raw Bittern, CDL, and CDP Based on the Scheme of Figure 1
batch no. 1 2
vol./L and K+ conc. (g L-1) of 30.5°Be´ bittern taken (1) 0.500 (16.8) 0.500 (16.8)
total K+ (g) in (1) 8.4 8.4
vol./L and K+ conc. (g L-1) of desulfating solution (2)
total K+ (g) in (2)
0.130 (22.23) 0.137 (21.82)
vol./L and K+ conc. (g L-1) of end bittern (3)
2.89
0.139 (0.7) 0.143 (0.8)
2.99
total K+ (g) in (3)
vol./L and K+ conc. (g L-1) in CDL (4)
0.10 0.11
0.116 (38.8) 0.106 (37.8)
total K+ (g) in (4)
total K+ (g) in CDP
% K+ recovery in form of CDP and CDL
4.50
6.02
93.18
4.01
6.53
92.54
Table 5. Volume Reduction during Carnallite Production from Desulfated Sea Bittern
no.
vol. of bittern (L)
wt. of bittern (kg)
vol. of desul. bittern (L)
wt. of desul. bittern (kg)
wt. of gypsum (kg)
wt. of total contents of beaker after evaporation (kg)
wt. of carnallite (kg)
vol. of end bittern (L)
wt. of end bittern (kg)
1 2
0.500 0.500
0.630 0.630
0.598 0.600
0.705 0.711
0.052 0.054
0.341 0.343
0.157 0.149
0.139 0.143
0.187 0.193
for estimation of the percent recoveries of these elements. The evolution of Br- concentration during processing of the brine is also shown in Figure 1. When the process is implemented on large scale, there will, of course, be numerous improvements that will be made to improve the efficiency of the process. For example, handling and sampling losses would be greatly
reduced and therefore the recoveries of Br- and K+ in the desired form would further increase. It would be advantageous to either solar evaporate the sea bittern to 34.5-35.0 0Be´ (sp gr 1.312-1.318) and then take it to the factory for desulfatation and further concentration through forced evaporation. As discussed above, at this point, the bromide concentration in the bittern is
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Table 6. Water Losses during Evaporation (Based on Table 5) batch no. 1 2 avg.
0Be ´
sp gr
37.2 37.3
1.3467 1.3479
water reduction (kg)
% reduction of water
total vol. reduction of bittern (L)
% reduction of bittern
0.364 0.368 0.366
34.10 34.34 34.22
0.447 0.447 0.447
76.28 75.76 76.02
Table 7. Byproduct Recovery during Different Processes A. Forced Evaporation is Resorted to Right from the Beginning after Desulfatation of Raw Bittern scale
water
gypsum
Mg(OH)2
KCl
Br
lab. plant
0.366 kg 303 m3
54 × 10-3 kg 45 MT
22 × 10-3 kg 18.32 MT
21.8 × 10-3 kg 18.16 MT
1.2 × 10-3 kg 1 MT
B. Solar Evaporation of Bittern is Carried Out up to 35 0Be´ (sp gr 1.2143) at which Point Br- and K+ Concentration Continuously Increase and Losses in Precipitated Solids are Negligible (see Table 2) and Undertaking Desulfatation of the Bittern at this Point scale
water
gypsum
Mg (OH)2
KCl
Br-
lab. plant
0.138 kg 115 m3
54 × 10-3 kg 45 MT
22 × 10-3 kg 18.32 MT
21.8 × 10-3 kg 18.16 MT
1.2 × 10-3 kg 1 MT
the highest achievable without significant losses in solid precipitates (Tables 2 and 7B). This would greatly minimize the energy cost of forced evaporation and maximize solar energy utilization without compromising on the convenience of factory processing. The difference between parts A and B of Table 7 is that 0.226 kg of water is solar evaporated in reaching 35 0Be´ from the original state and only 0.138 kg of water needs to be evaporated thereafter. (N. B. During the evaporation process that yields carnallite, water is simultaneously lost from the solution in the form of water of crystallization of carnallite leading to a higher degree of concentration of the bittern.) Whatever forced evaporation is undertaken in the factory should of course be with the aim of not only concentrating the bittern but also recovering water required in the process. There is a third option, which is to take the desulfated bittern (Table 7A) and do solar evaporation up to the onset point of carnallite formation and thereafter to do forced evaporation. The main problem with this option is that
if desulfatation needs to be done in the factory then material must be pumped in, then sent out to the ponds, and once again brought back to factory. Therefore, Table 7B is the preferred option. Also, if some end bittern were necessary for production of a sufficient quantity of calcium chloride, it would be best if the end bittern is first debrominated and then treated with lime since during the debromination process there is a minor decrease in concentration of constituents other than bromide.17 This would eliminate unnecessary recycling of the end bittern that is already enriched with bromide. As such, the end bittern requirement can be minimized by maximizing the recovery of CaCl2 produced in the reaction of MgCl2 and hydrated lime. This, however, needs to be done without unnecessary dilution since there would be an energy penalty in subsequent evaporation of that water. The washings obtained upon purification of the Mg(OH)2 filter cake, which would contain CaCl2, can be utilized for (i) slaking of quicklime and (ii) dilution of the
Figure 2. Idealized process for concentration of bromide in sea bittern with recovery of valuable co-products.
Ind. Eng. Chem. Res., Vol. 44, No. 9, 2005 2907
debrominated end bittern prior to treatment with hydrated lime. Although we have not processed the CDP in the present work, it is well-known that it can be subjected to hot leaching to obtain NaCl and KCl in pure forms.1,15,18 Figure 2 illustrates the idealized scheme, whereas Table 7B provides details of the product portfolio (except MgCl2 in the form of debrominated end bittern) obtainable in this manner. In conclusion, we have demonstrated the viability of obtaining end bittern from sea bittern with up to 8.4 g L-1 and >92% recovery of bromide. At the same time, potassium chloride, sodium chloride, gypsum, magnesium hydroxide, and magnesium chloride in concentrated solution form are obtained. Acknowledgment The authors thank Mr. R. N. Vohra, Mr. M. R. Gandhi, and Dr. A. S. Mehta for helpful discussions and the referees for their valuable suggestions. Literature Cited (1) Ullmann’s Encyclopedia of Industrial Chemistry, 6th ed.; WILEY-VCH: Weinheim, Germany, 2002; electronics release. (2) Perry’s Chemical Engineering Hand book, 7th ed.; McGrawHill: New York; pp 1-20. (3) (a) Jadhav, M. H.; Chowgule, V. V. Bromine concentration with rise in density of sea bitterns. Fifth International Symposium on Salt; Northern Ohio Geological Society: Ohio, pp 313-316. (b) Epstein, J. A. (Israel). Kim., Handasa Kim., “Processes and products in Palestine Potash Ltd”,23, 6, 8-10, 12 (Hebrew). CODEN: KHKIEZ. ISSN: 0792-609X. DOCUMENT TYPE: Journal CA Section: 53 (Mineralogical and Geological Chemistry) Section cross-reference(s): 49, 1995. (4) Vohra, R. N.; Ghosh, P. K.; et al. Recovery of common salt and marine chemicals from brine. US Patent No. 6,776,972, July 29, 2004. (5) Vohra, R. N.; Ghosh, P. K.; et al. A process for recovery of low sodium salt from bittern. Patent No. US2003143152; WO 03/ 064323, August 07, 2003. (6) Ghosh, P. K.; et al. Novel integrated process for the recovery of sulphate of potash (SOP) from sulphate rich bittern. US Patent
Application No: 10/814,778. March 30, 2004. PCT Application No: PCT/IN03/00463, 2003. (7) Ghosh, P. K.; et al. Improved process for simultaneous recovery of industrial grade potassium chloride and edible salt enriched with KCl (Low sodium salt) from bittern. US Patent Application No: 10/814 779, March 30, 2004; PCT Application No: PCT/IN 03/00449, 2003. (8) Vogel, A. A Textbook of Quantitative Inorganic Analysis, 4th ed.; ELBS, Longman Group Ltd.: England. (9) Burriel-Marti, F.; Ramirez Munoz, J. Flame Photometer A Manual of methods and application; Elsevier Publishing Co.: New York, 1957. (10) Willard, H. H.; Heyn, A. H. A. “Volumetric Determination of Bromide in Brines”, Ind. Eng. Chem., Anal. Ed. 1943, 15 (5), 321. (11) Bentor, Y. K. Some geochemical aspects of the Dead sea and the question of its age. Geochim. Cosmochim. Acta 1961, 25 (4), 239-240. (12) Ferna´ndez-Lozano, J. A. Recovery of Epsomite and Sylvite from Seawater Bittern by Crystallization. Fourth International Symposium on Salt; Northern Ohio Geological Society: pp 501510. (13) Choudhari, B. P. Potassic mixed salts and crystalline bischoffite from inland (Kutch) bitterns: A case study of Kharaghoda and Udoo bitterns. Indian J. Appl. Chem. 1969, 32 (6), 355359. (14) Joshi, J. M.; Sanghavi, J. R.; Sheshadri, K. Potassium chloride recovery from mixed salt using distiller waste liquor of soda ash plant. Chem. Age India 1966, 17 (8), 607-609. (15) Hildebrand, J. H. The extraction of potash and other constituents from seawater bittern. Ind. Eng. Chem. 1918, 10 (2), 96-105. (16) Kasikowski, T.; et al. Utilization of distiller waste from ammonia-soda processing. J. Cleaner Prod. 2004, 12 (7), 759-769. (17) Mehta, A, S.; Ghosh, P. K.; Shah H. N.; Sanghavi, R. J. Ideas for improvement emanating from audit of a bromine plant in the Greater Rann of Kutch. Indian J. Chem. Technol. 2003, 10, 644-653. (18) Kobe, K. A. Inorganic Process Industries; Mac-Millan & Co., Ltd., London, 1948; p 60.
Received for review September 9, 2004 Revised manuscript received January 12, 2005 Accepted January 14, 2005 IE049130X
