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 0 Be ´. 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 gL -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.MgCl 2 ‚ 6H 2 O) formation. Calcium chloride is generated from the reaction of MgCl 2 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 The concentration of bromide ion in seawater 1 is 0.065 gL -1 . This is in marked contrast to the concentration of ca. 4-6gL -1 in the Dead sea brine. 1 The mother liquor (bittern) obtained upon recovery of common salt from seawater, however, has a higher bromide concen- tration, typically 2-4gL -1 . This bittern has a density of 29-30 0 Be ´(F) 1.250-1.261), where the relationship between 0 Be ´ and specific gravity (F) for solution with specific gravity > 1, is given by 2 Further evaporation of sea bittern leads to substantial loss of bromide in kainite (KCl.MgSO 4 ‚3H 2 O), 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.MgCl 2 ‚6H 2 O). 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 90- 92%, by desulfating the sea bittern in a cost-effective manner and integrating bromine production with pro- duction of other marine chemicals. Recent applications of desulfatation of brine and bittern developed in our laboratory are the subject of several patents. 4-7 Experimental Work 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 0 Be ´ (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 well- established literature procedures. 8-10 Ca 2+ and Mg 2+ were estimated by complexometric titration with E. D. T. A.; K + and Na + were estimated by flame photometry; SO 4 2- 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 Carnal- lite Decomposed Liquor/End Bittern. Carnallite was obtained by evaporating desulfated bittern from 34 to 37 0 Be ´ (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) 2 2H 2 O] having purity of ca. 95% (w/w) The lime quantity taken was ca. 90% of the stoichio- metric requirement, which minimized the sliminess of * To whom correspondence should be addressed. E-mail: pkghosh@csmcri.org. Fax: +91-278-2567562. F) 145/(145 - 0 Be ´) (1) MgCl 2 + Ca(OH) 2 f Mg(OH) 2 V + CaCl 2 (L) (2) 2903 Ind. Eng. Chem. Res. 2005, 44, 2903-2907 10.1021/ie049130x CCC: $30.25 © 2005 American Chemical Society Published on Web 04/02/2005