Extraction of Bromine

Bromine is a dense, red, volatile, corrosive liquid (bp 59 °C) that is best made by oxidizing the small amount of Br in seawater with chlorine (higher bromide concentrations occur in the Dead Sea and in certain natural brines, e.g., in Arkansas and Michigan). The vapor of the resulting Br2 is then carried off in an air stream  

Reaction 12.21 illustrates the trend toward lower electronegativity (less oxidizing power) as one descends a periodic group. The bromine vapor is trapped in aqueous Na2C03 (in effect, a mild source of alkali) as bromide 

A qualitative similarity to the aqueous chemistry of chlorine will be evident. For each oxoanion of chlorine, there is a corresponding bromine species, although perbromate salts form only under certain strongly oxidizing conditions (e.g., oxidation of bromate ion in alkaline solution with F2 or XeF2) and in fact were unknown until 1968. 

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Most of the chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp bleaching, disinfectants, and textile processing. Further use is in the manufacture of chlorates, chloroform, carbon tetrachloride, and in the extraction of bromine. 

Magnesium sulfate heptahydrate may be prepared by neutralization of sulfuric acid with magnesium carbonate or oxide, or it can be obtained directly from natural sources. It occurs abundantly as a double salt and can also be obtained from the magnesium salts that occur in brines used for the extraction of bromine (qv). The brine is treated with calcium hydroxide to precipitate magnesium hydroxide. Sulfur dioxide and air are passed through the suspension to yield magnesium sulfate (see Chemicals frombrine). Magnesium sulfate is a saline cathartic. 

In addition to being the most widely used disinfectant for water treatment, chlorine is extensively used in a variety of products, including paper products, dyestuffs, textiles, petroleum products, pharmaceuticals, antiseptics, insecticides, foodstuffs, solvents, paints, and other consumer products. Most chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp bleaching, disinfectants, and textile processing. It is also used in the manufacture of chlorates, chloroform, and carbon tetrachloride and in the extraction of bromine. Among other past uses, chlorine served as a war gas during World War I. 

An application of the above order of reactivity is the use of chlorine in the extraction of bromine from sea water. 

Sea water contains aqueous bromide ions. Chlorine gas is used in the extraction of bromine from this source. 

In the chemical industry chlorine is used for the production of various chemical compounds, such as hydrochloric acid, hypochlorites, chlorates, bleaching powder, aluminium chloride, corrosive sublimate, cupric chloride, carbon tetrachloride, tin recovery from used cans, sulphuryl chloride, for extraction of bromine from Stassfurt waste liquors, etc. In the organic chemical industry it is used for the chlorination of aliphatic and cyclic organic compounds, for the preparation of medicaments, the manufacture of plastics, insecticides, fungicides and herbicides. Monochloracetic acid, ethylene chlorhydrine, chloral, chlor-... 

Of interest also is the high-temperature liquid-liquid extraction of molten silver dissolved in molten lead, the extraction solvent being molten zinc (Parkes process) this process is analogous to the familiar extraction of bromine from water using carbon tetrachloride, and is used to recover silver from lead ores. 

Extraction of brominated flame retardents with supercritical CO2... 

In Turkmenistan the extraction of bromine and iodine from brines produce effluents which caused considerable environmental damage. 

Hyotylainen, T., Hartonen, K., Saynajoki, S., and Riekkola, M. L., Pressurised hotwater extraction of brominated flame retardants in sediment samples, Chromatographia, 53, 301-305, 2001. 

Stripping consists of vaporizing a compound dissolved in a liquid (e.g. extraction of bromine from seawater). In order to do so, we bring an inert (non-soluble) gas into contact with the solution, the effect of which is to decrease the partial vapor pressure of the solute above the solution. 

In the extraction of bromine from seawater (reaction 22.3), seawater is first brought to a pH of 3.5 and then treated with Cl2(g). In practice, the pH of the seawater is adjusted with H2SO4, and the mass of chlorine used is 15% in excess of the theoretical. Assuming a seawater sanmle with an initial pH of 7.0, a density of 1.03 g cm, and a bromine content of 70 ppm by mass, what masses of H2SO4 and CI2 would be used in the extraction of bromine from 1.00 X lO L of seawater ... 

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