Question

Mention the method by which bromine is obtained from sea water?

Answer 1

You could extract the bromide from sea water in different ways, it will depend a lot on why you want to extract the bromide.

One method for neutron activation anaylsis would be to add silver nitrate and then to get the AgCl to act as a carrier for the small amount of AgBr. You could then centrifuge the mixture to remove the supernatant. Wash with water and then you could use NAA, but you will get a rather high background from the Ag and Cl in the sample.

Another option would be to add an oxidant and then use solvent extraction to extract the bromine. This has an advantage from a NAA point of view that the Ag and Cl background will be lower.

If you want to measure bromine in sea water you could try ion chromatography

But for a good separation of Br from sea water I have seen this method

http://pubs.acs.org/doi/abs/10.1021/ac50062a022

Use silver on zeolite to trap both chloride and bromide, as AgBr has a lower solubility than AgCl. I would expect that the Br to Cl ratio will change in favour more and more as you elute more and more sea water through the zeolite.

Next you would have to elute the pad first with something which only liberates the AgCl by dissolving it and then with some complexing agent which can dissolve both AgCl and AgBr. I would then suggest that if you were to use a Jones reducer to remove the silver from the solution to give you a nice and clean sample of bromide which can then be processed further.

Another alternative would be to use a silver surface in the following way, alter the redox potential of the sea water with an oxidant which converts the bromide to elemental bromine while not altering the form of the chlorine. Allow a silver surface to be in contact with this. With some luck this will remove the bromine by forming AgBr.

Then you can try to remove the AgBr with thiosulfate solution and then use the Jones reducer on it to get a bromide solution free of silver, I am basing this idea on a method which can be used for transferring Po onto silver disks.