Question

how can we purify bromine ?

Answer 1

If you mean purify a liquid that is already mostly bromine, then chill it almost to its freezing point (-7C), pour off the liquid bromine from any solids that may have formed (ice, e.g.), then continue to chill the bromine until it freezes. Pour off any liquid (which now is not bromine, because the bromine is frozen), take your block of bromine, thaw it out, and do the same thing one or two more times. If you mean how to get it out of salt or seaweed, then dissolve the rock salt, or smash up the seaweed, remove the chunky stuff with a sieve, use chloride (like from table salt) to convert bromide ion Br- to elemental bromine Br2, and purify it as above.