report of what i did this morning:
5ml of iodine tincture in a test tube is mixed with some toluene.
a mix of h2s2o8 and water is prepared (h2s2o8 reacts with water to yield h2so4 and h2o2) and is added drops by drops mixing the 2 phases in the test tube each time until the toluene is dark purple coloured.
then it is well mixed until the aqueous phase becomes completly yellow.
toluene phase is separated and is mixed in another test tube with a half concentrated solution of naoh, which is added drops by drops mixing each time until the toluene phase becomes yellow.
the aqueous phase is separated, cooled (2-3°C) and mixed in another test tube with some COLD 20% H2SO4...
the solution is filtered with a normal coffee filter and small crystals of iodines (less than 1mm) have been separated from solution... and the filtrate is yellow because of traces of iodine (solubility of iodine in water : 300mg per L)
to use naoh and then h2so4 again should avoid most of the problems due to the presence of ethanol and not reacted KI and even H2O2 when cristalizing and filtering the iodine, and other compounds that can be founded sometimes in iodine tincture...