Iodine From Kelp

10.13.2 Extract iodine from kelp See diagram 13.15.3 Iodine is one of the microelements necessary for the human body. Sea water contains about 0.000005% of iodine that can be absorbed and concentrated by some marine living beings. There are 1000-4000 mg of iodine existing as iodides in kelp of per thousand grams. Burning kelp gathers the iodides in ashes. Decoct the ashes in water, acidify the resultant iodide solution and then evaporate it to dryness. The follow-up oxidation with potassium dichromate produces iodine, which is then separated by sublimation. K2Cr2O7 + 6KI + 7H2SO4 ---> 4K2SO4 + Cr2(SO4)3 + 3I2 + 7H2O Weigh and cut 40 g of commercial dried kelp into small pieces and put them in an iron vessel. Burn the kelp chips with an electric heater in a fume cupboard until all the chips are completely turned into ash. Transfer the ashes to a beaker, add 40 mL of deionized water, heat and boil the suspension, and add more water to make the filtrate 30 mL after filtering. Add drop by drop dilute sulfuric acid (2 mol / L) to the filtrate until its value of pH becomes neutral. Put the neutralized filtrate in an evaporating dish, evaporate it by heating to dryness. The residues are parched and ground and uniformly mixed with 2 g of potassium dichromate. Transfer the mixture to a dry tall beaker. Stand a flask containing cold water on the mouth of the beaker. On heating the beaker to sublimate the produced iodine, iodine vapour condenses on the cooler sides of the flask. Stop heating when there is no violet red iodine vapour appearing any more. Collect the obtained iodine crystals.