Iodine reacts with hot concentrated nitric acid to form iodic acid. The iodic acid crystallizes out on cooling.
Occurrence of Iodine
Iodine naturally occurs in the environment chiefly as dissolved iodide in seawater, although it is also found in some minerals and soils. The element may be prepared in an ultrapure form through the reaction of potassium iodide with copper(II) sulfate. There are also a few other methods of isolating this element. Although the element is actually quite rare, kelp and certain other plants have the ability to concentrate iodine, which helps introduce the element into the food chain as well as keeping its cost down.
is found in the mineral Caliche, found in Chile, between the Andes and the sea. It can also be found in some seaweeds as well as extracted from seawater, however extracting Iodine from the mineral is the only economical way to extract the substance.
Extraction from seawater involves electrolysis, the brine is first purified and acidified using sulphuric acid and is then reacted with chlorine
. An Iodine
solution is produced but it is yet too dilute and has to be concentrated. To do this air is blown into the solution which causes the iodine to evaporate, then it is passed into an absorbing tower containing acid where sulfur dioxide (SO2) is added to reduce the iodine, the solution is then added to chlorine
again to concentrate the solution more, the final solution is the Iodine
at a level of about 99%.
Another source is from kelp. This source was used in the 18th and 19th centuries but is no longer economically viable.
In 2005, Chile was the top producer of iodine with almost two-thirds world share followed by Japan and the USA reports the British Geological Survey.
Isotopes of Iodine
There are 37 isotopes of iodine and only one, I-127, is stable.
Iodine-123 and iodine-125 are used in medicine as tracers for imaging and evaluating the function of the thyroid.
127I [74 neutrons]
Stable with 74 neutrons
129I [76 neutrons]
Half life: 1.57 x 107 years [ beta- ]
Decay Energy: 0.194 MeV
Decays to 129Xe.
Excesses of stable 129Xe in meteorites have been shown to result from decay of “primordial” iodine-129 produced newly by the supernovas which created the dust and gas from which the solar system formed.
I (half-llife 15.7 million years) is a product of cosmic ray spallation on various isotopes of xenon in the atmosphere, in cosmic ray muon interaction with tellurium-130, and also uranium
and plutonium fission, both in subsurface rocks and nuclear reactors. Nuclear processes, in particular nuclear fuel reprocessing and atmospheric nuclear weapons tests have now swamped the natural signal for this isotope. 129
I was used in rainwater studies following the Chernobyl accident. It also has been used as a groundwater tracer and as an indicator of nuclear waste dispersion into the natural environment.
131I (radioiodine) [78 neutrons]
Half life: 8.02070 days [ beta- ]
Decay Energy: 0.971 MeV
Decays to 131Xe.
Has been used in treating cancer and other pathologies of the thyroid gland.