Module:5
Lecture:26 Iodine
Dr. N. K. Patel
Module: 5
Lecture: 26
IODINE
INTRODUCTION
Iodine (I) is a chemical element which having atomic number 53. The
name came from Greek word ιώδιο, it means violet or purple colour, due to
the colour of elemental iodine vapour. Iodine was discovered by Bernard
Courtois at 1811. He isolated the iodine by treating seaweed ash with sulfuric
acid (H2SO4) by recovering sodium and potassium compounds.
The highly water-soluble iodide ion I-, found on earth which
concentrates the oceans and brine pools. Like the other halogens, free
iodine occurs mainly as a diatomic molecule I 2, and then only momentarily
after being oxidized from iodide by an oxidant like free oxygen. Iodine's high
atomic number makes it a relatively rare element in the universe. As it present
in ocean water, indicates its role in biology. It is the heaviest essential element
accepts tungsten, utilized widely by life in biological functions. Due to initial
low abundance as a crust-element, and leaching of soluble iodide by
rainwater, leads to number of deficiency problems in land animals and in
land human populations. About two billion people have the iodine
deficiency.
Iodine is required by higher animals and use to synthesize thyroid
hormones, which contain the element. Because of this function, radioisotopes
of iodine are concentrated in the thyroid gland along with nonradioactive
iodine. If it is inhaled, the radioisotope iodine-131concentrates in the thyroid,
but it is easily remedied with potassium iodide treatment.
MANUFACTURE
Raw material
Basis: 1000kg of Iodine from brine and chlorine (98% yield)
Oil-well brine
1160kg
Chlorine
445kg
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Module:5
Lecture:26 Iodine
Dr. N. K. Patel
Sulfurous acid
Reaction
395kg
Manufacture process
Stripped air
HCl
Cl2
Blow-out
tower
Iodine
absorption
tower
30% NaCl
stripped brine to
other plant use or
waste
Air
Sulfurous
acid
Sulfuric
acid
Chlorine
Treating
tank
Purified
brine
Crusher
Filter
Melting
kettle
H2O, Nacl, H2SO4 solution to
brine purification system or
other plant use
Iodine
Filter
H2SO4 solution to brine
purification system or other
plant use
Figure: Manufacture of Iodine from brine and chlorine
Block diagram of manufacturing process
Diagram with process equipment
Animation
Iodine production arises from treatment of natural brines which contain
about 65mg/l iodide. The oxidation of iodide for both types of brines was
affected by the addition of chlorine to clarified brine.
The purified brine was chlorinated using chlorine in the tower and from
the chlorinated brine; free iodine was stripped by an air stream. The brine was
pumped out for other plant use. Iodine was charged into the absorption
tower where air was stripped out and then the absorbed iodine was reduced
to hydrogen iodide by sulfurous acid.
Hydrogen iodide was chlorinated by adding chlorine into stream
immediately. The chlorinated reaction mass was filtered where NaCl, H2SO4
and water were separated out and sent for the brine purification. While
liberated solid iodine was melted in the presence of sulfuric acid, cast into
pigs. The melted mass was filtered again to remove sulfuric acid which can
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Module:5
Lecture:26 Iodine
Dr. N. K. Patel
be utilized for other plant uses and solid iodine was crushed and sent for the
packaging section.
Engineering aspects
 Use of ion-exchange resin
The newest process uses ion-exchange resins for adsorption of liberated
iodine through oxidization of brine. Amberlite IRA-400, an anion-exchange
resin is used to adsorbed liberated iodine in the form of polyiodide. After the
ion-exchange resin is saturated, it was discharged from the column and then
transferred to the elution column. Iodine was desorbed by using caustic
solution followed by sodium chloride. Then resin was regenerated and
returned to the adsorption column. An iodide and iodate ions rich elutriant
was acidified and oxidized to precipitate iodine. The crude iodine was
separated in centrifuge and purified with hot sulfuric acid.
 Material of construction
The material of construction used for the plant are high silicon iron,
Stelilite 6, Hastelloy C and stainless steel type 304, 309, 316, 317. These
materials have low corrosion rates. 5% solution of iodine in alcohol (95%) can
be corroded the stainless steel. Medium carbon steel containing 0.21%
carbon has a low corrosion rate in an iodine solution in benzene (26.8gm/l).
PROPERTIES
 Molecular formula
 Molecular weight
 Appearance







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Odour
Boiling point
Melting point
Density
Refractive index
Vapour pressure
Solubility
:I
: 126.90gm/mole
: Rhombic, violet-black crystals, metallic
luster
: Characteristic odour
: 185.20C
: 113.50C
: 4.93gm/cm3(solid at 250C)
: 1.647 at 200C,
: 51mm at 38.70C, 0.03mm at 00C (solid)
: Soluble in aqueous solution of HI and
iodies, solvents containing nitrogen
atoms such as pyridine, quinolone
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Module:5
Lecture:26 Iodine
Dr. N. K. Patel
USES
 Iodine is used in manufacturing of various iodine compounds,
antiseptics and germicides
 As catalyst in alkylation and condensation of aromatic amines to
reduce the friction of hard surface
 In the production of acetic acid and certain polymers
 It is important reagent in analytical chemistry
 Artificial isotopes are used in biological, biochemical and chemical
structure research
 As iodine having relatively high atomic number, low toxicity and ease
of attachment to organic compounds, it is a part of many X-ray
contrast materials in modern medicine
 Iodine has only one stable isotope and a number of iodine
radioisotopes are used in medical applications
 Iodine and its derivatives are generally used in nutrition
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