Iodine Sources
Iodine
No less than 99.6% of the earth’s mass can be accounted for by thirty-two of the chemical elements. The remaining 0.4% is apportioned among sixty-four elements, all of which are present as traces. Iodine is number 61 on this list, making Iodine one of least abundant non-metallic elements in the total composition of the earth.
Although not abundant in quantity, iodine is distributed almost everywhere. It is present in rocks, soils, waters, plants, animal tissues and foodstuffs. Except for a few rare occasions, elemental iodine is not readily found in nature. Iodine is mostly found combined with other elements, such as oxygen, hydrogen or carbon. Due to the ease with which it can accept or donate electrons in its ionic states, it is readily incorporated in inorganic salts or complex organic compounds such as the mammalian hormone thyroxine.
A few substances characteristically contain iodine in relatively large quantities. Natural accumulating organisms are seaweeds, sponges and corals. For industrial purposes, the main sources of Iodine are deposits of minerals, either as solid ore (Caliche) or in underground brines. The iodine in these deposits is chiefly of oceanic origin, transferred to the atmosphere as iodine-rich organic material and as gaseous iodine formed by photochemical oxidation of iodine at the ocean surface.
IODINE SOURCES AND CONCENTRATIONS
| Origin | Iodine Form | Typical Concentration |
| Underground Brines Caliche Ore Seaweed |
Sodium Iodide Calcium Iodate Sodium/Potassium Iodide |
30 – 150 ppm 400 ppm 950 ppm* |
*Dry basis.
Caliche is the name for the deposits of natural saltpeter containing minerals in the Atacama Desert of northern Chile and west of the Andes Mountains. Lautarite [Ca (IO3)2] and Dietzeite [7Ca (IO3)2] * 8CaCrO4], are the two crystalline forms in which iodine naturally occurs in caliche ore with an iodine content of around 0.04% (400 ppm).
To become part of the Caliche deposits, iodine was oxidized to iodate by photochemical reactions in the troposphere and at ground level in the nitrate fields.
In subsurface brines associated with oil and gas deposits, iodine occurs frequently as sodium iodide with an iodine concentration in the range of 30 to 150 ppm. About 45% of the iodine currently consumed in the world comes from brines processed in Japan, the USA, the Community of Independent States (CIS) and Indonesia.
Before the development of iodine extraction from caliche, seaweed was an important source. Today, no more than 2% of the total iodine consumption comes from this source. Some types of seaweed, particulary brown seaweeds of the Laminaria family, contain significant amounts iodine in the form of sodium and potassium iodide. Iodine concentration is variable, on average around 950 ppm in dried seaweed. Seaweed is grown by companies dedicated to production of this crop.
Iodine is obtained as a by-product in the processing of sodium alginate from seaweed. Yearly output is dependent on the crop and harvest efficiencies which are subject to environmental factors.