Iron & Manganese

Iron & Manganese

Iron rusts from disuse; water loses its purity from stagnation… even so does inaction sap the vigor of the mind  – Leonardo da Vinci

Iron / manganese, because they are rather closely related heavy metals are often found together. They give rise to similar problems in water supplies, and fortunately, they generally respond to the same treatment processes for their removal. Therefore, they are usually treated as one subject, although, as will be seen, they differ greatly in their chemistry.


IRON (Fe), Atomic Number 26, Atomic Weight (most abundant isotope) 56, is found in Group VIII of the Periodic Table of the Elements, right between manganese and cobalt, in Period 4. Iron has valences of +2 and +3, and readily combines with other elements. It is the fourth-most abundant element in the earth’s crust, outranked only by aluminum, silicon, and oxygen.

Because of its reactivity, iron is seldom found in its native state. One of the few places on earth where metallic, i.e. “native” iron is found is in Greenland, where it occurs as very small grains or nodules in basalt, an iron-bearing igneous rock.

Early records of human use of metallic iron are around 2000 BC in Egypt, Asia, Assyria and in China. It is almost certain, however, that the first metallic iron to be used was not derived from ores, but was obtained from meteorites.

Although gold, silver, copper, brass and bronze were in common use before iron, it was not until man discovered how to extract iron from its ores, about 1300 BC, that civilization began to develop rapidly.

MANGANESE (Mn), Atomic Number 25, Atomic Weight 55, is found in Group VII of the Periodic Table of the Elements. The name derives from the Latin Magnes (magnet). The element was discovered by Gahn, a Swedish mineralogist, in 1774. In the first series of transition metals, manganese is the element with the most oxidation states (-3 to +7), with the most important being +2, +4 and +7. It is this abundance of possible oxidation states that account for the rather complicated chemistry of the element.

Manganese is found in most soils at between 200 – 300 mg / kg (ppm). Many rocks contain 800-1400 mg / kg. The main uses of the metal include that of an alloying agent, as a cleaning agent for steel, cast iron and non-ferrous metals, in the manufacture of dry-cell batteries, glass, ceramics, paints and inks.


Although many of the ferrous and ferric (+2 and +3) salts, like chlorides or sulfates, are highly soluble in water, the ferrous ions are readily oxidized to the ferric state in natural surface waters, forming insoluble hydroxides. These precipitates tend to agglomerate, flocculate, settle or become adsorbed on surfaces, hence the concentration of iron is rarely high. In ground waters the pH and Eh (Equilibrium Potential – a measure of the oxidation state of a solid / solution) may be such that high concentrations of iron can remain in solution.

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