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Facts About Iron In The Water

Iron, even in small quantities, can be one of the most troublesome elements found in water. As little as 0.1 ppm (parts per million) of iron can cause staining of fixtures, sinks, flooring, and also most anything else it comes into contact with. Concentrations below 0.3 ppm can still have profound adverse effects in manufacturing processes.

Iron affects the tastes of foods and beverages, can contribute to the blockage of pipes, and can cause many other unwanted problems. In addition it can cause a rotten egg smell. Since it has so many undesirable properties, iron removal is an important phase of water treatment.

“Iron bacteria” is a term applied to a group of small organisms which appear to convert ferrous iron to the ferric state as part of their metabolism. These small organisms produce a rotten egg smell. It is suspected that these organisms may even attack steel pipe to obtain iron, thus causing a form of corrosion. As the iron bacteria grow, they develop masses of gelatinous and filamentous organic matter, which physically trap the ferric hydroxide produced. Heavy growths of these organisms have been known to plug pipes completely, but it is more common for clumps

In underground strata, far from the oxidizing effects of oxygen in air, conditions usually favor the reduction of the natural ferric iron deposits to the ferrous state.  Since the ferrous salts are highly soluble, ground water supplies frequently carry significant concentrations, and as this ferrous iron is in true solution, the water may be perfectly clear and colorless, with no visible evidence of the iron present. However, when ferrous iron is exposed to the atmosphere, oxygen from the air readily converts it to the ferric state. Ferric iron then reacts with the alkalinity in the water to form ferric hydroxide, the insoluble brown gelatinous matter which causes so much staining.

The corrosion of iron or steel water lines may also add iron to the water. Metal corrosion, an electro-chemical process, converts the elemental metallic iron to the soluble ferrous state. In the absence of oxygen and other oxidizing agents, the ferrous iron may be simply carried away with the water. Where oxidizing materials are present, the insoluble ferric hydroxide forms readily. This, too, may be carried along with the water, or since it is quite insoluble and gelatinous in nature, may deposit and stick inside the water lines. This is true even when natural ferrous iron is oxidized inside of pipes.

Ferric hydroxide which is deposited inside a water line has a tendency to lose water, particularly in hot water lines, according to the reaction: 2 Fe (OH)3 ————–> Fe2 O3 + H2O

This ferric oxide is the same rust which forms when an iron or steel structure is exposed to both air and moisture. During periods of high water flow, these rust particles may break free to cause rust stains on materials which comes into contact with water.

Iron may also be present in water in combination with organic matter. Many natural and man-made organic compounds will react, particularly with ferrous iron, to form heavily colored compounds which can cause severe staining. These compounds are usually very stable, and tie up the iron so that it is not free to react as are other forms. The iron bounds into such compounds called “chelated” or “organic” and clearly present problems in water treatment.