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The Stainers: Iron & Manganese

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There is little doubt when a water supply contains very much iron or manganese because of the brown to black stains which these minerals cause. The stains show up rapidly in sinks, and appear on laundered fabrics and every surface touched by the water. The Safe Drinking Water Act of 1974 provided a recommended Secondary Drinking Water Regulation which suggests limits of 0.3 mg/L (parts per million) of iron and 0.05 mg/L (ppm) of manganese because of the stains which may be caused by higher concentrations.

Iron and manganese produce unpleasant tastes when present in high concentrations, and can affect both flavor and color of foods. These impurities react with the tannins present in coffee, tea and some alcoholic beverages to produce a black sludge which affects both taste and appearance. An early form of ink was made by mixing iron salts with tannins. In nature, iron is found as several different oxides, carbonates and sulfides, and it is found as traces in many different minerals. Although man reduces the various iron ores to metallic iron, the metal has a strong tendency to revert to the more stable oxide forms. Iron exists in three states, which are related as follows:

The Three States Of Iron

Deep in the earth, far from the oxidizing effects of oxygen in the air, conditions favor the reduction of the natural ferric iron deposits to the ferrous state. Since the ferrous iron is quite soluble, it is readily dissolved and carried in groundwater, in clear and colorless solution. However, when this water is brought to the surface and exposed to oxygen in the air, it is rapidly converted back to the ferric state. The ferric iron then reacts with alkalinity in the water to form ferric hydroxide, the insoluble brown precipitate which causes so much staining. Similar reaction occur with manganese, although they are slower than with iron. Household bleaches can oxidize iron and manganese to the insoluble states, causing the staining problems when bleaches are used in laundering.

The corrosion of iron or steel water lines may also add iron to water. The partial oxidation of metallic iron to the ferrous state allows the iron to dissolve in the water, and to be carried through the water system. However, if oxygen is present or oxidizing agents are added, the insoluble ferric hydroxide id readily formed. This too may be carried through the water system, or may settle in the water lines during periods of low flow, to be stirred up and carried to the point of use during high water usage.

Iron and manganese may also be present in water in combination with organic matter. Many natural and man-made organic compounds will react with iron and manganese to form heavily colored materials which can cause severe staining. These materials are usually very stable, and resist breakdown and removal.

Iron bacteria and manganese bacteria are two special forms of organic growths sometimes found in water. Although they do not cause disease, these organisms are capable of using iron and manganese in their metabolism, and may even attack steel pipe to obtain iron. As the bacteria grow, they form masses of gelatinous and filamentous organic matter which trap the iron and manganese they use. Heavy growths can completely plug pipes, but usually break away during periods of high water flow to produce "slugs" of dirty, iron or manganese-laden water, with obnoxious tastes and odors. A brown, slime-like growth in a toilet flush tank is a good indication of the presence of such organisms in a water system.

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Rust Stain In Toilet Tank

Rust Stain In Sink

Rust Stain In Bath Tub

Rust Stain In Shower

Rust Stain In Dishwasher