Water Problems — Manganese - Page 2

Further, some surface waters and shallow wells contain organic or colloidal* manganese compounds. Manganese bacteria can also cause problems similar to those caused by iron bacteria-clogging, staining, etc.

Suspended insoluble manganic hydroxide, known as "black water," while not rare, is less common. This is probably due to the fact that a much higher pH is necessary to precipitate manganic hydroxide than is necessary to the production of ferric hydroxide.

Manganese bicarbonate in solution is colorless. The result is that unaerated deep well waters containing manganous ions are clear when freshly drawn. Exposure to the air soon converts the clear, soluble manganous ions into the black insoluble substance that is manganese dioxide. Then the trouble begins. The reactions occurring when manganous ions are converted to manganese dioxide are as follows:

Light concentrations of manganese can be removed with a water softener. Higher concentrations may be removed with oxidizing filters with considerable success. Very high manganese concentrations, or those complicated by organic matter, etc., call for chemical oxidation, as with iron, plus filtration.

Note that chlorine will not completely oxidize manganese unless the pH is above 9.5, whereas potassium permanganate is effective at pH values above 7.5. Thus, permanganate is the preferred oxidizing agent in most cases.

*Colloidal: Containing or pertaining to colloids which are insoluble particles. These particles are larger than molecules but small enough so that they remain suspended in a liquid without settling. A colloid does not affect the freezing point, boiling point or vapor tension of the liquid in which it is suspended.