水中铁的来源及处理
Source
Iron occurs naturally in ground waters in three forms, Ferrous Iron (clear waste
iron), Ferric Iron (red water iron), and Heme Iron (organic iron). Each can
exist alone or in combination with the others. Ferrous iron, or clear water iron
as it is sometimes called, is ferrous bicarbonate. The water is clear when drawn
but when turns cloudy when it comes in contact with air. The air oxidizes the
ferrous iron and converts it to ferric iron. Ferric iron, or ferric hydroxide,
is visible in the water when drawn; hence the name 搑ed water iron? Heme iron is
organically bound iron complexed with decomposed vegetation. The organic
materials complexed with the iron are called tannins or lignins. These organics
cause the water to have a weak tea or coffee color. Certain types of bacteria
use iron as an energy source. They oxidize the iron from its ferrous state to
its ferric state and deposit it in the slimy gelatinous materials that surround
them. These bacteria grow in stringy clumps and are found in most iron bearing
waters.
Treatment
Ferrous iron (clear water iron) can be removed with a softener provided it is
less than 0.5 ppm for each grain of hardness and the pH of the water is greater
than 6.8. If the ferrous iron is more than 5.0 ppm, it must be converted to
ferric iron by contact with a oxidizing agent such as chlorine, before it can be
removed by mechanical filtration. Ferric iron (red water iron) can simply be
removed by mechanical filtration. Heme iron can be removed by an organic
scavenger anion resin, or by oxidation with chlorine followed by mechanical
filtration. Oxidizing agents such as chlorine will also kill iron bacteria if it
is present.
