Iron in water
Iron makes up about 5% of the hard outer layer of the whole Earth’s crust. That is why nearly all sources of water (surface waters and wells) contain this metal. In natural waters iron is most often encountered in the form of ions Fe2+ and Fe3+, as well as in the form of organic and inorganic compounds (colloids, suspended solids, etc.).
In surface waters iron can be found as an impurity mostly by organic complexes (humates), as well as in forms of colloidal and finely-divided suspensions.
In ground waters, in the absence of dissolved oxygen, it usually resides in the form of Fe2+ ions.
Dissolved iron represents an aesthetical problem rather than a danger to health. Iron can be present in various forms in water. During heating, oxidization or chlorination, dissolved iron transforms from one form into another, and precipitates.
red deposits on the surface of sanitary ware and fittings
in initially transparent water red jelly-like sediment appears in the open air
the same happens during heating of water
jelly-like sediment doesn’t gravitate to the bottom
dark-brown hardly removable residue
color fabrics become colorless
drinks become darker
The content of iron in water is measured in mg per L. The level of iron 0.2 mg/L leads to generation of red deposits.
Water can contain several forms of iron. Total iron is the volume of all forms of iron contained in water.
Ferrous iron (Fe2+) is dissolved in water, and the water seems transparent. During oxidization (in the open air) the water a gains yellowish or reddish tone. Most often encountered in ground waters. The innovative method to remove iron (with production capacity in the range of 0.5-50 m3/hour) is represented by application of the complex filter media Ecomix. The traditional method is to oxidize this form to Fe3+, and filter it with pressure filters loaded with manganese green sand or MTM (with dosing or regeneration of potassium permanganate.
Ferric iron Fe3+ is the form that Fe2+ takes after oxidization. Such iron looks like a suspension, insoluble and non-settling residue. This form of iron is the most difficult to remove. Most often it is possible with filters loaded with manganese green sand, MTM or Birm. In the case of insignificant content, it can be removed with ordinary sediment filters.
Colloidal iron consists of iron particles which are very small (less than 0.1 micron), so they cannot be removed by sediment filters. Such iron generates suspension too. It is very rarely encountered. It is removed with oxidization or transformation into another form, and then sediment filtration is used.
Organic iron is a form of iron that created a compound with organic matter like tannins or humic acid. It can be colorless, yellowish or red. This iron is called organic, or complex iron. It is the hardest to remove due to its organic nature. Methods of purification: ion exchange, adsorption, oxidization.
Bacterial ironCertain (ferrous) bacteria use iron in metabolic processes. Bacterial iron can be jelly-like or fibrous. This iron sometimes generates surface film. Rarely encountered.