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Forms of Iron Found in Water

Iron will cause an orange stain and will many times be accompanied bymanganese and hydrogen sulfide gas odor. In combination with manganese, Ironstaining will sometimes be chocolate or brown. At high concentration (> .3ppm )

the iron will cause the water to have a metallic taste and metallic odor. The ironitself can exist in four forms:

1. Ferrous iron (often referred to as clear-water iron) - This form of iron isinvisible in the water just like dissolved sugar is. Just like sugar water, theiron can not be mechanically filtered from the water.

2. Ferric(often referred to as red-water iron) - It is called red water ironbecause it gives the water a cloudy colored appearance. The iron hasprecipitated and formed a solid that is no longer in solution - it has turnedto rust - "oxidized". This form of iron can be mechanically filtered. An easyway to remember which kind of iron is visible (ferrous or ferric) is to

remember that the "i" and the "c" at the end of the word ferric say thesame thing as "I see" it.3. Organic iron (sometimes called heme-iron or pink water iron)- This form is

actually iron combined with the dissolved organic matter (tannins) in thewater and is held solution with the organic materials. The water will appearclear but may or may not have color. Sometimes this iron will begin tooxidize and form a suspension in the water. We refer to this as colloidaliron.

4. Colloidal iron - This will look like red-water iron but can not be easilyfiltered. The iron has precipitated (turned to ferric iron) but the moleculesformed do not stick together in large enough pieces to settle to the bottom

of a container or be trapped with normal filtration. This water/solidcombination is called a colloid. To test if you have this type of water,collect a sample in a clear glass container. Shine a flashlight beamthrough the water and see if you can see the light ( tyndall effect) in thewater. Then, let the water set overnight. If you can see the beam of lightas it passes through the water and there was no settling of material on thebottom of the container, the chances are very good that you have colloidaliron.

Treatment

Ferrous iron can be treated two ways. The most common way is to use a waterconditioner or softener to remove the iron by ion exchange. This method can beused on almost any level of iron. We have treated iron concentrations in excessof 100ppm successfully with a water conditioner. This method will only besuccessful by itself if all the iron is in the ferrous form, the TDS is relatively low(generally

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3. Greensand Systems (NOT USED BY US)- This method uses a catalyticmedia (called greensand) coated with manganese that is treatedperiodically (like the salt regeneration of a softener) with potassiumpermanganate. The potassium permanganate acts as an oxidant (like thechlorine or air). When the iron in the water comes in contact with the

surface of media it oxidizes and the ferric iron is then filtered out bysticking to the media before it finds it way through the filter. We do not usethis method because these systems can easily bleed manganese into thewater and the potassium permanganate is not only poisonous, but, ifspilled, stains badly. The manganese that bleeds into the water can get tolevels high enough to be toxic. You will hear these filters referred to asiron filters, greensand filters or potassium permanganate filters.

Catalytic Media (NOT USED BY US)- This method uses a media similar togreensand. The media has many different trade names but is usually anaturally occurring mineral called pyrolucite (manganese dioxide). This

method of treatment counts on there being enough air in the water toprovide the oxygen necessary to turn the ferrous iron into ferric iron. Thismedia can also bleed manganese into the water. It doesn't work to removeiron in the water we find locally because there is not enough naturallydissolved oxygen. A second major draw back is that the media is so heavyit is very difficult to back wash properly with the flows available from mostresidential pumps.

Ferric iron can be removed by any of the backwashing filter commonly used.Since the iron is already oxidized the water, only needs to be filtered. Generallythe iron will be filtered with AG or Calcite filter media.

Organic iron is usually treated with an anion resin in a tank that uses salt like awater conditioner or softener. The resin usually is very expensive and has a shortlife( 1-2 years). At the end of the resins life, the resin must be replaced at a cost$400 or more dollars.

Colloidal Iron is probably the most difficult form of iron to deal with and usuallycomes with many other water problems. The treatment usually requires twosolution feed systems, static mixers, retention tanks and filters. The goal is to flocthe iron (make the particles grow large enough to filter) and then filter it. Theseare very expensive systems (typically $4000-$5000). There are no watertreatment companies that want to deal with this type of iron, very few that will andeven less know how. We have had very good success and will continue toprovide our solution to those who want it.

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