Water Conditioning Iron
Iron exists in two different states:
- Ferrous (Fe+2) or iron (II)
- Ferric (Fe+3) or iron (III)
Iron can be converted from ferrous iron (Fe+2) to ferric iron (Fe+3) by removal of an electron known as oxidation. This ability to be converted between different states is why iron is very useful to living organisms. All known forms of life require iron, however, because of its low solubility in water, iron is often a limiting nutrient. Elevated iron levels in drinking water can form insoluble precipitates that can stain plumbing, laundry, cooking utensils, and cause undesirable taste and colors in foods. The U.S. EPA set a secondary drinking water MCL at 0.3 mg/L.
Due to the insolubility of its ferric (Fe+3) form, the methods for measuring iron in water use a reducing agent to convert the iron in a sample to its soluble ferrous (Fe++2) form. The ferrous iron then reacts with a molecule to produce a colored complex, which is used to measure the concentration of iron in the sample. Because of the instability of the ferrous iron, which is easily changed to the ferric form when the solution comes in contact with air, determination of ferrous iron requires special precautions and may need to be done in the field at the time of sample collection. It is also advised to avoid long storage times or exposure of samples to light.
Hanna offers a variety of products to measure iron in water. These include benchtop, portable and the Checker HC meters. Also available are chemical test kits (CTKs).
Below are the most common products used in water conditioning.
Chemical Test Kits