Iron (Fe) in Water Treatment
Quick Answer
Iron (Fe) is a transition metal with atomic number 26. PubChem lists its standard state as solid and its relative atomic mass as 55.84.
Iron can cause reddish colour, metallic taste, deposits and iron-bacteria problems. Aeration or chemical oxidation followed by filtration is common; dissolved, colloidal and organically complexed iron require different treatment conditions.
Interesting Facts
- Iron carries oxygen in haemoglobin, while iron minerals also drive redox reactions in groundwater and treatment filters.
- Clear groundwater can turn orange after pumping because dissolved Fe(II) oxidises and forms Fe(III) solids on contact with air.
- That visible colour change explains why oxidation needs enough reaction time before filtration.
Water-treatment Design Implications
An element name alone is not enough to select treatment equipment. Confirm chemical form or speciation, total and dissolved concentration, pH, alkalinity, competing ions and the product-water target. Send the water-analysis results to Watermart to identify additional testing and shortlist processes before equipment is specified.
Summary Data Sources
Iron (Fe)
1. Basic Information
| Property | Value |
|---|---|
| Atomic Number | 26 |
| Symbol | Fe |
| Atomic Weight | 55.85 g/mol |
| Electron Configuration | [Ar]3d⁶4s² |
| Abundance in the Earth’s Crust | Fourth most abundant (about 5%) |
2. Physical and Chemical Properties
Iron is a silvery-gray metal that is chemically reactive. It forms two main series of chemical compounds: iron (II) or ferrous compounds that are two-valent, and iron (III) or ferric compounds that are three-valent. Iron oxidizes easily in moist air, forming rust, but is stable in dry air. It dissolves easily in dilute acids. Iron has a melting point of 1536°C and a boiling point of 2861°C. Its density is 7.8 g/cm³ at 20°C.
3. Presence in Water and Health Effects
Iron is often found in ground and surface water as a result of dissolution of iron-containing minerals. The concentration of iron in natural water usually ranges from 0.5 to 50 mg/L. Although iron is essential for the human body, excess iron in drinking water can cause aesthetic problems such as metallic taste, reddish color, and staining of clothing or sanitary supplies. Excess iron can also favor the growth of iron bacteria that can form slime in the water distribution system.
Iron is an essential nutrient for almost all living things, from microorganisms to humans. It is an essential part of hemoglobin, the red coloring agent of blood that transports oxygen through our bodies. However, iron deficiency or excess can cause health problems. Iron deficiency can lead to anemia, while excessive exposure to iron oxide dust or fumes can cause siderosis, a benign form of pneumoconiosis.
4. Water Treatment Applications and Removal Methods
Iron removal from water is a common practice in drinking and industrial water treatment. Some of the methods used include:
- Oxidation and Filtration: Dissolved iron is oxidized to insoluble form using oxidizers such as chlorine, potassium permanganate, or aeration, then removed through filtration.
- Ion Exchange: Cation exchange resins can remove dissolved iron, especially effective for low concentrations.
- Water Softening: The process of softening water with sodium can also remove dissolved iron.
- Reverse Osmosis: RO systems can remove most dissolved iron.
- Biological Treatment: Iron bacteria can be used to oxidize and precipitate iron in biofilter systems.
For water with high iron levels, a combination of methods is often used, such as oxidation followed by filtration and ion exchange.
5. Industrial Uses in Water Treatment
Although iron is generally considered a contaminant that needs to be removed, it also has several uses in the water treatment industry:
- Coagulants: Iron salts such as ferric chloride (FeCl₃) and ferric sulfate (Fe₂(SO₄)₃) are used as coagulants in water and wastewater treatment to remove suspended and colloidal particles.
- Phosphate Removal: Iron salts are used to precipitate phosphate in wastewater treatment, helping to prevent eutrophication of water bodies.
- Arsenic Removal: Iron hydroxide can adsorb arsenic, making it an effective method for removing arsenic from drinking water.
- Catalysts: Iron oxide is used as a catalyst in advanced oxidation processes for wastewater treatment.
8. Environmental Impacts and Sustainability Considerations
Although iron is a natural element and essential for life, excessive concentrations in aquatic ecosystems can cause problems. High levels of iron can:
- Lower oxygen solubility in water, affecting aquatic life.
- Cause precipitation that can damage habitats for fish and benthic organisms.
- Support the overgrowth of iron bacteria, which can disrupt the aquatic food chain.
From a sustainability perspective, iron removal from water can generate solid waste that needs to be properly managed. However, there is potential to recover and reuse iron from water treatment processes, for example as a raw material for industry or as a coagulant in wastewater treatment.