Iodine (I) in Water Treatment
Quick Answer
Iodine (I) is a halogen with atomic number 53. PubChem lists its standard state as solid and its relative atomic mass as 126.9045.
Iodine may occur as iodide, iodate or organic iodine and can participate in disinfection chemistry. Activated carbon, ion exchange and membranes may be relevant, but the objective may be controlling precursors rather than removing total iodine.
Interesting Facts
- Iodine is essential for thyroid hormones, while elemental iodine is named for the violet colour of its vapour.
- Iodide, iodate, molecular iodine and organic iodine behave differently in oxidation, adsorption and membrane processes.
- Iodine can disinfect emergency water, but dosage, contact time, taste, thyroid considerations and disinfection by-products limit routine use.
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
Iodine
1. Basic Information
| Atomic Number | 53 |
| Symbol | I |
| Atomic Weight | 126.90 g/mol |
| Category | Halogen |
2. Physical and Chemical Properties
Iodine is a lustrous purple-black non-metallic element. It is the most electropositive and least reactive halogen, although it can still form compounds with many elements. Iodine sublimes easily when heated, producing a purple vapor. The solubility of iodine in water is relatively low, but it dissolves well in some organic solvents.
In aqueous solution, iodine can form various species such as I-, I3-, IO-, IO3-, and IO4-. The standard reduction potential of the I2/I- pair is +0.58 V, indicating moderate oxidizing properties. Iodine can also form complexes with organic and inorganic molecules.
3. Presence in Water and Health Effects
Iodine occurs naturally in marine and freshwater environments, but concentration and species vary with geology, salinity, redox conditions and biological activity. Measure the relevant species rather than assuming a universal background concentration.
Iodine is required for thyroid hormones, but nutritional intake guidance is not a drinking-water treatment limit. Both inadequate and excessive intake can affect thyroid function, so a drinking-water decision needs the relevant health authority and total dietary context.
In the context of water treatment, small amounts of iodine are generally harmless. However, high concentrations can cause undesirable taste and odor, as well as potential health problems if consumed in excess over the long term.
4. Water Treatment Applications and Removal Methods
Iodine has several important applications in water treatment:
- Disinfection: Iodine is used as an alternative disinfectant, especially for emergency situations or field use. It is effective against bacteria, viruses, and protozoa.
- Water purification tablets: Iodine is often used in portable water purification tablets for hikers and explorers.
- Algae growth control: In some cases, iodine is used to control algae growth in water systems.
To remove iodine from water, several methods can be used:
- Activated carbon: Very effective in removing iodine and organic iodine compounds.
- Ion exchange: Strong anion resins can remove anionic iodine species such as I- and IO3-.
- Reverse osmosis: Effectively removes almost all forms of dissolved iodine.
- Distillation: Can remove iodine and its compounds from water.
- Chemical reduction: The use of reductants such as sodium thiosulfate can convert iodine to iodide which is easier to remove.
For water containing radioactive iodine (e.g. I-131), special removal methods such as selective ion exchangers or special adsorbents may be required.
5. Industrial Use in Water Treatment
Although not commonly used on a large scale, iodine has several industrial applications in water treatment:
- Industrial cooling systems: Iodine is sometimes used as a biocide in cooling systems to control microbial growth.
- Swimming pool water treatment: Some swimming pool water treatment systems use iodine as an alternative to chlorine.
- Seawater treatment: In desalination, iodine monitoring is important to optimize the process and prevent corrosion.
8. Environmental Impacts and Sustainability Considerations
Iodine has several environmental and sustainability implications in the context of water treatment:
- Biogeochemical cycles: The use and disposal of iodine can affect the natural cycling of iodine in the environment.
- Effects on aquatic ecosystems: High concentrations of iodine can affect aquatic organisms, especially at early developmental stages.
- Formation of by-products: Reaction of iodine with organic matter can produce potentially harmful organohalogen compounds.
- Microbial resistance: The use of iodine as a disinfectant can potentially lead to microbial resistance if not managed properly.
- Recovery and recycling: Technologies to recover and recycle iodine from wastewater are being developed, supporting a circular economy.