Iodin

Iodine

1. Basic Information

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 is naturally present in seawater at a concentration of about 0.06 mg/L. In freshwater, the concentration is much lower, usually below 0.005 mg/L. The main sources of iodine in water are weathering of rocks and minerals, and atmospheric deposition from the sea.

Iodine is an essential micronutrient for humans, required for the production of thyroid hormones. iodine deficiency can lead to goiter and cretinism. However, excess iodine is also harmful, as it can impair thyroid function and cause hyperthyroidism. WHO recommends a daily intake of 150 μg for adults.

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.

6. Case Studies and Real World Application Examples

Example 1: Use of Iodine in Emergency Situations After the 2010 Haiti earthquake, iodine-based water purification tablets were widely used to provide safe drinking water to disaster victims. This method proved effective in preventing outbreaks of waterborne diseases.

Example 2: Post-Fukushima Radioactive Iodine Removal After the 2011 Fukushima nuclear disaster, a specialized ion exchange technology was developed to remove radioactive iodine from contaminated water. This system utilizes ion exchange resins that are highly selective to I-131, enabling effective water decontamination.

Example 3: Iodine in Seawater Treatment for Aquaculture An aquaculture facility in Norway uses a seawater treatment system that involves monitoring and controlling iodine. The right concentration of iodine is necessary for fish health, but excess can cause problems. The system uses a combination of activated carbon filtration and ion exchange to precisely control iodine levels.

7. Regulatory Guidelines and Standards

The WHO guidelines for drinking water do not set specific limits for iodine, given its role as an essential nutrient. However, some countries have their own standards:

• European Union: There is no specific standard for iodine in drinking water.
• US: The EPA does not set a Maximum Contaminant Level (MCL) for iodine. However, for I-131 (radioactive), the MCL is set at 3 pCi/L.
• Japan: The maximum limit for iodine in drinking water is set at 0.1 mg/L.
• Australia: The guideline for iodine in drinking water is 0.5 mg/L, based on aesthetic considerations (taste and odor).

For wastewater, iodine discharge standards vary depending on local regulations and the type of receiving water body.

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.

9. Future Trends and Research in Water Treatment

Some of the research areas and emerging trends related to iodine in water treatment include:

• Development of more efficient and environmentally friendly iodine-based disinfectants.
• More selective and energy-efficient iodine removal technologies, including new nanomaterials and membranes.
• Better understanding of the role of iodine in the formation of disinfection by-products and their mitigation strategies.
• Use of iodine in advanced desalination systems to control biofouling and corrosion.
• More sensitive and real-time iodine detection and monitoring methods in water treatment systems.
• Studies on the long-term impact of low iodine levels in drinking water on human health.
• Development of portable water treatment systems using iodine for emergency situations and remote areas.

10. Interesting Facts Related to Water Treatment

• Iodine was the first water disinfectant used in space, used by NASA in the Apollo missions.
• Some seaweed species can accumulate iodine at up to 20,000 times the concentration in the surrounding seawater.
• Iodine-based water purification tablets have been used by the military for over 70 years for emergency drinking water provision.
• Natural mineral water from some sources can contain significant amounts of iodine, contributing to dietary iodine intake.
• The use of iodine in swimming pool water treatment can reduce eye irritation and odor compared to chlorine.
• Some freshwater microorganisms have the ability to oxidize iodide to iodine, affecting the iodine cycle in aquatic ecosystems.