Iridium (Ir)

1. Basic Information

2. Physical and Chemical Properties

Iridium is a hard, brittle, shiny and dense transition metal of the platinum group. It is silvery white in color and is reputed to be the most corrosion-resistant element. It is unaffected by air, water, and acids. Iridium has a very high melting point (2450°C) and boiling point of 4527°C. It has a very high density of 22.4 ^g/cm3 at 20°C. Iridium is insoluble in most solvents and has exceptional chemical resistance.

3. Presence in Water and Health Effects

Iridium is rarely found in natural water due to its rarity in the Earth's crust. Concentrations in terrestrial plants are usually below 20 ppb. The health effects of iridium exposure have not been widely studied due to its rarity. However, certain iridium compounds may cause irritation to the eyes, skin and gastrointestinal tract if exposed to large amounts. Inhalation of iridium dust may cause respiratory tract irritation.

4. Water Treatment Applications and Removal Methods

Although iridium is rarely a major contaminant in water, several methods can be used to remove it if needed:

• Ion exchange: Specialized anion exchange resins can be used to remove iridium chloroanion complexes from solution.
• Adsorption: Activated carbon or specialized adsorbents can bind iridium from water.
• Chemical precipitation: Precipitation of iridium as hydroxide or sulfide can be done at high pH.
• Membrane filtration: Technologies such as nanofiltration or reverse osmosis can remove nano-sized iridium particles.

5. Industrial Use in Water Treatment

Iridium has limited use in the water treatment industry due to its rare and expensive nature. However, some potential applications include:

• Catalysts: Iridium compounds can be used as catalysts in advanced oxidation processes to decompose organic contaminants in water.
• Electrodes: An iridium oxide coating on electrodes can improve efficiency in water treatment electrochemical processes.
• Sensors: Iridium-based sensors can be used to detect certain contaminants in water.

6. Case Studies and Real-World Application Examples

Examples of iridium use in water treatment are limited, but some studies show its potential:

• A Japanese study used iridium catalysts to oxidize difficult-to-degrade pharmaceutical compounds in wastewater.
• Research in China shows iridium oxide-coated electrodes can improve the efficiency of nitrate removal from groundwater.
• A company in the United States developed an iridium-based sensor to detect arsenic contaminants in drinking water with high sensitivity.

7. Regulatory Guidelines and Standards

Due to its rarity, there are no specific standards for iridium in drinking water or wastewater in most countries. However, as a heavy metal, iridium may be regulated under general guidelines for metals in water. The World Health Organization (WHO) has not set specific limits for iridium in drinking water.

8. Environmental Impact and Sustainability Considerations

Iridium is considered to have a relatively low environmental impact due to its rarity and inert nature. However, iridium mining and processing can have environmental impacts. Sustainability considerations include:

• Rarity: As one of the rarest elements in the Earth's crust, the use of iridium should be carefully considered.
• Recycling: Efforts to recycle iridium from used products are critical to sustainability.
• Alternatives: The development of more common alternatives for iridium applications can reduce reliance on this rare metal.

9. Future Trends and Research in Water Treatment

Several promising research directions and trends involve iridium in water treatment:

• Development of more efficient iridium catalysts for degradation of micropollutants in water.
• Utilization of iridium nanoparticles to improve the performance of filtration membranes.
• Research on iridium-based electrodes for more efficient seawater desalination.
• Exploration of new iridium compounds for photocatalysis in water purification.

10. Interesting Facts Related to Water Treatment

• Iridium is the most corrosion-resistant element known, making it very attractive for extreme water treatment applications.
• The name "iridium" comes from the Latin word "iris", meaning rainbow, due to the various colors of its iridium salts.
• Iridium is found in higher concentrations in some meteorites than in the Earth's crust, suggesting its cosmic origin.
• Although extremely rare, iridium has an important role in green technologies, including fuel cells and water electrolysis for hydrogen production.