Fluorine

Fluorine (F)

1. Basic Information

2. Physical and Chemical Properties

Fluorine is the most reactive and electronegative halogen element. Under normal conditions, fluorine is a toxic yellow-greenish gas. Fluorine is highly reactive and can react with almost any other element, even noble gases such as krypton, xenon, and radon. Some other important properties:

• Melting Point: -219,6°C

• Boiling Point: -188°C

• Electronegativity (Pauling scale): 4,0

• Atomic Radius: 0.135 nm

• Strong oxidizing agent

3. Presence in Water and Health Effects

In water, fluorine is present as fluoride ion (^F-). Small amounts of fluoride occur naturally in drinking water, food, and air. Fluoride plays an important role in maintaining healthy bones and teeth. However, excessive exposure can lead to tooth decay, osteoporosis, and disorders of the kidneys, bones, nerves and muscles. Inhaled fluorine gas can cause eye and nose irritation, and even death at high concentrations.

4. Water Treatment Applications and Removal Methods

Fluoride cannot be removed from water without first removing all anions with higher selectivity such as chloride or sulfate. Fluoride can be selectively removed using activated alumina media.

In wastewater, under acidic conditions, fluoride is present as HF and can be removed by acid sorbents such as weak base anion exchange resins. At neutral to alkaline conditions, strong base anion exchange resins are used to separate salts. For streams with high organic content that are prone to surface clogging, fouling resistant strong base anion exchange resins are recommended.

5. Case Study and Real World Application

Fluoride is often added to drinking water in an effort to prevent dental caries. Although controversial, this practice has been carried out in several countries including the United States. In addition, fluoride is also used in toothpaste as an anti-caries agent.

In industry, fluorine is used in plasma etching processes for semiconductor manufacturing, flat panel production, and microelectronmechanical fabrication. Fluorine is also used in the production of fluoropolymer plastics such as Teflon, refrigerants such as Freon, and uranium processing.

6. Regulatory Guidelines and Standards

The United States Environmental Protection Agency (EPA) sets the Secondary National Drinking Water Standard for fluoride at a maximum of 2 mg/L, with a recommendation to maintain an optimum level of 0.7 mg/L to prevent dental caries.

The World Health Organization (WHO) suggests fluoride concentrations in drinking water not exceed 1.5 mg/L to prevent the risk of dental fluorosis.

7. Environmental Impacts and Sustainability Considerations

Excessive exposure to fluoride in plants can stunt growth and reduce crop yields. Animals that consume plants with high fluoride content may accumulate fluoride in their bones, causing tooth and bone decay.

Although fluoride occurs naturally in the earth's crust, industrial activities such as coal combustion and aluminum production can increase fluoride levels in air and water. Therefore, proper waste management is required to minimize the release of fluoride into the environment.

8. Future Trends and Research in Water Treatment

Some of the fluoride-related research and development areas in water treatment include:

• Development of more selective ion exchange media and membranes for fluoride removal

• Optimization of defluorination processes using natural materials such as clay, zeolite, or agricultural biomass

• Integration of fluoride removal methods with general water treatment to improve efficiency and sustainability

9. Interesting Facts Related to Water Treatment

• Fluorine was the first halogen element discovered, identified by Henri Moissan in 1886.

• Fluorine is one of the most reactive elements and must be handled with great care in the chemical industry.

• Fluoride compounds are used in the aluminum production process to help melt alumina (_Al2O3) at lower temperatures.

• In water treatment, fluoride removal is often the last step after other anions such as chloride and sulfate are removed first.