Sodium

Sodium (Na)

1. Basic Information

2. Physical and Chemical Properties

Sodium is a soft, silver-colored metal that is highly reactive. It has a low melting point (97.5°C) and a boiling point of 883°C. Sodium reacts rapidly with water, producing sodium hydroxide and hydrogen gas. In air, sodium is rapidly oxidized to form a layer of sodium oxide. Sodium does not react with nitrogen, but can react with ammonia to form sodium amide. Sodium also reacts with alcohols and halogenated organic compounds.

3. Presence in Water and Health Effects

Sodium is the sixth most abundant element in the Earth's crust and the second most abundant ion in seawater after chloride. The main sources of sodium in water are weathering of rocks and minerals, and seawater intrusion. Sodium is important for human body functions, but excess sodium can cause hypertension and kidney problems. WHO recommends sodium intake of no more than 2 grams per day. Skin or eye exposure to sodium can cause irritation and burns.

4. Water Treatment Applications and Removal Methods

Sodium removal from water is generally done by:

• Ion exchange using cation exchange resin
• Reverse osmosis (RO)
• Electrodialysis
• Distillation
• Chemical precipitation (in some cases)

For water with low dissolved salt content, strong acid cation exchange resins are often used. Under alkaline conditions, weak acid cation exchange resins can provide higher capacity and easier regeneration. For water with high salt content, RO is generally more economical than ion exchange.

5. Industrial Uses in Water Treatment

Although sodium is generally removed from water, some sodium compounds are used in water treatment:

• Sodium hypochlorite (NaClO) for disinfection
• Sodium hydroxide (NaOH) for pH regulation
• Sodium carbonate (Na2CO3) for water softening
• Sodium bisulfite (NaHSO3) for dechlorination
• Sodium fluoride (NaF) for fluoridation of drinking water

6. Case Studies and Real World Application Examples

Example 1: Seawater Desalination in the Middle East Many countries in the Middle East use large-scale RO technology to remove sodium and other ions from seawater, producing fresh water for consumption and irrigation. For example, the Ras Al Khair desalination facility in Saudi Arabia can produce 1 million m3 of fresh water per day.

Example 2: Produced Water Treatment in the Oil and Gas Industry In the oil and gas industry, produced water often contains high levels of sodium. Companies such as Shell use a combination of technologies such as RO and ion exchange to remove sodium and other contaminants, enabling water reuse or safe disposal.

7. Regulatory Guidelines and Standards

In Indonesia, Permenkes No. 492/Menkes/Per/IV/2010 sets the maximum limit for sodium in drinking water at 200 mg/L. WHO does not set health-based guidelines for sodium in drinking water, but recommends levels below 200 mg/L based on taste considerations.

In the United States, the EPA sets the secondary contaminant level for sodium at 30-60 mg/L, primarily based on taste and not health considerations.

8. Environmental Impacts and Sustainability Considerations

Increased sodium levels in water bodies can cause:

• Changes in salinity that affect aquatic ecosystems
• Degradation of water quality for irrigation, causing soil sodicity
• Corrosion of water infrastructure

Sodium removal methods such as RO require high energy. Innovations such as low-pressure RO and energy recovery are constantly being developed to improve the sustainability of the process. Reuse of salt concentrate from desalination processes is also a focus of research to reduce environmental impact.

9. Future Trends and Research in Water Treatment

Some of the research areas and emerging trends include:

• Development of new RO membranes with better ion selectivity
• Capacitive deionization technology for energy-efficient sodium removal
• Integration of renewable energy in desalination process
• Use of nanomaterials to improve sodium removal efficiency
• Optimization of ion exchange resin regeneration process
• Development of real-time sodium sensors for water quality monitoring

10. Interesting Facts Related to Water Treatment

• Seawater on average contains about 10,500 mg/L of sodium, making it a major challenge in desalination.
• Some plants such as mangroves have natural mechanisms to remove excess salt, inspiring biomimetic research in water treatment.
• Sodium in water can come from the use of sodium-based water softeners, which ironically can increase sodium levels in drinking water.
• In some cases, sodium is added to drinking water to control corrosion of lead pipes.
• The use of sodium chloride (table salt) for water softening regeneration can contribute up to 50% of the sodium load in urban wastewater in some areas.