Magnesium (Mg)

1. Basic Information

2. Physical and Chemical Properties

Magnesium is a silvery-white light metal with a density of 1.74 g/cm³. The melting point is 650°C and the boiling point is 1107°C. Magnesium is very chemically reactive, easily oxidized in air to form a thin oxide layer. In powder form, magnesium is highly flammable and can produce bright white flames.

In water, magnesium forms Mg²⁺ ions that contribute to water hardness. Magnesium dissolves easily in dilute acids but is resistant to bases. Magnesium compounds are generally white in color and many are soluble in water.

3. Presence in Water and Health Effects

Magnesium is a common mineral found in natural water, especially groundwater that passes through rocks such as dolomite and limestone. Its concentration in drinking water usually ranges from 1-100 mg/L. Magnesium together with calcium causes water hardness.

Magnesium is an essential nutrient for the human body. Magnesium deficiency can cause various health problems such as heart and muscle disorders. However, excess magnesium in drinking water rarely causes direct health problems. More significant effects are technical problems such as scale formation on appliances and pipes.

4. Water Treatment Applications and Removal Methods

Magnesium removal is often necessary to reduce water hardness. Some commonly used methods include:

• Softening by ion exchange: Using cation exchange resin to replace Mg²⁺ ions with Na⁺ ions.
• Chemical precipitation: Adding lime or soda ash to precipitate magnesium as Mg(OH)₂.
• Reverse osmosis: RO membranes can remove most magnesium ions.
• Nanofiltration: Effective for reducing hardness including magnesium.
• Distillation: Evaporates water and re-condenses it, leaving behind dissolved minerals.
• Use of sequestrants: Chemicals such as polyphosphates that can bind magnesium and prevent scale formation.

The choice of method depends on the raw water quality, treatment objectives, and economic considerations.

5. Industrial Use in Water Treatment

Although magnesium is generally removed in water treatment, some magnesium compounds have important roles in the water treatment industry:

• Magnesium hydroxide (Mg(OH)₂) is used as a coagulant in wastewater treatment.
• Magnesium oxide (MgO) is used to adjust pH and alkalinity in water treatment systems.
• Magnesium sulfate (MgSO₄) is sometimes added to very soft water to increase its mineral content.
• Some water filters use magnesium-containing media to improve drinking water quality.

6. Case Studies and Real World Application Examples

Case 1: Water Softening for Industrial Boilers

A paper mill in Sumatra faced scaling problems in their boilers due to feed water containing 150 mg/L magnesium. They implemented a large-scale ion exchange softening system using cation resin. The system successfully reduced the magnesium concentration to less than 1 mg/L, significantly reducing scale formation and improving boiler efficiency.

Case 2: Brackish Water Treatment with Reverse Osmosis

A beach resort in Bali used an RO system to treat brackish water containing 400 mg/L of magnesium. With proper pretreatment and appropriate membrane selection, the system was able to remove more than 99% of the magnesium, producing high-quality fresh water for the resort's needs.

7. Regulatory Guidelines and Standards

In Indonesia, the Minister of Health Regulation No. 492/MENKES/PER/IV/2010 on Drinking Water Quality Requirements does not set a specific limit for magnesium. However, the standard for total hardness (which includes magnesium) is set at a maximum of 500 mg/L as CaCO₃.

The World Health Organization (WHO) does not set value guidelines for magnesium in drinking water as there is no consistent evidence of adverse effects. However, WHO advises that water with hardness above 200 mg/L may cause scale formation and soap use problems.

8. Environmental Impact and Sustainability Considerations

Magnesium is a natural element that is important to ecosystems. Magnesium removal from water does not have significant negative environmental impacts. However, some sustainability considerations include:

• Energy and chemical use in the magnesium removal process.
• Disposal of waste salt from the ion exchange softening process.
• Potential remineralization of water that is too soft to maintain mineral balance.
• Ecological impacts of discharging treated water with very low magnesium content to natural water bodies.

A more sustainable approach may involve the use of energy-efficient technologies, water recycling, and optimization of treatment dosages.

9. Future Trends and Research in Water Treatment

Some promising research areas and trends related to magnesium in water treatment include:

• Development of more efficient magnesium selective membranes for desalination.
• Utilization of nanotechnology for more effective magnesium removal.
• Studies on the health benefits of magnesium in drinking water and its implications for water quality standards.
• Development of more environmentally friendly and energy efficient water softening methods.
• Research on the utilization of magnesium removed from water for other applications, such as fertilizer production.
• Integration of magnesium treatment system with smart water technology for real-time optimization.

10. Interesting Facts Related to Water Treatment

• Seawater contains about 1,300 ppm of magnesium, making it the largest source of magnesium in the world.
• Several studies have shown that drinking water with sufficient magnesium content can contribute positively to heart health.
• Magnesium in water can affect the flavor of coffee and tea. Professional baristas often consider the magnesium content of water for the best brewing results.
• In wastewater treatment, magnesium can be used to precipitate phosphate, helping to reduce eutrophication in receiving water bodies.
• Some new desalination technologies are developing ways to extract magnesium from seawater as a valuable by-product.