Magnesium (Mg) in Water Treatment
Quick Answer
Magnesium (Mg) is an alkaline earth metal with atomic number 12. PubChem lists its standard state as solid and its relative atomic mass as 24.305.
Magnesium is one of the principal hardness ions. Lime softening, sodium-cycle ion exchange, nanofiltration or reverse osmosis can reduce it and help control scale.
Interesting Facts
- A magnesium atom sits at the centre of the chlorophyll molecule used in photosynthesis.
- Magnesium and calcium are both hardness ions, but their carbonate equilibria and scaling behaviour are not identical.
- Sodium-cycle softening reduces Mg²⁺ without reducing total dissolved salts; it exchanges the charge for Na⁺.
Water-treatment Design Implications
An element name alone is not enough to select treatment equipment. Confirm chemical form or speciation, total and dissolved concentration, pH, alkalinity, competing ions and the product-water target. Send the water-analysis results to Watermart to identify additional testing and shortlist processes before equipment is specified.
Summary Data Sources
1. Basic Information
| Atomic Number | 12 |
| Symbol | Mg |
| Atomic Weight | 24.305 g/mol |
| Electron Configuration | [Ne]3s² |
| Group | Alkaline earth (Group 2) |
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 common in natural water, especially groundwater influenced by dolomite and other magnesium-bearing minerals. Its concentration varies widely; measure magnesium together with calcium, alkalinity, pH and temperature when evaluating hardness and scale.
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.
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.