Magnesium Hydroxide: Properties, Applications, and Safety Overview

Magnesium hydroxide, with the chemical formula Mg(OH)₂, is a white, inorganic compound commonly known for its use as an antacid and laxative. It also plays vital roles in industrial applications, environmental treatment, and flame retardancy. Its low solubility in water, mild alkalinity, and non-toxic nature make it a versatile and widely used material in both pharmaceutical and industrial contexts.

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Chemical Identity

• Chemical Name: Magnesium Hydroxide

• Chemical Formula: Mg(OH)₂

• Molar Mass: 58.32 g/mol

• Appearance: White powder or crystalline solid

• Solubility in Water: Slight (≈ 0.0009 g/mL at 18 °C)

• pH of Aqueous Suspension: ~10.5 (mildly basic)

• Common Names: Milk of magnesia (when in suspension)

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Physical and Chemical Properties

Magnesium hydroxide is sparingly soluble in water, forming a suspension rather than a true solution. When in water, a small portion dissociates into Mg²⁺ and OH⁻ ions, giving it its basic nature. Upon heating, it decomposes into magnesium oxide (MgO) and water:

Mg(OH)₂ → MgO + H₂O (at temperatures above 350 °C)

This decomposition behavior is especially useful in fire retardant applications, as the endothermic reaction absorbs heat.

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Major Applications

1. Pharmaceutical Use

Magnesium hydroxide is widely used in medicine for its ability to neutralize stomach acid and to promote bowel movement.

• Antacid: Neutralizes excess gastric acid in conditions like indigestion or heartburn

• Laxative: Draws water into the intestines, softening stool and stimulating bowel movement

• Form: Commonly dispensed as milk of magnesia, a suspension in water

2. Flame Retardants

It is incorporated into plastics, rubber, and textiles as a flame-retardant filler. When exposed to heat, it decomposes and absorbs thermal energy, releasing water vapor and reducing fire propagation.

3. Wastewater Treatment

Magnesium hydroxide is used to:

• Neutralize acidic wastewater

• Precipitate heavy metals as hydroxides

• Control odor and corrosion in sewage systems by buffering pH and reducing hydrogen sulfide formation

4. Environmental Applications

Used in flue gas desulfurization to remove sulfur dioxide (SO₂) from industrial exhaust gases, and as a reagent to treat acidic soils in agriculture.

5. Pulp and Paper Industry

It helps control pH in bleaching processes and neutralizes waste streams during paper production.

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Handling and Storage

Although generally regarded as safe, magnesium hydroxide requires standard chemical handling protocols, especially in industrial settings.

Storage Recommendations:

• Store in a cool, dry area

• Keep container tightly sealed to prevent moisture uptake and contamination

• Avoid storage near acids, which can cause a neutralization reaction

Handling Precautions:

• Avoid inhalation of dust or prolonged skin contact

• Use gloves, goggles, and dust mask in bulk or powder form

• Ensure good ventilation during use

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Safety Profile

Magnesium hydroxide is considered non-toxic and non-corrosive when used as directed, particularly in pharmaceutical and food applications.

In Case of Overdose (Medicinal Use):

• May cause diarrhea, abdominal cramping, or electrolyte imbalance, especially in those with kidney issues

• Long-term overuse may result in magnesium toxicity in susceptible individuals

Environmental Impact:

• Safe for aquatic and terrestrial environments when used responsibly

• Excessive application in soil or water systems may alter pH balance

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Conclusion

Magnesium hydroxide is a mild yet effective base with wide-ranging applications across medicine, environmental treatment, fire safety, and manufacturing. Its natural abundance, low cost, and safe profile make it a reliable choice in both consumer and industrial products. Whether relieving an upset stomach or reducing fire risk in materials, magnesium hydroxide continues to prove its value as a versatile and dependable compound.

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