Magnesium Chloride: The Complete Industrial & Food Grade Guide 

What Is Magnesium Chloride?

Magnesium chloride is an inorganic salt with the chemical formula MgCl₂, naturally occurring in seawater, underground brine deposits, and salt lakes such as the Dead Sea and the Great Salt Lake. In its pure form, it appears as colorless, odorless crystals or flakes with strong hygroscopic properties — meaning it readily absorbs moisture from the air.

Two primary forms dominate the market:

Hexahydrate (CAS 7791-18-6) accounts for the vast majority of commercial demand because it is easier to handle, less corrosive to store, and suitable for most applications. Anhydrous (CAS 7786-30-3) is preferred for moisture-sensitive processes such as magnesium metal electrolysis and certain chemical syntheses.

Key physical properties:

● Molecular weight: 95.21 g/mol (anhydrous) / 203.30 g/mol (hexahydrate)

● Melting point: 714°C (anhydrous); hexahydrate decomposes at ~118°C

● Solubility: Highly soluble in water — 54.3 g/100 mL at 20°C

● pH: 5.0–7.0 (5% aqueous solution)

● Density: 2.32 g/cm³ (anhydrous) / 1.57 g/cm³ (hexahydrate)

Industrial De-Icing and Anti-Icing

Magnesium chloride is one of the most widely used chloride-based de-icers worldwide, second only to calcium chloride in cold-region road maintenance programs.

How It Works

When MgCl₂ dissolves in water, it dissociates into Mg²⁺ and Cl⁻ ions, lowering the freezing point of the solution through colligative action. A 30% magnesium chloride brine solution has a freezing point of approximately -33°C (-27°F), making it effective in extremely cold conditions where sodium chloride (rock salt) loses efficacy around -9°C (15°F).

Magnesium chloride is less corrosive to metals than calcium chloride and gentler on concrete and vegetation than sodium chloride, making it the preferred choice for environmentally sensitive areas, bridge decks, and airport runways.

Application Methods

Liquid brine spray

● (25–30% concentration): Applied pre-storm as anti-icing or post-storm for de-icing. Preferred for highway and municipal use.

Flake/pellet spread

● : Dry application with spreader trucks for parking lots, sidewalks, and commercial properties. Flakes dissolve faster than pellets.

Dust Control and Soil Stabilization

Unpaved roads, construction sites, and mining operations lose enormous amounts of fine particulate matter to wind and vehicle traffic. Magnesium chloride provides a cost-effective, long-lasting solution.

Food Grade Applications (E511)

In food manufacturing, magnesium chloride is designated as food additive E511 and serves several regulated functions. It is approved for use in the EU, US (FDA GRAS), Japan, and most international food standards.

Tofu Coagulation (Nigari)

The most culturally significant food application is as a coagulant in tofu production, where it is traditionally known as nigari in Japan. When added to heated soy milk, magnesium chloride causes the soy proteins to denature and aggregate into curds, which are then pressed into tofu blocks. Nigari produces tofu with a firmer, more traditional texture compared to calcium sulfate (gypsum).

Typical usage rate: 0.2–0.4% by weight of soy milk.

Other Food Industry Uses

Firming agent

● : Prevents softening in canned vegetables and fruits

Flavor enhancer

● : Provides a mild salty-mineral note in bottled water and sports beverages

Color retention

● : Helps preserve natural color in processed vegetables

Yeast nutrient

● : Supports fermentation in brewing and baking

Mineral fortification

● : Used in nutritionally fortified food products

Food grade magnesium chloride must meet stringent purity specifications:

● MgCl₂ content: ≥ 99.0% (hexahydrate basis)

● Heavy metals (as Pb): ≤ 10 ppm

● Arsenic: ≤ 3 ppm

● Mercury: ≤ 1 ppm

● Compliant with FCC, USP, or equivalent pharmacopoeia monographs

Water and Wastewater Treatment

Magnesium chloride plays specific roles in water treatment processes, particularly where pH control and coagulation are required.

Coagulation and Flocculation

In wastewater treatment, Mg²⁺ ions act as coagulants by neutralizing the negative surface charges on suspended colloidal particles — including dyes, organic matter, and fine silt. This charge neutralization causes particles to aggregate into larger flocs that settle or can be filtered out. Magnesium chloride is particularly effective in textile industry effluent, where it helps remove reactive and disperse dyes.

Compared to aluminum sulfate (alum) or ferric chloride, magnesium chloride produces less sludge and leaves lower residual metal concentrations in treated water — an advantage for facilities with strict discharge limits.

pH Buffering and Nutrient Source

In biological wastewater treatment systems, MgCl₂ serves as a source of magnesium — an essential micronutrient for microbial metabolism. Adequate magnesium levels (~5–15 mg/L) support healthy biomass growth in activated sludge processes and anaerobic digesters.

Swimming Pool Water Treatment

Magnesium chloride is sometimes used as an alternative to sodium chloride in saltwater pool chlorination systems that use magnesium-based electrolytic cells. The Mg²⁺ ions contribute to water softness and can reduce scaling on pool surfaces.

How to Choose the Right Grade

Selecting the correct grade of magnesium chloride depends on your specific application:

Frequently Asked Questions

What is the difference between magnesium chloride hexahydrate and anhydrous?

Hexahydrate (MgCl₂·6H₂O) contains approximately 47% crystal water by weight and appears as white flakes or crystals. Anhydrous (MgCl₂) has almost no water content and is a shiny white powder. Hexahydrate is the standard choice for de-icing, dust control, and food applications. Anhydrous is reserved for moisture-sensitive industrial processes such as magnesium metal production and certain chemical syntheses.

Is magnesium chloride better than calcium chloride for de-icing?

It depends on your priorities. Magnesium chloride is less corrosive to metals and less damaging to concrete and vegetation. It also works at slightly lower temperatures (-33°C vs -29°C). However, calcium chloride is more exothermic (releases more heat when dissolving) and typically costs slightly less per ton. For environmentally sensitive areas and infrastructure protection, magnesium chloride is generally the better choice.

How long does magnesium chloride dust control last?

A properly applied magnesium chloride treatment on an unpaved road or construction site typically lasts 4 to 12 weeks, depending on traffic volume, rainfall, and soil type. Heavily trafficked haul roads may require reapplication every 4–6 weeks, while low-traffic rural roads can remain dust-free for 3 months or more.

Can I use industrial grade magnesium chloride for food production?

No. Food production requires food grade magnesium chloride (E511) that meets strict purity limits for heavy metals, arsenic, and other contaminants. Industrial grade product may contain impurities that are not safe for human consumption. Always verify FCC/USP compliance and request a COA.

How should magnesium chloride be stored?

Store in a cool (below 35°C), dry, well-ventilated area away from moisture. Keep containers tightly sealed when not in use. Avoid storage near strong oxidizing agents or acids. Hexahydrate flakes are hygroscopic — exposure to humid air will cause caking and degradation.

What concentration of magnesium chloride brine is used for de-icing?

The standard concentration for liquid de-icing brine is 25–30% by weight. At 30% concentration, the freezing point of the solution reaches approximately -33°C. Higher concentrations do not significantly improve performance and increase material costs.

Conclusion

Magnesium chloride is a workhorse material in modern industry — from keeping winter logistics moving to producing traditional foods, from stabilizing construction sites to cleaning industrial wastewater. Understanding the differences between grades, forms, and application methods helps you specify the right product for your operational needs while managing costs.