Magnesium Carbonate Hydroxide: The Complete Industrial Guide

What Is Magnesium Carbonate Hydroxide?

Magnesium carbonate hydroxide (CAS 12125-28-9 / 39409-82-0), also known as basic magnesium carbonate or hydromagnesite, is an inorganic magnesium salt with the molecular formula 4MgCO₃·Mg(OH)₂·4H₂O (often simplified as Mg₅(CO₃)₄(OH)₂·4H₂O). It appears as a white, odorless crystalline powder that is practically insoluble in water, stable in air, and dissolves in dilute acids with effervescence.

This compound occupies a unique position in industrial chemistry: it serves simultaneously as a halogen-free flame retardant, a polymer filler, a food-grade anti-caking agent (E504), a precursor for high-purity magnesium oxide (MgO), and a key ingredient in ceramics, cosmetics, and construction materials.

Chemical & Physical Properties

Primary Industrial Applications

1. Halogen-Free Flame Retardant & Smoke Suppressant

This is the single largest and fastest-growing application segment. As regulatory pressure against halogenated flame retardants intensifies globally, magnesium carbonate hydroxide has emerged as a leading environmentally friendly alternative.

How it works:

● At ~350 °C, it decomposes endothermically, absorbing heat from the combustion zone

● Releases H₂O (steam dilution of flammable gases) and CO₂ (oxygen displacement)

● Forms a stable MgO char layer that insulates the underlying polymer

● Acts as an effective smoke suppressant by reducing volatile organic emissions

Target polymers:

PVC

● (rigid and flexible): cable sheathing, flooring, profiles

Polypropylene (PP)

● : automotive interior parts, appliance housings

Polyethylene (PE)

● : wire and cable insulation

EVA (ethylene-vinyl acetate)

● : cable compounds, solar panel encapsulants

PA (polyamide/nylon)

● : electrical connectors, structural components

Epoxy resins

● : printed circuit boards, electronic encapsulation

Neoprene rubber

● : conveyor belts, gaskets, hoses

Key advantage over ATH (aluminum trihydrate): Magnesium carbonate hydroxide decomposes at ~350 °C vs. ATH's ~220 °C, enabling processing in high-temperature thermoplastics where ATH would degrade prematurely. It also provides superior smoke suppression at equivalent loading levels.

2. Rubber & Elastomer Reinforcement

In the rubber industry, basic magnesium carbonate functions as both a reinforcing filler and an acid acceptor. It neutralizes trace hydrogen chloride (HCl) released during processing, vulcanization, and thermal aging of chlorinated polymers — improving compound stability and extending service life.

Key rubber applications:

● Neoprene (CR) compounding — acid scavenging and reinforcement

● EPDM gaskets and seals — heat resistance enhancement

● Silicone rubber — improved thermal stability

● Natural rubber/SBR — partial replacement of carbon black in non-black formulations

3. Food-Grade Anti-Caking Agent (E504)

Magnesium carbonate hydroxide is approved as food additive E504 in many jurisdictions. It absorbs moisture and prevents caking in powdered and granulated food products:

● Table salt (the original "When it rains, it pours" application by Morton Salt, 1911)

● Powdered sugar and dry beverage mixes

● Spice blends and seasoning powders

● Baking powder and flour mixes

The mechanism is straightforward: its hygroscopic nature traps ambient moisture before it can cause particle bridging and clumping, preserving free-flowing characteristics throughout the product shelf life.

4. Cosmetics & Personal Care

Used extensively in powdered cosmetic formulations for its absorbent, bulking, and pH-buffering properties:

● Face powders and body powders (mattifying, oil-absorbing)

● Dry shampoos (excess oil absorption)

● Toothpaste (mild abrasive and pH buffer)

● Deodorants and antiperspirants

● Bath products (water softening and pH control)

5. Refractory & High-Temperature Materials

When calcined, magnesium carbonate hydroxide produces high-purity magnesium oxide (MgO), the foundational material for basic refractory bricks used in steelmaking furnaces, cement kilns, and glass tanks. The controlled decomposition pathway yields MgO with predictable crystallite size and reactivity — properties that directly influence refractory brick density and corrosion resistance.

Additional high-temperature uses:

● Heat-insulating boards and blankets

● Fireproofing coatings and sprays

● Fire-extinguishing dry powder compositions

6. Ceramics & Glass

Ceramic bodies and glazes:

● acts as a fluxing agent at high temperatures, modifying melt viscosity and surface finish

Specialty glass:

● contributes magnesium oxide to the glass network, improving chemical durability and thermal shock resistance

Enamels and frits:

● opacity control and thermal expansion matching

7. Construction Materials

● Magnesium oxychloride (Sorel) cement — basic magnesium carbonate as MgO precursor

● Lightweight fire-resistant wallboard and panels

● Flooring compounds — fire resistance and dimensional stability

8. Sports & Gymnastics Chalk

Magnesium carbonate (typically the basic/hydroxide form) is the standard "chalk" used by gymnasts, rock climbers, weightlifters, and pole vaulters to improve grip by absorbing sweat from the hands. This niche but highly visible consumer application consumes several thousand metric tons annually.

9. Environmental & Filtration

● Flue gas desulfurization (FGD) — magnesium-based scrubbing

● Water treatment — pH adjustment and heavy metal precipitation

● Filtration media — process chemical production