What Are the Main Applications and Classifications of Magnesium Hydroxide?

You need a flame retardant, but you’re not sure which one fits your process. Choosing the wrong additive can lead to processing issues and compromise the final product’s quality.

Magnesium hydroxide is primarily used as a non-toxic flame retardant for plastics processed at high temperatures. It is also widely used in medicine as an antacid, and in environmental applications for wastewater treatment.

At our factory, we focus on aluminum hydroxide¹ (ATH), but many of our customers also work with its close cousin, magnesium hydroxide (MDH). Understanding the differences is key to making the right choice. They are both safe, mineral-based flame retardants, but they have unique properties that make them suitable for different jobs. This knowledge is not just technical; it’s essential for achieving the best performance and cost-effectiveness in your products. Let’s look at MDH’s uses and types more closely.

What are the main uses of magnesium hydroxide?

Your product needs fire safety and you want a single, reliable additive. You are looking for a versatile material that can serve multiple functions safely and effectively.

The main use of magnesium hydroxide is as a halogen-free flame retardant and smoke suppressant. It is also used medically as an antacid (Milk of Magnesia) and for environmental water-treatment.

Magnesium hydroxide² is truly a multi-purpose mineral. As a buyer in the pharmaceutical sector, you are likely already familiar with its medical applications. Its ability to safely neutralize acid in the stomach showcases its benign nature. This same gentle chemical property is valuable in other areas. In the industrial world, its biggest role is protecting plastics from fire. When mixed into polymers, it sits dormant until it senses high heat. Then, it releases water vapor, which cools the material and suffocates the fire. Its third major use is cleaning acidic industrial wastewater. It is a preferred choice because it is safer to handle than other caustic materials and it doesn’t cause secondary pollution. This versatility makes it a valuable raw material across many industries.

Is magnesium hydroxide toxic?

Product safety is your highest priority. When you hear the word "chemical," you immediately think about potential toxicity and long-term health risks for the end-user.

No, magnesium hydroxide is considered non-toxic and safe for human contact and consumption. Its safety is proven by its widespread use as the active ingredient in "Milk of Magnesia," a common over-the-counter antacid.

The safety of a flame retardant is a non-negotiable point for us and our customers. This is where magnesium hydroxide truly shines, much like our own aluminum hydroxide. The reason it’s so safe is that it’s a simple, naturally occurring mineral compound. When used as an antacid, it works by simply neutralizing excess stomach acid and then passes through the body. It is not a persistent or bioaccumulative substance that builds up over time. This established medical safety profile gives industrial users immense confidence. When you put MDH in a plastic or rubber product, you can be sure you are not introducing a harmful substance. It provides critical fire safety³ without the health concerns associated with older, halogenated chemicals.

What is the classification for the product magnesium oxide?

You’re seeing magnesium hydroxide (Mg(OH)₂) and magnesium oxide (MgO) mentioned together. This can create confusion and lead to using the wrong material for your application.

Magnesium oxide (MgO) is the stable ceramic powder left behind after magnesium hydroxide decomposes from heat. It is classified as a refractory material, valued for its extreme heat resistance, not as a flame retardant.

Understanding the relationship between these two is key. Magnesium hydroxide is the active flame retardant. Magnesium oxide is the byproduct of its work. The flame-retardant action is an endothermic decomposition, which looks like this:

Mg(OH)₂ (heat) → MgO + H₂O (water vapor)

The process absorbs heat and releases water. What’s left is magnesium oxide, an incredibly stable material that can withstand very high temperatures⁴. This resulting MgO layer helps to form a protective char on the surface of the burning material.

So, you use Mg(OH)₂ to stop a fire from starting. You use MgO for applications that need to stay stable in a fire, like furnace linings.

What is the industrial application of magnesium hydroxide?

You need a flame retardant for a plastic that is processed at a high temperature. Using the wrong one can cause it to activate too early, creating bubbles and ruining your product.

The main industrial application is as a flame retardant in plastics and composites that require high processing temperatures (above 220°C), such as polypropylene, polyamides, and wire and cable insulation.

This is the most important difference between my product, aluminum hydroxide (ATH), and magnesium hydroxide (MDH). It all comes down to temperature. Different plastics need to be heated to different temperatures to be molded into shape. ATH works perfectly for plastics like PVC or EVA, but it starts to decompose and release its water at around 220°C. If you try to process a plastic at 280°C with ATH mixed in, it will break down during manufacturing and cause defects. This is where you need magnesium hydroxide. It is more thermally stable and only starts decomposing around 330°C. This allows it to be used in higher-temperature engineering plastics without causing problems during production.

This makes MDH the ideal choice for applications that demand both high-performance plastics and non-toxic fire safety.

Conclusion

Magnesium hydroxide is a non-toxic mineral used as a high-temperature flame retardant, a safe medical product, and an environmental agent, offering excellent performance and a superior safety profile.