Magnesium Hydroxide Ultrafine Grinding Process: A Complete Guide to Technology Routes, Equipment Selection, and High-Value Applications

With increasingly stringent global environmental regulations and the deepening of the “dual carbon” strategy, magnesium hydroxide – as a non-toxic, smoke-suppressing, and non-corrosive green inorganic flame retardant – is experiencing explosive demand growth. Global magnesium hydroxide production reached 305,000 tonnes in 2022, with an output value of RMB 3.47 billion. However, the market value of magnesium hydroxide is closely linked to its purity, fineness, particle size distribution, and specific surface area. Ultrafine grinding, as a key technology for enhancing the added value of magnesium hydroxide products, has become a focal point for the industry. This article provides a comprehensive analysis of the process schemes, core equipment, and development trends for magnesium hydroxide ultrafine grinding.

1. Why Is Ultrafine Grinding Necessary for Magnesium Hydroxide?

The flame-retardant performance of magnesium hydroxide is closely related to its particle size. The smaller the particle size of the magnesium hydroxide flame retardant, the better its flame-retardant effect. As the particle size decreases, the specific surface area increases and surface properties change, which helps to improve dispersion and mechanical properties in polymer matrices.

Specifically, the core value brought by ultrafine grinding includes:

• Enhanced flame retardancy: Magnesium hydroxide decomposes endothermically at about 340°C, roughly 100°C higher than aluminium hydroxide, making it suitable for higher-temperature plastic processing. After particle refinement, the specific surface area can be increased to 30–50 m²/g, improving interfacial compatibility with the polymer matrix.
• Improved filler performance: Ultrafine powder disperses more uniformly in polymer materials, effectively reducing the required filling amount. In polyethylene, the addition of nano‑magnesium hydroxide can be reduced from 60% to 40%, while tensile strength retention increases from 50% to 80%.
• Better smoke suppression: Studies show that as the particle size of magnesium hydroxide powder decreases, the smoke‑suppression effect improves progressively.

Particle size reduction via grinding is more straightforward than many other processing routes, allowing low‑cost production of high‑grade powder with greater versatility.

2. Main Process Routes for Magnesium Hydroxide Ultrafine Grinding

Magnesium hydroxide ultrafine grinding is divided into two main technical routes: dry grinding und wet milling, each with its own application scenarios and process characteristics.

2.1 Dry Grinding Process

Dry grinding is the mainstream method for magnesium hydroxide ultrafine grinding, especially suitable for high‑purity magnesium hydroxide. Core equipment includes jet mills, ring roller mills, and ultrafine vertical roller mills.

Typical process flow:

Raw material (brucite ore or synthetic magnesium hydroxide) → Coarse crushing (Backenbrecher/hammer crusher) → Ultrafine grinding (jet mill/ring roller mill/vertical mill) → Classification → Collection → Finished product

High‑purity magnesium hydroxide is generally processed with a jet mill, which can easily produce ultrafine powder in the 1–74 μm range. A jet mill system typically includes, in sequence, a feed hopper, jet milling device, air classifier, cyclone collector, dust filter, and induced‑draft fan.

2.2 Wet Milling Process

Wet milling is another important route for ultrafine grinding, particularly suitable for producing sub‑micron or even nano‑sized particles. Its typical process is:

Raw material pre‑treatment (preliminary crushing, drying) → Slurry preparation (water + dispersant) → Wet milling (bead mill/stirred mill) → Classification → Drying → Finished product packaging

Wet milling uses water as the dispersion medium, with surfactants or dispersants added to form a stable slurry. Particle size reduction is achieved through impact and shear forces from high‑density grinding media (e.g., zirconium silicate beads).

Comparison between dry and wet routes:

3. Core Equipment Selection Comparison

Different ultrafine grinding equipment differs in principle, fineness, and energy consumption. Selection should be based on product targets and production scale.

3.1 Jet Mill – The First Choice for High‑Purity Ultrafine Grinding

The jet mill is a classic machine for magnesium hydroxide ultrafine grinding. Its working principle: compressed air, after cooling, filtering, and drying, is expanded through nozzles to form supersonic airflow that enters the grinding chamber. Material particles collide, impact, rub, and shear intensely at the intersection of multiple nozzle streams, achieving ultrafine size reduction.

Die wichtigsten Vorteile:

• Media‑free grinding – no metallic contamination, high purity
• High fineness – easily achieves D90 = 1–74 μm ultrafine powder
• Negative‑pressure operation – no dust pollution on site
• Some capability for particle shape modification

Technical parameters reference: final fineness 1–75 μm, feed size ≤5 mm, single‑unit output 1–4000 kg/h. Certain jet mill models can grind magnesium hydroxide powder down to 3000–10,000 mesh.

3.2 Ring Roller Mill – A Game Changer for Energy Saving and Cost Reduction

To address the high power consumption and high maintenance costs of traditional jet mills, the ring roller mill has emerged as a disruptive solution in the magnesium hydroxide ultrafine grinding field in recent years.

Magnesium hydroxide has relatively low hardness (Mohs ~2.5–3) but demands extremely high fineness and exhibits a certain stickiness. The ring roller mill, with its unique “impact + extrusion + grinding” three‑dimensional comminution mechanism, perfectly matches the grinding characteristics of magnesium hydroxide.

Real‑world application results (case of a large East China magnesium hydroxide flame retardant producer):

• Increased output: Under the same fineness (D97: 10 μm), the ring roller mill’s single‑unit capacity is over 30% higher than that of a jet mill.
• Reduced power consumption: Comprehensive power consumption per tonne is reduced by more than 35%, saving millions of yuan in electricity costs annually.
• Improved quality: Particles become rounder, flowability improves, and coupling agent utilisation is higher.
• Controllable particle size: Built‑in classifier speed is infinitely adjustable, allowing precise control of particle size distribution.

The ring roller mill can process magnesium hydroxide in a single pass to 325 mesh – 2500 mesh (D97), with the fraction below 2.5 μm accounting for about 40%. Grinding rolls and rings are made of special wear‑resistant alloy steel, extending service life by 2–3 times.

3.3 Ultrafeine Vertikalwalzenmühle – Another Choice for Large‑Scale Production

Ultrafine vertical roller mills (e.g., HLMX series) integrate ultrafine grinding and classification in one unit, suitable for large‑scale continuous production. They feature high single‑unit capacity and a high degree of automation, making them ideal for production lines with annual capacities of tens of thousands of tonnes or more.

3.4 Equipment Selection Recommendations

4. Key Application Areas of Ultrafine Magnesium Hydroxide Powder

Ultrafine magnesium hydroxide, with its triple functions of flame retardancy, smoke suppression, and filling, is widely used in the following fields:

4.1 Low‑Smoke Halogen‑Free (LSZH) Cable Compounds

Ultrafine magnesium hydroxide is one of the most important halogen‑free flame retardants for the wire and cable industry. In a typical formulation, 55 parts of ultrafine magnesium hydroxide (silane‑modified, 1 μm particle size) can achieve an oxygen index of 38 and UL94 V‑0 flame‑retardant rating.

4.2 Engineering Plastics and Rubber

Ultrafine magnesium hydroxide can be widely used in engineering plastics, epoxy resins, rubber, etc. After particle refinement, its dispersibility and compatibility in polymer matrices are significantly improved, helping to enhance the mechanical properties of finished products.

4.3 PVC Films and Mining Cable Sheaths

Studies show that ultrafine magnesium hydroxide can replace zinc borate and cobalt trioxide, providing better smoke‑suppression effects while meeting flame‑retardancy requirements. It is particularly suitable for applications with stringent flame retardancy and smoke‑suppression demands, such as mining cable sheaths and cable accessories.

4.4 Precursor for High‑Purity Magnesia

High‑purity ultrafine magnesium hydroxide is also an important raw material for producing high‑purity magnesia, silicon‑steel‑grade magnesia, and various active magnesia products.

5. Industry Development and Technology Trends

5.1 Ultrafine and Nano‑Sized Products Are the Main Focus

Reducing the particle size of magnesium hydroxide from 5–10 μm to 0.5–2 μm (ultrafine) or 50–200 nm (nano) via jet milling and wet grinding is the core direction of current technological development.

5.2 Continuous Breakthroughs in Scalable Production Technologies

Companies such as Hefei Zhongke Flame‑Retardant New Materials have applied for patents on scalable production of ultrafine magnesium hydroxide, achieving product sizes of D50: 1–2 μm. Large‑scale, low‑energy, continuous production is becoming the industry goal.

5.3 Continuous Upgrades of Dry‑Grinding Equipment

New‑generation dry ultrafine grinding equipment, represented by the ring roller mill, is challenging the traditional notion that “ultrafine grinding must be energy‑intensive”. Under the same fineness conditions, it delivers comprehensive benefits of over 30% higher output and over 35% lower power consumption.

5.4 Green Production Is Becoming Standard

Fully enclosed negative‑pressure operation, zero dust emissions, and low noise have become standard requirements for magnesium hydroxide ultrafine grinding production lines. Environmental performance indicators such as equipment sealing and system negative‑pressure operation directly affect a company’s market competitiveness.