Wollastonite is a naturally occurring chain silicate mineral with a unique acicular (needle‑like) or fibrous crystal morphology, combined with excellent properties such as high whiteness, low oil absorption, good electrical insulation, and heat resistance. As an important industrial mineral raw material, wollastonite is widely used in ceramics, coatings, plastics, rubber, metallurgical casting fluxes, and building materials. With downstream industries demanding increasingly refined and functional materials, particle size control of wollastonite powder has become a critical factor affecting its application performance. Among various grades, 325‑mesh (approx. 45 μm) wollastonite powder has become an ideal choice for many industrial applications due to its moderate particle size, reasonable specific surface area, and good dispersibility. This article provides a comprehensive analysis of the processing technology, core equipment selection, and quality control for 325‑mesh wollastonite powder.

1. Applications and Quality Requirements of 325‑Mesh Wollastonite Powder

1.1 Main Application Areas

325‑mesh wollastonite powder has a wide range of applications:

• Ceramic Industry: This is the largest downstream market for 325‑mesh wollastonite products, accounting for approximately 50% of total consumption. It is mainly used in the production of glazed tiles, art ceramics, sanitary ware, daily‑use ceramics, electrical ceramics, high‑frequency low‑loss radio ceramics, and chemical ceramics. In glaze raw materials, substituting wollastonite for white pigments enhances glaze gloss, reduces slurry viscosity, and significantly lowers costs.
• Coatings Industry: As a filler and extender, wollastonite powder’s high whiteness and brightness make it suitable for high‑quality white paints and coatings. Its acicular crystal structure also provides a matting function, resulting in smooth and glossy finishes.
• Plastics and Rubber: Wollastonite powder not only acts as a filler but can also partially replace asbestos and glass fibres as a reinforcing material, primarily to improve tensile and flexural strength while reducing costs. When incorporated into polymer matrices, it improves electrical insulation, chemical inertness, and heat resistance.
• Other Fields: Including papermaking, welding electrodes, metallurgical casting fluxes, friction materials, and insulation materials.

1.2 Key Quality Indicators

Typical requirements for 325‑mesh wollastonite powder in the paint and coating industry are:

2. Core Process Flow for 325‑Mesh Wollastonite Powder Processing

From raw wollastonite ore to 325‑mesh finished powder, the typical process involves the following main stages:

Stage 1: Crushing and Pre‑Classification

After hand‑sorting to remove impurities, large wollastonite ore blocks are coarsely crushed in a frantoio a mascelle, then medium‑crushed in a frantoio a cono oppure frantoio a urto. The material is crushed to a size suitable for the grinding mill feed (typically <30 mm). During the crushing stage, care must be taken to protect the acicular crystal structure. Using a long‑chamber jaw crusher ensures that the crushing forces are mainly compressive and frictional, avoiding over‑crushing and effectively preserving the acicular morphology of the coarse wollastonite particles.

Stage 2: Grinding (Core Stage)

The crushed material is conveyed by a bucket elevator to a storage hopper and then uniformly fed by a feeder into the grinding mill. For producing 325‑mesh ordinary wollastonite powder, Raymond mills, ball mills, or vertical roller mills are commonly used as dry‑grinding equipment. During grinding, the material is crushed under compression and attrition between the grinding rollers and the ring (or table).

Stage 3: Classification and Collection

The ground material is carried by the air stream into the classification system. By adjusting the classifier speed, air volume, and grinding pressure, the final product fineness can be precisely controlled. Qualified fine powder is collected by cyclone collectors or bag filters and sent to finished product silos; coarse particles are returned to the mill for regrinding, forming a closed‑circuit loop.

Stage 4: Finished Product Packaging

The collected 325‑mesh wollastonite powder, after passing quality inspection, is packaged and stored.

3. Comparison of Core Equipment Options

For producing 325‑mesh wollastonite powder, equipment selection directly affects production efficiency, product quality, energy consumption, and long‑term operating costs. The three main types of equipment currently available are:

3.1 Mulino Raymond – The Cost‑Effective Choice for Small‑to‑Medium Scale Production

Raymond mills are widely regarded as one of the ideal equipment options for processing 325‑mesh wollastonite powder. They operate on the principle of combining compression and attrition: grinding rollers rotate under centrifugal force against the grinding ring, applying pressure and shear to the material, while an air‑classifying system enables integrated continuous grinding and classification.

Core advantages:

• Precise suitability: Particularly suitable for non‑metallic minerals with Mohs hardness inferiore a 7 and moisture inferiore a 6%, which matches the physical characteristics of wollastonite (Mohs hardness 4.5–5.5).
• Dimensione delle particelle regolabile: By adjusting the classifier speed, air volume, and roller pressure, the mill can stably produce powder in the range of 80 to 400 mesh, fully covering the 325‑mesh requirement.
• Energy efficiency upgrade: Modern improved models with new pendulum‑type roller assemblies can increase output by about 40% while reducing unit energy consumption by about 30%.
• Environmental compliance: Good sealing combined with pulse dust collection systems effectively controls dust emissions.

Suitable scenarios: Small‑to‑medium production lines or enterprises with strict cost‑control requirements. Large GK‑series Raymond mills can achieve capacities of up to 55 t/h.

3.2 Vertical Roller Mill (VRM) – The Efficient Choice for Large‑Scale Continuous Production

Vertical roller mills (including ultrafine VRMs) integrate crushing, grinding, classification, drying, and conveying in a single unit, and have been increasingly applied in the wollastonite processing field in recent years.

Core advantages:

• High capacity: HLM‑series VRMs can achieve single‑unit outputs of 3–40 t/h, suitable for large‑scale continuous production.
• Wide fineness adjustment range: HLMX ultrafine VRMs, equipped with dynamic‑static combination classifiers, can adjust product fineness flexibly between 325 mesh and 2500 mesh (5–40 μm) .
• Stable operation: Equipped with PLC remote control systems, offering a high degree of automation.
• Low comprehensive cost: High classification efficiency, easy maintenance, and low operating costs.

Suitable scenarios: Large‑scale production, especially for lines with outputs above 10 t/h.

3.3 Mulino a sfere – A Traditional Option

Ball mills are one of the traditional grinding equipment options and can also be used to produce 325‑mesh wollastonite powder. They offer the advantages of mature technology and strong adaptability, but they lag behind Raymond mills and VRMs in terms of energy consumption, space requirements, and noise control.

3.4 Raccomandazioni per la scelta delle attrezzature

For the 325‑mesh moderate fineness requirement, although ultrafine VRMs, ball mills, or jet mills can also achieve this fineness, they are not the optimal choice due to high investment costs, high energy consumption, or complex processes. Raymond mills show clear advantages in cost‑performance, operational stability, and adaptability, especially for medium‑scale production lines. If the line is large‑scale (over 10 t/h) or if there are future plans to expand to finer particle sizes, the vertical roller mill is a more forward‑looking choice.

4. Key Points for Powder Quality Control

4.1 Precise Control of Particle Size Distribution

The 325‑mesh (approx. 45 μm) requirement demands precise control over the grinding and classification process. By adjusting the classifier speed and air volume, the product particle size distribution is kept concentrated, avoiding “over‑grinding” or “under‑grinding.” The 325‑mesh residue is generally required to be ≤0.15%.

4.2 Preservation of Acicular Crystal Morphology

The acicular crystal structure of wollastonite is the key to its reinforcing and strengthening functions. During the comminution process, care must be taken to preserve this morphology. Appropriate grinding equipment and process parameters should be used to avoid excessive grinding that would destroy the crystal shape.

4.3 Control of Whiteness and Purity

The whiteness of 325‑mesh wollastonite powder is generally required to be ≥90%. At the same time, impurities such as Fe₂O₃ must be strictly controlled (≤0.2%) to ensure performance in downstream applications.

5. Development Trends and Outlook

With downstream industries demanding ever‑higher material performance, wollastonite powder processing is exhibiting the following trends:

• Large‑scale production: Single‑line capacities continue to increase, and large equipment such as VRMs are being more widely adopted.
• Finer grinding: Extending from 325 mesh to finer grades (1250 mesh, 2500 mesh) to increase product added value.
• Functionalisation: Surface modification treatments are becoming increasingly common; coupling agents such as silanes are used to improve compatibility with polymer matrices.
• Intelligentisation: Deep integration of DCS distributed control and automation technologies.

Processing 325‑mesh wollastonite powder is a systematic project that integrates crushing, grinding, classification, and collection. From raw ore to finished product, equipment selection is the key factor determining the success of the production line. Raymond mills, with their mature technology, precise fineness control, and good cost‑performance, are the first choice for most medium‑scale projects; vertical roller mills, with their high capacity, low energy consumption, and flexible fineness adjustment, offer distinct advantages for large‑scale production. When selecting equipment, companies should comprehensively consider production scale, investment budget, product positioning, and future development plans to choose the process route that best fits their needs.