Key Technical Specifications for Ground Calcined Kaolin Powder Products

Introduction to Ground Calcined Kaolin

Ground Calcined Kaolin is a highly processed form of kaolin clay that has been thermally treated (calcined) and then precisely milled to achieve specific particle size distributions. This process enhances its properties, such as brightness, opacity, abrasiveness, and electrical resistivity, making it a critical raw material in industries like paper coating and filling, paints and coatings, plastics, rubber, ceramics, and advanced adhesives. The key to achieving the desired product quality lies in the precise control of its technical specifications during the grinding and classification stages.

Critical Technical Specifications

The performance of calcined kaolin in its final application is governed by a set of interdependent technical specifications. Understanding these parameters is essential for both producers and end-users.

1. Particle Size Distribution (PSD)

PSD is arguably the most critical specification. It directly influences properties like opacity, viscosity, gloss, and reinforcement.

Measured As: Typically reported as D50 (median particle size) and D97 (the particle size at which 97% of the sample is finer).
Target Ranges: For high-performance applications, a very fine and tightly controlled PSD is required, often with a D97 ≤ 10μm and sometimes as low as D97 ≤ 5μm for ultra-fine products.
Measurement: Laser diffraction analyzers are the standard equipment for determining PSD.

$Laser diffraction analysis of kaolin powder particle size distribution$

2. Brightness and Whiteness

This optical property measures the reflectance of blue light and is crucial for paper, paint, and plastic applications where visual appeal is paramount.

Measured As: GE Brightness (% reflectance at 457 nm) and L* (whiteness) values on the CIE scale.
Target Values: High-quality calcined kaolin typically exhibits GE brightness values above 90%.
Influencing Factors: Purity of the raw clay, effectiveness of processing (e.g., magnetic separation to remove iron impurities), and the calcination process itself.

3. Oil Absorption

This test indicates the porosity and surface area of the kaolin particles, which affects its performance in liquid systems like paints and plastics.

Measured As: Grams of linseed oil absorbed by 100 grams of pigment (g/100g).
Typical Range: Calcined kaolin generally has a higher oil absorption (e.g., 70-90 g/100g) compared to its hydrous counterpart due to its more porous structure.

4. Specific Surface Area (SSA)

SSA describes the total surface area per unit mass of powder (m²/g) and correlates with reactivity, adsorption capacity, and its effect on viscosity in slurries.

Measured By: BET nitrogen adsorption method.
Importance: A higher SSA often leads to higher reinforcement in rubber and increased viscosity in liquid systems, which must be managed with dispersants.

5. Residue

This specification indicates the amount of coarse particles present, which can be detrimental to surface finish and mechanical properties.

Measured As: Percentage of material retained on a specific mesh sieve (e.g., 325 mesh / 45μm or 200 mesh / 75μm).
Target: A very low residue, often less than 0.1% or even 0.01% on a 325-mesh sieve, is required for high-grade products.

Sieve shaker analyzing residue content in kaolin powder

The Role of Precision Grinding Technology

Achieving these stringent and often ultra-fine specifications consistently and efficiently requires advanced milling technology. The choice of grinding equipment is paramount. For the production of high-purity, ultra-fine ground calcined kaolin, our SCM Ultrafine Mill series represents an ideal technological solution.

Technical Advantages for Kaolin Processing:

High-Efficiency & Energy Saving: Offers twice the capacity of jet mills while reducing energy consumption by 30%. Its intelligent control system provides automatic feedback on product fineness, ensuring consistent quality.
High-Precision Classification: The integrated vertical turbine classifier ensures precise particle size cuts, eliminating coarse powder contamination and delivering a uniformly fine product essential for high-brightness kaolin.
Durable Design: Features special-material grinding rollers and rings that significantly extend service life. The innovative bearingless screw design in the grinding chamber enhances operational stability, reducing maintenance downtime.
Environmental Protection: Equipped with a pulse dust collector that exceeds international efficiency standards. The soundproof room design keeps operational noise below 75dB, ensuring a clean and quiet working environment.

For producers targeting the mid-range fineness market with higher capacity requirements, our MTW Series Trapezium Mill is another excellent option. With an output fineness of 30-325 mesh (up to 0.038mm) and capacities ranging from 3 to 45 tons/hour, it is renowned for its wear-resistant design, optimized air flow, and high transmission efficiency, making it a robust and cost-effective workhorse for kaolin processing.

Conclusion

The market for ground calcined kaolin demands products that meet exacting technical specifications for particle size, brightness, and physical properties. Consistently achieving these standards requires a deep understanding of the material science behind kaolin and, crucially, investment in advanced, reliable, and efficient grinding technology. Selecting the right milling equipment, such as our SCM Ultrafine Mill for ultra-fine applications or the MTW Trapezium Mill for high-capacity needs, is a fundamental strategic decision that directly impacts product quality, production cost, and overall operational success.

Industrial grinding mill in a modern mineral processing plant