Kaolin: The Fine Filler with Reinforcing Potential

Kaolin – a natural mineral with numerous application possibilities

Kaolin, also known as porcelain clay, white clay, or China Clay, is a natural raw material extracted in various countries around the world, not only in China as the name suggests, but also in Germany. It was named after the place Gaoling in China, where it was first discovered. The mineral is a fine white powder mainly composed of kaolinite, a compound of aluminum and silicate. Due to its unique properties, kaolin is often used as a filler in various economic sectors. In addition to the ceramic and paper industries, kaolin is used in many other sectors such as paint and coating production, elastomers, and the automotive industry, as well as rubber production. Furthermore, kaolin is also used in the pharmaceutical and cosmetic industries.

Chemistry and Mineralogy

Chemical formula: Al₂[Si₂O₅](OH)₄
Kaolin belongs to the phyllosilicate group and has a pronounced lamellar shape.

Technical Properties

High aspect ratio (1:40)
Pronounced lamellar structure
Density 2.6 g/cm³
Hardness 2 (Mohs)
Low thermal expansion coefficient:
5*10 6/K (bei T 20-300°C)
Chemically inert
High degree of whiteness
Reinforcing properties

HPF Kaolin: Products of the highest quality

The kaolin-based products distributed by HPF bear the following brands:

AKPure^®

refers to coarse calcined kaolin

CALK

offers very fine calcined kaolins

PHARMAKAOLIN

particularly suitable for cosmetics, body care, and pharmaceutical products

KAOLIN TEC

extremely lamellar kaolin, also surface-treated

CHINAFILL

types of natural kaolin in different particle sizes

Applications for kaolin polymers

Kaolin is also used in many other industrial sectors. It finds application in the cosmetic industry and as a white pigment for the painting production. It not only imparts color but also gloss and surface hardness. Soft kaolin is used in rubber production, for example in car tires. Additionally, kaolin is appreciated in industrial applications as an emulsifier and release agent.

Elastomers

Elastomers are solid but elastic polymers, such as fluoro elastomers or silicones. These polymers are used wherever high elasticity of the final product is important, such as in seals, tires, cables, hoses, conveyor belts, flooring, and medical technology. Various types of CHINAFILL are particularly suitable for seals in the automotive sector.

Elastomers – HPF Minerals

Rubber

Rubber is an extremely elastic material essential in our daily lives. It consists of vulcanized natural or synthetic latex. Rubber is found wherever elasticity is of particular importance, such as in tires, flooring, hoses, cables, and various household products. We offer various types of kaolin with the desired color and particle size distribution, combined with low heavy metal content and almost no moisture (free moisture <1%). Typical final applications for the calcined kaolins of the CALK series are rubber mixtures for extruded and molded components, such as washing machine door seals or pharmaceutical rubber stoppers.

Elastomers – HPF Minerals

Polyamide

With the product Kaolin TEC 110, we have succeeded in developing an efficient filler with good reinforcing properties at an excellent price-performance ratio. The use of platelet-shaped kaolin significantly improves the following mechanical properties in polyamide compounds:

Increase in tensile strength and tensile modulus
Increase in rigidity while maintaining toughness
Effective flame protection
Good price-performance ratio

Thermoplastics – HPF Minerals

Paints and Coatings

The use of light platelet-shaped kaolin is particularly suitable for dispersion and silicate paints. Good pigment distribution leads to excellent coverage. The calcined kaolins of the AKPure^® series are multifunctional fillers for decorative paints for interiors and exteriors, with excellent covering power and increased abrasion resistance.

Construction protection – HPF Minerals

Body Care and Pharmaceutical Applications

Natural pharmaceutical kaolin is particularly suitable for external cosmetic applications due to its high standards. Consistent product quality is of great importance, especially in the field of pharmaceutical applications. Our Pharmakaolin meets all the requirements of the Pharmacopoea Europaea for kaolin intended for external and internal use. This requirement profile is verified and certified for each batch by an external laboratory. For particularly sensitive microbiological requirements, we offer the possibility of additional treatment of our Pharmakaolin by irradiation. Furthermore, our pharmaceutical kaolin is dermatologically tested.

Application areas:

Peel-off facial masks
Face powder
Soaps and shower gels
Deodorants

Pharma – HPF Minerals

The versatile properties of kaolin

Kaolin is an extremely versatile mineral, widely used in various industrial sectors due to its characteristics. It has reinforcing properties, high tensile strength, is easily colorable, and hydrophilic.

Due to its natural whiteness, kaolin is an important raw material in paper production, where it is used as a filler and coating agent to improve print quality and increase surface smoothness. The fineness of kaolin particles allows for uniform distribution and high surface quality, making it particularly valuable in the ceramic industry.

In this sector, it is appreciated for its plasticity, which allows for easy shaping and molding. In addition to the ceramic and paper industries, kaolin is also used in the refractory industry due to its resistance to high temperatures and porosity; these properties allow for heat storage and insulation.

Kaolin is chemically stable and reacts little with other substances, which supports its use in various other industrial processes. In the pharmaceutical industry, kaolin is used for its ability to absorb toxins and harmful substances. In the paint and coating industry, kaolin is used as a filler and pigment. Its natural whiteness and plate-shaped particles improve coverage and brightness of paints.

In the rubber and latex industry, kaolin is often used as a filler and reinforcing agent. It optimizes strength, elasticity, and abrasion resistance.

Deposits and Extraction of Kaolin

Kaolin is found in two main types of deposits: primary and secondary. Primary deposits form through the alteration of feldspar, while secondary deposits derive from the transport and deposition of primary kaolins.

Globally, kaolin deposits are relatively rare but of great economic importance. Countries such as Germany, England, the United States, Japan, China, and India have significant deposits. The Quarzwerke group, of which Amberger Kaolinwerke is a part, is one of the world's largest producers.

In Germany, extraction is primarily concentrated in the Hirschau area in Bavaria. Other extraction sites are in Seilitz and Kemmlitz.

Deposits of Amberger Kaolinwerke in Germany

Since 1901, the Amberger Kaolinwerke (AKW) in Hirschau has become an important producer of raw materials in Europe. The success of this positive development is based on high-quality deposits and continuously improved and efficient processing technology.

Since 1995, the Amberger Kaolinwerke have been part of the Quarzwerke group, a family-owned company based in Frechen, near Cologne. The key to offering quality products lies in a diversified portfolio and access to various deposits in our international network.

Each deposit has its own mineralogical individuality, allowing us to access different types of kaolin with distinct quality parameters. This enables us to offer tailored products for the ceramic and paper industries, which are the main markets for Amberger Kaolinwerke.

More Information

Kaolin deposits in Hirschau and in the background Monte Kaolino

Caminau

The Caminau deposit, located in the province of Bautzen in Saxony, has geologically developed from the granodiorite of Lusatia. Extraction has been taking place since 1904.

The kaolin products from Caminau are particularly suitable for the paper, colored pencil, and cosmetic industries. This deposit is the northernmost in Lower Lusatia and has formed autochthonously through the alteration of the Lusatian granodiorite. It covers an area of 2,5 km², with the thickness of the extractable material varying from 20 to 50 meters.

The high degree of whiteness of Caminau kaolin is explained by the successive action of humic acid during the formation of lignite in the Tertiary.

Kemmlitz

Kemmlitz, with its open-pit mines and processing sites, is located in the vicinity of the town of Mügeln in northern Saxony, near Meißen. It hosts the most important kaolin deposits for fine ceramics in Germany, mainly due to their bright white color after firing, which makes them particularly suitable for porcelain and other fine ceramic products. The starting rock consists of primordial volcanic rocks, where erosion and the action of ice masses from the last ice age have led to the formation of kaolinized rhyolites in depressions of various sizes. For industrial extraction, this means that in Kemmlitz there are several small open-pit mines not connected to each other.

Kaolin is a unique and proven industrial mineral, also because it remains chemically inert over a wide pH range. Furthermore, kaolin is soft, non-abrasive, and conducts heat and electricity only to a limited extent. Due to the mineralogical individuality of the different deposits, the kaolins from Amberger Kaolinwerke and Kaolin EAD in Bulgaria, both part of the Quarzwerke group, are used in many applications with very specific requirements.

The Production of Kaolin

Kaolin, a white, soft, and moldable mineral, consists of fine, flat particles. It forms through the transformation of anhydrous aluminum silicates in rocks with high feldspar content, caused by alteration or hydrothermal processes. This transformation process, known as "kaolinization," transforms hard granite into the soft substance found in kaolin mines.

To use kaolin as an industrial raw material, it undergoes complex processing steps. In a wet mechanical processing, kaolin is separated from other minerals using washing drums, cascades of cyclones, and centrifuges. Subsequently, it is dehydrated through sedimentation, filtration, and drying. Some kaolin products are further refined by bleaching and magnetic separation.

The Production Process of Calcined Kaolin

The production of calcined kaolin takes place in rotary or batch kilns at temperatures above 1000°C, a process known as calcination. There are two different approaches:

Rotary kiln with powder addition: In this process, the result mainly depends on the particle size of the material used. Calcination of kaolin powder leads to a different particle morphology compared to calcination of bricks with subsequent grinding.
Batch kiln or rotary kiln with brick feed material and subsequent grinding process: Here, the particle size distribution is shaped by grinding processes, allowing targeted influences on hardness, oil absorption, particle size distribution, morphology, and purity. This process is two-stage.

During brick firing, particle sintering occurs. Grinding leads to compact particles with a rough surface structure. The choice of starting kaolin, temperature profile, and grinding process influence the final particle properties.

Sintering results in more compact and less porous high-performance fillers, reducing oil absorption and saving costly binders in the formulation.

The opacity and yield of paints containing coarse calcined kaolin, obtained by calcination of bricks and subsequent grinding, are comparable to those of coarse calcined kaolin produced by powder calcination.

Calcined kaolin belongs to the mineral group of silicates but has lost its crystal structure due to heating. It is no longer plate-shaped but resembles ground ceramic powder.

The History of Kaolin

Kaolin has a history dating back to antiquity. Its use began in China thousands of years ago, where it was used to produce fine porcelain. This marked the beginning of the porcelain industry, which later spread to Europe. In the 18th century, kaolin deposits were also discovered in Europe, particularly in Germany, England, and France. The industrial use of kaolin in the Western world contributed to the development of various industrial sectors, including the ceramic, paper, paint, and rubber industries. Over time, the use of kaolin has further diversified, and today it is found in a wide range of products, including plastics, cosmetics, and pharmaceuticals.

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FAQ

What properties does kaolin have?

Kaolin, also known as porcelain clay or white clay, is a fine, iron-free rock mainly composed of the clay mineral kaolinite. It is distinguished by its low hardness, which ranges from 2 to 2.5 on the Mohs scale, and a density of 2.6-2.68 g/cm³. Kaolin is plastic, refractory, and, when fired, forms a solid and dense body.

In which applications kaolin is used?

Kaolin has multiple applications. In the ceramic industry, it is the main component in the production of white porcelain and light-fired clay masses. In paper production, it is used as a filler and whitening agent to improve smoothness, brightness, and print quality of paper. Additionally, kaolin is used in cosmetics as a base for powders, in paints and coatings as a filler to improve covering power and surface hardness, and in the plastics industry to improve the elasticity modulus of polyethylene.

What benefits does kaolin have?

The effectiveness of kaolin in these applications is based on its particle fineness, high whiteness, and chemical resistance. In ceramics, it gives the final product strength and a smooth surface. In paper, it increases opacity and improves printability. In plastic processing, it improves the mechanical properties of products.

How is kaolin produced?

Kaolin forms through the alteration of silicate-rich rocks like granite and rhyolite, which are rich in feldspars and quartz. Hydrothermal fluids modify these rocks and change their chemical composition, leading to the formation of kaolin. After extraction, kaolin is processed to remove impurities and achieve the desired particle size for various applications.

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