Kaolin origin

Kaolin is a plastic raw material composed primarily of a clay mineral kaolinite.

The key raw material base of the company is situated in the region of Karlovy Vary where kaolin has been mined over the past 200 years. Other kaolin deposits are located in the area near Podbořany and in regions around Cheb and Znojmo. Sedlecký kaolin a. s. also extracts clays and natural sandstone.

With modern technology we attain economical and high-quality processing features in transforming raw materials into semi-finished as well as final products. One of our significant competitive advantages is the application of only natural (no chemistry) procedures in kaolin treatment.

Kaolines

Kaolin is the basic raw material for ceramics and paper industry. It is also used for various applications in chemical industry and other industrial branches.

Sedlecký kaolin a. s. produces various types of washed kaolins, which can be further valorized as calcined fillers or refractory raw materials. During processing of raw material into washed kaolins only ecologically friendly technological methods are used.

Take a look at the parameters of our kaolin products and the comparison of kaolin trade marks.

The theoretical composition of kaolinite is as follows

Al₂O₃ .2 SiO₂ .2 H₂O (39,5 % Al₂O₃, 46,5 % SiO₂, 13,9 % H₂O loss on ignition)

Kaolinite consists of lamellar particles usually less than 1 µm long and 0.1 µm thick. They are aligned in clusters or blocks (packets) which hold together in a more or less loose manner. Kaolinite particles firmly bind water; this bond and their basic shape cause the plastic behavior in contact with water.

The chemical structure of kaolin converges towards the theoretical kaolinite in accordance to its purity. The physical and technological properties are, to a large extent, influenced by the nature of the basic lamellar particles and their blocks, namely by their size, shape, the presence of various substances adsorbed on the particles, etc. Therefore, the differences in technological properties of various types of kaolin are much greater than the differences in their chemical composition.

Kaolin in the region around Karlovy Vary has emerged as a consequence of hydration of feldspar which, together with quartz, constitutes the basic element of a number of rocks, particularly of granite. The theoretical composition of the principal feldspar form is K₂O.Al₂O₃ .6SiO₂. Through its conversion, beside kaolinite, additional quartz is produced; for the most part, the alkaline components leach out.

The source material for the formation of raw kaolin is granite mineral, which emerged as a result of volcanic activity at the time when the earth crust was forming. Due to weathering which took place a few millions of years ago, the original material disintegrated into kaolin and quartz accompanied by larger or smaller amounts of other admixtures. In the then tropical climate, mechanical erosion impacted on the mineral and, at elevated temperatures, chemical corrosion took place in consequence of the effect that water saturated with CO₂ and humic acids leached out of the soil had on it.

Kaolin sources in the region of Karlovy Vary are primary deposits - kaolin remained in the place of its origin. To this very day, the original texture of the granite mineral is clearly conspicuous on the clots of the raw material during its quarrying.

The quarried raw material contains between 20 and 30 % of kaolin; the rest is made up of silica sand which is an integral part of the material. The degree of transformation (kaolinitization) of the original mineral decreases as we go deeper; the mineral containing over 20 % of kaolinite is usually used for quarrying purposes. By the effect of tectonic forces, the original granite massif in the region surrounding Karlovy Vary was disrupted many times already at the time of its formation. The particular granite crustal blocks split up already in the course of the solidification process of the common magma; after that, they have weathered under very dissimilar conditions. What occurred in consequence was the formation of a number of kaolin deposits that were geographically not far away from each other and yet they had different chemical and physical properties.