More about Kaolin - raw material and its mining

Kaolin is a pliable raw material, particularly formed by a clay, the mineral kaolinite.

The key raw material of Sedlecký Kaolin, a.s. can be found in the Karlovy Vary region where kaolin has been mined for over 200 years. Additional kaolin deposits are located in the Podbořany, Cheb and Znojmo districts. Sedlecký Kaolin, a.s. also mines clays and natural sandstone as secondary raw materials.

We achieve the economic and high-quality processing of raw materials into semi-finished and final products by employing modern technological procedures. Our competitive advantage lies in the utilization of purely natural kaolin processing procedures.

Kaolin forms an initial raw material for the ceramics industry and for paper production. Nevertheless, it is also used in many applications in the chemical and other industries.

Sedlecký Kaolin, a.s. produces washed kaolin, which can be further processed into calcinated fillers and heat-resistant sharpeners. Only environmentally-friendly technological procedures are used for processing raw kaolin into washed kaolin.

The following is the theoretical composition of kaolinite: Al2O3 .2 SiO2 .2 H2O (39.5% Al2O3, 46.5% SiO2, 13.9% H2O by annealing

Kaolinite is formed of plate particles (usually 1 µm long and 0.1 µm thick) arranged in clusters or blocks (packets), which are firmly or less firmly held together. Kaolinite particles make strong bonds with water which, together with their basic shape, is the cause of its pliable behaviour when in contact with water.

The chemical composition of kaolin is close to that of the theoretical kaolinite, depending on its purity. Its physical and technological characteristics are greatly influenced by the character of the basic plate particles and their blocks – size, shape, presence of various substances absorbed by the particles, etc. The differences in the technological characteristics of various kaolins are thus much greater than the given chemical composition differences.

The kaolins in the Karlovy Vary region were created by the hydration of feldspars which, together with silica, form the basic component of several rocks, particularly granite. The theoretical composition of the main feldspar form is K2O.Al2O3 .6SiO2; its transformation changes it into kaolinite and another silica; the alkali components are mostly infused.

The initial material of the raw original kaolin is granite rock created by volcanic activity when the Earth’s crust was being formed. This original material eroded millions of years ago and broke down into kaolin and silica, accompanied by larger or smaller volumes of other components. The tropical climate at that time exposed the rock to mechanical erosion. Moreover, chemical corrosion was also taking place under increased temperatures due to water saturated with CO2 and rock acids infused from the soil.

The deposits in the Karlovy Vary region are primary deposits – the kaolin has remained at its location of origin. The original granite rock texture is clearly visible even today when mining the raw material clods.

The mined raw material includes 20-30% kaolin; the rest is silica sand, which forms an inseparable part of the raw material. The transformation degree (kaolinization) of the original rock decreases with increasing depth. Only raw material with at least 20% kaolin is usually mined. Tectonic forces meant that the original granite massif in the Karlovy Vary region was frequently disturbed at the time of its origin. Individual granite blocks would divide only when the common magma solidified, whereupon they eroded under very different conditions. The process created many kaolin deposits with different chemical and physical characteristics, sometimes even located quite near each other.