High-purity kaolin features high brightness, soft texture, easy dispersion and suspension in water, good plasticity, and high adhesion, as well as excellent electrical insulation properties. It also boasts good resistance to acid solubility, very low cation exchange capacity, and good refractoriness. Consequently, kaolin has become a mineral raw material essential for dozens of industries, including papermaking, ceramics, rubber, chemicals, coatings, and more. Reports indicate that kaolin is also used in Japan as a substitute for steel in the manufacturing of cutting tools, lathe drills, and engine casings. Particularly in recent years, with the rapid development of modern science and technology, the application scope of kaolin has expanded even further. Some technical fields are now utilizing kaolin extensively as a material, including in high-temperature ceramic components for atomic reactors, space shuttles, and spacecraft.
Calcined kaolin for papermakingAlrightOur coal-based kaolin is processed from raw material through beneficiation, ultra-fine powder grinding, and calcination. It boasts a complete hexagonal lamellar structure, good porosity, a reasonable particle size distribution range, and ideal light scattering properties. Additionally, due to its high brightness, low wear value, and good oil absorption, it is aSureOur paint pigments, currently primarily used in the paper industry for coating applications, are known for their ability to reduce production costs, enhance paper properties, improve ink absorption rates, and offer good compatibility with other components, along with high viscosity.
Compared to raw kaolin, low-temperature calcined kaolin has reduced bound water content, increased silicon dioxide and alumina content, more active sites, altered structure, smaller and more uniform particle size. The curing characteristics curve of NR rubber compounds filled with low-temperature calcined kaolin is essentially the same as that filled with raw kaolin, with no change in Shore A hardness and an improved tensile strength. Both meet the industry standards for non-transparent soles of sports shoes in terms of physical properties.
Recently, ceramics, rubber, plastics, artificial leather, cement, refractory materials, chemicals, and agriculture have been widely used in various industries. With the continuous improvement of the high-alumina mining process, the application scope of kaolin will become increasingly extensive. Coalfield geological systems can, based on the actual situation, focus on the kaolin resources in coal measures strata and market demand. Kaolin, a widely existing non-metallic mineral in nature, was traditionally used for producing ceramics, refractory materials, and as a minor filler in plastics and rubber. As the economy develops in various fields, there is growing emphasis on the deep processing of kaolin. This not only allows for the acquisition of materials with special properties but also enhances economic benefits. One method of deep processing kaolin is to further heat, roast, and dehydrate the already washed and dried kaolin to transform it into meta-kaolin, which can be used as a filler in plastic cables to improve the insulation performance of the cable sheath. Common rubber fillers for footwear include organic fillers and inorganic fillers. Organic fillers include reclaimed rubber and recycled materials, while inorganic fillers include carbon black, calcium carbonate, titanium dioxide, magnesium carbonate, magnesium oxide, carbon black, and zinc oxide powder. Kaolin has become a rubber product filler developed in recent years.
But all applications of kaolin require it to be processed into a fine powder before being mixed with other materials for complete integration.
The cohesive property refers to the ability of kaolin to combine with non-plastic materials to form a plastic clay mass with certain drying strength. The determination of cohesive ability involves adding standard quartz sand (with a particle size composition of 70% between 0.25-0.15mm and 30% between 0.15-0.09mm) to the kaolin. The higher the sand content it can still maintain in the plastic clay mass and the higher the bending strength after drying, the stronger the cohesive ability of the kaolin. Generally, kaolin with strong plasticity also has strong cohesive ability.
Adhesiveness and thixotropy
Viscosity refers to a fluid's property of resisting relative flow due to internal friction, which is measured by its degree of viscosity (frictional force per unit area). The unit is Pa·s. The measurement of viscosity is typically done using a rotational viscometer, which gauges the rotational speed in kaolin slurry with a 70% solid content. Viscosity plays a significant role in the production process, not only as a crucial parameter in the ceramics industry but also having a major impact on the papermaking industry. According to data, for low-speed coating applications using kaolin as a paint, the required viscosity is about 0.5 Pa·s, while for high-speed coating, it should be less than 1.5 Pa·s.
Thixotropy refers to the property of mud that, after having solidified into a gel-like state and no longer flowing, returns to a fluid state when subjected to stress, and then gradually thickens back to its original state upon rest. It is characterized by the thickening coefficient and measured using an efflux viscometer and a capillary viscometer.
Viscosity and thixotropy are related to the mineral composition, particle size, and cation type in the mud. Generally, mud with higher montmorillonite content, finer particles, and exchangeable cations predominantly sodium exhibits higher viscosity and thickening coefficient. Therefore, in the process, it is common to increase viscosity and thixotropy by adding clay with strong plasticity and improving fineness. To reduce it, methods such as increasing diluent electrolytes and water are used.
Drying Performance
Drying properties refer to the characteristics of kaolin clay during the drying process, including drying shrinkage, drying strength, and drying sensitivity, etc.
Drying shrinkage refers to the shrinkage that occurs in kaolin clay after it loses water and dries. The clay typically undergoes dehydration and dries at temperatures between 40-60°C, with no more than 110°C, as moisture is expelled, particle distances shorten, and the length and volume of the sample shrink. Drying shrinkage is divided into linear shrinkage and volumetric shrinkage, which are expressed as percentages of the change in length and volume after the clay has dried to a constant weight. The linear shrinkage of kaolin is generally between 3-10%. The finer the particle size, the larger the specific surface area, the better the plasticity, and the greater the drying shrinkage. For the same type of kaolin, due to variations in mixed water, the shrinkage differs; more water results in greater shrinkage. In ceramic processing, excessive drying shrinkage can cause the body to deform or crack.
The drying strength refers to the flexural strength of clay after drying to constant weight.
Dry sensitivity refers to the ease with which a green body may deform or crack during drying. A higher sensitivity makes deformation and cracking more likely during the drying process. Generally, kaolin with high dry sensitivity (dry sensitivity coefficient K > 2) is prone to forming defects; those with lower sensitivity (dry sensitivity coefficient K < 1) are safer during drying.
Sinterability
Sinterability refers to the property of a shaped, solid, powdered kaolin body that spontaneously fills particle gaps and densifies when heated to near its melting point (usually over 1000°C). The state where the porosity decreases to a lower value and the density reaches a higher value is called the sintered state, and the corresponding temperature is known as the sintering temperature. As heating continues, the liquid phase in the sample increases, causing deformation, at which point the temperature is referred to as the transformation temperature. The interval between the sintering temperature and the transformation temperature is known as the sintering range. The sintering temperature and range are crucial parameters in the ceramic industry for determining the raw material formula and choosing the type of kiln. It is preferable for the test sample to have a low sintering temperature and a wide sintering range (100-150°C), which can be controlled through the addition of fluxing materials and proportionally blending different types of kaolin.
