Coal measure kaolin is associated with coal, and during the generation of kaolin, organic matter directly seeps into kaolin, and under a certain temperature and pressure, organic matter gradually transforms into fixed carbon, which exists in the crystallization gap with kaolin, making coal measure kaolin appear gray black or gray white. Directly produced products, without any chemical treatment, generally not more than 75% whiteness. In order to eliminate the influence of carbon, it is necessary to use high-temperature oxidation calcination and other methods to remove carbon to improve the whiteness of kaolin. Generally, the whiteness of kaolin in coal measures is greatly improved after calcination, and the whiteness of better quality ore can reach more than 90%. Calcined kaolin can remove organic matter and hydroxyl to improve the porosity and activity of the final product.

Picture of calcined kaolin in north China

Calcined kaolin ore

Kaolin calcined products at different temperatures have different physical properties. For example, excellent electrical properties can be obtained by calcination at low temperature (750℃), and the volume resistivity of PVC plastic can be improved exponentially by calcination at high temperature (950℃), which can obtain higher cleanliness, better oil absorption and large specific surface area. And has good cover rate and opacity, these characteristics can be used in the volume pigment in the paint or white pigment substitute and papermaking industry. Therefore, the calcination of kaolin should be based on the different use of the product, choose different calcination process.

Kaolin clinker

Kaolin finished