High temperature processing of kaolinitic materials

Calcination, is the process of heating a substance, to a temperature below its fusing point, with a resultant loss of water. It is one of the most important techniques currently used to enhance the properties, and therefore value, of kaolin. The overall aim of this project was to provide a better understanding of the principles of the kaolin calcination reaction in order to enhance the efficiency, quality and sustainability of the Imerys calcining operations. This research has shown a strong correlation between the chemistry of kaolin and the colour of the calcined product. This is due to the influence of contaminant materials on the colour of the hydrous kaolin, which in turn affects the calcined material. The strongest colour influencing factor is the presence of iron, particularly if it is present on the surface of the kaolin. Surface iron is currently reduced using a reductive bleaching process. This has an improving influence on even the most contaminated kaolins, however there can be quite a lot of interbatch variability. Despite its effect on colour the chemistry of kaolin has little influence on post calcination reactivity. Reactivity is due to physical factors such as particle and agglomerate size and the penetration of heat into the material. Any kaolin will calcine to produce a low reactivity product; provided the heat is able to penetrate into the bed and that the material is able to remain at temperature for sufficient time for the calcination reaction to occur. Another outcome of the research was the discovery that a higher temperature and shorter time period has little on the end calcined product but has implications for lower energy usage