Thermodynamic analysis of the influence of potassium on the thermal behavior of kaolin raw material

The mineralogy and thermal properties of two kaolin clay samples from Agua Blanca (Hidalgo-México) were determined by XRD, SEM-EDS, TGA-DSC techniques.Kaolin clay A contains a higher Al2O3 and lower impurities (K2O, TiO2, Fe2O3) amount than kaolin clay B, while the SiO2 amount is similar for both kaolin clays.A theoretical approach was carried out by a thermodynamic analysis considering the chemical composition of both kaolin clay samples with the FactSage 7.3 software.Stability phase diagrams were obtained to different K2O content from 0.1 to 3 wt % and temperatures in the range from 600 to 1600°C based on the chemical composition of the kaolin clay samples.The main mineralogical compounds predicted are andalusite (Al2O3×SiO2), K-Potash feldspar (K2O×Al2O3×6SiO2), and the SiO2 polymorphs (quartz, tridymite, and cristobalite) with small amounts of ferricpseudobrookite (Fe2O5Ti), and rutile (TiO2).As K2O content is increased, the amounts of mullite and tridymite decrease meanwhile the potash feldspar is increased at high temperatures.A liquid phase is formed at around 1350 and 1400°C for the kaolin clay samples A and B, respectively.The viscosity of the melt is increased for the evaluated K2O additions to 1400, 1500, and 1600°C.