Effects of thermal and chemical modification on the physical properties of Ugandan Mutaka Kaolin

Abstract

This study investigates the impact of thermal treatment at temperatures ranging from 600 ​°C to 1050 ​°C and chemical treatment using (COOH)₂·2H₂O and Al₂(MoO₄)₃ ​at concentrations of 0.01 ​M, 0.05 ​M, and 0.1 ​M. The modified kaolin samples’ pH, oil adsorption capacity, refractive index, specific gravity, and viscosity were examined. Comprehensive analyses were performed to characterize the modified kaolin samples. The spectrum results revealed dealumination, with a corresponding increase in silicon content due to chemical treatment, while the aluminum content decreased compared to thermal treatment results. As observed with the calcined kaolin sample, a significant portion of the OH stretch groups vanished with disappearance stretches along the bands at 1229.6 and 1009.2 ​cm⁻¹, corresponding to Si–O stretching vibrations. The specific gravity of calcined kaolin was observed to be relatively lower than TiO₂. Furthermore, the obtained pH of 4.0 or lower, or a pH of 9.0 or higher, is classified as corrosive. The ideal temperature range for achieving optimal oil absorption lies within the 800 ​°C–900 ​°C range, where metakaolin properties favor effective oil uptake. The chemical concentration had a notable impact on the dispersion of kaolin powders, in contrast to calcined kaolin. At 800 ​°C, calcined kaolin attained an almost ideal refractive index for water-based paints, closely aligning with the refractive index of water.