Kaolinite fusion in carbonate media: KAlSiO₄–NaAlSiO₄ phase transformations and morphological study

In this study, we report the thermal decomposition, phase transformation, and morphological change of two-component kaolinite-K₂CO₃ (KK) and three-component kaolinite-K₂CO₃–Na₂CO₃ (KKN) solid mixtures calcined at different temperatures. First, the conversion of kaolinite to the hexagonal and orthorhombic phases of KAlSiO₄ via heat treating in solid alkali media of K₂CO₃ is investigated. Then, the phase transformations and morphological changes for MAlSiO₄ as the product (M = K, K_0.75Na_0.25, K_0.5Na_0.5, K_0.25Na_0.75, Na), from KAlSiO₄ to NaAlSiO₄, are completely examined at 800 °C and 1100 °C. The as-made phases were characterized utilizing XRD, FT-IR, EDX and FE-SEM techniques. The results demonstrated that the most important factors having remarkable effect on the formation of different phases are the mole ratio of K/Na in initial applied carbonate media and the calcination temperature. The study provides the basic data and the methods for efficient and extensive application of natural kaolinite. (paper)