Thermal reactions of kaolinite with potassium carbonate

It was previously established that kaolinite reacts with K2CO3 on heating to form products of KSiAlO4 composition. In the present study we investigated the solid state reactions with K2CO3 Of four kaolinites of different thermal stability. The mixtures were calcined at temperatures ranging from 400-700degreesC and washed before or after boiling with the remaining K2CO3. FTIR spectra indicated that the X-ray amorphous material formed after calcining the mixtures at 500-590degreesC had a SiAlO4 tetrahedral framework. Attempts to convert the products to zeolites gave promising results. After calcining at 700degreesC under atmospheric pressure synthetic kaliophilite (KSiAlO4) was obtained. These conditions are appreciably milder than previously reported for kaliophilite syntheses. Conversion to kalsilite increased with decreasing thermal stability of the original kaolinite. In similar reactions with KCl much less K was incorporated into the amorphous phase and kaliophilite was not obtained. The reactions of the four kaolinites with K2CO3 or with KCl were similar in trend, but differed in detail.