Characterization and Potentiality of Calcined Kaolins for Metakaolin Production

Abstract

This study aims to optimize the calcination conditions of Egyptian kaolins to produce metakaolin as pozzolanic material. Technological samples were collected from the kaolin quarries at Sinai, Egypt. The kaolin and metakaolin samples were characterized using laser size analysis, XRD, IR, XRF, TG, SEM and BET. The results showed that 66% of the fired samples are of highly pozzolanic activity (≥700mg Ca(OH)2/g metakaolin). The optimum pozzolanic activity (1732mg Ca(OH)2/g metakaolin) is given after kaolin calcination at 550°C for 30mins due mainly to the high kaolinite/quartz ratio as well as the low total fluxes content of the raw kaolin samples. The fluxes promote the agglomeration of the metakaolin particles during calcination causing the decrease of the metakaolin surface area and consequently minimize the reactive sites available for reaction. The optimum metakaolin at 550°C for 30mins has a maximum surface area and low pore volume of 13.99 m^2/g and 0.116 cm^3/g, respectively. This is attributed to the fact that the smaller pores provide higher surface area per unit volume of the metakaolin. The optimization of kaolin calcination conditions has add-values for the industrial upscaling of kaolin into metakaolin.