Characteristic Investigations on Ethiopian Kaolinite: Effect of Calcination Temperature on Pozzolanic Activity and Specific Surface Area

Abstract

Kaolinite, a clay mineral, is an important industrial mineral which was gainfully utilized with several industrial significances. Towards mineral beneficiation, the present study aimed to investigate the effect of calcination temperature on the pozzolanic activity and specific surface area of Ethiopian kaolinite (Ek). The raw Ek and calcined Ek were characterized using different sophisticated techniques, such as XRD, FTIR, DSC, TGA, dynamic light scattering, electrophoretic light scattering, and SEM analysis. The pozzolanic activity and specific surface area of Ek particles were ascertained using Chapelle’s and Brunauer–Emmett–Teller methods, respectively, with some modifications. The results revealed that the calcination temperature had a great influence on pozzolanic activity and specific surface area of Ek. It was observed that the pozzolanic activity linearly increased with calcination temperature until 700°C and showed a maximal value of 1235 mg Ca(OH)2 g−1. On the other hand, beyond 700oC, the pozzolanic activity was inferred to be declined to 445 mg Ca(OH)2 g−1 at 1000°C due to agglomeration of calcined kaolinite (metakaolinite) and formation of spinel phase. A similar phenomenon was observed for specific surface area which increased with temperature until 700°C to exhibit the maximal values of 47.794 m2·g−1. Further, the investigation on zeta potential analysis showed that the magnitude value of the metakaolinite was observed to be less than the zeta potential value of the raw kaolinite, which indicated that the flocculation tendency of metakaolinite was greater than the kaolinite flocculation affinity in water.