Zeolites prepared from calcined and mechanically modified kaolins: A comparative study

Kaoliniferous sand and washed industrial kaolin obtained from it were calcined (750 °C) or milling prior to activation with NaOH. The changes were characterized by pH, cation exchange capacity (CEC), water capacity after calcination (WCC), particle size distribution (PSD) and specific surface area (SBET), as well as by X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermal methods (TGA and DTA), and scanning and transmission electron microscopy (SEM and TEM). Alkali activation of thermally or mechanically modified kaolin increased the cation exchange capacity from 2.4 to 292.8 and from 3.0 to 279.9 cmol kg−1 (samples WT and WM respectively). Alkali activation of mechanically modified kaoliniferous sand (OMA), and thermally and mechanically modified washed kaolin (WTA and WMA), yielded zeolite A. An unnamed zeolite, forming microspheres of 0.8–2.3 μm in size, was also formed in mechanically modified kaoliniferous sand (OMA), washed kaolin (WA) and calcined washed kaolin (WTA) after alkali-activation. Structural disorder in the mechanically modified washed kaolin (WMA) favored the formation of a single type of zeolite.