Mechanochemical treatment of Serbian kaolin clay to obtain a highly reactive pozzolana

Mechanochemical treatment of Serbian kaolin clay was performed in a planetary ball mill using two different milling media, hardened steel or zirconia vials and balls. The samples obtained after various milling times were characterized by particle size laser diffraction (PSLD), X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DTA/TGA) and Fourier-transform infrared (FTIR) analyses. The mechanochemical treatment induced amorphization of the kaolinite phase accompanied by dehydroxylation. It was found that for given milling parameters, amorphization mainly occurred in the milling period up to 15 min, and was completed after about 30 min of milling for both employed milling media. The pozzolanic activities were determined by the Chapelle method. Milling in the hardened steel milling medium had no significant influence on pozzolanic activity, even though there was accumulated iron contamination. For both milling media, a pozzolanic activity of 0.79 was obtained for the samples milled for 15 min and it remained almost unchanged with prolonged milling. The determined pozzolanic activity values were similar to those of commercial metakaolinite or metakaolinite obtained by calcination of the same clay, thereby, indicating that highly reactive pozzolana could be obtained by mechanochemical treatment of Serbian kaoline clay.