Structural alterations and thermal behaviour of mechanically activated alunite ore

Abstract

Alunite, a potassium alum, was activated mechanically in a planetary ball mill, and the effects of mechanical activation on the structure of alunite have been studied by particle size analysis, scanning electron microscopy, X-ray diffraction and the Fourier transform infrared spectroscopy. The results show that the activation procedure led to amorphisation and structural disordering in the alunite structure. Thermal decompositions of both non-activated and activated alunite samples have been studied by thermogravimetry (TG) and differential thermal analysis (DTA). In non-activated alunite, the dehydration reaction starts after 500 °C. On the contrary, the dehydration of mechanically activated alunite was started after 100 °C. It is observed by X-ray diffraction analysis and thermal analysis that dehydration and desulphation temperatures of alunite decreased with mechanical activation, owing to amorphisation and structural disordering in alunite.