Effect of mechanical activation on acid-leaching of kaolin residue

The effect of mechanical activation on leaching of a kaolin residue in hydrochloric acid (20 mass %) was investigated. The influence of mechanical activation on morphology and particle size was studied by scanning electron microscopy (SEM) and particle size analysis. The SEM images demonstrated that mechanical activation induced the transformation of the kaolin residue from needle-shaped particles to spherical particles. The particle size decreased. The XRD reflections of the raw residue disappeared after 4 h of mechanical activation. Thus, mechanical activation improved the acid leaching by changing the physicochemical properties of the residue. The apparent activation energies for leaching of the unground and ground residues were calculated to be about 43 kJ/mol and 24 kJ/mol, indicating that the leaching process of the unground residue was controlled by the surface chemical reaction and the ground residue was controlled by a diffusion process. Mechanical activation greatly improved the activity of the kaolin residue and affected the leaching kinetics, which reduced leaching temperature and leaching time.