Identification of the grinding mechanisms and their origin in a stirred ball mill using population balances

The objective of this work was to understand the origin of the stresses and the nature of the grinding mechanisms in a high-shear ball mill. The ball mill used was a Dynomill and the grinding media consisted of zirconium oxide beads. The ground powder was a poorly water soluble product. The particle size distribution was analyzed with laser diffraction. A population balance model enabled to calculate the breakage function from the experimental data. The breaking parameters were used to determine the grinding mechanism at different grinding conditions. The grinding mechanism depends on the orientation and intensity of the forces applied on the particles. The grinding mechanisms were determined from the grinding experiments and correlated to the movement of the grinding media in the grinding chamber and the applied mechanical stresses. The observed grinding mechanisms are cleavage and some fracture for coarse particles (15 pm), cleavage and abrasion for intermediate particles (0.8 mu m) and cleavage for fine particles (smaller than 0.15 mu m). The grinding mechanisms are related to the movement of the grinding media in the grinding chamber. Cleavage and abrasion of particles are the result of compression forces and shear in the centrifuged packed bed of grinding beads. The grinding mechanism does not change when changing the operating conditions and the packed bed of media is similar in the studied ranges of operating conditions. (C) 2009 Elsevier Ltd. All rights reserved.