Segregation in binary and polydisperse stirred media mills and its role on grinding effectiveness

Most industrial vertical stirred mills contain a non-uniform set of grinding media sizes. However, this fact is often ignored in simulations, which mostly use monodispersed media. The paper explores the fundamental dynamics of vertical mills when using multiple sizes of grinding media, by using DEM simulation. Our results suggest that by including both large and small media, one may be able to optimise its performance in several manners. The energy going into the contacts can be increased by including a second size, leading to more effective grinding. Including smaller media can also reduce the power draw of the mill, increasing the efficiency and sustainability of the mill. Finally, the natural segregation between different sizes creates different types of collision which grind different particle sizes more effectively. Segregation leads to smaller media at the bottom, so continuous processes can be optimised for fine grinding by feeding from the top, where the larger media are. This further enables control of the resulting product specifications.