A study of fine particle grinding in vertically stirred media mills via positron emission particle tracking technology and the discrete element method

This study provides a comprehensive understanding of the fine particle grinding process in stirred media mills. Calcium carbonate was chosen as the feed material. The experiments were firstly conducted in a laboratory scale vertically stirred media mill under various grinding conditions. The operating variables including specific energy, rotational speed, solids concentration, grinding media type, chemical additives (dispersant) were investigated. Then, the process was scaled up to a pilot scale mill. The performance of the pilot scale mill was compared to the laboratory scale mill regarding the product size (e.g. d80 ) and instantaneous power draw. Positron Emission Particle Tracking technology (PEPT) was used as a tool to study the motion of the grinding media in the laboratory scale stirred media mill. Some new stirrers were proposed and analysed. The PEPT results obtained under different operating conditions were demonstrated and analysed. The Discrete Element Method (DEM) based on the Hertz-Mindlin contact model was implemented to simulate the motion of the grinding media in both laboratory scale and pilot scale mills. A new type of stirrer is accepted by Imerys and used to produce the calcium carbonate in the industrial scale of grinding process. The energy saving is obtained up to 3 %compared to the standard stirrer currently used