Investigation of a novel, variable-orientation, pilot-scale mill using positron emission particle tracking

This study reports the first application of Positron Emission Particle Tracking (PEPT) to a continuous, variable-orientation stirred mill. PEPT is a non-invasive, non-destructive imaging technique that enables direct measurement of grinding media motion using a radiolabelled tracer. While PEPT has previously been applied to stirred milling systems, prior investigations have largely been limited to small, vertical, batch configurations. In contrast, the present work examines a mill operated under both batch and continuous conditions at five separate angles between the vertical and the horizontal. Significantly, the study found that the optimal angle for grinding media dynamics may not be either horizontal or vertical, indicating potential for future exploration of a new design space that could lead to novel, more sustainable processes. Continuous operation was also found to fundamentally alter the motion of the grinding media, inducing clear fluidisation and the formation of persistent recirculation loops. This appeared across all angles and was detrimental to grinding performance.