SAG mill design techniques and comprehensive design methodology

This paper reviews design and analysis techniques for Semi-Autogenous Grinding (SAG) mills, categorizing key variables into constraints, controls, operating conditions, and preferred outcomes. Experimental and numerical approaches including Grinding Media Trajectory (GMT) models for impact predictions, Population Balance Models (PBM) for Particle Size Distributions (PSDs) evolution, and Discrete Element Method (DEM) for particle dynamics are reviewed and compared based on input requirements and insights for SAG modelling. A novel design methodology is proposed that combines GMT for particle impact energy estimation, PBM for optimizing mill length and grate size to enhance throughput, and DEM for detailed charge dynamics, incorporating bidirectional feedback loops: DEM-refined collision energies update PBM breakage rates, while PBM-predicted PSDs refine GMT trajectories. This integration improves energy spectra and utilization, achieving better product grind size under varying operational constraints. Applied to a 1.8 m diameter SAG mill belly, the methodology yields an optimized design with 12 lifters at a 22.5° face angle and 0.138 m height, minimizing media-to-lifter impacts and reducing wear. The iterative process advances internal mill mechanics and charge-lifter interactions, offering substantial improvements over standalone techniques through validated multiscale predictions.