Causal Decomposition of Particle Size-Mediated Effects in Comminution-Derived Particle Systems During Gold Flotation

Particle size distributions produced during comminution are widely correlated with gold flotation performance, yet their interpretation as intrinsic particle characteristics is often confounded by particle generation mechanisms. This study applies a structural causal modelling framework to a controlled legacy flotation dataset (N = 11) generated using Vertical Shaft Impact (VSI) and High-Pressure Grinding Rolls (HPGRs) to distinguish particle size-mediated effects from non-size-mediated comminution effects. Structural decomposition showed that LS-HPGR exhibited a total recovery advantage of +8.60 percentage points relative to VSI, comprising a positive direct effect of +18.98 percentage points partially offset by a negative particle size-mediated effect of −10.37 percentage points. Counterfactual analysis confirmed that crusher-specific flotation responses persisted even under comparable particle size distributions. Crusher-specific effects were further interpreted in the context of measured comminution power and processing-time data. Particle size significantly influenced concentrate grade (p = 0.002) but showed only weak influence on recovery within the tested operating range. These findings demonstrate that particle size distributions function as mediating particle-scale properties rather than purely descriptive metrics, extending flotation process interpretation beyond conventional size–performance correlations.