Understanding gangue recovery in the JKHFmini: A small-scale fluidised bed flotation cell

The JKHFmini is a semi-batch-operated, small-scale fluidised bed flotation device that overpredicts mass recovery compared to full-scale HydroFloat® units. This study examines the underlying causes by quantifying the influence of operating variables on gangue recovery. Flotation tests were conducted in the JKHFmini using a statistical Design of Experiments (DoE) approach. It was observed that increasing water and air flow rates significantly increased overall mass recovery from 14.8% to 56.0%, while copper recovery increased from 55.2% to 85.2%. This increase in mass recovery was largely attributed to elevated gangue recovery in the elutriation zone, which rose from 1.4% to 49.2% under high fluidisation conditions. Gangue recovery in intermediate size fractions (+75 µm to + 106 µm) was found to be time-dependent, increasing throughout the flotation test. Results showed that approximately 74.0% of the total copper was recovered within the first 4 min, beyond which copper recovery increased marginally (<3%), while gangue recovery continued to increase. The cut size ( d50 c ) of elutriated gangue increased from 92 µm to 163 µm with increasing air and water flow rates and was well described by a regression model. The primary source of mass recovery overprediction in the JKHFmini was elevated gangue recovery in the elutriation zone, driven by near-uniform air and water distribution. These findings have important implications for interpreting JKHFmini results and small-to-full-scale predictions. While the JKHFmini reasonably predicts true flotation behaviour, elutriation effects and their impact on mass recovery must be predicted separately for full-scale applications.