Mechanisms of gangue transport and recovery in Reflux flotation cells under varying bias flux and salinity conditions

This study investigates the transport mechanisms by which hydrophilic gangue particles report to the product stream in the Reflux Flotation Cell (RFC) under a range of bias fluxes and salinity conditions. Bias flux defined as the difference between the wash water flux and the product water flux was systematically varied to establish negative, zero, and positive net liquid flow relative to rising bubbles. Fine silica (D₉₀ = 68 μ m) was used as a model hydrophilic gangue material, with experiments conducted in both 0 and 1  M NaCl to represent freshwater and saline process water conditions. Under negative bias (no wash water), silica recovery was dominated by bulk entrainment, reaching ∼14 wt% in freshwater and slightly higher in saline conditions. At zero bias, where net liquid flow was neutral, bulk entrainment was significantly minimised and bubble surface entrainment became the dominant mechanism. Silica recovery in this regime increased from ∼6 % (no salt) to ∼8 % (1  M NaCl), attributed to salt-induced aggregation promoting surface entrainment. Under positive bias, the downward liquid flow effectively washed gangue particles from bubble surfaces, reducing recovery to below 1 wt% in both salt and no-salt systems. Quantitative decomposition of recovery data showed that salt enhanced both bulk entrainment under negative bias and washability under positive bias, due to the formation of loosely bound aggregates. Single-bubble experiments confirmed that salt promotes surface loading via aggregation, and that such aggregates can be detached by downward liquid flow. To further characterise RFC hydrodynamics, bubbly zone length and bubble size distributions were analysed in both the vertical and inclined sections. Results demonstrated the role of inclined channels in promoting bubble segregation, with implications for improved gangue rejection.