Effects of fines on fluidised bed Flotation: Implications for HydroFloat™ operation on copper tailings

The HydroFloat™ cell has enabled improved recovery of coarse particles by operating in a fluidised-bed environment that overcomes the size limitations of conventional flotation. In practice, however, the feed to HydroFloat™ inevitably contains fine particles that can disrupt bed stability and degrade metallurgical selectivity. Although upstream desliming is routinely applied, the tolerance of the fluidised bed to residual fines and the mechanisms by which fines impair performance remain insufficiently quantified. This study systematically evaluates the effect of fines (<53 µm) on HydroFloat™ performance using deslimed copper tailings recombined with controlled proportions of slimes, ranging from 6 to 67 wt%. Pilot-scale flotation tests were supported by rheological measurements, automated mineralogical analysis (QEMSCAN), and UV–Vis spectroscopy to interrogate hydrodynamic, mineralogical, and reagent-related effects. Increasing fines content resulted in a monotonic increase in mass recovery driven predominantly by hydraulic entrainment, while flotation selectivity deteriorated sharply beyond 30–40 wt% fines. Elevated fines levels suppressed coarse particle recovery, increased slurry viscosity, and reduced collector availability through adsorption onto high–surface area particles. These results demonstrate that fines impose a practical upper limit on the stable and selective operation of HydroFloat™. While adjustments to fluidisation water rate can partially offset fines-induced instability over a narrow operating window, sustained selectivity requires effective upstream desliming and/or separate treatment of the fines fraction using flotation technologies better suited to ultrafine particles. The findings provide a quantitative basis for defining fines tolerance in fluidised-bed flotation and offer practical guidance for maintaining bed stability and metallurgical performance when reprocessing tailings or treating low-grade ores.