The effect of column height and internal baffling on the mixing of the liquid phase inside the collection zone of flotation columns was investigated in this work by RTD and the mixed cells-in-series-with-backflow and the axial dispersion models were used to interpret the experimental results. The increase in column height subtly affected the mixing process, by influencing the transition from plug-flow-like to mixed flow conditions. The backflow was calculated in all cases as approximately 10% of the net incoming liquid flow, and 4 to 14 perfectly mixed cells were found to represent the collection zone liquid-phase RTDs, with the higher number of cells corresponding to high liquid and low gas flowrates. Vertical baffles were found to enhance rather than attenuate the collection zone mixing.