The effect of vertical baffling, of the type and number of gas spargers and of the presence of packing material on the mixing process in a flotation column has been experimentally investigated. The presence of vertical baffles was found to accelerate considerably the liquid flow, leading to an almost complete mixing of the collection zone. Multiple gas spargers had also a similar effect, whereas the use of a bed of packing, made of short cylindrical glass tubes, effectively abated the mixing. Thus, packing seems the only means of altering the column internals in order to reduce the liquid-phase mixing. The mixing process seems to be related to flow instabilities generated at the gas spargers and possibly to gas- and/or liquid-phase inlet maldistribution.