Abstract: An impeller for use with apparatus to enhance mixing of a gas and a liquid, as used for example in froth flotation apparatus, having a substantially upright portion (11) substantially parallel to the axis of rotation (17), and a plurality of vanes (12) extending outwardly therefrom, at least some of the vanes (12) having an upper part (19) adapted to induce liquid flow generally downwardly towards the impeller and a lower part (20) adapted to induce liquid flow generally upwardly towards the impeller, wherein the impeller further comprises barrier means (14) at least partially dividing the upper and lower parts, and a gas input situated on the same side of the barrier means (14) as the lower part (20). The barrier means (14) may comprise a flange like member in a plane generally perpendicular to the axis of rotation (17) and may intersect, or be integral with at least part of the vanes.