A physical modelling technique has been used to evaluate the role of the zone between the feed inlet and the pulp-froth interface (pulp cleaning zone) to control gangue recovery in column flotation. The behavior of gangue was simulated using Ottawa sand having d(80) Of 150 mu m and 250 mu m. The column used had an internal diameter of 0.06 m and the dispersion height was maintained at 0.84 m. By varying the feed position, the average solid concentration in the pulp cleaning zone was estimated. The results obtained indicate that a 0.20 m separation between the feed inlet and the interface was sufficient to effect the rejection of coarse gangue particles. Under similar operating conditions, the finer material exhibited negligible changes in the solid hold-up in this zone, thus indicating that the transport mechanisms for fine and coarse particles in flotation columns are different. The implications of these findings in column flotation are discussed.