The behavior of the gangue material in the flotation froth was studied. Experiments were conducted in which hematite was floated in flotation cell and glass particles of approximately the same size were introduced into the froth. A continuous flotation cell of a special design was used, which allowed the collection of the particles which had dropped out of the froth. Glass particles with a range of contact angles (0degrees, 50degrees, 66degrees, and 82degrees) were used in the experimental program. To examine the effect of the hydrophobicities of the particles on the recovery of gangue mineral, mixtures of hydrophobic and hydrophilic glass in various ratios were used. The results suggest that the hydrophobic particles have a strong effect on the structure of the froth, which in turn influences the drainage of hydrophilic particles in the froth. (C) 2004 Elsevier Ltd. All rights reserved.