The separation of fine-gained titania from silica is an important industrial problem as the demand for titania continues. In this study we demonstrate how high-purity, synthetic, micron and sub-micron silica and titania particles may be separated by selective aggregation from an aqueous suspension. Specific electrolyte concentration and suspension pH were chosen through a colloid stability analysis. High-efficiency (up to 99.6 wt.%) separation of titania from a mixed silica-titania suspension (50%:50%) was achieved over a wide range of solid concentrations (0.03-2 wt.%) with an electrolyte concentration of 20 mM at pH 8. Analysis of the data revealed that separation efficiency improved as the solid concentration increased. The latter behaviour was attributed to a transition from 'free' to hindered settling of the flocs, which impacted on the entrapment of silica particles within titania floes. (c) 2005 Elsevier B.V. All rights reserved.