Coagulation and flocculation characteristics of celestite were investigated using CaCl2, MgCl2 and AlCl3 and anionic (A-150), cationic (C-573) and non-ionic (N-100) flocculants, respectively. Isoelectric point of celestite sample studied was found to be located at a pH of 2.6 using hindered settling technique. It was determined that the magnesium ion was more effective on the celestite suspension than calcium and aluminum ions and its effect significantly varied depending on concentration and pH of the suspension. The coagulation power values for magnesium ion increased rapidly towards the 5 x 10(-5) M concentration and reached a maximum value (similar to90%) at a pH of 11. While calcium and magnesium ions were not effective below neutral pH, aluminum ion caused the stabilization of the celestite suspension below pH 8.5. A-150 and N-100 polymers strongly flocculated the celestite suspension than C-573 polymer. While the celestite suspension with A-150 polymer was flocculated well at neutral and alkaline pH range, N-100 polymer was not much affected by the pH changes of the suspension. For the flocculation experiments with A-150 polymer at pH 11 with pre-addition of particular concentrations of calcium and magnesium ions into the suspension, i.e. destabilization process prior to the flocculation, the flocculation of the celestite suspension was enhanced by the coagulation process. (C) 2003 Elsevier B.V. All rights reserved.