Sodium oleate and tallow amine acetate (TAA) were used as surfactants for the shear flocculation of celestite. The shear-flocculation power values obtained with sodium oleate were higher than those obtained with TAA in terms of the concentrations used in the shear-flocculation experiments. In addition, sodium oleate and TAA were more effective on the celestite suspension in the pH ranges of 7-11 and 6-10, respectively. For the shear-flocculation experiments with sodium oleate at pH 11, with preaddition of calcium or magnesium ions at 5 x 10(-5) M and lower concentrations into the suspension, the shear-flocculation of the celestite suspension was promoted by the coagulation process due to the calcium and magnesium cations added. However, the shear-flocculation power values decreased due to the interaction between surfactant and cations at concentration values higher than 5 x 10-5 M for magnesium ions and 10(-3) M for calcium ion. Particularly, magnesium ions significantly reduced the shear-flocculation power values by slime coating of Mg(OH)(2) precipitates. (C) 2004 Elsevier Inc. All rights reserved.