In this study, sedimentation tests for individual minerals and artificially mixed minerals and bauxite ores were carried out to understand the effects of sodium tripolyphosphate (STPP) on the selective flocculation of diasporic-bauxite in the presence of Ca(2+) and Mg(2+) ions. It was found that STPP can mitigate the detrimental effects of Ca(2+) and Mg(2+) ions on the dispersion of diaspore and kaolinite. When separating bauxite from the mixtures of minerals and in the presence of Ca(2+) ions, STPP can serve as better dispersant than sodium carbonate. By jointly using STPP as a dispersant and PAAS as a flocculant, a flocculation concentrate with the mass ratio of Al(2)O(3)/SiO(2) (Al/Si) of 7.14 and Al(2)O(3) recovery of 89.97% was produced from the feed (Al(2)O(3)/SiO(2) = 5.64) in the presence of Ca(2+) ions. In contrast, with using sodium carbonate as the dispersant and PAAS as the flocculant, selectivity of the flocculation separation of diasporic-bauxite was deteriorated. These experimental data were satisfactorily interpreted by some chemical reactions occurring in the pulp, which were deduced from measured zeta potentials of the reaction resultant products and residual Ca(2+) concentrations of the pulp. (C) 2011 Elsevier Ltd. All rights reserved.