Effects of sodium tripolyphosphate and sodium carbonate on the selective flocculation of diasporic-bauxite in the presence of calcium and magnesium ions

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 Ca²⁺ and Mg²⁺ ions. It was found that STPP can mitigate the detrimental effects of Ca²⁺ and Mg²⁺ ions on the dispersion of diaspore and kaolinite. When separating bauxite from the mixtures of minerals and in the presence of Ca²⁺ 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 Al₂O₃/SiO₂ (Al/Si) of 7.14 and Al₂O₃ recovery of 89.97% was produced from the feed (Al₂O₃/SiO₂ = 5.64) in the presence of Ca²⁺ 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 Ca²⁺ concentrations of the pulp.