Abstract:A chemical method for removing calcium sulfate saturated solutions (0.016 mol/L CaSO₄) using barium chloride (BaCl₂·2H₂O) and sodium phosphate (Na₃PO₄) was experimentally studied. The main interest is to remove these ions from the solution through the precipitation of two solid species: sulfate (SO₄^2-) as barite (BaSO₄), and calcium (Ca²⁺) as hydroxyapatite (Ca₅(PO₄)₃OH). Additionally, a solid/liquid separation method (i.e., flotation) was explored, using oleic acid and dodecylamine as collectors. The results show that, the chemical treatment of saturated solutions at 60 °C, pH 11.5 and using 3.9 g/L BaCl₂·2H₂O and 1.6 g/L Na₃PO₄, promotes the precipitation of barium sulfate and calcium-deficient hydroxyapatite (Ca_10-x(HPO₄)_x(PO₄)_6-x(OH)_2-x), with residual concentrations of calcium and sulfate below 0.10 and 5 mg/L, respectively. The residual calcium concentration increases to 28 mg/L when using the same amount of reactants, at temperature and pH values below those quoted. The highest flotation recovery of hydroxyapatite with oleic acid at pH 9.5 was about 80%, while that of barite floated with dodecylamine at pH 6.5 was about 90%.

Key words: calcium; sulfate; dodecylamine; oleic acid; barite; hydroxyapatite; flotation separation