Thermodynamic and experimental studies on removal of calcium and sulfate ions from recycling water of complex sulfide flotation operations

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 (SO42−) 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 (Ca10–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%.