EFFECT OF PHOSPHATE AND SULFATE ON THE PRECIPITATION RATE AND POLYMORPHISM OF CALCIUM CARBONATE MINERALS IN SOLUTIONS WITH Mg²⁺ IONS

Abstract

Phosphate and sulfate are abundant inorganic anions in natural aqueous environments. To evaluate the effect of these inorganic anions on the precipitation rate and polymorphism of calcium carbonate (CaCO₃) minerals, precipitation experiments were performed in the systems containing phosphate or sulfate by the batch method using 100 mL solution at 25°C. Each solution contained 5.0 mM Ca²⁺ and Mg²⁺, and 20.0 mM HCO₃⁻ ions with 0.00, 0.01, 0.05, 0.1, 0.5, and 1.0 mM of phosphate or sulfate. Results indicated that phosphate tended to decrease the precipitation rate of CaCO₃ minerals and favored the formation of aragonite instead of calcite as a predominant polymorph with increasing the phosphate concentrations. Whereas, it was found that sulfate exhibited no significant effect on both precipitation rate and polymorphism of CaCO₃ minerals in solutions with sulfate concentrations up to 5.0 mM.