Due to the environmental policies and economic reasons, the water used in some flotation operations of complex sulfide ores is recirculated, causing the ion concentration of some species to increase over time, affecting the flotation of the minerals of interest. In this work, an experimental and thermodynamic analysis of the synthetic solutions was presented with a high content of calcium and sulfate ions. The study focused on evaluating the use of two aluminum compounds for the precipitation of Ca²⁺ and SO₄^2- in the form of ettringite. The amorphous aluminum hydroxide was found to be more efficient than the crystalline one, giving rise to 83% calcium and 91% sulfate removal. The XRD analysis of the solids showed the main reaction product of ettringite, accompanied by small amounts of calcite, due to the absorption of atmospheric carbon dioxide. The final solution after the chemical treatment showed residual calcium and sulfate concentrations below 200 mg/L. Finally, the kinetics of calcium removal appeared to correspond to a second order reaction with respect to calcium concentration, with an apparent activation energy of 53.48 kJ/mol, which may suggest that the ettringite precipitation process is governed by the chemical reaction.