Removal of High-Concentration Sulfate Ions from the Sodium Alkali FGD Wastewater Using Ettringite Precipitation Method: Factor Assessment, Feasibility, and Prospect

The feasibility of removal of sulfate ions from the sodium alkali FGD wastewater using the ettringite precipitation method was evaluated. Factors affecting the removal of sulfate ions, such as NaAlO2 dosage, Ca(OH)2 dosage, solution temperature, anions (Cl−, NO3− and F−), and heavy metal ions (Mg2+ and Mn2+), were investigated, and the optimal experimental conditions for the removal of sulfate ions were determined. Experimental results indicate that the ettringite precipitation method can effectively remove SO42− with removal efficiency of more than 98%. All the investigated factors have influences on the removal of sulfate ions, and among them, the dosage of reagents, solution temperature, and fluoride ions have the strongest influence. In addition, the method can effectively synergistically remove F− and heavy metal ions with removal efficiencies of more than 90% and 99%, respectively; meanwhile, Cl− and NO3− also can be removed minimally by the method. The result of actual wastewater treatment shows that the method is feasible for treating high-concentration sulfate wastewater. The ettringite precipitation method has the potential to be a commercial application in the future.