Evaluation of Precipitate Generation Due to Neutralization of Lime in Acid Mine Drainage from Daedeok Coal Mine

This study aimed to find the cause of the excessive sludge generated at the Daedeok mine drainage treatment plant.A lime neutralization experiment, water quality analysis, and measurement of the precipitate amount were conducted.Geochemical modeling was performed to predict the weight of the precipitate, and Fe-pH-Eh and gypsum-Ca-SO4 diagrams were prepared.When the acid mine drainage (AMD) was oxidized with hydrogen peroxide and neutralized with lime, the major contaminants were removed in the following order: Fet > Al > Mn, as the pH levels increased.Precipitation occurred at pH <5 at 6.4 g/L and at pH 7-8 at 1.9 g/L because the precipitation pH of Fe, Al, and gypsum were concentrated below pH 5.According to the geochemical modeling, Fe, Al, and Mn hydroxides accounted for approximately 30%, while gypsum accounted for approximately 70% of the total precipitate weight at pH 8.The significant sludge deposition in the settling pond was mainly attributed to the generation of gypsum.