Heavy Metal Removal and Precipitate Formation in Synthetic Acid Mine Drainage Using Calcined and Uncalcined Ca–Mg-Based Minerals

This study investigated the removal efficiency of heavy metals from highly contaminated synthetic acid mine drainage and characteristics of precipitates formed after reaction using Ca-Mg-based carbonate and hydroxide minerals under calcined and uncalcined conditions.The reaction media included CaCO 3 , Ca(OH) 2 , MgCO 3 , and Mg(OH) 2 , and their reaction characteristics were compared with those of CaO and MgO produced by calcination at 800.Heavy metal removal experiments were conducted under batch reaction conditions, and changes in pH and concentrations of Cd, Cu, Fe, Mn, and Zn were analyzed as a function of reaction time.In addition, X-ray diffraction (XRD) and thermogravimetric-differential thermal analysis (TG-DTA) were performed to evaluate the mineralogical and thermal characteristics of the media and reaction products before and after calcination.Among the uncalcined media, Ca(OH) 2 exhibited the highest pH increase (pH > 12) and showed high removal efficiency for most heavy metals.The calcined media exhibited faster pH increase and enhanced heavy metal removal efficiency compared to the uncalcined media.Under conditions with sufficient sulfate (SO 4 ), gypsum (CaSO 4 2H 2 O) was formed as the dominant precipitate in the Ca-based media, indicating sulfate immobilization, whereas no sulfate minerals were formed in the Mg-based media, and hydroxide or carbonate minerals were predominantly formed.