Effects of CO2 Degassing and pH Control on Sludge Formation in Acid Mine Drainage Treatment

Acid mine drainage from the (Samma)taejung coal mine was examined using water-quality analysis, degassing and neutralization trials, and geochemical modeling.The mine water was highly acidic (pH 3.34) and contained elevated levels of dissolved Fe, Al, Mn, Mg, SiO 2 , CO 2 , and SO 4 2-.Stoichiometric calculations estimated approximately 393 kg/day of precipitation, with secondary minerals derived from CO 2 , SO 4 2-, Ca, and Mg exceeding contaminant mass.Neutralization modeling showed that calcite precipitates around pH 6.5, while Mn(OH) 2 , brucite, and gypsum form sequentially above pH 9. Dissolved CO 2 was removed within 20 min of degassing, which controlled calcite precipitation.At pH > 9, gypsum and brucite formation were identified as the main cause of sludge generation.These findings suggest that combining CO 2 degassing with maintaining the neutralization reactor below pH 9 can reduce lime consumption and minimize sludge production.