Remediation of acid mine drainage with recycled concrete aggregates and fly ash

A study was conducted to evaluate the efficacy of recycled concrete aggregate (RCA) and off-specification fly ash (FA) in remediating acid mine drainage (AMD). The pH and AMD concentrations of calcium (Ca), magnesium (Mg), iron (Fe), chromium (Cr), copper (Cu), manganese (Mn) and zinc (Zn) were assessed. The effects of RCA particle size on pH and AMD metal concentrations were also investigated. Results showed that RCAs were effective in neutralising the acidic pH and lowering the AMD concentrations of iron, chromium, copper and zinc. The concentrations of calcium increased, but magnesium and manganese concentrations varied in the treatment process. FA acted as an additional source of metals and increased the concentrations of iron, copper and manganese significantly. Finer RCA particles were the most effective in raising the pH and reducing the AMD concentrations of magnesium, manganese and zinc. The concentrations of calcium, iron, chromium and copper remained unaffected by the RCA particle size. In addition, geochemical modelling indicated that sorption was the leaching controlling mechanism in untreated and FA-treated AMD, whereas it was solubility-controlled leaching in RCA-treated AMD. Finally, the research reported in this study suggests the use of RCA as an effective alternative to the conventional treatment methods for AMD remediation.