Use of acid mine drainage treatment sludge by combination with a natural soil as an oxygen barrier cover for mine waste reclamation: Laboratory column tests and intermediate scale field tests

Acid mine drainage (AMD) is often treated using active lime treatment, which generates a significant amount of sludge that contains mainly metal hydroxide precipitates, calcium sulfate, and unreacted lime. Previous work showed that sludge may have interesting geotechnical and geochemical properties to be used, in combination with a silty soil, as a part of covers (oxygen barriers) to prevent AMD generation from waste rock and tailings impoundments. The reuse of sludge can reduce the volume of natural soil required for site reclamation. Mixtures of sludge and a natural silty soil were tested in the laboratory (for over 500 days) and in field experiments (4 years) as an oxygen barrier cover placed over acid-generating tailings and waste rock. Data from the testwork include monitoring of leachate geochemical parameters (e.g. pH, conductivity, metal and sulfate content) and hydrogeological parameters (water content, suction, effluent flowrate). Results indicate that soil-sludge mixture is an efficient oxygen barrier.