Neutralization and uptake of pollutant cations from acid mine drainage (amd) using limestones and zeolites in a pilot-scale passive treatment system

Abstract

The exploration and beneficiation of mineral coal involve managing acid mine drainage (AMD), the acidic and metallic ion composition of which requires adequate treatment for disposal. In the present work, a passive pilot-scale AMD treatment system was developed using open channels of calcitic (CL-I and CL-II) and dolomitic (DL-I and DL-II) limestone beds and mixtures with natural zeolites (NZ) and functionalized zeolites (FZ). Investigated parameters include pH, electrical conductivity, total acidity, total alkalinity, and concentrations of aluminum, iron and manganese ions. DL-I, CL-II and mixtures of CL-II/NZ and CL-II/FZ increased pH levels from 3.3 to 7.9, 8.2, 7.9 and 7.6, respectively; increased total alkalinity levels from 0 mgCaCO3.L-1 to 20, 107, 42 and 34 mgCaCO3.L-1, respectively; and reduced total acidity levels by 95, 91, 90 and 90%, respectively. All beds promoted the removal of aluminum, iron and manganese ions, but the CL-II/FZ mixture was the most efficient due to both neutralization and a higher uptake of manganese ions (roughly 99%), which are pollutants that are typically difficult to remove. The study results reveal ways to transform passive treatment systems using limestone beds and unconventional materials such as zeolites, combine neutralization and adsorption mechanisms in the same operation, ensure a simple maintenance and operational system and improve the economic and environmental sustainability of related processes.