AN EXPERIMENTAL APPROACH TO THE STUDY OF THE PASSIVATION OF PERMEABLE CARBONATE BARRIERS FOR THE REMEDIATION OF ACID MINE SOLUTIONS

The formation of secondary mineral coatings reduces the lifetime of passive barrier systems to treat acid mine water. This process is studied here. Two different types of synthetic solution (Cl- or SO42- as anions) with Fe(III) concentrations ranging between 250 ppm and 1500 ppm and pH 2 have been injected into columns packed with calcite grains. Initially the columns eliminate the acidity and 100 % of the input Fe(III), but calcite deactivation causes a drop in removal efficiency from 100 % to less than 30%. Mineralogical, chemical and textural changes have been measured by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Tracer tests with Br-have also been applied to study possible porosity changes. All the experimental results will be used in the formulation of a reactive transport model that takes the effect of mineral coatings into account