Performance of slurry walls under acid mine drainage

Hydraulic barriers such as a bentonite slurry wall are often used at mine sites to control the seepage of acid mine drainage (AMD) and thereby prevent groundwater and surface water contamination. The overall permeability of the wall, which reflects its effectiveness, is governed by the hydraulic conductivity of both the bentonite filter cake and the soil bentonite backfill.;This thesis investigates the compatibility of AMD with slurry wall materials. It included three sections. The first section involved the development and evaluation of efficient flexible wall hydraulic conductivity equipment to study soil-waste interactions. Secondly, an experimental study of the hydraulic conductivity of slurry wall filter cake and soil-bentonite backfill materials permeated with AMD for prolonged periods of time was conducted. This also involved a study of the mineralogical alterations of clay minerals contacted with AMD. Thirdly, geochemical modelling was performed to predict the concentrations of key species present in effluents obtained from hydraulic conductivity experiments.;The experimental study involved three soils representing both slurry wall filter cake material and soil-bentonite backfill, which permeated with water, and then with AMD using both fixed and flexible wall permeameters. The results showed a considerable increase in k of the filter cake material but a decrease in k for the carbonate rich backfill material and no change in k for carbonate free backfill when permeated with AMD. The increase in k from ;Effluent samples collected from the bentonite samples during the k tests showed a rapid decrease in pH when permeated with AMD, while samples from the backfill material showed almost no change in pH for the whole testing period of 8 months. Chemical analysis of effluent solutions indicated poor retarding capacity by the filter cake material and strong retarding capacity in the case of the backfill soil. Heath Steele backfill soil provided some buffering during initial stages of permeation but produced acid effluents after a few pore volumes of flow. This suggests it would not be an effective long term backfill material in acid mine environments. Precipitation of secondary minerals such as gypsum and jarosites were confirmed using x-ray diffraction and scanning electron microscopy.;Equilibrium speciation modelling indicated basaluminite...