Mixed layer sub-tropical clayey soil-AMD percolation: Analysis of permeation limits and breakthrough patterns

The increasing population growth, depletion of natural recourses from mining and similar activities, and consequent insistent climate change have triggered diverse environmental challenges. It is well known that acid mine drainage (AMD) from mining operations in South Africa constitutes a serious environmental problem which requires heightened and crucial attention. The contamination threats from AMD presents a severe risk requiring prevention and mitigation measures for curbing consequential impacts on environmental and human health. This amassing challenge gave the study the impetus to investigate the permeation limits and breakthrough curves of a mixed layer subtropical clayey soil; kaolinite, halloysite and illite/vermiculite permeated with AMD towards establishing its mineral attenuation effectiveness for use as natural barrier against contaminant species in areas under AMD attacks. As such in this study, successive protracted permeation up to 24 pore volume passage of AMD through the soil medium was conducted using a laboratory scale bespoke column hybrid permeameter device. The results of the study showed that after approximately 2.4 pore volumes of 0.01N CaSO4, a baseline hydraulic conductivity of 1.3 × 10^-11 m/s was obtained for the soil which remained unchanged even after 19 pore volume of AMD seepage through the soil. The value was found to be below the accepted criterion of 1 10^-9 m/s specified for clay liner construction in South Africa but may as well be considered for use as a natural material in the construction of composite barriers for acid-generating wastes.