Interpretation of breakthrough curves and permeation parameters from sub-tropical kaolinite clayey soil-AMD interactions

Climate change, growth in population and rising pressures on natural recourses triggered by mining and similar activities have led to enormous environmental challenges. Acid mine drainage (AMD) from mining operations in South Africa causes severe environmental issues in need of drastic and lasting solutions. Contamination from AMD requires prevention and mitigation measures to address the various significant impacts on human and environmental health. This pressing challenge permitted the study to investigate and analyze the breakthrough curves and permeation parameters of a subtropical kaolinite clay mineral soil interacted with AMD towards determining its buffering efficacy as a natural contaminant barrier for use in sites prone to AMD contamination. Series of AMD permeation through the soil medium was conducted. The results of the study showed that after the percolation of roughly 2.4 pore volumes of 0.0IN CaSO₄, a baseline hydraulic conductivity of 2.6 × 10^-11 m/s was reached which slightly increased to 3.5 × 10^-11 m/s after introducing about 7 pore volumes of AMD. The values fluctuated between 3.3 × 10^-11 m/s and 3.4 × 10^-11 m/s on continued AMD permeation. However, an average value of 3.35 × 10^-11 m/s was recorded on termination of the test after 18 pore volume permeation. 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 can be incorporated into the construction of composite barriers for acid generating containment facilities.