Interpretation of breakthrough curves and seepage bounds from kaolinite, halloysite and illite/vermiculite mixed layer sub-tropical clayey soil-AMD interactions

The insistent climate change, population growth and depletion of natural recourses from mining and similar activities have triggered diverse environmental challenges. It has long been established that acid mine drainage (AMD) from mining operations in South Africa constitutes a serious environmental problem which requires dire attention. Contamination from AMD presents a severe risk requiring prevention and mitigation measures for curbing consequential impacts on environmental and human health. This increasing challenge led the study to investigate the breakthrough curves and seepage bounds of a kaolinite, halloysite and illite/vermiculite mixed layer subtropical clayey soil interacted with AMD in ascertaining its mineral buffering efficacy for use as natural contaminant barrier in areas under AMD attack. Sequential prolonged permeation up to 24 pore volume passage of AMD through the soil medium was done. The results of the study indicated that after approximately 2.4 pore volumes of 0.0IN CaS0₄, a baseline hydraulic conductivity of 1.3 x 10'" 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 X 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 acidproducing wastes.